Stack Exchange Network
Stack Exchange network consists of 181 Q&A communities including
Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
Visit Stack Exchange
Aviation Stack Exchange is a question and answer site for aircraft pilots, mechanics, and enthusiasts. It only takes a minute to sign up.
Sign up to join this community
Anybody can ask a question
The best answers are voted up and rise to the top
4 months ago
I'm practicing for my EASA PPL(A) exam and one of the questions I came across sound like this:
Calculated take-off mass = 1082 kg, calculated CG = 0.254 m, fuel burn
= 55 l on station 0.40 m.
D. 24.8 <- this is the correct answer
My question is how do I actually get to this answer?
This is what I tried:
14,6 cm would be the difference between the fuel burn station and calculated CoG (in cm)
1027 kg would be the difference between calculated T/O mass and fuel burned
803 cm/kg would be the removed mass
0,78 cm would be the CoG shift calculated
New CoG should be 25,4 (old CoG) - 0,78 which would mean 24,6
But yeah... that is not correct. So what am I missing here?
You are doing
1082 - 55 = 1027. The point that people are trying to make is that you have skipped the step you did correctly in the other problems you described.
1082 - (55 * 0.72) = 1,042.4kg. You are subtracting the 55 as if it is the weight of the fuel in kg, but it is not. 55 liters of AVGAS weighs 39.6kg. Being a PPL test I will take the liberty of assuming the density required is for AVGAS, and using that density the problem works:
274.828 (step 1)
-39.6 (step 2)
-15.84 (step 3)
1042.4 (step 4)
0.248 (step 6) 258.988 (step 5)
Weight(TO) * Arm(given) = 1082 * 0.254 = 274.828 kg-m
Weight(fuel burn) =
Volume(fuel burn) * Density(fuel) = -55l * 0.72 kg/l = -39.6 kg
Moment(fuel burn) =
Weight(fuel burn) * arm(fuel) = -39.6 kg * 0.4m = 15.48 kg-m
Weight(TO) - Weight(fuel burn) = 1082 - 39.6 = 1042.4 kg
Moment(TO) - Moment(fuel burn) = 274.828 - 15.48 = 258.988
Resulting CG Arm =
Moment(ldg) / Weight(ldg) = 258.988/1042.4 = 0.248m =
24.8 = You pass the test = you become a pilot = jackpot.
Jan 20 at 18:43
Max R Max R
3,522 1 1 gold badge 11 11 silver badges 16 16 bronze badges
log in to answer this question.
By clicking “Accept all cookies”, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our
Accept all cookies
Necessary cookies only