GB1565212A

GB1565212A - Ductecd fan propulsors

Info

Publication number: GB1565212A
Application number: GB5246875A
Authority: GB
Original assignee: British Hovercraft Corp Ltd
Current assignee: British Hovercraft Corp Ltd
Priority date: 1975-12-22
Filing date: 1975-12-22
Publication date: 1980-04-16

Description

(54) IMPROVEMENTS IN OR RELATING TO DUCTED FAN PROPULSORS (71) We, BRITISH HOVERCRAFT CORPORATION LIMITED, of Yeovil, in the County of Somerset, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to ducted fan propulsors, and in particular to such propulsors that are capable of both forward and reverse thrust operation.

A ducted fan propulsor usually includes a duct of generally circular cross-section having leading and trailing edges and being arranged to surround a power driven fan.

For maximum efficiency in the normal forward thrust mode of operation, that is with air flowing from the leading to the trailing edge so that the leading edge represents an air intake, it is essential that the leading edge is contoured to provide a flared intake, and that the trailing edge is of a substantially sharp configuration. However, this arrangement is of low efficiency when the propulsor is required to provide reverse thrust, and this is at least partially due to the undesirable sharp configuration of the trailing edge of the duct when functioning as an air intake.

It is an object of the present invention to improve the reverse thrust efficiency of a ducted fan propulsor.

According to the invention a ducted fan propulsor comprises a duct having a fan therein for inducing an air flow selectively in either direction through the duct, at least one end of the duct having an inflatable member that in deflated condition provides that duct end with an air outlet configuration, whereas in inflated condition the member provides that duct end with an air intake configuration, and means for inflating the member whenever the fan is to be operated to induce air flow through the duct in a direction such that the duct end functions as an intake.

One end of the duct may be of permanent air intake configuration, or alternatively both ends of the duct may be arranged for transformation between an air intake configuration and an air outlet configuration.

Preferably, that end of the duct which is in an air outlet configuration terminates at a substantially sharp edge, and may, conveniently, be formed by inclining an outer surface of the duct inwardly to meet a generally straight inner surface of the duct.

The inflatable member may comprise an annular sheet of flexible material having inner and outer edges of the annulus secured in substantially fluid-tight relationship to the duct so as to define an annular inflatable space bounded in part by the annular sheet and in part by the duct.

One form of propulsor in accordance with the invention has the inner edge of the annular sheet secured around the inner surface of the duct, and the outer edge of the annular sheet secured to an outer surface of the duct so that the annular sheet circumscribes the duct end, and when the sheet is inflated it assumes a curved shape between the inner and outer edges thereof with the inner surface of the duct forming a tangent to the curve so that the inflated member forms an outwardly flared continuation of the inner surface of the duct.

The inflatable member may be formed from impermeable elastic sheet material so as to permit it to expand when inflated.

Alternatively, the inflatable member may be biased in the deflated condition so as to assume a folded configuration against the duct. The inflatable member may be biased to the folded configuration by resilient means connected between it and the duct.

The resilient means may comprise springs or elastic cords located either externally or internally of the inflatable member. Additionally or alternatively, passageways in the duct may be arranged to be selectively connectible to a source of vacuum so as to return the inflatable member to a folded configuration in the deflated condition.

In another form of ducted fan propulsor in accordance with the invention, that end of the duct that in one phase of operation is in an air outlet configuration comprises an inner surface and a plurality of plates extending from hinged attachment with an outer surface so as to form with the inner surface a substantially sharp edge, the inflatable member being secured to and housed between the inner surface and the plates, whereby inflation of the member moves the plates away from the inner surface so as to transform that duct end to an air intake configuration.

Means may be provided in the duct structure for connection. during operation, between a suitable source of fluid pressure and the inflatable member. Such means may comprise at least one passageway arranged with one end opening into the interior of the space bounded in part by the inflatable member. The passageway may be in the form of a manifold in the body portion having a plurality of tappings connected to the space.

In another aspect the invention provides a ducted fan propulsor including a duct formed as a tubular body of generally circular transverse cross-section and having a contoured leading edge and a substantially sharp trailing edge. a power driven fan supported within the duct for inducing a flow of air selectively in either direction through the duct, a flexible inflatable member attached around the trailing edge of the duct, and means for inflating the member so as to provide a flared air intake whenever the fan is to be operated to induce a flow of air through the duct such that the trailing edge functions as an air intake.

