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.
