直升机飞行手册Rotorcraft flying handbook

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50

2,105

184

110

2,399

107.75

49.5

49.5

44

44

79.5

79.5

79.5

79.5

106

102

93.8

150,850

8,415

12,375

0

0

0

14,708

3,975

3,975

194,298

19,504

11,220

225,022

Longitudinal

2,500

2,300

2,100

1,900

1,700

1,500

C

L

91 93 95 97 99 101 103

260

256

252

248

244

240

236

232

1,100

1,050

1,000

950

900

850

800

750

700

Fuselage Station (CM from Datum)

Gross Weight - lb.

Gross Weight - KG

Fuselage Station (in. from Datum)

Main

Rotor

Most Fwd

CG with

Full Fuel

Longitudinal

(Point A)

Figure 7-9. Use the longitudinal CG envelope along with the computed CGs to determine if the helicopter is loaded properly.

Figure 7-10. Computed Lateral CG.

Weight Arm Moment

(pounds) (inches) (lb/inches)

Basic Empty Weight

Pilot

Fwd Passenger

Right Fwd Baggage

Left Fwd Baggage

Right Aft Passenger

Left Aft Passenger

Right Aft Baggage

Left Aft Baggage

Totals with Zero Fuel

Main Fuel Tank

Aux Fuel Tank

Totals with Fuel

CG

1,400

170

250

185

50

50

2,105

184

110

2,399

0

12.2

–10.4

11.5

–11.5

12.2

–12.2

12.2

–12.2

–13.5

13

–1.6

0

2,074

–2,600

0

0

0

–2,257

610

–610

–2,783

–2,484

1,430

–3,837

Lateral

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Lateral CG is often plotted against the longitudinal CG.

[Figure 7-11] In this case, –1.6 is plotted against 93.8,

which was the longitudinal CG determined in the previous problem. The intersection of the two lines falls well

within the lateral CG envelope.

C

L

260

256

252

248

244

240

236

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(lbs.)

Moment

(lb.-ins.

/1,000)

1,102 110.8

28.3 340

22.9 211

162.0 1,653

Aft CG Limit

Station 101.0

Forward CG Limit

Station 95.0

Figure 7-8. CG/Moment Chart.

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inches, the CG is 93.8. Plotting this CG against the

weight indicates that the helicopter is loaded within

the longitudinal limits (point A).

CALCULATING LATERAL CG

Some helicopter manufacturers require that you also

determine the lateral CG limits. These calculations are

similar to longitudinal calculations. However, since the

lateral CG datum line is almost always defined as the

center of the helicopter, you are likely to encounter

negative CGs and moments in your calculations.

Negative values are located on the left side while positive stations are located on the right.

Refer to figure 7-10. When computing moment for the

pilot, 170 pounds is multiplied by the arm of 12.2 inches

resulting in a moment of 2,074 pound-inches. As with

any weight placed right of the aircraft centerline, the

moment is expressed as a positive value. The forward

passenger sits left of the aircraft centerline. To compute

this moment, multiply 250 pounds by –10.4 inches. The

result is in a moment of –2,600 pound-inches. Once the

aircraft is completely loaded, the weights and moments

are totaled and the CG is computed. Since more weight

is located left of the aircraft centerline, the resulting

total moment is –3,837 pound-inches. To calculate CG,

divide –3,837 pound-inches by the total weight of 2,399

pounds. The result is –1.6 inches, or a CG that is 1.6

inches left of the aircraft centerline.

Weight Arm Moment

(pounds) (inches) (lb/inches)

Basic Empty Weight

Pilot

Fwd Passenger

Right Fwd Baggage

Left Fwd Baggage

Right Aft Passenger

Left Aft Passenger

Right Aft Baggage

Left Aft Baggage

Totals with Zero Fuel

Main Fuel Tank

Aux Fuel Tank

Totals with Fuel

CG

1,400

170

250

185

50

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340

pounds up to the line labeled “PILOT & PASSENGER

@STA. 83.2.” Go left and read the pilot/passenger

moment (28.3 thousand lb.-inches).

