China Civil UAV Theory Questions — Questions 689–698

Study note: the wing on the side you press toward loses lift. Pressing the aileron slightly to the right deflects the right aileron upward and the left aileron downward. This produces different lift on the two wings: the left airfoil changes, its camber increases, and lift increases; the right airfoil changes, its camber decreases, and lift decreases.

Study note: larger angle first, smaller speed second. With full flaps, the wing lift coefficient increases greatly, so the UAV can obtain enough lift at a lower speed, and therefore can descend at a larger descent angle and a smaller speed, ensuring descent efficiency while avoiding a stall. Options B and C do not match the speed and descent-angle characteristics of a full-flap descent.

Negative dynamic stability means that after an external disturbance, the aircraft not only cannot recover to its original stable state on its own, but the amplitude of its oscillation gradually increases over time. Study note: negative stability means continued divergence with ever-growing amplitude; other cases mean recovery to the original flight attitude.

Positive dynamic stability means that during flight, when disturbed externally, the aircraft can adjust its attitude, position, speed, and other states on its own and eventually return to its original stable state. Study note: negative stability means continued divergence with ever-growing amplitude; other cases mean recovery to the original flight attitude.

Study note: strong lateral and weak directional stability gives Dutch roll; weak lateral and strong directional stability gives spiral instability. (1) Strong directional stability and weak lateral stability lead to spiral instability; (2) weak directional stability and strong lateral stability lead to Dutch roll.

Study note: strong lateral and weak directional stability gives Dutch roll; weak lateral and strong directional stability gives spiral instability. (1) Strong directional stability and weak lateral stability lead to spiral instability; (2) weak directional stability and strong lateral stability lead to Dutch roll.

An aircraft's lateral stability mainly concerns stability in the lateral direction (perpendicular to the aircraft's longitudinal axis). This stability ensures that when disturbed externally (such as by wind shear or airflow disturbance), the aircraft can automatically return to its original stable flight attitude. Restoring the wings to level is a lateral-axis stability behavior, i.e., good lateral stability. Keeping heading is a vertical-axis stability behavior, i.e., good directional stability. Keeping the angle of attack is a longitudinal-axis stability behavior, i.e., good longitudinal stability.

Theoretical ceiling: the maximum altitude an aircraft can reach under specific conditions, usually including maximum thrust, the lightest load configuration (for example, only the pilot and necessary fuel), and the best aerodynamic performance. It is calculated without any operating limits or safety margins. Service ceiling: unlike the theoretical ceiling, the service ceiling accounts for actual operating conditions and limits, including the normal load (passengers and cargo), actually available thrust (which may be affected by engine aging or maintenance condition), and the operating margin needed to ensure safe flight. Service ceiling is therefore usually lower than theoretical ceiling.

The glide angle is the angle between the flight path and the horizontal plane.

When an aircraft moves forward, the shape and angle of the wing make airflow over the upper surface faster than over the lower surface, producing lift. This lift is not distributed uniformly over the wing; it has a central point, the center of pressure, which is the equivalent point at which lift acts on the wing and can be regarded as the point of application of lift.