The method which was developed in an earlier paper for calculating the lift on a thin jet-flapped aerofoil has been applied to the case in which the jet enters the main stream tangentially from a deflected flap. The lift derivative with respect to the (small) angle of deflection β is of the form

where , E being the ratio of flap length to aerofoil chord, and D0 a function both of E and of the jet momentum coefficient CJ. In the special case CJ = 0, Do vanishes and the classical results for attached flow on flapped aerofoils without super-circulation are obtained. More generally, Do has been evaluated over the range 0<CJ<5 for six ratios E between 0·02 and 0·50, using an electronic computer. The lift derivatives so found lie between those in the limiting cases of “deflection” (E = 0) and “incidence” (E=1) which were calculated in Reference 1. They show that the effectiveness of the jet-flap scheme might be greatly increased by blowing over flaps of the order of 20 or 30 per cent of the chord, rather than over the small “shrouds” which have hitherto been proposed.

This paper gives some identities concerning the flexibility of certain elastic structures, including flat plates, at the onset of buckling and subsequently. The identities have a useful application in determining the flexibility and the rate of change of flexibility with load for structures in which the mode in the buckled state changes continuously with load.

In this note Ward's “area-transfer rule” is modified in order to make it more suitable for configurations with fuselages or nacelles which are neither slender nor smooth (although they are assumed to have small profile slope). The body source strength of Ward's analysis, which is appropriate only for smooth, slender bodies, is replaced by a source strength which is valid more generally. However, the drag contributions of the body multi-sources and of the interference field are still neglected, so that the theory is tentative rather than rigorous.