GB2423971A

GB2423971A - Autogyro hovercraft

Info

Publication number: GB2423971A
Application number: GB0505109A
Authority: GB
Inventors: George W Davis
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-03-12
Filing date: 2005-03-12
Publication date: 2006-09-13
Also published as: GB0505109D0

Abstract

A hovercraft is provided with lift from air cushion means as well as from one or more autogyro rotor(s). The air cushion means may comprise a skirt which is adjustable in height, whilst a ski, wheel and/or float may be provided within the skirt. Also disclosed is a submergible rudder (figure 6) for an air cushion vehicle.

Description

Autogyro cum hovercraft

Description

Field of the Invention

The invention is related to craft which flies having two particular categories of lift, in particular to craft having at least air cushion lift (e.g. as known in a hovercraft) and also lift produced by autorotating rotor blades (e.g. as known in a gyroplane or autogyro). The autorotating rotor blades need air passing through them from below for them to rotate and produce lift. It is the forward motion of the craft which allows the air to pass through the rotor blades from below. It is the airstream from a means of propulsion (i.e. engine with propeller) which through a means of diversion in one embodiment gives the craft its lift so that it hovers above the surface across which it may also move.

This lift airstream may be taken from the main propulsion engine (i.e. the engine which propels the craft forward), normally by partitioning (i. e. dividing) a portion of this airstream as shown in FIGURE 4. The partitioned air is directed downwards to provide the air cushion which may be maintained by a skirt around the perimeter of the craft to contain the cushion of air below the craft. Alternatively the lift airstream of the craft may be provided by a separate lift engine as is well known in the art of hovercraft design.

Means of propulsion in the form of propeller blades are blades attached to an engine may propel the craft in a substantially horizontal direction which is parallel to the surface on and over which the craft is moving. Rotor blades in this craft are undriven (i.e. they are not attached to an engine) and rotate or rather autorotate due to the forward motion of the craft. For an understanding of the invention it is important to note the difference between rotor and propeller blades in an autogyro or gyroplane: the rotor blades are undriven, the propeller blades are driven. The rotor blades provide a net lift force which acts to lift the craft off the surface across which it may move. The propeller blades, which are driven by an engine, propel the craft across the surface over which it may move and are not intended to directly provide a lift force.

The invention may be used in manned craft optionally with a payload and may also be used in unmanned craft which are remotely controlled such as radio controlled model craft or drones controlled by person or computer. The invention may find application as a fast passenger or freight feny or search and rescue vessel and also as a craft in military applications where quick access to and over difficult terrain such as water and marshland is needed.

The invention is also related to submergible rudders for hovercraft.

The invention is also related to a float to be used with air cushion means.

Background of the Invention

A hovercraft in helicopter configuration with driven propeller and tail blade is known from US-A-4,984,754 and US-A-5,026,002 both to Yarrington. It is important to note that the autogyro or gyroplane does not normally have a collective control since the rotor blades are not driven. Furthermore since the rotor blades are not driven and as a direct consequence of this the autogyro or gyroplane has no tail rotor. As is well known in the art the tail rotor is required in a helicopter to provide anti-torque which counters the torque which is driving the main rotor blades. The different structural elements between helicopter and autogyro or gyroplane are shown in the publication Rotorcraft Flying Handbook: FAA - H808321, which is incorporated herein by reference.

The drawbacks of helicopter type air cushion craft are that such craft are complex in design and also require training as a helicopter pilot in addition to having familiarity with the dynamics of the hovercraft. They also appear have a small range and a rather small payload capability. Furthermore craft which are based on helicopter designs are expensive to build and maintain and to gain airworthiness certificates from the appropriate authorities.

Furthermore boats with autorotating blades in place of sails are also known US-A- 4,803,93 8 incorporated herein by reference. In contrast to this autogyros or gyroplanes with floats instead of or as well as wheels for landing gear are known from FR-A-2,25 1,473 and US-A-2,068,6 18, the latter also teaching small steerable rudder sections on the floats both of which are incorporated herein by reference. The autogyro with floats for landing on water suffers from the disadvantage of providing a large amount of friction between the landing surface and the autogyro or gyroplane.

