A remote pilot is planning a flight at a field with a pressure altitude of 6,000 feet. The outside air temperature is 25°C, well above the standard temperature for that altitude. How will this affect the sUAS's takeoff and climb performance?
- ADensity altitude has no effect on multirotor sUAS since they do not rely on airfoil lift
- BDensity altitude will be lower than pressure altitude, improving lift and climb performance
- CDensity altitude will be higher than pressure altitude, reducing lift and requiring more power for climb
- DDensity altitude will equal pressure altitude since temperature does not factor into the calculation
Show answer & explanationAnswer & explanation
Correct answer: C. Density altitude will be higher than pressure altitude, reducing lift and requiring more power for climb
Density altitude increases with temperatures above standard for a given pressure altitude. At 6,000 feet pressure altitude, standard temperature is about 3°C, so 25°C is significantly warmer, producing a high density altitude. This means the air is less dense, reducing propeller and rotor efficiency, decreasing lift, and requiring more power for takeoff and climb, just as it affects manned aircraft performance.
Why the other options are wrong
- A. Multirotor sUAS rely on rotor blades, which are airfoils affected by air density just like fixed-wing aircraft.
- B. Incorrect; warmer-than-standard temperatures increase, not decrease, density altitude.
- D. Temperature is a primary factor in the density altitude calculation, not pressure altitude alone.
Density Altitude Effects
Density altitude is pressure altitude corrected for non-standard temperature; higher-than-standard temperatures increase density altitude and reduce aircraft/rotor performance.
- High density altitude = thinner air = less lift
- Affects both fixed-wing and rotor-based sUAS
- Warmer temperatures and higher elevations increase density altitude
Memory trick: 'Hot and high, drones can't fly (as well).'