GB2264679A - Vtol aircraft. - Google Patents

Abstract

A VTOL aircraft comprising; at least one pair of lift fans (13) in space lateral relationship, each fan having turbine blades (14) (Fig 3) disposed around its periphery, the turbine blades (14) of the fans in each pair being interdigitated in a central region between the fans; at least one jet engine (20); ducting which channels the thrust produced by the jet engine (20) into two branches (24, 23), one branch channelling the thrust for use in conventional flight, the other channelling the thrust to the turbine blades (14), ideally at the point of interdigitation, and means (26) (Fig 2) by which the engine thrust is apportioned between the two branches (24, 23). A series of moveable (30, 31) (Fig 2) vanes are positioned intermediately between the engine (20) and the thrust apportioning means (26) in order to aid the directioning of the thrust, the movement being dependant on the movement of the thrust apportioning means (26). Wing fences (10) provide a degree of aerodynamic isolation. <IMAGE>

Description

VERTICAL TAKE-OFF AND LANDING AIRCRAFT The present invention relates to a vertical take-off and landing (VTOL) aircraft.

VTOL aircraft are well known to be capable of great manoeuvrability.

Typically such aircraft operate through the use of rotatable nozzles which direct the thrust from jet engines in order to fly. An example of this is the 'Harrier' in which nozzles in one direction provide thrust to propel the aircraft forward through the air in a conventional manner.

In this mode of operation lift is generated by air passing across the aerofoil wings. By rotating the nozzles so that they point towards the ground lift is directly generated and the aircraft is able to hover or change altitude whilst remaining geostationary. There are various nozzle positions between these extremes which produce a mixture of these two effects. The aircraft also possesses trim jets in the wing tips and at other points in order to provide the stability necessary to maintain a hover mode. This type of aircraft is however inherently very expensive because of its complex design. Its use of jet nozzles for the direct provision of lift means that when hovering it is very fuel inefficient. Furthermore, the direction of the thrust through convoluted ducting whether for hovering or in straight (conventional) flight mode is inherently inefficient as well.

Aviation Week & Space Technology page 57, July 29, 1991 discusses an advanced VTOL concept study with fan-in-wing engines. The concept envisages three fan engines in each wing each fan engine being supplied with high pressure air via a bleed from three internal turbine powerplants. The fan engines include the necessary machinery of a combustor, turbine and reduction gearing for operation. Two external cruise fans operate in a similar manner to those in the wings and provide forward thrust. In operation the wing mounted fans provide lift through holes in the wings above and below the fan units. These holes are closed in normal forward flight by louvers. Whilst the use of fan-in-wing engines improves the fuel efficiency in comparison to designs like the Harrier it is still a complex design that would be expensive to produce and service.

There is as a consequence a requirement for a simplified design of VTOL aircraft which is cheaper to build, maintain and operate.

According to the present invention there is provided a VTOL aircraft in which propulsive energy is apportioned by a valve between providing thrust to produce lift and producing lateral thrust for forward flight.

Because of the high power to weight ratios necessary to allow vertical take-off it is preferable if the propulsive energy is provided by a jet engine. Whilst various types of jet engines may be employed the preferred engine is a turbojet and ideally two turbojet engines are used to produce the thrust. The use of two turbojet engines enables an economical cruise mode in forward flight with one engine shut down. The use of two engines enhances the aircraft's performance and capabilities especially in respect of its hovering and vertical take off abilities.

If required the thrust can be diverted from its conventional lateral direction to the provision of lift at speed and enables a rapid gain in altitude combined with near zero incidence of pitch. Where low operational noise requirements dictate it may be preferable to use a turbofan engine.

In order to control the thrust in the manner of the invention it is necessary that appropriate ducting be adopted. This is especially so in relation to thrust diverted for the generation of lift as the thrust is required to be diverted from its conventional lateral flow direction and therefore needs to be appropriately channelled. Preferably the ducting branches in two with one branch used for lateral thrust whilst the other branch is used for the production of lift.

