Drones are the best choice for the most dangerous missions

 

The proportion of precision-guided weapons used in high-tech information-based warfare is increasing, and nuclear, biological and chemical weapons coexist, increasing the lethality and exposing participants to great danger. As a result, drones can replace human machines to perform the most dangerous tasks, minimizing casualties.

The technical basis of drones

 

The development of aviation technology is the basis to promote the development of UAV technology. Uav is an aircraft that relies on aerodynamic flight. How to make UAV fly stably and reliably with better and 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, aviation engine technology, flight control and navigation technology, avionics and electrical technology, etc. The early development of aviation technology mainly solves the problem that unmanned aerial vehicles such as aircraft can fly. The development of modern aviation technology promotes the development of UAV to the direction of higher and higher flight performance, better and better flight reliability, and stronger and stronger task execution ability.

 

The development of wireless data link technology is the condition to promote the development of UAVs to availability and practicality. Since the UAV is unmanned on board, 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 availability and practicality of the UAV. The development of modern data link technology has made the UAV data link develop in the direction of high speed, broadband, security, anti-interception and anti-interference ability, and promoted the practical ability of UAV to become stronger and stronger.

The main key technology of UAV development

 

The future development of UAVs in the direction of higher, faster, farther, more mobile and more efficient requires the following key technologies:

 

1, platform technology (comprehensive layout, pneumatic, lightweight structure, stealth);

 

2, large size composite material design (specification), processing technology (cost);

 

3, structural composite materials, UV resistant materials, light materials, high temperature resistant materials, etc.

 

4. Micro-machining and assembly technology, application of smart materials (rudderless flexible wings, micro and bionic drones);

 

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. The flight control system is the core system of the UAV to complete the whole flight process such as take-off (launch), air flight, mission execution, return landing (recovery), etc. It realizes the full authority control and management of the UAV, so it plays a key and decisive role in the function and performance of the UAV. Without flight control systems, modern unmanned aerial vehicles would not be able to fly and complete various tasks.

 

Uav flight control system generally includes three parts: sensor, on-board computer and servo actuator.

 

Uav control mode

 

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

 

The first two flight control methods are commonly used for the flight control of target aircraft, observation and other types of UAVs, and the third is often 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 the UAV according to the status information and task requirements of the UAV;

 

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

 

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

 

Airborne sensor

 

The commonly used sensors in UAV flight control system include angular rate sensor, attitude sensor, heading sensor, altitude airspeed sensor, aircraft position sensor, Angle of attack sensor, overload sensor, etc. The selection of sensors should be based on the preliminary design and simulation of the control law according to the control needs of the actual system.

 

1. Angular rate sensor

 

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

 

The selection of angular rate sensor should consider its measuring 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 node of the first-order bending vibration, and the installation axis should be parallel to the axis of the body to be felt, and special attention should be paid to the correctness of the polarity.

 

2, attitude, heading sensor

 

The attitude sensor is used to feel the pitch and roll Angle of the UAV, and the heading sensor is used to feel the heading Angle of the UAV. Attitude and heading sensor is an important part of UAV flight control system, which is used to realize attitude and heading stabilization and control.

 

The choice of attitude and heading sensor should consider its measuring range, accuracy, output characteristics, dynamic characteristics and so on.

 

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, with high installation accuracy requirements.

 

For the magnetic heading sensor to be installed in a relatively fixed place with minimal influence from ferromagnetic substances, the mounting should be made of non-magnetic materials.

 

3, altitude, airspeed sensor (or atmospheric data computer)

 

The altitude and airspeed sensor (or atmospheric data computer) is used to feel the flight altitude and airspeed of the UAV, and is a necessary sensor for altitude maintenance and airspeed maintenance. Air data system is composed of general air pitot tube and ventilation pipe.

 

The selection of altitude and airspeed sensor mainly considers the measuring range and measuring accuracy. Its installation is generally required to be near the pitot tube and shorten the pipeline as much as possible.

 

4. Aircraft position sensor

 

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

 

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

 

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

 

Boot device

 

Accurate guidance is the basis of UAV automatic landing. Due to the use of simple airfields, it is obviously not possible to use conventional instrument landing systems or microwave landing systems. Under this premise, there are the following methods to choose from.

 

1) Global Positioning System (GPS) : GPS is the navigation facility with the highest positioning accuracy so far, and has a wide range of applications in countries around the world. GPS as a precision approach and landing guidance system must be combined with INS and radio altimeters. Because GPS is vulnerable to the United States, it is not appropriate to rely on it too much.

