What is a drone?

Unmanned aerial vehicle (UAV) is an aircraft that uses wireless remote control or program control to perform specific aviation tasks. It refers to a powered aircraft that does not carry an operator. It uses aerodynamics to provide the required lift for the aircraft, and can fly automatically or be guided remotely. Can be used once and recycled.

2. Overall composition of UAV system

UAV system includes ground system, aircraft system, mission load and UAV user support personnel.

system

3. General classification of unmanned aerial vehicles

According to the purpose:

Jinying aerial drone, unmanned reconnaissance plane, target drone, special drone, decoy drone, etc.

According to the flight mode:

Fixed-wing UAV, rotary-wing UAV, flapping-wing UAV, airship.

4. Flight control of UAV

There is no pilot on the drone, so both the drone and the flight rely on "remote control" or "self-control flight".

(1) remote control flight

Remote control refers to the continuous remote control of the controlled object, mainly radio remote control.

Remote control signal: the remote control station sends radio waves and commands to the UAV through the transmitter, the receiver on the UAV receives and interprets the commands, the autopilot controls the rudder surface according to the commands, or controls the task load on the UAV through other interfaces. The remote control station is equipped with search and tracking radar. They measure the azimuth angle, pitch angle, distance and height of the drone relative to the ground at any time and input these parameters into the computer. After calculation, the actual flight trajectory of the UAV can be drawn. Compared with the predetermined flight path, the deviation can be found, and then the instruction is issued to correct it.

In addition, the drone is also equipped with a radio transponder, also known as a beacon. It can send a signal back to the radar after receiving the inquiry signal from the radar. Because the signal emitted by beacon is much stronger than the radar signal emitted by UAV, the detection distance of tracking radar can be increased.

Download signal: it is obviously not enough for the remote control command to contain only the track correction signal. No one will be affected by various factors during the flight, and the flight attitude of the drone is constantly changing, so the instruction also needs to include the correction of the flight attitude.

The sensors on the UAV have been collecting their own attitude information and sending it to the telemetry terminal through downlink signals. After analyzing this information, the telemetry terminal can give the remote control correction instruction of flight attitude.

Advantages and disadvantages of remote control flight;

In favor: it is beneficial to simplify the design of UAV and reduce the manufacturing cost.

Disadvantages: due to the limitation of radio range, the communication distance can only reach 320km ~ 480km；; Vulnerable to electronic interference.

(2) Autonomous flight

Self-controlled flight does not depend on ground control, and all actions are completed automatically. To this end, the aircraft needs a set of devices to ensure the correct flight course and attitude, which is the navigation device. Commonly used navigation equipment are:

1. Inertial navigation

On airborne equipment, it is generally called inertial navigation. Inertial navigation is a navigation method based on Newtonian mechanics. The acceleration of the carrier on three axes is measured by accelerometers installed on the carrier, and the instantaneous speed and position of the carrier are obtained by integral operation, and the attitude of the carrier is measured. Inertial navigation completely relies on airborne equipment to complete navigation tasks independently, does not rely on external information, and does not radiate energy to the outside world, so it is not easily disturbed and is not limited by meteorological conditions.

Inertial navigation system is a dead reckoning system. As long as the initial position and speed of the carrier are given, the system can calculate the position, speed and attitude information of the carrier in real time and navigate autonomously. With the increase of flight duration, the pure inertial navigation system will produce large errors due to integral accumulation, which will lead to the divergence of positioning accuracy with time. Therefore, inertial navigation systems generally work together with other navigation systems to improve positioning accuracy.

2. Satellite navigation

Global Positioning System (GPS) is a positioning system established in the United States, which can provide three-dimensional spatial position, speed and time of any point in the world, and has a global, all-weather and continuous accurate navigation system.

Global satellite navigation is divided into three parts, including space satellite, ground monitoring and satellite receiver. Installing a satellite receiver on the plane can get its own position information and time information, accurate to nanosecond level.

Other satellite navigation systems are in use all over the world: glonass in Russia, Galileo in Europe and Beidou system under construction in China.

