Flight.Training

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AVIATION COURSE CONTENTS Home Contents The Airplane ..................Illustrates basic airplane parts. Lift ................................Illustrates the Principles of Lift. Basic Aerodynamics.......Basic Flight principles. Pitot and Static Systems .Airspeed, Altimeter, Vertical Speed Gyroscopic Instruments..Attitude Indicator, Turn Indicators. Magnetic Compass.........Magnetic Compass and Compass Errors Engine Operation...........Throttle and Mixture Control Fuel System...................Components of the fuel system. Induction System...........Carbuerator Operation. Electrical System............General Electrical Busses and Breakers. Propulsion System .........Propeller and Controls. Stall Warning System .....Warnings of Impending Stall. Weight and Balance........How to calculate W/B. Aircraft Performance......Effects of air density on performance. Types of Airspace...........Airspace Definition, Airport Types and Flight Rules. Aeronautical Charts........Aeronautical Chart Synbols and their Meaning. Airport and AIM Data ...Airport Markings, Signs and Aircraft Operations. Navigation Methods .......Pilotage, VOR, LORAN, GPS Nav. Planning the Flight....... ....Terminology and Procedures. Principles of Weather......Air Masses, Fronts, Clouds, Fog, Ice. Weather Reports and Services ..WX Report Interpretation. Other Aviation Publications ....Important Information to consult. FAA Regulations...........Rules of the Road. Preflight Briefing....How to get preflight briefing from FAA. OTHER AVIATION STUFF OF INTEREST FAA Test Questions....FAA Test Prep Questions Guide to Meterology ... Basic Meterology and Weather Info Other Aviation Links ....A whole host of aviation information. Weather Links.............Actual weather & Educational material. Student Pilot Guide......Information concerning student training. http://www.uncletom2000.com/gs/contents.htm (1 of 2) [1/23/2003 11:18:45 AM] Flight Planning Data .....Fuel Prices, Planning Software, etc. LANDINGS................A host of aviation links. AVIATION COURSE CONTENTS http://www.uncletom2000.com/gs/contents.htm (2 of 2) [1/23/2003 11:18:45 AM] The Airplane Major Airplane Components A single engine airplane typically used by student pilots is shown above. The fuselage is the structure which houses the Pilot and passengers, as well as the instrument panel and controls. The Wings provide the major LIFT for the airplane. Ailerons are located near the outer portion of the wing. The ailerons operate in opposition to each other; i.e. when the left aileron is up, the right aileron is down. This configuration causes the aircraft to "roll" to the left. Placing the ailerons in the opposite position causes a roll to the right. Flaps are located on the inboard end of the wing, next to the fuselage. Flaps can be deployed during decent to landing to provide increased lift, and increased drag to slow the aircraft. Flaps permit a steeper decent without build-up of excessive speed. The horizontal stabilizer and elevators are located on the tail of the fuselage. The horizontal stabilizers are fixed. The elevators are hinged at the aft end of the stabilizers. The Elevators control the pitch (noseup or nose-down ) state of the aircraft. The vertical stabilizer is attached to the tail of the fuselage. The Rudder is hinged to the aft end of the vertical stabilizer. The Rudder permits the pilot to move the tail of the aircraft left or right by use of the rudder pedals in the cockpit.. The landing gear shown above is a "tricycle" type, which is comprised of the Main Gear and the Nose Wheel. Some aircraft, however, have a tail wheel instead of the nose wheel. These aircraft are usually of earlier design, and are lovingly called "tail draggers" by many pilots. Most "training type" aircraft have http://www.uncletom2000.com/gs/airplane.htm (1 of 2) [1/23/2003 11:18:47 AM] "fixed" landing gear; i.e. the gear remains stationary in flight and cannot be "retracted". Higher performance aircraft usually are equipped with "retractable" landing gear to reduce aerodynamic drag during flight..

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The engine and propeller provide the forward thrust necessary to attain sufficient speed to achieve flight. The engine is housed under the cowl, at the nose of the aircraft. Some aircraft have secondary control surfaces called Trim Tabs. These tabs can be located on the elevators to aid in maintaining pitch of the aircraft. Other tabs can also be located on the ailerons and rudder to aid in stabilizing the roll and yaw characteristics as an assist in maintaining the flight configuration selected by the pilot. Axes of Rotation The aircraft is free to move around 3 different axes. l The LONGITUDINAL AXIS is an imaginary line( line X - X ) from nose to tail. Rotation around the LONGITUDINAL axis is called ROLL. Roll is controlled by the ailerons. When the pilot turns the CONTROL WHEEL (or in some aircraft a control stick), to the RIGHT the right aileron deflects upward, while the left aileron deflects downward. This causes the right wing to produce less lift and the left wing to produce greater lift. This unequal lift causes the airplane to ROLL to the right as long as the ailerons remain in this condition. In order to stop the roll, it is necessary to neutralize the ailerons. The aircraft will remain in a "banked" condition until rolled back to level by application of opposite aileron action. l The LATERAL AXIS is an imaginary line ( line Y-Y ) from wingtip to wingtip. Rotation around the LATERAL axis is called PITCH. The "nose up" or "nose down" pitch of the aircraft is controlled by use of the elevator surfaces of the tail. When the pilot pulls the control wheel (or control stick) rearward, the elevators deflect upward, forcing the tail downward. This is referred to as a "nose up attitude". When the control wheel or stick is moved forward, the opposite reactions occur, causing a "nose down attitude". l The VERTICAL AXIS is an imaginary vertical line (line Z_Z )running through the center of gravity of the aircraft. Rotation around the VERTICAL axis is called YAW. Yaw is predominately controlled by use of the rudder. Left rudder pedal depression in the cockpit deflects the rudder surface to the left. This causes the tail of the aircraft to move to the right, creating a yaw to the left about the vertical axis. Application of right rudder similarly causes yaw to the right. Back to Home Back to Table of Conents To Principles of Lift The Airplane http://www.uncletom2000.com/gs/airplane.htm (2 of 2) [1/23/2003 11:18:47 AM] http://www.uncletom2000.com/gs/lift.htm LIFT When Lift is mentioned, most people think primarily of the wings. However there are several other surfaces which generate lift, although not necessarily in an upward direction. These are the Propeller, Elevators, Rudder, Ailerons, and Flaps. l Principles of Lift

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The structure of the wing best demonstrates the principle of airfoil lift. In the 19th century a scientist named Bernoulli discovered that the intenal pressure of a fluid (liquid or gas) reduces the faster the fluid flows. If you take a tube, and make the tube smaller in diameter in the middle, this creates a "neckeddown" section called a venturi. When air is forced through the pipe, as much air has to come out the exit as goes in the tube entrance. The air in the venturi section must travel faster to get through. Bernoulli found that the pressure at the venturi section was less than at the two ends of the pipe. This is because the speed of the air through the venturi section is traveling faster than at the ends of the tube. l The Airfoil The shape of a wing is called an AIRFOIL. Usually the bottom of the wing is flat or nearly flat. The top of the wing is curved, with the wing being thicker at the front edge of the wing, and tapering to a thin surface at the trailing edge of the wing. When a wing airfoil surface passes through the atmosphere, the atoms of the air on the top of the airfoil (shown as minus) must travel faster than their cousins (shown as plus) passing along the lower and flater surface. This occurs because the distance the air must pass over the curved top of the wing is longer than the distance along the lower surface. According to the Bernoulli Principle, the pressure above the wing is less than the pressure of air below it. Consequently, a pressure difference between the lower and upper surfaces exist. This results in LIFT being produced. The amount of lift depends on the airfoil design and the speed of the air over its surfaces. l Camber The curved surface of an airfoil is called Camber. It can be both Positive and Negative. The curved upper http://www.uncletom2000.com/gs/lift.htm (1 of 3) [1/23/2003 11:18:47 AM] surface of a wing is called Positive Camber. If the lower surface of the airfoil is curved downward, this would constitute a negative camber. l Chord The chord of a wing is an imaginary line from the leading edge to the trailing edge of the wing. The term is used in the definition of "Angle of Incidence" and "Angle of Attack" (defined later). l Angle Of Incidence The angle which the chord of the wing makes with the longitudinal centerline of the aircraft is known as the Angle of Incidence. This angle in a given aircraft never changes. It is fixed by the construc tion of the aircraft. l Angle Of Attack As the aircraft passes through the air it traverses a particular line of flight. The air passing by the surfaces of the aircraft in the opposite direction of travel is called the Relative Wind. The angle which the wing chord makes with this Relative Wind is called Angle of Attack. An increase in angle of attack increases both lift and drag. If the angle becomes to great, it will pass the Critical Angle of Attack. This is a point where the airflow over the wing becomes so disturbed that the wing ceases to produce lift. The wing then enters into a Stalled condition. Stalls will be described more fully later in this chapter. l Center of Pressure Even though the lift of an airfoil is distributed along its surface, the resultant force of all the lift forces can be considered to be at single point along the wing known as the Center of Pressure. l Center of Lift The Center of Lift( shown as CL in the diagram) is the same point as the Center of Pressure. You can think of all the lift of the wing as being a single force concentrated at this point on the wing. l Dihedral When you stand in front of an aircraft, looking toward the tail, the wings are usually higher at the wing tips than at the wing root (where the wing attaches to the fuselage). This upward angle from wing root to tip is called DIHEDRAL. http://www.uncletom2000.com/gs/lift.htm http://www.uncletom2000.com/gs/lift.htm (2 of 3) [1/23/2003 11:18:47 AM] On an aircraft with dihedral, when one wing drops, it will produce slightly greater lift than the other wing. The aircraft tends to return to a level status providing lateral stability to the aircraft. Back to Home Back to Table of Conents To Aerodynamics http://www.uncletom2000.com/gs/lift.htm http://www.uncletom2000.com/gs/lift.htm (3 of 3) [1/23/2003 11:18:47 AM] Aerodynamics Principles of Aerodynamics Flight involves a balance of forces. These forces are THRUST, DRAG, LIFT and WEIGHT. When Thrust and Drag are equal, the speed of the aircraft through the air (airspeed) will remain constant in smooth air. When Lift and Weight are equal, the aircraft will neither ascend or decend. Attitude The Attitude of an aircraft refers to it's relationship to the ground. When in a level attitude, the longitudinal centerline of the aircraft is approximately paralell to the earth's surface. In this attitude, the horizon will appear to be just about on the nose of the aircraft( i.e. the top of the engine cowling is approximately aligned with the horizon). When the nose of the aircraft is above the horizon, this is called a nose high attitude. If the nose is below the horizon, the aircraft is in a nose low attitude. Center Of Gravity The weight of the airplane, pilot and passengers, fuel and baggage is distributed throughout the aircraft, as shown by the small downward arrows in the diagram. However, the total weight can be considered as being concentrated at one given point, shown by the larger downward arrow. This point is referred to as the Center of Gravity. If the plane were suspended by a rope attached at the center of gravity ( referred to as the CG) it would be in balance. The Center of Gravity (CG) is affected by the way an aircraft is loaded. For example, if in a 4 place aircraft, there are 2 rather large individuals in the front seats, and no rear seat passengers or baggage, the CG will be somewhat toward the nose of the aircraft. If however, the 2 front seat passengers are smaller, with 2 large individuals in the rear seats, and a lot of baggage in the rear baggage compartment, the CG will be located more aft. http://www.uncletom2000.com/gs/aerodyn.htm (1 of 12) [1/23/2003 11:18:49 AM] Every aircraft has a maximum forward and rearward CG position at which the aircraft is designed to operate. Operating an aircraft with the CG outside these limits affects the handling characteristics of the aircraft. Serious "out of CG" conditions can be dangerous. Aircraft Balance An aircraft in straight and level flight is similar to a childs "teeter-totter". There is a balance point in the middle (called a fulcrum), with weight on both sides of the fulcrum. For the "teeter-totter" to be in balance, the downward forces on both sides of the fulcrum must be equal. In the diagram at right, the fulcrum of an aircraft in flight is the center of lift. Generally the CG is forward of the Center of Lift, causing the aircraft to naturally want to "nose down". The elevator located at the aft end of the aircraft provides the counterbalancing force to provide a level attitude in normal flight. Normally, the pilot will "trim" the elevators, by use of the trim tab control in the cockpit, to cause the elevators to provide the correct elevator balance force to relieve the pilot from constant elevator control. You can readily see that loading of the aircraft, which affects the CG, is a critical consideration in properly balancing the aircraft and it's controllability. If the pilot pulls back on the control wheel, an "up-elevator" condition results. This forces the tail downward, causing the aircraft to assume a "nose up" attitude. Likewise, a forward movement of the control wheel by the pilot causes a "down elevator" state. This causes the tail to rise, forcing the aircraft into a "nose low" attitude. By use of the elevator trim control (a small wheel or crank in the cockpit), the pilot can cause the aircraft to remain in a nose-up, level, or nose down attitude. As can be seen in the diagram above, when the CG is forward, a greater downward force is required by the elevators to produce a level attitude. Likewise, when the CG is aft, the elevators must produce less downward force to maintain level flight. NOTE: If the CG gets behind the Center of lift (the fulcrum) the aircraft becomes unstable because the CG is aft of the fulcrum. IT MAY BE POSSIBLE TO EXCEED THE TRIM CAPABILITY OF THE ELEVATORS SUCH THAT THE AIRCRAFT ALWAYS WANTS TO NOSE UP, AND BE UNSTABLE. Therefore the pilot must pay attention to proper loading of the aircraft. This will be discussed in greater detain under the subject of Weight and Balance. Effects Of Attitude Change Aerodynamics http://www.uncletom2000.com/gs/aerodyn.htm (2 of 12) [1/23/2003 11:18:49 AM] When the wing is in a given attitude with respect to the Relative Wind (R W) as shown in the diagram below, the wing produces a Vertical Lift Force (LIFT) which is perpendicular to the Relative Wind.. There is also a DRAG component operating parallel to the Relative Wind in opposition to the forward motion of the wing. Drag is created as a natural part of producing lift. These two forces intersect at a point called the CL (center of lift}, or is also called the CP (center of pressure]. The LIFT and DRAG force vectors can be resolved into a single force vector called the RESULTANT force. Envision if the Angle of Attack is increased. The Vertical Lift decreases in value, and the horizontal force of Drag increases. Therefore, when a pilot wants to slow the aircraft, the nose of the aircraft must be slowly raised into a greater "nose up" attitude, causing drag to increase, thus slowing the aircraft. This increase of angle of attack has limits, however. The wing design of most small aircraft, the wing has a "Critical Angle Of Attack" (somewhere around 18° to 20°) at which point the wing ceases to create sufficient lift to fly, and the wing STALLS. The air flowing over the wing becomes so disturbed that adequate lift to sustain flight ceases, and the aircraft pitches "nose down". This is a STALL. The primary way to recover from a stall is to push the nose further downward, thus decreasing the Angle Of Attack so that the wing flies again. Also, envision in the diagram, when the pilot pushes the nose down by use of forward elevator, the Angle of Atack decreases, thus decreasing the drag. Therefore, when power is held constant, the angle of attack (nose high, level, or nose low) provides "Airspeed Control". Assume for example, an aircraft has been cruising at 120 knots. When the aircraft enters the landing pattern of an airport, the pilot may want to reduce speed to 90 knots. The pilot must reduce power to prevent an altitude increase, and concurrently raise the nose of the aircraft so that the drag is increased sufficiently to slow the aircraft to 90. Later, when on the final approach for landing, the pilot may wish to slow even further, say to 70 knots. Power can be further reduced and the nose raised further, to again increase drag. In addition, the pilot may add 10,20 or 30 degrees of flaps to add an additional drag and lift. The important point is that ATTITUDE is the primary control of airspeed; not THROTTLE! However, if level flight is to be maintained, appropriate changes in power must be made whenever the pitch attitude is made to prevent gaining or loosing altitude. The Turn Aerodynamics http://www.uncletom2000.com/gs/aerodyn.htm (3 of 12) [1/23/2003 11:18:49 AM] In order to turn the aircraft, it must be placed into a BANKED state, where one wing is high, the other low. This state is pictured below. In order to bank the aircraft, the pilot must turn the control wheel (or move the control stick) to the left. The Right Aileron lowers This increases the angle of attack of that part of the right wing, causing the right wing to rise. At the same time, the Left Aileron raises. The angle of attack of that part of the left wing decreases, causing the left wing to lower. This increased lift of the Right and decreased lift of the Left Wing causes the aircraft to roll to the Left. NOTE: During the time the Right aileron is down, the right wing has MORE DRAG than does the left wing. The effects of this unequal drag is discussed later under Adverse Yaw. When the aircraft reaches the bank angle the pilot wishes, the ailerons must be neutralized. This causes equal lift by left and right wing, and the aircraft roll stops. Basically, the aircraft will remain in this banked attitude until the pilot rolls the aircraft back to level attitude by operating the control wheel ( or stick) in the opposite direction. Note in the diagram that some of theTotal Lift ( force T) goes into a Horizontal Force ( H ). This is the force which pulls the aircraft in a circular motion (turn). Note also that the Vertical Lift ( force V) becomes less. If the bank angle becomes large, say 45 degrees, the vertical lift is appreciably less. The pilot may have to hold some up elevator and/or add power to prevent loosing altitude. Adverse Yaw During the time that the ailerons are activated, an unwanted effect occurs. In the left turn shown above the pilot turns the control wheel to the left, raising the left aileron, and lowering the right aileron. The intent is to turn left. Unfortunately while the ailerons are activated, the left wing has less