F-22 Actuator Dynamic Stiffness (Impedance) Testing

Accurate understanding of flight control hydraulic actuator dynamic stiffness is critically important to the aeroelastic certification of fighter aircraft. A test program was conducted during the F-22 development phase to ensure that analysis models were accurately predicating the dynamic stiffness of the actuators for both hydraulically powered and hydraulically failed conditions. This paper presents the test approach, constraints, test methods, and test data analysis methods. Special emphasis is given to instrumentation design and accuracy requirements as this was considered critical to conducting a successful test.