The paper gives a précis account of studies made at the Rocket Propulsion Establishment of the Ministry of Aviation to determine the relationship between the specific weight and thrust of a liquid bi-propellent rocket engine.

Although the need for a better understanding of basic phenomena is established, the conclusion is reached that, within the selected premises, the minimum specific weight is achieved at a thrust level near 50,000 lb. The difference in specific weight between engines of 200,000 lb. thrust and 50,000 lb. thrust is only about 10 per cent and this is shown to be equivalent to only one per cent in propellent specific impulse. Although small, it is considered significant that a minimum has been established and this fact is used as an argument to justify the use of clusters of engines (generally four) to provide levels of thrust greater than 100,000 lb.

I should like in this paper to review some of the work on helicopter vibrations which has been done at Southampton University in the past few years. This has been mainly concerned with blade vibration and there have been parallel theoretical and experimental programmes. Complimentary research has been going on in the United States and the results support each other in an encouraging way.

With cruciform missiles it is usual to express overall aerodynamic forces and moments in terms of aileron, elevator and rudder angles. It is shown that an alternative formulation in terms of individual control angles is both more general and more revealing.

The fundamental assumption is that the overall coefficients can be expressed sufficiently accurately as the sum of independent control effects and of the mutual interference between adjacent controls. This assumption has been found to be valid over quite wide regions of supersonic Mach number, body incidence and control deflection for some typical cruciform rear control missiles. In principle the method applies at all speeds and to all types of layout, but it seems likely to be less widely applicable at subsonic and transonic speeds and to moving wing and canard layouts. The region of applicability is ultimately a matter of experimental investigation for each missile.

This new approach gives a clearer understanding of cross-coupling effects, simplifies and improves the accuracy of a mathematical model of the aerodynamic characteristics, and facilitates the interpolation of wind tunnel test measurements. These measurements are made on configurations with two adjacent controls deflected and the other two controls either always undeflected or always removed. The test programme can be matched more easily to the aerodynamic characteristics, and the testing time is much the same or significantly less than for a comparable programme involving combinations of aileron, elevator and rudder settings. Greater demands on experimental accuracy are imposed, however.

There is considerable scope for research work in investigating the applicability of the new technique to various types of missile layouts and to assessing the relative merits of having the two dummy controls undeflected or removed.

In ref. 1 Bennett derived the well-known expression for the power required to overcome the profile drag of the rotor blades for a helicopter in forward flight:

The power given by (1) is composed of two parts: the contribution of the torque of the profile drag with respect to the rotor axis and that of the drag of the rotor blades due to the forward motion (H-force).

Several methods for performance calculation of helicopters require the two parts of the profile-drag power separately, as they make use of the equation for the equilibrium of forces in the direction of flight, to which the rotor drag gives a contribution. In this note expressions for the two parts of the total profile-drag power are derived using the same method as indicated in the original work of Bennett. Numerical results are given.

As far as is known, no explicit solution exists in the literature for the displacement equations in u, v and w, for a uniform cylinder of arbitrary cross section subjected to a lateral pressure loading. However, the advent of Ref. 1 now makes available an admirable treatise devoted entirely to the analysis of thin elastic shells. The equations developed in this reference apply only to linear problems, i.e. the displacements are assumed to be small in comparison with the thickness of the shell, but they are general enough to include all shells of arbitrary curvature. Unfortunately the generality of these equations inhibits their immediate use to cylindrical shell problems, and it is the purpose of this note to present the essential features of the theory for non-circular cylinders.

I read Lt. Cdr. Whitehead’s article in the April Journal (p. 183) with considerable interest. As a summary of current problems I found it most illuminating. In my opinion however the author has rather over-simplified the mirror calculations and I feel that it may be worthwhile recording in slightly greater detail the basis of mirror calculations and the magnitude of the errors implicit in them.