A large number of far-field jet noise measurements obtained over a considerable period of time are presented, correlated in such a manner that they may be used to provide a complete noise assessment for any jet of which the performance parameters are known. The data are presented in two sections, one dealing with the problem of a static source near ground level, the other dealing with the case of a source in flight.

Much of the data was derived from Avon engine tests, but a wide range of other jet noise sources has also been encompassed. Comparisons are drawn which show good correlation to exist between the overall sound pressure levels produced by jets of all sizes. It appears also that even the spectra quoted, which are based only on Avon measurements, are valid over a fairly wide range of jet sizes and are not peculiar to the Avon engine.

The problem considered is the buckling of a rectangular plate under uniaxial compression. The ends may be either both clamped, both simply-supported or a mixture of the two. The sides may be elastically restrained against both deflection and rotation with any stiffnesses whatsoever. It is shown that the curve of buckling stress coefficient versus side ratio can be deduced in a simple manner from that of a plate with the same end conditions but with both sides simply-supported, provided only that the buckling stress coefficient and wavelength for an infinite strip with the same side conditions are known. Some correlations between the curves for the three types of end condition are discussed. It is also shown that if, for some given side ratio, the buckling mode is known, then it is always possible to deduce the rate of change of buckling stress coefficient with side ratio at that point. The argument is based upon an assumption which is shown to give very accurate results in a wide range of cases.

There appear in the literature some discrepancies in the various mathematical expressions for the upwash constituting the wall interference on a small lifting wing placed symmetrically in a rectangular tunnel with closed side-walls and open floor and roof. The representation of the interference field as that of a doubly infinite array of image doublets is shown to lead to divergence. An independent calculation by relaxation confirms the correctness of an analytical solution by expansion in Fourier series. The discrepancies are found to arise from incomplete flow conditions at the open boundaries, and it is shown in this paper how the various theories are reconciled.

After a retrospective discussion of Glauert's theorem concerning the wall interference on a small lifting aerofoil in a wind tunnel with mixed boundaries, a simple proof of the theorem is given for a tunnel having one rigid and one free boundary. It is shown that the theorem does not necessarily hold when there are two rigid walls and two free boundaries.

A new method of analysing the response of linear systems to sinusoidal excitation, which avoids the assumptions of present methods, is developed in this paper. It enables one to obtain the eigenvalues and righthand eigenvectors of a system with viscous damping from the response of the system. If the inertia matrix of the system is known, the damping and stiffness matrices can also be obtained. No assumptions are made about the form of these matrices, and the method is not restricted to systems with only small amounts of damping.

In view of the overall losses occurring in the bypass ducts of bypass engines a study has been made of the losses taking place at sudden changes of section which occur as the flow passes over compressor and turbine casings not properly faired. It has been shown that the normally estimated losses occurring at sudden contractions and expansions are greatly increased by the low discharge coefficient. When allowance is made for this, the losses at obstructions can be estimated reasonably accurately. It is shown that a fairing ahead of the blockages has to be quite extensive to produce the normally calculated loss and that all these results are reconcilable with the known losses of obstructions in semiinfinite flow. It is shown, however, that where obstructions are placed in series so that the flow areas are roughly in line, losses are much less than the total of the losses caused by the obstructions separately.

The validity and applicability of the static margin (stick fixed) Kn,

where

as defined by Gates and Lyon is shown to be restricted to the conventional flexible aircraft. Alternative suggestions for the definition of static margin are put forward which can be equally applied to the conventional flexible aircraft of the past and the integrated flexible aircraft of the future. Calculations have been carried out on simple slender plate models with both linear and non-linear aerodynamic forces to assess their static stability characteristics.