Various embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure I is a side elevation of a ducted fan propulsor in accordance with one embodiment of the invention, Figure 2 is a fragmentary sectioned view of that part of one end of the duct within the circle 'A' in Figure 1 when in an air inlet configuration, Figure 3 is a fragmentary sectioned view of that part of the other end of the duct within the circle 'B' in Figure 1 when in an air outlet configuration, Figure 4 is a part sectioned perspective view of a ducted fan propulsor in another embodiment of the invention, Figure 5 is a fragmentary sectioned view of part of one end of the ducted fan propulsor shown in Figure 4 when that end is in an air outlet configuration, Figure 6 is a similar view to that shown in Figure 5 but with the duct end in an air inlet configuration, Figure 7 is a part sectioned perspective view of a ducted fan propulsor in a further embodiment of the invention, Figure 8 is a fragmentary sectioned view of part of one end of the ducted fan propulsor shown in Figure 7 when in an air outlet configuration, Figure 9 is a similar view to that shown in Figure 8 with the duct end in an air inlet configuration.

Figure 10 is a fragmentary sectioned view of part of one end of a ducted fan propulsor when in an air outlet configuration in accordance with another embodiment of the invention, and Figure 11 is a similar view to Figure 10 but with the duct end in an air inlet configuration.

A ducted fan propulsor 21 in the embodiment of the invention shown in Figures 1, 2 and 3. includes a duct 22 comprising a tubular body portion of circular transverse cross-section surrounding a power driven fan 23 supported on a nacelle 24 located centrally of the duct 22, and supported by a plurality of struts 25. The duct 22 has a generally straight inner surface 26 and a shaped outer surface 27, and is terminated at opposed ends 28 and 29, respectively, that are formed as substantially sharp edges by inwardly inclining of the outer surface 27 to meet the inner surface 26. A fairing 30 is formed on the duct 22, and serves as a mounting for attaching the propulsor 21 to a vehicle. for example a hovercraft, for which the propulsor 21 provides the necessary motive power.

The fan 23 may be rotated in either direction so as to selectively induce a flow of air through the duct 22 either in the direction of arrow 31F or in the direction of arrow 31R. Ideally, that end of the duct 22 that functions as an air intake is curved so as to provide a flared air intake, whilst that end of the duct that functions as an air outlet has a substantially sharp edge. This is facilitated in the ducted fan propulsor 21 by the provision at each end 28 and 29, respectively, of an inflatable member 32 and shown in Figures 2 and 3.ember 3.

The inflatable member 32 at each duct end 28 and 29, respectively, is of annular shape and has an inner edge 33 attached by suitable means, such as clamping strips and bolts (not shown), around the inner surface 26 of the duct 22, so as to be adjacent the end thereof, and an outer edge 34 attached in a similar manner around the outer surface of the duct at a location spaced from the end thereof, so that the member 32 encloses the duct end.

The member 32 is formed from impermeable elastic sheet material so that when deflated, as shown in Figure 3, the member 32 lies adjacent the outer surface 27 of the duct 22 and conforms to its profile. Preferably, the surfaces 26 and 27 of the duct are relieved so that in the deflated position the member 32 is faired into the surfaces.

Means (not shown) are provided for introducing pressurised fluid into a space 35 (Figure 2) bounded in part by the member 32 and in part by the outer surface 27 of the duct 22, so as to inflate the member 32 away from the outer surface 27 of the duct 22 so that it assumes a curved shape, thereby converting the sharp edge of the duct end into a flared air intake, as shown in Figure 2.

When the member 32 is inflated, the inner surface 26 of the duct 22 forms a tangent with the curve of the member 32 so that the member forms an outwardly flared continuation of the inner surface of the duct.

In operation of the ducted fan propulsor 21, when the fan 23 is rotated so as to induce a flow of air through the duct 22 in the direction of the arrow 31F, the inflatable member 32 at the duct end 28 is inflated, as shown in Figure 2, thereby transforming this end of the duct into an air intake configuration. The inflatable member at the duct end 29 is left in the deflated condition so as to retain the sharp edge that is preferable for the air outlet configuration. When the direction of rotation of the fan is changed so that the flow of air through the duct is in the direction of arrow 31R then the inflatable member at the duct end 29 is inflated so as to transform this duct end into an air intake configuration, and the member at the duct end 28 is deflated so as to transform it into an air outlet configuration.The control system (not shown) for selecting the direction of rotation of the fan is automated so as to automatically cause inflation of the inflatable member at that duct end that will function as an air intake.

