An approximate method of estimating the effect of elastic deformability of the aircraft structure on the manoeuvre point. Parts 1 and 2

Abstract

This report, which is presented in two parts, develops an approximate method of estimating the effect of structural deformability on the manoeuvre point of an aircraft. The introduction outlines the scope of the complete work in relation to the work of Lyon and Ripley (R. & M. 2331 and 2415). Part I opens with a detailed discussion of the structural deformability of wings, unswept and swept, and proceeds on the basis of certain aerodynamic and structural approximations to derive relatively simple formulae for the calculation of the shift of manoeuvre point due to elastic camber, elastic wash-out (wing torsion and bending, and the effect of fuselage interference) and the direct effect of wing bending (which changes moment arms) on pitching moment. A summary and discussion of some comparative calculations of the effect of elastic wash-out, using the present method and that proposed by Lyon (R. & M. 2331) are included. They demonstrate the dangerously large shifts of manoeuvre point which may arise from elastic wash-out with swept wings and show that while the present method is somewhat less accurate than that of Lyon, it has the important advantage of being far less laborious in application. Part I1 examines the effects of fuselage and tailplane deformability, and at the same time investigates the effect of wing deformability (including root-region deformability) on the fuselage and tailplane contributions to manoeuvring stability. Bending of the fuselage, torsion of the (unswept) tailplane and deformability of the tailplane attachment are the main fuselage and tailplane effects considered, and among the subsidiary effects examined is that of engine nacelles situated in the wing. A simple procedure for numerical calculation of the fuselage and tailplane contributions to manoeuvre-point shift is set out and illustrated by a worked example, which demonstrates how elastic attachments of wing and tailplane may be used to augment the effect of the tailplane in counteracting the destabilizing effect of wing and fuselage. A simple description of the method of analysis used in Part 11, together with typical resuIts obtained from it, is given in section 12.