Autogyros with multiple rotor blades are known from US-A-6,089,501, also incorporated herein by reference.

A ground effect craft with submergible rudder is known from US-A-3,661, 111 incorporated by reference.

An autogyro with auxiliary rotor blade drive is known from US-A-4,653,705 to Benson and incorporated by reference.

General autogyro or gyroplane information is also available at the website www.gyropilot.co.uk which is incorporated herein by reference.

Air cushion designs are known from the publication "HOVERCRAFT: The Constructor's Guide" by Jeremy Kemp, published by the Hovercraft Club of Great Britain, 2002 with reference HCI 13, ISBN 0-906535-55-7 and the website www.hovercraft.org.uk both of which are incorporated herein by reference.

The disadvantages of the known hovercraft are that they have relatively high friction with the surface over which they move and thus have difficulty in approaching high speeds when close to or in contact with the surface and additionally have difficulty in steering at high speeds when close to or in contact with the surface.

The disadvantages of the known craft are overcome by the features of the invention as disclosed in the appended claims.

Summary of the invention

According to one embodiment the craft of the invention may be initially understood as a combination of a hovercraft with an autogyro. The advantages of combining the two category of craft (i.e. hovercraft and autogyro or gyroplane) give a surprising effect in that certain features of each category of craft are also required by the other, for example the forward propulsion means (i.e. the engine and propeller) and steering means (i.e. rudder control in the yaw axis), whist other features of each category of craft are exclusive to that craft (i.e. the separate lift means: the air cushion means of the hovercraft and the autorotating blade set of the autogyro or gyroplane) and when combined in the craft of the invention these separate lift means cooperate with each other in such a way as to improve the overall energy utilization of the craft.

Furthermore it is the forward motion of the craft of the invention which aids the inflow of air required for the autogyro or gyroplane whilst the lift of the autorotating rotor blades aids the air cushion lift and this allows more effective realization of the split of energy between lift and propulsion. It is the propulsion means which provides a forward motion to the craft of the invention and these means are not intended to directly provide a lift force. The forces of lift are provided directly by an air cushion and a set of autorotating blades.

The effect of the invention regarding energy efficiency is that the faster the craft of the invention travels progressively more of the power may be used for propulsion and less power for maintaining the air cushion lift since a portion of the lift required is now also supplied by the autorotating blades. The cyclic control of the autogyro or gyroplane may be used to vary the disc of the autorotating rotor blades in the pitch and roll axes and maintain the craft of the invention in ground effect.

Clearly the craft is not limited to operation in ground effect where it is considered to operate in the most energy efficient manner. Depending on the use of the craft it may be seen as a craft operating in a hovercraft mode or an aircraft mode. The hovercraft mode of operation operates mainly with the use of ground effect (i.e. the rotor blades may use the ground effect to increase the lift available). The aircraft mode of operation operates mainly out of ground effect (i.e. the rotor blades may not use the ground to derive any lift). Such a distinction between craft flying in ground effect and out of effect of ground is well known in aviation, particular with respect to fixed wing aviation. The invention is also related to a method of flying.

Alternatively the invention may be regarded as an autorotating lift craft (e.g. a gyroplane or autogyro) with air cushion means as landing gear.

The invention also concerns a float to be used with air cushion means.

The invention also concerns a submergible rudder which is controlled to be varied in angle with respect to the plane along the longitudinal axis of the hovercraft.

This submergible rudder, in one embodiment, is intended to cooperate with, but be independently controllable from, the rudder in the airstream of the propulsion means. In another embodiment the whole rudder is varied unlike conventional submerged rudders in boats and ships in which only a section of the rear (with respect to the direction of travel) of the rudder is normally controllable.

Details of specific embodiments are illustrated in the accompanying drawings.

In the drawings: FIG. 1 represents two views (head on view and view from the side) of a tractor gyroplane cum hovercraft according to the invention.

FIG. 2 represents a side view of a pusher autogyro cum hovercraft according to the invention.

FIG. 3 represents two views of a further embodiment of a pusher autogyro cum hovercraft according to the invention.

