The Jet Flap

Abstract

Throughout the animal kingdom powered flight is a surprisingly common attribute and whenever it occurs both the sustenation and the propulsion are provided by the same structural and aerodynamic mechanism. There is, in fact, but a single aerodynamic reaction which is divided, for convenience, into thrust and lift. In earlier times this convention was presumably not recognised, for the ornithopter appears to have formed for some centuries the principal technical basis of man's aspiration to heavier-than-air flight. Of the exceptions, Leonardo da Vinci's helicopter is now, of course, an accepted vehicle, but this lecture is concerned mainly with fixed-wing aircraft for which it is significant that success came only with the aeroplane, or, as Lachmann has recently put it, with the powered glider.