A Hexapod-Based Thrust Balance

The measurement of forces and moments produced by nozzles is needed for a wide range of applications. Typical thrust balances used for this purpose are three-axis translation stages equipped with load cells to measure forces along the three translation directions. Modern nozzles with thrust vectoring can be well served by thrust balances that measure moments as well as forces requiring additional complexity in the design. Sophisticated balances can be quite costly and difficult to integrate with high pressure nozzle supply lines. To address these shortcomings, a hexapod-based balance is proposed here. A hexapod is a six legged device often used for accurate micro-positioning and vibration damping (see, for example, McInroy and Hamman). Hexapods were originally investigated in the 60s for use in applications such as flight simulations. Here, the traditional hexapod design is adapted to a force/moment measurement device by replacing the typical actuators with load cells. The goal of the present work is to demonstrate the feasibility of such a device and demonstrate its use on a thrust stand. The theory associated with the thrust balance is first discussed and the hardware implementation is then presented. The progress to date on implementing this balance in a jet facility is briefly discussed. The lower inertia, tunability, and integration with the thrust stand all indicate that this is a design that might be considered in new thrust stands being developed.