The subject of tail buffeting first came into prominence in this country early in 1931 when the Accidents Investigation Sub-Committee of the Aeronautical Research Committee issued their report on the accident to a Junkers monoplane at Meopham, Kent. The Sub-Committee gave it as their opinion that tail buffeting was the probable primary cause of this accident, and recommended that the phenomenon should be investigated. At this time tail buffeting (Leitwerkschutteln) was quite well known in Germany, where the low-wing monoplane, which is peculiarly susceptible to this trouble, was a popular type of aircraft; and some full-scale experiments on the subject had already been made by the Deutsche Versuchsanstalt fiir Luftfahrt. The findings of the Accidents Investigation Sub-Committee caused an intensive study of buffeting to be undertaken both in Germany and in this country, and the enquiry was also taken up in the United States at a later date. As a result of these studies tail buffeting is now quite well understood, and methods for its avoidance have been established.

The accompanying Report No. B.A. 1083 of the Royal Aircraft Establishment demonstrates generally that a moving body or rider plane can be associated with a fixed body or plane for altering the aerodynamic properties of the combination for various useful purposes, and in particular, that rotating cambered rider planes, when associated with the front edge of a fixed wing of standard section (see Fig. 11) “are definitely advantageous” in improving the gliding conditions, and that “by increasing the size of the rotors relatively to the size of the wings, this superiority is increased.”

Previous experiments at the N.P.L. with various types of wings fitted alternately—with optimum wing-tip slots and with rotors—have shown that rotors can give about the same degree of lateral stability as tip slots, but over a much wider angular range. Other experiments with better rotors than used at the N.P.L. have shown that a more powerful stabilising effect over a wider annular range is to be obtained with rotors than with slots.

The suggestion has been put forward by Dr. A. P. Thurston that the characteristics of a wing can be considerably improved by adding self-starting rotors at or near the wing tips. It is claimed that by placing these on each wing near the leading edge improvements analogous to those of a slotted wing tip can be obtained together with slow landing characteristics. Previous experiments (1) have shown that rotors can give about the same degree of lateral stability as tip slots. The primary object of these experiments was to test the second assertion, and the criterion by which this should be judged was that the gliding angle should be as steep as possible for a given rate of descent.