GB2399324A

GB2399324A - A propulsion arrangement for vertical takeoff aircraft

Info

Publication number: GB2399324A
Application number: GB0305852A
Authority: GB
Inventors: John Edward Randell
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-03-14
Filing date: 2003-03-14
Publication date: 2004-09-15
Anticipated expiration: 2023-03-14
Also published as: GB0305852D0; GB2399324B

Abstract

A propulsion arrangement, allowing aircraft to takeoff vertically (VTOL) consists of a propeller 6, mounted beneath a wing, in order to discharge an air stream onto the underside of the wing. The wing may be constructed of two parts, an aileron 2, and flap 3, and a plurality of propellers or wings may be employed. Boundary surfaces may be employed on one or both sides of the wing or wings, said boundary surfaces being aligned with the direction of forward flight. The arrangement is used to allow aircraft to take off vertically.

Description

P30276tCB A Vertical Take-Off Aircraft The present invention relates to a

vertical take-off aircraft.

Provided that a large enough volume of air can be delivered by a propeller and that the air flow from it can be deflected downwards by a static wing to produce a vertical flow, an aircraft can take-off and land substantially vertically, and remain stationary, in the air.

In the practical realisation of such an aircraft, a large angle of inclination of the static wing is required. Due to the large inclination angle of the static wing, flow separation, with consequent loss of lift, is likely to occur at the upper surface of the static wing.

Figure 1 a is a schematic side view, in section, of a propulsion arrangement of a known aircraft which is not capable of vertical take-off.

Relerring to Figure la, early aerofoil sections 2 used for aircraft wings had a rounded leading edge L, a sharp trailing edge T. a convex upper surface and a lower surface, having a point of inflexion S. at which the curvature of the lower surface was reversed.

A flap 4 towards the rear of the aerofoil section 2 is hinged at the point of inflexion S and pivots from a horizontal flight position shown in unbroken lines to a take-off position shown by broken lines because the latter position was found to increase the lift available for take-off, thus reducing the speed required and therefore the length of runway necessary.

In the case of a twin-engined aircraft, engines were generally mounted on the wings of an aircraft so that the axis of rotation of the propeller 6 coincides with the leading edge L (as shown in Figure la). In this way, air is discharged across both the top and bottom surfaces of the wings. The discharge of air from the propeller across the top surface of a wing reduces flow separation at the upper surface of the wing. Nevertheless, the operation of a flap, as indicated by the arrow showing movement of the tip T. is limited by flow separation, which leads to aerodynamic stall of the aircraft, so that horizontal motion along a runway is still required for take-off and landing.

One aim of the invention is to provide an aircraft supported in the air by pressure, developed by the action of a propeller, on only the underside of the wing. In that way, a gradual transition from vertical to horizontal (forward) flight is facilitated.

Another separate aim of the invention is that air delivered by a propeller in a stream defined by a circular boundary is diverted downwards in a stable flow pattern.

It is yet another separate aim of the invention to provide an improved dual function wing which is able to lift the aircraft in forward flight or to derive lift from the flow from a propeller, as required.

According to a first aspect of the invention there is provided a propulsion arrangement for an aircraft, the propulsion arrangement comprising a propeller and a static wing, wherein the propeller is arranged to discharge and direct a stream of air onto substantially only an underside of the static wing.

In a preferred embodiment of the invention, the pressure of the air is sufficient to support the aircraft.

In another preferred embodiment of the invention, the propulsion arrangement is arranged such that air is directed but in a stable flow pattern.

In yet another preferred embodiment of the invention, the wing is dual function and is able to lift aircraft in forward flight or derive lift from the air flow from the propeller.

The static wing preferably comprises a wing which has two parts, a first fixed part and a second part which is movable (e.g. hinged) with respect to the first part. This allows the second part to be pivoted with respect to the first part so that the aircraft can be configured for vertical and horizontal flight.

The arrangement may comprise a plurality of propellers, which may cooperate with the static wing or a plurality of static wings.

The propulsion arrangement is preferably arranged so that the uppermost part of the discharge stream of the propeller is depressed by a part of the wing adjacent the leading edge of the wing. Most preferably, the boundary (e.g. uppermost part) the of the stream substantially coincides with the foremost part of the leading edge of the wing.

The lower part of the discharge stream may also act on the wing due to the arrangement.