The valve which is used to divert the thrust is situated to the rear of each engine housing and ideally along the axis of thrust output produced by the engines. With a similar arrangement for the ducting between the engine and the valve, frictional and turbulence losses are minimised when in conventional flight mode by ensuring a straight path and unimpeded path for the thrust to follow. The present invention with the valve in one position will result in all thrust being directed laterally from the craft in order to propel it forward. In this position lift can be produced in the conventional manner by airflow across the surface of the wings. However, as the valve is moved from the mentioned position a proportion of the thrust is diverted to the production of lift.The proportion of thrust diverted is dependent upon the degree to which the valve is moved from the sole provision of lateral thrust to the position for the sole provision of lift. Intermediate positions between the two extremes yields a mixture of the two effects.

In order to improve the efficiency of the valve diversion system it is preferable if a series of vanes are positioned intermediately between the engine and the valve to aid the direction of the thrust. The vanes preferably three in number are positioned parallel to one another at any one point but moveable depending upon the desired flight mode. As such their operation is preferably linked, conveniently mechanically, to the valve so that they co-operate. Therefore when in conventional flight mode the vanes are positioned so as to offer minimal resistance to the thrust as is also the case with the valve. However when operating in vertical take-off or hover mode the valve redirects the thrust away from the lateral flow it would normally take.The vanes help in this process of redirecting the flow and can improve the efficiency of the system whilst reducing the effect of the thrust impinging upon the valve.

The valve is preferably pivotal in operation and is conveniently attached at the branch in the ducting that delimits the position of the two ducts. To operate in the manner described above the valve must be capable of sealing one of the two conduits against the entry of engine thrust. It is therefore necessary that the valve be dimensioned to achieve this and the valve is conveniently provided as a deflectable flap.

This diverted thrust is preferably directed to drive fan units which rotate to provide the lift. Whilst the altitude ceiling is less with fan units incorporated than that of an equivalent conventional aircraft due to the mass of the fans and the associated drive mechanism it is however unnecessary to pressurize the cabin area to a conventional level and allows for a reduced fuselage mass. The aircraft can be theoretically more fuel efficient than a helicopter of the same payload capability. Operational speeds of the aircraft will probably be greater than is achievable with helicopters since the tip velocity of the fan units is unlikely to approach transonic levels during forward flight.

Preferably the fan units will possess a large area for the generation of momentum flux. This area should be much greater than the outlet area of the engines enabling a much lower power requirement for hovering than would be the case if lift were generated simply by directing the engine thrust downwards. Preferably the fan units are located in the wings of the aircraft and within the general plane of the wings in which they are located. They should be of slim thickness to reduce drag levels when the aircraft is in conventional flight mode and provided within fences which give a degree of aerodynamic isolation between the units and the surrounding aircraft structure. This has the effect of improving the aircraft's lift to drag ratio in forward flight.In certain cases it may be possible to achieve a further improvement in this parameter by driving the fan units at relatively low rotation rates when flying the aircraft at speed. In this way a small proportion of the turbine outflow from the engine is diverted to the fans in order to maintain a pressure differential to equate with that produced by the wings therefore providing continuity of lift across the wings and fan units.

Ideally there are equal numbers of fan units in each wing to balance the lift provided. In order to achieve economy of construction and use one fan unit should be present in each wing. These fan units should be of such a size that they provide the necessary flux momentum required to generate lift in excess of the gravitational influences on the aircraft.

The fans may be driven directly through the thrust impinging upon them such that the thrust is directed tangentially upon blades at the peripheral edges of the fan. Alternatively the thrust can be used to drive a turbine which is mechanically linked to the fan units. The linkage can be a worm drive which would act as a reduction gearing. In this case the engine thrust parameters (mass flow, gas velocity and pressure) would need to be suited to both lift and forward flight which may necessitate a split turbine configuration within the engine and ducting. Fan blade extensions which may otherwise be used would however become unnecessary, liberating additional area which could be used to increase the diameters of the portions of the fan units which would be driven by thrust.Furthermore it is thought that the energy transfer from the kinetic content in the turbine thrust to mechanical energy to drive the fans will be more efficient if a mechanical drive system is used. The power requirement for hovering may thus be lowered although at the expense of some additional mechanical complexity. Where a mechanical drive train is used to transmit power the fan units at least one turbine unit in addition to any in the engine itself is placed within the ducting from the engine allow for the conversion of thrust into mechanical energy and its take off to power the fan units.

