Abstract: A dynamic load fixture (DLF) applies a torsion load to a unit under test (UUT) to achieve the demanding aerodynamic load exposures encountered by a control actuation system (CAS) in flight. Instead of fixing the end of the torsion bar, the DLF controls the application of torque to the torsion bar, hence the UUT via a DLF motor. The dynamic load can be independent of the angular rotation of the UUT, which allows the DLF to more effectively reproduce desired acceptance tests such as torque-at-rate and nonlinear loads. Furthermore, application of the loads through a torsion bar allows the system the compliance needed to generate precise loads while allowing for the flexibility of changing torsion bars to test a wide variety of UUT on one test platform. To achieve the demanding aerodynamic load exposures encountered by a CAS in flight, the controller must be able to respond both very fast and very precisely.

Abstract: A dynamic load fixture (DLF) for testing a unit under test (UUT) includes a lateral load system that applies a time-varying lateral load profile to the UUT drive shaft and an encoder that measures its angular rotation. An isolation stage suitably constrains the encoder from rotating about the axis while allowing it to move in other directions in which the application of the lateral force induces motion. The lateral load system includes a load bearing around the drive shaft, an actuator that applies a lateral force to the load bearing, a force sensor for measuring the applied lateral force, and a lateral controller for adjusting a command signal to the actuator to implement a lateral load profile. The DLF may also include a torsion load system that applies a time-varying torsion load profile to the drive shaft.