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发表于 2009-3-21 00:09:35
area. Only after the first two items are assured, shouldyou try to communicate with anyone.Another important part of managing workload is recognizing a work overload situation. The first effect ofhigh workload is that you begin to work faster. Asworkload increases, attention cannot be devoted to several tasks at one time, and you may begin to focus onone item. When you become task saturated, there is noawareness of inputs from various sources, so decisionsmay be made on incomplete information, and the possibility of error increases. When becoming overloaded, you should stop, think,slow down, and prioritize. It is important that youunderstand options that may be available to decreaseworkload. For example, tasks, such as locating an itemon a chart or setting a radio frequency, may be delegated to another pilot or passenger, an autopilot, ifavailable, may be used, or ATC may be enlisted toprovide assistance.SITUATIONAL AWARENESSSituational awareness is the accurate perception of theoperational and environmental factors that affect theaircraft, pilot, and passengers during a specific periodof time. Maintaining situational awareness requiresan understanding of the relative significance of thesefactors and their future impact on the flight. When situationally aware, you have an overview of the totaloperation and are not fixated on one perceived significant factor. Some of the elements inside the aircraftto be considered are the status of aircraft systems, youas the pilot, and passengers. In addition, an awarenessof the environmental conditions of the flight, such asspatial orientation of the helicopter, and its relationship to terrain, traffic, weather, and airspace must bemaintained.To maintain situational awareness, all of the skillsinvolved in aeronautical decision making are used. Forexample, an accurate perception of your fitness can beachieved through self-assessment and recognition ofhazardous attitudes. A clear assessment of the status ofnavigation equipment can be obtained through workload management, and establishing a productiverelationship with ATC can be accomplished by effective resource use.OBSTACLES TO MAINTAINING SITUATIONALAWARENESSFatigue, stress, and work overload can cause you to fixate on a single perceived important item rather thanmaintaining an overall awareness of the flight situation. A contributing factor in many accidents is adistraction that diverts the pilot’s attention from monitoring the instruments or scanning outside theaircraft. Many cockpit distractions begin as a minorproblem, such as a gauge that is not reading correctly,but result in accidents as the pilot diverts attention tothe perceived problem and neglects to properly controlthe aircraft.Complacency presents another obstacle to maintainingsituational awareness. When activities become routine,you may have a tendency to relax and not put as mucheffort into performance. Like fatigue, complacencyreduces your effectiveness in the cockpit. However,complacency is harder to recognize than fatigue, sinceeverything is perceived to be progressing smoothly. Forexample, you have just dropped off another group offire fighters for the fifth time that day. Without thinking, you hastily lift the helicopter off the ground, notrealizing that one of the skids is stuck between tworocks. The result is dynamic rollover and a destroyedhelicopter.OPERATIONAL PITFALLSThere are a number of classic behavioral traps intowhich pilots have been known to fall. Pilots, particularly those with considerable experience, as a rule,always try to complete a flight as planned, please passengers, and meet schedules. The basic drive to meetor exceed goals can have an adverse effect on safety,and can impose an unrealistic assessment of pilotingskills under stressful conditions. These tendencies ultimately may bring about practices that are dangerousand often illegal, and may lead to a mishap. You willdevelop awareness and learn to avoid many of theseoperational pitfalls through effective ADM training.Marginof SafetyPilot CapabilitiesTaskRequirementsPreflight Takeoff Cruise Approach &LandingTaxi TaxiTimeFigure 14-9. Accidents often occur when flying task requirements exceed pilot capabilities. The difference betweenthese two factors is called the margin of safety. Note that inthis idealized example, the margin of safety is minimal duringthe approach and landing. At this point, an emergency or distraction could overtax pilot capabilities, causing an accident.14-9Peer Pressure—Poor decision making may be based upon an emotional response to peers, rather than evaluating a situationobjectively.Mind Set—A pilot displays mind set through an inability to recognize and cope with changes in a given situation.Get-There-Itis—This disposition impairs pilot judgment through a fixation on the original goal or destination, combined with adisregard for any alternative course of action.Scud Running—This occurs when a pilot tries to maintain visual contact with the terrain at low altitudes while instrumentconditions exist.Continuing Visual Flight Rules (VFR) into Instrument Conditions—Spatial disorientation or collision with ground/obstaclesmay occur when a pilot continues VFR into instrument conditions. This can be even more dangerous if the pilot is notinstrument-rated or current.Getting Behind the Aircraft—This pitfall can be caused by allowing events or the situation to control pilot actions. A constantstate of surprise at what happens next may be exhibited when the pilot is getting behind the aircraft.Loss of Positional or Situational Awareness—In extreme cases, when a pilot gets behind the aircraft, a loss of positional orsituational awareness may result. The pilot may not know the aircraft's geographical location, or may be unable to recognizedeteriorating circumstances.Operating Without Adequate Fuel Reserves—Ignoring minimum fuel reserve requirements is generally the result ofoverconfidence, lack of flight planning, or disregarding applicable regulations.Flying Outside the Envelope—The assumed high performance capability of a particular aircraft may cause a mistaken beliefthat it can meet the demands imposed by a pilot's overestimated flying skills.Neglect of Flight Planning, Preflight Inspections, and Checklists—A pilot may rely on short- and long-term memory,regular flying skills, and familiar routes instead of established procedures and published checklists. This can be particularly true
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发表于 2009-3-21 00:09:48
