FAA Aerodynamics of sUAS 1 — Questions and Answers
Question 1: In straight-and-level, unaccelerated flight, which statement about the four aerodynamic forces is correct?
- Lift equals weight and thrust equals drag (Correct answer)
- Lift exceeds weight and thrust exceeds drag
- Thrust equals lift and weight equals drag
- Drag exceeds thrust and weight equals lift
Correct answer: Lift equals weight and thrust equals drag
In unaccelerated level flight, opposing forces must be equal — lift balances weight and thrust balances drag.
Question 2: What effect does high density altitude have on sUAS rotor performance?
- Rotor efficiency increases due to lower air resistance
- Rotor efficiency decreases because less dense air generates less lift per revolution (Correct answer)
- High density altitude only affects fixed-wing aircraft, not multirotors
- Rotors generate the same lift regardless of density altitude
Correct answer: Rotor efficiency decreases because less dense air generates less lift per revolution
Thinner air at high density altitude means each rotor revolution moves less air mass, reducing lift and requiring higher RPMs to maintain hover.
Question 3: Which combination of environmental conditions results in the highest density altitude?
- High elevation, cold temperature, low humidity
- Low elevation, hot temperature, high humidity
- High elevation, hot temperature, high humidity (Correct answer)
- Low elevation, cold temperature, high humidity
Correct answer: High elevation, hot temperature, high humidity
High elevation reduces pressure, hot temperatures reduce air density, and high humidity displaces denser oxygen molecules — all three factors combine to create maximum density altitude.
Question 4: What is 'ground effect' as it applies to multirotor sUAS operations?
- Turbulence created by flying close to the surface
- Increased rotor efficiency caused by reduced induced drag when flying close to the ground (Correct answer)
- Vibration felt by the aircraft when landing on uneven terrain
- Reduced battery consumption due to lower altitude air pressure
Correct answer: Increased rotor efficiency caused by reduced induced drag when flying close to the ground
Ground effect occurs when rotor downwash is interrupted by the ground surface, reducing induced drag and increasing lift efficiency within approximately one rotor diameter of the surface.
Question 5: As an sUAS enters a steeper banked turn, what happens to the load factor and power requirement?
- Both load factor and power requirement decrease
- Load factor increases and power requirement increases (Correct answer)
- Load factor increases but power requirement decreases
- Both remain constant regardless of bank angle
Correct answer: Load factor increases and power requirement increases
In a banked turn, the vertical component of lift must still support the aircraft's full weight, so total rotor thrust must increase — raising both load factor and power draw.
Question 6: What is 'vortex ring state' in the context of multirotor sUAS operations?
- The normal circular airflow pattern around propellers during cruise
- A dangerous condition where the aircraft descends into its own rotor downwash, causing loss of lift (Correct answer)
- Vortices formed at propeller tips that improve efficiency
- A favorable aerodynamic state that reduces power during descent
Correct answer: A dangerous condition where the aircraft descends into its own rotor downwash, causing loss of lift
Vortex ring state occurs during a steep, slow powered descent when rotor downwash recirculates back into the rotor disc, causing the rotor to lose lift in a potentially unrecoverable condition.
Question 7: How does increasing altitude above sea level affect the relationship between true airspeed and indicated airspeed?
- True airspeed equals indicated airspeed at all altitudes
- True airspeed is greater than indicated airspeed at higher altitudes (Correct answer)
- Indicated airspeed is greater than true airspeed at higher altitudes
- True airspeed decreases relative to indicated airspeed as altitude increases
Correct answer: True airspeed is greater than indicated airspeed at higher altitudes
At higher altitudes with less dense air, the aircraft must move faster (true airspeed) to achieve the same dynamic pressure reading (indicated airspeed) as at sea level.
FAA Aerodynamics of sUAS 1
In straight-and-level, unaccelerated flight, which statement about the four aerodynamic forces is correct?