VTOL AIRCRAFT EXHAUST DUCTING SYSTEM

FIELD OF THE INVENTION

The present invention relates to a VTOL aircraft exhaust ducting system particularly, although not exclusively, envisaged for use in improving the controllability of the VTOL aircraft wen in vertical flight.

BACKGROUND OF THE INVENTION

In a VTOL aircraft with a single large centrally located fan with a cabin located underneath (referred to as an underslung cabin), it is desirable to exhaust air from the fan as fas as possible away from the axis ofthe fan. This gives the maximum ground effect and greatest control leverage. It also minimises problems such as pressure bubble under the VTOL aircraft when close to the ground and avoids instability caused by such down under the aircraft wings.

In the prior art most VTOL aircraft with an underslung cabin have a circular wing and the exhaust is deflected downwardly just below the perimeter ofthe wing.

Circular wings are inherently unstable and of little practical use. Conventional wings have substantially straight leading and trailing edges and have a bulbous front section and a tapered rear section. This shape does not lend itself to the tubular exhaust of a circular wing since the tubular exhaust requires a large number of doors to seal the ducts form operation in conventional flight.

VTOL aircraft have lift ducts which typically have tight radii on the final downward bend. For efficiency of operation this requires a relatively large number of deflector vanes.

Where the exhaust duct is used of thrust in more than one direction, such as for providing lateral and vertical movement, then it is desirable for the duct to face as much as possible in the opposite direction to the desired force.

When the exhaust ducts are activated while the aircraft is travelling at high speed, such as during transition, it is desirable that the opening ofthe duct does not significantly effect the stability ofthe aircraft and so should commence operation in a largely neutral position.

When the exhaust duct is not in operation, it is desirable to have them sore in a manner which does not effect the efficiency of the forward flight of the VTOL aircraft. It is also desirable that such exhaust ducts have large radii at their bends and a length of ducting after each bend to increase efficiency.

I have developed a system of exhaust ducts for a VTOL aircraft which overcome these

problems.

SUMMARY OF THE INVENTION

Therefore it is an object of the present invention to provide a VTOL aircraft exhaust ducting system which is simple and effective. In accordance with one aspect of the present invention there is provided a VTOL aircraft exhaust ducting system for a wing of a VTOL aircraft, the exhaust ducting system comprising: at least one forward lift duct and at least one rear lift duct each including a nozzle located respectively proximate the leading edge and the trailing edge ofthe wing, the nozzle being moveable from a first position in which the nozzle moves to close off an exhaust from a lift fan ofthe VTOL aircraft, and conforms to the shape of the wing and a second position in which the nozzle moves to opens up for directing air downwardly for providing vertical lift, the nozzles increasing the length of the exhaust path so as to improve the pitch, roll and yaw control which can be exercised over the VTOL aircraft. The exhaust ducting system also includes control ducts which have a constant cross- section as they are moved between directing 100% of exhaust gases downwardly and directing 100% of the exhaust gases upwardly so as to achieve an continuous degree of control during manoeuvring ofthe VTOL aircraft.

BRIEF DESCRIPTION OF THE DRAWINGS An exemplary embodiment of the present invention will now be described with reference to the accompanying drawings in which :-

Figure 1.1 is a lower plan view of a VTOL aircraft incoφorating an exhaust ducting system in accordance with the preset invention;

Figures 1.2 and 1.3 are cross-sectional perspective views taken on line 1-1 of Figure 1.1, and respectively show the nature of passage of exhaust gases from the VTOL aircraft through the exhaust ducting system, and the VTOL aircraft without the exhaust gas flows;

Figures 2.1 to 2.3 are respectively cross-sectional view on a longitudinal slice of the VTOL aircraft of Figure 1.1 showing the orientation of lift control ducts for controlling the VTOL aircraft; Figure 3 is a comparison between the exhaust ducting system of the present invention and that of my US Patent 5,407,150, showing how much longer the exhaust path is in the case ofthe present invention; and,

Figures 4.1 and 4.2 are longitudinal cross-sectional views showing a set of control ducts of

the exhaust ducting system ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In Figure 1.1 there is shown a VTOL aircraft 10 having a delta wing 12 under which is located a cabin 14. The wing 12 includes forward lift duct exhausts 20, rear lift duct exhausts 22, forward control duct exhausts 24 and rear control duct exhausts 26 - as more particularly shown in Figures 2.1 to 2.3 and Figures 4.1 and 4.2.

The exhausts 20 to 26 each have an exhaust air masses flowing through them as shown in Figure 1.2. The larger air masses represent the flow of air through the lift duct exhausts 20 and 22 and the smaller air masses represent the flow of air through the control duct exhausts 24 and 26. It can be seen that the footprint of the forward lift control exhausts 20 is outside the shadow of the wing 12 which produces a relatively large leverage effect to achieve good stability when in vertical hover and flight mode and to improve pitch yaw and roll control. The relative sizes is also shown in the size ofthe air masses 30, 32,34 and 36 respectively which each ofthe ducts 20 to 26 produces in response to air intake masses 38..

