NASA-TN-D-7411

Abstract

The stability and control characteristics of a four-engine turbofan STOL transport model having an externally blown jet flap have been investigated by means of the flying-model technique in the Langley full-scale tunnel. The flight characteristics of the model were investigated under conditions of symmetric and asymmetric (one engine inoperative) thrust at lift coefficients up to 9.5 and 5.5, respectively. Static characteristics were studied by conventional power-on force tests over the flight-test angle-of-attack range including the stall. In addition to these tests, dynamic longitudinal and lateral stability calculations were performed for comparison with the flight-test results and for use in correlating the model results with STOL handling-qualities criteria. <br>The results of the investigation showed that in either the four-engine condition, or with one engine inoperative, longitudinal motions of the model were heavily damped over the test angle-of-attack range. The model was easy to fly up to a lift coefficient of about 4, but the longitudinal control power became marginal at higher lift coefficients because of reduced free-stream dynamic pressure. Laterally, the model was difficult to fly because of a lightly damped Dutch roll oscillation which was easily excited by the use of rudder control. Adequate damping of the oscillation could be achieved, however, by the addition of artificial stabilization about the roll and yaw axes. With one outboard engine inoperative, lateral trim could be restored by use of differential flap deflection, asymmetric leading-edge blowing, and rudder deflection. In trimmed, three-engine flight, the stability and controllability of the model were not noticeably different from what they had been during four-engine operation. The results of dynamic longitudinal and lateral stability calculations were found to be in good agreement with the flying-model result.