China Civil UAV Theory Questions — Questions 376–385

Study note: when GPS is an option, choose GPS. Inertial navigation is costly and heavy and accumulates error over time; a pitot tube determines speed from airflow pressure and does not suit multi-axis aircraft with low-speed, hovering characteristics. GPS is precise, cheap, and light, suiting multi-axis aircraft.

Study note: when GPS is an option, choose GPS. Multi-axis aircraft generally use GPS navigation rather than inertial navigation, for these reasons: (1) accuracy — inertial navigation accuracy is affected by gyroscope and accelerometer errors, Earth's rotation, and gravity changes, making it less accurate than GPS and other satellite navigation; (2) maintenance and calibration — inertial systems need frequent maintenance and calibration, which can be more difficult on small multi-axis aircraft; (3) cost — inertial systems are expensive and may not be economical for low-cost multi-axis aircraft; (4) reliability — inertial navigation works on physical principles, so for some missions its reliability may be lower than other systems; for example, in high-speed flight, air resistance can affect inertial navigation accuracy. Further reading: platform inertial navigation systems are typically used on large aircraft such as airplanes and missiles, using a stable physical platform carrying gyroscopes and accelerometers for stable, accurate measurements. Strapdown inertial navigation is mounted directly on the airframe without a stable platform, using advanced mathematical algorithms and computer processing to eliminate errors and provide position, speed, and attitude information.

If voltage is low, return home if possible; if return is impossible, choose a forced landing. Pulling the throttle straight to 0 loses power and crashes the aircraft.

When direction cannot be determined, increasing throttle may accelerate the UAV into a dangerous area — the wrong response. One-key return brings the UAV back within visual range to observe and determine nose direction. Resetting the gimbal can determine nose direction from the image.

The more turns in a motor's coils, the lower the speed at the same voltage: each coil carries magnetic flux, more turns mean greater flux, and for the same voltage the motor faces greater resistance, so its speed drops.

The faster a UAV flies, the faster it moves relative to its surroundings, so relatively less light enters the camera — like sitting in a fast-moving car and feeling the outside looks darker than when still. To ensure correct exposure (proper image brightness) with relatively less light, exposure must be increased to let in more light so the photo is not too dark.

A gimbal's main function is to carry the camera and, through its built-in motors and stabilization algorithms, cancel UAV shaking to provide a stable shooting platform. A gimbal also usually has control functions, letting the user adjust the camera's angle and direction.

Fiberglass is too heavy and is a brittle material, unsuitable for multirotor UAVs.

A multi-axis UAV is a UAV with three or more rotor axes.

Autorotation descent capability means that when an aircraft loses power or active control, it can maintain a safe descent using lift generated by its rotors or propellers autorotating. A multi-axis aircraft's structure means its rotors have no autorotation capability.