Abstract: The invention arose in the design of vertical takeoff craft where a bladed rotor directs a jet of fluid over a curved surface so that the jet is turned from a radial direction towards an axial direction to create lift. These craft have stability problems when an attempt is made to hover close to the ground or to a vertical surface and for this reason such craft have been confined to paper proposals and unsuccessful experimental models. In accordance with the invention, the craft is designed so that its rotor and other moving parts have a large angular momentum. In this way, a gyroscopic effect is achieved, sufficient to give positive stability to the craft, eliminating the aforementioned problem.

Abstract: There have been past proposals for air vehicles employing the Coanda effect. In these proposals, a jet of fluid, usually air, is made to flow radially outwardly over 5 a dome-shaped canopy to create lift. A cross-section through the canopy is curved to follow a segment of a circle or it may have a radius of curvature that increases in the direction of flow. In the invention, the radius (r) of the canopy curve decreases towards the downstream direction (x) in a way that is related to the decrease in the width of 10 the jet as it flows over the surface. This means that the radius of curvature decreases (instead of increasing) towards the downstream direction with the rate of decrease being progressively less rapid towards the downstream direction.

Abstract: The invention arose in the design of vertical takeoff craft where a bladed rotor directs a jet of fluid over a curved surface so that the jet is turned from a radial direction towards an axial direction to create lift. These craft have stability problems when an attempt is made to hover close to the ground or to a vertical surface and for this reason such craft have been confined to paper proposals and unsuccessful experimental models. In accordance with the invention, the craft is designed so that its rotor and other moving parts have a large angular momentum. In this way, a gyroscopic effect is achieved, sufficient to give positive stability to the craft, eliminating the aforementioned problem.

Abstract: In aeronautical devices where a fluid such as air flows over a surface (1) to create lift or thrust, improved performance can be obtained by energising a so-called 5 “boundary layer” (10) of the fluid flow close to the surface. This is known to help prevent separation of the fluid flow stream from the surface thereby maximising the lift or thrust achieved. The invention provides a facility (7A) for controlling the mechanisms (7) used for energising the boundary layer so as to selectively increase or decrease the effect 10 in different areas. When this is done for example on different sides of an air vehicle, it provides an effective mechanism for steering the vehicle.

Abstract: There have been past proposals for air vehicles employing the Coanda effect. In these proposals, a jet of fluid, usually air, is made to flow radially outwardly over a dome-shaped canopy to create lift. A cross-section through the canopy is curved to follow a segment of a circle or it may have a radius of curvature that increases in the direction of flow. In the invention, the radius (r) of the canopy curve decreases towards the downstream direction (x) in a way that is related to the decrease in the width of the jet as it flows over the surface. This means that the radius of curvature decreases (instead of increasing) towards the downstream direction with the rate of decrease being progressively less rapid towards the downstream direction.

Abstract: The invention concerns craft of the type in which a fan directs a jet of fluid (4) over a curved canopy (1). The canopy (1) is shaped to divert the flow from a radial to an axial direction to produce lift. A problem is that rotation of the fan causes unwanted rotation of the canopy (1). The problem is solved using vanes (6) on the canopy (1) that have an adjustable surface area; and by providing a control system to adjust the effective surface area so as to compensate for the tendency of the rotor to rotate the canopy. The vanes (6) can be designed to slide in and out of the canopy (1) to obtain the required adjustment. In a preferred arrangement the vanes are arranged between upstream and downstream ends of the flow at a position where the effects of changes in swirl angle with varying rotor speed at least partially compensate for consequential changes in the tendancy for the canopy to spin.