FAA Flight Instructor Airplane (FIA)Aerodynamics and Principles of FlightMedium
A flight instructor is teaching about high-lift devices. A student asks why extending plain flaps increases the maximum lift coefficient of the wing. The most accurate explanation is that flaps:
- Aincrease the effective camber of the airfoil, allowing a higher maximum lift coefficient before the critical angle of attack is reached
- Bdecrease the angle of incidence, reducing the angle of attack needed for a given lift
- Cincrease wing area only, which proportionally increases total lift
- Deliminate wingtip vortices, reducing induced drag and increasing lift
Show answer & explanationAnswer & explanation
Correct answer: A. increase the effective camber of the airfoil, allowing a higher maximum lift coefficient before the critical angle of attack is reached
Plain flaps increase the camber of the airfoil when deflected, which increases the maximum coefficient of lift the wing can generate. This allows the same lift to be produced at a lower airspeed, or greater lift at the same airspeed and angle of attack.
Why the other options are wrong
- B. Flaps do not change the fixed angle of incidence of the wing to the fuselage.
- C. Plain flaps primarily change camber, not wing area (unlike Fowler flaps, which do increase area).
- D. Flaps do not eliminate wingtip vortices; some flap types can actually slightly increase induced drag.
Flaps and Camber
Flaps increase wing camber (and in some designs, wing area) to increase the maximum coefficient of lift, allowing lower stall speeds and steeper approach angles.
- Plain flaps primarily increase camber
- Fowler flaps increase both camber and wing area
- Increased camber raises maximum lift coefficient (CL max)
- Flaps also increase drag, aiding steeper descents
Memory trick: 'Flaps curve it more' — increased camber means more lift at lower speed