Joseph L. Johnson, Jr.
A wind tunnel investigation has been carried out to determine the static longitudinal stability and trim characteristics of a sweptback-wing jet-transport model equipped with an external-flow jet-augmented flap. The investigation included tests of the model to determine the effects of wing position, vertical position of the horizontal tail, and size of the horizontal tail. The results of the investigation indicated that static longitudinal stability and trim could be achieved up to a lift coefficient of about 6 with a horizontal tail having an area of about 25 percent of the wing area. In order to achieve this result, it was necessary to locate the horizontal tail well above the chord plane of the wing and to incorporate both variable incidence and an elevator. For the flap-down, power-off condition, the downwash factor was found to be relatively large (0.8 to 0.9). The downwash factor decreased with increasing momentum coefficient, the greatest reduction occurring for the low tail position. In order to obtain a given amount of stability, larger tail areas were therefore required for the low tail position than for the high tail position. Results of calculations comparing the relative merits of various trim devices for use on airplanes equipped with jet-augmented flaps indicated that a fixed canard surface utilizing jet augmentation would provide longitudinal trim and stability at a given lift coefficient for less overall jet thrust than a conventional tail, a free-floating canard surface, or a trim-jet arrangement.
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