Weight and Balance g

Weight and Balance g

INTRODUCTIONAviation has been one of the most dynamic industries since its beginning. New aircraft are continually being developed with improvements over previous models. Improvements in design have, in many cases, tended to increase the importance of the proper loading and balancing of today's airplanes. Weight-and-balance calculations are performed according to exact rules and specifications and must be prepared when aircraft are manufactured and whenever they are altered, whether the airplane is large or small. The constantly changing conditions of modern aircraft operation pre-sent more complex combinations of cargo, crew, fuel, passengers, and baggage. The necessity of obtaining maximum efficiency for all flights has increased the need for a precise system of controlling the weight and balance of an aircraft.

FUNDAMENTAL PRINCIPLES

In a previous chapter, the laws of physics were discussed. Included were discussions of specific gravity and balance, together with explanations of levers. These principles form the basis for computing weight-and-balance data for an air-plane and will be reviewed briefly here.

Force of GravityEvery body of matter in the universe attracts every other body with a certain force that is called gravitation. The term gravity is used to refer to the force that tends to draw all bodies toward the center of the earth. The weight of a body is the result of all gravitational forces acting on the body.

Center of GravityEvery particle of an object is acted on by the force of gravi-ty. However, in every object there is one point at which a single force, equal in magnitude to the weight of the object and directed upward, can keep the body at rest, that is, can keep it in balance and prevent it from falling. This point is known as the center of gravity (CG).

The CG might be defined as the point at which all the weight of a body can be considered concentrated. Thus, the CG of a perfectly round ball would be the exact center of the ball, provided that the ball was made of the same material throughout and that there were no air or gas pockets inside (see Figure 7-1). The CG of a uniform ring would be at the center of the ring but would not be at any point on the ring itself (see Figure 7-2). The CG of a cube of solid material would be equidistant from the eight corners, as shown in Figure 7-3. In airplanes or helicopters, ease of control and maneuverability require that the location of the CG be within specified limits.

Location of the CGSince the CG of a body is that point at which its weight can be considered to be concentrated, the CG of a freely sus-pended body will always be vertically beneath the point of support when the body is supported at a single point. To lo-cate the CG, therefore, it is necessary only to determine the point of intersection of vertical lines drawn downward from two separate points of support employed one at a time. This technique is demonstrated in Figure 7-4, which shows a flat, square sheet of material lettered A, B, C, and D at its four corners, suspended first from point B and then from point C. The lines drawn vertically downward from the point of suspension in each case intersect at the CG.

The CG of an irregular body can be determined in the same way. If an irregular object, such as the one shown in

FIGURE 7-1 Center of gravity of a ball.

147

FIGURE 7-2 Center of gravity of a ring.

Figure 7-5, is suspended from a point P in such a manner that it can turn freely about the point of suspension, it will come to rest with its CG directly below the point of suspen-sion, P. If a plumb line is dropped from the same point of suspension, the CG of the object will coincide with some point along the plumb line; a line drawn along the plumb line passes through this point. If the object is suspended from another point, which will be called A, and another line is drawn in the direction indicated by the plumb line, the in-tersection of the two lines will be at the CG. In order to veri-fy the results, the operation can be repeated, this time with the object suspended from another point, called B. No mat-ter how many times the process is repeated, the lines should pass through the CG; therefore, it can be shown that the CG of the object lies at the point of intersection of these lines of suspension. Therefore, any object behaves as if all its weight were concentrated at its CG.

s \• \^ \ \ \

s

/

FIGURE 7-5 Locating the CG in an irregular body.

The General Law of the LeverIn Chapter 2 the law of levers was explained; it will be re-peated briefly here to show how it relates to the weight and balance of an airplane.

Wrenches, crowbars, and scissors are levers used to gain mechanical advantage, that is, to gain force at the expense of distance or to gain distance at the expense of force. A lever, in general, is essentially a rigid rod free to turn about a point called the fulcrum. There are three types of levers, but the study of weight and balance is principally interested in the type known as a first-class lever. This type has the fulcrum between the applied effort and the resistance, as shown in Figure 7-6.

In Figure 7-6 the fulcrum is marked F, the applied effort is E, and the resistance is R. If the resistance, R, equals 10 lb [4.535 kg], and it is 2 in [5.08 cm] from the fulcrum, F, and if the effort, E, is applied 10 in [25.4 cm] from the fulcrum, it will be found that an effort of 2 lb [0.907 kg] will balance the resistance, R. In other words, when a lever is balanced, the product of the effort and its lever arm (distance from the fulcrum) equals the product of the resistance and its lever arm. The product of a force and its lever arm is called the

moment of the force.

fl=10LB10"

FIGURE 7-4 Location of the CG.

£=2LB

FIGURE 7-3 Center of gravity of a cube.

148 Chapter 7 Weight and Balance

FIGURE 7-6 First-class lever.

The general law of the lever is as follows: If a lever is in balance, the sum of the moments tending to turn the lever in one direction about an axis equals the sum of the moments tending to turn it in the opposite direction. Therefore, if the lever is in balance, and if several different efforts are ap-plied to the lever, the sum of the moments of resistance will equal the sum of the moments of effort.

Moment of a Force and EquilibriumThe tendency of a force to produce rotation around a given axis is called the moment of the force with respect to that axis.

The amount and direction of the moment of a force de-pend upon the direction of the force and its distance from the axis. The perpendicular distance from the axis to the line of the force is called the arm, and the moment is measured by the product of the force and the arm. Thus, a force of 10 lb [4.536 kg] acting at a distance of 2 ft [0.6096 m] from the axis exerts a turning moment of 20 ft-lb [2.765 kg-m].

In order to avoid confusion between moments tending to produce rotation in opposite directions, those tending to produce a clockwise rotation are called positive and those tending to produce counterclockwise rotation are called negative. If the sum of the positive, or clockwise, moments equals the sum of the negative, or counterclockwise, mo-ments, there will be no rotation. This is usually expressed in the form EM = 0. The symbol E is the Greek letter sigma, and EM means the sum of all the moments, M, both positive and negative.

In Figure 7-7 a moment diagram is shown, with mo-ments about the point A. M, acts in a counterclockwise di-rection, with a force of 1 lb [0.4536 kg] at a distance of 3 ft [0.9144 m]; therefore, the value of M, is -3 ft-lb [-0.4148 kg-m]. M2 acts in a counterclockwise direction, with a force of 2 lb [0.9072 kg] at a distance of 2 ft [0.6096 m], thus pro-ducing a moment of -4 ft-lb [-0.5528 kg-m]. M3, acting in a counterclockwise direction with a force of 1 lb [0.4537 kg] at a distance of 1 ft [0.3048 m], produces a moment of -1 ft-lb [-0.1383 kg-m]. A/4 acts in a clockwise direction, with a force of 4 lb [1.814 kg] at 2 ft, which makes a moment of +8 ft-lb [+1.105 kg-m]. Thus, -3 - 4 - 1 + 8 = 0. The sum of the negative moments is equal to the positive mo-ment; therefore, there is a condition of equilibrium, and there is no rotation about point A.