The ducted fan propulsor in the embodiment of the invention shown in Figures 4, 5 and 6, has one duct end 28 formed in a permanent air intake configuration. The other duct end 29 is formed in a trailing edge configuration with a substantially sharp edge, and is provided with an inflatable member 32 for transforming it into an air intake configuration when the propulsor operates in reverse thrust.

In this embodiment as shown in Figures 5 and 6, a passageway 36 is provided through the body portion of the duct 22. One end 37 of the passageway 36 opens into the space 35 and the other end (not shown) is arranged for selective connection, during operation, to a source of fluid pressure and a source of suction. Such a connection may, conveniently, be routed through the fairing 30 (Figure 4). The fluid pressure may be either liquid or gaseous.

A plurality of horizontally arranged return springs 38 are spaced around the duct 22 and connected between attachments 39 on the outer surface 27 of the duct 22 and attachments 40 on an outer surface of the member 32. Attachments 40 are located at a position which corresponds with an innermost fold line of the member 32 when in its deflated position, as illustrated in Figure 5.

Figures 7 to 9 inclusive illustrate a ducted fan propulsor in a further embodiment of the invention, the duct 22 again having one end 28 formed of permanent air intake configuration. In this embodiment, as shown in Figures 8 and 9, a passageway 36 in the form of a circular manifold is provided within the body portion of the duct 22 and is connected to the space 35 through a plurality of branch pipes 41. A main supply passageway (not shown) serves to connect passageway 36 to a suitable external supply.

The return springs are located internally of the member 32 within the space 35 so as to extend between attachments 39, located in recesses 42 in the outer surface 27 of the duct 22, and attachments 40 on an inner surface of the member 32, these attachments 40 being located at approximately the outermost extent of the member 32 when in its inflated position (Figure 9). The edge 33 of the member 32 is bifurcated and attached to both the inner surface 26 and the outer surface 27 of the duct 22 in the vicinity of the end 29.

A plurality of rigid plates 43 are located in side by side relationship around the outer surface 27 of the duct 22. Each plate 43 has an inner edge 44 attached through a hinge 45 to the outer surface 27 of the duct 22, and is of a length so that when the member 32 is deflated, an outer edge 46 forms the sharp edge of the duct end 29. An inner surface of each plate 43 is bonded to the member 32.

The sides of each plate 43 are tapered inwardly from its inner edge 44 (see Figure 7) and the plates 43 are curved to conform to the radius of the duct 22. The outer surface 27 of the duct 22 is relieved such as at 47 (Figure 9), and these features combine to ensure that when the member 32 is deflated and folded against the outer surface 27, the plates 43 form a uniform continuation of the profile of the outer surface 27 from the hinged attachments 45 to the outer edge 46 around the entire diameter of the duct 22.

The plates 43 open and close in the manner of petals during inflation and deflation of the member 32, and due to the attachment of the inner surface of the metal plates 43, especially adjacent their outer edges 46 to the member 32. the plates 43 provide a restraint on the inflated shape of the member 32. Instead of inflating against atmospheric pressure, a part of the member 32 is inflated against the surface of the plates 43 so that this portion of the member 32 remains straight and forms a tangent with the unconfined generally semicircular portion of the member which forms the flared air intake during reverse thrust operation.

Thus this arrangement provides an improved aerodynamic shape for the air intake during reverse thrust operations, thereby further increasing the efficiency of the propulsor during this mode of operation. Additionally, the plates 43 serve to protect the inflatable member 32 in both the inflated and deflated configurations, and the outer edges 46 of the plates 43 are arranged to provide the sharp trailing edge end of the duct 22 during forward thrust operations.

In the embodiment of the invention shown in Figures 10 and 11, the return springs 38 are again located internally of the member 32 within the space 35. The attachements 39 of the springs 38 are located at the inner end of an annular recess 48 provided in the body portion of the duct 22. The recess 48 has substantially parallel side portions located parallel with the inner surface 26 of the duct 22, and is arranged so that when the member 32 is deflated it is drawn into the recess 48 and is folded about a single fold line only, this fold line being determined by the line of attachments 40 between each spring 38 and the member 32.

