China Civil UAV Theory Questions — Questions 266–275

Radar is unaffected by cloud and haze; visible-light and infrared imaging both use light waves and are affected. Synthetic Aperture Radar (SAR) uses electromagnetic waves, so it is unaffected by cloud and haze and can even see through vegetation and surface cover. Further reading: SAR is a high-resolution imaging radar that produces optical-like high-resolution radar images even in extremely low visibility. It synthesizes a large equivalent antenna aperture from a small real aperture using the relative motion between radar and target (also called synthetic aperture radar). SAR features high resolution, all-weather operation, and the ability to defeat camouflage and penetrate cover.

A multirotor has three or more rotors, usually four or more rotor shafts in pairs. Three-rotor (tricopter) UAVs are uncommon; to counter rotor torque they usually add a vector servo.

Treat 12000mAh as the whole battery pack's capacity. Maximum current = 12000mAh × 3C = 12Ah × 3C = 36A, so option A.

This question tests the concept of motor kV. A motor's kV value is the no-load RPM increase per 1 volt added: it is the RPM gained at no load for each additional 1V. A 1000kV motor gains 1000 RPM per volt. No-load speed = 1000kV × 11.1V = 11100 RPM, so option C is correct.

By Newton's third law (action and reaction), each spinning motor drives its propeller and applies a reaction torque to the airframe. To cancel the reaction torque, adjacent propellers on a multirotor spin in opposite directions, so their reaction torques cancel each other. An octocopter therefore needs 4 normal props and 4 reverse props.

Study note: when diagonal is an option, choose diagonal. This question tests motor-failure handling. The usual response to a motor failure is to stop the diagonal motor: stopping the diagonal motor balances the aircraft's dynamics, so it can stay stable while continuing its mission or landing safely.

A 60A ESC's maximum sustainable operating current is 60A. For the ESC to perform at its best, the battery's maximum output current should exceed the ESC's rated current. Note: this current is the maximum current the battery can deliver, not the continuous current during steady flight.

This question tests normal and reverse props. A normal prop rotates counterclockwise viewed from above, abbreviated CCW (counter-clockwise). A reverse prop rotates clockwise viewed from above, abbreviated CW (clockwise).

A brushless ESC has 8 wires; a brushed ESC has 7. Brushless ESC: 2 input wires to the power supply (thick), 3 output wires to the motor, 3 DuPont wires to the flight controller (thin). Brushed ESC: 2 input wires to the power supply (thick), 2 output wires to the motor, 3 DuPont wires to the flight controller (thin).

Study note: with one parenthesis, choose “general”. This is a power-line worker exam question.