There is a total force of 8 lb [3.629 kg] acting downward, and unless the axis is supported by an upward force of 8 lb, there will be downward movement but no rotation.

Aircraft CG Range and LimitsThe first-class lever is in balance only when the horizontal CG is at the fulcrum. However, an aircraft can be balanced in flight anywhere within certain specified forward and aft limits if the pilot operates the trim tabs or elevators to exert an aerodynamic force sufficient to overcome any static un-balance. CG locations outside the specified limits will cause unsatisfactory or even dangerous flight characteristics.

The allowable variation within the CG range is carefully determined by the engineers who design an airplane. The CG range usually extends forward and rearward from a point about one-fourth the chord of the wing, back from the leading edge, provided that the wing has no sweepback. The exact location is always shown in the Aircraft Specifica-tions or the Type Certificate Data Sheet. Heavy loads near the wing location are balanced by much lighter loads at or near the nose or tail of the airplane. In Figure 7-8, a load of 5 lb [2.268 kg] at A will be balanced by a load of 1 lb [0.4536 kg] at B because the moments of the two loads are equal.

Since the CG limits constitute the range of movement that the aircraft CG can have without making it unstable or unsafe to fly, the CG of the loaded aircraft must be within these limits at takeoff, in the air, and on landing. In some cases, the takeoff limits and landing limits are not exactly the same, and the differences are given in the specifications for the aircraft.

Figure 7-9 shows typical limits for the CG location in an airplane. As previously stated, these limits establish the CG range. The CG of the airplane must fall within this range if the airplane is to fly safely; that is, the CG must be to the rear of the forward limit and forward of the aft limit.

CG and Balance in an AirplaneThe CG of an airplane may be defined, for the purpose of balance computations, as an imaginary point about which the nose-heavy (-) moments and tail-heavy (+) moments are exactly equal in magnitude. Thus, the aircraft, if sus-pended from that point (CG), would have no tendency to ro-tate in either direction (nose-up or nose-down). This condition is illustrated in Figure 7-10. As stated previously, the weight of the aircraft can be assumed to be concentrated at its CG.

The CG with the aircraft loaded is allowed to range fore and aft within certain limits that are determined during the flight tests for type certification. These limits are the most forward- and rearward-loaded CG positions at which the aircraft will meet the performance and flight characteristics required by the FAA. These limits may be expressed in

1 LB 2 LBS 1 LB

4 LBS

Mi M2 M3 t

8

LBS FIGURE 7-7 Moment diagram.

r

FIGURE 7-8 Balancing of the load.

Fundamental Principles 149

ACTUAL C G LOCATION

FIGURE 7-9 Center-of-gravity limits.

The MAC is usually given in the aircraft's Type Certifi-cate Data Sheet when it is required for weight-and-balance computations; therefore the person working on the airplane is expected to have only a general understanding of its meaning. For simplicity purposes, most light-aircraft manu-facturers express the CG range in inches from the datum, while transport-category aircraft are expressed in terms of percentages of the MAC.

LIMITS FWDAFT

WEIGHT-AND-BALANCE TERMINOLOGY

FIGURE 7-10 Airplane suspended from the CG location.

terms of a percentage of the mean aerodynamic chord (MAC) or in inches forward or to the rear of the datum line.

The relative positions of the CG and the center of lift of the wing have critical effects on the flight characteristics of the aircraft. Consequently, relating the CG location of the chord of the wing is convenient from a design-and-operations standpoint. Normally, an aircraft will have ac-ceptable flight characteristics if the CG is located some-where near the 25% average chord point. This means the CG is located one-fourth of the total distance back from the leading edge of the average wing section (see Figure 7-11). Such a location will place the CG forward of the aerody-namic center for most airfoils.

The mean aerodynamic chord (MAC) is established by the manufacturer. If the wing has a constant chord, the straight-line distance from the leading edge to the trailing edge (the chord) would also be the MAC. However, if the wing is tapered, the mean aerodynamic chord is more com-plicated to define. The MAC is the chord of an imaginary airfoil which has the same aerodynamic characteristics as the actual airfoil. The MAC is established by the manufac-turer, who defines its leading edge (LEMAC) and trailing edge (TEMAC) in terms of inches from the datum. The CG location and various limits are then expressed in percent-ages of the chord.

Before proceeding with explanations of the methods for computing weight-and-balance problems, it is important to have a good understanding of the words and terms used.

Arm. The arm is the horizontal distance in inches from the datum to the center of gravity of the item. The algebraic sign is plus (+) if measured aft of the datum and minus (-) if measured forward of the datum (see Figure 7-12).

Center of gravity (CG). The CG is a point about which the nose-heavy and tail-heavy moments are exactly equal in magnitude. If the aircraft were suspended from this point it would be perfectly balanced. Its distance from the ref-erence datum is found by dividing the total moment by the total weight of the airplane.

Center of gravity range. The operating CG range is the distance between the forward and rearward limits within which the airplane must be operated. These limits are indicated on pertinent FAA Aircraft Type Certificate Data Sheets (see Figure 7-13) or in aircraft weight-and-balance records, and they meet the requirements of the Federal Aviation Regulations (FARs).

Datum (reference datum). The datum is an imaginary ver-tical plane or line from which all horizontal measure-ments of arm are taken (see Figure 7-12). The datum is established by the manufacturer. Once the datum has been selected, all moment arms must be taken with refer-ence to that point. The location of the datum may be found in the aircraft's Type Certificate Data Sheet (see Figure 7-13).

'///////A

NOSE-HEAVY (-) MOMENT

oAIRCRAFT CG

CG = 25% MAC

LEVEL REFERENCE (UPPER TAILCONE)

WING LEADING EDGE

THE DATUM IS 66.25 IN AHEAD OF THE WING LEADING EDGE.A = 33.0

B ■- 90.0

FIGURE 7-11 Percent of mean aerodynamic chord.


FIGURE 7-12 Leveling diagram. (Piper Aircraft Corp.)