drag; the right wing has more drag. This causes the airplane to want to turn to the Right, and not to the left. This tendency to turn in a direction opposite to the intended turn direction is called ADVERSE YAW. So how does the pilot overcome this tendency to initially turn in the wrong direction? He uses the Rudder. By applying just the right amount of rudder in the direction of the turn, the pilot can offset the adverse yaw. When the pilot does this correctly, applying just the right amount of rudder, a Coordinated turn results. If the pilot applies too little or too much rudder, anUn-Coordinated turn results. How the quality of the turn is measured will be covered in the Instruments section. If the pilot uses too little rudder, the nose of the aircraft wants to stay yawed opposite the turn. The rest of the aircraft wants to "slip" toward the inside of the turn. Aerodynamics http://www.uncletom2000.com/gs/aerodyn.htm (4 of 12) [1/23/2003 11:18:49 AM] If the pilot applies too much rudder, the tail wants to remain outside the radius of the turn, and a "skid" results. Its similar to the rear end of an automobile wanting to skid outside the turning radius of a car. Therefore, a principle use of the rudder is to control the adverse yaw while rolling into a bank. Slips A slip is created by applying rudder in the opposite direction to the turn. This is called Cross Controlling. There are 2 forms of the slip. l Side Slip l Forward Slip Side Slip This manuever is primarially used to compensate for a cross wind while landing. If the wind is from the right of the aircraft, the aircraft will drift to the left side of the runway unless some force is applied in the opposite direction keep the aircraft straight with and on the centerline of the runway. The pilot uses a Right Side Slip to compensate for the leftward drift caused by the wind. The pilot turns the control wheel to the right to initiate a right turn, but simultaneously applies opposite Left rudder just enough to keep the aircraft from turning. Thus the pilot induces just enough right side slip to offset the leftward wind drift. This way, the pilot can keep the aircraft both over the centerline of the runway, and aligned with the runway. This prevents a "side load" on the landing gear on touchdown. Forward Slip The forward slip is used primarially on aircraft with no flaps. This configuration is used to loose altitude quickly without increasing airspeed. In this manuever, the pilot simultaneously turns the aircraft left or right, and applies a lot of opposite rudder so the side of the aircraft is presented to the relative wind. It is almost like slipping a sled down a hill somewhat sideways. The pilot maintains this configuration until the desired altitude is lost, whereupon he neutralizes controls to continue straight flight. Since most modern aircraft have effective flaps to slow the aircraft on landing, and to allow a steeper decent, the forward slip in usually unnecessary. Some aircraft manufacturers state that forward slips should not be made with flaps deployed. Stalls and Spins The angle of attack which produces maximum lift is a function of the wing design, and is called the CRITICAL ANGLE OF ATTACK. A stall occurs when the Critical Angle of Attack is exceeded. Smooth air flow across the upper surface of the wing begins to separate and turbulence is created along Aerodynamics http://www.uncletom2000.com/gs/aerodyn.htm (5 of 12) [1/23/2003 11:18:49 AM] the wing surface. Lift is lost and the wing quits “flying”. THE STALL IS A FUNCTION OF EXCEEDING THE CRITICAL ANGLE OF ATTACK, AND CAN OCCUR AT ANY AIRSPEED , ANY ATTITUDE, AND ANY POWER SETTING. On most aircraft, the stall starts at the wing root, and progresses outward to the wing-tip. The wings are designed in this manner so that the ailerons are the last wing elements to loose lift. Flap and gear extension affect the stall characteristics. In general, flap extension creates more lift, thus lowering the airspeed at which the aircraft stalls. Recovery from a stall requires that the angle of attack be DECREASED to again achieve adequate lift. This means that the back pressure on the elevators must be reduced. If one wing has stalled more than the other, the first priority is to recover from the stall, then correct any turning that may have developed. A CG that is too far rearward can significantly affect the ease of stall recovery. The aft CG may inhibit the natural tendency of the nose to fall during the stall. It may be necessary to force a “nose down” attitude to recover. Although weight does not have a direct bearing on the stall, an overloaded aircraft will have to be flown at an unusually higher angle of attack to generate sufficient lift for level flight. Therefore the closer proximity to the critical angle of attack can make an inadvertent stall due to pilot inattention more likely. Snow, ice or frost on the wings can drastically affect lift of the wing. Even a small accumulation can significantly inhibit lift and increase drag. Due to the reduced lift, the aircraft can stall at a higher-thannormal airspeed. Takeoff with ice, snow or frost on the wings should never be attempted. Stall recognition can come several ways. Modern aircraft are equipped with stall warning devices (usually an audible signal) to warn of proximity to the critical angle of attack. The aircraft may vibrate, control pressures are probably "mushy", the "seat of the pants" sensation that the aircraft is on the verge of loosing lift, and other sensations can tip off the pilot of an impending stall. Practice of slow flight and stalls at altitude is invaluable training in stall recognition. A spin is a stall that has continued, with one wing more stalled than the other. The aircraft will begin rotation around the more stalled wing. The spin may become progressively faster and tighter until the stalled condition is "broken" (stopped). Usually spin recovery procedures are covered in the Pilot Operating Handbook (POH) for the given type of aircraft. If one is not available, the following is the suggested spin recovery technique. a. Close the throttle. Power usually aggravate the spin. b. Stop the rotation by applying opposite rudder. c. Break the stall with positive forward elevator pressure. d. Neutralize the rudder when rotation has stopped. e. Return to level flight. Secondary Controls Aerodynamics http://www.uncletom2000.com/gs/aerodyn.htm (6 of 12) [1/23/2003 11:18:49 AM] Trim There are some secondary "pilot-controlled" functions which can "trim" the elevators, rudder and ailerons for improved straight and level flight, thus freeing the pilot from constant attention and control of the major control surfaces. Most small aircraft have only Elevator Trim. As the sophistication of an aircraft design increases, Rudder Trim and Aileron Trim are added. In most cases, the elevator trim is an additional moveable surface on one of the elevator assemblies which causes a “nose up”, “level”, or “nose Down” trimmed attitude. In some aircraft, rudder trim and aileron trim can also be accomplished by pilot from the cockpit.. The purpose of the trim action is to compensate for variations in aircraft loading or other minor factors which may tend to cause deviation from straight and level flight. Flaps Flaps are moveable surfaces on the trailing edge of the wing similar in shape to the ailerons. they are usually larger in surface area. They are located on inboard end if the wing next to the fuselage. Both sides are activated together so they do not produce a rolling action like the ailerons. Flaps are usually deployed in "degree" increments. In small aircraft deployment is usually in 10 degree increments from zero degrees (non-deployed) to 40 degrees maximum. Larger or more sophisticated aircraft may have a different range of settings. Normally, the flaps operate electrically through a 4 or 5 position switch located on the instrument panel. In earlier aircraft the flaps were operated using a manual flap handle. Deployment of flaps increases both the lift and drag of the wing. Flap activation increases the angle of attack across the wing / flap section. At 10 degrees, more lift than drag is produced. As the flap angle is increased more drag and less lift is produced for each increment of deployment. The primary use of flaps is in landing. They permit a steeper decent without increase in airspeed. Flaps may be used in certain take-off situations(usually 10°) on short or soft fields. Dynamics of Flight Drag Just as wind friction causes drag in an automobile, aerodynamic friction and displacement of air during flight creates aerodynamic DRAG. Drag occurs any time that air is displaced from its normal stable condition. Air has density and weight, and although compressible, it still requires energy to displace. l INDUCED DRAG occurs as a by-product of lift. l PARASITE DRAG results from friction with surfaces and appendages, and impact with structures Aerodynamics http://www.uncletom2000.com/gs/aerodyn.htm (7 of 12) [1/23/2003 11:18:49 AM] such as struts, landing gear, antennas, etc.. Induced Drag Induced drag results from the creation of lift. The amount of drag depends on the airfoil design of the wing, its camber and angle of attack. Also due to the way the air flows across the wing during flight, vortices are generated at the wing tips which add to the induced drag component. . Parasite Drag Parasite drag is an unwanted resistance of the air to an object traveling through e air. The 3 types of parasite drag are Form, Skin and Interference as demonstrated below. Form Drag The form of the object and the effective frontal surface it presents to the air has a significant effect on the amount of drag generated. As shown in (A), a surface such as shown would present much more "frontal" drag than it would is it were rotated 90 degrees as in (B). Drag can be reduced in the aircraft design by streamlining objects such as wing struts to minimize the frontal appearance to the air flow. Skin Friction Even though the form in (A) above is re-oriented to shape (B), there is still some form drag. In addition, there is friction between the skin of the surface and the air flow. It is obvious that if the surface is dirty, has frost, ice or other obstructions, that drag will increase. Effects of skin drag can be reduced by smooth surfaces and flush riveting in the design, and by keeping the surface clean and waxed by the owner. Interference Drag Surfaces at angles to each other as in (C) create turbulence in the region of the joint. This occurs most frequently at the intersection of the fuselage and wing Pitch, Power and Performance The amount of lift that a wing generates is a function of it's design (camber, area, etc.), speed through the Aerodynamics http://www.uncletom2000.com/gs/aerodyn.htm (8 of 12) [1/23/2003 11:18:49 AM] air, air density, and angle of attack. The effects of air density will be treated in more detail in a later chapter. The three aircraft shown above can all be in constant altitude flight, but at different airspeeds. Maintaining a fixed altitude at a given airspeed requires the pilot to control two factors; (1) Angle of Attack and (2) Power. The angle of attack is controlled by the up, neutral, or downward trim position of the elevators. The power, is controlled by the "power setting" of the engine and propeller. For a "fixed pitch" propeller, this means adjusting the engine RPM. For a variable pitch propeller, this means adjusting both the throttle and the propeller pitch control. The left aircraft could be at a 10 degree nose-up attitude with an indicated airspeed of say 70 nautical miles per hour (knots). The center aircraft could be at cruise with a 0 degree attitude and 110 knots. The right aircraft could be in a slightly high speed decent at minus 3 degrees of pitch and an indicated airspeed of 140 knots (abbreviated kts). The pilot can control the Pitch, Power and Performance of the aircraft and can fly at a considerable range of attitudes, speeds and power settings. Lift versus Drag An aircraft with a given total gross weight can be operated in level flight over a range of power settings and airspeeds. Since Lift and Weight must be equal in order to maintain level flight, it is obvious that there is a relationship between Lift (L), Airspeed (V), and Angle of Attack (AT). This relationship can be "generalized" with the following expression. (Note: the expression is not an exact equation). Lift = Angle of Attack x Velocity Since angle of attack and speed also have a relationship to Induced Drag and Parasite Drag, the relationship of Lift/Drag is shown by the graph below. Aerodynamics http://www.uncletom2000.com/gs/aerodyn.htm (9 of 12) [1/23/2003 11:18:49 AM] Parasite drag increases with speed. Induced drag decreases with speed. The SUM of the two drags (Total Drag curve) shows that there is only one airspeed for a given airplane and load that provides MINIMUM total drag. This is the point M which is the maximum lift over drag ratio (L/D). It is the airspeed at which the aircraft can glide the farthest without power (maximum glide range). This is the airspeed which should immediately be set up in the event of a power failure. This maximum glide airspeed is different for each aircraft design. The Pilot Operating Handbook should be consulted for this airspeed and the pilot should memorize it to eliminate need to search manuals during an emergency. Ground Effect An aircraft can be flown near the ground or water at a slightly slower airspeed than at altitude. This is known as Ground Effect. The airflow around the left aircraft at altitude can flow around the surface of the aircraft in a normal manner. The airflow around thr right aircraft is disturbed by the proximity to the ground. The normal downwash of air produced by the wing and tail surfaces cannot occur, and the air becomes compressed under these surfaces. A "cushioning" effect occurs which allows the airplane to fly at slightly slower airspeed than at altitude. The maximum ground effect occurs at approximately 1/2 the wingspan above the ground. It is this effect which causes the plane to seem to float when near the ground on landing. It also allows the aircraft to be Aerodynamics http://www.uncletom2000.com/gs/aerodyn.htm (10 of 12) [1/23/2003 11:18:49 AM] "pulled" off the ground before adequate climb speed is achieved. Load Factor The load factor is the total load supported by the wings divided by the total weight of the airplane. In straight and level flight, the load factor is 1; i.e. the weight supported by the wings is equal to the weight of the loaded aircraft. The load factor is described as 1G Force. With a load factor of 1, the G force is 1. In other terms, the load supported by the wings equals the total weight of the loaded aircraft. In a turn, the weight of the aircraft increases due to the addition of centrifugal force. The rate of turn determines the total weight increase. A faster turn (steeper bank) generates greater centrifugal force. The centrifrugal force is straight out from the center of the turn. When the downward weight of the aircraft is mathematically resolved with the horizontal centrifrugal force, the load on the wings is the Resultant Load. In a 45 degree banked turn, the resultant load factor is approximately 1.4 G. In other words, the load on the wings is 1.4 times the loaded weight of the aircraft. In a 60 degree banked turn, the load factor is 2G. The load on the wings is TWICE the loaded weight of the aircraft. The G force is greater than 1 in a loop maneuver for the same reason; i.e. a centrifugal force adds to the airplane’s weight. An abrupt change from level to nose down creates an upward centrifugal force, decreasing the G load to less than 1G. Aerodynamics http://www.uncletom2000.com/gs/aerodyn.htm (11 of 12) [1/23/2003 11:18:49 AM] Aerodynamics The effects of the bank angle is shown in the graph on the right. The G Force is shown on the Left Side, and the Bank Angle is shown on the bottom of the graph. The maneuver of most importance to the private pilot is the forces in a turn. The most critical time is in tu rns in the traffic patern, when airspeeds are low, and the attention to bank angle and airspeed may be distracted by other duties. Back to Home Back to Table of Conents To Pitot & Static System http://www.uncletom2000.com/gs/aerodyn.htm (12 of 12) [1/23/2003 11:18:49 AM] Pitot and Static System Pitot and Static System The Pressure System The pitot-static pressure system provides the source of air pressure for the l ALTIMETER (ALT) l VERTICAL SPEED INDICATOR (VSI) l AIRSPEED INDICATOR (ASI) > The two parts of the system are (1) the pitot tube and pressure line (2) the static pressure system and lines. The pitot tube is normally mounted on the leading edge of a wing. The pitot tube on an aircraft used only for flight under Visual Flight Rules (VFR) may not be heated to prevent icing. Aircraft to be used under Instrument Flight Rules (IFR) are heated electrically, to prevent icing when operating in visible moisture and cold temperatures. A switch in the cockpit controls Pitot heat. The static pressure port is normally found on the side of the fuselage. On later model aircraft, an alternate static source is provided inside the cockpit. The pilot can select the internal static source if the outside source becomes clogged with ice.. When the pilot selects the alternative source, the instruments http://www.uncletom2000.com/gs/pitot.htm (1 of 7) [1/23/2003 11:18:50 AM] relying on the static pressure may operate slightly differently. 1. The altimeter (ALT) may indicate a higher-than-actual altitude. 2. The vertical speed indicator (VSI) will momentarily indicate a climb, then will settle back the initial indication. 3. The Airspeed Iindicator (ASI) will indicate greater-than-normal airspeed. Altimeter (ALT) THE ALTIMETER The Altimeter (ALT) allows the pilot to determine the height above Mean Sea Level (MSL). Correct altitude indication is very important for several reasons. a) The pilot must be sure the aircraft is being flown high enough to clear terrain and other obstacles. b) The pilot must maintain altitude according to certain air traffic rules and instructions to minimize the possibility of mid-air collision. c) The pilot can often select more favorable winds at certain altitudes. d) True Airspeed calculation requires that the altitude be known. The Altimeter measures the pressure of the outside air. A small bellows inside the altimeter which contains a constant pressure inside expands when the aircraft climbs, and contracts when the aircraft decends. This bellows is connected to a gear arrangement which causes the hands to turn as the bellows expands or contracts. The altimeter is essentially a barometer which is measuring the outside air pressure, but the indications on the dial indicate hundreds and thousands of feet. Most altimeters have either 2 or 3 pointers. If 2 pointers, the longer one indicates hundreds of feet, and the shorter pointer indicates thousands of feet. A third very short pointer which indicates ten's of thousands altitude exist on some altimeters. The indication in the diagram shown below is 1,430 feet. Altimeter Setting. The altimeter is an aneroid barometer. It is correct only when in a known atmosphere. An International Standard Atmosphere has been defined as a barometric Sea Level pressure of 29.92 inches of Mercury (Hg), and a temperature of 15 degrees Celsius. Effects of Atmospheric Pressure Changes Whenever the altimeter is in a non-standard temperature and pressure the altimeter reads incorrectly, and an adjustment means must be provided to compensate for the non-standard conditions. Atmospheric pressure change has the greatest effect on the instrument. Pitot and Static System http://www.uncletom2000.com/gs/pitot.htm (2 of 7) [1/23/2003 11:18:50 AM] On modern altimeters, an adjusting knob and scale is provided to allow adjustment for non-standard pressure. In the diagram of the altimeter face above, a window on the right of the instrument shows a graduated barometric scale, called the altimeter setting. The pilot can adjust the altimeter setting with the knob on the lower left. The setting shown is 30.00.