Reduction factors are often used to reduce the size of

large numbers to manageable levels. In figure 7-7, the

scale on the loading graph gives you moments in thousands of pound-inches. In most cases, when using this

type of chart, you need not be concerned with reduction factors because the CG/moment envelope chart

normally uses the same reduction factor. [Figure 7-8]

After recording the basic empty weight and moment of

the helicopter, and the weight and moment for each

item, total and record all weights and moments. Next,

plot the calculated takeoff weight and moment on the

sample moment envelope graph. Based on a weight of

1,653 pounds and a moment/1,000 of 162 pound-inches,

the helicopter is within the prescribed CG limits.

COMBINATION METHOD

The combination method usually uses the computation method to determine the moments and center of

gravity. Then, these figures are plotted on a graph to

determine if they intersect within the acceptable envelope. Figure 7-9 illustrates that with a total weight of

2,399 pounds and a total moment of 225,022 pound-

FUEL@ STA. 108.5

PILOT& PASSENGER@ STA. 83.2

0

100 200 300 400 500

4

8

12

16

20

24

28

32

36

MOMENT (THOUSANDS OF LBS.-IN.)

LOAD WEIGHT (LBS)

Figure 7-7. Moments for fuel, pilot, and passenger.

190

180

170

160

150

140

130

120

110

100

1,100 1,200 1,300 1,400 1,500 1,600 1,700

LOADED WEIGHT (POUND)

LOAD MOMENT/1000

(POUNDS - INCHES)

1. Basic Empty Weight..................

2. Pilot and Front Passenger........

3. Fuel...........................................

5. Baggage...................................

TOTALS

Weight

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most airplanes, where discharging a passenger is

unlikely to adversely affect the CG, off-loading a passenger from a helicopter could make the aircraft unsafe

to fly. Another difference between helicopter and airplane loading is that most small airplanes carry fuel in

the wings very near the center of gravity. Burning off

fuel has little effect on the loaded CG. However, helicopter fuel tanks are often significantly behind the center

of gravity. Consuming fuel from a tank aft of the rotor

mast causes the loaded helicopter CG to move forward.

As standard practice, you should compute the weight

and balance with zero fuel to verify that your helicopter

remains within the acceptable limits as fuel is used.

A B

C

D

F

1,600

1,500

1,400

1,300

1,200

1,100

104 105 106 107 108 109

Baggage Compartment

Loading Lines

Fuel Loading

Lines

E

Figure 7-6. Loading chart illustrating the solution to sample

problems 1 and 2.

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SAMPLE PROBLEM 3

The loading chart used in the sample problems 1 and 2

is designed to graphically calculate the loaded center of

gravity and show whether it is within limits, all on a

single chart. Another type of loading chart calculates

moments for each station. You must then add up these

moments and consult another graph to determine

whether the total is within limits. Although this method

has more steps, the charts are sometimes easier to use.

To begin, record the basic empty weight of the helicopter, along with its total moment. Remember to use the

actual weight and moment of the helicopter you are flying. Next, record the weights of the pilot, passengers,

fuel, and baggage on a weight and balance worksheet.

Then, determine the total weight of the helicopter.

Once you have determined the weight to be within prescribed limits, compute the moment for each weight

and for the loaded helicopter. Do this with a loading

graph provided by the manufacturer. Use figure 7-7 to

determine the moments for a pilot and passenger

weighing 340 pounds and for 211 pounds of fuel.

Start at the bottom scale labeled LOAD WEIGHT.

Draw a line from 211 pounds up to the line labeled

“FUEL @ STA108.5.” Draw your line to the left to

intersect the MOMENT scale and read the fuel moment

(22.9 thousand lb.-inches). Do the same for the pilot/passenger moment. Draw a line from a weight of

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You can determine if a helicopter is within weight and

CG limits using a loading chart similar to the one in

figure 7-6. To use this chart, first subtotal the empty

weight, pilot, and passengers. This is the weight at

which you enter the chart on the left. The next step is to

follow the upsloping lines for baggage and then for fuel

to arrive at your final weight and CG. Any value on or

inside the envelope is within the range.

SAMPLE PROBLEM 1

Determine if the gross weight and center of gravity are

within allowable limits under the following loading

conditions for a helicopter based on the loading chart

in figure 7-6.

To use the loading chart for the helicopter in this example, you must add up the items in a certain order. The

maximum allowable gross weight is 1,600 pounds.

