FAA Ground School Practice Test

What causes an airplane (except a T-tail) to pitch nosedown when power is reduced and controls are not adjusted?

1. Increased lift on the wings

2. Changes in weather conditions

3. Reduced downwash on the elevators from the propeller slipstream

4. Increased aerodynamic resistance

The correct answer is: Reduced downwash on the elevators from the propeller slipstream

When the power of an airplane (not configured with a T-tail) is reduced, there is a notable shift in the airflow and the dynamics at play. The correct answer revolves around the impact of reduced thrust on the airflow over the tail section of the aircraft. As power is reduced, the slipstream – which refers to the air accelerated by the propeller – diminishes. This reduction in the propeller's slipstream results in decreased downwash over the horizontal stabilizer and elevators. The elevators depend on consistent and effective airflow to generate the necessary control forces. When the downwash is lessened, the elevators experience a reduced effectiveness, leading to less lift being produced at the tail. Consequently, the tail begins to lose lift relative to the wings, and the nose of the aircraft starts pitching downwards. This consequence is not the result of increased lift on the wings or a direct impact of changing weather conditions; those factors affect the overall flight but do not explain the immediate behavior of the aircraft in a situation of reduced power. Additionally, while increased aerodynamic resistance could influence the performance and handling characteristics, it does not specifically address the fundamental change in lift dynamics at the tail that directly causes the nose-down pitch in response to reduced engine power.