of experienced pilots.OPERATIONAL PITFALLSFigure 14-10. All experienced pilots have fallen prey to, or have been tempted by, one or more of these tendencies in their flyingcareers.14-10autorotation. The first successful example of this typeof aircraft was the British Fairy Rotodyne, certificatedto the Transport Category in 1958. During the 1960sand 1970s, the popularity of gyroplanes increased withthe certification of the McCulloch J-2 and Umbaugh.The latter becoming the Air & Space 18A.There are several aircraft under development using thefree spinning rotor to achieve rotary wing takeoff performance and fixed wing cruise speeds. The gyroplaneoffers inherent safety, simplicity of operation, and outstanding short field point-to-point capability.TYPES OF GYROPLANESBecause the free spinning rotor does not require anantitorque device, a single rotor is the predominateconfiguration. Counter-rotating blades do not offerany particular advantage. The rotor system used in agyroplane may have any number of blades, but themost popular are the two and three blade systems.Propulsion for gyroplanes may be either tractor orpusher, meaning the engine may be mounted on thefront and pull the aircraft, or in the rear, pushing itthrough the air. The powerplant itself may be eitherreciprocating or turbine. Early gyroplanes wereoften a derivative of tractor configured airplaneswith the rotor either replacing the wing or acting inconjunction with it. However, the pusher configuration is generally more maneuverable due to theplacement of the rudder in the propeller slipstream,and also has the advantage of better visibility for thepilot. 15-1January 9th, 1923, marked the first officially observedflight of an autogyro. The aircraft, designed by Juan dela Cierva, introduced rotor technology that made forward flight in a rotorcraft possible. Until that time,rotary-wing aircraft designers were stymied by theproblem of a rolling moment that was encounteredwhen the aircraft began to move forward. This rollingmoment was the product of airflow over the rotor disc,causing an increase in lift of the advancing blade anddecrease in lift of the retreating blade. Cierva’s successful design, the C.4, introduced the articulated rotor, onwhich the blades were hinged and allowed to flap. Thissolution allowed the advancing blade to move upward,decreasing angle of attack and lift, while the retreatingblade would swing downward, increasing angle ofattack and lift. The result was balanced lift across therotor disc regardless of airflow. This breakthrough wasinstrumental in the success of the modern helicopter,which was developed over 15 years later. (For moreinformation on dissymmetry of lift, refer to Chapter 3—Aerodynamics of Flight.) On April 2, 1931, the PitcairnPCA-2 autogyro was granted Type Certificate No. 410and became the first rotary wing aircraft to be certifiedin the United States. The term “autogyro” was used todescribe this type of aircraft until the FAA later designated them “gyroplanes.”By definition, the gyroplane is an aircraft that achieveslift by a free spinning rotor. Several aircraft have usedthe free spinning rotor to attain performance not available in the pure helicopter. The “gyrodyne” is a hybridrotorcraft that is capable of hovering and yet cruises inFigure 15-1. The gyroplane may have wings, be either tractor or pusher configured, and could be turbine or propeller powered.Pictured are the Pitcairn PCA-2 Autogyro (left) and the Air & Space 18A gyroplane.15-2When direct control of the rotor head was perfected,the jump takeoff gyroplane was developed. Under theproper conditions, these gyroplanes have the ability tolift off vertically and transition to forward flight. Laterdevelopments have included retaining the direct control rotor head and utilizing a wing to unload the rotor,which results in increased forward speed.COMPONENTSAlthough gyroplanes are designed in a variety of configurations, for the most part the basic components are thesame. The minimum components required for a functional gyroplane are an airframe, a powerplant, a rotorsystem, tail surfaces, and landing gear. Anoptional component is the wing, which is incorporatedinto some designs for specific performance objectives.AIRFRAMEThe airframe provides the structure to which all othercomponents are attached. Airframes may be weldedtube, sheet metal, composite, or simply tubes boltedtogether. A combination of construction methods mayalso be employed. The airframes with the greateststrength-to-weight ratios are a carbon fiber material orPowerplantRotorAirframeLanding GearTailSurfacesDirect Control—The capacity forthe pilot to maneuver the aircraftby tilting the rotor disc and, onsome gyroplanes, affect changes inpitch to the rotor blades. Theseequate to cyclic and collective control, which were not available inearlier autogyros.Unload—To reduce the component of weight supported by therotor system.Prerotate—Spinning a gyroplanerotor to sufficient r.p.m. prior toflight.the welded tube structure, which has been in use for anumber of years.POWERPLANTThe powerplant provides the thrust necessary for forwardflight, and is independent of the rotor system while in
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发表于 2009-3-21 00:10:00
flight. While on the ground, the engine may be used asa source of power to prerotate the rotor system. Overthe many years of gyroplane development, a widevariety of engine types have been adapted to the gyroplane. Automotive, marine, ATV, and certificatedaircraft engines have all been used in variousgyroplane designs. Certificated gyroplanes arerequired to use FAA certificated engines. The cost of anew certificated aircraft engine is greater than the costof nearly any other new engine. This added cost is theprimary reason other types of engines are selected foruse in amateur built gyroplanes.ROTOR SYSTEMThe rotor system provides lift and control for the gyroplane. The fully articulated and semi-rigid teeteringrotor systems are the most common. These areexplained in-depth in Chapter 5—Main Rotor System.The teeter blade with hub tilt control is most commonin homebuilt gyroplanes. This system may also employa collective control to change the pitch of the rotorblades. With sufficient blade inertia and collectivepitch change, jump takeoffs can be accomplished.TAIL SURFACESThe tail surfaces provide stability and control in the pitchand yaw axes. These tail surfaces are similar to an airplane empennage and may be comprised of a fin andrudder, stabilizer