Gurney Flaps on Slender and Nonslender Delta Wings

Abstract

A parametric low-speed wind-tunnel study has been undertaken of the effects of Gurney flap height on the aerodynamic characteristics of delta wings with sweep angles of 40, 60, and 70 . Flap effects on lift and drag are consistent with previous two-dimensional data when wing geometry is accounted for by using the change in zero-lift incidence rather than lift and using the relative flap area rather than flap height. Flap deployment primarily affects the attached-flow potential lift on delta wings, with vortex lift being almost unchanged. Induced-drag factors are considerably reduced as flap height is increased, but this is due to the use of flat-plate models with near-zero leadingedge suction. For control applications, pitch/lift ratios are similar to those for delta wings with conventional trailingedge flaps, but the trim-drag penalties are much higher. An aft shift in loading associated with Gurney flap deployment leads to large aft movements of the aerodynamic center, which significantly reduces control capability.pitching-moment coefficient at zero lift C N = normal force coefficient, N=qS C NP = potential flow component of normal force C NV = vortex lift component of normal force D = drag h = projected flap height (measured from lower surface) K P = potential lift factor, C L K V = vortex lift factor k = induced-drag factor, C D C D min AR=C 2 L L = lift q = dynamic pressure, 1 2 V 2 q = lift increase factor on flap height S = wing area S f = flap frontal area, hb t = wing thickness = angle of attack 0L = zero-lift angle of attack 0P = zero-lift angle of attack for potential lift component 0V = zero-lift angle of attack for vortex lift component = leading-edge sweep angle

Aerodynamic Load Alleviation Using Minitabs

“…The fit's quality is improved slightly by the introduction of a variable n parameter, increasing from 0.5 to 0.63. This increase is consistent with the conclusions of Greenwell [19]. In addition, the inviscid theory of Woods [15] dramatically overpredicts the change in lift, with a q factor of 3.32 opposed to 2.27 for the theory of Liu & Montefort [14] and poorly fits the data with R 2 = 0.16.…”

“…The square-root relationship has been compared to experiments [16][17][18] with a good agreement. In addition, linear empirical relationships based on the increase in circulation have been developed [19], however, these compare less favorably to the literature as a whole. Experiments [20] indicate that placement upstream of the trailing edge (xf/c ≥ 0.90) yields a smaller change in lift than placement directly at the trailing edge.…”

An Experimental Study of Mini-Tabs for Aerodynamic Load Control

“…This suggests that there is some effect of the type of airfoil. When n is allowed to vary, an improved fit is observed in both cases for an increase to n = 0.5997 and 0.6345 for all and NACA0012 profiles respectively This indicates a higher lift augmentation is observed at higher mini-tab heights than predicted by thin airfoil theory, consistent with the work of Greenwell 30 .…”

“…Where q is a parameter determined dependent on Reynolds number and airfoil profile and n is an exponent found by Liu & Montefort to be 0.5, however later work by Greenwell 30 suggests a value close to 0.7.…”