Control in pitch, yaw and roll whilst hovering can be achieved by air bleed from the turbine compressor stages of the engine providing flow to controllable jets mounted in the wing tips, nose and tail in a manner similar to that used in the Harrier VTOL aircraft. The transition from lift to forward flight is ideally accomplished progressively through proportional operation of the thrust divertor valve. Control in forward flight is achieved through the use of conventional moveable aerodynamic surfaces.

Because the present invention is a VTOL aircraft there is a need for it to be made to a specification giving it a low overall mass. Therefore certain parts of the aircraft should be made from lightweight high strength materials. In particular such materials should be used for components which experience bending or high shear loads such as the fan unit by virtue of flexing of the wings.

The invention will now be described by way of example only and with reference to the accompanying diagrams of which: Figure 1 shows an aircraft incorporating the invention; Figure 2 shows a thrust divertor valve of the invention; Figure 3 shows a view of a fan unit as used in the aircraft of figure 1; and, Figure 4 shows a sectional drawing of the fan unit of figure 3 along line A-A.

With reference to the figures 1 to 4 a pilotless VTOL aircraft (1) comprises a fuselage (2) of generally circular form which at its forward end is bowed out in comparison to the rest of the fuselage, the bowed area representing a stowage area (3). To the rear of the bowed section, the fuselage tapers and attached to the rear end of the fuselage there is a tailplane (4) comprising rudder (5) and elevators (6).

A pair of wings (7) is connected to the fuselage (2) through a spur (8) upstanding from the forward end of the fuselage. The spur is fixed centrally and positioned longitudinally to the top of and towards the front of the fuselage and the wings are attached at their central position to the spur. The wings possess a broad central section (9) defined by two low ridges forming fences (10) around the wings. The wing tips are terminated by similar fences (11). The central section has two large circular holes through it (12) in the plane of the wings.

These holes house two large fan units (13) positioned in the same plane relative to each other and the wing, with both fan units being aligned perpendicular to the axis of the fuselage such that the peripheral edges of the fan units possess blades (14) that are at one point interdigitated. The fan units are held in position by being fixed to axles, partly shown in (15) through a hole (not shown) in the centre of each fan unit, the axles being supported in position by a triangular bracket (16) affixed to the wing. The bracket comprises three equiangular arms (17) fixed at the end of each arm to the aircraft wing.

The axles relating to each of the fan units are mechanically linked via a bar (18) with two universal joints (19) at each end, to each of the fan unit axles.

Two turbojet engines (20) are mounted parallel to each other near to the nose of and axially with the fuselage. The turbojet engines have compressor fans (21) at their front which are open to the atmosphere.

An arrangement of ducting (22) otherwise envelopes the each of the engines with the ducting extending from the rear of the engines so as to conceal their presence except for the fans (21). The ducting is branched into two just beyond the rear of the engine with one branch being axial (23) to the engine and terminating to the atmosphere a short distance beyond the branch. The other branch (24) extends upwards and generally away from the engines penetrating the wing structure where the separate ducting from each engine is formed into a single duct by a shroud (25) positioned on the upper surface of the wings. The shroud is directed tangentially to and terminates at the series of blades that are attached to the peripheral edges of the fans units.

A divertor valve (26) which in use is hidden from view by the ducting, is slidably and pivotally positioned at the branch of the ducting (27).

