China Civil UAV Theory Questions — Questions 631–640

Considering safety and economy, civil aviation needs a stable atmospheric environment. At the boundary between the upper troposphere and lower stratosphere, airflow is relatively stable with little turbulence, providing a relatively smooth flight environment for airliners.

At constant temperature, higher pressure compresses air more, increasing density: density is directly proportional to pressure.

Mach number is the ratio of object speed to sound speed. In the troposphere, sound speed decreases with height; an aircraft climbing at constant speed keeps its speed fixed while sound speed falls, so Mach number increases.

At plateau airports, low air density requires greater speed for lift, so landing speed is higher and the landing roll is longer.

Study note: like a car that cannot brake, it runs longer. Standing water increases resistance during the takeoff roll, slowing acceleration, delaying reaching takeoff speed, and lengthening the takeoff roll.

Study note: troposphere, stratosphere, mesosphere, ionosphere, exosphere. From low to high: troposphere, stratosphere, mesosphere, ionosphere, and exosphere. Troposphere: temperature falls with height. Stratosphere: temperature first stays constant or changes little, then rises with height. Mesosphere: temperature falls with height. Ionosphere: temperature rises rapidly with height (also called the thermosphere). Exosphere: no clear vertical temperature pattern.

Study note: density is directly proportional to pressure and inversely proportional to absolute temperature. From P = RρT, ρ = P/(RT), so density is directly proportional to pressure and inversely proportional to absolute temperature.

Exposure bias is unrelated to low-temperature and humid environment factors. In low temperatures, battery performance drops and endurance shortens, requiring power battery insulation before takeoff. In cold, humid environments, the aircraft and camera equipment may ice up during flight.

A pressure altimeter measures height from the pressure-height relationship, and pressure is strongly affected by temperature, so temperature changes mainly affect the pressure altimeter.

Study note: the faster, the less affected. At high cruise speed, wind speed has relatively less effect on ground speed (airspeed = ground speed + wind component), so wind influence is smaller.