Fuel/POH question

[blopes]

Hi, I didn't understand much what you mean by 3/4's however you can do that in this way:
Using a reference to datum line, so supose that the index of the fuel thanks is 42.0 ( like in C152) using your data u find the CofG moment envelope simple doing this :
Maximum Fuel Weight x 42 =
= [.72x(22USGAL x 3.78)x2.205] x 42 / 1000 = 5.545 lb.ins instead of 99lbs

datum line index for thanks: 42.0
using: .72 specific gravity
3.78 convert USG -> Litres
2.205 Kg -> Lbs

you can find the datum line index at the Manual of aircraft , if its a cessna , should be in section 6 Mass & Balance.


to determine the total endurance you most take in considerantion various parameters like Pressure Altitude, RPM, TEMP ... you can do it like that you most check the section 5 of your manual if its a cessna or the correspondent for Performance

but to obtain endurance basically you use the fuel consumption per time unit, ex: at 4000' BHP = 63% Standard TEMP -> 5.1 GPH

with 18 usable 18/5.1 = 3.53 ~ 3h32 min

bye!
Bruno