Attached to the divertor valve is a cam follower (28) that is positioned within a track (29) and which in conjuction with the pivot define a path over which the valve is moveable. Three slightly curved vanes (30) are fixed in position between the engine turbine output (not shown) and before the divertor valve. Pivotally attached to the end of each vane closest to the divertor valve is a further vane (31) which tapers towards the valve. The valve is mechanically linked to the moveable vanes (not shown) such that the vanes act to help in directing the thrust as dictated by the position of the valve within the ducting branch. The track is arranged to make the cam follower and hence the valve follow a path such that the valve is not fouled by the moveable vanes in passing between the two extreme valve positions. In normal flight mode operation thrust from the engines passes through the ducting with the moveable vanes and valve in position A. The thrust is thus directed out of the ducting lateral (32) to the aircraft. This causes the aircraft to move forwards through the air and any lift is generated by the action of the air mass incident upon the wing surfaces.

When there is a requirement for lift to be generated in a more direct fashion to enable the aircraft to hover or undertake vertical take off or landing, then the moveable vanes and valve are moved to position B.

The engine outflow is directed by the vanes and the divertor valve to follow the ducting into the shroud on top of the wing and then tangentially at an angle of 20 on to the blade surfaces at the point of interdigitation of the fan unit blades. The bulk of the flow energy is extracted and causes the fan units to move in contra-rotation and give rise to a momentum flux from the top of the wing to the underside therefore generating lift. The mechanical linkage of the fan units through the shaft ensures equal speed of rotation and prevents contact of the blades at the point of interdigitation.

The aircraft may be suitable for carrying passengers and is capable of take off and landing in environments such as city centres where space difficulties tend to be present. Furthermore the use of multi-bladed, shrouded fan units can result in noise levels that are lower overall than for a helicopter of equivalent load capacity. The aircraft and inhabitants of areas surrounding its take off and landing sites should be free from low frequency noise resulting from the passage of rotor blades above the fuselage as experienced in a conventional helicopter.

Claims (1)

1. A VTOL aircraft in which propulsive energy is apportioned by a valve between providing thrust to produce lift and producing lateral thrust for forward flight.

2. A VTOL aircraft as claimed in claim 1 characterised in that the propulsive energy is provided by a jet engine.

3. A VTOL aircraft as claimed in claim 1 or 2 characterised in that the propulsive energy is provided by two turbojet engines 4. A VTOL aircraft as claimed in any one of the previous claims characterised in that the thrust is channelled through ducting which branches in two with one branch used for lateral thrust whilst the other branch is used for the production of lift.

5. A VTOL aircraft as claimed in any one of the previous claims characterised in that the valve is situated to the rear of each engine housing along the axis of thrust output by the engines.

6. A VTOL aircraft as claimed in any one of the previous claims characterised in that the valve is pivotal in operation.

7. A VTOL aircraft as claimed in claim 6 characterised in that the valve is pivotally attached at the branch in the ducting that delimits the position of the two ducts.

8. A VTOL aircraft as claimed in any one of the previous claims characterised in that a series of vanes are positioned intermediately between the engine and the valve to aid the direction of the thrust.

9. A VTOL aircraft as claimed in claim 9 characterised in that the vanes are positioned parallel to one another.

10. A VTOL aircraft as claimed in claim 8 or 9 characterised in that each vane is moveable.

11. A VTOL aircraft as claimed in claim 10 characterised in that movement of the vanes is linked to movement of the valve.

11. A VTOL aircraft as claimed in any one of the previous claims characterised in that the thrust used for the production of lift is directed to drive fan units which rotate to provide lift.

13. A VTOL aircraft as claimed in claim 12 characterised in that the fan units possess a large area.

14. A VTOL aircraft as claimed in claim 12 or 13 characterised in that the fan units are located in the wings of the aircraft and within the general plane of the wings within which they are located.

15. A VTOL aircraft as claimed in any one of claims 12 to 14 characterised in that the fan units are provided within fences which provide a degree of aerodynamic isolation between the units and surrounding aircraft structure.

16. A VTOL aircraft as claimed in claim 14 or 15 characterised in that there are equal numbers fan units in each wing.

17. A VTOL aircraft as claimed in any one of claims 12 to 16 characterised in that the thrust is used to drive the fans units directly.

18. A VTOL aircraft as claimed in any one of claims 12 to 16 characterised in that the thrust is used to drive turbine which is mechanically linked to the fan units.

19. A VTOL aircraft specifically as herein described and with reference to the accompanying drawings.