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.

Based on earlier theories of mechanical, electrical and magnetic relaxation phenomena, the paper discusses a simple mathematical model representing qualitatively the basic characteristics of “internal” damping in solid materials. The model is assessed with respect to variation with frequency of stiffness and loss factor at simple harmonic oscillations, and is applied to oscillatory systems with discrete parameters and to continua.

The method of generalised conical flows has previously been developed subject to the condition that the upwash divided by the streamwise co-ordinate to the power ĸ, where ĸ is the order of the conical flow, must have vanishing (ĸ+1)th derivative with respect to the conical co-ordinate. In the present paper this restriction is removed. The results are also used to discuss the effect of the application of the leading edge attachment condition on the wing pressure and geometry.

A method of deriving a dynamic stiffness matrix for any non-uniform beam is presented. In particular, the case of a linearly tapered cantilever beam is considered, and excellent results are found with the use of only a few elements.

An exact plate analysis is given for torsion-type modes whose wavelength and deflection pattern are repetitive in the spanwise direction. It is shown that for short wavelengths there are regions of localised curling at the leading and trailing edges.

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.

The complete analytical solution is presented to a problem formulated in an earlier issue of this publication.

An investigation of the effect of a root gap is extended to the oscillatory pitching motion of a slender wing. Potential theory is used and the unsteady forces are shown to be reduced by the gap as drastically as the steady. These results cast doubt on measurements made by the technique of half-model testing. Viscous flow in the gap is discussed with reference to the possible types of model mount. The effect of viscosity may be to reduce the gap loss, but the extent of the improvement is uncertain.