The wing 12 has a leading edge 40 and a trailing edge 42. An upper surface of the wing 12 is closed off by gull wing doors 44, below which is located a lift fan 46 and four lift ducts 48 and 50. The lift ducts 48 are disposed towards the leading edge 40 and the lift ducts 50 are disposed towards the trailing edge 42. The lift ducts each have a nozzle 60 which is hinged to the wing 12 for pivoting from a closed position as shown in Figure 2.1 and an open position as shown in Figure 2.3. The nozzle 60 ofthe forward lift duct exhausts 20 are hinged at one end ofthe nozzle 60 so as to allow the nozzle 60 to hinge out of the wing 12, whereas the nozzle 60 of the rear lift duct exhausts 22 hinge intermediate the length of the nozzle 60. Preferable the nozzle 60 ofthe rear lift duct exhausts 22 opens at an acute angle to air passing over the underside of the wing 12 so as to avoid scooping air into the lift duct 50. Also, by such direction of opening the rear lift duct nozzles 60 can act as an air brake. Further, those nozzles 60 serve to produce a venturi effect when the exhaust 22 is first opened. This has the effect of drawing air through the lift ducts 50 which initiates rotation ofthe lift fan 46 for easing the load that a drive motor experiences when the lift fan 46 is turned on.

The forward exhausts 20 have exhaust deflecting vanes 64, an air deflecting vane 66 and a double hinged door 68. The angle of the vanes 64 is controllable for controlling the direction of the exhaust air masses 30 for propelling the VTOL aircraft 10 in forward and reverse flight. The air deflecting vanes 64 assist the smooth flow of air around the bend of the nozzles 60. And the double hinged doors 68 maintain the seal of the lift duct 48 regardless of the disposition of the nozzle 60 of the forward exhausts 20. The forward

exhausts 20 have the effect of conducting the exhaust gases further outward from the lift fan 46 which produces the improvements in control and handling as described hereinabove

The rear exhausts 20 are similar in construction to the forward exhausts and like numerals denote like parts The main difference is that the nozzles 60 of the rear exhausts 22 has a door 70 which is substantially planar and capable of acting as an air brake

The control duct exhausts 24 each comprise a pair of duct doors 80, and an upper vane 82 and a lower vane 84 The duct dors 80 pivot at their juncture and pivot outwardly in the direction of arrows 88 to allow air to flow from the fan to an upward or a downward direction or an combination of both The vanes 82 and 84 are hinged to the control duct at their upstream end and are coupled together proximate their downstream end The coupling ensures that the cross-sectional area of the control duct exhaust 24 remains constant even when the direction ofthe flow of air is being altered

The control duct exhaust 26 is conveniently in the form of a rotary splitter 90 with an upwardly disposed conduit 92 and a downwardly disposed conduit 94 Rotation of the splitter 90 can block air as shown in Figure 4 2 and allow the flow of air as shown in Figure 4 1 - for the purposes of controlling the attitude ofthe VTOL aircraft 10

In use, when taking off from the ground, the VTOL aircraft 10 has the lift exhausts 20 and 22 set down as shown in Figure 2 3 Air then flows through the ducts 48 and 50 and out of he exhausts 20 and 22 at a relatively large distance form the lift fan 46 for achieving better stability when in vertical flight During transition to horizontal flight the nozzles 60 are angled backwardly as shown in Figure 2.2 As the forward speed ofthe VTOL aircraft 10 increases the angle of the nozzles 60 can be set less until they are closed as shown in Figure 2 1 (at which time the gull wings doors 44 are also closed)

Fine control of he attitude of the aircraft during vertical take-off and transition to horizontal flight is achieved with the control exhausts 24 and 26 These are set as shown in Figure 4 1 for vertical flight and as shown in Figure 4 2 for horizontal flight

The exhaust ducting system of the present invention has the advantage that the exhaust gases are directed to a relatively large distance from the lift fan so as to achieve better stability for the VTOL aircraft when in vertical flight It also has the advantage that the amount of forward thrust from the lift exhausts 20 and 22 during transition decreases gradually and controllably Further the exhausts 24 have a constant cross-section regardless of their disposition which ensures smooth transfer of air between up and down exhausting modes which results in more confident control ofthe VTOL aircraft 10

The increase in the distance that the exhaust air travels out from the lift fan in shown in Figure 3

Modifications and variations such as would be apparent to a skill addressee are considered within the scope ofthe present invention. For example, other numbers ofthe exhausts 20 to 26 could be used.