UAV system with its flexible, long-term flight and “zero casualties” characteristics almost penetrated into all fields of battlefield space. The outstanding performance of UAV in recent local wars has aroused the great attention of the military of all countries, especially the military powers. It has become a key node and an important part of the information weapons and equipment system, and plays an irreplaceable role in the fields of information support, information confrontation and Firepower Strike.

Compared with manned aircraft, the advantages of UAV are mainly reflected in the following five aspects:

First, it can carry out air missions for a long time;

Second, it can replace manned aircraft to enter the nuclear / biological / chemical and other polluted environment to carry out tasks;

Third, there are no pilot casualties, and the political and military risks are small;

Fourth, because of ignoring the human factor, it can bear a greater load, and the stealth and mobility of the aircraft can achieve a qualitative leap;

Fifthly, the life-cycle cost is low and the combat efficiency cost ratio is high. Compared with satellite, UAV system has the advantages of timeliness, pertinence and flexibility.

The position and function of UAV

UAV is a good tool for seizing information right

UAV can provide long-term and lasting battlefield information support services, and can obtain and analyze battlefield information in real time. UAV has the ability of multi-dimensional integration, global coverage, continuous real-time, accurate and fine information perception; UAV Systems of different types and altitudes form information support networks covering the battlefield from low altitude to near space area, such as communication, navigation and positioning, forming flexible, mobile, multi-level and three-dimensional comprehensive information support capabilities of space-based and near space-based, which improves the efficiency of command and enhances the joint and flexibility of operations.

UAV is an important pillar of battlefield information countermeasure in the future

Information countermeasure refers to the implementation of electronic jamming, electronic deception, electronic decoy, network attack and anti radiation destruction to the enemy’s information system. Different types of UAV systems can meet the needs of strategic, campaign and tactical multi-level information countermeasure capability, provide different types of “soft” and “hard” information countermeasure means, provide combat capability from tactical information countermeasure support to strategic campaign information countermeasure attack, and realize all frequency, all time and all-weather information attack on enemy information system, Form a multi-level information warfare force system framework.

UAV will become the leading force in air combat

UAV will be able to detect and attack time sensitive targets, accurately attack enemy’s important targets in depth, fight near space and cross atmosphere, and become the leading force of air combat in the 21st century. In joint operations, UCAVs can perform air defense suppression tasks and coordinate various forces to strike the enemy territory in depth; Cooperating with the ground and sea forces, UAV can indicate the target and carry out fire correction for the ground and sea weapons, so as to improve the strike accuracy; UAVs can also perform combat assistance, battlefield management, theater missile defense, anti mine, psychological warfare, etc.

UAV is the best choice to perform the most dangerous tasks

The proportion of precision guided weapons used in high-tech information warfare is increasing. With the coexistence of nuclear, biological and chemical weapons and the increase of lethality, the participants will face great danger. Therefore, UAV can perform the most dangerous task instead of UAV and avoid casualties to the maximum extent.

Technical basis of UAV

The development of aviation technology is the foundation to promote the development of UAV technology. UAV is a kind of aircraft which depends on aerodynamics. How to make UAV fly stably and reliably with better performance depends on the application and development of aviation technology.

Aviation technology includes aerodynamic technology, flight dynamics technology, aviation structure technology, aviation material technology, aeroengine technology, flight control and navigation technology, avionics and electrical technology, etc. the early development of aviation technology mainly solves the problem that UAV and other aircraft can fly. The development of modern aviation technology promotes UAV to become more and more high in flight performance Flight reliability is getting better and better, and the ability to perform tasks is becoming stronger and stronger.

The development of wireless data link technology is the condition to promote the development of UAV to usability and practicality. Because the UAV is pilotless, it must rely on the ground control station to realize its control and flight status monitoring through the wireless data link, so the wireless data link is the condition to promote the UAV to be available and practical. The development of modern data link technology makes the UAV data link develop towards the direction of high speed, broadband, confidentiality, anti interception and strong anti-interference ability, and promotes the UAV practical ability more and more strong.

Key technologies of UAV development

In the future, UAV will develop in the direction of higher, faster, farther, more mobile and more efficient

1. Platform technology (integrated layout, aerodynamics, lightweight structure, stealth);

2. Large scale composite design (specification), processing technology (cost);

3. Structural composite materials, UV resistant materials, lightweight materials, high temperature resistant materials, etc;

4. Micro machining and assembly technology, application of intelligent materials (flexible wing without rudder surface, micro and bionic UAV);

5. Advanced launch recovery technology;

6. Miniaturization and integration of weapons and equipment;

7. Stealth technology;

8. Power technology;

9. Communication technology;

10. Intelligent control technology;

11. Airspace management technology;

UAV Flight Control Technology

Flight control and management system is one of the key systems of UAV. Flight control system is the core system for UAV to complete the whole flight process, such as take-off (launch), air flight, mission execution, return landing (recovery), etc. it realizes full authority control and management for UAV, so it plays a key and decisive role in the function and performance of UAV. If there is no flight control system, it is impossible for modern UAV to fly in the sky and complete various tasks.

