FAA Flight Instructor Airplane (FIA)Aerodynamics and Principles of FlightHard
A pilot is flying below the airspeed for maximum lift/drag ratio (L/D max) and decides to slow down further without adding power, intending to maintain altitude. What will happen, and why is this speed range called the region of reversed command?
- AThe airplane will accelerate on its own due to reduced parasite drag
- BAirspeed will stabilize automatically because induced drag decreases as speed decreases
- CAirspeed will decrease further and more power will be required to maintain altitude, the opposite of normal command
- DLess power will be required to maintain the slower airspeed and altitude
Show answer & explanationAnswer & explanation
Correct answer: C. Airspeed will decrease further and more power will be required to maintain altitude, the opposite of normal command
Below L/D max, induced drag dominates and increases sharply as airspeed decreases further, requiring more power (not less) to maintain altitude at slower speeds. This is the opposite of the normal relationship above L/D max, where more power produces more speed, hence the term 'region of reversed command' or 'back side of the power curve.'
Why the other options are wrong
- A. Reduced parasite drag at low speed is outweighed by rapidly increasing induced drag, so the airplane will not accelerate on its own.
- B. Airspeed does not self-stabilize; without added power, drag exceeds thrust and speed continues to decay, risking a stall.
- D. Less power is required above L/D max, not below it; below L/D max, more power is needed as speed decreases.
Region of Reversed Command
The speed range below L/D max (minimum drag speed) where additional power is required to fly slower and maintain altitude, the opposite of the normal power-speed relationship.
- Also called the 'back side of the power curve'
- Occurs during slow flight, approach, and landing configurations
- Requires pitch for airspeed and power for altitude control technique
Memory trick: Behind the curve, more power is needed just to go slower