Two floating head skin friction gages have been designed and tested to directly measure the skin friction coefficient for the undefined flow in a SCRAM-jet engine. The skin friction gage designs contain a floating head that is supported by ball bearings which allow it to move in any horizontal direction and restrain it from any vertical motion. The shearing force caused by the supersonic flow deflects the floating head parallel to the flow direction. Strain gages mounted across a small gap between the bottom of the floating element and the bottom clamp provide the restoring force on the floating head. These strain gages also measure the floating head deflection caused by the flow shearing force. The steel model design was built and tested to determine the feasibility of the design concept. The results from the supersonic wind tunnel at Mach 2.4 were reasonable but the steel model was unable to correctly respond to the short-duration flow of the shock tunnel. A skin friction gage made of a machinable ceramic called Macor was then designed to increase the resonant natural frequency (3600 Hz) and the insulating properties of the gage. Consequently, the Macor model floating head design is capable of measuring the skin friction coefficient in short duration, high enthalpy supersonic flows as well as long duration supersonic flows. The Macor model design yielded skin friction coefficient values near the expected value of 0.0014 when placed in a supersonic tunnel at both Mach 2.4 and Mach 3.0 and in a Mach 3.0 shock tunnel. / Master of Science

The design of skin friction gages has been explored analytically and experimentally for measuring skin friction in high-speed, short-duration flow. Several gage designs were considered. One promising gage design used a floating element, while another was microfabricated using sputtering techniques. All of the gages were physically modeled to determine the output caused by Mach 2 unheated flow. Frequency response analysis was also performed on the floating element and sputtered design to determine their ability to make measurements in the millisecond time range. Temperature and normal pressure effects were a source of measurement error, and techniques were developed for minimizing the error due these effects. Tests were made in Mach 2 flow and the results of these tests are discussed. Recommendations are provided as to how the gages can be improved for further testing. / Master of Science