Empty weight (EW). The empty weight of an aircraft in-cludes the weight of the airframe, power plant, and re-quired equipment that has a fixed location and is normally carried in the airplane. For aircraft certificated under FAR Part 23, the empty weight also includes unus-able fuel and full-operating fluids necessary for normal operation of aircraft systems, such as oil and hydraulic fluid. For older aircraft not certificated under FAR Part 23, in place of full oil, only the undrainable oil is includ-ed in the empty weight. The current aircraft empty weight must be kept as a part of the permanent weight-and-balance records.

Empty-weight center of gravity (EWCG). The, empty-weight CG is the CG of the aircraft in its empty condition

and is an essential part of the weight-and-balance record that must be kept with the permanent aircraft records.

Empty-weight CG range. The EWCG range is established so that when the EWCG falls within this range, the air-craft-operating CG limits will not be exceeded under standard loading conditions. The EWCG range shown for many light airplanes is listed in the aircraft specifications or the Type Certificate Data Sheet and may eliminate further calculations by technicians making equipment changes (see Figure 7-13).

Fleet empty weight. The fleet empty weight is used by air carriers as an average basic empty weight which may be used for a fleet or group of aircraft of the same model and configuration. The weight of any fleet member can-

DEPARTMENT OF TRANSPORTATION FEDERAL AVIATION ADMINISTRATION

TYPE CERTIFICATE DATA SHEET

Engine:

Fuel:Engine Limits: Propeller. Propeller Limits:

Airspeed Limits

Flight Maneuvering Load Factor (g's)

CG Range: Datum:

Leveling Means:

Empty-Weight CG Range:

Maximum Weight:

No. of Seats: Maximum Baggage: Fuel Capacity:

Never exceedMax. structural cruisingManeuveringFlaps extended

Flaps down

Forward limit Aft limit

+8.6 in- +10.2 in

Takeoff Landing

Front tank (total) (usable)

Rear tank (total) (usable)

Utility Category211mph(183kts)186mps(162kts)124 mph (108 kts)

99 mph ( 86 kts)

+4.4 -1.8

+ 2.0 -1.8

+ 10.6 in (18% MAC) + 17.7 in (30% MAC)

1829 lb 1763 lb

2 at +22.7 in 1101b at+55.119.8 (at -6.7 in) 19.020.8 (at+55.1 in) 20.6

Acrobatic Category211 mph (183 kts)186 mph (162 kts)146 mph (127 kts)99 mph ( 86 kts)

+6.0 -3.0+2.0 -2.0

10.6 in (18% MAC) 15.3 in (26% MAC)

1675 lb 1675 lb

2 at+22.7 in None

19.8 (at -6.7 in) 19.0

0 0

Lycoming 10360 B2F with "Christen" inverted oil system, or Lycoming AEIO36O-B2F fuel injected.

91/96 minimum aviation grade gasoline. For all operations 2700 rpm (180 hp). Hoffman HO 29-180-170(Utility and Acrobatic Categories)Statis rpm at maximum permissible throttle setting—2250 ± SODiameter 70.9 in. No cutoff permitted.

See NOTE 3 for acrobatic maneuvers. Flaps up

Wing leading edge at 51 in from airplane center line. (Length of wing chord at datum 59 in).

Longitudinal: Left canopy rail Lateral: Top of bulkhead #2.

Oil Capacity:

Rear tank must be empty for operations in acrobatic category. Minimum fuel quantity for acrobatics: 2.6 gal.Maximum capacity: 2 galMinimum: 0.5 galMaximum oil quantity for acrobatics: 1.5 gal

FIGURE 7-13 Sample Type Certificate Data Sheet.

Weight-and-Balance Terminology 151

t not vary more than the tolerance established by the ap-plicable government regulations.

LEMAC. LEMAC is the abbreviation for the leading edge of the mean aerodynamic chord.

Leveling means. Leveling means are the reference points used by the aircraft technician to insure that the aircraft is level for weight-and-balance purposes (see Figure 7-12). Leveling is usually accomplished along both the longitu-dinal and lateral axis. Leveling means are given in the Type Certificate Data Sheet (see Figure 7-13).

Loading envelope. The loading envelope includes those combinations of airplane weight and center of gravity that define the limits beyond which loading is not approved.

Main-wheel center line (MWCL). The MWCL is a verti-cal line passing through the center of the axle of the main landing-gear wheel.

Maximum gross weight. The maximum gross weight is the maximum authorized weight of the aircraft and its contents as listed in the Type Certificate Data Sheet (Figure 7-13).

Maximum landing weight. The maximum landing weight is the maximum weight at which the aircraft may nor-mally be landed (see Figure 7-13).

Maximum ramp weight. The maximum ramp weight is the maximum weight approved for ground maneuver. (It in-cludes the weight of the start, taxi, and run-up fuel.)

Maximum takeoff weight. The maximum takeoff weight isthe maximum allowable weight at the start of the takeoffrun (see Figure 7-13). ,

Mean aerodynamic chord (MAC). The MAC is the length of the mean chord of the wing as established through aerodynamic considerations. For weight-and-balance pur-poses it is used to locate the CG range of the aircraft. The

location and dimension of the MAC, where used, will be found in the aircr

aft specifications, the Type Certificate Data Sheet (see Figure 7-13), the flight manual, or the aircraft weight-and-balance record.

Minimum fuel. Minimum fuel for weight-and-balance computations is no more than the quantity of fuel re-quired for j h of operation at rated maximum continuous power. It is calculated on the maximum except takeoff (METO) horsepower and is the figure used when the fuel load must be reduced to obtain the most critical loading on the CG limit being calculated. The formula usually used in calculating minimum fuel is \ METO hp = mini-mum fuel in pounds (e.g., { X 360 hp = 180 lb of fuel).

Moment The moment is the product of the weight of an item multiplied by its arm. Moments are expressed in pound-inches (lb-in). The total moment of an aircraft is the weight of the aircraft multiplied by the distance be-tween the datum and the CG.

Moment index. The moment index is a moment divided by a constant, such as 100, 1000, or 10 000. The purpose of using a moment index is to simplify weight-and-balance computations of large aircraft where heavy items and long arms result in large, unmanageable numbers.

Standard weights. For general weight-and-balance purpos-es, the following weights are considered standard:

GasolineTurbine fuelLubricating oilWaterGeneral aviation crew

and passengersAir-carrier passenger (summer) Air-carrier passenger (winter)

6 lb/gal [2.75 kg/gal] 6.7 lb/gal [3.0 kg/gal] 7.5 lb/gal [3.4 kg/gal] 8.3 lb/gal [3.75 kg/gal] 170 pounds [77 kg]

per person160 pounds [72.5 kg] 165 pounds [75 kg]

DATUM STA. 0.