FIG. 4 represents tail section of a hovercraft which may be used in the craft of the invention.

FIG.5 represents the hovercraft floats in a pusher autogyro cum hovercraft according to the invention FIG. 6 represents the submergible rudder hovercraft according to the invention FIG. 7 represents three views of an autogyro cum hovercraft with two rotor blade systems according to the invention.

Description of the invention

A hovercraft is normally designed with the air cushion substantially parallel to the surface on which the craft is to move across. The surface may be liquid or solid.

Such a craft normally has at least one propeller mounted on an engine and positioned so as to propel the craft across the surface. The air cushion means is provided by a skirt which is normally provided, entirely or partially, around the outer circumference of the craft so as to provide a seal for a cushion of air located below the craft and between craft and the surface over which it is moving.

Furthermore means are provided to draw air in from outside the craft so as to inflate the skirt. The craft has a rudder section which is normally located in the air stream of the forward propulsion propeller. The rudder section may be formed of a single or multiple rudders normally within the circumference defined by the rotating propulsion propeller tip but optionally may be designed outside this circumference as is the case for the design of the rudder sections in the Twinstarr autogyro, designed and produced by Don Farnngton.

In addition to these features the craft of the invention has a set of rotor blades which when rotating form a disc, the plane of which is substantially parallel to the plane of air cushion. The axis of rotation of the rotor blades is substantially perpendicular to the plane of the air cushion. In straight and level condition for the craft the rotor blade tips form a disc which is substantially parallel to the ground surface. Details of how and why the rotor tip disc is not exactly neither parallel to the surface nor symmetrical about the axis of rotation are not given here. Details of the precise rotor blade tip disc geometry are given in the FAA handbook referred to above as well as "Development of the Autogiro: a technical perspective", J. Gordon Leishman, a paper presented at the Hofstra University Conference From Autogiro to Gyroplane- The Past, Present & Future of an Aviation History, Hofstra University, NY, April 25&26, 2003, incorporated herein by reference.

The controls of the craft of the invention appear very similar to those of a conventional autogyro since propeller blades are provided as part of the propulsion means to move the craft (i.e. propulsive force being controlled by a throttle lever from a cockpit)and a rudder section (i.e. for control of the craft about the yaw axis) being controlled by pedals from the cockpit and a cyclic control stick being provided to control the cyclic pitch of the disc formed by the autorotating blades(i.e. for roll and pitch axes). In addition to these controls the pilot will also have controls for the air cushion which determine when the air cushion is operated and the ride height provided by the air cushion means. In the craft of the invention the propulsion means are provided to propel the craft forward and are not intended to directly provide a lift force.

The known design of an autogyro or gyroplane (either tractor or pusher type) has a propeller and rotor whose tail section includes a rudder and optionally horizontal stabilizer(s). This can be seen from the aforementioned prior art in US-A- 4,653,705 to Benson. In addition to these known features the craft of the invention has an air cushion landing gear shown schematically in the upper diagram of FIGURE 3.

In a single engine craft which uses a vane (and ducting) to split the airstream for use as air to inflate the skirt of the hovercraft (shown schematically in FIGURE 4) as well as providing air for thrust to propel the craft over the surface, it is calculated that in the mainly hovercraft-mode (as opposed to the mainly aircraft- mode) the craft of the invention will, for comparable power setting and cruising speed, have a reduced engine power required for air cushion lift and thus make additional engine power available for forward propulsion of the craft. This effectively increases the payload and endurance capacity of the craft over equivalently powered hovercraft of previously known designs.

In a preferred embodiment the craft has only one set of rotor blades. Nevertheless multiple rotor gyros such as known from US6,089,501 will also benefit from the features of the invention. A design with two separate sets of rotor blades is shown in FIGURE 7.

In one embodiment an extended cowling is envisaged which would extend to collect the portion of the propeller airstream closest to the fuselage. This design is shown schematically in FIGURE 1. The cowling is controlled to extend in a radial movement out from the fuselage. Ducting which is partially within the body of the fuselage is used to conduct the collected portion of air to the air cushion.

