WO2009027742A1

WO2009027742A1 - Coanda effect air vehicle

Info

Publication number: WO2009027742A1
Application number: PCT/GB2008/050749
Authority: WO
Inventors: Geoffrey Hatton
Original assignee: Gfs Projects Limited
Priority date: 2007-08-28
Filing date: 2008-08-28
Publication date: 2009-03-05
Also published as: GB0716560D0; GB2452255A

Abstract

In a vertical-take-off air vehicle, a rotary impeller (3) causes air to flow over convex outer surfaces (1) to create lift. In accordance with the invention air is also caused to flow under one or more outer surfaces (5) at a selected circumferential position or positions. Stability is improved by orienting the vehicle so that a surface (5) is facing towards the wind. Forward, horizontal movement of the vehicle can be controlled by flaps (9) that allow air to be constrained to flow optionally under or over this surface (5). The surface (5) may be offset from adjoining surfaces (1) so that the flow of air can conveniently be diverted beneath it. The walls (1 and 5) may be connected together by one or more side walls (5A) curved so that the flow of air on each side imparts a turning moment opposing an opposite moment caused by the impeller (3).

Description

COANDA EFFECT AIR VEHICLE

This invention relates to an air vehicle comprising an impeller for causing air to flow radially outwardly from a central point over a convex outer surface of the vehicle. These vehicles use a phenomenon known as the Coander effect to create lift. The Coander effect offers the potential for vertical take-off aircraft where, unlike conventional helicopters, the payload is not located directly in the stream of air responsible for creating lift.

Vehicles of the aforementioned type have until now been restricted to experimental or novelty designs. One reason for this is that they are relatively unstable and difficult to control, particularly in windy conditions. This invention arose from a theory that these problems arise because the airflow responsible for lift, being exposed on an outer surface of the vehicle, is necessarily disturbed by any wind conditions that the vehicle may encounter.

According to the invention there is provided an air vehicle comprising an impeller for causing air to flow radially outwardly from a central point over a convex outer surface of the vehicle to create lift; characterised by means for causing the air to flow primarily under an outer surface of the vehicle at a selected circumferential position.

By employing the invention, and orienting the vehicle so that the aforementioned "selected" position is facing towards the wind, it is believed that it will become possible to improve the stability of the craft significantly.

The air flow at the "selected" position is preferably diverted, by a concave inner surface, towards a downward direction, thereby supplementing lift generated by the flow over the convex outer surface. Forward, horizontal movement of the vehicle can be controlled by a mechanism e.g. in the form of flaps that allows air to be constrained to flow optionally under or over a canopy at opposite sides of the vehicle. By opening a flap on one side of the vehicle, and thereby causing the air flow to escape from beneath the canopy, the vehicle can be caused to move in a direction towards the opposite side.

The canopy, in the region of the or each "selected position" may be defined by a wall that is offset, from an adjoining wall or walls so that the flow of air can conveniently be diverted beneath it. This offset wall may be connected to the adjoining wall or walls of the canopy by one or more side walls shaped, preferably in a curve, so that the flow of air on each side imparts a turning moment opposing an opposite moment caused by the rotary impeller.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: -

Fig 1 is an isometric view of a vertical take-off air vehicle constructed in accordance with the invention;

Fig 2 is a plan view of the vehicle; and

Fig 3 is a cross-section though the line A - A of Fig 2.

Referring to the drawings, the illustrated craft comprises a framework (not shown) supporting eight generally trapesoidal panels 1 and 5 arranged about a central axis X - X to form a dome shaped canopy 2. At the top of the canopy is an axial fan 3 driven by, in this particular embodiment, an electric motor (not shown). In alternative embodiments the motor could be replaced by an internal combustion engine. The fan blades (not shown) rotate in a clockwise direction as viewed in Fig 2 and, in use, drive air downwardly onto a baffle 4 (Fig 3) which diverts the air flow radially over the top surface of the panels 1. Positioned at two selected circumferential regions, on diametrically opposite sides of the canopy, are raised panels 5. These are spaced above the level of panels 1 but are similarly curved to complete the dome-shaped contour of the canopy.

