FAA Commercial Pilot Airplane (CAX)Aerodynamics and PerformanceEasy
On a total drag curve (parasite drag plus induced drag) plotted against airspeed, at airspeeds slower than the speed for L/D max, which drag component dominates the total drag?
- AParasite drag and induced drag are equal at all airspeeds below L/D max
- BParasite drag exceeds induced drag at these low speeds
- CInduced drag exceeds parasite drag at these low speeds
- DInduced drag is negligible at any speed below L/D max
Show answer & explanationAnswer & explanation
Correct answer: C. Induced drag exceeds parasite drag at these low speeds
Induced drag varies inversely with the square of airspeed and dominates at low speeds/high angles of attack, while parasite drag varies directly with the square of airspeed and dominates at high speeds. The two curves cross at L/D max, where total drag is minimum; below that speed, induced drag is the larger component.
Why the other options are wrong
- A. They are only equal exactly at L/D max, not throughout the low-speed range.
- B. Parasite drag dominates ABOVE L/D max speed, not below it.
- D. Induced drag is actually largest, not negligible, at low airspeeds.
Parasite vs Induced Drag Crossover
Parasite drag increases with the square of airspeed; induced drag decreases with the square of airspeed. They are equal at L/D max, the point of minimum total drag.
- Induced drag dominates at low speed/high AOA
- Parasite drag dominates at high speed
- Total drag is minimum where the two curves cross (L/D max)
Memory trick: Slow and draggy from lift (induced), fast and draggy from friction (parasite).