UAV flight control system generally consists of sensors, airborne computer and servo actuator.

UAV control mode

The flight control system of UAV is full time and full authority. The flight control mode can be divided into program control (time program control), remote control (remote command control through ground station) and autonomous flight control (two-dimensional, three-dimensional or four-dimensional).

The first two flight control modes are commonly used for the flight control of target aircraft, observation aircraft and other types of UAVs, and the third is commonly used for the flight control of reconnaissance aircraft, attack aircraft and other types of UAVs.

In the remote control mode, the ground operator controls the flight of UAV according to the status information and mission requirements of UAV;

In the autonomous control mode, the flight control system automatically controls the flight of UAV according to the aircraft status information and mission planning information obtained by sensors.

In the semi autonomous control mode, on the one hand, the flight control system controls the flight of UAV according to the aircraft status information and mission planning information obtained by sensors; on the other hand, it receives the remote control command from the ground control station to change the flight status.

Airborne sensors

The commonly used sensors of UAV flight control system include angular rate sensor, attitude sensor, heading sensor, altitude airspeed sensor, aircraft position sensor, angle of attack sensor, overload sensor and so on. The selection of sensors should be based on the preliminary design and Simulation of the control law.

1. Angular rate sensor

Angular rate sensor is one of the basic sensors of flight control system, which is used to sense the rotation angular rate of UAV around the body axis to form angular rate feedback, improve the damping characteristics and stability of the system.

The selection of angular rate sensor should consider its measurement range, accuracy, output characteristics, bandwidth and so on.

The angular rate sensor should be installed near the center of gravity of the UAV and at the wave node of the first-order bending vibration. The installation axis should be parallel to the axial direction of the body to be felt, and special attention should be paid to the correctness of the polarity.

2. Attitude and heading sensors

The attitude sensor is used to sense the pitch and roll angle of UAV, and the heading sensor is used to sense the heading angle of UAV. Attitude and heading sensors are important parts of UAV flight control system, which are used to realize the function of attitude and heading stabilization and control.

The selection of attitude and heading sensors should consider the measurement range, accuracy, output characteristics and dynamic characteristics.

The attitude and heading sensors should be installed near the center of gravity of the aircraft, and the vibration should be as small as possible.

For the magnetic heading sensor to be installed in the least affected by ferromagnetic materials and relatively fixed place, the mounting parts should be made of non-magnetic materials.

3. Altitude, airspeed sensor (or air data computer)

Altitude and airspeed sensors (or air data computer) are used to sense the flight altitude and airspeed of UAV. They are necessary sensors for altitude maintenance and airspeed maintenance. In general, the air data system is composed of airspeed tube and ventilation pipeline.

The selection of altitude and airspeed sensors mainly considers the measurement range and accuracy. It is generally required to be installed near the airspeed tube and shorten the pipeline as much as possible.

4. Aircraft position sensor

Aircraft position sensor is used to sense the position of the aircraft, which is the necessary premise of flight trajectory control. Inertial navigation equipment and GPS satellite navigation receiver are typical position sensors.

The selection of aircraft position sensor generally considers the navigation accuracy, cost and availability related to flight time.

Inertial navigation equipment has the requirements of installation position and high installation accuracy. The installation of GPS receiver should avoid the problem of antenna occlusion.

Boot device

Precise guidance is the basis of UAV automatic landing. Due to the use of simple airports, it is obviously impossible to use the general instrument landing system or microwave landing system. On this premise, the following methods are available.

1) Global positioning system (GPS): GPS is the navigation facility with the highest positioning accuracy so far, and it is widely used in countries all over the world. GPS must be combined with ins and radio altimeter when it is used as precision approach and landing guidance system. Because GPS is easily restricted by the United States, we should not rely too much on it.

2) Regional positioning system (RPS): regional positioning system (RPS) realizes the positioning of air targets by placing 4-6 devices (which are equivalent to positioning satellites in function) in a certain area on the ground.

3) Ground auxiliary guidance facilities: locate the aircraft through the ground precision optical system or guidance radar, and then transmit the positioning information to the flight control computer through the uplink data link.

