| High maneuverability and stealth are important features for the new generation aircraft. In order to reduce the flight resistance and radar reflection area, the interior loading pattern of the payload has been adopted generally for the new generation aircraft. When released, the door opens quickly, and the payload is launched at a speed and attitude, which is separated from the aircraft, and then the door closes. In the state of ultra-sonic flight, when the door opens quickly or at a certain open angle, the flow field is very complex, and the airflow near the vicinity of the leading edge of the cavity will produce high-intensity pressure oscillations, and then the oscillations would be counterproductive on the door, so complex multi-variable shock loads have effect on the door. Therefore, before finalize the design of the aircraft door structure, the wind tunnel test is required, through carrying out the airloads measurement technology research in the high speed motion state, and analyzing the variation rule of the dynamic airloads, it is significant for the door structure design and safety payload launch.In this paper, the forces of door which are located in the high-speed flow field have been analyzed, and according to the principle force and moment equivalence translation, the shock loads measurement is equivalent to the three forces and three moments measurement. For the purpose of the measurement of door shock loads in fast motion, piezoelectric quartz sensors are used as force-sensitive elements for the force balance, and the structure and arrangement of the sensors are studied, and four supports type based on triaxial piezoelectric sensors is proposed to measure the multi-component dynamic airloads, and a six-component force measurement model of the piezoelectric balance is established. The calibration technology of the piezoelectric balance has been studied, and static calibration process is optimized, which the effect of piezoelectric sensor charge drift on measurement results is reduced, and static performance of the piezoelectric balance is improved.Currently, by the limit of conditions in wind tunnel test, full-size aircraft door airloads measurement can not be carried out, and the usual approach is based on similar criteria, which uses a certain scale aircraft door model to conduct aerodynamic force in wind tunnel test. Aiming at this demand, a simulated door open motion device is developed. The device consists mainly of the drive mechanism, transmission mechanism, actuators and measuring mechanism. Rotation angle of the door with full closed-loop control method is adopted to improve the accuracy of the position of the door, and intermediate transmission mechanism uses a fan anti-backlash gear structure to ensure the door motion smoothly at the high speed flow field and meet the area of attack requirement. The finite element analysis is used to analyze the structure of the device, and the orders of main vibration mode and natural frequency are obtained. Therefore, the door open motion device could meet the requirements of the wind tunnel test.The dynamic characteristics of the test system have been studied. Exciting way is adopted to apply the variable frequency and amplitude shock loads to the balance, and the dynamic calibration is conducted to study the performance of measuring dynamic loads. Pulsed excitation method is used, and the balance output signals have been transformed by FFT, and then the natural frequency and the frequency response curve of the scale are obtained. The frequency is higher than the actual in the wind tunnel test. The least squares method is adopted to get minimum mean square error between test results and the theoretical model as the criteria of modal parameter identification. The test system theoretical transfer function model is established, and dynamic performance of test system domain has been obtained. Combined with the test system features consisting of multiple second-order systems, and based on the test system transfer function, the acceleration mathematical compensation model based on time series has been proposed. The test system acceleration curve under ideal unit step response is obtained. The experimental results show that the proposed acceleration compensation method can effectively compensate airloads shock oscillations caused by acceleration in the short duration wind tunnel test. The system dynamic test accuracy has been improved.When the door opens quickly, the door and its transmission components have certain inertia. Therefore, the inertial force has aliasing in the balance measuring results. In this paper, the calculation method of the inertia for each component has been studied, and the mathematical model of separation of door inertial force with high rotational speed is established. The normal force and side force variations compensation models caused by the changes of door centroid position have been established. With the airloads frequency characteristic in wind tunnel test, a dynamic six-component force signal processing method is proposed on the basis of combined of multi-resolution analysis Wavelet threshold processing and HHT. This method can effectively solve the nonlinear and non-stationary signal processing problems.The wind tunnel test results show that the proposed measurement method can be effectively used to measure multi-component dynamic airloads when the door opens. The first-order natural frequency of the device is161.13Hz. The blockage of wind tunnel test model is0.99%, the door movement angle error is within0.05°, and the shortest open/close time between0°and110°is55ms. The maximum measurement non-linearity error and repeatability of the piezoelectric balance are respectively0.06%and0.19%, and the interference error is less than1.94%, which meet hypersonic aircraft door movement and its multi-component airloads measurement requirements. Therefore, through carrying out the door dynamic airloads measurement technology research in this article, it is very significant to the new generation aircraft door design, material selection, investigate sound generations induced by self-sustained oscillations, internal influencing correlation of flow field as well as the solution of related airloads problems. |
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