balance record of the aircraft. It has no usefulness in itself, but serves as a basis for other computations and not as an indication of what the loaded c.g. will be. The EWCG is computed at the time of weighing, using formulas established for tailwheel- and nosewheel-type aircraft.
Empty Weight Center of Gravity Range The EWCG range is an allowable variation of travel within the c.g. limits. When the EWCG of the aircraft falls within this range, it is impossible to exceed the EWCG limits using standard specification loading arrangements. Not all aircraft have this range indicated on the Aircraft Specifications or Type Certificate Data Sheets.
Where it is indicated, the range is valid only as long as the aircraft is loaded according to the standard specification. The installation of items not listed in the specification will not permit use of this range.
Operating Center of Gravity Range The operating c.g. range is the distance between the forward and rearward c.g. limits indicated in the pertinent Aircraft Specification or Type Certificate Data Sheets. These limits, deternined at the time of design and manufacture, are the extreme loaded c.g. positions allowable within the applicable regulations controlling the design of the aircraft. These limits are shown in either percent of MAC (mean aerodynamic chord) or inches from the datum of the aircraft.
The loaded aircraft c.g. location must remain within these limits at all times. Accordingly, detailed instructions for determining load distribution are provided on placards, loading charts, and load adjusters.
Mean Aerodynamic Chord The MAC is the mean average chord of the wing. An airfoil section is a cross section of a wing from leading edge to trailing edge. A chord is usually defined as an imaginary straight line drawn parallel to the airfoil through the leading and trailing edges of the section. The MAC of a constant chord wing would be the same as the actual chord of the wing. Any departure from a rectangular wing plan form will affect the length of the MAC and the resulting distance from the MAC leading edge to the aircraft wing leading edge. Figure 3-4 shows the MAC for a sweptwing The aircraft c.g. is usually placed at the maximum forward position of the center of pressure on the MAC to obtain the desired stability. Because of the relationship between the c.g. location and the moments produced by aerodynamic forces, the greatest of which is lift, the c.g. location is generally expressed with respect to the wing. This is done by specifying c.g. in percent of the wing's The location of the MAC, in relation to the datum, is given in the Aircraft Specifications or Type Certificate Data Sheets, the weight and balance report, or the aircraft flight manual.
Compute the c.g. location in percent of MAC
(1) Find the difference between the distance to the empty weight c.g. location from the datum and the distance to the leading edge of MAC from the datum.
(2) Divide the difference by the length of the MAC.
(3) Multiply the answer by 100.
(4). The final answer is then expressed in percent.
An example problem that utilizes the equation for computing percent of MAC is shown in figure
3-5.
Aircraft Leveling Means Reference points are provided for leveling the aircraft on the ground. They are designated by the manufacturer and are indicated in the pertinent Aircraft Specifications. The most common leveling procedure is to place a spirit level at designated points on the aircraft structure. Some aircraft have special leveling scales built into the airframe structure. The scale is used with a plumb bob to level the aircraft longitudinally Weighing Points In weighing an aircraft, the point on the scale at which the weight is concentrated is called the weighing point. When weighing light- to mediumweight land planes, the wheels are usually placed on the scales. This means that the weighing point is, in effect, the same location obtained by extending a vertical line through the center line of the axle and onto the scale.
Other structural locations capable of supporting the aircraft, such as jack pads on the main spar, 57
MAC
241.9"
848.2" 786.2" = Datum• FIGURE 3-4. The c.g. shown in relation to MAC.
may also be used if the aircraft weight is resting on the jack pads. The weighing points should be clearly indicated in the weight and balance report.
Zero Fuel Weight The zero fuel weight is the maximum allowable weight of a loaded aircraft without fuel. Included in the zero fuel weight is the weight of cargo, passengers, and crew. All weights in excess of the zero fuel weight must consist of usable fuel.
Minimum Fuel The term "minimum fuel" should not be interpreted to mean the minimum amount of fuel required to fly an aircraft. Minimum fuel, as it applies to weight and balance, is the amount of fuel that must be shown on the weight and balance report when the airplane is loaded for an extremecondition check.
The minimum fuel load for a small aircraft with a reciprocating engine for balance purposes is based on engine horsepower. It is calculated in the METO (maximum except take-off) horsepower and 58
Datum X MAC H = Distance from the datum to the EWCG - 170 inches.
