FAA Aviation Mechanic Powerplant (AMP)Fuel, Induction and LubricationMedium
A mechanic is calculating the weight of fuel to be loaded onto an aircraft. The aircraft requires 75 gallons of Jet A fuel. If the specific gravity of Jet A is 0.80, what is the weight of the fuel in pounds? (Assume water weighs 8.35 pounds per gallon).
- A501 pounds
- B600 pounds
- C626.25 pounds
- D670 pounds
Show answer & explanationAnswer & explanation
Correct answer: A. 501 pounds
First, calculate the weight of one gallon of Jet A: 8.35 lbs/gallon (water) * 0.80 (specific gravity of Jet A) = 6.68 lbs/gallon. Then, multiply by the total gallons: 6.68 lbs/gallon * 75 gallons = 501 pounds.
Why the other options are wrong
- B. Incorrect; this would be if specific gravity was 0.96 or if water weight was 8 lbs/gal and specific gravity 1.
- C. Incorrect; this would be if specific gravity was 1 (like water), i.e., 8.35 * 75 = 626.25 lbs.
- D. Incorrect calculation; likely a miscalculation of specific gravity or water weight.
Fuel Weight Calculation (Specific Gravity)
Calculating the weight of aviation fuel by multiplying its volume by the weight of water per gallon and the fuel's specific gravity.
- Weight of fuel = Volume × (Weight of water per gallon × Specific Gravity).
- Specific gravity is a ratio of a substance's density to water's density.
- Essential for accurate weight and balance calculations.
Memory trick: Gallons times water's weight, then times specific gravity, for fuel's true weight.