It is advantageous with a tractor configuration craft to ensure that the rotor blade direction of rotation is aided by the propeller wash. The propeller wash is that air which the propeller causes to spiral down the fuselage. This appears to be especially noteworthy where the horizontal point of location of the axis of rotation of the rotor blades is located close to the propeller.

In FIGURE 3 a pusher autogyro cum hovercraft according to the invention is shown which is configured with a conventional autogyro rudder section in the propeller airstream. As is conventional with single seater autogyros the propeller in this embodiment is unducted. In FIGURE 2 a pusher autogyro is shown which shows a ducted propeller where the rudder section (not shown) is within the duct as is normal for a hovercrafl design. The conventional air intake geometry of a ducted propeller is shown in FIGURE 4. The rudder section (not shown) may be located within the duct downstream of the propeller.

The propulsion means may be provided alternatively by ajet engine or other conventional means of propulsion know in the aviation field.

Research applications The craft of invention, since it may fly close to the ground and it may (i.e. depending on particular territorial legislation) not require certification as an aircraft. Such a craft allows experimentation on the optimization of autogyro design and control including the possibility to examine in a relatively cost effective environment features such as blade orientation, thrustline geometry and asymmetrical design considerations. Thus since the craft of the invention possesses many of the attributes of the known autogyro it is anticipated that information gained in experimentation with the craft of the invention will be relevant, with the appropriate modifications, for the design improvement of the known autogyro or gyroplane.

The craft of the invention will also provide a valuable source of information in the control of craft in the multiple separate sources of lift category. A known problem in such craft (i.e. fixed with rotating wing) is the control of the autorotating blades at higher airspeeds where an increasing amount of lift is provided by the fixed wing structure and the blades are required to be slowed to minimize drag.

The craft of the invention allows the study of control schemes of craft having two separate category sources of lift, this in the case of the invention being air cushion lift and autorotating blade lift. Furthermore the craft of the invention allows for only one engine to be used but optionally the craft may have more than one.

It is noted that with normal hovercraft designs the thrustline by design is high with respect to the vertical position of the center of gravity and that the driver normally assumes a position low in the craft, below the thrustline. This means that the thrust force then acts to force the nose down. This is normal in the design of a conventional hovercraft. However by varying the position of the driver or the height of the duct and propeller of the craft the position of the thrustline with respect to the center of gravity of the craft may be modified. For the design of a conventional autogyro a thrustline passing through or very close to the center of gravity is indicated.

Instrumentation may be provided to allow the separate measurement of the amount and degree of the sources of lift. This information may be required to allow the safe transition from one source of lift to the other, to allow the safe transition from one source of lift to both and to allow safe transition from both to only one.

Other instrumentation may include an inclinometer for measuring the inclination of the mast to the vertical and also for indicating the rate of change of inclination.

This may provide information on the possible onset of PlO; pilot induced oscillation. Furthermore instrumentation of the rotor rpm as well as rotor angular acceleration gives an indication of disc or rotor blade loading. An axial force measurent between the rotor and the mast of the autogyro measured along the axis of rotation gives a further indication of disc or rotor blade loading.

Variable drop length skirt In a further aspect to the invention as an autorotating lift craft the length of the drop of the air cushion skirt may be variable and controlled to have an extended length during take off and landing or when conditions of weather and surface of travel (e.g. swell of waves) indicate that this would be preferable. This allows for the use of air cushion flight at higher height above ground level than is normally the case for a similar conventionally designed hovercraft. The longer vertical drop may occasionally be necessary to seal the craft at an appropriately safe height so that the air cushion lift may be used when the craft is in proximity to the landing strip.

The features of the invention may also be used on craft having in total more than these two separate categories of source lift, as for example in a craft having fixed wing lift structures as well as autorotating lift and air cushion lift structures.

Float with air cushion combination In a preferred embodiment shown schematically in FIGURE 5 there may also at least one wheel or float which on loss of air cushion pressure or on dynamically varying ride height conditions increases the friction between the craft and the surface (e.g. a metalled or sea runway). Increased friction is required for stopping after landing and also during a prerotation process which takes place prior to take off. Decreasing the air cushion pressure may provide increased friction.

