FAA Commercial Pilot Airplane (CAX)Aerodynamics and PerformanceEasy
A student pilot experiences an engine failure and wants to maximize gliding distance to a suitable landing site. At which airspeed should the airplane be flown?
- AThe airspeed for minimum sink rate
- BThe airspeed for best rate of climb, Vy
- CThe airspeed that produces the maximum lift-to-drag ratio
- DManeuvering speed, Va
Show answer & explanationAnswer & explanation
Correct answer: C. The airspeed that produces the maximum lift-to-drag ratio
Maximum gliding distance is achieved at the airspeed where the lift-to-drag ratio (L/D) is greatest, since this minimizes total drag relative to lift, allowing the airplane to travel the farthest horizontal distance per foot of altitude lost.
Why the other options are wrong
- A. Minimum sink rate airspeed maximizes time aloft, not distance covered.
- B. Vy maximizes rate of climb under power, not unpowered glide distance.
- D. Va is a structural limit speed, unrelated to glide distance.
Best Glide Speed (L/D Max)
The airspeed that produces the maximum lift-to-drag ratio, resulting in the greatest gliding distance for a given altitude loss.
- Best glide speed ≠ minimum sink speed
- Occurs at minimum total drag airspeed
- Published for each aircraft in the POH
- Changes with weight and configuration
Memory trick: Max L/D means max glide, ride the drag curve's low point!