X = Distance from the datum to the MAC leading edge = 150 inches.
C = Length of MAC = 80 inches.
H - X
c.g. in % of MAC= × 100 170 - 150 % of MAC = × 100 = 80 20 × 100 = 25% 80 FIGURE 3-5. Finding percent of MAC.
is the figure used when the fuel load must be reduced to obtain the most critical loading on the
c.g. limit being investigated. Either of 2 formulas may be used.
Formula 1:
Minimum fuel =12 gallons per horsepower.
hpX1½X6 lb.
1200X1½X6=1200X1½X6=600 lb. fuel.
Formula 2:
Minimum fuel =½ lb. per engine horsepower.
hp×½=minimum fuel.
1200 × ½=600 1b. fuel.
This will be the minimum pounds of fuel required for the forward or rearward weight check.
For turbine-engine powered aircraft, the minimum fuel load is specified by the aircraft manufacturer.
The fuel tank location in relation to the c.g. limit affected by the computation determines the use of minimum fuel. For example, when a forward weight check is performed, if the fuel tanks are located forward of the forward c.g. limit, they are assumed to be full. If they are located aft of the forward c.g. limit, they are assumed to be empty.
If the minimum fuel required for a particular aircraft exceeds the capacity of the tanks located forward of the forward c.g. limit, the excess fuel must be loaded in the tanks that are aft of the forward c.g. limit. When a rearward weight check is conducted, the fuel loading conditions are opposite to those used for the forward check.
Full Oil Full oil is the quantity of oil shown as oil capacity in the Aircraft Specifications. When weighing an aircraft, the oil tank may either contain the number of gallons of oil specified or be drained. When an aircraft with full oil tanks is weighed, the weight of the oil must be subtracted from the recorded readings to arrive at the actual empty weight. The weight and balance report must show whether weights include full oil or if the oil tanks were drained.
Tare Weight Tare includes the weight of all extra items, such as jacks, blocks, and chocks on the weighing scale platform, except that of the item being weighed.
The weight of these items, when included in the scale reading, is deducted to obtain the actual weight of the aircraft.
AIRCRAFT WEIGHING PROCEDURE Before beginning a study of aircraft weighing procedure or attempting the actual weighing of an aircraft, it is necessary to become familiar with the weight and balance information in the applicable Aircraft Specification or Type Certificate Data Sheet.
The specification for Taylorcraft, model BC and BCS airplanes, illustrated in figure 3-6 has been reproduced in its entirety. A few of the items need explaining; the rest are sell-explanatory.
The designation 2 PCLM is read "2-place, closed land monoplane" and indicates that the airplane seats two persons, has an enclosed cockpit, can be operated from the solid part of the earth's surface, and has only one wing. Two PCSM indicates that the airplane is a "2-place, closed sea monoplane." It should be noted that the c.g. range, EWCG range, and the maximum weight are different for the landplane and the seaplane. The location of the seats indicates a side-by-side arrangement. The datum and the leveling means are shown in the portion of the specification that is pertinent to all models. Since the datum and the leveling means are directly connected to weight and balance, they would be among the first items referred to in planning the weighing operation.
Although the location or arrangement of the 59
DEPARTMENT OF TRANSPORTATION A-696 FEDERAL AVIATION ADMINISTRATION Revision 16
TAYLORCRAFT BC BCS12-D BCS BC12-D1 BC-65 BCS12-D1 BCS-65 BC12D-85 BC12-65 (Army L-2H) BCS12D-85 BCS12-65 BC12D-4-85 BC12-D BCS12D-4-85 9 September 1969 AIRCRAFT SPECIFICATION NO. A-696 Type Certificate Holder. Taylorcraft Aviation Corporation 104 Prospect Street Alliance, Ohio 44601 I-Model BC, 2 PCLM, Approved August 24, 1938; Model BCS, 2 PCSM, Approved April 5, 1939 Engine. Continental A-50-1 (see item 114(a) for optional engines) Fuel. 73 min. grade aviation gasoline Engine Limits. For all operations, 1900 r.p.m. (50 hp.)
Propeller Limits. Diameter: Maximum 83 in.