NOSE GEAR

WEIGHING POINT

■W. L. 102.01

MAIN GEAR

HORIZONTAL CG.

152 FIGURE 7-14 Weighing and measuring. (Cessna Aircraft Co.)

Chapter 7 Weight and Balance

Station. A station is a location along the airplane fuselage given in terms of distance in inches from the reference datum. The datum is, therefore, identified as station zero (see Figure 7-14). The station and arm are usually identi-cal. An item located at station 50 would have an arm of 50 in.

Tare. Tare is the weight of the equipment necessary for weighing the airplane (such as chocks, blocks, slings, jacks, etc.) which is included in the scale reading but is not a part of the actual weight of the airplane. Tare must be subtracted from the scale reading in order to obtain the actual weight of the airplane.

TEMAC. TEMAC is an abbreviation for the trailing edge of the mean aerodynamic chord.

Undrainable oil. That portion of the oil in an aircraft lubri-cating system that will not drain from the engine with the aircraft in a level attitude is called the undrainable oil. This oil is considered a part of the empty weight of the aircraft.

Unusable fuel. Unusable fuel is the fuel that cannot be con-sumed by the engine. The amount and location of the un-usable fuel may be found in the Type Certificate Data Sheet (see Figure 7-13). Unusable fuel is a part of the aircraft's empty weight.

Usable fuel. Fuel available for flight planning is called us-able fuel.

Useful load. The useful load is the weight of the pilot, copi-lot, passengers, baggage, and usable fuel. It is the empty weight subtracted from the maximum weight.

Weighing point. The weighing points of an airplane are those points by which the airplane is supported at the time it is weighed. Usually the main landing gear and the nose or tail wheel are the weighing points (see Figure 7-14). Sometimes, however, an airplane may have jacking points from which the weight is taken. In any event, it is essential to define the weighing points clearly in the weight-and-balance record.

DETERMINATION OF THE EWCG LOCATION

Weighing the AircraftWeighing aircraft with accurately calibrated scales is the only sure method of obtaining an accurate empty weight and CG location. The use of weight-and-balance records in ac-counting for and correcting the aircraft weight-and-balance location is reliable over limited periods of time. Over ex-tended intervals, however, the accumulation of dirt, miscel-laneous hardware, minor repairs, and other factors will render the basic-weight and CG data inaccurate. For this reason, periodic aircraft weighings are desirable; however, they are not required of aircraft operated under FAR Part 91. This is not the case for air-taxi and air-carrier aircraft, which are required by the FARs to be periodically weighed. Aircraft may also be required to be weighed after they are painted; when major modifications or repairs are made; when the pilot reports unsatisfactory flight characteristics, such as nose or tail heaviness; and when recorded weight-and-balance data are suspected to be in error.

Weighing EquipmentThe type of equipment which is used to weigh aircraft varies with the aircraft size. Three types of scales are commonly used to weigh aircraft. Each type is equally effective in ob-taining accurate results. The three types of scales are plat-form scales, portable electronic weighing system using load pads, and electronic load cells used in conjunction with jacks.

Light aircraft are often weighed on beam-type platform scales, such as those illustrated in Figure 7-15. Platform scales require the use of jacks or ramps to position the air-craft on the scales.

A portable electronic weighing system makes it possi-ble to find the weight and balance of large and small aircraft without jacking (see Figure 7-16).. The system consists of

FIGURE 7-15 Weighing an airplane with platform scales. (Piper Aircraft Corp.)

Determination of the EWCG Location 153

■"-'.■-*■■ .-

FIGURE 7-16 Portable electronic weighing system. (Evergreen Weigh, Inc.)

electronic platform scales as necessary to weigh each wheel or pair of wheels on the aircraft, signal amplifiers, a digital CG indicator, a digital gross-weight indicator, and a power panel. Each scale consists of a platform supported by strain-gauge transducers, usually no more than 3 in [7.62 cm] in height. Ramps are supplied with the platforms so that the aircraft can easily be towed to position on the scales. The signals from the scales provide the information that is pre-sented on the digital CG and gross-weight indicators. For larger aircraft the weighing pads may be recessed so that they are level with the floor to facilitate locating the aircraft on the scales.

Another method used to weigh large aircraft is to use electronic load cells. These cells are strain gauges whose resistance changes in accordance with the pressure applied to them. A load cell is placed between a jack and a jack point on the aircraft, with particular attention paid to locat-ing the cell so that no side loads will be applied (see Figure 7-17). When weight readings are taken, the entire airplane weight must be supported on the load cells.

The output of the load cells is fed to an electronic instru-ment that amplifies and interprets the load-cell signals to provide weight readings. The instrument is adjusted to pro-vide a zero reading from each load cell before the aircraft is weighed. After weighing, the cells are checked again and the reading is adjusted to compensate for any change noted.

Whichever type of system is selected, only weighing equipment that is maintained and calibrated to acceptable standards should be used.

Equipment PreparationWhen preparing to weigh an aircraft, the accuracy of the scales must be established. This can be done in accordance with instructions provided by the manufacturer of the scales or by testing the scales with calibrated weights. When there is nothing on the scales, the reading should be zero. Note: Most electronic scales require a specified warm-up period.

All the equipment that will be required to perform the weighing procedures should be located prior to beginning the weight check. The following is a list of equipment com-monly used when weighing an aircraft:

1. Jacks or ramps2. Wheel chalks3. Level4. Plumb lines5. Steel measuring tape6. Hydrometer (for testing the specific gravity of the fuel)8. Tools and gauges for strut deflation and inflation9. Nitrogen bottles for strut inflation

Aircraft PreparationIn order to obtain an accurate determination of the aircraft's weight and center of gravity, it is important that the aircraft be properly prepared for weighing.

Specific weighing preparations and procedures will vary with the model of the aircraft being weighed. However, the following information will provide general guidance.

The aircraft should be clean and free from excessive dirt, grease, moisture, or any other extraneous material before weighing. The aircraft should be dry before it is weighed; thus an aircraft should never be weighed immediately after it is washed.

All equipment to be installed in the aircraft and included in the certificated empty weight should be in place for weighing. Each item must be in the location that it will oc-cupy during flight, as shown on the aircraft equipment list. All equipment, such as carpets, seat belts, oxygen masks, and so on, should be placed in their normal location. All tools and other working equipment must be removed before weighing.

Unless otherwise noted in the Type Certificate Data Sheet, the oil system and other operating fluids should be checked to see that they are full. Items that should be filled to operating capacity include lubricating oil, hydraulic fluid, oxygen bottles, and fire extinguishers.