Characteristics, advantages and application importance of UAV Flight Control Technology

4) Visual guidance: the airport scene captured by the photoelectric equipment on the UAV (which should be locked at a certain angle at this time) is superimposed with the UAV’s attitude, heading, airspeed, altitude and other information to form a HUD image similar to that on the UAV. Combined with the airport personnel’s visual results for the UAV, the UAV is manually guided to approach and land.

Servo mechanism

Servo actuator, also known as steering gear, is the executive part of flight control system. Its function is to receive the flight control command, amplify the power, and drive the steering surface or engine throttle to deflect, so as to control the UAV attitude and trajectory.

Servo actuator can be divided into electric servo actuator, hydraulic servo actuator and electro-hydraulic hybrid servo actuator. UAV usually uses electric servo actuator.

Flight control law

Flight control law is an important part of flight control system. It is a kind of mapping relationship between the command and various external information to the aircraft actuators. The design of flight control law is to determine this mapping relationship, so that the aircraft has the flight quality that meets the system requirements in the whole flight envelope. The design of flight control law is based on the system development mission contract and related top-level technical documents. According to these documents, the various qualities or performances of the aircraft with control system are formed. Based on the analysis of the characteristics of the uncontrolled aircraft, in order to achieve the required flight qualities or performances, the preliminary structure of the control law is determined, and then the parameters of the control law are determined by using the design method of automatic control. Through nonlinear full simulation, semi physical simulation and flight test, the structure and parameters of the control law are verified or adjusted to meet the requirements of flight quality or performance. The design process of control law is an iterative regression process.

Structure of control law

First of all, the control surface of the aircraft should be clear. The general control surface consists of elevator, aileron, rudder, flap, canard, speed reducer, etc. According to the performance requirements of UAV and the characteristics of UAV, the structure of control law is determined. The control law includes longitudinal control law and lateral heading control law. According to the mission requirements of UAV, the following control law structure is selected.

Pitch angle stabilization and control

Pitch angle stabilization and control loop generally needs pitch angle and pitch angular velocity feedback signal, and its general control law structure is shown in the figure.

Roll angle stability and control

Roll angle stabilization and control loop generally needs roll angle and roll angle speed feedback signal, and its general control law structure is shown in the figure.

Course stability and control

The general structure of heading angle stability and control is shown in the figure. Among them, the control structure uses the aileron to control the course, which has high control efficiency, but the sideslip angle is large; The rudder is used to control the course, the control efficiency is low, and the roll angle feedback is used to partially eliminate the sideslip angle; Using aileron and rudder to control heading angle has the characteristics of high control efficiency and small sideslip angle.

Height control

Altitude control consists of pitch inner loop and outer loop. The pitch inner loop is generally composed of pitch angle and pitch angular velocity feedback, and the outer loop of altitude control is generally in the form of proportion + integral + differential, as shown in the figure.

Airspeed control

Airspeed control is divided into throttle airspeed control, pitch airspeed control and drag airspeed control. Throttle airspeed control realizes airspeed control by adjusting engine throttle, pitch airspeed control changes aircraft angle of attack by elevator deflection, so as to change aircraft aerodynamics to realize airspeed control, drag airspeed control realizes airspeed control by changing resistance by deflecting resistance plate.

Due to the large time delay of the engine, the throttle airspeed control is generally relatively slow, and the pitch airspeed control and drag airspeed control have the characteristics of relatively fast response.

Lateral deviation control

Lateral deviation control can realize lateral track control. Lateral deviation control is generally realized by aircraft roll control, which is composed of roll inner loop and roll outer loop. The deviation distance is the distance relative to the expected route and the difference between the expected route and the actual route. The difference control is generally used in cruise flight phase, and the no difference control is mainly used in precise control phase, such as landing.

Lifting speed control

The lifting speed control is generally used in the leveling stage of automatic wheel landing, and its control structure is composed of pitch inner loop and lifting speed outer loop, as shown in the figure.

UAV data link technology

Data link is one of the main components of UAV system. The design involves remote control and telemetry, tracking and positioning, image transmission, microwave communication, satellite communication, anti-jamming communication, antenna servo, automatic control and computer application, etc. it is a complex information system engineering.

Data link function

1. Remote control of UAV and airborne mission equipment;

2. Telemetry of UAV and airborne equipment;

3. Tracking and positioning of UAV;

4. Real time transmission and processing of UAV reconnaissance information.

telemechanics

Remote control is an essential function of UAV data link, which is used to realize the remote operation of UAV and mission equipment. The command and data from the ground control console or manipulator are transmitted and decoded by coding, uplink (from the TT & C station to the UAV) wireless channel, and then sent to the flight control computer (or directly) to operate the UAV and mission equipment.

