China Civil UAV Theory Questions — Questions 203–212

Knowledge point — directional and omnidirectional antennas: ① Omnidirectional antennas: uniform radiation over 360° in the horizontal pattern, i.e., no directionality as commonly described. Omnidirectional antennas are generally used in communication systems for short distances, wide coverage, and low cost. ② Directional antennas: radiation over a certain angular range in the horizontal pattern, i.e., directional as commonly described. Directional antennas are generally used in communication systems for long distances, small coverage, high target density, and high frequency utilization. Common antenna types: ① Omnidirectional: whip antennas, mushroom-head antennas, cloverleaf antennas. ② Directional: panel antennas, Yagi antennas, helical antennas, parabolic antennas (dishes).

Exhaust Gas Temperature (EGT) is the temperature at the engine turbine outlet section after gas is discharged from the combustion chamber and passes through the high-speed rotating turbine. Aircraft engine exhaust gas temperature is an important parameter for monitoring engine working condition, usually measured by a K-type thermocouple; if exhaust gas temperature exceeds the specified value, it may damage the combustion chamber, turbine blades, exhaust nozzle and other engine components.

The main functions of the UAV ground station are command and control, and mission planning.

Vision and hearing are the senses people most commonly use to receive external information, and ground station systems typically provide visual (display) and auditory (speaker) output devices.

Command information display content: command code, transmitted status, received status.

Basic concept: what is engine knocking? Whether gasoline or diesel engines, they work through four strokes: intake of fuel-air mixture (diesel engines take in air) — compression — combustion and work — exhaust, cycling repeatedly. When the engine takes in fuel vapor and air mixture, before the compression stroke reaches the designed ignition position, factors beyond control cause the fuel-air mixture to ignite and burn on its own. The enormous impact force from combustion opposes piston motion, causing engine vibration — this phenomenon is called knocking. Knocking is divided into perceptible knocking and imperceptible knocking. Perceptible knocking usually causes engine shaking, even noticeable body shaking; imperceptible knocking mainly manifests as increased engine noise. Explanation for this question: from the causes of knocking, during the compression stroke, an excessive compression ratio causes unburned fuel-air to self-ignite. With high intake pressure, the compression ratio is larger, making knocking more likely. At low engine speed, the intake and compression stroke timescales are stretched, so the effect of thermal radiation on the in-cylinder mixture keeps accumulating, causing excessively high mixture temperature at the end of compression, which is easily affected by pressure waves after the spark plug fires (pressure waves travel faster than the flame front), further raising temperature to the ignition point and causing knocking. Moreover, at low speed, in-cylinder airflow is weaker, flame propagation speed is lower, further increasing knocking tendency. Also, at low speed, exhaust is less thorough, residual exhaust gas fraction in the cylinder is higher, and the exhaust gas consists mostly of polyatomic molecules such as CO2, H2O, NOx, with a high isentropic exponent, so temperature does not easily drop; especially under heavy load, hot exhaust gas raises in-cylinder temperature, increasing knocking tendency. Knowledge point: engine knocking causes (not exam content): ① Ignition timing too advanced: to give the piston power immediately upon entering the power stroke after the compression stroke ends, ignition is usually advanced before the piston reaches top dead center (since burning takes time from ignition to completion). Excessively early ignition means most of the fuel-air has already burned while the piston is still in the compression stroke, and the remaining unburned fuel-air self-ignites under extreme pressure, causing knocking. ② Excessive carbon deposits in the combustion chamber: besides increasing the compression ratio (creating high pressure), carbon deposits can create hot spots or sparks on their surfaces, causing engine knocking. ③ Excessively high engine temperature: excessively high intake temperature in a hot environment, or poor engine cooling water circulation, causes high engine temperature and knocking. ④ Incorrect air-fuel ratio: an excessively lean fuel-air mixture raises combustion temperature, and higher combustion temperature raises engine temperature; an incorrect air-fuel ratio naturally causes knocking easily. ⑤ Fuel octane rating too low: octane rating measures fuel knock resistance; higher octane means stronger knock resistance. In a high-compression-ratio engine, combustion chamber pressure is higher, so fuel with low knock resistance easily causes knocking. ⑥ Insufficient fuel cleanliness: physical and chemical impurities in fuel, including some aromatic substances, can also self-ignite during engine compression, forming knocking.

The core function of the electronic fuel injection control system is to precisely control fuel injection quantity and timing so it matches intake air to form a suitable mixture. The electronic fuel injection control system monitors intake air through sensors (such as intake airflow sensors and throttle position sensors), then the ECU (electronic control unit) calculates the required fuel amount and injects fuel through injectors into the intake path, where it mixes with air and enters the cylinder for combustion. Therefore, the electronic fuel injection control system is installed on the intake system.

This question explicitly describes controlling the UAV 'on the basis of an attitude control mechanism,' so choose 'attitude remote control.' In manual correction mode, both the inner and outer loops of flight control participate. In attitude remote control mode, the inner loop participates and the outer loop does not. In control-surface remote control mode, neither the inner nor the outer loop participates.

Data: no commands uplink, no information downlink; data transmission: no telemetry downlink. The data transmission link is usually used for two-way data transmission between the UAV and the ground station, including uplink commands from the ground station to the UAV (such as route planning and mission adjustments) and downlink data returned by the UAV to the ground station (such as flight status and telemetry parameters). Option analysis: Being unable to replan route waypoints online and send mission commands: replanning routes and sending commands are uplink functions, unrelated to downlink interruption. If the uplink is normal, commands can still be sent. Rule out this option. The ground station stops updating the UAV's telemetry data: the UAV's flight status, battery voltage, position and other telemetry data are transmitted to the ground station via the downlink. After downlink interruption, the ground station cannot obtain real-time data. Choose this option. Loss of UAV aerial photography image transmission: image transmission usually goes through an independent image transmission link (such as an image transmission module), unrelated to the data transmission link's downlink channel. If the image transmission link is normal, images can still be displayed. Rule out this option.

If an engine spark plug has a problem, it may fail to start. The spark plug is the key component for igniting the mixture; if the spark plug cannot work normally, it cannot ignite the mixture and the engine cannot start. At the same time, during engine operation, if the spark plug fails, the engine may also suddenly stall.