FAA Commercial Pilot Airplane (CAX)Aerodynamics and PerformanceEasy
A student pilot asks why extending flaps allows the airplane to fly and land at a slower speed. Which explanation is correct?
- AFlaps increase the maximum coefficient of lift the wing can produce, lowering the stall speed
- BFlaps decrease induced drag, allowing slower flight
- CFlaps increase wing area only, with no effect on lift coefficient
- DFlaps reduce the wing's aspect ratio, increasing stall speed
Show answer & explanationAnswer & explanation
Correct answer: A. Flaps increase the maximum coefficient of lift the wing can produce, lowering the stall speed
Flaps increase wing camber, which raises the maximum coefficient of lift (CLmax) the wing can generate before stalling. Since stall speed is inversely related to the square root of CLmax, a higher CLmax allows a lower stall speed.
Why the other options are wrong
- B. Flaps typically increase induced drag at a given speed, not decrease it.
- C. Some flap types also add area, but the key stall-speed benefit comes from increased CLmax, not area alone.
- D. Flaps do not change aspect ratio, and increasing camber lowers, not raises, stall speed.
Flaps and CLmax
Flaps increase wing camber and CLmax, allowing the airplane to generate the same lift at a lower airspeed, thus reducing stall speed.
- Stall speed is inversely proportional to the square root of CLmax.
- Flaps also increase drag, aiding steeper approach angles.
- Some flap types increase wing area as well as camber.
Memory trick: More camber, more lift, less speed needed to stay up.