Flight Preparation and Planning Exam

[pilot_lara]

If anyone could help explain the calculations for this question i would be grateful. Got a PPL exam coming up....

An aeroplane has a planned take-off weight of 2,750 pounds and its calculated centre of gravity (CG) position is 85.00 inches aft of datum. During the flight the planned fuel burn is 300 lb from a position 75.00 inches aft of datum. What is the calculated CG position in inches aft of datum for landing?

 

[kath]

Let's call: Mfuel = 300 lb, and Meverythingelse = 2450 lbs.
and the two moment arms are: Lfuel = 75 and Leverythingelse = unknown.
But we do know that at the beginning of the flight, that (Mfuel*Lfuel + Meverythingelse*Leverythingelse) = (Mtotal*85)
Solve for Leverythingelse.