Airspeed Limits. Landplane: Level flight or climb 105 m.p.h. (91 knots) (True Ind.) Glide or dive 131 m.p.h. (114 knots) Seaplane: Level flight or climb 95 m.p.h. (83 knots) Glide or dive 129 m.p.h. (112 knots) Center of Gravity (C.G.) Range. Landplane: (+14.5) to (+19.7) Seaplane: ( + 15.1) to (+ 19.4) Empty Weight C.G. Range. Landplane: (+ 15.3) to (+ 18.5) Seaplane: (+ 15.9) to (+18.3) When empty weight C.G. falls within pertinent range, computation of critical for and aft C.G. positions is unnecessary. Ranges are not valid for non-standard arrangements.
Maximum Weight. Landplane: 1100 Ib. (S/N 1407 and up are eligible at 1150 lb.)
Seaplane: 1228 Ib.
Number of Seats. 2 (+23) Maximum Baggage. 30 Ib. (+ 40) Fuel Capacity. 12 gal. (-9). See itcm 115 for auxiliary tank.
Oil Capacity. 4 quart. (-21) Control Surface Movements. Elevators: Up 25° Down 27° Rudders: Right 26° Left 26° Ailerons: (Not available) Serial No. Eligible. 1001 and up Required Equipment. Landplane: 1 or 4, 104, 202, 203, 210(a), 401 Seaplane: 1 or 4, 104, 205, 401 Specifications Pertinent to All Models.
Datum. Leading edge of wing Leveling Means. Upper surface of horizontal stabilizer Certification Basis. Part 04 of the Civil Air Regulations effective as amended to May 1, 1938. Type Certificate No. 696 issued.
Production Basis. None. Prior to original certification, an FAA representative must perform a detailed inspection for workmanship, materials and conformity with the approved technical FIGURE 3-6. A typical aircraft specification.
landing gear is not shown in figure 3-6, this information is given in the Aircraft Specification or Type Certificate Data Sheets and the maintenance manual. The location of the wheels has important significance, since this can be used as a doublecheck against actual measurements taken at the time of weighing.
Weighing an Aircraft Weighing an aircraft is a very important and exacting phase of aircraft maintenance and must be carried out with accuracy and good workmanship. Thoughtful preparation saves time and prevents mistakes.
To begin, assemble all the necessary equipment,
1. Scales, hoisting equipment, jacks, and leveling equipment.
2. Blocks, chocks, or sandbags for holding the airplane on the scales.
3. Straightedge, spirit level, plumb bobs, chalk hne, and a measuring tape.
4. Applicable Aircraft Specifications and weight and balance computation forms.
If possible, aircraft should be weighed in a closed building where there are no air currents to cause incorrect scale readings. An outside weighing is permissible if wind and moisture are negligible.
Prepare Aircraft For Weighing Drain the fuel system until the quantity indication reads zero, or empty, with the aircraft in a level attitude. If any fuel is left in the tanks, the aircraft will weigh more, and all later calculations for useful load and balance will be affected.
Only trapped or unusable fuel (residual fuel) is considered part of the aircraft empty weight. Fuel tank caps should be on the tanks or placed as close as possible to their correct locations, so that the weight distribution will be correct.
In special cases, the aircraft may be weighed with the fuel tanks full, provided a means of determining the exact weight of the fuel is available. Consult the aircraft manufacturer's instructions to determine whether a particular model aircraft should be weighed with full fuel or with the fuel drained.
If possible, drain all engine oil from the oil tanks. The system should be drained with all drain valves open. Under these conditions, the amount of oil remaining in the oil tank, lines, and engine is termed residual oil and is included in the empty weight. If impractical to drain, the oil tanks should be completely filled.
The position of such items as spoilers, slats, flaps, and helicopter rotor systems is an important factor when weighing an aircraft. Always refer to the manufacturer's instructions for the proper position of these items.
Unless otherwise noted in the Aircraft Specifications or manufacturer's instructions, hydraulic reservoirs and systems should be filled; drinking and washing water reservoirs and lavatory tanks should be drained; and constant-speed-drive oil tanks should be filled.
