Low-speed wind-tunnel tests on the de havilland sea venom with blowing over the flaps

Abstract

This report contains the results of low-speed tunnel tests of longitudinal stability on a modified Sea Venom Mk. 21 fitted with blowing over the flaps. At each flap angle, a range of values of the sectional momentum coefficient was tested. As a typical example, the increase in trimmed CL at constant incidence resulting from blowing at flaps 60 deg was about 0.45, the increase in CLMAX being somewhat smaller. The equivalent reduction in approach speed of 10 to 15 kt predicted from the tunnel results was later achieved in flight. The tunnel results suggested a beneficial reduction in minimum-drag speed due to blowing, particularly at large flap angles. Trim changes were large, amounting to about 8 deg on the all-movable tail at flaps 60 deg. A comparison is made between estimated and measured effects of blowing. It is shown that, whilst the lift and pitching-moment increments resulting from flap blowing can be estimated fairly closely, the drag increments at large flap angles are much larger than would be expected, The additional drag tends to decrease the minimum-drag speed and increase the minimum drag, and may affect the take-off and landing performance appreciably. The effect will be unfavourable in the first case and favourable in the second. A flight/tunnel comparison is included of the lift increments resulting from blowing. At flaps 40 deg, agreement is good, but at larger flap angles, the lift increments measured in flight were less than those measured on the model. Possible reasons f0r this are discussed. There is a favourable Reynolds-number effect on CLMAX which is found to be somewhat larger for the blown flap than for the unblown flap.