FAA Airline Transport Pilot (ATM)Transport Aerodynamics and High-Altitude OperationsEasy
Two wings have the same planform area and airfoil section, but Wing A has a long span with a narrow chord (high aspect ratio) while Wing B has a short span with a wide chord (low aspect ratio). At the same lift coefficient, which wing produces less induced drag, and why?
- AWing B, because low aspect ratio wings generate lift more efficiently at low airspeeds
- BWing B, because its shorter span reduces the size of the wingtip vortices
- CWing A, because spreading lift over a longer span weakens the wingtip vortices and reduces downwash
- DWing A, because a higher aspect ratio increases wing loading and reduces the angle of attack required
Show answer & explanationAnswer & explanation
Correct answer: C. Wing A, because spreading lift over a longer span weakens the wingtip vortices and reduces downwash
Induced drag is inversely proportional to aspect ratio for a given lift coefficient. A high aspect ratio wing spreads the same total lift over a longer span, producing weaker wingtip vortices and less downwash-induced drag than a short, wide (low aspect ratio) wing.
Why the other options are wrong
- A. Aspect ratio does not change lift efficiency at low speed in this way; it's about drag, not lift generation.
- B. Reversed logic; a shorter span concentrates lift, strengthening tip vortices.
- D. Aspect ratio does not by itself increase wing loading; wing loading depends on weight and area, not span shape.
Aspect Ratio and Induced Drag
Aspect ratio (span²/area) is inversely related to induced drag for a given lift coefficient; higher aspect ratio wings produce weaker wingtip vortices and less induced drag.
- High AR wings (gliders) minimize induced drag
- Low AR wings (fighters, deltas) trade drag efficiency for structural/speed benefits
- Induced drag dominates at low speed/high AOA
Memory trick: Long skinny wings = less swirl = less drag