3. Doppler navigation

Doppler navigation is a common autonomous navigation system for aircraft, and its working principle is Doppler effect.

Doppler navigation system consists of magnetic compass or gyroscope, Doppler radar and navigation computer. A magnetic compass or gyroscope is similar to a compass and is used to measure the heading angle of an unmanned aerial vehicle. Doppler radar continuously emits electromagnetic waves to the ground along a certain direction to measure the flight speed and drift angle of UAV relative to the ground. According to the ground speed and drift angle data provided by Doppler radar and the heading data provided by magnetic compass or gyroscope, the navigation computer can continuously calculate the flight route of UAV.

Doppler navigation system can be used in various meteorological conditions and terrain conditions, but due to the cumulative error of measurement, the system will increase the error with the increase of flight distance, so it is generally used for integrated navigation.

4. Integrated navigation

Integrated navigation refers to the combined use of two or more navigation systems to achieve complementarity and improve navigation performance. At present, the navigation systems actually used in aircraft are basically integrated navigation systems, such as GPS/ inertial navigation, Doppler/inertial navigation and so on. Among them, GPS/ inertial navigation integrated navigation system is the most widely used.

5. Terrain-aided navigation

Terrain-aided navigation refers to a method that compares the pre-stored characteristic data of some areas in the flight path with the relevant data measured in the actual flight process to implement navigation correction. Its core is to divide the terrain into several small grids, and input its main features such as average elevation into a computer to form a digital map.

Terrain-aided navigation technology uses airborne digital map and wireless altimeter as auxiliary means to correct the error of inertial navigation system, thus forming a new navigation system. The fundamental difference between digital map and navigation method is that digital map can only play an auxiliary correction role in the main navigation system.

Terrain-aided system can be divided into terrain matching and scene matching.

◆ Terrain matching: also called terrain height correlation. The principle is that the geographical coordinates of any point on the earth's surface can be determined according to the contour lines or landforms of its surrounding areas. After flying for a period of time, a series of terrain elevations of the real flight path can be obtained. The measured data is associated with the stored digital map to determine the grid position corresponding to the aircraft trajectory. Because the latitude and longitude values corresponding to each point in the grid are determined in advance, digital maps can be used to correct inertial navigation.

◆ Scene matching: also called scene association. The difference between it and map matching is that the information input to the computer in advance is not only the altitude parameters, but also the scene information of the predetermined flight trajectory obtained by camera, which is digitized and stored on the airborne equipment. In flight, the scene in the flight path is obtained by airborne camera equipment, and the position of the aircraft is determined by comparing with the pre-stored data.

Advantages and disadvantages of autonomous flight;

Pro: the voyage has increased; Work independently without contacting the ground station.

Disadvantages: The complicated autonomous navigation system and control system increase the weight and cost.

(3) combination of remote control and automatic control

Modern UAV alternately uses remote control or automatic control in different flight segments, which can make full use of their respective advantages and overcome each other's shortcomings.

5. Take-off and landing of drones.

The take-off and landing of manned aircraft are two "difficulties" in flight, especially drones.

(1) UAV takes off

1. The mother machine is put into use.

Someone took the drone to the sky and put it in the right place to take off. This method is simple, flexible and has a high success rate, and can increase the range of the UAV.

2. Rocket boost

With the help of solid rocket booster, the drone took off from the launcher. This take-off mode occupies a small launch site and is suitable for frontier positions, mountains or ships.

3. Take-off sports car

UAV is mounted on a wheeled cart and propelled by the engine of UAV. When it reaches this speed, the drone will be lifted off the car.

In this way, the ready-made airport conditions can be used to take off without complicated landing gear, and the take-off sports car is simple in structure and economical.

4. Vertical takeoff

Take off using the take-off principle of helicopter. For example, the Golden Eagle 2 fixed-wing vertical take-off UAV can take off and land vertically, hover, with heavy load and high time limit.

5. Landing gear operation and takeoff

Like someone flying a plane, use your landing gear to run and take off.

Step 6 burn the fire by hand

This kind of launching method is the simplest, which is caught by one or two people and takes off by the drone's own power.

