WO1997017241A1

WO1997017241A1 - Ground effect vehicle

Info

Publication number: WO1997017241A1
Application number: PCT/AU1996/000698
Authority: WO
Inventors: Michael John Leslie
Original assignee: Sea Wing International Pty. Ltd.
Priority date: 1995-11-06
Filing date: 1996-11-05
Publication date: 1997-05-15
Also published as: EP0859715A4; NZ320036A; AUPN638795A0; EP0859715A1

Abstract

A ground effect vehicle has a fuselage (1) for operation in water. Wings (5) curve downwardly from each side of the fuselage. In plan the wings are triangular with leading edges jutting at right angles to the fuselage. In front elevation the wings are attached high on the fuselage and exhibit a compound downward curve to tips at the level of the bottom of the fuselage. The angle of attack of each wing increases gradually from the root area to a maximum along the wing and then decreases towards the wing tip. The high angle of attack at mid-wing gives high lift at low speeds but the increase in drag occasioned thereby does not become significant until air speeds over 180 knots. This makes for a fail-safe design as the wing will not fly out of ground effect irrespective of the installed horsepower. The diverging tail fins (19, 20) minimise banking on turns thus maintaining the air cushion under the outboard wing.

Description

TITLE: GROUND EFFECT VEHICLE

This invention relates to an improved vehicle which relies on the known ground effect to achieve more efficient operation of the vehicle.

BACKGROUND OF THE INVENTION

Ground effect is achieved when an aerofoil is operating close to the ground plane, and in this position the lift generated by the aerofoil can be increased by up to 45% and the drag decreased by up to 70% as compared to the same aerofoil operating in free flight away from the ground plane. This increase in efficiency is achieved in two ways. Firstly the proximity of the ground plane suppresses the usual "trailing edge vortices" formed behind the wing tips, and secondly, the down wash off the top of the wing is restricted. This down wash is normally responsible for creating considerable "induced drag" when it mixes and eddies with the air that has passed under the wing. In ground effect, the air that has passed under the wing is more compressed and is generally less turbulent than when the wing is in free flight.

While the ground effect is utilised by sea birds, was utilised by the Wright brothers, and also by conventional aircraft to increase their range, over the last 25 years extensive research and development work has been undertaken world-wide to establish the fundamental design criteria for high efficiency ground effect vessels for marine environments.

One of the most efficient examples of such a craft is the Lippisch reverse delta plan form craft known as the X-114, an example of which is described in US 3,190,582. In this craft the wings extend slightly downwardly from the fuselage to the wing tips which terminate in upwardly and outwardly extending winglets. In plan the leading edge of the wing is generally at right angles to the fuselage. Although the chord section of the wing varies from the root chord to the wingtip chord, the angle of attack of the wing is constant along is length. This craft is designed to operate either in the ground effect plane or in free flight, and thus the craft is classified as an aeroplane.

Lippisch continued development as exemplified by US patents 3,830,179; 3,611 ,111 and 3,627,235. The vehicle of this latter patent has been under development by a German company Rhein Flugzeugbau under the name of "Airfish 3". Another such vehicle has been developed in the former U.S.S.R. by The Centre for Life Saving Technology designated EYSKA 1 as described in Janes Surface Skimmers 1991 page 368.

There has been further development based on the Lippisch design of the reverse delta plan form, the Chinese XTW series of ground effect craft is described in Janes High-Speed Marine Craft, twenty-sixth edition 1993-94 which has a typical power to weight efficiency of 10kg/kW, the surface clearance being 6 metres which is 50% of the wingspan above water. Propellers are mounted at the leading edge of the wing, apparently in an attempt to gain some power assisted ram effect, but limits the use on water to a maximum of 1 metre wave height.

It is an object of this invention to provide a ground effect vehicle which will operate over greater wave heights.

It is a further object of the invention to provide a ground effect vehicle which will have a short take off run while being a long range craft necessary for the Australian coast line.

It is a still further object of the invention to provide a ground effect vehicle which is not classified as an aircraft.

A still further object of the invention is to provide a ground effect vehicle which is limited to ground effect flight, and thus cannot partake of free flight out of the ground effect area.