In a preferred embodiment of the invention, the wing is trapezoidal when viewed flow-wise from the front. In another embodiment, the wing has two parts, one which is parallel to a horizontal plane though the fuselage and another which is at an angle of between 55 and 65 degrees (preferably about 60 degrees) to the plane of the one part. A third part may also be arranged at an angle of between 55 and 65 degrees (preferably about 60 degrees) to the plane of the one part.

The wing may comprise two parts; the first part comprising the leading edge and the second part comprising the trailing edge which is known. When the first part meets the second part at a point of inflection, an angle of between;10 degrees and 40 degrees may exist between a vertical line through the point of inflection and the line along the surface of the underside of the second part (i.e. an angle of 100 to 130 degrees between a plane through the first part and a line along the surface on the underside of the second part.

Most preferably, the angle is about 25 degrees.

In one preferred embodiment, the static wing is enclosed on one side by a bounding surface aligned with the direction of motion in forward flight. In another preferred embodiment, the static wing is enclosed on two sides by a bounding surface aligned with the direction of motion in forward flight.

In a still further embodiment two propellers are utilised which are counter-rotating.

According to a second aspect of the invention there is provided a wing for an aircraft, which wing is arranged for horizontal flight and for vertical flight, wherein the wing is arranged to divert air in a direction transverse to the substantially horizontal flow from a propeller in only one direction (i.e. continuously downwards). s

In a preferred embodiment of the invention, the wing is arranged as a turning vane for vertical flight, and the wing has a stagnation point on the underside which enables the flow to be diverted downwards sharply without excessive energy losses and which maintains the lift force produced by the wing in substantially the same position in both horizontal and vertical flight to facilitate transition between the two modes of flight.

According to a third aspect of the invention there is provided an aircraft comprising a propulsion arrangement unit in accordance with the first aspect of the invention and/or a wing in accordance with the second aspect of the invention.

Other preferred features of the invention are set out in the following description.

A reaction wing arrangement and an aircraft accommodating such an arrangement will now be described, by example only, and with reference to the remaining accompanying figures, in which, Figure lb is another side view in section of a propulsion arrangement, in particular a propeller and a wing arrangement, in accordance with the invention, Figure 2a is a schematic side view of a propeller and turning vane, Figure 2b is an isometric view, showing how the propeller and turning vane of Figure 2a cooperate to direct the flow of air, Figure 3a is a further side-view showing the air flow through a reaction wing arrangement in accordance with the invention, Figure 3b is a plan view showing the air flow, Figure 4 is a side view in section showing another reaction wing arrangement in accordance with the invention, Figure 5 is plan view of the wing arrangement of Figure 4, Figure 6 is a front view of the wing arrangement of Figures 4 and 5, Figure 7 is another front view of the wing arrangement of Figures 4 to 6 showing air flow therethrough, Figure 8 is a front view of an aircraft having two wing arrangements accommodated thereon, Figure 9 is a perspective view of the aircraft of Figure 8, Figure 10 is a plan view of the aircraft of Figures 8 and 9, Figure 11 is a side view, and a partial cross section on a vertical plane through the centre line of the fuselage, of the aircraft of Figures 8 to 10, Figure 12 is a vertical section of another reaction wing arrangement in accordance with the invention, Figure 13 shows the reaction wing arrangement of Figure 12 in forward flight, Figure 14 is another view of the wing of Figures 12 and 13 in flight, Figure 15 is yet another view of the reaction wing arrangement of Figures 12 to 14, Figure 16a is a side view, partly in vertical section through the fuselage, of another aircraft in accordance with the invention, Figure 16b is another side view, partly in vertical section, of the aircraft of Figure 16a, pitched for vertical flight, Figure 1 7a is a front view of half of the aircraft of Figures 1 6a and 1 6b, Figure 1 7b is a plan view of the half aircraft of Figures 1 6a, 1 6b and 1 7a, Figure 1 8a is a front view of the half aircraft of Figures 1 6a, 1 6b, 1 7a, 1 7b, Figure 1 8b is a plan view of the aircraft of Figures 1 6a, 1 6b, 1 7a, 1 7b, Figure 19a is a front view of yet another reaction wing arrangement in accordance with the invention, Figure 1 9b is a plan view of the reaction wing arrangement of Figure 1 9a, Figure l9c is a prospective view of the reaction wing arrangement of the Figures 19a and 19b, Figure 20a is a front view of an aircraft in accordance with the invention accommodating wing arrangements as shown in Figures 19a, l9b, and l9c, Figure 20b is a plan view of the aircraft of Figure 20a, Figure 21 is a front view of another aircraft in accordance with the invention, and Figure 22 is a simple perspective view showing part of an aircraft in accordance with the invention.

