FAA Commercial Pilot Airplane (CAX)Aerodynamics and PerformanceEasy
During a cross-country flight, a pilot notices that the airplane's total drag is at its minimum. At this point, what is the relationship between parasite drag and induced drag?
- AParasite drag is approximately equal to induced drag.
- BParasite drag is significantly less than induced drag.
- CParasite drag is significantly greater than induced drag.
- DParasite drag is zero, and induced drag is at its maximum.
Show answer & explanationAnswer & explanation
Correct answer: A. Parasite drag is approximately equal to induced drag.
The point of minimum total drag for an airplane occurs when parasite drag and induced drag are approximately equal. This speed also corresponds to the best glide speed (L/D max).
Why the other options are wrong
- B. Incorrect, this describes flight at slower speeds than L/D max.
- C. Incorrect, this describes flight at faster speeds than L/D max.
- D. Incorrect, parasite drag is never zero in flight, and induced drag is not necessarily at maximum.
Minimum Total Drag Speed
The airspeed at which an airplane experiences the least amount of total drag, occurring when parasite drag and induced drag are approximately equal. This speed corresponds to the maximum lift-to-drag ratio (L/D max).
- Total drag is the sum of parasite and induced drag.
- Parasite drag increases with airspeed squared.
- Induced drag decreases with airspeed squared.
- The minimum total drag point is where the two curves intersect.
Memory trick: When parasite and induced drag hug, total drag is snug.