UAS Systems, Propulsion, and Control Links
Know the machine
Systems questions test the subsystems and their failure signatures: airframe, propulsion (electric motors/ESCs or combustion engines), power (batteries, BMS, fuel), flight controller and sensors (IMU, barometer, magnetometer, GNSS), payload, and the C2 link. For each, know what happens when it degrades and what the pilot sees.
Concepts to master
- Propulsion: brushless motors and ESCs; propeller diameter/pitch versus thrust and current draw. A damaged or unbalanced propeller causes vibration that corrupts IMU data and can trigger unexpected attitude corrections.
- Batteries: lithium-polymer cells; C-rate, voltage sag under load, and why a battery at 30% under load may recover to 40% when unloaded - do not be fooled into extending the flight. Storage voltage, swelling, and thermal runaway are safety topics.
- Sensors and redundancy: IMU and compass calibration; magnetometer errors from nearby metal or power lines cause toilet-bowling or yaw errors. GNSS accuracy and the difference between GNSS and barometric altitude.
- Control link and antenna: line-of-sight, polarization, and the effect of the aircraft's orientation on link quality.
- Maintenance and pre-flight: firmware state, propeller condition, motor temperature, and log review.
Traps and a rule of thumb
Traps: trusting a recovered battery percentage; calibrating the compass in a bad location; assuming redundancy means immunity (two sensors can disagree, and the flight controller must choose); and ignoring vibration as a cause of "random" attitude anomalies.
Rule of thumb - the "one failure" test: for each subsystem, ask what the aircraft does if it fails now, and whether that behavior is safe in the current location. If the answer is "it returns through the building", change the plan or the failsafe altitude before takeoff.