Control Surface and Wing Stability Problems

Abstract

SummaryThis paper seeks to draw from current research work on flutter and related problems results of general design significance; and, avoiding mathematics, endeavours to set these results out in relation to past and present problems.A preliminary section of the paper indicates the main stability and allied troubles concerned and draws attention to the general similarity between wings and tailplanes in relation to these troubles. The remainder of the paper is then devoted to a discussion of the problems involved in terms of wings and ailerons.For this purpose a “ stiffness diagram ” is constructed for a typical wing, indicating the relative stiffnesses, etc., required to prevent wing-aileron flutter, wing flutter, aileron reversal, and wing divergence. By means of this diagram the course of recent history in relation to wing-aileron flutter and aileron reversal is illustrated, and attention is then given to present and future tendencies and problems. The current tendency to employ wings of high density—arisingly largely from high wing loadings—is making wing flutter the problem of immediate importance, and ways of avoiding the provision of increased stiffness as usually adopted to prevent this trouble, as well as to prevent aileron reversal and wing divergence, are discussed.Appendices are given commenting on the variation of wing flutter speed with altitude and on the modern tendency to usa wings of low flexural stiffness.

The changing scene of structural airworthiness

“…The four aeroelastic problems which were recognised' 23 As we have seen, proper mass-balancing was recognised as the cure for the first of these ills. While increased stiffness, particularly torsional stiffness, was recognised as the main route by which the structural engineer could control the remaining three aeroelastic phenomena, even the earliest researchers looked for alternative routes.…”

“…A few years later Pugsley, having developed a stiffness criterion' 25 ' as a function of wing density, asked whether increasing wing densities would mean further increases in stiffness or whether one could find some practical means of cutting across the wing flutter, aileron reversal and wing divergence boundaries' 23 '.…”

The United Kingdom's contributions to the development of aeronautics. Part 3. The development of the streamlined monoplane (the 1920s-1 940s)

“…He also pointed out the importance of control circuit stiffness in his investigation of the non-linear characteristics of the popular Frise aileron' 189 ). Much of this work he reviewed' 193 ) in 1937, from which Fig. 68 has been adapted.…”

The Second Lanchester Memorial Lecture

“…There is an opportunity here for a clearing up: instead of using pV 2 or \pV 2 we can use pM 2 where \ is the ambient pressure 1 '", and the dependence on Macl number can then be absorbed into a single function This suggestion has also been made in America <53) . I such a change worthwhile?…”

“…Periodically, the Royal Aeronautical Society has published papers on aeroelasticity which have been in the nature of surveys of the problems of the day: for example, Pugsley's lecture of 1937 (2) , my own paper' 3 ' and lecture**' of 1946, and Broadbent's lecture of 1956 (5 '. At this point I would like to express my grateful appreciation to Mr. Broadbent for his help in the planning and writing of this lecture, especially the part dealing with the problems of the past decade: he has an intimate knowledge of this period, and my own slight acquaintance derives largely from contacts with him and his work.…”