ITEM POUNDS

Basic empty weight 1,040

Pilot 135

Passenger 200

Subtotal 1,375 (point A)

Baggage compartment load 25

Subtotal 1,400 (point B)

Fuel load (30 gallons) 180

Total weight 1,580 (point C)

1. Follow the green arrows in figure 7-6. Enter the

graph on the left side at 1,375 lb., the subtotal of

the empty weight and the passenger weight.

Move right to the yellow line. (point A)

2. Move up and to the right, parallel to the baggage

compartment loading lines to 1,400 lb. (Point B)

3. Continue up and to the right, this time parallel to

the fuel loading lines, to the total weight of 1,580

lb. (Point C).

Point C is within allowable weight and CG limits.

SAMPLE PROBLEM 2

Assume that the pilot in sample problem 1 discharges

the passenger after using only 20 pounds of fuel.

ITEM POUNDS

Basic empty weight 1,040

Pilot 135

Subtotal 1,175 (point D)

Baggage compartment load 25

Subtotal 1,200 (point E)

Fuel load 160

Total weight 1,360 (point F)

Follow the blue arrows in figure 7-6, starting at 1,175

lb. on the left side of the graph, then to point D, E, and

F. Although the total weight of the helicopter is well

below the maximum allowable gross weight, point F

falls outside the aft allowable CG limit.

As you can see, it is important to reevaluate the balance

in a helicopter whenever you change the loading. Unlike

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positive and negative values.

Weight Arm Moment

(pounds) (inches) (lb/inches)

Basic Empty Weight

Oil

Pilot

Forward Passenger

Passengers Aft

Baggage

Fuel

Total

CG

1,700

12

190

170

510

40

553

3,175

116.5

179.0

65.0

65.0

104

148

120

109.9

198,050

2,148

12,350

11,050

53,040

5,920

66,360

348,918

Max Gross Weight = 3,200 lbs. CG Range 106.0 – 114.2 in.

Figure 7-5. In this example, the helicopter’s weight of 1,700

pounds is recorded in the first column, its CG or arm of 116.5

inches in the second, and its moment of 198,050 poundinches in the last. Notice that the weight of the helicopter,

multiplied by its CG, equals its moment.

Lateral

Datum

+ –

+ –

Front View

Top View

7-5

Once you are satisfied that the total weight is within

prescribed limits, multiply each individual weight by

its associated arm to determine its moment. Then, add

the moments together to arrive at the total moment for

the helicopter. Your final computation is to find the

center of gravity of the loaded helicopter by dividing

the total moment by the total weight.

After determining the helicopter’s weight and center

of gravity location, you need to determine if the CG

is within acceptable limits. In this example, the

allowable range is between 106.0 inches and 114.2

inches. Therefore, the CG location is within the

acceptable range. If the CG falls outside the acceptable limits, you will have to adjust the loading of the

helicopter.

LOADING CHART METHOD

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7-4

The lateral reference datum, is usually located at the

center of the helicopter. The location of the reference

datums is established by the manufacturer and is

defined in the rotorcraft flight manual. [Figure 7-4]

ARM—The horizontal distance from the datum to any

component of the helicopter or to any object located

within the helicopter is called the arm. Another term

that can be used interchangeably with arm is station.

If the component or object is located to the rear of the

datum, it is measured as a positive number and usually is referred to as inches aft of the datum.

Conversely, if the component or object is located forward of the datum, it is indicated as a negative number and is usually referred to as inches forward of the

datum.

MOMENT—If the weight of an object is multiplied by

its arm, the result is known as its moment. You may

think of moment as a force that results from an object’s

weight acting at a distance. Moment is also referred to

as the tendency of an object to rotate or pivot about a

point. The farther an object is from a pivotal point, the

greater its force.

CENTER OF GRAVITY COMPUTATION—By totaling the

weights and moments of all components and objects carried, you can determine the point where a loaded helicopter would balance. This point is known as the center

of gravity.

WEIGHT AND BALANCE METHODS

Since weight and balance is so critical to the safe operation of a helicopter, it is important to know how to

check this condition for each loading arrangement.

Most helicopter manufacturers use one of two methods, or a combination of the methods, to check weight

and balance conditions.

