In a recent Technical Note, Bradshaw offered additional thought on an earlier note by Markland and myself. In doing so he wrote of the efficiency of a diffuser which was confused with the pressure recovery coefficient, Cp. In view of the great significance when designing engine intakes, combustion chambers, nuclear reactor plant and even heating and ventilating systems of even minute improvements in duct efficiency, the distinction is further discussed.

The following is an attempt to show the gains and losses achieved when a rotating cylinder is used to create additional lift during the take-off and landing of an aircraft.

A hundred-year old theory lies behind the results (the “Magnus” effect), which, up to the present day has not been put to practical use in flight for increasing CL. Many proposals and tentative designs have been studied at major Research Establishments, notably A.V.A. Gottingen and the RAE but experimental studies on aircraft converted for the purpose have yet to be made.

Limited test results show that the CL on a rotating cylinder can be as great as 15 providing that sufficient care is taken to approach infinite aspect ratio by means of end-plates on a high aspect ratio cylinder. The one great disadvantage with the cylinder is the high drag coefficients produced. However, there seems no reason why a fairing should not be placed in the wake to reduce the drag to that corresponding to a blunt-nosed thick aerofoil section.

In a recent paper the suggestion is made that “it would be sensible when discussing the flow to use a Mach number based on the actual propagation velocity in the given circumstances.”

This directs attention to the deeper question of whether or not a Mach number however defined is a rational parameter in terms of which to express effects of flow.

In certain cases the quantity γp/ρ occurs quite naturally, regardless of any physical interpretation that can be given to it.

Let Г be a closed curve in the z-plane with p-axis of symmetry. The mapping function

maps in general the interior of the unit circle |ξ| < 1 on to the interior of Г such that ξ=0 is transformed into z=0.

The linear vibrating system of two degrees of freedom, see Fig. 1, whose mathematical solution is well known (see for example ref. 1), is nevertheless on the verge of being too awkward for manipulation in the design office. It is of considerable interest as the basis of a vibration absorber and techniques continue to be developed for investigating the effects of changing the design constants on the properties of the system and the more complicated ones derived from it.