 

2) Regional Positioning System (RPS) : The regional positioning system (RPS) locates aerial targets by placing 4 to 6 devices (which can be called pseudo-satellites) functionally equivalent to positioning satellites in a certain area on the ground.

 

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

4) Visual guidance: The real-time airport scene captured by the photoelectric equipment on the UAV (which should be locked at a certain Angle at this time) is superposed with the UAV's attitude, heading, airspeed, altitude and other information to form a flat display screen similar to that of the manned aircraft, and combined with the airport personnel's visual results of the UAV, the aircraft is manually guided to approach and land.

 

servomechanism

 

Servo actuator, also known as the steering gear, is the executive part of the flight control system. Its role is to receive flight control commands, perform power amplification, and drive the rudder surface or engine throttle deflection, so as to achieve the purpose of controlling the attitude and trajectory of the UAV.

 

Servo actuating equipment can be divided into electric servo actuating equipment, hydraulic servo actuating equipment and electro-hydraulic hybrid servo actuating equipment. Electric servo actuators are usually used on drones.

 

Flight control law

 

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

 

Control law structure

 

First, the control surface of the aircraft should be defined. The general control surface consists of elevators, ailerons, rudders, flaps, canards, and deceleration plates. The control law structure is determined according to the performance requirements of UAV and the characteristics of uncontrolled UAV. The control law includes longitudinal control law and transverse course control law. According to the mission requirements of the UAV, select the following control law structure.

 

Pitch Angle stabilization and control

 

Pitch Angle stabilization and control loop generally requires pitch Angle and pitch Angle velocity feedback signals, and its general control law structure is shown in the figure.

Talk about modern UAVs and their key flight control technologies (military)

Roll Angle stabilization and control

Roll Angle stabilization and control loop generally require roll Angle and roll Angle speed feedback signals, the general control law structure is shown in the figure.

Talk about modern UAVs and their key flight control technologies (military)

 

Course stabilization and control
 

The general structure of course Angle stabilization and control is shown in the figure. Among them, the control structure uses ailerons to control the course, which has higher control efficiency, but the sidesslip Angle in the control is larger; 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. The combination of aileron and rudder to control course Angle has the characteristics of high control efficiency and small sideslip Angle.
 

Talk about modern UAVs and their key flight control technologies (military)

 

Altitude control
 

The height control consists of an inner pitch loop and an outer pitch loop. The pitch inner loop is generally composed of pitch Angle and pitch Angle velocity feedback, and the height control outer loop is generally in the form of ratio + integral + differential, as shown in the figure.

Talk about modern UAVs and their key flight control technologies (military)

 

Airspeed control

Airspeed control is divided into throttle airspeed control, pitch airspeed control and resistance airspeed control. Throttle airspeed control realizes airspeed control by adjusting engine throttle airspeed control, pitch airspeed control changes aircraft Angle of attack through elevator deflection, thereby changing aircraft aerodynamic force to achieve airspeed control, and drag airspeed control realizes airspeed control by deflecting resistance plates to change resistance.

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

Talk about modern UAVs and their key flight control technologies (military)

 

Lateral deviation control
 

Lateral deviation control enables lateral track control. The lateral deviation control is generally realized by the roll control of the aircraft, which consists of the roll inner loop and the side deviation outer loop. The deviation distance is the distance relative to the expected route, that is, the difference between the expected route and the actual route. Differential control is generally used in the cruise flight phase, while non-differential control is mainly used in the precision control phase, such as landing.

Talk about modern UAVs and their key flight control technologies (military)

Talk about modern UAVs and their key flight control technologies (military)

 

Lifting speed control

 

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

Talk about modern UAVs and their key flight control technologies (military)

 

Uav data link technology

 

Data link is one of the main components of UAV system. The design involves many technical fields such as remote control telemetry, tracking and positioning, image transmission, microwave communication, satellite communication, anti-interference communication, antenna servo, automatic control and computer application. 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 drones;

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

Remote control technology

Remote control is an essential function of UAV data link, which is used to achieve remote operation of UAV and mission equipment. The instructions and data from the ground control console or manipulator are encoded, transmitted and decoded through the uplink (test and control station to the drone) wireless channel, and sent to the flight control computer on board (or directly) to operate the drone and mission equipment.

