Fuel/POH question

[Captain Spam Can]

If someone could clarify that im doing this right it would be grateful, thanks.
Lets say C150 total fuel tanks full=22us gallons but 2 gallons each side is unusable. To work out CofG and Fuel consumption on 3/4's full...

To get the CofG moment envelope you take 22 divide by 4 then times 3 = 16.5. Work this out in Ibls it equals 99Ibs (taking into consideration Spec. Grav.). So this 99Ibls goes in your table to get the Total Moment.

Now when working out the fuel consumption on this you take 16.5US gallons - 4 Gallons of Unusable fuel which gives 12.5US Gallons then divide that by the Burn..lets say 4.6 Gallons an hr, which gves a total endurace of 2hrs 43mins.Is this correct?

I wasnt sure weather to do it this way or take the 4 Gallons right at the beginning from 22, then work on 18 to get CofG and Fuel consump

[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

[Captain Spam Can]

What i meant by 3/4's, was 3/4 of the tank full.

thanks for your help.

[FlyingForFun]

I wasnt sure weather to do it this way or take the 4 Gallons right at the beginning from 22, then work on 18 to get CofG and Fuel consump

Right second time around.

The basic empty weight, and the aircraft's moment on the w+b schedule, includes unusable fuel. So, if the total fuel you're starting with includes unusable fuel as per your example, then you need to subtract this from your calculations before starting to avoid double-counting it. It is only the usable fuel which you need to include in your w+b calculations.

In your example, you need to clarify exactly what you mean by 3/4 tanks. Do you mean your tanks contain 3/4 of the total fuel? Or 3/4 of the useable fuel.

If 3/4 of the total fuel, then the fuel carried is 16.5 gallons. Subtract the 4 gallons of unusable fuel to get the usable fuel carried (12.5 gallons), then continue as per your description (but no need to subtract unusable fuel again).

If 3/4 of usable fuel, then the tanks can hold (22-4)=18 gallons usable fuel. The usable fuel carried is 3/4 of this, i.e. 13.5 gallons, now continue with this as per your description (but no need to subtract unusable fuel again).

Hope that answers it,

FFF
---------------

[homeguard]

W & B

Some time back the Basic Empty weight did not include unusable fuel and engine oil. The original page of the C150 Pilots Operating Manual most likely will reflect that. You should refer to the current weight and balance report which should be relatively recent. Unless it too is very old it most likely includes unusable fuel and engine oil within the basic weght but always check! If so, as already made clear, for further calculations oil and unusable fuel should be ignored.

[Captain Spam Can]

FFF.

Cheers hats made it clearer

thanks