Thrust Reverser Effects on Fighter Aircraft Aerodynamics

Wind tunnel studies were conducted using a 0.025 scale model of an F-18 type of configuration with thrust reversers in the Northrop 21X 30 in. low-speed wind tunnel at conditions representative of the aircraft on approach. A feature of these tests was a systematic buildup of reverser jets and tail surface components in order to identify and understand the major aerodynamic forces that the reversers generate on the tail surfaces. It is shown that the upper jets produce a blockage between the twin vertical tails and that this plays a key role in the reverserinduced effects. In sideslip or with the rudders deflected, this blockage is asymmetric and results in increases in directional stability and rudder effectiveness. In pitch, the blockage produces a download on the vertical tails but the resulting upwash on the horizontals greatly reduces the incremental pitching moment on the aircraft. The reverser jets induce a strong entrainment flow on the horizontal tails, which amplifies the tail load, resulting in either a pitch-up or a pitch-down, depending on the tail setting.