China Civil UAV Theory Questions — Questions 396–405

The landing gear is the component that contacts the ground during takeoff and landing.

Advancing blade airspeed = aircraft forward speed + blade rotational speed; retreating blade airspeed = aircraft forward speed − blade rotational speed.

Hovering does not involve forward flight, so it does not involve forward-flight parasite drag balance. Further reading: drag is a purely aerodynamic force parallel to the relative airflow, generally composed of two parts: induced drag and parasite drag. Induced drag accompanies lift production and increases with airspeed. It is the component of lift perpendicular to the chord in the aircraft's direction of motion. So if the wing produces no lift, induced drag is zero; conversely, the faster the speed, the greater the induced drag. Parasite drag is the general term for all drag not caused by lift production: drag from the aircraft surface disturbing smooth airflow and creating vortices. This drag does not come from lift production but from the body moving through the atmosphere. Parasite drag increases with airspeed and includes friction drag, interference drag, and pressure differential drag.

When turning in forward flight at 10km/h, the aircraft's forward speed and inertia affect the turn. The aircraft needs a larger bank angle to overcome the inertia from forward speed and achieve the turn. So bank angles differ between hover turns and 10km/h forward-flight turns: smaller in hover turns, larger in forward-flight turns.

In wind hover, the UAV must apply a force component toward the wind to counter it, so the windward side sits slightly lower. In a headwind, the nose faces the wind, so the nose pitches down. Option A is correct. To avoid rollover in wind, the aircraft should hover nose into the wind. Option B is wrong. In a crosswind hover, the aircraft drifts downwind, so the stick should be pushed toward the direction the wind comes from to counter it. Option C is wrong.

Since the mechanical structure has not changed, the center of gravity has not changed, so it needs no attention.

In forward flight, the rear rotors speed up, tilting the UAV forward to gain a forward force component.

A multi-axis aircraft is a precision instrument requiring shock absorption. Option A's measures emphasize shock absorption and protect the aircraft better; option B's suitcase transport lacks shock absorption and is more likely to cause damage than option A.

When the center of gravity is above or below the multirotor power plane, the positional relationship between the center of gravity and the lift center changes. For example, with the center of gravity above the power plane, gravity and lift do not act on the same vertical line during flight, producing a moment rotating the aircraft about its center of gravity. Likewise, a center of gravity below the power plane produces a similar destabilizing moment. Such destabilizing moments make it hard to keep the aircraft stable in flight and increase control difficulty. When the center of gravity is above or below the power plane, the unstable state forces the control system to spend more time and energy countering the destabilizing moment to change flight state, so control response becomes sluggish and maneuverability decreases. In hover, the center of gravity and the combined wing lift force lie on the same vertical line, so no moment rotating the aircraft about its center of gravity occurs, and hover power consumption does not increase.

Due to limits on endurance, communication range, and flight speed, multi-axis aerial photography aircraft are unsuitable for very-long-distance surveillance.