INTRODUCTION This Item gives a method for the prediction of the drag due to lift for swept wings of straight taper with camber and twist@ alone or in combination with a body. It may be applied to wings with mild cranks through the use of an 'equivalent' straight-tapered wing@ a geometric construction that is described in Addendum A of Item No. 76003 (Derivation 3). The angle of attack range includes the regime where there may be a full or partial loss of leading-edge suction and the formation of leading-edge vortex flow@ but widespread flow separation over the main part of the wing is not addressed. The method applies for subsonic flow and when boundary-layer transition occurs near the wing leading edge. Item No. 95025 (Derivation 10) contains a method for the prediction of drag due to lift for planar wings. The method invokes the concept of attainable leading-edge suction to cater for the effects of wing section geometry (Derivations 17 and 18). For wings of low aspect ratio the lift associated with the leading-edge vortex is estimated by extended forms of the Polhamus analogy (Derivations 13@ 15 and 16). Derivations 20 to 22 show that the calculation of attainable suction for non-planar wings may be made by using the same equations that apply to planar wings provided that a reliable estimate can be made of the theoretical leading-edge suction distribution. They demonstrate that this can be done by using the theoretical distribution for a planar wing of identical planform in conjunction with a corrected local angle of attack. It is also necessary in the calculation of vortex lift to allow for the inboard migration of the leading-edge vortex as it travels back over the wing. It is not sufficient to assume that all the vortex lift acts at the leading edge@ and the local surface slope is of consequence as it determines the direction of the force. The method of Item No. 95025 has been extended through the incorporation of both these concepts although the detailed calculation of the corrected angle of attack is quite different. The prediction of the inboard migration rate of the leading-edge vortex is based on the work of Derivation 19@ the simplest of the published options available. The method is unsuited to hand calculations and has been programmed as ESDUpac A9625. In Derivation 24 the method for estimating attainable suction was improved over the earlier versions in Derivations 17@ 18 and 21. The revised set of required relationships is set out in Appendix A@ with some discussion. These have all been applied in the programmed method. Full details of the development of the method are not given because the basic philosophy of the technique remains as summarised in Section 3.2 of Item No. 95025. Moreover@ Derivation 24 provides a fully-comprehensive description of the development of the whole method and does not simply confine itself to the improvements made. It is therefore an ideal references for users who wish to know more of the intricacies involved. The overall model for a wing is detailed in Section 3. Section 4 indicates a simple extension to include wing-body configurations. Section 5 discusses accuracy and applicability. Section 6 lists the Derivation and References and Section 7 describes the input and output for the programmed version of the method.
ESDU 96025 A-1999 history
1999ESDU 96025 A-1999 DRAG DUE TO LIFT FOR NON-PLANAR SWEPT WINGS UP TO HIGH ANGLE OF ATTACK AT SUBSONIC SPEEDS