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If the altimeter is not periodically readjusted to the local barometric pressure, the plane will be too high if the local sea level pressure pressure is higher than 29.92 and will be too low if the local sea level pressure is less than 29.92 in. Hg. As one flies cross country, the altimeter should be adjusted every 100 miles or so. If flying from a low to a higher pressure area, the aircraft will be higher than indicated if appropriate altimeter adjustment is not made periodically. For example, if the altimeter indicates 5000 feet, it will actually be above 5000 feet when in the higher pressure area. Likewise, when flying from a high pressure area to a lower pressure area, the aircraft will be falsely low if no adjustment is made. If the altimeter is indicating 5000 feet, the aircraft will be below 5000 feet when in the lower pressure area.. The altimeter setting can be obtained in flight from any Air Traffic Control facility or from any FAA Flight Service Station. If taking off from an airport where no contact can be made with such a facility, set the altimeter to the altitude of the airport prior to takeoff. When flying at or above 18,000 feet (Flight Level 180) the altimeter must be set to 29.92. These altitudes are primarially used by fast jet aircraft. Since there is no possibility of ground collision, all aircraft operate with the same altimeter setting. Effects of Temperature Temperature affects the indicated altitude. The effect is not as drastic as pressure changes. Altimeters in small aircraft have no simple means to compensate for non-standard temperature. The effect is similar to Pitot and Static System http://www.uncletom2000.com/gs/pitot.htm (3 of 7) [1/23/2003 11:18:50 AM] high and low pressure changes. When going from low temperature to higher temperature, the aircraft will be higher than the indicated altitude. When going from high temperature to low, the aircraft will be lower than indicated on the altimeter. The pilot should keep this in mind if terrain clearance is a factor in the flight. MEMORY AID: From high to low (pressure or temperature) LOOK OUT BELOW. When flying over mountainous terrain, atmospheric conditions can cause the altimeter to indicate erroneous altitude by as much as 1,000 feet. Therefore, a generous margin of safety should be planned when flying over mountainous terrain.. Vertical Speed Indicator (VSI) The mechanism of the VSI is similar to the altimeter except the bellows contains a small calibrated hole that allows the pressure inside the bellows to slowly adjust to the same pressure as in the case. Therefore the pressure inside the bellows is similar to what it was a few seconds ago. If the change in pressure is slow, the up or down reading will be small. If the up or down altitude change is large over a short time, the rate of climb or decent will be large. If the pressure both inside and outside the bellows stays the same, the VSI will indicate zero. The single pointer indicates level flight (indicating 0), climb in feet per minute ( pointer deflected upward), and decent in feet per minute (pointer deflected downward). In small piston engine powered aircraft, the rate of climb will usually be less that 1000 feet per minute. Usual rate of decent enroute or approach to landing will be in the 500 feet per minute range. When flying straight and level, the instrument should indicate zero. Also when sitting stable on the ground the instrument should indicate zero. Most instruments are equipped with a small adjusting screw to calibrate the zero position when the aircraft is at rest on the ground. Pitot and Static System http://www.uncletom2000.com/gs/pitot.htm (4 of 7) [1/23/2003 11:18:50 AM] Airspeed Indicator (ASI) The Airspeed Indicator (ASI) measures the speed of the aircraft through the air. This should not be confused with groundspeed. Winds can affect how fast the aircraft tracks over the ground. Groundspeed is seldom the same as airspeed. Principle of Operation "Impact" air hiting the opening of the pitot tube which is pointing in the direction of travel creates a pressure in the pitot tube line. This pressure is connected by a small tube to the inside of a bellows in the ASI instrument. The outside atmospheric static pressure enters the case from the static line. The mechanism inside the ASI therefore measures the difference between the pitot pressure and the static pressure. Since the impact pressure of the pitot tube is proportional to the speed through the air, the speed through the air is indicated by the instrument. Indicated Airspeed (IAS) The color coding of the airspeed indicator has meaning. The color arcs are as follows. White Arc - Stall Speeds and Flap operating Range ----- -- Lower end of arc is the Power Off Stall speed with flaps and landing gear in the landing position. ----- -- Upper end of arc is the maximum flaps extend speed. Green Arc - Normal operating airspeed range ------- Lower end of arc is the power off stall speed clean (flaps and gear up) ------- Upper end of arc is maximum structural cruise speed. (Max normal operating speed). Yellow Arc - Caution range. Avoid this area unless in smooth air. Red Line - Never exceed speed. -------This is the maximum speed at which the aircraft can operate safely. ------- It should never be intentionally exceeded. Pitot and Static System http://www.uncletom2000.com/gs/pitot.htm (5 of 7) [1/23/2003 11:18:50 AM] Calibrated Airspeed (CAS) Although aircraft designers attempt to keep airspeed errors to a minimum, it is not possible to achieve complete accuracy throughout the complete range of the instrument. Two types of errors can be introduced. a. Installation error caused by the static ports sensing erroneous pressure. This is due to the unpredictability of the effects of the slipstream around the aircraft at various speeds and attitudes. b. The pitot tube does not always present the same frontal appearance to the atmosphere at varying attitudes. The pilot should consult the Pilot Operating Handbook (POH) for the table applicable to the aircraft being flown. True Airspeed (TAS) As altitude increases , air density decreases. The impact pressure at the port of the pitot tube is less at higher altitudes. The airplane is actually traveling through the air faster than indicated on the ASI. Consequently as altitude increase, Indicated Airspeed decreases. A mathematical correction factor must be applied to Indicated Airspeed (or Calibrated Airspeed) to arrive at a correct True Airspeed (TAS). This calculation can be made with he E6B Flight computer, or an approximate correction can be made by adding 2 percent per 1,000 feet of altitude to the IAS. EXAMPLE: Given IAS is 140kt and ALT is 6,000 feet. Find TAS. 2% x 6 = 12% (.12) 140 x 0.12 = 16.8 140 + 16.8 = 156.8 kt. (TAS) Some airspeed indicators have built-in adjustment scales that allows the pilot to adjust the instrument for temperature and pressure. Both the IAS and TAS can be read from such an airspeed indicator. V Speeds The Pilot Operating Handbook normally lists various airspeeds for differing situations and conditions. The definition of the usual V speeds is shown below. is an abbreviation for Velocity. VA. ..... design maneuvering speed VFE.... Maximum flap extend speed VLE.... maximum landing gear extend speed Pitot and Static System http://www.uncletom2000.com/gs/pitot.htm (6 of 7) [1/23/2003 11:18:50 AM] VLO....maximum landing gear operating speed VNE....never exceed speed VNO...maximum structural cruising speed VR......rotation speed VS0.... the power-off stalling speed or minimum flight speed in landing configuration VS1.... the power-off stalling speed (clean) with flaps and landing gear retracted. VX...... best angle of climb speed VY......best rate of climb speed Best Glide Speed Back to Home Back to Table of Conents To Gyroscopic Systems Pitot and Static System http://www.uncletom2000.com/gs/pitot.htm (7 of 7) [1/23/2003 11:18:50 AM] GYROSCOPIC INSTRUMENTS Gyroscopic Instruments Gyroscopic instruments may be driven either electrically or by vacuum. In most light aircraft the Turn Coordinator (TC) is electrically driven. Usually the Heading Indicator (HI) and Attitude Indicator (AI) are vacuum driven. Gyroscopic Principles Any spinning object possesses gyroscopic characteristics. The central mechanism of the gyroscope is a wheel similar to a bycycle wheel. It's outer rim has a heavy mass. It rotates at high speed on very low friction bearings. When it is rotating normally, it resists changes in direction. The gyroscope exhibits two predominant characteristics. Rigity in Space Precession Rigidity in Space. The gyroscope resists turning. When it is "gimbaled" ( free to move in a given direction) such that it is free to move either in 1, 2 or 3 dimensions, any surface such as an instrument dial attached to the gyro assembly will remain rigid in space even though the case of the gyro turns. The Attitude Indicator (AI) and the Heading Indicator (HI ) use this property of rigidity in space for their operation. The HI responds only to change of heading. The AI responds to both changes in Pitch and in Roll. Precession Precession is the deflection of a spinning wheel 90 ° to the plane of rotation when a deflective force is applied at the rim. If a force is applied the top of the rim (the plane of rotation), the precession (turn) will be 90° in the horizontal plane to the left. The Turn Coordinator (TC) uses this precession property. For example, then taxiing on the ground, the Turn Coordinator will move, with the small airplane in the instrument showing a bank, even though the aircraft is level. The banking of the small aircraft presentation indicates only that the aircraft is turning. The Vacuum System The Attitude Indicator (AI) and the Heading Indicator (HI) n light aircraft are usually driven by a vacuum system. The principal components are shown below. Not shown are auxillary devices such as valves, filters etc. A pump provides the vacuum to the AI and HI through a system of vacuum lines. A Vacuum Gauge is attached to the lines which gives the pilot an indication that adequate vacuum is being http://www.uncletom2000.com/gs/gyro.htm (1 of 5) [1/23/2003 11:18:51 AM] generated. Heading Indicator (HI) The Heading Indicator (HI) uses the principle of Rigidity In Space for it’s operation. The Gyro is mounted such that it registers changes around the vertical axis only; i.e. direction changes. The compass card attached to the gyro appears to the pilot as though it is turning. In reality, it and the attached gyro are remaining rigid in space, while the aircraft and case turn about the gyro. The HI is not automatically synchronized with the magnetic compass. It must be set to the compass heading while level on the airport surface prior to take-off. The HI gyroscope may precess in small amounts over time. Therefore, the HI should be checked against the compass in 15 minute intervals. The check should be done only while flying in straight, level and unaccelerated flight. If adjustment is required, the heading can be reset using the adjustment knob shown. The compass card has letters for the cardinal headings N, E, S, and W. Each numbered interval is every 30 degrees. The graduations are further divided by the longer marks every 10 degrees, and intervening short marks at the 5 degree points. GYROSCOPIC INSTRUMENTS http://www.uncletom2000.com/gs/gyro.htm (2 of 5) [1/23/2003 11:18:51 AM] A significant advantage of the HI over the magnetic compass is its steadiness in turbulence and various aircraft movements. As will be discussed later in the section on the magnetic compass, the compass can have several errors introduced during turns, acceleration and deceleration. The HI is unaffected by these maneuvers and by turbulence, and is a reliable instrument as long as the precession re-adjustment in made in timely fashion. Some makes of HI’s may "tumble" , loosing their gyroscopic characteristics, if subjected to more than 55 degrees of pitch or bank. In this condition, the heading card spins rapidly, and cannot be used for navigation until reset by the adjustment knob. Attitude Indicator (AI) The Attitude Indicator shows rotation about both the longitudinal axis to indicate the degree of bank, and about the lateral axis to indicate pitch (nose up, level or nose down). It utilizes the rigidity characteristic of the gyro. It is gimbaled to permit rotation about the lateral axis indicating pitch attitude, and about the longitudinal axis to indicate roll attitude. The principal parts of interest to the pilot are: · The miniature wings attached to the case remain parallel to the wings of the aircraft. · The horizon bar which separates the top (light) and bottom (dark) halves of the ball · The degree marks on the upper periphery of the dial. The first 3 on both sides of center are 10 degrees apart, then 60 degree bank marks, and 90 degree bank arks. Fifteen degrees of bank is called a standard rate turn. The adjustment knob is used to adjust the wings up or down to align with the horizon bar. This allows adjustment to the height of the pilot. Preferably, the adjustment should be made when level on the ground. When the wings are aligned with the horizon bar, the aircraft is in level flight. If the wings are above the horizon bar, the aircraft is in a climb. Wings below the horizon bar indicates a decent. The upper blue GYROSCOPIC INSTRUMENTS http://www.uncletom2000.com/gs/gyro.htm (3 of 5) [1/23/2003 11:18:51 AM] part of the ball represents the sky. The miniture airplane wings (fixed to the case) represent the wings of the aircraft. In the past, the instrument has been refered to as "an artificial horizon". When in a left turn, the blue portion of the ball will have rolled to the right, as tho you were looking at the horizon over the nose of the aircraft. In a right turn, the blue portion will have rolled to the left. Turn and Slip Indicator The instrument is comprised of two components. · The turn needle is an electrically driven gyroscope which indicates the rate of turn. The marks (often called the doghouse) on either side of center represents a bank angle of 15 degrees. This is termed a Standard Rate Turn. The rate of turn is 3 degrees per second. It takes 2 minutes to turn 360 degrees. · The glass level containing the black ball is called the Inclinometer. It provides the pilot with a measure of the Turn Quality. During both straight and level flight and during turns the ball should stay centered. The Turn and Slip Indicator acts as a partial backup to the Attitude Indicator in that it shows rate of turn. This type of instrument is usually found in older aircraft. Turn Coordinator The Turn Coordinator is similar to the Turn and Slip indicator. It is found in more modern aircraft. The main difference is in the presentation of the turn. A miniature airplane is used to show the bank instead of a needle. GYROSCOPIC INSTRUMENTS http://www.uncletom2000.com/gs/gyro.htm (4 of 5) [1/23/2003 11:18:51 AM] There are 2 marks on each side. The upper ones indicate level flight when the wing align with them. The lower marks indicates a bank angle of 15 degrees, which produces a standard rate turn. When the aircraft turns right, the minature aircraft in the instrument indicated a right bank. When turning left, it indicates a left bank. Turn Quality The inclinometer in both the Turn and Slip Indicator and the Turn Coordinator measures the turn quality. As mentioned previously, when in a turn, part of the lift of the wing goes into "turning" the aircraft. This is called the Horizontal Component of Lift (HCL). This HCL is directed toward the center of the turn. Also, a force directed outward and away from the center of the turn exists. This is called Centrifugal Force (CF). For the turn to be coordinated these two opposing forces must be equal. When they are equal, the ball in the inclinometer will remain in the middle. When too much rudder is applied, a skid results. The Centrifrugal Force is bigger than the Horizontal Component of Lift (HCL). This makes the ball go toward the outside of the inclinomenter (i.e. the ball in NOT in the middle). When insufficient rudder is applied, a slip results. The Horizontal Component of Lift (HCL) is larger than the Centrifrugal Force (CF). The ball rolls toward the lower side( or inside) on the inclinometer. The term step on the ball is often used as a memory aid in overcoming a slip or skid. In actuality, more rudder pressure (or less bank) must be applied in a slip. Less rudder pressure (or more bank) must be applied in a skid. In both cases correction must be made so that HCL = CF to keep the ball centered. Back to Home Back to Table of Conents To Magnetic Compass GYROSCOPIC INSTRUMENTS http://www.uncletom2000.com/gs/gyro.htm (5 of 5) [1/23/2003 11:18:51 AM] Magnetic Compass Magnetic Compass The magnetic compass is the only instrument in the aircraft by which the pilot determines the direction of flight. Magnets in the compass cause it to align with the Magnetic North Pole. The compass card has the four cardinal headings shown as N, E, S, and W. Numbers appear every 30 degrees. Long vertical marks occur in 10 degree increments, with intervening short marks at 5 degree points. The compass card containing the magnets are mounted on a small pivot point in the center of the card assembly. This allows the compass card to rotate and float freely. It is somewhat like suspending a paper cup, upside down, on a pencil point located at the center of the cup bottom. The enclosure is filled with white kerosene to provide a medium to dampen out some vibration and