The fuel should be drained from the aircraft unless other instructions are given. Fuel should be drained with the air-craft in the level position to make sure that the tanks are as empty as possible. The amount of fuel remaining in the air-craft tanks, lines, and engine is termed unusable fuel, and its weight is included in the empty weight of the aircraft. In special cases the aircraft may be weighed with full fuel in the tanks, provided that a definite means is available for de-termining the exact weight of the fuel.

FIGURE 7-17 Electronic load cells.

154 Chapter 7 Weight and" Balance

Weighing AreaThe aircraft should be weighed inside a closed building to

, avoid errors that may be caused by wind. Hangar doors and windows should be kept closed during the weighing process. The floor should be level. All fans, air condition-ing, and ventilating systems should be turned off.

Positioning the AirplaneThe aircraft should be placed in the weighing area. The air-craft's exterior should be checked to see that there is no in-terference with work stands and other equipment. If the main wheels are used as reaction points, the brakes should not be set because the resultant side loads on the scales or weighing units may cause erroneous readings.

The aircraft should be positioned securely on the scales. If the wheels are used as weighing points, it is advisable to use chocks on the scales both fore and aft so that the aircraft does not roll during the weighing procedure. Remember that items such as chocks and tail stands that are placed on top of the scales during weighing are considered tare weight. Tare weight must be subtracted from the scale readings. Tare weight items are generally weighed on different scales be-cause aircraft scales are likely to be inaccurate in the lower range readings.

An airplane must be level to obtain accurate weighing information. Leveling is usually accomplished along both the longitudinal and the lateral axis. The leveling means are given in the Type Certificate Data Sheet. The leveling means are the reference points used by the aircraft techni-cian to insure that the aircraft is level for weight-and-balance purposes.

One method used on many light aircraft is to set a spirit level on a longitudinal structural member to establish the longitudinal level position and another level across a lateral structural member to establish the lateral level position. This same basic procedure is accomplished in some air-craft by the installation of two nut plates on the side of the fuselage. Screws can be placed in these nut plates and lon-gitudinal level is determined when a spirit level placed on the extended screws is level, as shown in Figure 7-18.

Some aircraft use a plumb bob and a target to estaonsn the level on both axes. In the DC-10 airplane, an inclinome-ter consisting of a plumb bob and grid plate is provided in the right wheel well, and brackets for spirit levels are locat-ed in the nose-gear wheel well. In Figure 7-19 locations of the leveling means for the DC-10 are shown.

The inclinometer indicates degrees of roll or pitch. The plumb bob is suspended by a cord and is secured in a stowage clip when not in use. During leveling operations, the plumb bob is released from the clip and is suspended by its cord over the grid plate. The level attitude of the airplane is established by the location of the plumb bob in relation to the grid-plate markings.

When a higher degree of leveling accuracy is required, spirit levels are used. The two sets of brackets provided in the nose-gear wheel well are used to support the levels in both longitudinal and lateral axes.

Weighing ProcedureThe scale reading should be given a period of a few minutes to stabilize. The weights of the weighing points should be recorded to provide information needed for the CG determi-nation. Several readings are taken for each reaction point, and the average reading is entered on the aircraft weighing form.

With the aircraft in the level position, it is necessary to measure and record the weigh point locations on the weigh-ing form. On some aircraft the exact location of the weigh points will be provided in the aircraft flight manual or main-tenance manual. If the location of weighing points is not provided, the exact location of the weighing points must be accurately measured while the aircraft is in the level posi-tion and then recorded for use in the weight-and-balance computation. The location of the datum is provided in the Type Certificate Data Sheet.

For aircraft where the datum passes through the aircraft, a plumb bob is dropped from that point to the floor. For air-craft where the datum is located ahead of the aircraft, a ref-erence point should be located on the aircraft from which a plumb bob can be dropped to locate the datum. Once the datum is located on the floor, the plumb bob is suspended from each of the weighing points. The technician can mea-sure these distances by projecting the required points to the hangar floor. To project these points to the hangar floor, a plumb bob may be suspended so that it is approximately one-half inch above the floor. When the swing of the plumb bob dampens, a cross mark is made on the floor directly under the tip of the plumb bob. The main reaction points are projected to the floor in the same manner. After marking the crosses for the two main gear points, a chalked string is stretched between them. The string is then snapped to the floor, leaving a chalk line between the main reaction points. The nose or tail reaction point is projected to the hangar floor in a similar manner, as is shown in Figure 7-20.

After these points are projected to the floor, it is a simple matter to measure the required dimensions. When measur-ing these distances, the tape must be parallel to the center line of the aircraft. Measurements made from the main reac-^ tion points are taken perpendicular to the chalk line joining these two points. When fuselage and wing jack points are

Determination of the EWCG Location 155FIGURE 7-18 Leveling longitudinally. (Piper Aircraft Corp.)

LONGITUDINAL LEVELING BRACKETS

FIGURE 7-19 Locations for leveling means on a DC-10 airplane. (McDonnell Douglas Corp.)

used as reaction points in weighing the aircraft, it is unnecessary to measure dimensions. These points will remain fixed and their moment arms may be found in the aircraft records. Care must be taken to use the fixed reaction points indicated in the records for the particular aircraft being mea-sured. Because of manufacturing tolerances and minor model changes, the fixed reaction points are not necessarily identical for all aircraft of a particular type.

The weight of the tare should be recorded either before or after weighing the aircraft, and the tare weight should then be subtracted from the total weight obtained from the scales.

When data for comparison are available, an attempt should be made to verify the results obtained from each

LATERAL LEVELING BRACKETS

LONGITUDINAL LEVELING BRACKETS

STA 595 STA

1516- 1FT 8 INCHES

.3 FT 4 INCHES

11 FT 4 INCHES

LATERAL LEVELING BRACKETS

FIREWALL DATUM

FIGURE 7-20 Locating weighing points.


weighing. Verification may be made by comparing results with a previous weighing of an aircraft of the same model.

Computing CG LocationAfter the necessary dimensions and weights have been ob-tained, the empty weight and the empty weight CG can be calculated. Empty weight is the total of the three scale read-ings after subtracting the weight of tare items, plus or minus calibration errors. This weight is important for subsequent calculation of maximum weight and also is a necessary fac-tor in the determination of the CG.

Center-of-gravity computations may be figured by several methods. The formulas used in computing the center of gravity are varied. Whenever possible, the manufacturer's weight-and-balance formulas and diagrams should be used, as shown in Figure 7-21. Although most manufacturers use similar formulas, they use different letter designations for different items. If these formulas are not available, a stan-dard formula may be used for the EWCG computation.