and elevator. An aft mounted ductenclosing the propeller and rudder has also been used.Many gyroplanes do not incorporate a horizontal tailsurface.On some gyroplanes, especially those with an enclosedcockpit, the yaw stability is marginal due to the largefuselage side area located ahead of the center of gravity. The additional vertical tail surface necessary tocompensate for this instability is difficult to achieve asthe confines of the rotor tilt and high landing pitch attitude limits the available area. Some gyroplane designsincorporate multiple vertical stabilizers and rudders toadd additional yaw stability.Figure 15-2. Gyroplanes typically consist of five major components. A sixth, the wing, is utilized on some designs.15-3LANDING GEARThe landing gear provides the mobility while on theground and may be either conventional or tricycle.Conventional gear consists of two main wheels, and oneunder the tail. The tricycle configuration also uses twomains, with the third wheel under the nose. Early autogyros, and several models of gyroplanes, use conventional gear, while most of the later gyroplanesincorporate tricycle landing gear. As with fixed wingaircraft, the gyroplane landing gear provides the groundmobility not found in most helicopters.WINGSWings may or may not comprise a component of thegyroplane. When used, they provide increased performance, increased storage capacity, and increasedstability. Gyroplanes are under development withwings that are capable of almost completely unloading the rotor system and carrying the entire weightof the aircraft. This will allow rotary wing takeoffperformance with fixed wing cruise speeds. 15-3]Figure 15-3. The CarterCopter uses wings to enhanceperformance.15-416-1Helicopters and gyroplanes both achieve lift throughthe use of airfoils, and, therefore, many of the basicaerodynamic principles governing the production of liftapply to both aircraft. These concepts are explained indepth in Chapter 2—General Aerodynamics, and constitute the foundation for discussing the aerodynamicsof a gyroplane.AUTOROTATIONA fundamental difference between helicopters andgyroplanes is that in powered flight, a gyroplane rotorsystem operates in autorotation. This means the rotorspins freely as a result of air flowing up through theblades, rather than using engine power to turn theblades and draw air from above. Forcesare created during autorotation that keep the rotorblades turning, as well as creating lift to keep the aircraft aloft. Aerodynamically, the rotor system of agyroplane in normal flight operates like a helicopterrotor during an engine-out forward autorotativedescent.VERTICAL AUTOROTATIONDuring a vertical autorotation, two basic componentscontribute to the relative wind striking the rotor blades. One component, the upward flow of airthrough the rotor system, remains relatively constantfor a given flight condition. The other component is therotational airflow, which is the wind velocity across theblades as they spin. This component varies significantly based upon how far from the rotor hub it ismeasured. For example, consider a rotor disc that is 25feet in diameter operating at 300 r.p.m. At a point onefoot outboard from the rotor hub, the blades are traveling in a circle with a circumference of 6.3 feet. Thisequates to 31.4 feet per second (f.p.s.), or a rotationalblade speed of 21 m.p.h. At the blade tips, the circumference of the circle increases to 78.5 feet. At the sameoperating speed of 300 r.p.m., this creates a blade tipDirection of FlightRelative Wind Relative WindDirection of FlightFigure 16-1. Airflow through the rotor system on a gyroplane is reversed from that on a powered helicopter. This airflow is themedium through which power is transferred from the gyroplane engine to the rotor system to keep it rotating.ResultantRelativeWindWind due to Blade RotationUpwardAirflowFigure 16-2. In a vertical autorotation, the wind from therotation of the blade combines with the upward airflow toproduce the resultant relative wind striking the airfoil.
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16-2speed of 393 feet per second, or 267 m.p.h. The resultis a higher total relative wind, striking the blades at alower angle of attack. ROTOR DISC REGIONSAs with any airfoil, the lift that is created by rotorblades is perpendicular to the relative wind. Becausethe relative wind on rotor blades in autorotation shiftsfrom a high angle of attack inboard to a lower angle ofattack outboard, the lift generated has a higher forwardcomponent closer to the hub and a higher vertical component toward the blade tips. This creates distinctregions of the rotor disc that create the forces necessary for flight in autorotation. Theautorotative region, or driving region, creates a totalaerodynamic force with a forward component thatexceeds all rearward drag forces and keeps the bladesspinning. The propeller region, or driven region, generates a total aerodynamic force with a higher verticalcomponent that allows the gyroplane to remain aloft.Near the center of the rotor disc is a stall region wherethe rotational component of the relative wind is so lowthat the resulting angle of attack is beyond the stalllimit of the airfoil. The stall region creates drag againstthe direction of rotation that must be overcome by theforward acting forces generated by the driving region.AUTOROTATION IN FORWARD FLIGHTAs discussed thus far, the aerodynamics of autorotationapply to a gyroplane in a vertical descent. Becausegyroplanes are normally operated in forward flight, thecomponent of relative wind striking the rotor blades asa result of forward speed must also be considered. Thiscomponent has no effect on the aerodynamic principlesthat cause the blades to autorotate, but causes a shift inthe zones of the rotor disc.As a gyroplane moves forward through the air, the forward speed of the aircraft is effectively added to theResultantRelativeWindRotational Airflow (267 m.p.h. or 393 f.p.s.)Upward Airflow(17 m.p.h. or 25 f.p.s.)TIPRotor Speed: 300 r.p.m.FResultantRelativeWindRotational Airflow(21 m.p.h. or 31 f.p.s.)Upward Airflow(17 m.p.h. or 25 f.p.s.)HUBVERTICAL AUTOROTATIONFigure 16-3. Moving outboard on the rotor blade, the rotational velocity increasingly exceeds the upward component of airflow,resulting in a higher relative wind at a lower angle of attack.Driven RegionDriving RegionStallRegionDriven Region(Propeller)Driving Region(Autorotative)Stall RegionFVERTICAL AUTOROTATIONRotationalRelative WindLiftLiftTAFTAFTotalAerodynamicForce Aftof Axis ofRotationDragChord LineInflow UpThrough RotorResultantRelative WindTotalAerodynamicForceForwardof Axis ofRotationDragInflowAxis ofRotationAxis ofRotationAxis ofRotation(Blade is Stalled)TAFDragInflowLiftFigure 16-4. The total aerodynamic force is aft of the axis ofrotation in the driven region and forward of the axis of rotation in the driving region. Drag is the major aerodynamicforce in the stall region. For a complete depiction of forcevectors during a vertical autorotation, refer to Chapter 3—Aerodynamics of Flight (Helicopter), Figure 3-22.16-3relative wind striking the advancing blade, and subtracted from the relative wind striking the retreatingblade. To prevent uneven lifting forces on the two sidesof the rotor disc, the advancing blade teeters up,decreasing angle of attack and lift, while the retreatingblade teeters down, increasing angle of attack and lift.