Inspect the aircraft to see that all items included in the certificated empty weight are installed in the proper location. Remove items that are not regularly carried in flight. Also look in the baggage compartments to make sure they are Replace all inspection plates, oil and fuel tank caps, junction box covers, cowling, doors, emergency exits, and other parts that have been removed. All doors, windows, and sliding canopies should be in their normal flight position. Remove excessive dirt, oil, grease, and moisture from the Properly calibrate, zero, and use the weighing scales in accordance with the manufacturer's in- Some aircraft are not weighed with the wheels on the scales, but are weighed with the scales placed either at the jacking points or at special weighing points. Regardless of what provisions are made for placing the aircraft on the scales or jacks, be careful to prevent it from falling or rolling off, thereby damaging the aircraft and equipment. When weighing an aircraft with the wheels placed on the scales, release the brakes to reduce the possibility of incorrect readings caused by side loads on the scales.
All aircraft have leveling points or lugs, and care must be taken to level the aircraft, especially along the longitudinal axis. With light, fixed-wing airplanes, the lateral level is not as critical as it is with heavier airplanes. However, a reasonable effort should be made to level the light airplanes around the lateral axis. Accuracy in leveling all aircraft longitudinally cannot be overemphasized.
Measurements The distance from the datum to the main weighing point centerline, and the distance from ol
the main weighing point centerline to the tail (or nose) weighing point centerline must be known to determine the c.g. relative to the main weighing point and the datum.
An example of main weighing point to datum and main weighing point to tail weighing point is shown in figure 3-7. See figure 3-8 for an example of main weighing point to datum and main weighing point to nosewheel measurements.
These distances may be calculated using information from the Aircraft Specifications or Type Certificate Data Sheets. However, it will often be necessary to determine them by actual measurement.
Datum After the aircraft has been placed on the scales (figure 3-9) and leveled, hang plumb bobs from the datum, the main weighing point, and the tail or nose weighing point so that the points of the plumb bobs touch the floor. Make a chalk mark on the floor at the points of contact. If desired, a chalk line may be drawn connecting the chalk marks. This will make a clear pattern of the weighing point distances and their relation to the datum.
Record the weights indicated on each of the scales and make the necessary measurements while the aircraft is still level. After all weights FIGURE 3-7. Main weighing point to datum and main weighing point to tail weighing point.
Datum FIGURE 3-8. Main weighing point to datum and main weighing point to nose weighing point.
Datum 618# 68 94" 155# 622# FIGURE 3-9. Weighing an aircraft using platform scales.
and measurements are obtained and recorded, Scule Net the aircraft may be removed from the scales.
Weigh the tare and deduct its weight from the Weighing scale reading Tare weight scale reading at each respective weighing point point (Ibs.) (Ibs.) (Ibs.)
where tare is involved.
Left main wheel 622.00 -5.00 617.00 Right main wheel 618.00 -4.00 614.00 Noşewheel 155.00 -3.00 152.00 Balance Computation To obtain gross weight and the c.g. location of the loaded airplane, first determine the empty weight and the EWCG location. When these are known, it is easy to compute the effect of fuel.
crew, passengers, cargo, and expendable weight as they are added. This is done by adding all the weights and moments of these additional items and re-calculating the c.g. for the loaded airplane.
The scale readings and measurements recorded Total 1,383.00 This gives the aircraft weight as weighed.
Empty Weight C.G.
The c.g. location is found through the progressive use of two formulas. First calculate the total moments using the following formulas:
Moment = Arm X Weight on the sample form in figure 3-10 form the basis Net for the examples of computing the empty weight Weight point weight Arm Moment and the empty weight c.g. (Ibs.) (in.) (Ib.-in.)
Left main 617.0 68" = 41,956.0 wheel Empty Weight Right main 614.0 68" 41,752.0 The empty weight of the aircraft is determined wheel by adding the net weight on each weighing point. Nosewheel 152.0 × -26" -3,952.0 The net weight is the actual scale reading, less the tare weight. 1,383.0 79,756.0 63
WEIGHING FORM MAKE ... Rotary MODEL. SERIAL .. 0242 N . 411 DATUM LOCATION Leading edge of wing at root Aircraft weighed with full oil.
