Movable derivative is the derivative of the aerodynamic coefficients and the aerodynamic moment coefficient of the aircraft the aircraft dimensionless rotational angular velocity or rate of change of attitude angle, is to develop the control system design of the aircraft and dynamic quality analysis indispensable original aerodynamic parameters, it is related to the flight of the aircraft quality, autopilot control system designed to control law and an important aspect of flight safety. For a long time, at home and abroad aerodynamic research institutions have been committed to dynamic derivatives wind tunnel test technology research and numerical simulation analysis of the aircraft, and for all types of aerospace offers a number of basic test data developed aircraft.
Necessity measured dynamic derivatives
Expansion of modern advanced fighter aircraft and missile flight envelope, including maneuvers at high angles of attack and sideslip with the situation, in recent years makes it dynamic stability studies more seriously. Non-linear flow phenomena in such flight conditions have dynamic stability characteristics of the aircraft and missiles have a strong impact. Under this condition to predict an aircraft dynamic characteristics and design of the flight control systems, as well as aircraft stall / spin analysis, it is necessary to know the number of dynamic stability (dynamic derivative) is turned. Further, high angle of attack of the aircraft to aircraft dynamic stability Derivatives sensitivity analysis shows the side cross-derivative produced by longitudinal movement, that is, cross-coupling derivative, a significant effect on the stability of the aircraft. This indicates that the measurement comprises damping derivative , cross derivative of the necessity of the dynamic guide, including a cross-coupled derivative.
Test Introduction
Exciting means and a power control system
This dynamic derivatives apparatus main test system is the excitation device. Excitation means and the excitation means partial longitudinal lateral excitation device two. By changing the way of support, or switch to a different struts, in the form of motion or change the excitation means, the excitation means can be realized longitudinal pitching vibration model and heave vibration; transverse rolling vibration exciting means may be implemented model, yaw and translational vibration . Two devices are in common by the DC motor driving a gear reducer , the output shaft of the eccentric reducer associated slider mechanism, the slider mechanism by the eccentric rotation into linear motion is transmitted to the vertical, and then through different support means or different means are implemented in the form of five kinds of vibration model. Eccentric means from the excitation of the eccentric slide stepless adjustment, by varying the eccentricity by changing the amplitude. The entire apparatus is mounted on the tunnel under the turntable, the turntable center coincides with the center of balance. By turntable strut angle and rotation angle variation may be combined with the angle of attack and sideslip angle .
Balance and Test System
To meet the cross-derivative, measuring the number of cross-coupled transduction, using a six-component balance rod. Data acquisition and processing system consists NEFF620 / 600 data acquisition means, V AX- Ⅱ microcomputer and a microcomputer composed of PC, while the balance of the six channel signal and a displacement signal channel acquisition, processing, real-time calculation may be dispatched derivative.
Resolution NEFF620 / 600 data acquisition device 16 is, having a programmable gain and sample and hold functions, the maximum sampling rate of 10 million times / second. Since the data processing effective signal balance signal is very weak, and are often drowned in the noise, through analysis and simulation test data analysis authentication, select the optimal separation of the small-signal detection, effectively separate real aerodynamic data . Full digital acquisition and processing method than the original analog instrument can save 70% of the operating time of the wind tunnel, and without human intervention in the testing process, to avoid the errors caused by manual operation and physical strength, energy consumption, improve the automation the extent and accuracy of the test.
Test Model
As a vibration test system, the movable derivative measurement should ensure the operating frequency away from the scale model of the system natural frequency . This requires balance model of the system natural frequency is higher. To achieve this condition, one is to increase the stiffness of the balance, the second is to reduce the weight of the model. In the prior art the level of the test conditions, there can be greatly improved balance of stiffness, weight and so reduce the model inertia are the main means of improving the natural frequency of the system. Movable guide test model is generally used with metal or with metal skeleton structure of carbon fiber housing FRP housing framework structure, it will ensure a sufficient stiffness and strength, but also reduce the weight of the model and the moment of inertia .