This paper describes part of a detailed study of annular jets of different diameter ratios. From the overall pressure and spectral measurements of conical and basic annular jets of five diameter ratios the coherent structures of the standing vortices, wake vortices, jet vortices, lower wake induced vortices and wake induced vortices can be isolated and their effects assessed. The findings are supported by the available multi-exposed schlieren photographs of both the conical and basic annular jets. The causes for the presence or absence of the additional trains of vortices in the jet flow can also be evaluated by the variation of the diameter ratio. For the standing vortices and wake vortices within the flow behind the interface good correlation is found with the available pressure behind the interface.

A first order panel method has been developed for calculating the incompressible potential flow about arbitrary three-dimensional wings. The method utilises a distribution of source and vorticity singularities on the mean camber surface of the wing and solves for the distribution by satisfying the boundary condition of zero normal flow at selected points on the surface of the wing. The method takes less computing time compared to other existing first order methods for the comparable numerical accuracy. This method can handle wings having cusped trailing edges and thin sections.

The problem of energy transfer between an airstream and a wing in sinusoidal motion has been investigated by a series of authors beginning with Frazer who in 1939 considered the power input required to maintain forced oscillations of an aeroplane wing in flight. More recently Nissim introduced an ‘aerodynamic energy concept’ as the basis for the design of active control systems for flutter suppression. In this paper the author reconsiders the energy characteristics of the aerodynamic matrix in terms of the network concepts of resistive and reactive elements, corresponding to energy dissipation and energy storage respectively. A dual formulation of Nissim’s method is described and an extension proposed that takes account of aerodynamic energy storage in addition to aerodynamic energy dissipation.

While it has long been known that added fluid mass may be important in the dynamics of parachutes, due to inadequate or incorrect derivation and/or implementation of the added mass tensor its full significance in the stability of parachutes has yet to be appreciated. The concept of added mass is outlined and some general conditions for its significance are presented. Its implementation in the parachute equations of motion is reviewed, and the equations used in previous treatments are shown to be erroneous. A general method for finding the equivalent external forces and moments due to added mass is given, and the correct, anisotropic forms of the added mass tensor are derived for the six degree-of-freedom motion in an ideal fluid of rigid body shapes with planar-, twofold- and axisymmetry, These derivations may also be useful in dynamic stability studies of other low relative density bodies such as airships, balloons, submarines and torpedoes. Full nonlinear solutions of the equations of motion for the axisymmetric parachute have been obtained, and results indicate that added mass effects are more significant than previously predicted. In particular, the component of added mass along the axis of symmetry has a strong influence on stability. Better data on unsteady forces and moments on parachutes are needed.