unwanted oscillations. A "lubber line" in etched on the glass face of the instrument to enable exact reading of the compass. Magnets in the compass align themselves along a Magnetic North-South orientation. Whenever the aircraft is headed toward magnetic North, the compass will indicate N. If the aircraft turns from this direction, the magnets in the compass still align to this N-S direction. Similar to a gyro, the case of the compass and the lubber line is fixed to the aircraft. Thus when the airplane turns, the the case turns about the compass card. The lubber line will then show a reading other than North. Compass Errors Magnetic lines of force surround the Earth, flowing from the North to South Magnetic poles. The magnetic field strength is greatest near the magnetic poles and weakest at the Equator. Several compass errors can occur. These are: 1. Magnetic Variation 2. Compass Deviation 3. Magnetic dip 4. Compass Card oscillation http://www.uncletom2000.com/gs/compass.htm (1 of 4) [1/23/2003 11:18:52 AM] Magnetic Variation The Magnetic North Pole and the True North Pole are not at the same location on the surface of the earth. Magnetic Variation at any given location on the earth’s surface is the difference between the Compass North and True North. The map below shows the magnetic variation at various locations in the US. The Agonic Line is the line of zero degree variation. It proceeds from upper Michigan through central South Carolina. Variation values to the East of the agonic line are called Westerly Variation; i.e. the magnetic north pole is West of True North. Likewise, the variation values west of the agonic line are known as Easterly Variation; i.e. the Magnetic North Pole is East of True North. Magnetic North changes in small amounts each year. Aeronautical charts are updated periodically to correct for this yearly change. When plotting a course on an aeronautical chart, the degrees of heading are measured against latitude and longitude lines. This is called a True Course (TC) because it is being measured relative to the True North Pole. Since the pilot relies on the magnetic compass for direction, the pilot will be steering the aircraft relative to the Magnetic North Pole. Therefore, the pilot must convert the True Course (TC), as plotted on the navigation chart, to a Magnetic Course (MC) by which to steer using the compass. . To convert from TC to MC, Westerly Variations must be ADDED to TC to get MC (see right hand example below). MC = TC + VAR. (MC = 45° + 10° = 55°). In other words, the pilot must steer 55° magnetic to fly over a true course of 45°. Likewise, Easterly Variation must be SUBTRACTED from TC to get MC (see left hand example below). Compass Deviation Magnetic deviation is the difference between the compass indications when installed in the aircraft compared to the indications when the compass is outside the aircraft. The cause of this difference is that the compass magnets can be influenced by magnetic fields within the aircraft due to electronic equipment and other factors. These magnetic disturbances may cause the compass readings to be slightly in error. Such errors are called Compass Deviation.. In other words, the compass reading when inside the aircraft "deviates" from a normal reading. To determine compass deviation, the aircraft is parked on a compass rose painted on a level surface such as a Magnetic Compass http://www.uncletom2000.com/gs/compass.htm (2 of 4) [1/23/2003 11:18:52 AM] ramp or taxiway. All of the electronic equipment is powered on as in normal operation. The nose of the aircraft is placed on the Magnetic North marking on the ground. Deviation in the compass reading (from North) is recorded. The aircraft is then rotated to 30 degrees to the right, and the deviation noted. The aircraft is turned in increments of thirty degrees through the 360 degrees, and deviation from the proper reading is noted. This procedure is called swinging the compass. These errors are posted on a Deviation Card placed at the lower portion of the compass. For example, it may state for a course of 180, steer 178°. Usually the errors are only a few degrees, but should be taken into consideration by the pilot then tracking a given magnetic course. Compass Dip Errors Any time the compass card is not perfectly level, the magnets dip downward toward the earth. The result is that the compass does not correctly align with Magnetic North the same as when the card is level. This results in erroneous indication while in the non-level state. Dip occurs under 2 conditions. 1. During turns from the north and south. (i.e. Plane is in a bank. 2. During acceleration or deceleration while on an East or West heading. Compass Turning Errors When the aircraft initiates a right turn from the North, the dip of the compass causes the compass to initially indicate a turn IN THE OPPOSITE DIRECTION (i.e. the compass turns left). The amount of initial error is approximately equal to the Latitude position of the aircraft. If at a 30 degree latitude, and a right turn from North is initiated, the compass card will initially turn LEFT to 330 degrees. As the right turn to the EAST proceeds, the compass will start to catch up, so that when EAST (090) degrees is reached the compass will indicate correctly, even though the aircraft is still banked. If the turn is LEFT from NORTH, the compass will turn right to 030 degrees, and will catch up by the time WEST (270) degrees is reached.

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THEREFORE, WHEN TURNING FROM NORTH, THE COMPASS LAGS. If turning to the North, you will have to roll back to straight and level approximately 30 degrees prior to reaching North on the compass. When turning from SOUTH, the opposite action occurs; the compass LEADS by the amount of the degrees Latitude. If at 30 degrees Latitude, the lead will be approximately 30 degrees. If you are turning to the South, you will have to roll back to straight and level approximately 30 degrees past South reading. MEMORY AID: Turn to N, Under Shoot. Turn to South, Over Shoot. Compass Acceleration Errors When the aircraft is on an East or West heading, acceleration or deceleration of the aircraft causes the compass card to tilt forward or backward, respectively. This tilting causes the compass card magnets to swing downward toward the earth, which in turn causes the compass to rotate to an incorrect indication. This error is maximum when on an East or West heading, and gradually diminishes to zero when a North or Magnetic Compass http://www.uncletom2000.com/gs/compass.htm (3 of 4) [1/23/2003 11:18:52 AM] South heading is reached. Acceleration of the aircraft causes the compass to erroneously swing to the North. Deceleration causes erroneous rotation toward the South . Again, the error is approximately equal to the Latitude degrees of the aircraft location. At 30 degrees Latitude, acceleration causes the swing to a northerly reading to be approximately 30 degrees. Once the acceleration ceases, and the aircraft assumes a constant forward velocity, the compass will return to it’s original East or West reading. In like manner, deceleration of he aircraft causes an erroneous swing to a southerly reading of approximately 30 degrees at the same Latitude.. MEMORY AID: A N D S - Accelerate North, Decelerate South Back to Home Back to Table of Conents To Engine Fundamentals Magnetic Compass http://www.uncletom2000.com/gs/compass.htm (4 of 4) [1/23/2003 11:18:52 AM] The Engine Engine Most light aircraft use a conventional 4 stroke engine. It operates similarly to an automobile engine. There may be 4, 6, or 8 pistons in the engine. The four strokes are: 1. Intake 2. Compression 3. Power 4. Exhaust · Intake Stroke - The piston goes downward during the intake stroke. A valve called the Intake Valve is open, such that an air/fuel mixture enters the cylinder through the carburetor. During this operation a second valve, the Exhaust Valve closed. · Compression Stroke - During this stroke, the piston is forced upward by the crankshaft. Both the Intake and Exhaust valves are closed. Consequently the air/fuel mixture in the closed cylinder is compressed by the upward movementof the piston. · Power Stroke - As the piston nears the top of the cylinder, the spark plugs fire under control of the magnetos. There are 2 spark plugs in each cylinder, with a separate magneto supplying the electrical spark current to each plug. The spark ignites the fuel/air mixture, causing an explosion to occur in the cylinder. This forces the cylinder downward, and imparts power to the crankshaft. While one cylinder is performing the power stroke, other cylinders are in some phase of the other three strokes. Therefore the power stroke is the only one contributing to propulsion of the aircraft. · Exhaust Stroke - When the piston reaches the bottom of the power stroke, the Exhaust Valve opens. The piston is pushed upward by the crankshaft, causing the burned fuel / air mixture to be purged from the cylinder. The exhaust valve closes, and the piston is now in a position for another intake stroke. The pistons connect to the crankshaft through connecting rods. They attach the piston, which has an updown motion, to the crankshaft which turns in a rotary motion. The crankshaft is usually directly connected to the propeller. In some aircraft, a gear arrangement connects the propeller to the crankshaft. The crankshaft may also drive auxiliary devices such as the Magnetos, Vacuum Pumps, Alternator and other devices. The connection may be directly or through lleys, belts and gears. The ignition system is comprised of the magnetos and spark plugs, and is independent of the electrical system. Even if the alternator and battery are inoperable, the ignition system continues to function. If there is insufficient battery power to crank the engine, the engine can be started on most small aircraft by http://www.uncletom2000.com/gs/engine.htm (1 of 2) [1/23/2003 11:18:53 AM] “hand propping”. This is a procedure wherein the propeller is turned swiftly by hand to get the magneto system to fire, and start the engine. It is similar to pulling the starter cord on a lawn mower. EXTREME CAUTION MUST BE EXERCISED WHEN HAND PROPPING AN ENGINE. A meter within the cockpit called the Tachometer indicates the engine Revolutions per Minute (RPM). Monitoring devices such as the Oil Pressure and Oil Temperature gauge in the cockpit may be attached to the engine. Back to Home Back to Table of Conents To Fuel System The Engine http://www.uncletom2000.com/gs/engine.htm (2 of 2) [1/23/2003 11:18:53 AM] Fuel System Fuel System Most modern aircraft are equipped with 2 or more fuel tanks (or cells). In high wing aircraft, the cells are housed in the wings. Since they are higher than the engine, the fuel flows down to the engine by the force of gravity. A typical high wing system is shown at right. On low wing aircraft fuel pumps are required. To initially get fuel to the engine for starting, an electrical “boost pump” is turned on to pump fuel to the engine. After the engine is started, a mechanical fuel pump driven by the engine feeds fuel to the engine. The electric boost pump can now be turned off. Each fuel tank is equipped with a drain valve located at the lowest point in the tank. This drain allows the pilot during preflight walk-around to check for and drain off any water which may have accumulated in the fuel tank. There is usually another drain located at the lowest part of the fuel piping system. This valve must also be drained during pre-flight to eliminate any water which may have accumulated in the fuel lines. Associated with this drain is a fuel strainer which filters out foreign matter which may be in the fuel system. A vent line allows air to enter the tank as fuel is used. During hot weather, fuel may expand and overflow through the vent when tanks are full. A fuel selector valve located inside the cockpit allows the pilot to select which tank(s) are to be in use during flight. Most small aircraft operate with the selector set on Both, such that both the left and right fuel tanks are simultaneous feeding fuel to the engine. The pilot may set the selector on Left or Right tank as a means of equalizing the loading of the aircraft. Usually, the selector should be set to both for take-off and landing. Pilots of low wing aircraft should exercise caution in their fuel management if tank selection is other than both. Running a tank dry can cause the engine to quit and vapor lock to occur in the fuel lines. It may be impossible to restart the engine under these conditions. There is a fuel gauge in the cockpit for each fuel tank. The lower 1/4 of the fuel gauge indication is http://www.uncletom2000.com/gs/fuel.htm (1 of 3) [1/23/2003 11:18:53 AM] marked with a red line as a caution to the pilot of a low fuel condition. The pilot should never rely on the fuel gauge as the sole measure of fuel remaining. The gauges on aircraft are subject to a variety of indicator errors. The pilot should therefore double check the fuel remaining based on the power setting of the engine in flight and time in flight. Inside the cockpit a fuel mixture control and a fuel primer pump are located on the instrument panel. The mixture control is used to adjust the air/fuel mixture for the altitude being flown. It allows the pilot to adjust the fuel/air ratio entering the engine. As altitude is gained, the intake air becomes less dense. Less fuel must be fed through the carburetor to permit the fuel/air mixture to remain correct proportion. If leaning is not accomplished by the pilot, a rich mixture (too much fuel) results. This is not only wasteful of fuel, but can result in fouled spark plugs due to carbon and soot buildup on the spark plugs. A rough running engine results. An additional gauge called an Exhaust Gas Temperature Gauge can be installed in the aircraft as an aid in achieving the proper “leaning” of the engine. The fuel primer is a plunger that can be used in cold weather to inject fuel directly into the carburetor as an assist in starting the engine in cold conditions. Three different grades of fuel are used in reciprocating engine aircraft. These grades are designated by octane rating and are color coded so the pilot can insure the proper grade of fuel is being pumped into the tanks. These grades are: OCTANE RATING..........FUEL COLOR · ..... 80/87........ ..... ..... .........Red · .......100LL (low lead). ..... ....Blue · ...... 100/130.... ..... ..............Green When refueling, if the appropriate grade of fuel is not available, USE THE NEXT HIGHER GRADE. Using a lower grade can cause overheating and damage to the engine. Sparks during refueling can be an extreme fire hazard. The following precautions should be taken when refueling is in progress. 1. Attach a ground wire between the fuel pump or truck to a metal part of the aircraft. This will neutralize any static charge which may exist between the pump and the aircraft. 2. The fuel nozzle should be grounded to the side of the fuel filler hole during refueling. 