In a further preferred embodiment the craft has more than one wheel within the skirt of the air cushion landing gear. This provides a fail safe landing for the landing on a hard surface such as a runway or field. If the air cushion should fail the craft will nevertheless land safely on the hard surface. This also allows the use of liquid (in the case of a float) or hard (in the case of a wheel or ski) surface for both take off and landing.

It is also envisaged that in place of a wheel a float could be used or indeed a combination of a wheel and float as devices to increase friction with the landing surface. Known amphibious craft contain such float-wheel combination assemblies and indeed such known assemblies may also be accommodated within the skirt of the air cushion craft according to an aspect of the invention. Clearly other devices (e.g. a retractable keel/rudder which is deployed during landing or when advantageous when in proximity with the cruising or landing surface) may be used to dynamically increase friction with the landing surface.

A float, according to one aspect of the invention, provides the required buoyancy as well as friction in case of loss of air cushion pressure and a deflation of the skirt. This may be required when moving at lower speeds over the surface or runway in windy conditions (i.e. crosswind) which may drive the craft off an intended course if only the air cushion means provides the friction with the ground or surface. During landing, where the speed of the craft is continuously slowed, the conditions of wind are particularly important, in general regardless of direction, and a crosswind being particularly important when in flight and on approach and during landing. However even when stationary or approaching stationary in the presence of a strong headwind (i.e. a wind directly in a direction opposite and in line to the direction of landing) also in a crosswind, it may be difficult to come to a halt and taxi without the presence of additional friction from at least one wheel. It is noted that the friction provided by the skirt may not be sufficient to give the required level of control.

A float in one embodiment of the invention may also optionally contain rudder means.

Within normal operation the float of the invention is either not used at all or only transiently used in landing or in traversing rough terrain. In the case of a loss of lift air through a malfunction (e.g. water ingress to prevent air flow) or otherwise the craft will rest on the float or floats. As seen in the embodiment of FIGURE 5 the air of the air cushion passes for above, then splits and passes down the side of each of the floats before exiting at the bottom of the float. The skirt of the air cushion means providing a seal as the air passes from above and down the sides of each of the floats.

Multiple rotors Embodiments are also envisaged with more than one autorotation category source of lift, preferably this would take the form of two rotor blades spaced along the length of the air cushion craft as shown schematically in FIGURE 7. Such designs normally have clearance between the disc arcs described by the rotating blades, however overlapping blade discs are also possible where means are also provided to prevent blade interference. Furthermore a craft according to the invention in which the autorotating blades are partially powered may also be envisaged. As mention above an autogyro with auxiliary rotor blade drive is known from US-A-4,65 3,705 to Benson. As mentioned by Benson in the aforementioned patent the propulsion airstream on the rudder section (i.e. the yaw force from propeller and rudder) may be sufficient to provide the small amount of anti-torque required to overcome the small amount of rotation drive to the rotor blades. The use of auxiliary rotor blade drive to partially power the rotor system effectively decreases the angle of attack that the rotating disc of the rotor blades makes with the inflow air for a given speed of the craft. Interleaved multiple rotor designs are also envisaged to benefit from the invention.

The design of a craft benefiting from the features of the invention is a compromise between factors which depend on the intended use of the craft. For example if the craft is never to move out of air cushion lift (e.g. Freight transport or Feny duty), the design may make increased use of ground effect (e.g. by using fixed wing structures) which together with the autorotating blades contributes to the stability of the craft.. Additiohally the craft may be larger and lay less emphasis on aerodynamic design. However, an air cushion craft operated predominantly in ground effect may of course move out of air cushion lift (i.e. fly at altitude with autorotating source of lift only) but in this design the craft would fly less efficiently than a craft where more emphasis has been laid on the aerodynamic design.

Aerodynamic design is more important for craft which are intended to move out of air cushion lift for longer periods of time.

