Accounting for laminar run and trip drag in supersonic cruise performance testing

Recent experimental assessment of cruise performance for a supersonic transport has led to re- evaluation of some time-honored techniques for trip drag correction. Two wind tunnel tests were conducted on a wing/body configuration. Results were obtained at Mach 2.4 and Reynolds number 6.4 million. This paper presents a method for determining certain corrections to the drag near the cruise angle of attack. These account for the trip drag associated with attempts to induce boundary-layer transition and for the effect of any laminar flow which persists on the model despite these efforts. Extensive flow visualization using a subliming chemical revealed that the boundary-layer trip was not consistently effective. Part of the upper surface exhibited delayed transition for even the largest trip heights tested. Laminar run corrections based on measured transition locations were computed using flat- plate skin friction formulae. Once corrected for laminar run, the drag was constant for small trip heights before linearly increasing with trip height. Therefore, a trip drag correction is only required for those trip heights beyond the drag plateau. We conclude that correction for laminar run is essential, and must precede evaluation of trip drag. Neither correction is negligible at the level of accuracy desired.