Fundamentally, the CG is the point at which all the weights of the aircraft can be considered to be concentrated. The average location of these weights can, therefore, be ob-tained by dividing the total moment (weight X arm) by the total weight. The process then involves multiplying each measured weight by its arm to obtain a moment and then adding the moments.

Extra care must be taken in these types of empty-weight calculations if one or more of the arms is located ahead of the datum. In this event, the algebraic sign of the arm and moment will be negative. It should be remembered that a positive number (the weight) times a negative number (the arm) results in a negative number (the moment). Following the multiplication step, additional care must be taken when adding wheel moments to obtain the total moment and when dividing the total moment by the total weight to obtain the CG. In all these mathematical operations, the algebraic sign must be observed.

A set of formulas used quite extensively today is con-tained in the FAA Advisory Circular 43.13.1A. and is

CENTER OF JACK POINT

Scale Position Scale Reading Tare Symbol Net Weight

Left Wheel L

Right Wheel R

Nose Wheel N

Sum of Net Weights (As Weighed) W

DATUM STA 0.0

LEVEL ON LEVELING SCREWS

N-111.92

(A) - (N) x (B) ; X )x ( ) IN

W

CG ARM = 111.92+ X IN

Item Moment/1000 Weight (Lb) X CG Arm (In) = (Lb-ln)

Airplane Weight (From Item 5, Page 6-8)Add: Unusable Fuel (2 Gal at 6 Lbs/Gal) 12 162.1 1.9Equipment ChangesAirplane Basic Empty Weight

FIGURE 7-21 Sample airplane weighing. (Cessna Aircraft Co.)

Determination of the EWCG Location 157

NOSE-WHEEL-TYPE AIRCRAFT

DATUM LOCATED FORWARD OF THE MAIN WHEELS

CG = D -FX L W

TAIL-WHEEL-TYPE AIRCRAFT

DATUM LOCATED FORWARD OF THE MAIN WHEELSCG = D + Rx L W

NOSE-WHEEL-TYPE AIRCRAFT

DATUM LOCATED AFT OF THE MAIN WHEELS

TAIL-WHEEL-TYPE AIRCRAFT

DATUM LOCATED AFT OF THE MAIN WHEELS

CG = - D + FX L WCG = -D RX L W

CG = distance from datum to center of gravity of aircraft IV = weight of aircraft at time of weighingD = horizontal distance measured from datum to main wheel weighing point L = horizontal distance measured from main wheel weighing point to nose or tail weighing point F = weight at nose weighing point R - weight at tail weighing point

FIGURE 7-22 Different arrangements of the formula for EWCG.

shown in Figure 7-22. This system uses four separate for-mulas. The user selects one of these formulas, depending upon the weighing points and the datum location in refer-ence to the weighing points. These formulas simplify the calculations in several ways. In effect, the datum is mathe-matically moved to the main gear by this process, resulting in relatively small moments, which are easy to handle in weight-and-balance calculations. A major benefit of the use of these formulas is the elimination of multiplication steps that involve negative arms and negative moments. In the first diagram of Figure 7-22, the datum is at the nose of the airplane, and since the airplane is of the tricycle-gear type, the CG must be forward of the MWCL. The part of the for-mula F x LAV gives the distance of the CG forward of the MWCL. This distance must then be subtracted from the dis-tance D to find the distance of the CG from the datum.

In the second diagram, the airplane is of conventional tail-wheel type, and so the CG must be to the rear of the MWCL. With the datum at the nose of the airplane, it is nec-essary to add the datum-line distance, D, to the R X LAV distance to find the EWCG from the datum line.


In the third diagram, the CG and the MWCL are both for-ward of the datum line; therefore, both distances are nega-tive. For this reason the CG distance from the MWCL and the datum distance from the MWCL are added together, and the total is given a negative sign.

The fourth diagram shows a condition where the CG is positive from the MWCL but negative from the datum line. The datum to the MWCL is a negative distance, and the CG from the MWCL is a positive distance. Therefore, the EWCG from the datum line is the difference between the two distances and, in this case, carries a negative sign.

Computing EWCG for a Tricycle-Gear AirplaneIn Figure 7-23 a tricycle-gear airplane is weighed, and it is found that the nose-wheel weight is 320 lb [145.1 kg], the right-wheel weight is 816 lb [370.1 kg], and the left-wheel weight is 810 lb [367.4 kg]. The datum, which is located at the nose of the airplane, is 40 in [101.6 cm] forward of the nose-wheel center line and 115 in [292.1 cm] forward of the

FIGURE 7-38 A balance computer. (Continental Air Lines)

TOTAL TAKEOFF FUEL-LBS.CAUTION

AFTER LOADING PASSENGERS, CARGO. AND FUEL BALLAST AND BEFORE LOADING USABLE FUEL, THE APRPLANE CG MUST BE WITHIN THE FORWARD AND AFT ZERO FUEL LIMITS AS LABELED.

LOADING INSTRUCTIONS ON THE REVERSE SIDE

2. Position a scale and jack under each jack pad andraise the helicopter clear of the floor.

3. Level the helicopter with the jacks as explained in thesection on weighing airplanes.

4. Balance each scale and record its reading.5. Lower the helicopter to the floor surface and weigh the

jacks, blocks, and any other equipment used betweenthe scales and the helicopter. Deduct this tare weight from

the scale readings to obtain net scale readings. The total of the net scale readings is the as-weighed weight of the helicopter.

A typical example of net weights is 513 lb [232.7 kg] for the forward left scale, 522 lb [236.8 kg] for the forward right scale, and 1063 lb [482.2 kg] for the aft scale. The as-weighed weight is then the sum of the net scale weights, or 20981b [951.6 kg].

Weight and Balance for a Helicopter 171

MAC. The flight engineer is therefore always able to deter-mine whether the weight of the aircraft and the location of the CG are within specified limits. The attitude sensor deter-mines whether the aircraft is in the correct attitude (level) for an accurate measurement of CG location.

WEIGHT AND BALANCE FOR A HELICOPTER

The weight-and-balance principles and procedures which have been discussed in connection with airplanes apply gen-erally to helicopters, with one important difference: Most helicopters have a much more restricted CG range than do airplanes. In some cases this range is less than 3 in [7.62 cm]. When loading helicopters, it is also often a requirement to calculate the horizontal CG as well as the fore-and-aft CG. The exact location and length of the CG range is speci-fied for each helicopter and usually extends a short distance fore and aft of the main-rotor mast (the center of lift) or in the center of a dual-rotor system. Ideally, the helicopter should have such perfect balance that the fuselage remains horizontal while in a hover and the only cyclic adjustment required should be that made necessary by the wind. The fuselage acts as a pendulum suspended from the rotor. Any change in the CG changes the angle at which it hangs from this point of support. Many recently designed helicopters have loading compartments and fuel tanks located at or near the balance point.

