Effects of longitudinal elastic camber on slender aircraft in steady symmetrical flight Parts I and II

Abstract

PART I Estimation of the Effect of Longitudinal Elastic Camber on Trim and Manoeuvrability of Slender Aircraft. An approximate method of estimating the effect of aeroelasticity on the longitudinal trim and quasi-steady manoeuvrability of slender aircraft has been developed. It is assumed that, structurally, the aircraft behaves as a 'free-free' beam, subject only to longitudinal bending, and that the total chordwise aerodynamic loading (including that due to elastic camber) varies linearly with local angle of attack, and is thus calculable by superposition of a number of 'elementary' distributions. It is then possible to set up the differential equation for the deflected beam, and by solving it on a digital computer, in conjunction with the equations of overall equilibrium, obtain the distributions of elastic camber, the angles of attack of the centreline chord and the elevon angles appropriate to the aircraft in trimmed level flight and in the steady pull-up manoeuvre. The theory is developed in detail for the cases where the loading due to elastic camber is assumed to be in accordance with slender-wing theory and piston theory respectively. The practicability of the method has been demonstrated by application (using slender-wing theory) to a possible design for a supersonic (M = 2.2) transport aircraft, and from the calculations, some tentative conclusions have been drawn regarding the likely order of the effects for such an aircraft. PART II A Further Investigation of the Effects of Longitudinal Elastic Camber on Slender Aircraft in Steady Symmetrical Flight Including Estimates of the Effect on Shear Forces and Bending Moments. The method developed in Part I for the estimation of the effect of longitudinal elastic camber on trim and manoeuvrability of slender aircraft has been used for further calculations relating to the design for a supersonic (M = 2.2) transport aircraft, which was studied in that Part. Some of the earlier calculations have been repeated using piston theory instead of slender-wing theory for the estimation of the incremental loading due to elastic camber. In addition, estimates have been made of the effect of deformations on the longitudinal distributions of shear force and bending moment in quasi-steady symmetric manoeuvres. The results have been used to demonstrate the importance of allowing for aeroelastic effects when computing loading actions on slender aircraft, and to draw attention to the need for a reliable method of specifying the loading on such aircraft due to arbitrary distributions of elastic warp, superposed on known initial incidence distributions.