1. Main weighing point is located (- " forward) (+68" aft) of datum.
2. Tail or nose weighing point is located (-26" forward) (+ " aft)of datum.
Weighing Point Reading Scale - Tare Weight = Net X Arm = Moment
3. Left Main Wheel 622.00 -5.00 817.00 68" 41,956.00 Right Main Wheel 618.00 -4.00 614.00 68" 41,752.00
5. Sub-Total 1,240.00 - 9.00 1,231.00 68" 83,708.00
6. Tail or Nose Wheel 155.00 -3.00 152.00 - 26" -3,952.00
7. Total as Weighed 1,395.00 - 12.00 1,383.00 57.67 79,756.00 Space for listing of Items when Aircraft is not Weighed Empty.
Net Item Weight Arm Moment
8. Oil - 8 gallons @ 7.5 p/p/g -60.00 - 30.00 1,800.00 Aircraft Empty Weight & c.g. 1,323.00 61.64" 81,556,00 Maximum Allowable Gross Weight 1,773 pounds Useful Load 450 pounds Computed by: Frank A. Adams A & P Number:_1366968 FIGURE 3-10. Sample weighing form.
Item Net Arm Moment weight (1bs.) (in.) (lb.-in.)
then divide the sum of the moments by the total weights involved: Acft. total as 1,383.0 57.67 79,756.0 weighed -ess oil, & gallons -60.0 -30.00 1,800.0
c.g. = Total moment 79,756.0 gallon @ 7.5 Ibs. per Total weight 1,383 Aeft. empty 1,323.0 81,556.0 = 57.67 in. weight and moment Consequently, the c.g., as weighed, is 57.67 in. Again using the formula:
from the datum. Total moment 81,550.0 Since the aircraft was weighed with the oil c.g. = Total weight 1,323 tank full, it is necessary to remove the oil to = 61.64 in.
obtain the empty weight and empty weight c.g. The EWCG is located 61.64 in. aft of the datum.
Datum +23' + 6" - 56" + 9.0° + 18.70
196.0" Tail wheel weight = 50 Ibs.
Tail wheel arm = 198.0" Empty weight (without oil) = 950 Ibs.
Datum location = leading edge of wing.
Engine = 100 hp.
CG range = (+9.0") to (+18.7").
Fuel capacity = 40 gal @ +23".
Number of seats - 3 (one @ + 6" and two @ +34").
Maximum gross weight = 1775 ibs.
Oil capacity = 8 qts @ -41".
Maximum baggage =50 Ibs @ +56".
Note: (This airplane can be flown from either the front or rear seat.)
FreURE 3-11. Schematic diagram for forward weight and balance check.
The maximum allowable gross weight as shown in the Aircraft Specifications is 1,733 pounds. By subtracting the aircraft empty weight from this figure, the useful load is determined to be 450 pounds.
WEIGHT AND BALANCE EXTREME CONDITIONS The weight and balance extreme conditions represent the maximum forward and rearward
c.g. position for the aircraft.
An aircraft has certain fixed points, fore and aft, beyond which the c.g. should not be permitted at any time during flight. A check should be made to ensure that the c.g. will not shift out of limits when crew, passengers, cargo, and expendable weights are added or removed. If the limits are exceeded and the aircraft is flown in this condition, it may lead to insufficient stability, with resulting difficulty in controlling the aircraft.
Adverse loading checks are a deliberate attempt to load an aircraft in a manner that will create the most critical balance condition and still remain within the design c.g. limits of the aircraft.
It should be noted that when the EWCG falls within the EWCG range, it is unnecessary to perform a forward or rearward weight and balance check. In other words, it is impossible to load the aircraft to exceed the c.g. limits, provided standard loading and seating arrangements are used.
Forward Weight and Balance Check To make this check, the following information is needed:
1. The weight, arm, and moment of the empty aircraft.
2. The maximum weights, arms, and moments of the items of useful load that are located ahead of the forward c.g. limit.
3. The minimum weights, arms, and moments of the items of useful load that are located aft of the forward c.g. limit.
The example shown in figure 3-11 presents one method of conducting an extreme-condition check.
This method makes it easy to visualize exactly where the weights of various loading arrangements are distributed and how they affect c.g. location.
Using the data given in figure 3-11, determine if the airplane can be loaded to cause the c.g. to go beyond its limits.
The minus moment of -615.0 is subtracted from the sum of the plus moments:
13,855.0
- 615.0 13,240.0 THIRD STEP: Find the most forward c.g. position by dividing the total moments by the total weight.