The information in this section applies to a Bell Model 206L Long Ranger helicopter. This information, however, is typical of instructions for leveling, weighing, and com-puting the CG location for a helicopter.

LevelingFor leveling, a level plate is located on the cabin floor ap-proximately 4.0 in [10.16 cm] forward of the aft seat and left of the helicopter center line. This is shown in Figure 7-41. A slotted level plate is located directly above the level plate. The leveling procedure is then as follows:

1. Hang a plumb bob from the small hole in the slottedlevel plate and suspend it in such a manner that the plumbbob is just above the level plate on the cabin floor.

2. Position the helicopter on a level surface in an enclosed hangar.

3. Position three jacks under the helicopter at the jackand tie-down fittings that are permanently installed. Twoforward jack fittings are located at station 55.16, and the aftfitting is located at station 204.92.

4. Adjust the aft jack at the aft jack fitting until the helicopter is approximately level. The forward end of the landing-gear skid tubes should still be in contact with theground.

5. Adjust all three jacks evenly until the helicopter islevel, as indicated when the point of the plumb bob is directly over the intersection of the cross lines of the level plate.This position is shown in Figure 7-41.


REF ITEM WEIGHT MOMENT/ 100

1. BASIC EMPTY WEIGHT

2. PAYLOAD

3. ZERO FUEL WEIGHT (SUB-TOTAL) (DO NOT EXCEED MAXIMUM ZERO FUEL WEIGHT)

4. FUEL LOADING

5. RAMP WEIGHT (SUB-TOTAL) (DO NOT EXCEED MAXIMUM RAMP WEIGHT OF POUNDS^

6. LESS FUEL FOR TAXIING

7. TAKEOFF WEIGHT (DO NOT EXCEED MAXIMUM TAKEOFF WEIGHT OF POUNDS)

8. LESS FUEL TO DESTINATION

9. LANDING WEIGHT (DO NOT EXCEED MAXIMUM LANDING WEIGHT OF POUNDS)

FIGURE 7-37 Typical transport-category aircraft weight-and-balance loading form.

Weighing

A helicopter may be weighed with platform scales or by means of electronic load cells mounted on jacks. The in-structions given here are for weighing with scales.

The helicopter should be weighed in a configuration as near empty weight as possible. Empty-weight condition al-lows for the weight of the basic helicopter together with seats, ballast, special equipment, transmission oil, hydraulic fluid, unusable fuel, and undrainable oil. The baggage com-partment should be empty. Weighing is accomplished as follows:

1. Position the scales in an approximately level area and check them for proper adjustment to the zero position. The weighing should be done in an enclosed area to avoid the adverse effects of wind, such as flapping rotors and body sway.

FIGURE 7-39 Transducer installed in the axle of a Boeing 747 airplane.

\ <;..

LEFT WING GEAR

RIGHTWINGGEAR

LEFT BODY GEAR

RIGHT BODY GEAR

TRANSDUCERS UPPER EQUIPMENT CENTER, LEFT

P6 CB PANEL

FWDOUTBD 115V AC

FWD LH WING PWRAFT INBD GEAR

JUNCTIONSIG 400 ~ GND

SERVICE BUSOUTBD BOX

AFT INBD

FWD FLIGHT ENGINEER'S PANEL

OUTBD RH WING GEAR

JUNCTIONPWR ooFWD

INBD PWRAFT

OUTBD BOX SIG GW % MACAFT

INBDWEIGHT-AND-

BALANCESIG INDICATOR/

CONTROL PANEL

FWD COMPUTER

OUTBD LH BODY GEAR

JUNCTION

.. PWR PWR TRANSDUCERSFWD INBD SIG

AFT SIG

OUTBD LH AXLEINBD NOSE GEAR

PWR ,------------------,FWD SIG

OUTBDFWD INBD

RH BODY GEAR

^ PWR PWR % RH AXLE NOSE GEAR

AFT OUTBD

AFT INBD

— JUNCTION BOX

SIG--------►

SIG

ATTITUDE

ATTITUDE SENSOR

MAIN EQUIPMENT CENTER

SOLENOID

FIGURE 7-40 Block diagram of the weight-and-balance system for a Boeing 747 airplane.

Determining CG LocationThe CG location for a helicopter is determined in the same manner as for other aircraft. In the case of the Bell Model 206L, the datum line is at the 0.0 fuselage station, which is just forward of the nose of the helicopter, as shown in Fig-ure 7-42. The CG location aft of the datum line is found as follows:

moment of forward weights + moment of rear weights

CG location =

total net weight

Chapter 7 Weight and Balance

The location of the forward weighing point is 55.16 in [140.1 cm] aft of the datum line at FS 55.16, and the loca-tion of the rear weighing point is at FS 204.92.

The sum of the weights indicated by the forward scales is 1035 lb [469.9 kg], and the moment is 1035 X 55.16 = 57 090.6 in-lb [657.84 kg-m]. The moment of the aft weight is 1063 X 204.92 = 217 829.95 in-lb [2509.9 kg-m]. The total moment is then 274 920.55 in-lb [3167.8 kg-m]. When this is divided by the total net weight of the helicopter, the CG location is found to be 131.04 in aft of the datum line.

If a helicopter when weighed does not include all the

172

1. SLOTTED LEVEL PLATE2. AFT JACK FITTING3. JACKS4. LEVEL PLATE5. FORWARD JACK FITTINGS6. PLUMB BOB

FIGURE 7-41 Leveling a helicopter. (Bell Helicopter Textron)

equipment required for the empty-weight condition, these items must be added. The weights must be added to the as-weighed weight, and the moments must be computed and added to the original computed moment. The result is a total weight known as the derived weight and a slightly different CG location.

If the fmal empty-weight CG location does not fall with-in the limitations set forth in the empty-weight CG location chart, ballast plates are installed either forward or rearward in specified locations. Ballast is never added in both for-ward and rearward locations. The forward ballast location in the Bell Model 206L helicopter is at +13 (FS 13.0), and the rearward ballast location is at +377.18 (FS 377.18) as

shown in Figure 7-42. The ballast requirement is computed in the way described earlier in the section on correcting the CG location of airplanes.

REVIEW QUESTIONS

1. Define center of gravity.2. What is the general law of the lever?1. What is the condition that exists when the sum of

the positive moments equals the sum of the negativemoments?