(2) UAV landing

1. Landing gear roller skating landing

Just like someone flying a plane, landing with their own landing gear. This method is generally used by large drones.

Parachute landing

The drone is recovered by parachute suspension. This method is suitable for small UAV. For large unmanned aerial vehicles, the reliability of parachute recovery is not high, the operation is difficult and the loss rate is high.

3. Air recirculation

At present, the way of using large aircraft to recover drones in the air is only adopted by the United States. Using this recycling method, large aircraft must have an air recycling system. In addition to the resistance umbrella and the main umbrella, the UAV also needs a hook umbrella, a sling and a rotatable shedding mechanism. The big plane hangs the hook umbrella and sling of the drone with a hook, twists the drone with a winch and hangs it away in the air. This recycling method will not damage the drone, but every time it is recycled, a large aircraft will be dispatched, which is costly and requires high pilot driving skills.

4. Intercept network recovery

Using interception network system to recover UAV is one of the recycling methods widely used by small UAV in the world. Interception network system usually consists of interception network, energy absorption device and automatic guidance equipment. The energy-absorbing device is connected with the interception net, and its function is to absorb the energy of the drone hitting the net and prevent the drone from being damaged after bouncing off the net. Automatic guidance equipment is usually a TV camera placed behind the net or an infrared receiver installed on the interception grid, which will report the deviation of the UAV's return route to the ground station in time.

5. Air cushion landing

A "rubber skirt" is installed around the belly of the drone, and there is an airbag with a hole in the middle. The engine presses air into the airbag, and the compressed air is ejected from the airbag hole, forming a high-pressure air area-an air cushion below the abdomen.

The biggest advantage of air cushion landing is that UAV can land on uneven ground, mud, snow or water, and it is not limited by terrain conditions. Secondly, both large and small drones can be used with high recovery rate.

6. UAV flight platform

The flight platform of UAV is mainly composed of six parts: fuselage, wing, tail, landing gear, automatic flight control system and power system.

1. fuselage

The fuselage is mainly used for loading engine, fuel, mission equipment, power supply, control system, etc. And through it, the wing, tail wing, landing gear and other parts are connected into a whole.

2. Wings

Wings are the main components used to generate lift in aircraft. The wings of fixed-wing UAV include straight wings, swept wings and delta wings. The following figure shows some common wings:

Straight wings are more suitable for low-speed aircraft, while swept wings and delta wings are more suitable for high-speed aircraft.

There are also ailerons on the wing to control the tilt of the aircraft, but when the left and right ailerons deflect in different directions, a rolling moment will occur, which is the tilt motion of the aircraft.

3. Tail wing

The tail consists of a vertical tail and a horizontal tail. For some UAVs with special structures, there may be no vertical tail or flat tail.

Vertical tail: installed vertically at the tail of the fuselage, its main function is to keep the direction balance and control of the fuselage. There is usually a rudder at the trailing edge of the vertical tail to control the direction.

Horizontal tail: installed horizontally at the tail of the fuselage, its main function is to maintain pitch balance and pitch control.

4. Landing gear

The landing gear is used to make the UAV take off, land, taxi and park on the ground or water.

Landing gear is the most diverse part of UAV, because UAV has many launch/recovery methods. The landing gear of large UAV is composed of landing gear and devices to improve landing performance. After take-off, the landing gear is retracted to reduce flight resistance. The landing gear of most drones is very simple and does not fold when flying; Small UAV launched/recovered by ejection and blocking net does not need landing gear; Small unmanned aerial vehicle launched by hand without landing gear; The UAV landing device for parachute recovery can be said to be a parachute.

5. Flight automatic control system

The automatic flight control system includes an automatic control command forming device and a transmission control device. The automatic command forming device comprises an autopilot, related sensors and navigation equipment; The transmission control device includes all devices from the control command output point to the control surfaces such as horizontal tail, aileron and rudder, which are used to transmit control commands and change flight state.

6. Power plants

Aircraft power plant is a device used to generate pulling force (such as propeller aircraft) or pushing force (such as jet aircraft) to make the aircraft move forward. The power of modern UAV is mainly divided into turbojet engine and turbofan engine.