In modern advanced UAV system, the role of remote control can be summarized as follows:

1. Long distance control of UAV flight;

2. Remote control of UAV airborne equipment;

3. Transmission of uplink ranging code;

4. Uplink transmission of UAV navigation data (including route setting or modification data, TT & C station position, UAV position determined by TT & C station, differential GPS correction data, etc.).

Remote control is very important for UAV, and its reliability, anti-jamming and anti interception ability should be paid attention to. The transmission of remote control command and data is usually carried out at a low code rate, so it is not difficult to ensure sufficient channel level. Improving the design redundancy can increase the reliability of the remote control, and the anti-jamming and anti interception ability of the remote control can be increased through spread spectrum or frequency hopping and data encryption.

Telemetry technology

Telemetry is a necessary monitoring means to understand the status of UAV and implement remote control. The telemetry data (including the data of flight status sensors and the detection data of airborne equipment status) from the onboard flight control computer or directly from various parts of the aircraft are encoded, transmitted and decoded in the downlink (from the UAV to the TT & C Station) wireless channel, and transmitted back to the TT & C station. The flight status of the UAV can be observed in real time through the data comprehensive display, And the working state of the task equipment. With the help of these data, operators can easily manipulate UAV and its mission equipment to complete various tasks. With the help of the downlink telemetry channel, the antenna of the TT & C station can track the UAV and measure the azimuth of the UAV. By comparing the telemetry code with the telemetry code, the oblique distance measurement between UAV and TT & C station can be completed. From the azimuth and slant distance, the position of UAV relative to TT & C station can be determined by using the height data from telemetry.

In the modern advanced UAV system, the function of telemetry is as follows:

1. Downlink transmission of UAV flight status data;

2. Downlink transmission of UAV airborne equipment status data;

3. The ranging code is transmitted downward to realize the ranging of UAV;

4. Provide beacon for tracking and angle measurement of TT & C station.

Telemetry is also very important for UAV. The error of data transmission will mislead the operator, which may lead to misoperation and accidents. The design of UAV telemetry should pay attention to the quality of data transmission. The telemetry data rate may be similar to or slightly higher than that of the remote control data, and it is not difficult to ensure sufficient channel level. Usually, error correction coding and other measures are adopted to improve the transmission quality of telemetry data.

Tracking and positioning technology

Tracking and positioning is to provide UAV position data continuously and in real time. This is not only the requirement of operating UAV, but also the requirement of locating reconnaissance target.

For the UAV that can fly autonomously, telemetry is used to send the navigation data back to the TT & C station in real time to realize the tracking and positioning of UAV. However, in some cases that can not completely rely on the aircraft navigation and positioning, it is necessary for the TT & C station to measure the angle and range of the UAV, determine the relative position between the UAV and the TT & C station, and then combine with the position of the TT & C station itself to realize the tracking and positioning of the UAV. Sometimes, the data of navigation and positioning can be fused with the data of measurement and control station. This combined positioning method not only increases the redundancy, but also improves the positioning accuracy.

For long-distance flying UAV, the antenna of TT & C station generally adopts high gain directional antenna. In this way, not only the signal level is increased, but also the anti-interference ability of the downlink channel is improved. If this kind of high gain directional antenna can track UAV automatically, that is, it has the ability of tracking and angle measurement, then combined with the ranging function, it can realize the tracking and positioning of UAV.

Because the flight altitude of UAV is relatively low, the elevation angle of UAV to TT & C station is small, and most UAVs are equipped with altitude sensors, so it is unnecessary to measure the elevation angle in most cases, and the tracking can be completed by manual or digital guidance in the elevation direction, which is conducive to reducing the complexity of the system.

Information transmission technology

UAV information transmission is to transmit video reconnaissance information acquired by airborne mission sensors to TT & C station through downlink wireless channel. Video reconnaissance information is divided into image reconnaissance and electronic reconnaissance. The signal form of image reconnaissance information is different due to the type of image sensor, including analog or digital TV signal of TV camera, image data signal of imaging radar or line scan camera. Electronic reconnaissance information is band limited analog signal.

Information transmission is the key for UAV system to complete reconnaissance mission. The quality of transmission is directly related to the ability of finding and identifying targets. Reconnaissance information requires a much higher transmission bandwidth than remote control and telemetry data (usually several megahertz, the highest can reach tens of megahertz, or even hundreds of megahertz). Therefore, the design of video reconnaissance information transmission channel is often the most difficult part of UAV wireless channel design. In order to simplify the system, video information transmission and telemetry can share one channel.

Editor in charge: GT

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