The aerodynamic characteristics of flaps

Abstract

This report collects and summarises the results of work that has been done both in this and other countries on the aerodynamic characteristics of flaps prior to and during the period of the war. The report has both a philosophical and practical aim, viz., to demonstrate, as far as possible, such underlying unity as exists in the behaviour of the large variety of flaps that have been developed and investigated, and hence to present charts and tables which will enable designers to predict with acceptable accuracy the characteristics of any particular flap arrangement. In section 2 a brief description of the various flaps considered is given, and these are also illustrated in Fig. 1. Section 3 is devoted to a discussion of the definitions of the lift, drag and pitching moment increments, based on the normal and on the effective (extended or reduced) wing chords. Section 4 deals in some detail with split and plain flaps, whilst section 5 is devoted to the simple slotted flaps of the Handley Page and N.A.C.A. types. A large variety of flaps classified as high-lift flaps are considered in section 6, these include Fowler flaps, double Fowler flaps, N.A.C.A. single and doubleslotted flaps, single and double Blackburn flaps, Blackburn flaps with flap leading-edge slots, Blackburn flaps with inset slots, Blackburn flaps with deflected shrouds and Venetian-blind flaps. The main characteristics of these high-lift flaps are also summarised in Table 2. The effect of wing-body interference on the drag and lift increments of split and slotted flaps is discussed in section 7, whilst section 8 summarises the aerodynamic effects of wing leading-edge slots. The effect of flaps on induced drag is dealt with in section 9. A discussion of the characteristics of nose flaps, with particular reference to the type developed and tested by Kruger in Germany is given in section 10. A brief discussion on brake flaps is given in section 11, whilst the allied subject of dive recovery flaps is examined in section 12. Because of its topical interest, such information as is available on the characteristics of flaps on swept-back wings is summarised in section 13. Section 14 is devoted to a summary of the main formulae and conclusions developed in the report. The bibliography at the end was compiled with the object of providing as representative a list as possible of the main reports and papers to which a reader might wish to refer for more detailed information.