Analytic and Experimental Verification of the NOTAR Circulation Control Tail Boom

This paper addresses the recent analytical modeling and whirl stand testing performed on the NOTAR (No Tail Rotor) demonstrator helicopter's circulation control tail boom. In initial flight tests, the demonstrator aircraft required flow control fences on the tail boom to achieve the desired circulation control performance. This work was performed to find a more fundamental solution than the fences. An initial analytical model describing the demonstrator's flow field was used to develop design solutions to the fences. After testing revealed the full extent of the flow interactions, the model was modified to provide a more complete representation of the flow field. The whirl stand tests showed that the flow coming off the fuselage interfered with the tail boom's efficiency and that the demonstrator's single, uniform slot was not optimum for all configurations tested. These results imply the solution to NOTAR demonstrator's tail boom inefficiency will be from design changes that eliminate fuselage/tail boom interference and that distribute blowing along the slot(s) to minimize longitudinal pressure gradients.