The application of Senther sensors on fighter jet ejection seats
Firstly, the definition of an ejection seat was found on Baidu Baike: an ejection seat is a seat used by pilots. In the event of an aircraft crash, it relies on the power device under the seat to eject the pilot from the cabin, and then opens the parachute to safely land. It is a seat type rescue device. The ejection chair was invented by Germans during World War II.The ejection chair initially used compressed air as the ejection power, but the difficulties in developing airtight maintenance technology and insufficient power ultimately led to the failure of the first "Generation 0 ejection chair" of this kind. Later, scientists successfully developed the "1st generation ejection chair" using rocket power. In modern times, the ejection chair has become a fully automatic programming device. As long as the pilot pulls the ejection handle, the process from ejecting the seat to landing by parachute will be automatically completed according to the program.
So, according to the requirements of the product of the ejection seat, this article combines the testing system of the ejection seat and uses the storage testing method of the testing system accompanying the ejection from the seat. A testing system is designed to test the main acceptance indicators of the ejection cylinder, such as peak acceleration and derailment speed. The ejection test confirms that the system is reliable and has advantages such as small size, simple structure, and easy operation compared to the original system, while completing the established functions. The development of this testing system has guiding significance and practical application value for the product design and quality inspection of the aircraft seat held ejection cylinder, and has been applied in practice
In airplanes, especially fighter jets, the lives of crew members are crucial. When encountering danger, in emergency situations, using seat ejection devices to eject personnel and seats together from the cabin can achieve rapid detachment from the aircraft to ensure life safety. The working parameters of the ejection cylinder in the seat ejection device are very important. The ejection cylinder uses explosives to explode the mechanical lock of the ejection cylinder,Under the thrust of gunpowder explosion gas, the seat and passengers are pushed out along the guide rail. During the process of pushing out the seat, there are two main requirements: the overload should be small, otherwise the passengers cannot bear the speed quickly, otherwise it will endanger their lives. Before installing the seat ejection device, an ejection test should be conducted on the seat ejection cylinder,The inspection of the ejection cylinder to ensure that it meets the requirements is carried out on a test bench simulating aircraft seats. The main test indicators include the maximum overload value and peak time, as well as the derailment speed of the seat when ejected from the track (using 830-50-3 acceleration sensors), vibration and impact testing of personnel on the seat (using 890 three-axis seat acceleration sensors), displacement of the seat belt tension after personnel are subjected to force on the seat (D211-2000 seat belt displacement sensor), and the degree of tightening of the seat belt on personnel (D211-2000 seat belt displacement sensor) and other factors.
To complete the inspection of the ejection cylinder, a simulation ejection method is used to simulate the ejection test bench, which mainly includes guide rail simulation seats and counterweights, ignition mechanisms, recovery systems, etc. The testing system used adopts hard wire testing technology, and the sensor is a corrugated tube sensor. The derailment signal is obtained through mechanical contact switches on the guide rail, and the derailment speed is converted through testing with a height tower and a camera. The data is recorded using a photosensitive recording oscilloscope and paper tape. The main shortcomings of this system are that static calibration of the sensor is required before each test. The signal lines that need to be reconnected during the test need to be manually measured and recorded. The entire test process is complex and time-consuming.
This article introduces a storage testing system for catapult testing, which simplifies the testing and data processing process, improves testing accuracy, and achieves ideal results while ensuring testing functionality. It also recommends the application of relevant sensors, system key technologies, and their implementation in this testing system
(1) Sensor selection
The sensor is related to the testing accuracy of the system. According to the testing requirements, this system mainly tests the acceleration motion equation of the seat on the guide rail after the launch of the catapult. The low-frequency signal acceleration curve is similar to the chamber pressure curve during artillery launch, but the action time is in seconds. To avoid the influence of mechanical vibration and electromagnetic interference, the sensor frequency band is selected from 0 to 30Hz.According to the peak acceleration of the ejection seat, the range of the acceleration sensor is selected as (± 10G; ± 25G; ± 50G; ± 100G), and the 839-50-3 acceleration sensor is specifically designed for this application. The position of the seat cushion on the dummy seat is recommended to use the 890 three-axis seat acceleration sensor in this system; The acceleration sensor for the dummy body is recommended in this testing system as 819-50-3 single axis acceleration sensors;It is recommended to use a D211-2000 seat belt displacement sensor for the pull-out test of the seat belt on the dummy. Due to the fact that the sensor needs to be ejected together with the seat, it must have a certain level of impact resistance to meet the above requirements, as well as a high overload capacity. In the system design, a piezoresistive sensor with good low-frequency performance, strong overload resistance, high reliability and accuracy for measurement is selected.
