A2 CofC - Drone Certificate of Competency UAS Flight Performance Principles Questions and Answers — Questions and Answers
Question 1: A remote pilot attaches an aftermarket payload to their UAS, causing the Centre of Gravity (CG) to shift significantly behind the manufacturer's recommended aft limit. What is the most likely flight characteristic they will experience?
- Increased longitudinal stability and sluggish pitch control.
- A tendency for the UAS to pitch up and reduced longitudinal stability. (Correct answer)
- Improved forward flight speed due to better aerodynamics.
- No noticeable change, as the flight controller will compensate.
Correct answer: A tendency for the UAS to pitch up and reduced longitudinal stability.
A Centre of Gravity (CG) that is too far aft (rearward) makes the UAS tail-heavy. This reduces the authority of the forces used to maintain pitch stability, leading to longitudinal instability and a dangerous tendency for the nose to pitch up. This can result in a stall or a complete loss of control.
Question 2: If the take-off mass of a multirotor UAS is significantly increased by adding a heavy camera, which of the following performance changes is most likely to occur?
- Increased agility and faster response to control inputs.
- Longer flight duration due to increased momentum.
- Greater resistance to changing direction and reduced flight endurance. (Correct answer)
- A lower power requirement for take-off.
Correct answer: Greater resistance to changing direction and reduced flight endurance.
Increasing the mass also increases the aircraft's inertia. This makes it more resistant to changes in its state of motion, meaning it will be slower to accelerate, decelerate, and turn. The motors must also work harder to lift the extra weight, which significantly increases power consumption from the battery and therefore reduces the overall flight endurance.
Question 3: During a co-ordinated level turn, a remote pilot banks their UAS at a 60-degree angle. What is the approximate load factor experienced by the aircraft's structure?
- 1G
- 1.5G
- 4G
- 2G (Correct answer)
Correct answer: 2G
In a co-ordinated level turn, the load factor increases with the angle of bank. The load factor is calculated as 1 divided by the cosine of the bank angle. The cosine of 60 degrees is 0.5. Therefore, the load factor is 1 / 0.5 = 2G. This means the UAS structure is supporting twice its actual weight.
Question 4: A remote pilot plans a flight on a cold winter day in the UK, with an ambient temperature of 2°C. The LiPo batteries for their UAS have been stored in their vehicle overnight. What is the most significant impact this will have on flight performance?
- The battery's chemical reaction will be slower, leading to a significant voltage drop and reduced flight time. (Correct answer)
- The battery will provide a higher voltage, increasing motor performance.
- The cold, dense air will improve propeller efficiency, extending the flight time.
- The flight controller may report an inaccurate battery level, but performance will be unaffected.
Correct answer: The battery's chemical reaction will be slower, leading to a significant voltage drop and reduced flight time.
The chemical reactions inside a LiPo battery are less efficient at low temperatures. This increases the battery's internal resistance, which causes a significant drop in voltage under load. This leads to a drastic reduction in available power and overall flight time. It is a key safety principle to warm batteries to approximately 20°C before flying in cold conditions.
Question 5: Which of the following environmental conditions would result in the highest performance from a UAS's motors and propellers?
- High altitude on a hot, humid day.
- Low altitude on a hot, humid day.
- Low altitude on a cold, dry day. (Correct answer)
- High altitude on a cold, dry day.
Correct answer: Low altitude on a cold, dry day.
Motors and propellers are most efficient in dense air, as the propellers can generate more lift for a given RPM. Air is densest at low altitudes, in cold temperatures, and with low humidity (as water vapour is less dense than dry air). Therefore, a low altitude on a cold, dry day provides the highest air density and thus the best flight performance.
Question 6: When operating a fixed-wing UAS, what is the direct effect on its stall speed when it enters a co-ordinated, level turn?
- The stall speed decreases because the inner wing is moving slower than the outer wing.
- The stall speed increases due to the increased load factor. (Correct answer)
- The stall speed remains the same regardless of bank angle.
- The stall speed is only affected by the aircraft's mass, not the turn itself.
Correct answer: The stall speed increases due to the increased load factor.
To maintain altitude in a turn, the total lift produced by the wings must be greater than the aircraft's weight to provide both a vertical component (to oppose weight) and a horizontal component (to cause the turn). This increase in total lift is known as the load factor. Since stall occurs at a specific angle of attack, and more lift is being demanded at any given airspeed in the turn, the speed at which the wing will stall is higher. The stall speed increases in proportion to the square root of the load factor.
A2 CofC - Drone Certificate of Competency UAS Flight Performance Principles Questions and Answers
A remote pilot attaches an aftermarket payload to their UAS, causing the Centre of Gravity (CG) to shift significantly behind the manufacturer's recommended aft limit.
What is the most likely flight characteristic they will experience?