A pilot is flying an aircraft at a constant altitude. If the pilot increases the engine thrust, causing the aircraft to accelerate forward, which of the four forces of flight must also increase to maintain constant altitude?
- AWeight
- BThrust
- CDrag
- DLift
Show answer & explanationAnswer & explanation
Correct answer: D. Lift
When thrust increases and the aircraft accelerates forward, its speed increases. According to Bernoulli's principle and the lift equation, an increase in airspeed (assuming constant angle of attack) directly leads to an increase in lift. To maintain a constant altitude, lift must balance weight. If speed increases, lift increases, and to prevent climbing, the pilot might need to adjust the angle of attack or other controls, but fundamentally, the ability to generate more lift is a direct consequence of increased speed.
Why the other options are wrong
- A. Weight is constant and does not change with thrust or speed.
- B. Thrust is the force causing the acceleration, but lift is the force that directly opposes weight to maintain altitude.
- C. Drag will increase with increased speed, but it does not directly maintain altitude; it opposes motion.
Lift and Airspeed
Lift is the aerodynamic force that opposes gravity, keeping an aircraft in the air. For a given wing design and angle of attack, lift is directly proportional to the square of the airspeed.
- Generated by airflow over the wings.
- Increases with airspeed, wing area, and angle of attack.
- Must balance weight for level flight.
Memory trick: Thrust pulls, Drag fights, Lift floats, Weight bites.