Review Questions 173

RUDDER GUST LOCK

AILERON GUST LOCK

FIGURE 15-13 Gust locks on an airplane. (Cessna Aircraft Co.)

main and tail rotor blades should be secured if a helicopter is parked in an area subjected to turbulence created by jet, prop, or rotor blast from other aircraft.

JACKING AND HOISTING AIRCRAFT

From time to time in performing maintenance and inspec-tion procedures, it becomes necessary to jack or hoist the aircraft. In the jacking or hoisting of aircraft, it is essential that the operation be performed according to the manufac-turer's instructions. The points where hoisting or jacking fit-tings are attached to the aircraft are designed to withstand the stresses imposed when the aircraft is hoisted or jacked. If the aircraft is lifted or jacked at a point other than those designed for the operation, severe damage will often be caused. The locations of jacking points for a light twin-engine aircraft are shown in Figure 15-14.

Jacking AircraftSince jacking procedures and safety precautions vary for different types of aircraft, only general jacking procedures and precautions are discussed here. Consult the applicable aircraft manufacturer's maintenance instructions for specific jacking procedures. In jacking one wheel only, a small jack can be used at the landing-gear jack pad. This procedure is employed when tires are being changed and when brakes are being repaired or serviced. When only one set of wheels has to be raised, a low single-base jack is used, as shown in Figure 15-15. Before the wheel is raised, the remaining wheels must be chocked fore and aft to prevent

movement of the aircraft. The wheel should be raised only high enough to clear the floor.

For jacking the complete aircraft, wide-base jacks, such as the large tripod types shown in Figure 15-16, should be used because of the greater stability they afford. The size and configuration of the aircraft will dictate the type and number of jacks needed to raise it. Many small aircraft are raised by using a jack under each wing spar and a weighted tail stand, as shown in Figure 15-17 on page 346. If this method is used, be sure to consult the manufacturer's rec-ommendations on the amount of weight needed. Transport-category aircraft may use several jacks, with three or four jacks being used to raise the aircraft and additional jacks being inserted to stabilize it after it has been jacked up. Fig-ure 15-18 on page 346 illustrates the jack points on a Boe-ing 747. The airplane is provided with three main jacking points and five stabilizing jacking points. The primary jack-ing points are at the wing-body junction and the tail. The five stabilizing points are located with one at the nose and two under each wing.

Many aircraft have jack pads located at the jack points. Others have removable jack pads or jacking adapters that are inserted into receptacles prior to jacking (see Figure 15-19 on page 347). The correct jack pad should be used in all cases. The function of the jack pad is to ensure that the aircraft load is properly distributed at the jack point and to provide a convex bearing surface to mate with the concave jack stem.

Typical jacking procedures and precautions for raising an aircraft are as follows:

1. Place the aircraft in a hangar, if possible, to avoid the - effects of wind. (Head the airplane into wind if it is to be jacked outside.)

Jacking and Hoisting Aircraft 343

1 2 . 5 5

LDL

FIGURE 15-14 Jacking

points for a light twin-

engine aircraft. (Cessna Aircraft Co.)

MAIN JACK POINT LHMAIN JACK POINT RH

FS 186. 20

NOSE JACK POINT

FIGURE 15-15 Jacking a single set of wheels.

344 Chapter 15 Ground Handling and Safety2. See that the areas under and around the airplane are

clear of obstructions (such as ladders, work platforms, orentry stands).

3. If any other work is in progress on the aircraft, ascertain if any critical panels have been removed. On some aircraft the stress panels or plates must be in place when theaircraft is jacked to avoid structural damage.

4. Install the landing-gear ground locks if applicable.5. Place the jacks directly under the center of each jack

point and extend the jacks until they touch the jack points(most accidents during jacking are the result of misalignedjacks).

6. Check the legs of the jacks to see that they will notinterfere with the operations to be performed after the aircraft is jacked, such as retracting the landing gear.

7. Station one person at each jack, if possible. Operateall jacks evenly so that the airplane remains as nearly levelas possible.

8. Keep the amount of lift to an absolute minimum andalways within the safe limits of the jack.

9. Set the locking devices on the jacks to prevent accidental lowering of the airplane.

JL

■ INTEGRAL RAM LOCKNUTS

ELECTRICAL-CENTRAL CONTROL CONSOLE

FIGURE 15-16 Typical tripod jack.

TYPICAL TRIPOD JACK

PRESSURE GAGE

MANUAL CONTROLS

10. Hold any climbing on the aircraft to an absolute minimum, and avoid violent movements by persons who are required to go aboard.

To lower an aircraft, the following jacking instructions apply:

1. Before lowering the aircraft, make certain that thelanding gear is down and locked and that all ground-lockingdevices are properly installed.

2. Check the area under and around the aircraft to insurethat it is free from all equipment and workstands.

3. Release the mechanical locks, then slowly and carefully release the pressure, lowering the jacks evenly. Cau-

tion: As the aircraft is lowered, watch that the oleo struts do not bind up.

4. As soon as possible, remove the jacks out from under the aircraft.

HoistingIt is often necessary to hoist airplanes and helicopters in order to perform certain service and maintenance opera-tions. When hoisting the entire airplane or any of the air-plane components, it is recommended that hoisting slings, manufactured specifically for the airplane, be used. These slings are designed to lift the airplane or components from the approximate center of gravity. Most fuselage hoist

Jacking and Hoisting Aircraft 345

FIGURE 15-17 Jacking a small airplane. (Piper Aircraft Co.)

80.7 TONS (EACH) DURING JACKING. 100 TONS (EACH) JACKED WEIGHT INDOORS.

15 TONS(EACHSIDE)

GROUND LINE

JACKING LINE

19.7 TONS

FIGURE 15-18 Jacking arrangement for a Boeing 747 aircraft. (Boeing Commercial Aircraft Co.)

slings are adjustable to allow for different weight and cen-ter-of-gravity variations. Figure 15-20 illustrates an aircraft and its components being hoisted with a sling.

GROUND-SUPPORT EQUIPMENT

Ground-support equipment is needed primarily for the oper-ation of aircraft on the ground when the aircraft engines are not operating. In some cases, small ground-support units, such as battery carts, preoil units, and test units, are used

346 Chapter 15 Ground Handling and. Safety

with light aircraft, but this is not usually a regular and ongo-ing procedure, as it is with large aircraft. Ground-support units for large aircraft include electrical power supplies, air-conditioning and/or air-supply units, hydraulic test units, and various service units.. The units used on a regular basis are those supplying electric power and air for starting en-gines, ventilating, heating, and cooling.

Electrical Power SuppliesElectrical power for light aircraft is usually supplied by means of a battery cart. Such carts contain one or more

Weight and Balance g

Documents