In assessing the true extent of technical development of any kind the mind naturally seeks a standard for comparison. When considering structural development the standard chosen could well be that associated with the end of the Second World War. In preparing this paper, therefore, it appeared profitable, and certainly it has been extremely interesting for the author, to review the structure of some of the aircraft then in quantity production.

The behaviour of an elastic aircraft in flight may be divided into dynamic and static cases with an intermediate class of phenomena under the heading of stability. The dynamic category is concerned with flutter and divergence effects and since these are destructive when they occur they are naturally given precedence in the aeroelastic analysis of an aircraft.

Having eliminated these dynamic effects by suitable design it is natural to turn to the static case which assesses the manoeuvrability of the aircraft. With the advent of sweepback and the attainment of higher Mach numbers it becomes increasingly difficult to determine the behaviour of modern aircraft even when regarded as rigid.

Detailed investigations of the two-dimensional characteristics of thin aerofoil sections with small leading-edge radius have been made by Gault and McCullough. They found that at angles of incidence well below the stalling angle of the section, the laminar boundary layer separated from the surface near the nose, became transitional away from the surface, and re-attached to the aerofoil as a turbulent layer a little farther downstream. Beneath the separated layer, a “bubble” vortex was formed lying parallel to the leading edge, its rotation being such that the flow adjacent to the surface was towards the leading edge.