In modern advanced unmanned aerial systems, the role of remote control can be summarized as follows:

1. Remote control of UAV flight;

2. Remote control of UAV airborne equipment;

3, uplink ranging code transmission;

4. Uplink transmission of data for UAV navigation (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 UAVs, its reliability, anti-interference and anti-interception capabilities should be paid full attention to. The transmission of remote commands and data is generally carried out at a lower bit rate, and it is not difficult to ensure adequate channel levels. Improving the design redundancy can increase the reliability of the remote control, and the anti-jamming and anti-interception capability of the remote control can be increased through spread spectrum or frequency hopping and data encryption.

telemetry

Telemetry is a necessary monitoring method to know the status of UAV and implement remote control. Telemetry data from the flight control computer or directly from various parts of the plane (including the data of the flight status sensor and the detection data of the status of the airborne equipment) are transmitted and decoded through the wireless channel of coding, downlink (UAV to the measurement and control station), and returned to the measurement and control station. Through the comprehensive display of data, the flight status of the UAV can be observed in real time. And the working status of the mission equipment. With the help of these data, the operator can easily manipulate the UAV and its mission equipment to complete various tasks. With the help of the downlink telemetry channel, the antenna of the monitoring and control station can also track the UAV and measure the azimuth of the UAV. By comparing the distance measurement code returned by telemetry with the distance measurement code sent, the slant distance measurement of the UAV relative to the test and control station can be completed. From the azimuth Angle and oblique distance, using the height data returned by telemetry, the position of the UAV relative to the monitoring and control station can be determined.

In modern advanced unmanned aerial systems, the role of telemetry is:

1. Downlink the various flight status data of the UAV;

2. Downlink the status data of the airborne equipment of the UAV;

3, downlink transmission of ranging code, to achieve the ranging of the UAV;

4. Provide beacon for measuring and controlling station to track Angle measurement.

Telemetry is also very important for drones, and errors in data transmission can mislead operators and potentially lead to misoperations and accidents. The quality of data transmission should be emphasized in the design of UAV telemetry. Telemetry data rates may be similar to or slightly higher than remote data, and ensuring adequate channel levels is not difficult. Error correcting coding and other measures are usually adopted to improve the transmission quality of telemetry data.

Tracking and positioning technology

Tracking and positioning refers to the continuous and real-time provision of UAV position data. This is not only the requirement of operating the UAV, but also the need of positioning the reconnaissance target.

For the unmanned aerial vehicle that can fly autonomously, the navigation and positioning data of the aircraft can be transmitted back to the monitoring and control station in real time by telemetry, and the tracking and positioning of the unmanned aerial vehicle can be realized. However, in some cases that cannot completely rely on the navigation and positioning of the aircraft, it is necessary for the measurement and control station to measure the Angle and distance of the UAV, determine the relative position of the UAV and the measurement and control station, and then combine the location of the measurement and control station itself to achieve the tracking and positioning of the UAV. Sometimes, the navigation and positioning data of the aircraft and the measurement data of the measurement and control station can be fused, which not only increases the redundancy, but also helps to improve the positioning accuracy.

For the UAV flying long distance, the antenna of the T&C station generally adopts the high-gain directional antenna. In this way, it is beneficial to increase the signal level and improve the anti-interference ability of the downlink channel. If this high-gain directional antenna can automatically track the UAV, that is, it has the ability to track and measure the Angle, then combined with the ranging function can realize the tracking and positioning of the UAV.

Since the flight height of the UAV is relatively low, the elevation Angle of the UAV to the monitoring and control station is small, and most of the UAV itself is equipped with height sensors, so in most cases there is no need to measure the pitch Angle, and the tracking can be completed by manual or digital guidance in the pitch direction, which is conducive to reducing the complexity of the system.

Information transmission technology

Uav information transmission is to transmit the video reconnaissance information obtained by the airborne mission sensor to the T&C station through the downlink wireless channel. Video reconnaissance information is divided into two kinds: image reconnaissance and electronic reconnaissance. The signal form of image reconnaissance information varies according to the type of image sensor, including analog or digital television signals from television cameras, and picture data signals from imaging radar or line-scan cameras. Electronic reconnaissance messages are band-limited analog signals.

Information transmission is the key to UAV reconnaissance. The quality of transmission is directly related to the ability of finding and identifying the target. Reconnaissance information requires a much higher transmission bandwidth than remote and telemetry data (generally several megahertz, up to tens of megahertz, or even hundreds of megahertz). Therefore, the video reconnaissance information transmission channel design is often the most difficult part of the UAV wireless channel design. To simplify the system, video transmission and telemetry can share a single channel.