(For a complete discussion on dissymmetry of lift, referto Chapter 3—Aerodynamics of Flight.) The lowerangles of attack on the advancing blade cause more ofthe blade to fall in the driven region, while higherangles of attack on the retreating blade cause more ofthe blade to be stalled. The result is a shift in the rotorregions toward the retreating side of the disc to a degreedirectly related to the forward speed of the aircraft.REVERSE FLOWOn a rotor system in forward flight, reverse flow occursnear the rotor hub on the retreating side of the rotordisc. This is the result of the forward speed of the aircraft exceeding the rotational speed of the rotor blades.For example, two feet outboard from the rotor hub, theblades travel in a circle with a circumference of 12.6feet. At a rotor speed of 300 r.p.m., the blade speed atthe two-foot station is 42 m.p.h. If the aircraft is being
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发表于 2009-3-21 00:10:29
operated at a forward speed of 42 m.p.h., the forwardspeed of the aircraft essentially negates the rotationalvelocity on the retreating blade at the two-foot station.Moving inboard from the two-foot station on theretreating blade, the forward speed of the aircraftincreasingly exceeds the rotational velocity of theblade. This causes the airflow to actually strike thetrailing edge of the rotor blade, with velocity increasing toward the rotor hub. The size of thearea that experiences reverse flow is dependent prima-rily on the forward speed of the aircraft, with higherspeed creating a larger region of reverse flow. To somedegree, the operating speed of the rotor system also hasan effect on the size of the region, with systems operating at lower r.p.m. being more susceptible to reverseflow and allowing a greater portion of the blade toexperience the effect.RETREATING BLADE STALLThe retreating blade stall in a gyroplane differs fromthat of a helicopter in that it occurs outboard from therotor hub at the 20 to 40 percent position rather than atthe blade tip. Because the gyroplane is operating inautorotation, in forward flight there is an inherent stallregion centered inboard on the retreating blade. to figure 16-5] As forward speed increases, the angle ofattack on the retreating blade increases to prevent dissymmetry of lift and the stall region moves furtheroutboard on the retreating blade. Because the stalledportion of the rotor disc is inboard rather than near thetip, as with a helicopter, less force is created about theaircraft center of gravity. The result is that you may feela slight increase in vibration, but you would not experience a large pitch or roll tendency.ROTOR FORCEAs with any heavier than air aircraft, the four forcesacting on the gyroplane in flight are lift, weight, thrustand drag. The gyroplane derives lift from the rotor andForwardDriven RegionDriving RegionStallRegionRetreatingSideAdvancingSideFigure 16-5. Rotor disc regions in forward autorotative flight.ForwardFlight at42 kt42kt42kt42kt42kt2'Area ofReverse flow42ktRotor Speed 300 r.p.m.Figure 16-6. An area of reverse flow forms on the retreatingblade in forward flight as a result of aircraft speed exceedingblade rotational speed.16-4rotor blades turn, rapid changes occur on the airfoilsdepending on position, rotor speed, and aircraft speed.A change in the angle of attack of the rotor disc caneffect a rapid and substantial change in total rotor drag.Rotor drag can be divided into components of induceddrag and profile drag. The induced drag is a product oflift, while the profile drag is a function of rotor r.p.m.Because induced drag is a result of the rotor providinglift, profile drag can be considered the drag of the rotorwhen it is not producing lift. To visualize profile drag,consider the drag that must be overcome to prerotatethe rotor system to flight r.p.m. while the blades areproducing no lift. This can be achieved with a rotor system having a symmetrical airfoil and a pitch changecapability by setting the blades to a 0° angle of attack.A rotor system with an asymmetrical airfoil and a builtin pitch angle, which includes most amateur-builtteeter-head rotor systems, cannot be prerotated withouthaving to overcome the induced drag created as well.THRUSTThrust in a gyroplane is defined as the component oftotal propeller force parallel to the relative wind. Aswith any force applied to an aircraft, thrust acts aroundthe center of gravity. Based upon where the thrust isapplied in relation to the aircraft center of gravity, a relatively small component may be perpendicular to therelative wind and can be considered to be additive tolift or weight.In flight, the fuselage of a gyroplane essentially acts asa plumb suspended from the rotor, and as such, it isthrust directly from the engine through a propeller.The force produced by the gyroplane rotor may bedivided into two components; rotor lift and rotor drag.The component of rotor force perpendicular to theflight path is rotor lift, and the component of rotor forceparallel to the flight path is rotor drag. To derive thetotal aircraft drag reaction, you must also add the dragof the fuselage to that of the rotor.ROTOR LIFTRotor lift can most easily be visualized as the liftrequired to support the weight of the aircraft. When anairfoil produces lift, induced drag is produced. Themost efficient angle of attack for a given airfoil produces the most lift for the least drag. However, the airfoil of a rotor blade does not operate at this efficientangle throughout the many changes that occur in eachrevolution. Also, the rotor system must remain in theautorotative (low) pitch range to continue turning inorder to generate lift.
