FAA Flight Instructor Airplane (FIA)Aerodynamics and Principles of FlightMedium
A CFI is teaching a client about the two components of total drag. The client asks which condition produces the greatest induced drag, the drag associated with the formation of wingtip vortices.
- AHigh airspeed with flaps fully extended
- BHigh airspeed with a low angle of attack
- CCruise flight at low altitude and moderate airspeed
- DLow airspeed with a high angle of attack, such as during slow flight
Show answer & explanationAnswer & explanation
Correct answer: D. Low airspeed with a high angle of attack, such as during slow flight
Induced drag is a byproduct of lift production and is directly related to angle of attack; it is greatest when the wing must operate at a high AOA to generate the needed lift at low airspeed, which strengthens the pressure differential feeding the wingtip vortices. Induced drag decreases as airspeed increases and AOA decreases.
Why the other options are wrong
- A. Flap extension changes camber but high airspeed still keeps required AOA low, minimizing induced drag.
- B. High airspeed with low AOA produces minimal induced drag since less lift-generating pressure differential exists.
- C. Cruise flight is typically near minimum total drag, not maximum induced drag.
Wingtip Vortices and Induced Drag
Wingtip vortices form from air spilling around the wingtip from the high-pressure lower surface to the low-pressure upper surface; the resulting induced drag is greatest at low airspeed/high AOA.
- Induced drag increases as airspeed decreases
- Strongest vortices occur when heavy, slow, and clean (e.g., short final)
- Winglets reduce induced drag by disrupting vortex formation
Memory trick: Slow and heavy = swirly and heavy drag