13,240.0 - = 11.17 in.
1,185 Since the total moment is plus, the answer must be plus. Therefore, the forward extreme position of the c.g. is located at 11.17 aft of the datum.
The forward c.g. limit for this example airplane is +9.0 in. aft of the datum; therefore, it is easy to see that it can be safely flown with this loading arrangement.
FIRST STEP: Load the airplane as follows:
Oil -8 qts. a -41 in.= (15.0 Ibs.) (-11 in.).
Pilot - 170 1bs. @ +6 in. = (170.0 Ibs.) (+6 in.).
Fuel, minimum-50 Ibs. @ + 23 in.= (50.0 Ibs.)
(+ 23 in.).
No passengers.
No baggage.
Fill any fuel tanks which are ahead of the forward limit. If the fuel tanks are to the rear of the forward limit, use the minimum required amount of fuel.
Rearward Weight and Balance Check To establish that neither the maximum weight nor the rearward c.g. limit is exceeded, the following information is needed:
1. The weight, arm, and moment of the empty aircraft.
2. The maximum weights, arms, and moments of the items of useful load that are located aft of the rearward c.g. limit.
3. The minimum weights, arms, and moments of the items of useful load that are located ahead of the rearward c.g. limit.
SECOND STEP: Total all weights and moments. The most rearward c.g. position is found by Item Weight (Ibs.) (in.) Arm Moments (Ib.-in.) case the airplane is loaded so that it will be tail- repeating the three steps that were followed in making the most forward c.g. check, except in this Acft. EW 950.0 + 12.3 + 11,685.0 heavy- Oil 15.0 -41.0 615.0 Pilot 170.0 + 6.0. + 1,020.0 FIRST STEP: Load the airplane in a manner that Fuel (min.) 50.0 + 23.0 + 1,150.0 will make it most tail-heavy.
Total 1,185.0 13,240.0 Oil-8 qts. @ -41 in.= (15.0 lbs.) (-41 in.).
The above figures require careful consideration.
Notice that each weight is multiplied by its arm to obtain its moment. All the weights are added to obtain 1,185 Ibs., the total weight. However, when adding the moments, all the plus moments are added:
11,685.0 1,020.0 1,150.0 Pilot - 170 1bs. @ + 6 in. = (170.0 1bs.) (+6 in.).
Fuel (max.) -40 gals. @ + 23 in. = (240.0 1bs.)
(+ 23 in.).
Passengers-two @ 170 Ibs. each-340 Ibs. @ + in. in. = 1bs.) 1bs.) (+34 in.).
Baggage (max.) -50 Ibs. @ +56 in. = (50 Ibs.)
(+ 56 in.).
Fill any fuel tanks which are aft of the rear limit. If the fuel tanks are forward of the rear 13,855.0 limit, use the minimum required amount of fuel.
SECOND STEP: Total all weights and moments movable ballast under all loading conditions for as shown here: which such ballast is necessary.
Weight Arm Moments Item (Ibs.) (in.) (lb.-in.)
Controlling c.g. Position With Ballast Oil Acft. EW 950.0 15.0 + 12.3 -41.0 + 11,685.0 615.0 c.g. exceeds the forward c.g. limit under certain Figure 3-12 shows an example aircraft whose Pilot 170.0 + 6.0 + 1,020.0 loading conditions. The forward weight and bal- Fuel (max.) 240.0 +23.0 + 5,520.0 ance check proves that with only the pilot and Passengers (two) 340.0 +34.0 + 11,560.0 minimum fuel aboard, the forward c.g. is exceeded.
Baggage (max.) 50.0 + 56.0 + 2,800.0 Total 1,765.0 31,970.0 Most forward c.g. check THIRD STEP: Find the most rearward c.g. posi- Weight Arm Moments tion by dividing the total moments by the total Item (1bs.) (in.) (Ib.-in.)
weight.
Most rearward c.g. when loaded as shown in Acft. EW 1,600.0 + 15.6 + 24,960.0 figure 3-11: Oil 22.5 - 22.0 495.0 31,970.0 = 18.11 in. Fuel (min.) Pilot 115.0 170.0 + 10.0 + 18.0 + 1,700.0 + 2,070.0 1,765 The rearward c.g. limit for this example airplane Total 1,907.5 +28,235.0 is +18.7 in. aft of the datum; therefore, it can be Total moment flown safely with this loading arrangement. Most forward c.g.= Total weight 28,235 INSTALLATION OF BALLAST = 1,907.5 = 14.8 in.