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发表于 2009-3-21 00:10:43
Some gyroplanes use small wings for creating lift whenoperating at higher cruise speeds. The lift provided bythe wings can either supplement or entirely replacerotor lift while creating much less induced drag.ROTOR DRAGTotal rotor drag is the summation of all the drag forcesacting on the airfoil at each blade position. Each bladeposition contributes to the total drag according to thespeed and angle of the airfoil at that position. As theLiftResultantThrustResultantThrustLiftResultantDragRotorDragFuselageDragResultantWeightWeightFigure 16-7. Unlike a helicopter, in forward powered flight the resultant rotor force of a gyroplane acts in a rearward direction.16-5subject to pendular action in the same way as a helicopter. Unlike a helicopter, however, thrust is applieddirectly to the airframe of a gyroplane rather than beingobtained through the rotor system. As a result, differentforces act on a gyroplane in flight than on a helicopter.Engine torque, for example, tends to roll the fuselagein the direction opposite propeller rotation, causing itto be deflected a few degrees out of the vertical plane. This slight “out of vertical” condition isusually negligible and not considered relevant for mostflight operations.STABILITYStability is designed into aircraft to reduce pilot workload and increase safety. A stable aircraft, such as a typical general aviation training airplane, requires lessattention from the pilot to maintain the desired flightattitude, and will even correct itself if disturbed by agust of wind or other outside forces. Conversely, anunstable aircraft requires constant attention to maintaincontrol of the aircraft.ReactiveTorque onFuselageTorqueApplied toPropellerFigure 16-8. Engine torque applied to the propeller has anequal and opposite reaction on the fuselage, deflecting it afew degrees out of the vertical plane in flight.Pendular Action—The lateral orlongitudinal oscillation of the fuselage due to it being suspendedfrom the rotor system. It is similarto the action of a pendulum.Pendular action is further discussed in Chapter 3—Aerodynamics of Flight.There are several factors that contribute to the stabilityof a gyroplane. One is the location of the horizontalstabilizer. Another is the location of the fuselage dragin relation to the center of gravity. A third is theinertia moment around the pitch axis, while a fourth isthe relation of the propeller thrust line to the verticallocation of the center of gravity (CG). However, theone that is probably the most critical is the relation ofthe rotor force line to the horizontal location of thecenter of gravity.HORIZONTAL STABILIZERA horizontal stabilizer helps in longitudinal stability,with its efficiency greater the further it is from thecenter of gravity. It is also more efficient at higherairspeeds because lift is proportional to the square ofthe airspeed. Since the speed of a gyroplane is not veryhigh, manufacturers can achieve the desired stabilityby varying the size of the horizontal stabilizer, changing the distance it is from the center of gravity, or byplacing it in the propeller slipstream.FUSELAGE DRAG(CENTER OF PRESSURE)If the location, where the fuselage drag or center ofpressure forces are concentrated, is behind the CG,the gyroplane is considered more stable. This is especially true of yaw stability around the vertical axis.However, to achieve this condition, there must be asufficient vertical tail surface. In addition, the gyroplane needs to have a balanced longitudinal center ofpressure so there is sufficient cyclic movement toprevent the nose from tucking under or lifting, aspressure builds on the frontal area of the gyroplane asairspeed increases.PITCH INERTIAWithout changing the overall weight and center ofgravity of a gyroplane, the further weights are placedfrom the CG, the more stable the gyroplane. For example, if the pilot's seat could be moved forward from theCG, and the engine moved aft an amount, which keepsthe center of gravity in the same location, the gyroplanebecomes more stable. A tightrope walker applies thissame principle when he uses a long pole to balancehimself.PROPELLER THRUST LINEConsidering just the propeller thrust line by itself, if thethrust line is above the center of gravity, the gyroplanehas a tendency to pitch nose down when power isapplied, and to pitch nose up when power is removed.The opposite is true when the propeller thrust line isbelow the CG. If the thrust line goes through the CG or16-6nearly so there is no tendency for the nose to pitch upor down. ROTOR FORCE
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Because some gyroplanes do not have horizontal stabilizers, and the propeller thrust lines are different, gyroplane manufacturers can achieve the desired stabilityby placing the center of gravity in front of or behind therotor force line. Suppose the CG is located behind the rotor force line inforward flight. If a gust of wind increases the angle ofattack, rotor force increases. There is also an increasein the difference between the lift produced on theadvancing and retreating blades. This increases theflapping angle and causes the rotor to pitch up. Thispitching action increases the moment around the centerof gravity, which leads to a greater increase in the angleof attack. The result is an unstable condition.If the CG is in front of the rotor force line, a gust ofwind, which increases the angle of attack, causes therotor disc to react the same way, but now the increasein rotor force and blade flapping decreases themoment. This tends to decrease the angle of attack, andcreates a stable condition.TRIMMED CONDITIONAs was stated earlier, manufacturers use a combinationof the various stability factors to achieve a trimmedgyroplane. For example, if you have a gyroplane wherethe CG is below the propeller thrust line, the propellerthrust gives your aircraft a nose down pitching momentwhen power is applied. To compensate for this pitchingmoment, the CG, on this type of gyroplane, is usuallylocated behind the rotor force line. This location produces a nose up pitching moment.Conversely, if the CG is above the propeller thrust line,the CG is usually located ahead of the rotor force line.Of course, the location of fuselage drag, the pitch inertia, and the addition of a horizontal stabilizer can alterwhere the center of gravity is placed.Propeller ThrustPropeller ThrustCenter of Gravity Center of GravityHigh Profile Low ProfileRotorForceRotorForceFigure 