3. The fuel truck should be grounded to both the aircraft and the ground. Do not use automotive fuel unless the engine has been specially modified for automotive fuel use. Back to Home Back to Table of Conents To Induction System Fuel System http://www.uncletom2000.com/gs/fuel.htm (2 of 3) [1/23/2003 11:18:53 AM] Fuel System http://www.uncletom2000.com/gs/fuel.htm (3 of 3) [1/23/2003 11:18:53 AM] INDUCTION SYSTEM Induction System The engine receives ram air through an intake in the lower front portion of the engine cowling. An air filter is placed at the intake end of the duct. This filter removes dirt, dust and foreign matter from entering the carburetor. The air passes through an airbox, then to the carburetor intake. In the event that the airflow to the carburetor becomes blocked by carburetor ice or intake ice, an alternate heated air source can be selected by the pilot by pulling out a carburetor heat control in the cockpit. Use of the heated air will result in approximately 75 to 100 RPM drop. A throttle is located on the instrument panel in the cockpit. When the throttle is closed, it is pulled rearward toward the pilot until it is stopped by mechanical means. At this setting, the engine continues to run, but at “idle” speed (a few hundred RPM). As the throttle is moved forward, the throttle valve in the carburetor opens allowing more air into the carburetor, thus increasing the RPM. When the throttle is full forward maximum RPM results. The throttle can be locked into a set position with a friction lock so that in cruise flight the power setting will remain set. This relieves the pilot from constant attention to the throttle. Carburetor The carburetor provides 2 principal functions. · It mixes the fuel with the air in the proper proportion · It regulates the amount of air (and thus fuel) that enters the engine. The the air is routed from the intake through ducts into the carburetor. The carburetor on most engines are of the updraft type; i.e. the carburetor is mounted on the bottom of the engine, and the fuel/air mixture is sucked upwardto the engine. When the carbuerator heat control in the cockpit is pulled on, heated air enters the carbuerator. The air source comes from inside the cowling, and passes through a “heat” box to warm the intake air. The heated air can be selected when atmospheric conditions are conducive to carburetor icing or the normal intake duct become blocked by ice at the induction port and air filter. The carburetor is equipped with a small chamber containing fuel and a float valve. The valve maintains a constant amount of fuel in the chamber. This provides a constant and sufficient source of fuel to satisfy the fuel demands of the engine. The main air duct of the carburetor is a tubular structure which decreases in diameter near the middle of the duct, then increases in diameter near the intake manifold end of the carburetor. This is called the “venturi”. This decreased diameter creates a vacuum in accordance to the Bernoulli principle. The fuel intake port is located in this section. A metered amount of fuel is sucked into the carburetor. The fuel http://www.uncletom2000.com/gs/induct.htm (1 of 4) [1/23/2003 11:18:54 AM] vaporizes into fine particles in the intake air flow. This atomized fuel and air mixture is of proper proportion to cause correct burning of the fuel/air mixture in the engine. The fuel / air mixture is set by design to be correct for operation at sea level. As the engine is operated over a range of altitudes and air densities, the pilot can adjust the mixture via manual means in the cockpit. It is called the “mixture control”. The correct mixture adjustment procedure is covered in the Pilot Operating Handbook (POH) for the given aircraft. Some aircraft are equipped with an Exhaust Gas Temperature Gauge in the cockpit. A proper fuel/air mixture will produce a given exhaust gas temperature. The pilot can adjust the fuel / air mixture to a fairly accurate measurement by observing that the exhaust gas temperature is within the proper range. The throttle regulates the amount of fuel/air that enters the engine, thereby controlling the power that the engine develops. On aircraft with a “fixed pitch” propeller, the throttle directly controls the engine RPM. On aircraft with a variable pitch propeller, a Manifold Pressure Gauge directly measures the engine power being developed. A propeller pitch control controls the propeller blade angle. The power setting of the engine requires adjustment of both the throttle and propeller pitch control. The carbuerator has an accelerator pump which will provide a “burst” of additional fuel for quick development of maximum horsepower, such as performing a go around from landing approach. An economizer valve allows the engine to idle when the throttle closed. Icing The predominate forms of icing affecting engine operation are carbuerator ice, throttle ice and induction ice. Carbuerator Icing Carburetor icing is a constant concern to the pilot when operating in high humidity and visible moisture conditions. Whenever the outside temperature is 20° to 70° F, ice creation in the throat of the carburetor is a possibility. Due to the Bernoulli effect and the vaporization of the fuel in the venturi, the temperature of the fuel / air mixture can be as much as 50 degrees lower than the outside air. Induction Icing INDUCTION SYSTEM http://www.uncletom2000.com/gs/induct.htm (2 of 4) [1/23/2003 11:18:54 AM] The air induction port at the front of the cowling can become partially or totally clogged with ice when air temperatures are 32° F or below while flying in visible mousture. This is known as “impact” ice, and is most prevalent when the Outside Air Temperature (OAT) in around 25° F and super-cooled moisture exists. Throttle Ice Throttle ice in the carburetor occurs most often when the throttle is partially closed. This can occur at low cruise speeds or near idle situations such as approach to landing. Some manufacturers recommend that the alternate air source (carburetor heat on) be used anytime the power setting of the aircraft is below a certain point even though high atmospheric moisture content is not present. For fixed pitch propeller configurations, most aircraft should use carburetor heat below 2000 - 2100 RPM. The location of ice in the carbuerator is shown in the diagram at right. The vaporization of the fuel in the venturi additionally cools the throttle area. Even a small amount of ice in the carburetor or the induction system will reduce power. Usually this condition is detected by a gradual drop in RPM (or Manifold Pressure). Application of carburetor heat will usually cause an additional temporary decrease in power, but as the ice melts, the power should be restored. If icing is persistent, it may be necessary to operate with some carburetor heat on continuously. Fuel Injection In these systems, the air intake system is similar to carbuerated systems. However, the fuel is not vaporized in a venturi, but rather is injected directly into the engine cylinder just prior to the spark plugs firing. A specific amount of fuel is injected and an appropriate amount of air is vented though the air induction system to provide for proper combustion. There are several advantages to fuel injected systems. · Less susceptibility to icing · Fuel flow is better controlled · Faster throttle response since the fuel is directly injected into the cylinder. · Better distribution of fuel to each cylinder. · Easier starting in cold weather. Some disadvantages are: · Starting a hot engine can sometimes be difficult. · Vapor lock during ground operations on hot days. · Difficult engine re-start if engine quit due to fuel starvation.

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INDUCTION SYSTEM http://www.uncletom2000.com/gs/induct.htm (3 of 4) [1/23/2003 11:18:54 AM] Back to Home Back to Table of Conents To Electrical System INDUCTION SYSTEM http://www.uncletom2000.com/gs/induct.htm (4 of 4) [1/23/2003 11:18:54 AM] Electrical System Electrical System Most small aircraft are equipped with a 28 volt direct current electrical system. The system is powered by an Alternator which drives the electrical devices and stores energy in the battery. A simplified diagram is shown at below. Not shown are the starter, and starter switch, and various other electrical regulators and devices. Electrical System The Master Switch (labled MS) causes the electrical system to connect the electrical buses and devices to the battery. The battery provides the power to crank the starter. Once the engine is running, power is supplied by the alternator and the battery is recharged. Numerous circuit breakers feed off the Primary Electrical Bus, and provide individual circuits to power the electrical devices. Although the arrangement will vary from one make and model aircraft to another, the basic principles are the same. By providing numerous circuit breakers and dividing the electrical load into several different circuits, a malfunction in one system can be turned off without adversely affecting the other circuits. The breakers will be labeled as to their general use, and the amperage will be marked on the face of the breaker push button. On older model aircraft, fuses are used instead of circuit breakers. Usually an alternator light is located on the instrument panel to provide a means for the pilot to determine alternator is providing power to the system. In addition, an ammeter on the instrument panel can determine the general health of the electrical system. After the battery is used for starting, a considerable “charge” should be shown, indicating that the alternator is replenishing the power drained from the battery during engine cranking. If the indicator shows zero while electronic equipment is ON, failure of the alternator to charge the battery is indicated. A second bus is provided to power the electronic and avionics equipment. This bus is connected to the Primary Bus via the Avionics Switch. This switch should not be turned on until the engine is started to prevent the possibility of high voltage transient currents resulting from engine starting from feeding into sensitive electronic equipment. The pilot should also turn this switch OFF prior to engine shut-down for the same reason. Prior to start-up the pilot should check the status of all circuit breakers as a part of the pre-flight check. A “tripped” breaker will project out farther from the control panel than does a properly functioning breaker. Pushing the breaker in will reset it to it’s normal operating position. If it pops out again, there is a malfunction in the circuit which it feeds, and repair should be made prior to flight. The pilot should turn on the master switch during the walk-around pre-flight inspection to insure that the rotating beacon and strobe lights (If present) are functioning. If all or part of the flight is to occur at night, the navigation lights, instrument panel lights, taxi and landing lights should also be checked for http://www.uncletom2000.com/gs/elecsys.htm (1 of 2) [1/23/2003 11:18:54 AM] proper operation. Back to Home Back to Table of Conents To Propulsion System Electrical System http://www.uncletom2000.com/gs/elecsys.htm (2 of 2) [1/23/2003 11:18:54 AM] Propulsion System Propulsion System The propeller is a rotating airfoil. It is subject to drag, stalls and other aerodynamic factors that apply to any airfoil. The propeller provides the thrust to pull the aircraft through the air. As seen at right, the cross section near the hub of the propeller is thick, and has a fairly large angle of attack. The angle of attack and the thickness decreases toward the tip of the blade. Since the linear speed at the tip is much faster than at the hub the change in angle of attack provides uniform thrust along the surface of the blade. The propeller is normally connected directly to the engine crankshaft. Some aircraft , however, employ gear arrangements between the engine and the propeller. Propellers fall into two main categories. · Fixed Pitch · Controllable pitch Controllable pitch propellers allow the pilot to set the pitch of the blades, either directly or via a governor, to the best angle for the flight condition and performance desired. Usually for takeoff, a fairly “flat” angle of attack and high engine RPN is used to produce maximum horsepower and thrust. As altitude is gained the pilot can reduce RPM and increase pitch for a cruise climb condition. Once cruise altitude is reached the throttle, mixture and propeller pitch can be adjusted for the desired cruise performance. The pilot has only one method of controlling thrust on fixed pitch propellers; that being adjusting engine RPM. With controllable pitch propellers, the pilot can adjust two controls; these being RPM (throttle) and Manifold Pressure (propeller pitch control). The Tachometer indicates RPM and the Manifold Pressure Gauge indicates the manifold pressure. On constant speed propellers, a governor automatically adjusts the pitch of the propeller blade whenever the engine throttle setting is changed. Low RPM and High Manifold pressure should be avoided, as this places undue stress on engine components, and can lead to eventual engine failure. For any given blade angle, the propeller has an ideal geometric pitch. It is designed to travel a certain distance in one revolution. However, due to slippage, the ideal geometric pitch is never attained. Therefore the effective pitch is always less than the geometric pitch. The propeller is never 100% efficient. Back to Home Back to Table of Conents To Stall Warning System http://www.uncletom2000.com/gs/propul.htm [1/23/2003 11:18:55 AM] Put_Your_Title_Here Stall Warning System Most aircraft are equipped with a Stall Warning system of some type. On some older aircraft, a small moveable flap located on the leading edge of the wing engages an electrical switch in the cabin, which activates a stall warning buzzer or horn. On some later aircraft, the system is pneumatic, with a small slot in the leading edge of the wing. Both types sense approach to stall, and sounds a device in the cabin, warning of impending stall. Back to Home Back to Table of Conents To Weight and Balance http://www.uncletom2000.com/gs/stalwarn.htm [1/23/2003 11:18:55 AM] Weight and Balance WEIGHT AND BALANCE Overview Weight affects the flight performance of an aircraft in many respects. An airplane which is overloaded will be deficient in performance because: Higher takeoff speed is required. Longer take-off run. Reduced rate of climb performance Shorter range of flight Reduced cruise speed Reduced maneuverability Higher stall speed Higher landing speed Longer landing roll Balance Principles As shown in the figure below, the aircraft is somewhat like a childs "teeter-totter" with respect to longitudinal balance. For the plank to be in balance, The sum of the moment s on each side of the pivot point (fulcrum) must be equal. A MOMENT is simply the weight multiplied by a moment arm (distance) from some reference point. In this example, the moments are measured from the center fulcrum point. http://www.uncletom2000.com/gs/wb.htm (1 of 9) [1/23/2003 11:18:57 AM] As seen, the plank is in balance because the sum of the moments on each side equals 5000 pound inches. If a weight on either side is moved, or a weight is changed, the plank will no longer be in balance. An aircraft in flight is very similar. The pivot point (fulcrum) is the located at the Center of Lift of the wing. The load on the left is the total weight of the aircraft located at the Center of Gravity (CG) with a counter-balancing force on the right provided by the elevators. Note that if the location of the CG or the weight on the left changes, the elevator force must also change in order to maintain the balance. Also note, if the fulcrum (center of wing lift) changes, the elevator force must be changed to maintain a balanced condition. Such an event can occur when the angle of attack and/or engine thrust is changed. The Center of Gravity As previously stated, the weight of an aircraft and its load is distributed throughout the aircraft as shown below by the small downward arrows. All of the small individual weights can be resolved into one single weight acting at the Center of Gravity and shown as the large arrow.. Weight and Balance http://www.uncletom2000.com/gs/wb.htm (2 of 9) [1/23/2003 11:18:57 AM] From the analogy of the plank above, we can see that if we change either the weight of the aircraft, or the center of gravity, this in turn changes the force (either up or down) that the elevator must produce. For each aircraft design, the manufacturer specifies a maximum weight for operation of the aircraft, and also a maximum forward and rearward location of the Center of Gravity (CG). This is called the CG RANGE. For safe operation, the aircraft must be operated within these parameters. In order to calculate where the center of gravity is located, the manufacturer specifies some point in the aircraft as a reference point (DATUM). In many Cessna 172 type aircraft, the datum is located at the lower firewall of the cabin, just ahead of the rudder pedals. You as a pilot do not need to know where this is located in order to calculate weight and balance, as the manufactirer provided moment arm and/or Weight and Balance http://www.uncletom2000.com/gs/wb.htm (3 of 9) [1/23/2003 11:18:57 AM] moment in the weight and balance tables for the aircraft. An aircraft mechanic must know where whis point is, however, if equipment change is made to the aircraft which changes either the aircraft CG or Empty Weight. An airplane is designed and certified to withstand specified loading on it’s structure. As long as the gross weight and load factor are within limits, the aircraft can be operated safely. Continued operaton of an aircraft in an overloaded condition can cause structural failures. Metal fatigue is hastened, and can lead to stress failures even in normal operating modes. Effect on Wing Loading The location of the CG affects the total load which the wings must sustain. If the CG is at or near the Center of Lift of the wing the elevators do not have to generate much (if any) downward force. If the CG is aft of the center of lift, the elevators must produce an upward force. If the aircraft is nose heavy (forward CG) the load on the wing and elevator surfaces will be greater. An aft CG location causes the airplane to require more "nose down" elevator for stall recovery. A forward CG enhances stall recovery as the aircraft will naturally want to "nose down". Definitions MOMENT ARM -- a horizontal distance of an object measured from a defined “datum” point to the CG of the object, usually measured in inches. A (+) arm means the object is behind the datum. A (-) arm indicates the object is forward off the datum point. MOMENT -- the product of a moment arm and the associated weight. (Weight x Arm) EMPTY WEIGHT-- the combined weight of the aircraft, and permanently mounted equipment. It includes unusable fuel and hydraulic fluid. Most manufactures include the oil in the empty weight. Center of Gravity -- the point at which the airplane will be in balance. CG Limits -- the most forward and most rearward CG points specified by the manufacturer for safe control. CG Range -- the distance from the most forward and rearward CG points as specified for the given aircraft. DATUM -- a point in the aircraft from which all moment arms are measured. FUEL LOAD -- the weight of the useable fuel. It does not include unusable fuel in the tanks and lines. GROSS WEIGHT-- Total weight of aircraft, fuel, passengers and baggage. Weight and Balance http://www.uncletom2000.com/gs/wb.htm (4 of 9) [1/23/2003 11:18:57 AM] MAX LANDING WEIGHT - Maximum gross weight allowed for landing. MAX RAMP WEIGHT -- Maximum gross weight prior to taxi and take-off. MAX TAKEOFF WEIGHT -- the maximum allowable weight at start of takeoff run USEFUL LOAD -- Gross weight minus the empty aircraft weight. STANDARD WEIGHTS -- Gasoline 6 lb. per gal; Oil 7.5 lb. per gal. (US Measure) Methods of Determining Weight and Balance The method of determining weight and balance may vary with aircraft manufacturer and type of aircraft.