In this embodiment, two passageways 36 in the form of manifolds are provided in the body of the duct 22 and are located, respectively, on either side of the recess 48.

Each passageway 36 is connected into the area of the recess 48 through a plurality of branch pipes 41. As in the previous embodiment, a main supply passageway (not shown) serves to connect each passageway 36 to a suitable external supply.

For forward thrust operation of either of the ducted fan propulsors shown in Figures 4 or 7, the fan 23 is arranged to draw air through an air intake defined by the permanently contoured leading edge end 28 and to exhaust the air through an air outlet defined by the sharp trailing edge end 29. The inflatable member 32 is retained in close proximity to the surfaces of the duct 22 around the sharp trailing edge end 29, so that the operational benefits in the form of maximum efficiency of a duct 22 having a contoured intake and a sharp outlet are retained during this phase of operation.

When the propulsor is required to function in a reverse thrust mode by drawing air through an intake defined by the trailing edge end 29, the member 32 is inflated by fluid pressure in the space 35, so that the sheet assumes a curved form to provide a contoured air intake, thereby increasing the efficiency of the propulsor 21 during this mode of operation. It is recognised that the permanently contoured end 28 is not as efficient as a sharp edge when operating as an air outlet end in the reverse thrust mode; however, the provision of the contoured air intake will provide a useful increase in efficiency in this mode of operation.

Thrust from a ducted fan propulsor in accordance with the invention is transmitted to a vehicle, for example a hovercraft, through the fairing 30 by which the propulsor is mounted. Conveniently, power and control lines for the propulsor are routed through the fairing 30.

Of course the embodiments hereinbefore described with reference to and shown in the accompanying drawings are by way of example only. and it is to be understood that various modifications may be made without departing from the scope of the invention.

For example. especially in the embodiments of Figures 4 to 6 and Figures 10 and 11, a plurality of rigid tie members may be provided between the inner surface of the inflatable member 32 and the duct 22, so as to restrain the inflated shape of the member 32 to take up an improved aerodynamic configuration.

In the embodiment of Figures 4 to 6 inclusive, the passageway 36 may be arranged to be selectively connectible to a source of fluid pressure and a source of suction. The connection may be automatically operated so that when forward thrust of the propulsor is selected, the passageway 36 is connected to a source of suction so that the inflatable member 32 is retained in a retracted position, and when reverse thrust is selected the passageway 36 is connected to a source of fluid pressure which fills the space 35 so as to cause the member 32 to extend to the inflated position. During inflation of the member 32, the inflation pressure is such as to overcome the tension of the return springs 38. When forward thrust is resumed, the springs 38 in combination with the evacuation of the space 35, ensure that the member 32 does not simply collapse in a random manner against the outer surface 27 of the duct 22, by causing it to fold neatly to conform closely to the shape of the duct, thereby retaining the desirable sharp configuration during forward thrust operation.

Again, in the embodiment of Figures 7 to 9 inclusive, the passageway 36 is shown as a manifold but may be selectively connected to fluid pressure or suction sources in a similar manner. The return springs 38 are located within the space 35 and combine with the source of suction to cause the member 32 to take up a neatly folded configuration when it is deflated.

Yet again, in the embodiment of Figures 10 and 11, the space 35 may be evacuated by a source of vacuum so as to act with the springs 38 to draw the sheet 32 into a retracted position within the recess 48. This may be facilitated by the branch lines 41 opening into the chamber 48.

WHAT WE CLAIM IS: 1. A ducted fan propulsor comprising a duct having a fan therein for inducing an air flow selectively in either direction through the duct, at least one end of the duct having an inflatable member that in deflated condition provides that duct end with an air outlet configuration, whereas in inflated condition the member provides that duct end with an air intake configuration, and means for inflating the member whenever the fan is to be operated to induce air flow through the duct in a direction such that the duct end functions as an intake.

2. A ducted fan propulsor as claimed in Claim 1, wherein one end of the duct is permanently of air intake configuration.

3. A ducted fan propulsor as claimed in Claim 1 or Claim 2, wherein that end of the duct that functions as an air outlet terminates at a substantially sharp edge.

4. A ducted fan propulsor as claimed in any one of the preceding Claims, wherein the inflatable member comprises an annular sheet of flexible material having inner and outer edges secured to the duct in a substantially fluid-tight manner.

