Dynamic ground effect for a cranked arrow wing airplane

CDCLFlight-determined ground effect characteristics for anF-16XL airplane are presented and correlated with wind Cmtunnel predictions and similar flight results from otheraircraft. Maneuvers were conducted at a variety ofCxflightpath angles. Conventional ground effect flight testmethods were used, with the exception that spacepositioning data were obtained using the differential C zglobal positioning system (DGPS). Accuracy of theDGPS was similar to that of optical tracking methods, DGPSbut it was operationally more attractive. The dynamicflight-determined lift and drag coefficient increments FSwere measurably lower than steady-state wind-tunnel GPSpredictions. This relationship is consistent with theresults of other aircraft for which similar data are havailable. Trends in the flight measured lift incrementscaused by ground effect as a function of flightpath anglewere evident but weakly correlated. An engineeringmodel of dynamic ground effect was developed based onlinear aerodynamic theory and super-positioning offlows. This model was applied to the F-16XL data setand to previously published data for an F-15 airplane. Inboth cases, the model provided an engineering estimateof the ratio between the steady-state and dynamicdata sets.