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These methods are: 1. Center of Gravity Calculations 2. Center of Gravity Graphs 3. Center of Gravity Tables 4. Loading Schedules (Placards) Center of Gravity Calculations To determine the location CG, add up all the weights and all the moments. Divide the sum of the moments by the sum of the weights. This is illustrated in the diagram. All moments aft of the datum are positive numbers. All moments forward of the datum are negative. In the example, the oil is the only negative moment since it is forward of the DATUM.. Calculate the weight of oil at 7.5 pounds per gallon. Calculate fuel at 6 pounds (US) per gallon. The procedure to calculate the CG is as follows: 1. Add up all weights, including empty aircraft 2. Multiply each weight by it’s moment arm in inches to get the moment for that item. 3. Add up all the moments 4. Divide the sum of the moments by the total weight to get the CG A TYPICAL W/B PROBLEM ITEM WEIGHT lbs MOMENT ARM in. MOMENT LB IN Weight and Balance http://www.uncletom2000.com/gs/wb.htm (5 of 9) [1/23/2003 11:18:57 AM] A = AIRCRAFT 1000 6 6000 P = PILOT 150 11 1650 B = BAGGAGE 40 32 1280 O = OIL 7.5 -4 -30 F = FUEL 120 16 1920 TOTAL 1317.5 CG? 10820 In the example, CG? = 10820/1317.5 = 8.21 in. aft of the datum. Loading Graph Frequently the manufacturer provides a graphical method for determining weight and balance. Determine the load moment for each load item using the appropriate line in the graph. For example, for pilot and front seat passenger, total the combined load weight. Go up the Load Weight axis (Y axis) to the pilot & passenger weight. Then go horizontal to the pilot & passenger line (Red line). Then go down to the X axis to find the load moment/1000. Do the same for fuel (blue line), rear passengers (green Line) and baggage (black line). Total up the weight and the Load Moments. EXAMPLE: Determine the Load and moment from the loading graph above for each of the following load items. Weight and Balance http://www.uncletom2000.com/gs/wb.htm (6 of 9) [1/23/2003 11:18:57 AM] Weight and Balance Using Loading Graphs Weight and Balance Weight **Moment Empty Weight 1,364 51.7 Front Seats 400 15.0 Baggage 120 11.5 Fuel (38 gal) 228 11.0 Oil (2 gal) 15 - 0.2 TOTAL 2,127 89.0 Derive the values as follows: 1. Empty Weight and moment are values provided by the manufacturer. 2. Pilot & Passenger - Add weight for Pilot and Passenger. In this example 400lb. Go up the left side (Y axis) of the graph to 400 lb. weight, then horizontal to the “Pilot & Passenger” line. Read vertically down from the intersection to the horizontal (X) axis, and read a Moment/1000 value of 15.0. 3. Baggage - The baggage weight is 120 lb. Go up left side of the upper graph to a load of 120 lb. Continue horizontally to intersect the “baggage” line. Go downward from this intersection and read a Moment/1000 value of 11.5. 4. Fuel -- 38 gallons at 6 pounds per gallon is 228 pounds. Go up the left side of graph to a weight value of 228 lbs., then horizontally to intersect the“fuel line. Go downward to read a Moment/1000 value of 11.0. 5. Oil was not included in the empty weight of this aircraft, therefore it must be entered into the calculation. Two gallons of oil is 15 lb. The moment is -0.2 lb-in. Loading Envelope Once the total weight and the total moment/1000 is found, use the load and CG envelope to ascertain that the aircraft is properly loaded. Go up the left side to a total load of 2127 lbs. Draw a horizontal line. Go along the bottom scale to find the loaded aircraft moment / 100 value of 89.0. Draw a vertical line. The aircraft is properly loaded if the intersection of the horizontal and vertical lines is within the envelope. http://www.uncletom2000.com/gs/wb.htm (7 of 9) [1/23/2003 11:18:57 AM] According to this envelope, if the weight is greater than 2300 pounds, the aircraft is overloaded. If the intersection is outside the envelope laterally, the loading is out of proper CG range. Center of Gravity Tables Some manufacturers provide tables instead of graphs or calculation. This method is fairly lengthy, and is used infrequently for small aircraft. Therefore this method will not be covered herein. Weight Shift and Change The approach to solving both Weight Change and Weight Shift is the same. The simplest method is to REMOVE a changed item, and to ADD the new or shifted item into the new location. Weight Change Example 1: An airplane takes off with a Gross Weight of 6230 lb., and a CG of 79.0. The CG of the fuel is at 87.00 aft of datum. What is the New CG location after 50 gallons of fuel is burned? Procedure: Subtract the Weight and Moment of the burned fuel from the initial values to arrive at a new set of values. At 6 pounds per gallon, the burned fuel weight is 300 pounds. WEIGHT CHANGE PROBLEM Weight and Balance http://www.uncletom2000.com/gs/wb.htm (8 of 9) [1/23/2003 11:18:57 AM] WEIGHT CG MOMENT Initial Weight 6230 79.00 492,170 Burned Fuel -300 87.00 -26,100 New Weight 5930 New CG 466,070 NEW CG (after Fuel Burned) = 466,070 / 5930 = 78.59 Weight Shift Example 2: The gross weight of the aircraft is 3,000 lbs. with a CG of 60 in. Since takeoff, 25 gallons of fuel has been used. The fuel cell CG is 65 in. aft of Datum (Station 65). Also, a 200 pound passenger moves from Station 50 to Station 90. (Note: Some problems will state the CG location as "Station". The 50 and 90 are CG location in inches aft of datum respectively). Find New CG. Procedure: 1. Subtract burned Fuel 2. Subtract Passenger who moves from the old location. 3. Add passenger who moves to the new location. WEIGHT SHIFT PROBLEM Weight CG Station Moment Initial Loading 3000 60.00 180,000 Fuel Burned -150 65.00 9,750 Passenger Off -200 50.00 -10,000 Passenger On +200 90.00 +18,000 New Totals 2850 New CG 178,250 New Cg = 178,250 / 2850 = Station 62.54 Back to Home Back to Table of Conents To Aircraft Performance Weight and Balance http://www.uncletom2000.com/gs/wb.htm (9 of 9) [1/23/2003 11:18:57 AM] Aircraft Performance Aircraft Performance Factors Affecting Performance Performance of the aircraft depends on the density of the air in which it flies. Factors affecting air density are: 1. Barometric pressure 2. Altitude 3. Temperature 4. Humidity Standard Atmosphere Definition The International Standards Association (ISA) has defined a Standard Atmosphere as: · Sea Level Barometric Pressure of 29.92 inches of Mercury (in. Hg) · Sea Level Temperature of 15° Celsius (15° C or 59° F) · Relative humidity of 0 % · Standard temperature lapse rate of 2° C per 1000 feet altitude · Standard pressure lapse rate of 1 in. Hg per 1000 feet altitude · A standard decrease in density as altitude increases The standard atmosphere definition provides a means for instrument and aircraft manufacturers to specify the performance of their products in a uniform way. This definition was arrived at by studying the average sea level pressure and temperature over a number of years, seasons, and locations around the world. Seldom will an aircraft be in standard atmosphere conditions. In order to define peformance of an instrument or an aircraft in a non-standard atmosphere, conversions must be applied to adjust the readings or performance numbers to agree with the standard atmosphere. This adjustment is called Density Altitude, and will be more fully defined later in this chapter. Effects of Non-standard Air Density Air Density decreases: · With Air Temperature Increase · With Altitude Increase · With Humidity Increase · With Barometric Pressure Decrease http://www.uncletom2000.com/gs/perf.htm (1 of 12) [1/23/2003 11:18:59 AM] With lower air density: · The engine develops less power. · The propeller produces less thrust. · The wings produce less lift. This results in: · Longer takeoff run · Poorer climb performance · Longer landing distance Density Altitude Density altitude is a way of relating the density of the air you are in compared to the standard atmosphere. Three atmospheres are illustrated. The Standard Atmosphere (29.92 in. Hg and 15 degrees Celsius) in middle shown in gray. A less dense atmosphere (A ) (lower pressure and/or Higher Temperature) is shown on the right in red. A more dense atmosphere (B) (higher pressure and/or Colder Temperature) is illustrated on the left in blue. Aircraft Performance http://www.uncletom2000.com/gs/perf.htm (2 of 12) [1/23/2003 11:18:59 AM] Aircraft Performance http://www.uncletom2000.com/gs/perf.htm (3 of 12) [1/23/2003 11:18:59 AM] If you are at an actual (true) altitude at location A in atmosphere (A) (the red atmosphere on the right), you will have to go to altitude (A') in the Standard Atmosphere to find the same air density. This altitude in the standard atmosphere at (A') is called the DENSITY ALTITUDE. Similarly, if you are at atmosphere (B) (colder or high pressure shown as blue on the left) the air will be more dense than standard. Therefore you will have to go down to a lower actual altitude in the standard atmosphere at (B') to find the equivalent air density. This equivalent altitude in the Standard Atmosphere is the DENSITY ALTITUDE. The reason that you need to convert your actual non-standard altitude (and thus your non-standard air density) to the standard density altitude is that all performance charts and data is based on a standard atmosphere. For example, if you are at a high altitude runway already, and the atmosphere pressure is low and temperature is high, it will require a significantly longer take off run than you may be accustomed to at your lower home base. If you are not aware of the effects of density altitude on your aircraft performance, it could lead to serious consequences. Density Altitude Calculations Density Altitude can be found in two ways · Using conversion charts · Using the E6B Flight Computer

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Density Altitude calculation is a 2 step process. Step 1. Find Pressure Altitude Pressure Altitude adjusts for pressure difference between your air and standard atmosphere. The question is “What would your altimeter read if you were in a standard atmosphere at your current actual altitude?” This altitude is called PRESSURE ALTITUDE. Pressure Altitude can be determined two ways. · In the aircraft, adjust your altimeter setting to 29.92 in. Hg (standard pressure), and read the altitude value shown by the altimeter needles. Or... · Apply a correction factor from a Pressure Altitude Correction Table as shown below. PRESSURE ALTITUDE CONVERSION TABLE In. Hg Conv. Factor In. Hg Conf. Factor In. Hg Conv. Factor In. Hg Conv. Factor 28.0 1824 28.8 1053 29.6 298 30.3 -348 28.1 1727 28.9 975 29.7 205 30.4 -440 Aircraft Performance http://www.uncletom2000.com/gs/perf.htm (4 of 12) [1/23/2003 11:18:59 AM] 28.2 1630 29.0 863 29.8 112 30.5 -531 28.3 1533 29.1 768 29.9 20 30.6 -622 28.4 1336 29.2 673 29.92 0 30.7 -712 28.5 1340 29.3 579 30.0 -73 30.8 -803 28.6 1148 29.4 485 30.1 -175 30.9 -893 28.7 1148 29.5 392 30.2 -257 31.0 -983 EXAMPLE: Airport Altitude = 2367 ft Altimeter Setting = 30.40 In. Hg Conversion Factor= -440 feet (from table ) Pressure Altitude = Airport Altitude + Conversion Factor =2367+(- 440) = 1927 NOTE: If your barometric pressure is not shown in the table (say a value such as 30.35) you will have to interpolate to get the correct pressure altitude adjustment. Step 2. Find Density Altitude Density Altitude uses Pressure Altitude as a basis, and adds in a correction factor for non-standard temperature. Calculate Density Altitude using: 1. PRESSURE ALTITUDE and 2. Outside Air Temperature (OAT) · Use E6B Flight Computer (see E6B instruction book) · Use Density Altitude Chart like the one shown below. Density AltFor Example: If you found the Pressure Altitude, doing either of the steps cited above, to be 4000 feet, and the outside Air Temperature (OAT) is 16° , do the following on the chart to find Density Altitude. Locate 16° C on bottom scale. Go vertically up to intersect the 4000 foot Pressure Altitude slanted line (blue line). Go left horizontally (blue line) to read Density Altitude = 5000 feet from the left side scale. You have now adjusted for the difference from standard temperature by using the chart. The red line on the chart is a Standard Atmosphere Temperature line. Performance charts provided by the manufacturer are based on Standard Atmosphere. Therefore you must adjust your current situation (barometric pressure and temperature) to Standard Atmosphere. This is done by calculating your Density Altitude, then using this Density Altitude as the altitude in the Aircraft Performance http://www.uncletom2000.com/gs/perf.htm (5 of 12) [1/23/2003 11:18:59 AM] manufacturers performance table when interpreting the performance table data. Aircraft Performance Charts Aircraft Performance Charts state performance figures in standard atmosphere conditions. Takeoff Performance You should consult the manufacturers Pilot Operating Handbook for the aircraft to be flown for take-off performance tables or graphs. Takeoff performance is influenced by several factors. · Adverse conditions 1. High density altitude (high altitude runway, low pressure, high temperature) 2. Runway conditions - mud, soft field, slush, snow, tall grass, rough surface, uphill 3. Tailwind (downwind takeoff) 4. High gross weight or overload 5. High Humidity · Favorable conditions 6. Low density altitude (low altitude runway, low temperature, high pressure) 7. Downhill runway 8. Headwind 9. Low weight 10. Low Humidity Takeoff performance data shown in the manufacturers' charts indicates the minimum runway requirements necessary for successful takeoff. Any factor that adversely affects the takeoff distance must be taken into account to insure safe operation. Consider that the listed minimum distance is for standard atmospheric conditions, ideal runway and wind conditions. TAKEOFF