The raised panels 5 have curved edges 5A and are joined to adjoining edges IA of the panels 1 by side walls 6. These edges and walls 6 are curved so as to spiral in an anticlockwise direction from the top to the bottom of the canopy.

Positioned centrally on each raised panel 5 is an opening 8 and hinged flap 9, the latter being controlled by a steering mechanism not shown.

In use, the vehicle operates as follows.

A flow of air from the fan 3, diverted radially by the baffle 4, flows over the outer surface of the vehicle in all areas of the panels 1. This flow produces a lifting force by virtue of the Coander effect, raising the vehicle into the air.

A minority part of the air flow passes horizontally into a space below the raised panels 5, the lower, concave, surface of these panels divert ing the air flow to a downward direction, thereby creating further lift to supplement the lift produced by the airflow over the upper surface of panels 1.

Air flowing over the convex, outer surfaces and the concave, inner surfaces of side walls 6 produces a clockwise turning moment on the vehicle thereby counteracting the anticlockwise moment applied by the clockwise rotating rotor of the fan 3. Adjustable vanes (not shown) or other known techniques may be deployed on the side walls 6 or elsewhere on the outer surface of the vehicle to control the position of rotation of the vehicle about its axis X-X.

Horizontal movement of the vehicle relative to the surrounding air may be required either for the purpose of keeping the vehicle stationary relative to the ground in windy conditions or for the purpose of moving the vehicle relative to the ground, or a combination of these effects. This is achieved by adjusting the vanes (or equivalent) so that the raised panels 5 face respectively in the desired forward and rearward directions and then opening the downstream flap 9. The resulting jet of air issuing partly horizontally form the opening 8 drives the vehicle forward relative to the air. Furthermore, because the raised panels ensure that air from the fan and responsible for Coander lift does not flow over an exposed surface of the vehicle on its windward side, wind velocity does not, to the extent experienced in previous designs, interfere with the stability of the vehicle. This is particularly beneficial in gusty conditions because gusts cannot be predicted and therefore their effect cannot easily be compensated for.

It is pointed out that many variations to the illustrated design could be made without departing from the scope of the invention as defined by the accompanying Claims. For example, the illustrated arrangement, by which raised panels are used to protect air flow from the fan from the effects of the wind, could be replaced by a facility for diverting the air flow to beneath selected panels 1 on the windward side thereby eliminating the need for the raised panels 5. Other modifications include the possibility of using a radial instead of an axial fan and of course it would be possible to form the canopy to define a continuous smooth outer surface instead of the illustrated construction where there are discernable edges between adjoining canopy panelsl, 5 and walls 6.

Claims

1. An air vehicle comprising an impeller for causing air to flow radially outwardly from a central point over a convex outer surface of the vehicle to create lift; characterised by means for causing the air to flow primarily under an outer surface of the vehicle at a selected circumferential position.

2. An air vehicle according to Claim 1 characterised by a raised portion of the said surface at the said selected position, arranged to allow air from the impeller to flow beneath it.

3. An air vehicle according to Claim 2 characterised by side walls joining the said raised portion of the surface to the remaining parts

4. An air vehicle according to Claim 3 in which the impeller is a rotary impeller, the operation of which tends to cause unwanted rotation of the craft and further characterised in that the side walls are arranged and/or shaped so that air flow along them produces a force opposing the unwanted rotation.

5. An air vehicle according to Claim 2, 3 or 4 characterised by a controllable vent arranged to allow air to flow outwardly through the convex outer surface.

6. An air vehicle according to any preceding Claim characterised by means for causing the selected position to face a direction of the air velocity of the vehicle.

7. An air vehicle according to any preceding claim characterised in that there are more than one of the said selected positions separated from each other.