In a craft intended for extended use out of air cushion lift the craft may be characterized as an autogyro or gyroplane with air cushion landing gear. In such a design the skirt of the air cushion may occupy substantially the same area as that occupied by the conventional landing gear (i.e. Wheels, floats, a combination of wheels and floats or skis) with the tail section being left substantially as in the normal designs for autorotating lift craft. It is envisaged that horizontal stabilizers may be included in a tail section to improve the horizontal stability of the craft. It is noted that the rudder section of a conventional autogyro or gyroplane craft may be used with little or no modification with the features of the invention. This is shown schematically in upper FIGURE 3. The rudder section is not shown in the lower FIGURE 3 which shows the detail of the unducted propeller and the air intake for the air cushion.

Submergible rudder hovercraft A further aspect to the invention is to provide an air cushion craft which has a submergible rudder as shown schematically in FIGURE 6. The craft according to an embodiment of this aspect of the invention maintains a rudder section in the duct of the propeller, as in the normally configured hovercraft, but in addition to this also has a submergible rudder, which may be in more than one section, with sections being fixed or controllable by the operator. It is important for this aspect of the invention to note the difference between the two rudders: one rudder is above water the other rudder is below. The submergible rudder is below the water. In one embodiment a submergible rudder section is steerable over its entire length. Such a submergible rudder adds stability to a hovercraft. The hovercraft is then operated in much the same way as light aircraft in which the wind has to be taken into account before taking up a heading to give the calculated track to make good. Thus the track made good is that of the orientation of the submerged rudder or the submergible rudder section and not that of the centerline of the craft.

The centerline of the craft would normally be in line with the heading.

An embodiment is also envisaged in which the rudder section is stiffly attached to a platform of the hovercraft. This platform is then displaceable with respect to a further platform on which the propulsion means is located. The craft according to the submergible rudder aspect of the invention may also benefit from the autorotating lift design aspect of the invention.

General considerations In all embodiments described it is understood thecraft of the invention may operate at least partially in ground effect.

It may also be recommended for correct operation of the craft of the invention that a hang test be performed in the normal way as for conventional autogyros. For example build instructions for autogyro KB-2 from Ken Brock Manufacturing indicate that the autogyro must show a nose down condition of between 0 and 5 degrees from the horizontal during the hang test if flight is to be attempted successfully. Further information on this autogyro is available at www.kenbrockmfg.com.

It may also be worthy of note that the operation of prerotation in the craft of the invention should not take place with the air cushion operational and without a separate means of anchorage. If the air cushion is active, on account of the lowered friction, then a further means of anchorage for the craft is needed. A retractable submergible rudder may for instance provide the means of anchorage.

Alternative means of increasing friction between the traveling surface and the craft may be envisaged. Alternatively, the craft of the invention may be designed such that the craft moving forward provides sufficient yaw from the propeller and rudder sections which counteract the prerotation torque in a similar way as mentioned above with respect to the partially powered embodiment based on the Benson patent.

Claims

Claims I. A craft which may hover in proximity to a surface due to the

lift force of an air cushion provided by air cushion means and having propulsion means to propel the craft and also having in addition to the lift of the air cushion a further source of lift characterized in that said further source of lift is provided by rotor blades which autorotate due to the motion of the craft.
2. A craft as in claim 1 wherein the air cushion means includes a skirt attached to the craft which seals a cushion of air between the craft and a surface over which it may move.
3. A craft as in claims I or 2 further having a variable length skirt of the air cushion to adjust the hovering height of the craft.
4. A craft as in claims I or 2 or 3 further having within a skirt of the air cushion a ski, a wheel, a float or combination, or multiples, thereof.
5. A craft as in claim I further having more that one separate set of autorotating blades.
6. Float for an aircraft characterized in that air cushion means are provided so that when the float is not in motion but in proximity to a landing surface the air cushion means causes an air cushion to be located in contact with a landing surface and the float so that the float is raised clear of the landing surface.
7. Float as in claim 6 in that the air cushion means is provided by a skirt attached to the float.
8. Submergible rudder in an air cushion craft, such as a hovercraft, a major plane of the rudder being variable in alignment to the plane along the longitudinal axis of the hovercraft.
9. Air cushion craft of claim 1 with the submergible rudder of claimS which is

retractable.
10. Method of flying a craft in which the following steps are required: forming an aircushion between said craft and the surface allowing the craft to hover propelling said craft providing an autorotating lift force as a result of movement of the craft.

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