16-9. A gyroplane which has the propeller thrust line above the center of gravity is often referred to as a low profile gyroplane. One that has the propeller thrust line below or at the CG is considered a high profile gyroplane.Figure 16-10. If the CG is located in front of the rotor force line, the gyroplane is more stable than if the CG is located behind therotor force line.Blade Flapping—The upward or downward movement of the rotorblades during rotation.17-1Due to rudimentary flight control systems, early gyroplanessuffered from limited maneuverability. As technologyimproved, greater control of the rotor system and moreeffective control surfaces were developed. The moderngyroplane, while continuing to maintain an element ofsimplicity, now enjoys a high degree of maneuverability as a result of these improvements.CYCLIC CONTROLThe cyclic control provides the means whereby you areable to tilt the rotor system to provide the desiredresults. Tilting the rotor system provides all control forclimbing, descending, and banking the gyroplane. Themost common method to transfer stick movement tothe rotor head is through push-pull tubes or flex cables. Some gyroplanes use a direct overheadstick attachment rather than a cyclic, where a rigid control is attached to the rotor hub and descends over andin front of the pilot. Because of thenature of the direct attachment, control inputs with thissystem are reversed from those used with a cyclic.Pushing forward on the control causes the rotor disc totilt back and the gyroplane to climb, pulling back onthe control initiates a descent. Bank commands arereversed in the same way.THROTTLEThe throttle is conventional to most powerplants, andprovides the means for you to increase or decreaseengine power and thus, thrust. Depending on howthe control is designed, control movement may ormay not be proportional to engine power. With manygyroplane throttles, 50 percent of the control travelmay equate to 80 or 90 percent of available power.This varying degree of sensitivity makes it necessaryFigure 17-1. A common method of transferring cyclic control inputs to the rotor head is through the use of push-pull tubes,located outboard of the rotor mast pictured on the right.Figure 17-2. The direct overhead stick attachment has beenused for control of the rotor disc on some gyroplanes.17-2for you to become familiar with the unique throttlecharacteristics and engine responses for a particulargyroplane.RUDDERThe rudder is operated by foot pedals in the cockpitand provides a means to control yaw movement of theaircraft. On a gyroplane, this control isachieved in a manner more similar to the rudder of anairplane than to the antitorque pedals of a helicopter.The rudder is used to maintain coordinated flight, andat times may also require inputs to compensate forpropeller torque. Rudder sensitivity and effectivenessare directly proportional to the velocity of airflow overthe rudder surface. Consequently, many gyroplanerudders are located in the propeller slipstream andprovide excellent control while the engine is developingthrust. This type of rudder configuration, however, isless effective and requires greater deflection when theengine is idled or stopped.HORIZONTAL TAIL SURFACESThe horizontal tail surfaces on most gyroplanes arenot controllable by the pilot. These fixed surfaces, orstabilizers, are incorporated into gyroplane designs toincrease the pitch stability of the aircraft. Some gyroplanes use very little, if any, horizontal surface. Thistranslates into less stability, but a higher degree ofmaneuverability. When used, a moveable horizontal
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发表于 2009-3-21 00:11:19
surface, or elevator, adds additional pitch control of theaircraft. On early tractor configured gyroplanes, theelevator served an additional function of deflecting thepropeller slipstream up and through the rotor to assistin prerotation.COLLECTIVE CONTROLThe collective control provides a means to vary therotor blade pitch of all the blades at the same time, andis available only on more advanced gyroplanes. Whenincorporated into the rotor head design, the collectiveallows jump takeoffs when the blade inertia is sufficient. Also, control of in-flight rotor r.p.m. is availableto enhance cruise and landing performance. A simpletwo position collective does not allow unlimited controlof blade pitch, but instead has one position for prerotationand another position for flight. This is a performancecompromise but reduces pilot workload by simplifyingcontrol of the rotor system.Figure 17-3. Foot pedals provide rudder control and operation is similar to that of an airplane.18-1rotating portion of the head to the non-rotating torquetube. The torque tube is mounted to the airframethrough attachments allowing both lateral and longitudinal movement. This allows the movement throughwhich control is achieved.FULLY ARTICULATED ROTOR SYSTEMThe fully articulated rotor system is found on somegyroplanes. As with helicopter-type rotor systems, thearticulated rotor system allows the manipulation ofConing Angle—An angulardeflection of the rotor bladesupward from the rotor hub.Undersling—A design characteristic that prevents the distancebetween the rotor mast axis andthe center of mass of each rotorblade from changing as theblades teeter. This precludesCoriolis Effect from acting on thespeed of the rotor system.Undersling is further explainedin Chapter 3—Aerodynamics ofFlight, Coriolis Effect (Law ofConservation of AngularMomentum).Gyroplanes are available in a wide variety of designsthat range from amateur built to FAA-certificated aircraft. Similarly, the complexity of the systems integrated in gyroplane design cover a broad range. Toensure the airworthiness of your aircraft, it is importantthat you thoroughly understand the design and operation of each system employed by your machine.PROPULSION SYSTEMSMost of the gyroplanes flying today use a reciprocatingengine mounted in a pusher configuration that driveseither a fixed or constant speed propeller. The enginesused in amateur-built gyroplanes are normally provenpowerplants adapted from automotive or other uses.Some amateur-built gyroplanes use FAA-certificated aircraft engines and propellers. Auto engines, along withsome of the other powerplants adapted to gyroplanes,operate at a high r.p.m., which requires the use of a reduction unit to lower the output to efficient propeller speeds.Early autogyros used existing aircraft engines, whichdrove a propeller