FAA Commercial Pilot Airplane (CAX)Navigation and Flight PlanningHard
A commercial pilot loads an airplane near its maximum gross weight for a cross-country flight instead of a lighter, partial-fuel configuration. Compared to the lighter loading, how will the heavier gross weight most likely affect fuel planning for the same cruise altitude and airspeed?
- ARange will increase because higher weight improves the airplane's glide ratio at cruise
- BFuel burn will remain the same because engine power settings are independent of gross weight
- CFuel burn will increase because additional power is required to overcome increased induced drag, reducing range for a given fuel quantity
- DFuel burn will decrease because a heavier airplane produces less induced drag at cruise speed
Show answer & explanationAnswer & explanation
Correct answer: C. Fuel burn will increase because additional power is required to overcome increased induced drag, reducing range for a given fuel quantity
A heavier airplane requires a higher angle of attack to maintain the same altitude and airspeed, increasing induced drag. Overcoming this drag requires more power and fuel flow, which reduces the achievable range for a given amount of usable fuel.
Why the other options are wrong
- A. Glide ratio is degraded, not improved, by increased weight, and this doesn't apply to powered cruise flight.
- B. Power required changes directly with weight due to changes in induced drag.
- D. Heavier weight increases, not decreases, induced drag at a given airspeed.
Gross Weight Effect on Fuel Range
Increasing an airplane's gross weight increases induced drag at a given airspeed and altitude, requiring more power and fuel flow, which reduces range for a fixed fuel load.
- Heavier weight requires higher AOA to generate needed lift, increasing induced drag
- More power/fuel flow is needed to maintain cruise speed and altitude at higher weight
- Range and endurance decrease as gross weight increases for the same fuel quantity
Memory trick: Heavier plane, hungrier engine