Tiltrotor Test Rig Aerodynamic Tares

The Tiltrotor Test Rig (TTR) is a NASA facility designed to test full-scale proprotors in the National Full-Scale Aerodynamics Facility (NFAC). The first wind-tunnel entry included measurements of aerodynamic loads (tares) on the spinner without a rotor. The TTR has an onboard balance for direct measurement of rotor loads, so these tares comprise only spinner loads. Spinner tares also affect shaft loads measured independently of the balance. The results show that in axial flow, spinner drag is a linear function of dynamic pressure as expected, but at other flow angles, spinner loads include substantial lift and drag. Furthermore, there is a pronounced Magnus effect when the spinner is sideways to the flow. There is a sharp change in aerodynamic load at 90-deg yaw angle, indicating separation. Equations were developed to characterize the spinner tares at any arbitrary combination of yaw angle and airspeed.