(2) Control circuit design
In the control circuit, the amplification factor of the signal amplification circuit is designed according to the sensitivity of the sensor and the input voltage range of the testing system. The filtering design is based on the testing signal requirements. In order to respond to low-frequency signals and resist high-frequency electromagnetic mechanical vibration interference, a digital filter is used in the design. The frequency band of the system is designed as low-pass filtering, and the upper limit cutoff frequency is selected as 40Hz.The signal triggering method adopts an internal triggering mode, which ensures the normal and timely triggering level design based on the vibration triggering signal caused by simulated ejection firing. The communication setting can be carried out through the data processing module before testing according to the testing range. If you do not want to develop and test this system yourself, it is recommended to use the IN-3062 portable network distributed cloud intelligent collection online data acquisition analyzer.
(3) Software design of data processing module
The design of data processing module is based on software as the core, and processing software has been developed using high-level language. It communicates with the storage testing module through computer serial port. The main functions include parameter setting, initialization setting, read back control, display control, calculation, storage, etc
(4) Power selection
In order to facilitate the acquisition and replacement of power supply during use, the storage testing module uses a 3-5 V power supply. In the design, two 1.5 No. 5 batteries are selected, and the circuit is transformed by the power chip to supply power to the sensor and testing system
Experimental testing
Before the experiment, the storage testing module is fastened to the ejected seat with screws, and the parameters are set and initialized as close as possible to the center of gravity of the seat through a communication interface. After launch, testing and data storage are carried out. Finally, the recorded data is transmitted to the computer data processing module through the communication interface for processing, display, and inspection.
In general fighter jets, there are two types of seat ejection devices, namely the loading and unloading seats, which are located in the driver's seat. When ejected, the seat flies upwards along the track and is located in the gunner's position. When ejected, the seat flies downwards along the track and is located in the gunner's position. The testing system designed in this study conducted separate loading and unloading tests on the ejection cylinder. The storage system recorded the acceleration data of the seat and counterweight from the moment the primer was fired to the moment they flew off the track, and the acceleration curve can be displayed.
The above figure shows the seat acceleration curve obtained from a certain upper bounce test. Based on the recorded data, the seat acceleration curve obtained from the lower bounce test can be analyzed through the data processing module to determine whether the tested parameters meet the design specifications of the seat ejection cylinderThe main factors that affect the testing accuracy of the system include the sampling frequency of the precision acquisition system for seat three-axis acceleration sensors, seat belt tension sensors, and seat belt displacement sensors. The calculation error in the off-track speed test of this system uses a piezoresistive high-precision sensor, which can meet the testing accuracy requirements after static and dynamic calibration. The sampling frequency of the testing system is, and the error caused by the measured acceleration process can be ignored. For the off-track speed test, due to the use of theoretical calculation methods, the off-track speed calculated through acceleration integration has errors, especially after the acceleration signal is low-pass filtered,The calculated derailment speed is lower than the actual value, which can cause unqualified products to be mistakenly detected as qualified during product inspection. After measuring the derailment speed, the deviation value was obtained. Through software correction in the data processing module, this problem was properly resolved. In addition, the sensors, signal processing circuits, and data memory of this testing system are highly integrated, which improves the stability and anti-interference ability of the system. After comparison with the original testing system, the testing function of this system can fully meet the inspection requirements, with higher testing accuracy and more accurate testing results.
conclusion
After experimental testing, the designed system can fully meet the testing requirements of the seat ejection cylinder, and can record the acceleration signal of the entire ejection process. The recorded acceleration adopts a 12 bit AD conversion, with high accuracy. After reading back, it is convenient to calculate and display the required test indicators. Currently, the system has been applied in the seat ejection test of a certain aircraft, achieving good experimental results and improving experimental efficiency. We highly recommend the following types of sensors and detailed explanations for their application in this system:
Senther 830&839 are specially designed for high-precision three-axis acceleration sensors on seat rails (main application models: 839-50-3; 839-20-3; 830-50-9; 830-20-9)
Senther 819- High precision single axis acceleration sensors with various displacement positions on the specially designed dummy (main application models: 819-50-3; 819-10-3)
Sensher 817- High precision single axis damping accelerometer with displacement on the body of a specially designed dummy (main application models: 817-50-3; 817-200-3)
Sensor D211-2000 Special Design Dummy Seat Belt Pullout Displacement Sensor
Sensor 890- Seat Static Three Axis Acceleration Speed Sensor
Sensor 790A - Seat Dynamic Three Axis Acceleration Sensor
For more application case sharing, please contact the professional technical service team of Senther Technology.
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