A wind-tunnel investigation of the directional and longitudinal stability of the Javelin aircraft at transonic speeds, including comparison with flight test results

Abstract

Directional and longitudinal stability measurements have been made on a 1/72 scale model of the Javelin aircraft at Mach numbers up to 1.12 in R.A.E. Bedford, 3 ft Wind Tunnel. Observations were made of the flow over the fin and the wing by the oil-flow technique. The results show directional instability near sonic speed, as observed in flight, due to shock-induced separation on the fin; this appears to have been caused by the wing trailing-edge shock wave, strengthened by the flow fields of the fin and rear fuselage. A small change in the shape of the rear fuselage delayed the separation to a higher wing incidence and eliminated the instability. For the model with the tail-on, the curves of pitching moment against normal force had stable slopes except near zero lift at isolated Mach numbers. The stability decreases at high incidence at M = 0.7 and at moderate incidences around M = 0.93. Flight and tunnel test results were in good qualitative agreement. The significant effect of a small distortion of the fuselage shape at the tail (such as might be made to accommodate a supporting sting) on directional stability is of general importance from the point of view of wind-tunnel testing.