Ballast is used in an aircraft to attain the desired c.g. balance. It is usually located as far aft or as far forward as possible to bring the c.g.
within limits using a minimum amount.of weight.
Ballast that is installed to compensate for the removal or installation of equipment items and that is to remain in the aircraft for long periods is called permanent ballast. It is generally lead bars or plates bolted to the aircraft structure. It may be painted red and placarded: PERMA- NENT BALLAST-DO NOT REMOVE. In most cases, the installation of permanent ballast results in an increase in the aircraft empty weight.
Temporary ballast, or removable ballast, is used to meet certain loading conditions that may vary from time to time. It generally takes the form of lead shot bags, sand bags, or other weight items that are not permanently installed. Temporary ballast should be placarded: BALLAST _ LBS.
REMOVAL REQUIRES WEIGHT AND BAL- ANCE CHECK. The baggage compartment is usually the most convenient location for temporary ballast.
The places for carrying ballast should be properly designed, installed, and plainly marked. The aircraft operation manual must include instructions regarding the proper placement of the re- Without ballast placed somewhere aft to bring the c.g. within the designated limits of +16.5 in.
to +20.0 in., the aircraft is unsafe to fly when loaded with the pilot and minimum fuel. The problem of determining how many pounds of ballast are needed to move the c.g. within the approved limits can be solved by using the following formula:
Ballast weight needed:
(Weight of acft as loaded) (Distance out of limits) Arm from variable weight location to limit affected Inserting in the formula the applicable values:
Weight of the aircraft as loaded = 1907.5 Distance out of limit = +1.7 in.
Arm from variable weight location to the limit affected =53.5 in.
We obtain the following:
(1907.5) (1.7) needed in the baggage 60.6 Ibs., ballast weight
53.5 compartment.
When the mathematical computation ends in a fractional pound, use the next higher whole pound as the actual ballast weight. Consequently, 61.0 pounds must be placed in the baggage compartment to bring the c.g. safely within the c.g. range.
Datum 22" + 10' +34 + 70 CG range
16.5" to 20.0" 162" Tail wheel arm = 166".
Tail wheel weight = 115 Ibs.
CG range = (+16.5") to (+20.0") Fuel capacity = 38 gal @ 18" (19 gal. in each wing Maximum baggage = 100 Ibs @ 70' Maximum gross weight = 2620 Ibs.
A/C EW (without oil) = 1600 Ibs.
Datum = leading edge of wing.
Engine = 230 hp.
Oil capacity = 12 qts @ -22".
Number of seats = 4 (two @ + 10" and two @ +34").
Note: Flight controls in front seat only.
FIGURE 3-12. Example aircraft whose c.g. exceeds the forward c.g. limit.
A final forward weight and balance check should Most Rearward c.g. check.
be made to prove that by adding 61.0 pounds of Weight Arm Moments ballast in the baggage compartment, this aircraft Item (Ibs.) (in.) (lb.-in.)
could be safely flown with minimum fuel aboard.
Place a placard in the cockpit in a conspicuous Acft. EW 1,600.0 + 15.6 24,960.0 place for the pilot, or anyone concerned, to see. Oil 22.5 -22.0 495.0 The placard should read: FOR SOLO FLIGHT Fuel (max.) 228.0 + 18.0 4,104.0 CARRY A MINIMUM OF 61.0 POUNDS IN Pilot 170.0 + 10.0 1,700.0 BAGGAGE COMPARTMENT. Passenger 170.0 + 10.0 1,700.0 Passengers (two) 340.0 + 34.0 11,560.0 Baggage (max.) 100.0 + 10.0 7,000.0 Maximum Load Conditions Total 2,030.5 50,529.0 termine whether the airplane shown in figure 3-12 A rearward weight and balance check will de- Most rearward c.g. - Total weight Total moments can be flown safely when fully loaded without exceeding the aft c.g. limit or its maximum gross = 50,529.0 = 19.21 in.
weight. 2,630.5 68