COMPUTATIONAL METHOD

With the computational method, you use simple mathematics to solve weight and balance problems. The first

step is to look up the basic empty weight and total

moment for the particular helicopter you fly. If the center of gravity is given, it should also be noted. The

empty weight CG can be considered the arm of the

empty helicopter. This should be the first item recorded

on the weight and balance form. [Figure 7-5]

Next, the weights of the oil, if required, pilot, passengers, baggage, and fuel are recorded. Use care in

recording the weight of each passenger and baggage.

Recording each weight in its proper location is

extremely important to the accurate calculation of a

CG. Once you have recorded all of the weights, add

them together to determine the total weight of the

loaded helicopter.

Now, check to see that the total weight does not exceed

the maximum allowable weight under existing conditions. In this case, the total weight of the helicopter is

under the maximum gross weight of 3,200 pounds.

Figure 7-4. The lateral reference datum is located longitudinally through the center of the helicopter; therefore, there are

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WEIGHT AND BALANCE

CALCULATIONS

When determining whether your helicopter is properly

loaded, you must answer two questions:

1. Is the gross weight less than or equal to the maximum allowable gross weight?

2. Is the center of gravity within the allowable CG

range, and will it stay within the allowable range

as fuel is burned off?

To answer the first question, just add the weight of the

items comprising the useful load (pilot, passengers,

fuel, oil, if applicable, cargo, and baggage) to the basic

empty weight of the helicopter. Check that the total weight

does not exceed the maximum allowable gross weight.

To answer the second question, you need to use CG or

moment information from loading charts, tables, or graphs

in the rotorcraft flight manual. Then using one of the

methods described below, calculate the loaded moment

and/or loaded CG and verify that it falls within the allowable CG range shown in the rotorcraft flight manual.

It is important to note that any weight and balance computation is only as accurate as the information provided.

Therefore, you should ask passengers what they weigh

and add a few pounds to cover the additional weight of

clothing, especially during the winter months. The baggage weight should be determined by the use of a scale, if

practical. If a scale is not available, be conservative and

overestimate the weight. Figure 7-2 indicates the standard weights for specific operating fluids.

The following terms are used when computing a helicopter’s balance.

REFERENCE DATUM—Balance is determined by the

location of the CG, which is usually described as a

given number of inches from the reference datum. The

horizontal reference datum is an imaginary vertical

plane or point, arbitrarily fixed somewhere along the

longitudinal axis of the helicopter, from which all horizontal distances are measured for weight and balance

purposes. There is no fixed rule for its location. It may

be located at the rotor mast, the nose of the helicopter,

or even at a point in space ahead of the helicopter.

[Figure 7-3]

Aviation Gasoline (AVGAS) . . . . . . . . . . . . . . . . . . .6 lbs. / gal.

Jet Fuel (JP-4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5 lbs. / gal.

Jet Fuel (JP-5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.8 lbs. / gal.

Reciprocating Engine Oil . . . . . . . . . . . . . . . . . . 7.5 lbs. / gal.*

Turbine Engine Oil . . Varies between 7.5 and 8.5 lbs. / gal.*

Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8.35 lbs. / gal.

* Oil weight is given in pounds per gallon while oil capacity

is usually given in quarts; therefore, you must convert the

amount of oil to gallons before calculating its weight.

Figure 7-2. When making weight and balance computations,

always use actual weights if they are available, especially if

the helicopter is loaded near the weight and balance limits.

Datum

+ –

Figure 7-3. While the horizontal reference datum can be anywhere the manufacturer chooses, most small training helicopters have the horizontal reference datum 100 inches

forward of the main rotor shaft centerline. This is to keep all

the computed values positive.

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the helicopter to a stop. In the event of engine failure and

the resulting autorotation, you may not have enough

cyclic control to flare properly for the landing.

A forward CG will not be as obvious when hovering into

a strong wind, since less rearward cyclic displacement is

required than when hovering with no wind. When determining whether a critical balance condition exists, it is

essential to consider the wind velocity and its relation to

the rearward displacement of the cyclic control.

CG AFT OF AFT LIMIT

Without proper ballast in the cockpit, exceeding the aft

CG may occur when:

• A lightweight pilot takes off solo with a full load

of fuel located aft of the rotor mast.

