FAA Part 107 Drone Practice Test

How does high density altitude affect the efficiency of a UAV propeller?

1. Propeller efficiency is increased

2. Propeller efficiency is decreased

3. There is no effect on propeller efficiency

4. Propeller efficiency is doubled

The correct answer is: Propeller efficiency is decreased

High density altitude affects the efficiency of a UAV propeller primarily due to the decrease in air density that occurs at higher altitudes. As a UAV climbs to a higher density altitude, the air becomes less dense, which means there are fewer air molecules for the propeller blades to push against. This reduction in available air reduces the overall thrust that the propeller can generate. Propeller efficiency is defined as the ratio of useful power output to the power input. When the air density diminishes, the propeller cannot generate as much lift and thrust, leading to a decrease in its efficiency. As a result, the UAV may require more throttle input to achieve the same flight performance, further affecting its power consumption and overall fuel efficiency. Understanding the impact of high density altitude on propeller efficiency is critical for UAV operators, as it influences flight planning, performance expectations, and safety considerations. Being aware of these factors can help in making informed decisions when operating drones in various environmental conditions.