UAS Maintenance 3 — Questions and Answers
Question 1: What does IMU (Inertial Measurement Unit) calibration correct for in a UAS?
- Battery discharge rate during flight
- Sensor drift caused by temperature changes and vibration (Correct answer)
- Radio frequency interference from ground stations
- GPS signal multipath errors during navigation
Correct answer: Sensor drift caused by temperature changes and vibration
IMU calibration corrects for sensor drift caused by temperature changes and vibration, ensuring accurate attitude estimation for stable flight.
Question 2: A UAS shows abnormal vibration during hover. What is the most likely first cause to investigate?
- Compass interference from metal structures
- Unbalanced or damaged propellers (Correct answer)
- Incorrect GPS satellite count
- Flight controller processor overload
Correct answer: Unbalanced or damaged propellers
Unbalanced or damaged propellers are the most common cause of abnormal vibration and should be inspected first before investigating other systems.
Question 3: When inspecting the airframe of a carbon fiber UAS after a minor collision, what specific defect should the operator look for?
- Discoloration from heat exposure
- Delamination, cracks, or white stress marks in the carbon fiber (Correct answer)
- Surface scratches on painted components
- Loose antenna wire routing
Correct answer: Delamination, cracks, or white stress marks in the carbon fiber
Carbon fiber can delaminate or develop stress cracks internally that appear as white marks, compromising structural strength even when surface damage looks minor.
Question 4: What is the recommended action when a motor shows signs of overheating after a flight?
- Douse the motor with water to cool it rapidly
- Allow it to cool naturally, then inspect windings for burns or damage (Correct answer)
- Immediately run the motor at low throttle to cool it evenly
- Replace the motor only if it emits smoke during the next flight
Correct answer: Allow it to cool naturally, then inspect windings for burns or damage
After allowing the motor to cool naturally, inspect the windings for burns or damage to determine if it is still airworthy before the next flight.
Question 5: How often should gimbal motors and bearings typically be inspected on a commercially operated UAS?
- Only when image stabilization noticeably degrades
- Per the manufacturer's maintenance schedule or after heavy use (Correct answer)
- Once per year regardless of flight hours
- After every 500 flights without exception
Correct answer: Per the manufacturer's maintenance schedule or after heavy use
Gimbal motors and bearings should be inspected per the manufacturer's maintenance schedule or following periods of heavy use to prevent stabilization failures.
Question 6: What is the purpose of a compass calibration on a UAS?
- To reset the flight controller's attitude reference
- To map local magnetic field variations so heading data is accurate (Correct answer)
- To synchronize the GPS and barometer readings
- To update the geofence database for the operating area
Correct answer: To map local magnetic field variations so heading data is accurate
Compass calibration maps local magnetic field variations so the UAS can determine accurate heading, which is critical for stable GPS-assisted flight.
Question 7: What maintenance step is critical after replacing a propeller on a UAS?
- Updating the flight controller with new propeller weight data
- Verifying correct rotation direction and secure fastener torque (Correct answer)
- Re-calibrating the GPS module to account for changed weight
- Adjusting the ESC timing for the new propeller pitch
Correct answer: Verifying correct rotation direction and secure fastener torque
After propeller replacement, verifying correct rotation direction and ensuring fasteners are torqued to specification prevents propeller separation or improper thrust.
UAS Maintenance 3
What does IMU (Inertial Measurement Unit) calibration correct for in a UAS?