• A lightweight pilot takes off with maximum baggage allowed in a baggage compartment located

aft of the rotor mast.

• A lightweight pilot takes off with a combination

of baggage and substantial fuel where both are aft

of the rotor mast.

You can recognize the aft CG condition when coming

to a hover following a vertical takeoff. The helicopter

will have a tail-low attitude, and you will need exces-

Forward CG

CG Directly Under The Rotor Mast Aft CG

Figure 7-1. The location of the center of gravity strongly influences how the helicopter handles.

7-3

sive forward displacement of cyclic control to maintain a hover in a no-wind condition. If there is a wind,

you need even greater forward cyclic.

If flight is continued in this condition, you may find it

impossible to fly in the upper allowable airspeed range

due to inadequate forward cyclic authority to maintain a

nose-low attitude. In addition, with an extreme aft CG,

gusty or rough air could accelerate the helicopter to a

speed faster than that produced with full forward cyclic

control. In this case, dissymmetry of lift and blade flapping could cause the rotor disc to tilt aft. With full forward cyclic control already applied, you might not be

able to lower the rotor disc, resulting in possible loss of

control, or the rotor blades striking the tailboom.

LATERAL BALANCE

For most helicopters, it is usually not necessary to

determine the lateral CG for normal flight instruction

and passenger flights. This is because helicopter cabins are relatively narrow and most optional equipment is located near the center line. However, some

helicopter manuals specify the seat from which you

must conduct solo flight. In addition, if there is an

unusual situation, such as a heavy pilot and a full

load of fuel on one side of the helicopter, which could

affect the lateral CG, its position should be checked

against the CG envelope. If carrying external loads in

a position that requires large lateral cyclic control

displacement to maintain level flight, fore and aft

cyclic effectiveness could be dramatically limited.

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mechanic. When the revised weight and moment are

recorded on a new form, the old record is marked with

the word “superseded” and dated with the effective

date of the new record. This makes it easy to determine

which weight and balance form is the latest version.

You must use the latest weight and balance data for

computing all loading problems.

BALANCE

Helicopter performance is not only affected by gross

weight, but also by the position of that weight. It is

essential to load the aircraft within the allowable centerof-gravity range specified in the rotorcraft flight manual’s weight and balance limitations.

CENTER OF GRAVITY (CG)

The center of gravity is defined as the theoretical point

where all of the aircraft’s weight is considered to be

concentrated. If a helicopter was suspended by a cable

attached to the center-of-gravity point, it would balance

like a teeter-totter. For helicopters with a single main

rotor, the CG is usually close to the main rotor mast.

Improper balance of a helicopter’s load can result in

serious control problems. The allowable range in which

the CG may fall is called the “CG range.” The exact

CG location and range are specified in the rotorcraft

flight manual for each helicopter. In addition to making

a helicopter difficult to control, an out-of-balance loading condition also decreases maneuverability since

cyclic control is less effective in the direction opposite

to the CG location.

Ideally, you should try to perfectly balance a helicopter

so that the fuselage remains horizontal in hovering

flight, with no cyclic pitch control needed except for

wind correction. Since the fuselage acts as a pendulum

suspended from the rotor, changing the center of gravity changes the angle at which the aircraft hangs from

the rotor. When the center of gravity is directly under

the rotor mast, the helicopter hangs horizontal; if the

CG is too far forward of the mast, the helicopter hangs

with its nose tilted down; if the CG is too far aft of the

mast, the nose tilts up. [Figure 7-1]

CG FORWARD OF FORWARD LIMIT

A forward CG may occur when a heavy pilot and passenger take off without baggage or proper ballast

located aft of the rotor mast. This situation becomes

worse if the fuel tanks are located aft of the rotor mast

because as fuel burns the weight located aft of the rotor

mast becomes less.

You can recognize this condition when coming to a

hover following a vertical takeoff. The helicopter will

have a nose-low attitude, and you will need excessive

rearward displacement of the cyclic control to maintain

a hover in a no-wind condition. You should not continue

flight in this condition, since you could rapidly run out

of rearward cyclic control as you consume fuel. You also

may find it impossible to decelerate sufficiently to bring