PERFORMANCE 0000' & 59 deg F 2500' & 50 deg F 5000' & 41 deg F 7500' & 32 deg F GROSS WT. POUNDS IAS@50' MPH HEAD WIND GRND RUN CLEAR 50' OBS GRND RUN CLEAR 50' OBS GRND RUN CLEAR 50' OBS GRND RUN CLEAR 50' OBS 2300 68 0 865 1525 1040 1910 1255 2480 1565 3855 2300 68 10 615 1170 750 1485 920 1955 1160 3110 Aircraft Performance http://www.uncletom2000.com/gs/perf.htm (6 of 12) [1/23/2003 11:18:59 AM] 2300 68 20 405 850 505 1100 630 1480 810 2425 2000 63 0 630 1095 735 1325 905 1625 1120 2155 2000 63 10 435 820 530 1005 645 1250 810 1685 2000 63 20 275 580 340 730 425 910 595 1255 1700 58 0 435 780 520 920 625 1095 765 1370 1700 58 10 290 570 355 680 430 820 535 1040 1700 58 20 175 385 215 470 270 575 345 745 Wind direction and velocity significantly affect takeoff distance. A direct headwind will greatest provide takeoff assist. A 90° crosswind will give no assistance in takeoff. A tailwind component significantly increases the takeoff roll. Gross weight affects takeoff performance. Increased gross weight: · Requires a higher takeoff speed in order to achieve sufficient lift. · Results in reduced acceleration due to greater inertia. · Increases rolling friction , further reduceing acceleration. Gusting or strong crosswinds require that the aircraft be held on the ground until definite liftoff can be achieved. Once liftoff has occured, sufficient speed is needed to prevent settling back onto the runway. If the landing gear contacts the runway when in a sideways drift, undue stress is placed on the landing gear. Glide Performance Glide performance is the distance that the aircraft will glide with an inoperative engine. The best distance is attained by gilding at an angle of attack that provides the maximum lift/drag ratio (L/Dmax). In the event that the engine becomes inoperative, it is important to establish the maximum glide airspeed as quickly as possible. This will permit the maximum radius of emergency landing options. While gliding toward a suitable landing area, effort should be made to identify the cause of the failure. If time permits, an engine restart should be attempted as shown in the start-up check list. Climb Performance The Pilot Operating Handbook will contain a Climb Performance chart or Table similar to the one below for a given aircraft. Note that 4 different tables are provided. (Sea Level, 5000 ft, 10,000 ft and 15,000 ft). Note that these altitudes are PRESSURE ALTITUDES and the respective temperatures are Standard Aircraft Performance http://www.uncletom2000.com/gs/perf.htm (7 of 12) [1/23/2003 11:18:59 AM]

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Temperatures for those altitudes. In other words, the values are given for standard Density Altitudes. MAXIMUM RATE OF CLIMB DATA Sea Level & 59° F 5000' & 41° F 10,000' & 23° 15,000 & 5° F Gross Weight lbs. Ind. Airspeed mph Rate of climb ft/min Fuel Used gal. Ind. Airspeed mph Rate of Climb ft/min Fuel Used gal Ind. Airspeed Ft/min Rate of Climb ft/min Fuel Used gal. Ind. Airspeed mph Rate of Climb ft/min Fuel Used gal 2300 82 645 1.0 81 435 2.6 79 230 4.8 78 22 11.5 2000 79 840 1.0 79 610 2.2 76 380 3.6 75 155 6.3 1700 77 1085 1.0 76 825 1.9 73 570 2.9 72 315 4.4 NOTES: 1. Flaps up, full throttle, mixture leaned above 3000 feet for smooth operation. 2. Fuel Used includes, warm-up and take-off allowance. 3. For hot weather, decrease rate of climb 20 ft/min for each 10°F above standard day for the particular altitude. Example: Given: Gross weight 2000 lb: Pressure Alt. 5000 ft: Temperature 61° F. SOLUTION: The rate of climb is 610 at 5000 feet pressure altitude and standard temperature of 41° F. Since the temperature is 20° F higher that the standard 41°, subtract 40 feet per minute from the 610, to get a rate of climb = 610 - 40 = 570 ft/min. Climb performance depends on the aircraft’s reserve power or thrust. Reserve power is the available power above that required to maintain level flight at a given airspeed. If an aircraft requires only 120 horsepower for a given cruise, and the engine is capable of delivering 180 hp., then the reserve horsepower available for climb is 60 hp. Two airspeeds are important to the climb performance. These are: Vx Best Angle of Climb Vy Best Rate of Climb These V-speeds are defined in the POH. The Best Angle of Climb produces the greatest altitude in a given distance. The principal use of Best Angle of Climb is for clearing obstacles on take-off. The Best Rate of Climb produces the greatest altitude over a given period of time. It is predominately used as climb to cruise altitude. Many of the same factors that affect take-off and cruise performance also affect climb performance. Adverse effects: · Higher than Standard Temperature Aircraft Performance http://www.uncletom2000.com/gs/perf.htm (8 of 12) [1/23/2003 11:18:59 AM] · High Humidity · Lower than Standard Pressure · Heavy Weight Heavy weight requires a higher angle of attack to develop adequate lift. The increased drag results in poorer climb performance. It takes longer to attain cruise altitude and requires the engine to develop full power for a longer period of time. Consult the POH for Climb Performance data for the aircraft to be flown. Cruise Performance The cruise performance can be specified two ways. · Maximum Range · Maximum Endurance Maximum Range is the distance that an aircraft can fly at a given power setting. is requires maximum speed versus fuel flow. Maximum Duration is the maximum time the aircraft can fly. This requires that the flight condition must provide for a minimum of fuel flow. CRUISE AND RANGE PERFORMANCE ALTITUDE RPM % PWR TAS MPH GAL/HR END HRS RANGE MI. 2500 2600 81 136 9.3 3.9 524 2500 2500 73 129 8.3 4.3 555 2500 2400 65 122 7.5 4.8 586 2500 2300 56 115 6.6 5.4 617 2500 2200 52 108 6.0 6.0 645 4500 2600 77 135 8.8 4.0 539 4500 2500 69 129 7.9 4.5 572 4500 2400 62 121 7.1 5.0 601 4500 2300 56 113 6.4 5.5 628 4500 2200 51 106 5.7 6.1 646 6500 2700 81 140 9.3 3.8 530 6500 2600 73 134 8.3 4.2 559 6500 2500 66 126 7.5 4.7 587 6500 2400 60 119 6.8 5.2 611 6500 2300 54 112 6.1 5.7 632 Aircraft Performance http://www.uncletom2000.com/gs/perf.htm (9 of 12) [1/23/2003 11:18:59 AM] 8500 2700 77 139 8.8 4.0 547 8500 2600 70 132 7.9 4.4 575 8500 2500 63 125 7.2 4.9 599 8500 2400 57 118 6.5 5.3 620 8500 2300 52 109 5.9 5.8 635 10500 2700 73 138 8.3 4.2 569 10500 2600 66 130 7.6 4.6 590 10500 2500 60 122 6.9 5.0 610 10500 2400 55 115 6.3 5.4 625 10500 2300 50 106 5.7 5.9 631 Crosswind Performance Takeoffs and landings under significant cross wind conditions can be dangerous and should be avoided. Crosswinds can be so strong that the sideways drift cannot be sufficiently overcome by using a “side slip ” into the wind to compensate for the wind drift. Excessive side load on the landing gear can cause gear failure or an upset aircraft. Aircraft Performance http://www.uncletom2000.com/gs/perf.htm (10 of 12) [1/23/2003 11:18:59 AM] The Maximum Crosswind Component for the aircraft will be listed in the Aircraft Performance http://www.uncletom2000.com/gs/perf.htm (11 of 12) [1/23/2003 11:18:59 AM] POH. The maximum crosswind is usually about 20% of the landing configuration stall speed. The diagram above can be used to calculate the headwind and crosswind components. For most light aircraft, the maximum tested crosswind component is in the 12 to 15 knot range. In the chart, the numbers around the periphery of the chart mark the degrees difference between the wind and the runway heading (magenta lines). The radial lines are are in 5° increments with numbers on each 10° line. For example, with a wind of 150° at 30 kt and landing on runway 12 (120°), the degrees of crosswind will be 150° - 120° = 30°. Locate the 30° radial line out from the lower left of the graph. This is the differential between the wind direction and thr runway heading. Follow the 30° radial line (magenta) to the 30kt wind arc (blue). A vertical line (blue) from this intersection will be the cross-wind component of 15 kts. This is the same as if you had a wind of 15 kts directly from the side. If you plot a horizontal (blue) line, you will see that your headwind component is 26 kts. This is the same effect as if you had a direct headwind of 26 kts. Landing Performance The minimum landing distance is attained by landing at the minimum safe speed which allows sufficient margin above the stall speed for satisfactory control and go-around capability. Gross weight and headwind are important considerations in determining minimum landing distance. Excessive airspeed above that recommended in the POH will significantly increase landing distance. High density altitude increases landing distance. As a rule of thumb, the increase in landing distance is about 3.5% for each 1,000 feet in density altitude. Braking A number of factors affect braking. A wet, icy or snow covered runway will appreciably decrease braking ability. In crosswinds or gusty conditions, higher than normal approach speed will improve controllability, but will require longer rollout to stop. A down-sloping runway also increases stopping distance. Braking immediately after touchdown is ineffective because the wings are still producing lift. The pilot should use the natural aerodynamic drag as much as possible to slow the aircraft. Maintain up-elevator to a high angle of attack as long as possible. The nose of the aircraft will settle naturally as airspeed is dissipated. Therefore it is not necessary (and is unwise) to force the nosewheel hard onto the runway. After touchdown, hold up-elevators during braking to reduce the load on the nosewheel. Avoid severe braking to minimize stress on the nose gear and scrubbing of rubber from the main gear tires. Gross weight affects stopping ability. Heavy loads and high touchdown speeds result in greater forward momentum, and require significantly more runway than normal. The most critical conditions for landing performance sult from some combination of high gross weight , high density altitude and unfavorable wind conditions. These conditions produce the greatest landing distance and require the greatest dissipation of energy by the brakes. Back to Home Back to Table of Conents To Airspace Definition Aircraft Performance http://www.uncletom2000.com/gs/perf.htm (12 of 12) [1/23/2003 11:18:59 AM] AIRSPACE AND AIRPORT TYPES AIRSPACE AND AIRPORT TYPES In September 1993 the FAA adopted the International Civil Aviation Organization (ICAO) definition of airspace segments. The ICAO classifications of airspace are named A through G. The classification of “F” is not used in the USA. NOTE: It will be helpful while studying this chapter to have a Sectional Aeronautical Chart available. Refer to the front panel of the chart as well as to content of the chart as you study this chapter. The 3 predominant types of airspace are: · Positive Control (Class A) - White · Controlled (Class E - Yellow ) · Uncontrolled (class G) - Magenta Class G Airspace ATC exercises no jurisdiction over Class G airspace. It is the airspace shown in magenta at left, and generally extends from the ground up to 1200 feet above ground level (AGL). As such it is classified as Uncontrolled airspace. ATC exercises some jurisdiction, at varying degrees to all other airspace. Thus all other airspace is classifies as Controlled airspace. Class A -- Positive Control ATC exercises complete control in the Positive Controlled airspace. Jet aircraft is the primary user of Class A airspace. It ranges from 18,000 feet (Flight Level 180) to 60,000 feet (FL600). Altitudes 18,000 feet and above are called Flight Levels. Class A airspace is not specifically charted on aeronautical charts. Operation is in accordance to Instrument Flight Rules (IFR). The aircraft must be equipped with appropriate IFR instrumentation, including a Mode C altitude reporting Transponder. The Pilot must be Instrument rated. An IFR flight plan is required. ATC exercises full control of route, speed, and altitude. ATC is responsible for aircraft separation in Class A airspace. See AIM Chapter 3 for further data on Class A Airspace Class E -- Controlled Class E airspace is from altitude 1200 feet Above Ground Level (AGL) up to 18,000 feet. All airspace from http://www.uncletom2000.com/gs/airspace.htm (1 of 10) [1/23/2003 11:19:01 AM] 14,500 feet (MSL) to 18,000 feet (MSL) is Class E. It contains the Low Altitude Victor airway system. These airways are designated on the aeronautical charts as blue lines about 1/16 inch wide, and have numbers like V12, V245, etc. written on them. They are roads in the sky. All Victor airways are Class E extending 6 nautical miles each side of the airway centerline. In mountainous terrain, class G airspace may exist from the surface to 14,500 feet outside the boundaries of the airway. In non-mountainous terain (such as Eastern US) all the airspace above 1200 AGL is Class E unless specified otherwise. ATC exercises no control over flights operating under Visual Flight Rules (VFR) in Class E airspace. Radio communication and Transponder are not required. Specific cloud clearance and visibility requirements apply to Class E airspace. These are listed in the chart at the end of this section. ATC does exercise control of aircraft operating under Instrument Flight Rules (IFR). IFR flights must maintain altitudes, routes and speeds a directed by ATC. IFR flights must be capable of communicating with ATC, and must be Mode C Transponder equipped (capable of reporting altitude to the radar scope). There are no specific certification requirements, other than normal pilot certificates. Class E airspace may be designated from the surface upward as extension to class B, C, and D airspace (defined later) to accommodate IFR traffic requirements. Class E airspace will extend downward to 700 feet AGL around uncontrolled airports that have published instrument approach procedures.

