Private Pilot License (PPL) Aerodynamics Practice Exam

According to the relationship of forces on an airplane, what is the correct equation?

1. Thrust + Drag = Lift

2. Thrust = Drag and Lift = Weight

3. Thrust - Drag = Weight

4. Lift + Weight = Thrust

The correct answer is: Thrust = Drag and Lift = Weight

The relationship of forces acting on an airplane in steady, level flight is described by the equation Thrust = Drag and Lift = Weight. This means that during level flight, the amount of thrust produced by the aircraft's engines must equal the drag force acting on the aircraft. This balance ensures that the aircraft maintains a constant forward speed without accelerating or decelerating. Simultaneously, lift generated by the wings must equal the weight of the aircraft for it to maintain altitude. When these two sets of forces are balanced, the aircraft can achieve steady flight. If thrust is greater than drag, the aircraft will accelerate; if lift is greater than weight, the aircraft will climb. Understanding this balance is crucial for pilots as it allows them to manage the aircraft's performance during various phases of flight, including takeoff, cruising, and landing. The equation encapsulates the fundamental principles of aerodynamics and aircraft operation, helping pilots optimize their maneuvers and maintain control of the aircraft.