FAA Part 107 Remote Pilot (UAG)Loading and PerformanceMedium
A pilot plans to launch a multirotor sUAS from an airport at 6,500 feet MSL on a hot summer day with high humidity. Compared to standard sea-level conditions, how will performance be affected?
- ANo change because density altitude only affects fixed-wing aircraft
- BImproved performance because motors work harder in thin air
- CReduced performance due to high density altitude decreasing air density
- DImproved performance due to thinner air reducing drag
Show answer & explanationAnswer & explanation
Correct answer: C. Reduced performance due to high density altitude decreasing air density
High elevation, high temperature, and high humidity all raise density altitude, meaning the air behaves as if it were even thinner than the actual altitude suggests, reducing lift and rotor/motor efficiency for both fixed-wing and multirotor aircraft.
Why the other options are wrong
- A. Density altitude affects all aircraft, including multirotors, since rotors rely on air density for lift.
- B. Motors do not work 'harder' with benefit in thin air; they produce less thrust for the same power.
- D. Reduced drag does not offset the larger loss of lift and thrust.
Density Altitude Effects
High density altitude (from heat, elevation, or humidity) reduces air density, decreasing lift, power output, and propeller/rotor efficiency for any aircraft type.
- Caused by high temperature, elevation, or humidity
- Reduces available lift and thrust
- Affects fixed-wing and multirotor aircraft alike
Memory trick: Hot, high, and humid = 'thin air three' zaps your power.