BRIEF STATEMENT OF THE INVENTION

Thus there is provided according to the invention a vehicle capable of operation above ground or water in the ground effect area but not in free flight, said vehicle comprising a fuselage, wings, tail assembly with elevator and rudder, propulsion means, and a hull for operation in water, wherein said wings extend downwardly from each side of the fuselage and each being substantially triangular in plan and terminate in winglets at the wing tip, the leading edge of each wing being in plan at right angles to the fuselage, the root rib of each wing extending from the leading edge of the respective wing to the rear of the fuselage, each wing having in front elevation a compound downwardly curved wing section terminating in said upstanding winglets, the angle of attack of each wing increasing from the root area to a maximum along the wing and then decreasing towards the wing tip.

In a preferred form the maximum angle of attack is such that at higher speeds stagnation is promoted under the wing to defeat and counteract some of the lift on top of the wing thus preventing free flight.

It is preferred also that the wing root is at the upper portion of the fuselage and the wing tip at a level near the bottom of the fuselage.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more fully describe the invention reference will now be made to the accompanying drawings in which:

Figure 1 is a perspective view of one form of craft embodying the invention,

Figure 2 is a plan view of the craft of Figure 1 ,

Figure 3 is a front elevation showing the curvature of the wings, and

Figure 4 is a sectional side view showing the profile of the wing from wing root to wing tip.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in the drawings, the ground effect craft comprises a fuselage with a hull 2 and undercarriage 3. However as the craft is primarily designed for operation on and over water, the undercarriage will be retracted into the hull for operation on water, the undercarriage only being extended when it is required to beach the craft or run it onto a ramp or into a hanger for maintenance. At the rear of the fuselage there is a tail assembly 4 and wings 5 attached to the fuselage at the upper portion of the fuselage.

Each wing 5 extends at its root area from the leading edge 6 to adjacent the rear of the fuselage 1 as shown in Figs 1 , 2 and 4 with the trailing edge 7 extending from the wing tip 8 to the rear of the fuselage 1. Each wing in front elevation has a compound curved shape, the wing curving downwardly from the leading edge at the root chord at the upper portion of the fuselage to the wing tip at a lower position adjacent to or on the same level as the hull 2. Thus as shown the wing extends in a curve downwardly to the wing tip which is on or level with the lower portion of the fuselage.

Thus each wing is a reverse delta in plan form, the leading edge being generally normal to the fuselage. Figure 4 shows the wing section at various ribs, the chord length decreasing from the root rib 10 through ribs 11 , 12, 13, 14 to the tip rib 15, which thus results in the reverse delta plan form with the leading edge being generally normal to the fuselage. It is noted that the angle of attack of the wing varies throughout its length, from the root rib, increasing to a maximum at rib 13, and then decreasing again to the tip rib 15. In a preferred form the wing has an angle of attack of 8° at the root, increasing to 14° and then decreasing to 8° at the tip. Each wing has winglets 16 at the tip, the winglets extending upwardly at an angle and having adjustable ailerons 17. The winglets and ailerons reduce the wing tip vortex losses and provide banking and cross wind control to the craft.

As shown in front elevation, each wing curves downwardly, thus having a negative anhedral, or anhedral. However the anhedral angle is not constant across the span of the wing, and gradually increases along the span of the wing to a maximum towards the wing tip. This in combination of the reverse delta plan form of the wing creates a compound undersurface shape of the wing, resulting in efficient operation as later described.

The craft is powered by at least one engine mounted in the fuselage and driving ducted propellers or fans 21 mounted above the fuselage. The tail assembly includes the conventional elevator 18 and rudders 19. However the tail assembly comprises two fins 20 inclined in a Vee formation supporting the stabiliser and elevator 18 at their top. Thus there are two rudders, one on each inclined fin 20.

The hull 2 is formed with two outboard portions 22 and 23 which extend rearwardly to breakaway 24. Between the outboard portions 22 and 23 the undersurface 25 of the hull slopes downwardly and rearwardly from the front edge 26 to a section 27 where the surface then slopes rearwardly and downwardly to the section 28 where it merges into the bottom-of the outboard portions 22 and 23.

With this shape of hull 2, during take off on water the forward motion will raise the pressure of the air under the hull, thus assisting in the lift of the craft. Also just prior to lift off, bubbles of air will be formed in the water under the rear portion of the hull, reducing the drag, and lift off occurs with a clean breakaway due the shape of the rear portion 24 of the hull. When on the water the craft is stabilised by the wing tips having small pontoons 30 which rest in the water.

In order to reduce the take off and landing runs to a minimum it is essential to have greatest wing lift at low air speeds, and in order to achieve lift at low air speeds, the angle of attack must be high. This is achieved by the wing of the present invention which has a varying angle of attack along its span, the higher angles of attack giving high lift at low air speeds, and the lower angles of attack providing greater lift at higher air speeds.

