Development Of Five Components Stick-piezoelectric Wind Tunnel Balance

High mobility, reliability and accuracy are important characteristics of the new generation driving force aircraft. When running with high speed flow field in the atmosphere, the surrounding unsteady aerodynamic load is directly related with the aircraft’s reliability and accuracy. The wind tunnel test is necessary operated before its practical application, but design space of wind tunnel balance (core measurement equipment) very limited, which is restricted by test condition and the measurement requirements cannot be meted by the traditional composite piezoelectric balance. Therefore, by conducting bar type piezoelectric balance aerodynamic load in high speed flow field measurement technology research, the reasonable design and production of piezoelectric balance applying specific space is implemented, which has important significance in aircraft’s precise measurement of aerodynamic load and practical application.In this paper, force analysis of the aircraft model is done and aerodynamic load of wind tunnel balance is obtained. In the aspect of force and moment measurement in specific space, based on anisotropic elastic theory and anisotropic elasticity theory, the nonlinear polarization field law under multi-dimensional forces is acquired. The surface piezoelectric field equations between multidimensional forces and coupling induced charge are derived to output charge by the way of subdivision surface domain. Meanwhile, by using the piezoelectric effect models of ANSYS, simulation analysis of the quartz wafer under multidimensional forces is completed, obtaining the distribution of electric potential and electric field. Then the balance’s measuring principle is ultimately acquired.To ensure efficient measurement of five-dimensional aerodynamic load, the overall structural design of piezoelectric balance, including the combination of piezoelectric crystal group (core measuring element), is very important. The balance is mainly composed of combined piezoelectric crystal group, preload block, heat insulation, crystal group support platform and shielding, etc. According to the specification standard, the taper of balance front-end and after-end is respectively 1:5 and 1:10; the heat insulation is placed on both sides of crystal group to reduce temperature’s influence; crystal group support platform is designed to fix crystal group location and the reasonable placement of signal wire; in order to reduce charge drift, the outside of crystal group is covered with shielding to guarantee measurement accuracy in high speed flow field.After design of piezoelectric balance, careful assembly between the piezoelectric element and other parts is significant to reduce each component’s interference. From single chip to the whole combination process of crystal, the production of crystal group is not a simple wafer superposition, but sensitivity and parallel precision is as high as possible by parallelism’s inspection and correction in structured process of crystal group. What’s more, it has actually a complex process, such as the cutting precision of crystal, the choice of electrode material and shape, the using of chip binder and agglutination process, etc.The static and dynamic characteristics of five-axis force beam piezoelectric balance are researched. Firstly, by using the step-by-step loading method, the performance of the beam piezoelectric balance under different static forces is tested, obtaining the relevant static performance indexes, such as linearity, repeatability and accuracy. Then, in order to acquire the following performance to the output signal of the balance, the exciter test with the variable vibration frequency is done, by using the exciter to apply variable-frequency exciting force on the balance, the relationship between the force input and electrical signal output is built. Finally, the temperature drift experiment is completed to check the balance’s sensitivity to temperature.The results of the performance experiment show that the measurement method with the five-axis force beam piezoelectric balance can realize the measurement of five components of dynamic force in the separation phase of aircraft. The maximum linearity, repeatability and accuracy of the piezoelectric balance are 1.28%,1.53% and 4.8% respectively, meeting the measurement requirements of dynamic force in hypersonic flow field. The five-axis force beam piezoelectric balance measuring technique presented in the paper can not only provide a theoretical foundation for the development of chipset which can measure the shear force and torque, and small-size multidimensional piezoelectric measurement system, also has a great research significance for structure optimization design and the performance enhancement of the new generation aircraft.