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These areas around uncontrolled airports where the Class E airspace goes down to 700 feet AGL instead of the standard 1200 feet AGL are depicted on Aeronautical Charts by a wide shaded magenta colored band around the airport. The reason the Class E airspace extends nearer to the ground is to provide a controlled airspace transition area for aircraft operating IFR and making an IFR approach. See AIM Chapter 3 for further data on Class E Airspace Class G -- Uncontrolled Most Class G airspace is that space from the surface up to 1200 feet. However, there are areas in mountainous terrain where airspace outside the Victor Airways is Class G from the ground to 14,500 feet AGL. Class G space may underlie Classes B, C, and D, but has no specific symbol indicated on the chart. The presence of the airspace is implied. Less stringent minimum cloud clearance and visibility requirements apply to VFR flight in Class G space since ATC does not maintain jurisdiction over this airspace. See last page of this section. As mentioned in the Class E section, airports with published instrument approached have class E airspace extending down to 700 feet AGL. Obviously, in these areas, Class G only extends from the surface to 700 feet AGL. Uncontrolled Airports Airports without a control tower are classifies as uncontrolled. Three types of uncontrolled airports are shown below. AIRSPACE AND AIRPORT TYPES http://www.uncletom2000.com/gs/airspace.htm (2 of 10) [1/23/2003 11:19:01 AM] The airport on the right does not have an instrument approach or a control zone around the airport. The airspace overlying this type airport is Class G up to 1200 feet, then Class E above. It is depicted on the charts as a magenta circle (unpaved) or a solid circle with white runways (paved). The airport in the middle has a Class E Control Zone around it, depicted by the dotted circle around it. If the line is magenta in color, it is a control zone at an airport where an FAA Flight Service Station (FSS) is on the field but no control tower. The FSS provides airport traffic advisory service. Class E airspace extends down to the surface. The zone is depicted on charts as a dashed MAGENTA circle around the airport. These airports usually have instrument approach procedures as well. The airport at left has an instrument approach procedure for the airport. Such airports have a broad lightly shaded magenta band around them. Within the outer edge of the band, Class G airspace only extends up to 700 feet AGL. Class E extends down to 700 feet to provide a transition zone for aircraft making instrument approaches to the airport. The transition area is approximately 5 miles in radius. Controlled Airports These are airports that have sufficient air traffic to warrant a Control Tower, and in some cases Approach Control and Ground Control Radar. They are used by air carrier operations, and can have a mix of jet, high performance piston and turbine aircraft, as well as smaller single engine aircraft. The control tower is responsible for aircraft separation within its jurisdiction. Certain clearances must be obtained from ATC for operations on the airport surface, and within the controlled airspace around the airport. There are 3 Classes of airspace around controlled airports. The type of airspace depends upon the traffic volume AIRSPACE AND AIRPORT TYPES http://www.uncletom2000.com/gs/airspace.htm (3 of 10) [1/23/2003 11:19:01 AM] and types of flight. These Classes are B, C, and D airspace Class D -- Airports with Control Tower The lowest level of control is at airports with a low volume of traffic. It has a control tower and is depicted on the aeronautical charts as shown below. Class D airports are depicted on aeronautical charts by a blue dashed circle around the airport symbol. Within the dashed circle is a number enclosed in a dashed square. This number indicates the top of the Class D airspace, expressed in hundreds of feet (MSL). In the diagram, the top is 4,600 feet MSL This airspace may have a Class E extension as shown in the diagram for an IFR approach transition area. The control tower has jurisdiction within the Class D airspace which is 5 Statute Miles radius around the control tower. The top of the Class D airspace extends 2500 feet above the surface of the airport. Two way radio contact must be maintained with the Control Tower while in this airspace. The pilot should contact the control tower prior to entering the airspace. See AIM Chapter 3 for further data on Class D Airspace Terminal Radar Service Areas (TRSA) Some Class D airports have a local radar service called a Terminal Radar Service Area.(TRSA). The service is available for conflict resolution and traffic sequencing to departing and arriving aircraft. However contact with the radar is not mandatory and the pilot may decline the service. These airports are depicted on the aeronautical charts in the normal Class D manner, but have a dark gray circular line around the airport out at the boundary of the radar service range. Wilmington N.C. and Augusta Ga. are examples of airports with TRSA. There is no specified regulatory radius for the radar service. See AIM Chapter 3 for further data on Terminal Radar Service Area Class C Airspace (Mandatory Radar) Class C airspace has two concentric tiers. The inner circle is 5 nautical mile core area extending to 4000 feet above the surface. It is similar in function to Class D airspace where the tower usually maintains jurisdiction. A shelf area with an outer radius of 10 nautical miles surrounds the core area. It extends from 1200 feet AGL to 4000 feet AGL. The airspace is depicted on charts as 2 concentric magenta circles. For example, an airport with a surface altitude of 500 feet MSL is depicted above. The left diagram is a side profile of the airspace. The right diagran shows how the airspace is depicted on the aeronautical chart. The ceiling of the Class C airspace is 4,500 feet (MSL). This is calculated as runway altitude of 500 feet plus 4000 feet. The floor of the outer shelf is 1,700 feet MSL. (1200 + 500 feet). The space under the shelf is Class G. These altitudes are indicated by 45 over SFC for the core circle, and 45 over 17 on the outer shelf. AIRSPACE AND AIRPORT TYPES http://www.uncletom2000.com/gs/airspace.htm (4 of 10) [1/23/2003 11:19:01 AM] Contact with Approach and Departure Radar Control is mandatory within the core and shelf airspace. During takeoff and landing, the tower and radar controller coordinate their activity. You will be told by either controller when to switch frequency to the other controller. Aircraft must be capable of two-way communication with the radar facility and the tower. A 4096 Altitude Reporting (Mode C) Transponder is required when operating within, under or above Class C airspace. Before entering Class C airspace, the pilot MUST establish communication with the radar service. Radio contact with radar and/or tower must be maintained when in this airspace. You may request Flight Following Radar Service outside the 10 mile shelf. It may be granted on a workload permitting basis. The service can usually be provided to about a 20 NM radius of the airport. See AIM Chapter 3 for further data on Class C Airspace Class B -- Large Terminal Airports Large terminal areas such as the New York, Chicago, and Los Angeles areas have a high volume of air traffic. The airspace around these airports is under rigid control of ATC, and are called Class B airspace. AIRCRAFT MUST HAVE ATC CLEARANCE PRIOR TO ENTRY INTO THIS AIRSPACE. The airspace is composed generally of three concentric tiers. A core area around the airport is generally is surrounded by two additional shelf areas extending approximately 30 nautical mile radius from the primary airport. The core area extends from the surface to 10,000 feet AGL. The second shelf has a wider radius and has both a floor and a ceiling. The ceiling is the same as the inner circle. The floor may vary at differing altitudes in various sections to accommodate smaller airports that underlie the middle tier of airspace. The third shelf extends out approximately 30 Nm from the airport. It has the same ceiling as the other two tiers, but has a higher floor than the middle shelf. This floor may also be variable in altitude to accommodate airports lying beneath the Class B airspace. The actual configuration of the airspace varies to accommodate local operational requirements. The purpose of the Class B structure is to allow large high performance jet traffic to transition down to landing at the airport under IFR procedures, and with positive control and traffic separation. Class B operational rules require: · Two way radio capable of communication with ATC. · Private pilot (or special student certification). Several airports prohibit student operations entirely. · Altitude reporting Transponder (Mode C). ·If operating IFR, an operable VOR or TACAN receiver. NOTE: Student pilots must have had training in Class B operations and appropriate sign-off of a Certified Flight AIRSPACE AND AIRPORT TYPES http://www.uncletom2000.com/gs/airspace.htm (5 of 10) [1/23/2003 11:19:01 AM] Instructor. A student may not operate from the following Class B airports. Atlanta Hartsfield Airport, GA Newark Airport, NJ Boston Logan Airport, MA New York Kennedy, NY Chicago O’Hare Airport IL New York LaGuardia, NY Dallas/Ft.Worth Airport, TX San Francisco Airport, CA Loa Angeles Airport, CA Washington National Airport, DC Miami Airport, FL Andrews AFB, MD See AIM Chapter 3 for further data on Class B Airspace Mode C Veil Around Class B airspace is an area called the Mode C Veil. It is shown as a thin blue concentric line of 30 Nautical Mile radius around the Class B airport. An altitude reporting Transponder (Mode C) is required within this area and when operating under the floor or above the ceiling of the Class B airspace. Radio communication with ATC is not required as long as you stay outside the Class B airspace. Special Use Airspace A number of “special use” airspace areas exist for various usage. It means that certain activities have been confined to those areas of airspace. Limitations are placed on aircraft operations in these areas which are not a part of the activity. These are: · Prohibited areas · Restricted areas · Warning Areas · Military Operations Areas · Alert Areas · Controlled Firing Areas · Military Training Routes · Air Defense Identification Zone · Temporary Restricted Areas Prohibited and Restricted airspace are regulatory use airspace whose rules are defined by FAR Part 73. Warning areas, MOA’s, Alert Areas, National Security Areas, and controlled firing areas are non-regulatory special use airspace. Prohibited Areas These are areas over which flight by civilian aircraft is prohibited by FAA Regulation. Operation within such an AIRSPACE AND AIRPORT TYPES http://www.uncletom2000.com/gs/airspace.htm (6 of 10) [1/23/2003 11:19:01 AM] area can be justification for military interception or other action. The area around the White House in Washington D.C. is an example. The symbol is a blue feathered box shown at right with the words Prohibited in or near the box. See Aeronautical Information Manual AIM 3-31 PROHIBITED AREAS . Restricted Areas These are designated areas in which flight, although not totally prohibited, are subject to certain restrictions. These areas denote the existence of unusual, often invisible, hazards to aircraft. Such activities may be artillery firing, aerial gunnery, or guided missiles. Penetration of these areas without authorization of the controlling agency may be extremely dangerous. They are marked on the charts by blue feathered boundaries. An identifying number such as R-5306 will be listed near or within the area. A listing on the bottom of the aeronautical chart identifies the area by number, and indicates the location of the area, the altitude limits of the space, the time of use, and the name of the controlling agency. It is good practice to plan to avoid such areas. If penetration of such an area is planned, the controlling agency should be consulted as to the status of activity in the area prior to any penetration. For more information, see AIM 3-32 RESTRICTED AREAS Warning Areas These are areas outside the 3 mile limit from shore in international airspace. They are similar to Restricted Areas. Activities which are unusual or may be dangerous to aircraft may be in progress. They cannot however be designated as Restricted Areas since they are over international waters Warning areas are also identified by a blue feathered box with a number (such as W-74). Information concerning these areas is listed on the aeronautical charts in the same section as Restricted Areas. One should treat a Warning Area the same as a Restricted area, and follow the same procedures. For more information, see AIM 3-33. WARNING AREA Military Operation Areas (MOA) MOAs consist of airspace of defined vertical and lateral limits for the purpose of separating certain military training activities and IFR traffic. They are depicted by magenta colored feathered areas similarly to Prohibited, Restricted and Warning areas. They are denoted by names such as Beaufort MOA within or near the MOAdefined area. ATC can grant clearance to IFR traffic through an MOA if adequate IFR separation can be assured. If not, ATC will restrict routing IFR traffic through the area. Most military training activities necessitate acrobatic or abrupt maneuvers. Pilots operating under VFR should exercise extreme caution whole flying in an MOA when military activity is being conducted. Military pilots on officially designated operations are exempt from conducting aerobatic maneuvers on the regions of Victor Airways. AIRSPACE AND AIRPORT TYPES http://www.uncletom2000.com/gs/airspace.htm (7 of 10) [1/23/2003 11:19:01 AM] VFR pilots should maintain caution when flying through an MOA when it is active. Pilots should contact a Flight Service Station (FSS) within 100 miles of the MOA to obtain real-time report of activity within the MOA. Prior to entry, pilots should contact the controlling agency for traffic advisories. Information about MOAs is listed in the same location on the aeronautical chart as the Restricted and Warning area information. The data is printed in Magenta. For mor information, see 3-34. MILITARY OPERATIONS AREAS (MOA) Alert Areas Alert areas are shown on charts to inform pilots of areas where intensive pilot training or other types of unusual aerial activity may take place. The area is depicted in a similar manner to the other special use areas, but indicated by a blue outline with the area crosshatched as shown. For more information, see AIM 3-35. ALERT AREAS Controlled Firing Areas These areas contain operations such as artillery firing. They are not marked on charts, and pilots need not avoid. Spotter aircraft, radar or ground personnel monitor for aircraft in the area, and firing is suspended immediately upon the approach of aircraft. See AIM 3-36. CONTROLLED FIRING AREAS Military Training Routes Military training routes are used by high speed military aircraft conducting low and medium level high speed training activity. The routes above 1500 feet AGL are designed to be flown mostly under IFR rules. They may occur in either IFR or VFR meteorological conditions. The routes at 1500 feet and below are generally developed to be flown under VFR rules. Flight visibility must be 5 miles or more, with ceilings 3000 feet or more. MTR’s with no segment above 1500 feet will be designated by a 4 digit number; i.e. IR 1206, VR 1207. Routes that include one or more segments above 1500 feet are designated by 3 digit numbers; i.e. IR206, VR207. The routes are shown on aeronautical charts are gray in color, and will have numbers like IR718 or VR4003. Vigilance should be observed when operating near or crossing an MTR. Contact FSS within 100 miles to obtain current information on the activity along the MTRs. Give FSS your altitude and route of flight and destination when requesting MTR information. For further information, see 3-41. MILITARY TRAINING ROUTES (MTR) Temporary Restricted Areas The FAA may publish temporary restricted areas that may be due natural disaster, or other events, in which AIRSPACE AND AIRPORT TYPES http://www.uncletom2000.com/gs/airspace.htm (8 of 10) [1/23/2003 11:19:01 AM] unauthorized civilian flight is inadvisable or may interfere with rescue or relief efforts. These temporary restrictions are published through the system called “Notices To Airmen” (NOTAMS). They are disseminated through the FAA Flight Service Stations. Contact FSS prior to any flight which may be in the vicinity of such events as air crashes, earthquake damage, floods, etc. Airspace Rules The various types of airspace have rules concerning weather limitations and equipment requirements for operation in the given airspace. The listing below summarizes these requirements. Standard VFR Cloud Clearance and Visibility Hereinafter, reference will be made to standard VFR Rules for Cloud Clearance and Visibility. These are: VFR Couud Clearance and Visibility Rules Visibility Above Cloud Below Cloud Horizontal Below 10,000 ft. 3 1000 ft 500 ft 2000 ft Above 10,000 ft. 5 1000 ft. 1000 ft. 1 SM. Class A Airspace Rules l Operations - Instrument Flight Rules Only l ATC Clearance Required - Yes l Radio Contact Required - Yes l Minimum Pilot Qualifications - Instrument Rating l Mode C Altitude Encoding Transponder Required - Yes l Cloud Clearance Requirements - None (IFR Rules apply) Class B Airspace Rules While in Class B airspace, the following rules apply. l Operations Permitted - IFR and VFR l ATC Clearance Required - Yes l Radio Contact Required - Yes l Minimum Pilot Qualifications - Private (Student if Signed-Off) l Mode C Altitude Reporting Transponder required - Yes l Cloud Clearance Requirements below 10,000 ft. - Clear of Clouds l Cloud Clearance Requirements above 10,000 ft. - Standard VFR l VFR Visibility Requirements below 10,000 ft. - Standard VFR l VFR Visibility Requirements above 10,000 feet - Standard VFR Class C Airspace Rules While in Class C airspace, the following rules apply. l Operations Permitted - IFR and VFR AIRSPACE AND AIRPORT TYPES http://www.uncletom2000.com/gs/airspace.htm (9 of 10) [1/23/2003 11:19:01 AM] l ATC Clearance Required - IFR - Yes : VFR - No l Radio Contact Required - Yes l Minimum Pilot Qualifications - Student l Mode C Altitude Reporting Transponder required - Yes l Cloud Clearance Requirements below 10,000 ft. - Standard VFR l Cloud Clearance Requirements above 10,000 ft. - Standard VFR l VFR Visibility Requirements below 10,000 ft. - Standard VFR l VFR Visibility Requirements above 10,000 feet - Standard VFR Airspace Class D Rules While in Class D airspace, the following rules apply. l Operations Permitted - IFR and VFR l ATC Clearance Required - IFR -Yes: VFR - No l Radio Contact Required - Yes l Minimum Pilot Qualifications - Student l Mode C Altitude Reporting Transponder required - No l Cloud Clearance Requirements below 10,000 ft. - Standard VFR l Cloud Clearance Requirements above 10,000 ft. - Standard VFR l VFR Visibility Requirements below 10,000 ft. - Standard VFR l VFR Visibility Requirements above 10,000 feet - Standard VFR Airspace Class G Rules While in Class G airspace, the following rules apply. l Operations Permitted - VFR l ATC Clearance Required - No l Radio Contact Required - No l Minimum Pilot Qualifications - Student l Mode C Altitude Reporting Transponder required - No l Cloud Clearance Requirements below 10,000 ft. - Clear of Clouds (Day) : Standard VFR (night) l Cloud Clearance Requirements above 10,000 ft. - Standard VFR (day and Night l VFR Visibility Requirements below 10,000 ft. - 1 SM (day): 3 SM (night) l VFR Visibility Requirements above 10,000 feet - Standard VFR (day and night) Back to Home Back to Table of Conents To Aeronautical Charts AIRSPACE AND AIRPORT TYPES http://www.uncletom2000.com/gs/airspace.htm (10 of 10) [1/23/2003 11:19:01 AM] Chart Symbols Aeronautical Charts Chart Types Three types of charts are used for VFR flight. These are: · Wide Area Charts(WAC) - Scale 1:1,000,000 ( 1 inch = 13.7 Nm) · Sectional Chart.................- Scale 1:500,000 ( 1 inch = 6.86 Nm) · VFR Terminal Charts........- Scale 1:250,000 ( 1 inch = 3.43 Nm) Most pilots use the Sectional chart. It provides good detail of topographical features, and is good for both the Student pilot as well as experienced pilot. Since the WAC chart covers twice the area of the Sectional, pilots flying higher performance aircraft may prefer this chart. It shows less topographical features. It contains most of the electronic navigation features that are shown on the sectional charts. Both the WAC and Sectional charts show the Victor Airways. VFR Terminal Charts are published for areas of concentrated air traffic, such as Charlotte, NYC, Los Angeles, etc. These charts show many more details. They contain landmarks often used by controllers not shown on the other chart types. Charts show significant terrain and topographical detail, location of cities and towns, airports, navigational aids, prohibited, restricted and special use airspace, and many other symbols. Longitude and Latitude A system of X-Y coordinates is used to define a point on the earth's surface. These coordinates are called Meridians (longitude) and Parallels (latitude). Meridians span from the north pole to the south pole, and are measured in degrees from the PRIME MERIDIAN. It runs north and south through Greenwich, England. Measurement is either EAST or WEST from the Prime Meridian, and continues around the earth until they meet at meridian 180.The measurement, either East or West is measured in degrees, minutes and seconds. This measurement is called “Longitude”. The example dot on the diagram is at Longitude 30° 45’ W ( 30 degrees, 45 minutes West). http://www.uncletom2000.com/gs/chartsym.htm (1 of 9) [1/23/2003 11:19:04 AM] Meridians are not parallel. They converge at the poles, and have maximum distance between them at the equator. They represent the direction to True North. At the equator, one minute of arc longitude equals one nautical mile. The only place where 1° longitude = 1 Nm is on the equator. As one moves toward either pole, the lateral distance across one degree becomes less and less, and approaches zero at the pole. Since the earth makes one revolution of 360 degrees within 24 hours, it moves 15° in one hour.