However the wing sections having a greater angle of attack generate increased drag at higher speeds and they actually promote stagnation under the wing. This pocket of stagnation in turn leaks air over the trailing edge, increases velocity components in the downwash air stream, and at high airspeeds ultimately defeats some of the lift on the top wing surface. It has surprisingly been found however, that the increase in drag only becomes significant at airspeeds over 180 knots, and actually prevents the wing from ever achieving flight out of ground effect. Thus the wing has an effective fail safe design, for irrespective of the installed horsepower, the craft will not achieve free flight out of ground effect.

The compound wing profile of the present invention also provides an excellent Lift/Drag efficiency. In the previous designs an efficiency of 20% of the wing span above the surface was considered good. It has been found that the aspect ration of the wing in a ground effect operation greatly influences the overall efficiency in terms of Lift/Drag. While the Lift/Drag efficiency of the present wing design is not high when flying at a height of 10% of the wing span, when flying at a height over 10% of the wing span, the positive effect of the under wing shape becomes significant. Thus when operating at 30% of wing span above the ground plane there is a Lift/Drag coefficient of 37. When flying 20% which is still acceptable.

Thus the craft is very efficient when operating at a height of around 30% of the wing span which gives adequate clearance when operating over waves.

The tail assembly by utilising the Vee tail arrangement provides that during a standard rudder turn, the Vee tail arrangement forces the vessels outboard wing to push down on the cushion under the wing to thus hold the wing down to avoid any air cushion losses normally encountered when making a banked turn. Such losses would reduce the craft's surface clearance. This however can result in a turn of large radius. This can be overcome by using the wing tip ailerons to bank the craft to a small degree, so that the cushion losses under the outboard wing are held to a minimum, and provided of course there is sufficient surface clearance.

The craft of the invention can be used as a passenger ferry, for cargo and freight transport and even for surveillance duties. The craft is a quick mode of transport between islands and around coastal waters.

Thus there is provided according to the invention a ground effect craft which is efficient in operation, has a high weight to power ratio, and also a high Lift/Drag ratio, and although one form of the invention has been described in some detail, it is to be realised that the invention is not to be limited thereto, but can include variations and modifications falling with in the spirit and scope of the invention.

Claims

1. A vehicle capable of operation above ground or water in the ground effect area but not in free flight, said vehicle comprising a fuselage, wings, tail assembly with elevator and rudder, propulsion means, and a hull for operation in water, wherein said wings extend downwardly from each side of the fuselage and each being substantially triangular in plan, the leading edge of each wing being in plan at right angles to the fuselage, the root rib of each wing extending from the leading edge of the respective wing to the rear of the fuselage, each wing having in front elevation a compound downwardly curved wing section terminating in said upstanding winglets, the angle of attack of each wing increasing from the root area to a maximum along the wing and then decreasing towards the wing tip.

2. A vehicle as defined in claim 1 wherein the wings are attached to the upper portion of the fuselage and extend outwardly and downwardly to the wing tips at a plane level with the lower portion of the hull.

3. A vehicle as defined in claim 2 wherein the anhedral angle of the wing increases along the span of the wing towards the wing tip.

4. A vehicle as defined in claim 1 wherein winglets at each end of the drawings each extend upwardly and outwardly, an aileron on each of the winglets to assist in the turning and banking of the vehicle.

5. A vehicle as defined in claim 1 wherein the tail assembly comprises two upwardly extending fins diverging from each other, rudders on each fin, and a horizontal stabiliser joining the tops of the fins, and an elevator on the stabiliser, whereby in use the inclined fins assist in minimising the banking of the vehicle to maintain the air cushion under the outboard wing.

6. A vehicle as defined in claim 1 wherein the angle of attack along the wing is such that the large angle of attack assists in producing lift at low air speeds, and at higher speeds causes drag and stagnation under the wing so that free flight of the vehicle out of the ground effect is prevented.

7. A wing for a vehicle adapted to operate in the ground effect area of flight, said wing having a varying angle of attack along the wing from-the wing root to the wing tip, said angle of attack increasing from the wing root to a maximum and then decreasing towards the wing tip, said maximum angle of attack being such that lift is created at low speeds but that at higher speeds the stagnation and loss of lift occurs such that the vehicle cannot operate out of the ground effect area.

8. A wing as defined in claim 7 wherein the wing is of reverse delta plan form.

9. A wing as defined in claim 8 wherein the wing is of varying anhedral, the anhedral angle increasing along the span of the wing.