FAA Sport Pilot Airplane (SPA)Aircraft Performance and SystemsMedium
Many high-wing light sport airplanes use a gravity-feed fuel system instead of relying primarily on an engine-driven fuel pump. What is the primary advantage of this design?
- AIt completely eliminates the possibility of vapor lock in all flight conditions
- BIt allows for higher fuel pressure needed by turbocharged engines
- CFuel flows from tanks mounted above the engine to the carburetor by gravity, reducing dependence on a mechanical pump
- DIt significantly increases the total usable fuel capacity of the aircraft
Show answer & explanationAnswer & explanation
Correct answer: C. Fuel flows from tanks mounted above the engine to the carburetor by gravity, reducing dependence on a mechanical pump
In a gravity-feed system, wing-mounted fuel tanks are positioned above the carburetor, allowing fuel to flow downward by gravity alone. This provides a simple, reliable fuel delivery method that continues even if an engine-driven pump were to fail.
Why the other options are wrong
- A. Incorrect — vapor lock can still occur under certain heat and fuel volatility conditions.
- B. Incorrect — gravity feed provides low, not high, fuel pressure and is not used for turbocharged high-pressure systems.
- D. Incorrect — fuel system type does not affect total tank capacity.
Gravity-Feed Fuel System
A fuel delivery system, common in high-wing airplanes, where fuel tanks positioned above the engine allow fuel to flow to the carburetor by gravity without requiring a fuel pump.
- Common on high-wing light sport/general aviation aircraft
- Provides simple, reliable fuel delivery without mechanical pump dependency
- Low-wing aircraft typically require engine-driven or electric fuel pumps
Memory trick: High wing, fuel falls down by gravity alone