in the tractor configuration. Severalamateur-built gyroplanes still use this propulsion configuration, and may utilize a certificated or an uncertificated engine. Although not in use today, turbopropand pure jet engines could also be used for the propulsion of a gyroplane.ROTOR SYSTEMSSEMIRIGID ROTOR SYSTEMAny rotor system capable of autorotation may be utilizedin a gyroplane. Because of its simplicity, the most widelyused system is the semirigid, teeter-head system. Thissystem is found in most amateur-built gyroplanes. In this system, the rotor head is mountedon a spindle, which may be tilted for control. The rotorblades are attached to a hub bar that may or may nothave adjustments for varying the blade pitch. Aconingangle, determined by projections of blade weight,rotor speed, and load to be carried, is built into the hubbar. This minimizes hub bar bending moments andeliminates the need for a coning hinge, which is usedin more complex rotor systems. A tower block provides the undersling and attachment to the rotor headby the teeter bolt. The rotor head is comprised of abearing block in which the bearing is mounted andonto which the tower plates are attached. The spindle(commonly, a vertically oriented bolt) attaches theFigure 18-1. The semirigid, teeter-head system is found onmost amateur-built gyroplanes. The rotor hub bar and bladesare permitted to tilt by the teeter bolt.Tower PlatesHub BarTower BlockBearing BlockTeeter BoltSpindle BoltTorque TubeFore / Aft Pivot BoltLateral Pivot Bolt18-2rotor blade pitch while in flight. This system is significantly more complicated than the teeter-head, as itrequires hinges that allow each rotor blade to flap,feather, and lead or lag independently. When used, the fully articulated rotor system of a gyroplane is very similar to those used on helicopters, whichis explained in depth in Chapter 5—Helicopter Systems,Main Rotor Systems. One major advantage of using afully articulated rotor in gyroplane design is that it usually allows jump takeoff capability. Rotor characteristicsrequired for a successful jump takeoff must include amethod of collective pitch change, a blade with sufficientinertia, and a prerotation mechanism capable of approximately 150 percent of rotor flight r.p.m.Incorporating rotor blades with high inertia potential is
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desirable in helicopter design and is essential for jumptakeoff gyroplanes. A rotor hub design allowing therotor speed to exceed normal flight r.p.m. by over50 percent is not found in helicopters, and predicates arotor head design particular to the jump takeoffgyroplane, yet very similar to that of the helicopter.PREROTATORPrior to takeoff, the gyroplane rotor must first achievea rotor speed sufficient to create the necessary lift.This is accomplished on very basic gyroplanes by initially spinning the blades by hand. The aircraft is thentaxied with the rotor disc tilted aft, allowing airflowthrough the system to accelerate it to flight r.p.m.More advanced gyroplanes use a prerotator, whichprovides a mechanical means to spin the rotor. Manyprerotators are capable of only achieving a portion ofthe speed necessary for flight; the remainder isgained by taxiing or during the takeoff roll. Becauseof the wide variety of prerotation systems available,you need to become thoroughly familiar with thecharacteristics and techniques associated with yourparticular system.MECHANICAL PREROTATORMechanical prerotators typically have clutches or beltsfor engagement, a drive train, and may use a transmission to transfer engine power to the rotor. Frictiondrives and flex cables are used in conjunction with anautomotive type bendix and ring gear on many gyroplanes. The mechanical prerotator used on jump takeoff gyroplanes may be regarded as being similar to the helicoptermain rotor drive train, but only operates while the aircraft is firmly on the ground. Gyroplanes do not have anantitorque device like a helicopter, and ground contact isnecessary to counteract the torque forces generated bythe prerotation system. If jump takeoff capability isdesigned into a gyroplane, rotor r.p.m. prior to liftoffmust be such that rotor energy will support the aircraft through the acceleration phase of takeoff. Thiscombination of rotor system and prerotator utilizesthe transmission only while the aircraft is on theground, allowing the transmission to be disconnectedfrom both the rotor and the engine while in normalflight.HYDRAULIC PREROTATORThe hydraulic prerotator found on gyroplanes usesengine power to drive a hydraulic pump, which in turndrives a hydraulic motor attached to an automotive typebendix and ring gear. This system alsorequires that some type of clutch and pressure regulation be incorporated into the design.Figure 18-2. The fully articulated rotor system enables thepilot to effect changes in pitch to the rotor blades, which isnecessary for jump takeoff capability.Figure 18-3. The mechanical prerotator used by many gyroplanes uses a friction drive at the propeller hub, and a flexible cable that runs from the propeller hub to the rotor mast.When engaged, the bendix spins the ring gear located on therotor hub.18-3ELECTRIC PREROTATORThe electric prerotator found on gyroplanes uses anautomotive type starter with a bendix and ring gearmounted at the rotor head to impart torque to the rotorsystem. This system has the advantage ofsimplicity and ease of operation, but is dependent onhaving electrical power available. Using a “soft start”device can alleviate the problems associated with thehigh starting torque initially required to get the rotorsystem turning. This device delivers electrical pulses tothe starter for approximately 10 seconds before connecting uninterrupted voltage.TIP JETSJets located at the rotor blade tips have been used in several applications for prerotation, as well as for hoverflight. This system has no requirement for a transmissionor clutches. It also has the advantage of not impartingtorque to the airframe, allowing the rotor to be poweredin flight to give increased climb rates and even the abilityto hover. The major disadvantage is the noise generatedby the jets. Fortunately, tip jets may be shut down whileoperating in the autorotative gyroplane mode.INSTRUMENTATIONThe instrumentation required for flight is generallyrelated to the complexity of the gyroplane. Some gyroplanes using air-cooled and fuel/oil-lubricated enginesmay have limited instrumentation.ENGINE INSTRUMENTSAll but the most basic engines