Drone Pilot Practice Exam

What is the effect of high density altitude on the efficiency of a UAV propeller?

1. Propeller efficiency is increased

2. Propeller efficiency remains unchanged

3. Propeller efficiency is decreased

4. Propeller efficiency varies with temperature

The correct answer is: Propeller efficiency is decreased

High density altitude occurs when the air is less dense, which can be influenced by factors such as altitude, temperature, and humidity. In this condition, the efficiency of a UAV propeller decreases. This happens because propellers generate lift by moving air; however, when the air is less dense, there are fewer air molecules available for the propeller to bite into. As a result, the propeller is less effective at generating thrust and lift, which can negatively impact the UAV’s performance, including its ability to climb and maintain stable flight. While propeller efficiency can vary with temperature, high density altitude specifically refers to conditions where the density of the air is decreased regardless of these variations, making lower efficiency the consistent outcome under those circumstances. Therefore, understanding how density altitude affects air density helps clarify why propeller efficiency decreases in such situations.