The forces on an aerofoil have been measured at various angles of incidence for 0.5 < R < 2,000.

Below R = 2 the lift is found to be given approximately by :—

L, = (3/2) µlV sin 2x

and the drag at all angles of incidence tends to:

D = µlV.

An approximate theoretical estimate is also given of the effect of spacing, on the drag of a series of flat plates at R → o.

1. Piercy, Piper and Preston (1) and Piercy, Preston and Whitehead (2) have developed a family of aerofoils which are the inverses of hyperbolas. These calculations give a family with a finite tail angle, equal to the angle between the asymptotes. It may sometimes be preferable to have a rounded trailing edge. It is the purpose of this note to describe a family whose members are inverses of ellipses.

2. It will be seen that, if the centre of inversion is on the major axis produced, symmetrical sections will result; whilst, if the centre is just off the major axis, a cambered section will be produced; and the inverse of the major axis (which is a circle) can be taken as the camber line.

To-day all altitudes up to, and including, the stratosphere are within the scope of aviation. The engines must therefore be provided with highly developed superchargers so as to obtain high performance even at these altitudes. The single or multi-stage superchargers necessary to accomplish this become an integral part of the engine and exercise a distinct influence on its general construction.

In many types of engine the supercharger is built on to the accessory drive end, that is the rear of the engine, so that the supercharger shaft lies co-axially or parallel with the crankshaft.