This 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.

Transport aviation is expanding rapidly in America both because of improved business conditions and the excellent record of the transport companies. The new aeroplanes being laid down, both land transports and boats are, on the average, twice the size of their immediate predecessors measured in terms of gross weight. Never before in the history of our industry has there been such a large increase in size in such a short period (Fig. 1). Coupled with the demand for larger aeroplanes is the requirement for decidedly higher cruising speeds. To meet these demands the total thrust horse-power per aeroplane has been materially increased. Operating costs are becoming more and more important due to the competition among air lines, as well as between them and other forms of transportation. The engineer is consequently forced to give serious consideration to utilising the power available in the most efficient manner, as well as to reducing maintenance costs.

Before the publication of the results of my original work connected with experimental researches in the Laboratory of the Polytechnical Institute of Warsaw (where I had the help of Prof. Huber and the collaboration of Mr. Kurowski and Mr. Maksymowicz), I want to give here some reproduction of the paper of Mr. W. F. Kisielew in “ Technica Vozdushnogo Flota,” No. 1, 1936, on the design of multispar wings. The results obtained here are very different from those obtained in the above article.

The methods of calculation of the stresses are well-known for monospar and two-spar cantilever wings (compare series of articles in the Reports of I.B.T.L.— Institute of Research for Aeronautics in Warsaw), but present-day methods of construction require more and more attention to be paid to multispar wings as described in this paper.