Propulsion-airframe interactions predictability

An illustration of the possible magnitude of the transonic performance prediction problem is shown. These results derived from a careful and systematic set of tests run on a jet effects model, an aerodynamic and force model, and a pressure model, evaluated test techniques and wind tunnel effects. The results were then carefully compared with flight test data where significant discrepancies in zero-lift drag were observed. A vigorous review of the test techniques identified a number of potential error sources. Some of these were thought to be aircraft roughness and protuberances, tunnel anomalies, sting/model support corrections, and hot gas effects. In addition, there were questions on model metric splitline location and magnitude of corrections for scale and Reynolds number. Flight test inlet/engine characteristics were thought to differ, also, from those of the calibration settings in the ground facilities.