Flow Complexities of Slender Wing Rock

Abstract

IntroductionM ILITARY design trends toward the use of unmanned, nless aircraft 1 have renewed interest in the unsteady aerodynamics of slender wing rock. One important aspect of the problem of wing rock control is the potential impact of typical con gurational details on delta-wing aircraft, such as the presence of a centerbody. Early experimental results for a sharp-edged 80-deg delta wing indicated that breakdown of the leading-edgevortices played a role 2,3 ( Fig. 1). It could be shown that rather than being the cause of the wing rock problem, the breakdown phenomenon limited the growth of the limit-cycle amplitude. 4 By the consideration of the effect of the roll-induced sideslip on the effective leading-edge sweep of the windward (dipping) wing-half, an upper limit for the limit-cycle amplitude could be determined. 5,6 The measured start of wing rock (Fig. 1a) is in good agreement with the prediction 7 that, for zero bearing friction, loss of roll damping should occur at a¸20 deg (Fig. 2). Bearing friction caused the delay to a = 25 deg of the loss of roll damping in the test of a pure delta-wing model 3 (Fig. 1a). It will be shown that the earlier start of wing rock for the other model 3 was caused by the presence of a centerbody or fuselage.As even unmanned combat aircraft are likely to have a fuselage or centerbody of some kind, it is important to know that the effect of a centerbodyon delta-wingaerodynamicscan be large. 8 Experimental results for a 69.33-degdelta-wing-body con gurationdemonstrated that the centerbody promoted vortex breakdown. 9 This could be explained by the body-induced camber effect, 8,10 which according to experimental results for the effect of static camber, 11 would have promoted breakdown, in agreement with the experimental results. Figure 3 shows con gurational details of the models giving the results in Fig. 1. Whereas the Langley model 2 behaves essentially as a pure, sharp-edgeddelta wing, the other model 3 has a centerbody. Because of its bluntness, 12 it behaves as a cylindricalcenterbody, 9, 10 promoting vortex breakdown, thereby causing a reduction of the maximum wing rock amplitude. The earlier loss of roll damping, before the predictedvalue 7 a ¼ 20 deg (Fig. 2), could also have been caused by the presence of the centerbody.By limiting the wing area, the centerbody acts to increase the effective leading-edge sweep, thereby causing earlier loss of roll damping.The experimental results 13 in Fig. 4 show that when a pointed ogive-cylinder centerbody, similar to the one used in Ref. 9, is moved aft to start behind the wing apex, as in the case of the extensively tested 65-deg delta-wing-body con guration, 13 instead of promoting breakdown, the body delayed vortex breakdown to occur 30% or more aft of the measured position for a pure 65-deg deltawing. 14 It is described in Ref. 5 how this is the expected result when the pointed ogive-cylinder body is moved aft, as shown in Fig. 4, Presented as Paper 99-0141 at a) Measured wing rock amplitude 2;3 b) Flow visualization of vorte...

The investigation of lateral/heading characteristics and the influence of jet control at high attack angle

“…For the oscillations appearing on the wing-body configurations, early research state that the main cause to the asymmetric vortices appearing in the forebody. Wind-tunnel experimental data provided by Ericsson [3,4] showed that the wing also has a large effect on the wing oscillations at small and medium attack angles. Han [5] used numerical methods to investigate the rock characteristics of the wing-body assembly and obtained a more specific flow field structure than the experiments.…”