5. A ducted fan propulsor as claimed in Claim 4, wherein the inner edge of the annular sheet is secured around the inner surface of the duct and the outer edge of the annular sheet is secured around the outer surface of the duct so as to enclose the duct end, whereby when the sheet is inflated it assumes a curved shape between the inner and outer edges thereof with the inner surface of the duct forming a tangent to the curve so that the inflated member forms an outwardly flared continuation of the inner surface of the duct.

6. A ducted fan propulsor as claimed in any preceding Claim, wherein the inflatable member is formed from impermeable elastic sheet material.

7. A ducted fan propulsor as claimed in any one of Claims 1 to 5, wherein in the deflated condition the inflatable member is biased to assume a folded configuration.

8. A ducted fan propulsor as claimed in Claim 7, wherein resilient means are connected between the inflatable member and the duct to bias the inflatable member to the folded configuration.

9. A ducted fan propulsor as claimed in Claim 8 wherein the resilient means comprises springs.

10. A ducted fan propulsor as claimed in Claim 7, Claim 8 or Claim 9, wherein the member is biased to assume a folded configuration against an external surface of the duct.

11. A ducted fan propulsor as claimed in Claim 7, Claim 8 or Claim 9, wherein the member is biased to assume a folded configuration such that it is housed at least in part within an annular recess formed in an external surface of the duct.

12. A ducted fan propulsor as claimed in Claim 1 or Claim 2, wherein an end of the duct that during one phase of operation is in an air outlet configuration comprises an inner surface and a plurality of plates extending from hinged attachment with an outer surface of the duct to form with the inner surface a substantially sharp edge, and an inflatable member secured to and housed between the plates and the inner surface whereby inflation of the flexible member moves the plates away from the inner surface so as to transform that duct end to an air intake configuration.

13. A ducted fan propulsor as claimed in any one of the preceding Claims, wherein means for inflating the member comprise at least one passageway in structure of the duct having an end opening into the interior of the space that is bounded in part by the member, and being arranged during operation for connection to a source of pressurised fluid.

14. A ducted fan propulsor as claimed in Claim 13, wherein the or each passageway in the duct structure is selectively connectible to the source of pressurised fluid and to a source of vacuum.

15. A ducted fan propulsor including a duct formed as a tubular body of generally circular transverse cross-section and having a contoured leading edge and a substantially sharp trailing edge. a power driven fan supported within the duct for inducing a flow of air selectively in either direction through the duct, a flexible inflatable member attached around the trailing edge of the duct. and means for inflating the member so as to provide a flared air intake whenever the fan is to be operated to induce a flow of air through the duct such that the trailing edge functions as an air intake.

16. A ducted fan propulsor substantially as hereinbefore described with reference to and as shown in Figures 1, 2 and 3 of the accompanying drawings.

17. A ducted fan propulsor substantially

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Again, in the embodiment of Figures 7 to 9 inclusive, the passageway 36 is shown as a manifold but may be selectively connected to fluid pressure or suction sources in a similar manner. The return springs 38 are located within the space 35 and combine with the source of suction to cause the member 32 to take up a neatly folded configuration when it is deflated. Yet again, in the embodiment of Figures 10 and 11, the space 35 may be evacuated by a source of vacuum so as to act with the springs 38 to draw the sheet 32 into a retracted position within the recess 48. This may be facilitated by the branch lines 41 opening into the chamber 48. WHAT WE CLAIM IS:

1. A ducted fan propulsor comprising a duct having a fan therein for inducing an air flow selectively in either direction through the duct, at least one end of the duct having an inflatable member that in deflated condition provides that duct end with an air outlet configuration, whereas in inflated condition the member provides that duct end with an air intake configuration, and means for inflating the member whenever the fan is to be operated to induce air flow through the duct in a direction such that the duct end functions as an intake.

17. A ducted fan propulsor substantially

as hereinbefore described with reference to and as shown in Figures 4, 5 and 6 of the accompanying drawings.

18. A ducted fan propulsor substantially as hereinbefore described with reference to and as shown in Figures 7, 8 and 9 of the accompanying drawings.

19. A ducted fan propulsor having at least one duct end convertible between and air outlet configuration and an air inlet configuration substantially as hereinbefore described with reference to and as shown in Figures 10 and 11 of the accompanying drawings.