FAA Ground School Practice Test

What is the relationship of lift, drag, thrust, and weight when the airplane is in straight-and-level flight?

1. Lift exceeds weight and thrust exceeds drag

2. Lift equals weight and thrust equals drag

3. Lift equals drag and thrust exceeds weight

4. Thrust exceeds drag and weight exceeds lift

The correct answer is: Lift equals weight and thrust equals drag

In straight-and-level flight, the airplane maintains a constant altitude and a steady path, which means that the forces acting on it are balanced. For this balance to occur, the lift generated by the wings must equal the weight of the airplane. Lift is the aerodynamic force that acts upward against weight, which is the force of gravity pulling the airplane down. When an aircraft is flying straight and level, these two forces must be equal to prevent any climb or descent. Additionally, in order to maintain a constant speed in straight-and-level flight, the thrust produced by the engine must also equal the drag acting on the aircraft. Drag is the aerodynamic resistance encountered by the aircraft as it moves through the air, and for the aircraft to not accelerate or decelerate, thrust must match drag. Therefore, the correct relationship among these forces in straight-and-level flight is that lift equals weight and thrust equals drag, ensuring stable flight without changes in altitude or speed.