require monitoringinstrumentation for safe operation. Coolant temperature, cylinder head temperatures, oil temperature, oilpressure, carburetor air temperature, and exhaust gastemperature are all direct indications of engine operation and may be displayed. Engine power is normallyindicated by engine r.p.m., or by manifold pressure ongyroplanes with a constant speed propeller.ROTOR TACHOMETERMost gyroplanes are equipped with a rotor r.p.m. indicator. Because the pilot does not normally have directcontrol of rotor r.p.m. in flight, this instrument is mostuseful on the takeoff roll to determine when there is sufficient rotor speed for liftoff. On gyroplanes notequipped with a rotor tachometer, additional pilotingskills are required to sense rotor r.p.m. prior to takeoff.Figure 18-4. This prerotator uses belts at the propeller hub to drive a hydraulic pump, which drives a hydraulic motor on therotor mast.Figure 18-5. The electric prerotator is simple and easy to use,but requires the availability of electrical power.18-4Certain gyroplane maneuvers require you to know precisely the speed of the rotor system. Performing a jumptakeoff in a gyroplane with collective control is oneexample, as sufficient rotor energy must be available
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for the successful outcome of the maneuver. Whenvariable collective and a rotor tachometer are used,more efficient rotor operation may be accomplished byusing the lowest practical rotor r.p.m. SLIP/SKID INDICATORA yaw string attached to the nose of the aircraft and aconventional inclinometer are often used in gyroplanesto assist in maintaining coordinated flight. AIRSPEED INDICATORAirspeed knowledge is essential and is most easilyobtained by an airspeed indicator that is designed foraccuracy at low airspeeds. Wind speed indicatorshave been adapted to many gyroplanes. When no air-speed indicator is used, as in some very basicamateur-built machines, you must have a very acutesense of “q” (impact air pressure against your body).ALTIMETERFor the average pilot, it becomes increasingly difficultto judge altitude accurately when more than severalhundred feet above the ground. A conventional altimeter may be used to provide an altitude reference whenflying at higher altitudes where human perceptiondegrades.IFR FLIGHT INSTRUMENTATIONGyroplane flight into instrument meteorological conditions requires adequate flight instrumentation and navigational systems, just as in any aircraft. Very fewgyroplanes have been equipped for this type of operation.The majority of gyroplanes do not meet the stabilityrequirements for single-pilot IFR flight. As larger andmore advanced gyroplanes are developed, issues of IFRflight in these aircraft will have to be addressed.GROUND HANDLINGThe gyroplane is capable of ground taxiing in a mannersimilar to that of an airplane. A steerable nose wheel,which may be combined with independent main wheelbrakes, provides the most common method of control. The use of independent main wheelbrakes allows differential braking, or applying morebraking to one wheel than the other to achieve tightradius turns. On some gyroplanes, the steerable nosewheel is equipped with a foot-operated brake ratherthan using main wheel brakes. One limitation of thissystem is that the nose wheel normally supports only afraction of the weight of the gyroplane, which greatlyreduces braking effectiveness. Another drawback is theFigure 18-6. A rotor tachometer can be very useful to determine when rotor r.p.m. is sufficient for takeoff.Figure 18-7. A string simply tied near the nose of the gyroplane that can be viewed from the cockpit is often used toindicate rotation about the yaw axis. An inclinometer mayalso be used.Figure 18-8. Depending on design, main wheel brakes can beoperated either independently or collectively. They are considerably more effective than nose wheel brakes.18-5inability to use differential braking, which increasesthe radius of turns.The rotor blades demand special consideration duringground handling, as turning rotor blades can be a hazard to those nearby. Many gyroplanes have a rotorbrake that may be used to slow the rotor after landing,or to secure the blades while parked. A parked gyroplane should never be left with unsecured blades,because even a slight change in wind could cause theblades to turn or flap.18-619-1As with most certificated aircraft manufactured afterMarch 1979, FAA-certificated gyroplanes are requiredto have an approved flight manual. The flight manualdescribes procedures and limitations that must beadhered to when operating the aircraft. Specificationfor Pilot’s Operating Handbook, published by theGeneral Aviation Manufacturers Association (GAMA),provides a recommended format that more recent gyroplane flight manuals follow. This format is the same as that used by helicopters,which is explained in depth in Chapter 6—RotorcraftFlight Manual (Helicopter).Amateur-built gyroplanes may have operating limitations but are not normally required to have an approvedflight manual. One exception is an exemption grantedby the FAA that allows the commercial use oftwo-place, amateur-built gyroplanes for instructionalpurposes. One of the conditions of this exemption is tohave an approved flight manual for the aircraft. Thismanual is to be used for training purposes, and must becarried in the gyroplane at all times.USING THE FLIGHT MANUALThe flight manual is required to be on board the aircraftto guarantee that the information contained therein isreadily available. For the information to be of value,you must be thoroughly familiar with the manual andbe able to read and properly interpret the various chartsand tables.WEIGHT AND BALANCE SECTIONThe weight and balance section of the flight manualcontains information essential to the safe operation ofthe gyroplane. Careful consideration must be given tothe weight of the passengers, baggage, and fuel prior toeach flight. In conducting weight and balance computations, many of the terms and procedures are similar tothose used in helicopters. These are further explainedin Chapter 7—Weight and Balance. In any aircraft,failure to adhere to the weight and balance limitations prescribed by the manufacturer can beextremely hazardous.SAMPLE PROBLEMAs an example of a weight and balance computation,assume a sightseeing flight in a two-seat, tandem-configured gyroplane with two people aboard. The pilot,seated in the front, weighs 175 pounds while the rearseat passenger weighs 160 pounds. For the purposes of
