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Aviation Maintenance Technician Handbook–General

FAA-H-8083-30B Version 2023
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Chapter 6

Aircraft Weight & Balance

Formula 4 Tail wheel airplanes with the datum aft of the main wheels.

Formula: ( R × L) ; CG = – D + ; W

Datum Forward of the Airplane–Nosewheel Landing Gear

The datum of the airplane in Figure 6-29 is 100" forward of the leading edge of the wing root, or 128" forward of the the airplane (W) is 2,006 lb.

Figure 6-25. Center of gravity envelope for the Piper Seneca.
Figure 6-25. Center of gravity envelope for the Piper Seneca.

The location of the CG may be determined by using this

Formula: formula: ; ( F × L ) ; CG = D ; W ; ( 340 × 78 ) ; = 128 ; 2,006 ; = 114.8

The CG is 114.8" aft of the datum. This is 13.2" forward of the main-wheel weighing points, which proves the location of the datum has no effect on the location of the CG so long as all measurements are made from the same location.

Datum Aft of the Main Wheels–Nosewheel Landing Gear

The datum of some aircraft may be located aft of the main wheels. The airplane in this example is the same one just discussed, but the datum is at the intersection of the trailing edge of the wing with the fuselage. The distance (D) between the datum of the airplane in Figure 6-30 and the main-wheel weighing points is 75", the weight of the nosewheel (F) is 340 lb, and the distance between main wheels and nosewheel (L) is 78". The total net weight of the airplane (W) is 2,006 lb. The location of the CG may be determined by using this

Formula: formula: ; ( F × L ) ; CG = D + ; W ; ( 340 × 78 ) ; = 75 + ; 2,006 ; = –88.2

The CG location is a negative value, which means it is 88.2" forward of the datum. This places it 13.2" forward of the main wheels, the same location as it was when it was measured from other datum locations.

Location of Datum

It makes no difference where the datum is located if all measurements are made from the same location.

Datum Forward of the Main Wheels–Tail Wheel Landing Gear

Figure 6-26. Example airplane being weighed. The datum is 70" forward of the wing root leading edge.
Figure 6-26. Example airplane being weighed. The datum is 70" forward of the wing root leading edge.
Figure 6-27. Specifications and weighing specific data for tricycle gear airplane.
Figure 6-27. Specifications and weighing specific data for tricycle gear airplane.

ward of the wing root leading edge.

Locating the CG of a tail wheel airplane is done in the same way as locating it for a nosewheel airplane except the formulas use R × L rather than F × L. W W

The distance (D) between the datum of the airplane in Figure 6-31 and the main-gear weighing points is 7.5", the weight of the tail wheel (R) is 67 lb, and the distance (L) between the main-wheel and the tail wheel weighing points is 222". The total weight of the airplane (W) is 1,218 lb. Determine the CG by using this formula: