WO2011004187A2

WO2011004187A2 - Coanda effect vehicle

Info

Publication number: WO2011004187A2
Application number: PCT/GB2010/051115
Authority: WO
Inventors: Lee Whitcher; Steve Potter
Original assignee: Aesir Limited
Priority date: 2009-07-06
Filing date: 2010-07-06
Publication date: 2011-01-13
Also published as: GB2471663A; GB0911668D0; WO2011004187A3

Abstract

A Coanda vehicle comprises a canopy (1) having an upper convex surface (7), an impeller (2, 5), means (1, 3)defining a path for fluid which passes through the impeller and curves from a relatively axial direction to a relatively radial direction, the path terminating at a position adjacent the said surface so that fluid flow over the surface produces lift. The invention proposes the use of a deflector (8) located in the said path so that fluid flows over opposite surfaces of the deflector, the deflector being curved in the same direction as the curvature of the path. By employing the invention it becomes possible to change the velocity profile across the fluid path, this offering a potential for improved performance.

Description

Coanda Effect Vehicle

[0001] This invention relates to an air vehicle of the type that uses the Coanda Effect to divert a flow of fluid thereby producing lift.

[0002] The Coanda effect is a phenomenon which tends to keep a jet of fluid attached to a surface over which it flows. In the case of a Coanda effect air vehicle, the jet of fluid is an air flow and this can be produced using an axial fan or by a radial fan.

[0003] Coanda effect air vehicles are capable of hovering and have advantages over conventional hovering vehicles. For example, they can operate safely close to vertical surfaces. Also, the "canopy" that is responsible for the Coanda effect provides a natural enclosure for the payload. However, as with all air vehicles, a fundamental design problem always present is to achieve greater net lift. The present invention addresses this problem in Coanda craft.

[0004] In general it has been found that axial fans are better for larger Coanda craft whilst radial fans are better for small craft. In both cases, the air enters the fan in a generally axial direction i.e. parallel to the axis of rotation of the fan blades but is diverted radially before flowing over the surface responsible for producing lift. In the case of an axial fan, this diversion of the flow towards the radial direction occurs downstream of the fan blades whereas, for a radial fan, the diversion occurs upstream of the fan.

[0005] In a typical axial fan arrangement, the axially flowing air stream from the fan is diverted to the radial direction by an annular duct defined between a canopy of the craft and a shroud spaced above it. Measurements of air flow, in such a craft at the outlet of the duct, have shown that the velocity is greatest close to the canopy and is least close to the shroud; and that turbulence can occur at the latter position.

[0006] According to the invention there is provided a Coanda vehicle comprising a canopy having an upper convex surface, an impeller, means defining a path for fluid which passes through the impeller and curves from a relatively axial direction to a relatively radial direction, the path terminating at a position adjacent the said surface so that fluid flow over the surface produces lift characterised by a deflector located in the said path so that fluid flows over opposite surfaces of the deflector, the deflector being curved in the same direction as the curvature of the path.

[0007] By employing the invention it becomes possible to change the velocity profile across the fluid path, this offering a potential for improved performance. Preferably the deflector is arranged so as to create a more uniform velocity of flow with respect to height above the Coanda surface and has been found that this is especially beneficial in achieving improved lift. However there may be benefits in making the arrangement so that the velocity decreases towards the surface. [0008] In most cases the curved surface responsible for producing the lift will extend around a central axis. The airstream will be directed into an annular shape so as to flow over this surface and the deflector will preferably have a corresponding annular shape so as to be effective around the whole of the annular airstream. There are other possibilities. For example, the deflector could be formed from a series of individual segments arranged around the axis.

[0009] The fact that the deflector has a significant effect on lift can be used to control the vehicle. In such an arrangement, the deflector would be adjustable. For example, where the deflector is in the form of an annular ring, it could be mounted on three or more adjustable posts so that its axis could be swivelled relative to the axis of the fan.

[0010] An example of one way in which the invention may be performed will now be

described with reference to the accompanying drawings in which: -

[0011] Fig 1 is a perspective view, shown partly broken away to reveal interior details of an air vehicle constructed in accordance with the invention;

[0012] Figs 2A and 2B are schematic diagrams illustrating the effect of a deflector included in the vehicle shown in Fig 1 ; and

[0013] Fig 3 is a block diagram showing a control system for the vehicle of Fig 1.

[0014] Referring to Fig 1 there is shown a vertical take off aircraft having a canopy 1

defining an aerodynamic surface of double convex curvature and an axial fan 2. The fan is driven by an engine or motor, not illustrated, housed within the canopy 1. The fan 2 and the canopy 1 have a common axis of symmetry X - X.

[0015] A shroud 3 is supported by struts 3 A above the canopy and extends circumferentially around the fan 2 such as to define a duct 4 within which the fan 2 is housed.

[0016] Air is drawn axially into the fan 2 along the axis as indicated by the arrows 5 and is expelled as a radial jet 6 over a surface 7 of the canopy, this surface having double convex curvature. By virtue of the Coanda effect the jet follows the curve of canopy, diverted from an approximately radial direction, towards an approximately axial direction; and the jet finally parts from the canopy surface at its lower edge 8. This diversion of the jet towards the vertical axis generates vertical lift.

[0017] Because of the rotary action of the fan 2, the air expelled from it has a circumferential velocity component. The struts 3 A are designed as aerofoils, angled to counteract this effect and have adjustable vanes 3B to control yaw, i.e. rotation about the axis X - X.

[0018] Downstream of the fan 2, the duct 4 is curved to divert the air stream from an axial direction to a radial direction. In this curved region is located an annular deflector 8 mounted on three supporting posts 9 (only one visible on Fig 1) spaced equidistantly about the axis X -X. The supporting posts normally hold the deflector in a datum position where its axis is the same as axis X- X. However, each post 9 can be adjusted, using actuators 10, so as to tilt the axis of the deflector relative to the main axis X - X. A cross-section of the deflector 8, through a plane of the axis X - X, is curved so as to follow the curvature of the duct 4. In the illustrated embodiment, the curvature of the deflector is approximately such as to follow the mid point between the canopy and the shroud but this is not essential and some beneficial effect can be expected providing there is some curvature in the same direction.

[0019] Measurements of air velocity have been made at the output of the duct 4 i.e. at the upstream end of the jet of air passing over the Coanda surface 7. Fig 2A shows these measurements when the deflector 8 was removed whilst Fig 2B shows measurements made with the deflector 8 in position. From Fig 2 it can be seen that an uppermost region R of the jet stream, adjoining the downstream edge of the shroud is subject to turbulence, resulting in a backward or negative flow velocity. This significantly degrades the lift of the craft as compared with the arrangement where the deflector 8 is in position as shown in Fig 2B where there is no area of negative velocity flow.

[0020] Fig 3 shows a microcontroller 11 and an inertial measurement unit (IMU) 12, housed within the canopy 1. The IMU is conventional and includes gyros, accelerometers and magnetometers to obtain an accurate estimate of the aircraft's instantaneous attitude/ orientation defined as angles of pitch, roll and yaw. The microcontroller receives instruction signals from a user interface 13 via a communication channel 14. These instruction signals represent the desired pitch, roll and yaw angles of the craft. To understand these angles it is helpful to designate a particular point on the canopy 7 as being the "front" of the craft. Yaw is any angle of rotation about the X - X axis of the front of the craft relative. Pitch is the angle by which the axis X - X is displaced from the vertical in a plane passing through the axis and the front of the craft. Roll is the angle by which the axis X - X is displaced from the vertical in a plane passing through the axis and normal to the aforementioned plane.

[0021] Using the output from the IMU 12 as a reference, the microcontroller 11 compares the desired yaw angle with the actual yaw angle (this is the angle of rotation about the axis X - X) and produces an error signal that operates actuators 3C, located within the shroud 3, to adjust the vanes 3B (Fig 1) until the error signal reaches zero. Normally these error signals will be identical so that the vanes 3B are adjusted in synchronism. However it is possible to introduce a differential between these signals causing the vanes 3B to be deflected differently thereby supplementing the pitch and roll adjustment to be described in the following paragraph.

[0022] The microcontroller 11 also compares the desired pitch and banking angles with those detected by the IMU 12 and generates correction signals to operate the actuators 10. These actuators are thereby caused to change the axis of the deflector 8 to produce the required change in roll and pitch angles. [0023] If the aircraft is to employ an Automatic Flight Control System (AFCS), the instruction signals fed from line 14 to the microcontroller will be automatically calculated by some mathematical algorithm as opposed to being manually inputted by a pilot. This algorithm will take into account such factors as aircraft attitude, heading, its inherent dynamics, and desired location in its calculation of instruction signal. The manner in which the aircraft responds to an error signal is dependent upon the aircraft's inherent dynamics and, as such, the AFCS can be tuned to manipulate the instruction signal to achieve an optimal response. Higher level control will enable the aircraft to automatically fly between waypoints and respond to unpredictable events such as the introduction of an obstacle or terrain anomaly. In addition, an external human operator will be able to override the predetermined flight plan with manual commands which, rather than take direct control over the aircraft itself, inform the AFCS of a new desired position. This operation will be performed dynamically and remotely in a manner known in the field of aircraft control systems via some wireless telemetry system.

[0024] The inclusion of the deflector 8 in a craft like that illustrated has been shown to

improve its performance very significantly. However, the illustrated craft represents just one way in which the invention may be used. There are many variations within the scope of the invention as defined by the accompanying Claims. For example, it would be possible to include more than one vane, one above the other; and, where a radial, rather than an axial fan is employed, the deflector could be positioned upstream of the fan so as to continue to produce its beneficial effect where the air flow is diverted from the axial to radial direction. Other possible variations include the use of a combustion jet instead of a fan, and the use of the invention in underwater craft instead of air vehicles.

Claims

[0001] A Coanda vehicle comprising a canopy(l) having an upper convex surface (7), an impeller (2, 5), means 1, 3) defining a path for fluid which passes through the impeller (5) and curves from a relatively axial direction to a relatively radial direction, the path terminating at a position adjacent the said surface so that fluid flow over the surface (7) produces lift characterised by a deflector (8) located in the said path so that fluid flows over opposite surfaces of the deflector, the deflector being curved in the same direction as the curvature of the path.

[0002] A Coanda air vehicle according to Claim 1 characterised in that the impeller is an axial fan (2, 5) and that the deflector (8) is arranged downstream of the fan.

[0003] A Coanda vehicle according to Claim 1 or 2 characterised in that the fluid path and the deflector are annular.

[0004] A Coanda vehicle according to Claim 3 characterised by an adjustment

mechanism (9, 10) whereby an axis of the deflector (8) can be varied relative to an axis of a stream of fluid.