TM 1-1520-238-10
6-6
Change 4
Section III.
FUEL AND OIL
6.11 OIL WEIGHT AND MOMENT.
For weight and balance purposes, oil is considered a part
of aircraft basic weight.
6.12 FUEL WEIGHT AND MOMENT.
When the actual or planned fuel loading (pounds or gal-
lons) and type is known, the total fuel weight and mo-
ment/100 can be determined from the fuel moment Tables
6-2 and 6-3. The tables present data for JP–4, JP–5, and
JP–8 based on the approximate density for these fuels at
15 degrees centrigrade. The following information is pro-
vided to show the general range of fuel density to be ex-
pected. Density of the fuel will vary depending on fuel tem-
perature. Density will decrease as fuel temperature rises
and increase as fuel temperature decreases at the rate of
approximately 0.1 lb/gal for each 15 degree centrigrade
temperature change. Density may also vary between lots
of the same fuel at the same temperature by as much as
0.5 lb/gal. The full tank usable fuel weight presented in the
tables for density closest to that of the fuel being used
may be used for mission planning. The aircraft fuel gage
system was designed for use with JP–4, but does tend to
compensate for other fuels and provide acceptable read-
ings. When possible the weight of fuel onboard should be
determined by direct reference to aircraft fuel gages.
6.12.1 Fuel Moments.
The forward fuel moment cal-
culations are complicated by the L-shape of the tank. Con-
sider the tank being filled from empty to 132.8 gallons; the
fuel cg remains constant at 150.6 inches. From 132.8 gal-
lons to full (156 gallons), the cg of the total fuel moves aft
linearly to 153.7 inches at capacity. The aft fuel cg is
constant at 255 inches.
6.13 AUXILIARY FUEL TANKS.
WARNING
A slight increase in the risk of post–
crash fire exists if a mishap occurs after
tanks are pressurized. Crashworthiness
of the fuel system is reduced by external
fuel tanks, which are designed for
FERRY MISSION ONLY. External fuel tank
installation is prohibited for use in tacti-
cal missions.
The auxiliary fuel tanks are installed on the wing pylons in
sets of two or four and are for extending the helicopter
ferry range. Plumbing from the fuselage to the tank is pro-
vided with each tank. Each tank has a capacity of approxi-
mately 230 gallons. Table 6-4 lists the weight and mo-
ment/100 of each fuel tank, wing plumbing and total fuel
for JP-4, JP-5, and JP-8. Note that the data are given for
one tank, wing plumbing, and indicated fuel so that any
combination can be determined. The table can be used
for inboard and outboard locations because the small mo-
ment/100 differences can be ignored. Remember to add
the tank, and specific fuel together for one location, then
multiply by 2 or 4 depending on the number of tanks car-
ried. Add wing plumbing for 2 or 4 tanks as appropriate.
