A concept employing tangential blowing was investigated experimentally as a possible means for mitigating buffet response of fighter aircraft empennage. Wind tunnel tests of a 4.7 % scale model of the F-15 Fighter were run in the Subsonic Aerodynamics Research Laboratory (SARL), WPAFB, OW. Tangential blowing was introduced from three points: (a) the nest, (b) the wing root leading edge, and (c) the gun bump, using symmetric blowing from both sides of the model. Individual blowing from each of the three locations was used, as were all combinations, and results were compared to baseline data without blowing. The model was equipped with one flexible tail and one rigid tail, and instrumented so that oscillatory pressures could be measured on both tails, and vibratory root bending and torsion moments and tip acceleration on the flexible tail. Angles of attack (AOA) from 0 to 32 degrees, and yaw angles of-4, 0, +4 degrees were investigated. Two dynamic pressures (Q) were employed 30 and 56 psf, both to check on data scaling and to assess the blowing effectivity at two Q's. Generally, an influence of blowing was seen in the response and the pressures, but it is difficult to cite complete general trends in a simple statement. Most cases showed some reduction in response from blowing, though the broadband and narrowband results differed as to the degree and trend, especially bending response as compared to torsion, and especially depending on the combination of AOA and yaw angle considered. In some cases, blowing actually increased response slightly. The wing blowing position was the most effective, the gun position was the next most effective, while the nose was the least effective. This type of tangential blowing appears to reflect a Coanda effect, since the blowing was injected well upstream of the empennage, but closely followed the model surfaces until reaching the tails. The results suggest further investigation and application is merited. This work was sponsored by the Air Force Research Laboratory (AFRL) under their Unsteady Aerodynamics Integrated product Team (IPT) effort. The results of the tests, data acquisition, data reduction, and the evaluation of the effectivity of the blowing are detailed in a three volume Report, [1]-[3]. This paper is a brief summary of that work, and extends a earlier paper, [4] which gave a status report of work through Fall 1997. A separate effort under this IPT employed pizeoelectric actuators and modern control methods as another means for mitigating buffet response on the empennage of this model.