Referring to Figure lb, a reaction wing arrangement (for an aircraft) comprises a wing (having an aerofoil section 2 and a flap 4) and a propeller 6 arranged upstream of the aerofoil section.

it will be appreciated that the propeller 6 is arranged in a lower than conventional position, it being arranged so that the discharge from it (denoted by the broken line) is directed over only the underside of the wing.

The flap 4 is shown lowered until a trailing edge T of the flap is vertically below a point of inflection (or cusp) S at which the curvature of the wing is reversed and at which the flap is hinged. It can be seen from Figure lb that an angle of between 10 and 40 exists between a vertical line xl through the point (of inflection) S and a line x2 along the surface of the flap 4 proximal the point of inflection (as it departs therefrom). in the specific embodiment shown, the angle is about 25 . With this arrangement, flow separation will occur at the upper surface of the wing in forward movement, but if the volume of air delivered by the propeller 6 is sufficient then the defection downwards of the air stream from the propeller will produce a reaction force on the wing which is able to support and lift an aircraft. l he aircraft will then be capable of vertical flight.

If the propeller 6 and wing are arranged as shown in Figure l(b) for vertical flight the wing acts as a turning vane which has a stagnation point, point S. on the underside.

The function of a stagnation point on the underside of a wing for vertical flight will be described with reference to a design of turning vane. A vertical section through a simple turning vane shown in Figure 2(a) is a quadrant lO of a circle. The quadrant to has a point L at the leading edge in the horizontal plane through the uppermost point of the propeller arc and is of a radius equal to the diameter of the propeller 6 so a point T at the trailing edge lies in the horizontal plane through the lowermost point of the propeller arc and the quadrant to forms a complete barrier to the flow. The deflection of the flow downwards follows the surface of the quadrant turning vane l O as shown by the arrow 12. The arcuate path from point L to point T is much greater than an arcuate path of smaller radius starting at a lower level, such as shown by the arrow 14 in Figure 2(b). The flow at a lower level therefore tends to cross through the stream, as shown by lO the arrow 16 in Figure 2(b). This causes a secondary circulation to be set up, as illustrated in Figure 2(b) by vortexes 18L and 18R, in which air is circulated in contra-rotating vortexes as shown by the arrows 201, and 20R. A circle 22 (shown in broken line) indicates the area of the propeller arc 24 in the horizontal plane through the lowermost point T of the turning vane. This circle 22 will only exist as a boundary if a solid surface (in the form of an elbow) contains the flow. If the turning vane is of cylindrical form (with the axis A of the cylinder at right angles to the direction of flow as shown in Figure 2(a)) the flow spreads, fanning out so that air is discharged to the sides. To achieve lift efficiently from the propeller discharge, a vertical discharge of air is necessary. Secondary flow vortexes set up at a sharp bend are known to cause high energy losses and it is generally accepted that sharp elbows should be avoided in favour of sweeping bends of long radius to avoid the high losses caused by secondary circulation. In the case of an aircraft wing to be used as a turning vane this is not practicable. The object of the invention is to turn the propeller discharge sharply, in the manner of an elbow, without incurring the high losses associated with strong secondary vortex generation of the kind shown in Figure 2(b) by the vortexes 1 8L and 1 8R.

In accordance with the invention, a stagnation point S is formed on an underside of a wing. The stagnation point, S. is formed by a reversal of curvature in the underside of the wing, as shown in Figure 3(a), at the intersection of the two circular arcs LS and ST.

The circular arc LS is centred on a point A, which lies in a horizontal plane through the uppermost point of the propeller arc and on a line inclined forwards at an angle of 60 degrees to the horizontal through point T. The arc LS subtends an angle of 120 degrees at the centre A. The perpendicular to line AT through point S passes through point B. the lowermost point of the propeller arc 24. The barrier formed by the two arcs, LS and ST, which make up the underside of the wing section causes a displacement downwards at the leading edge L, as shown by the arrow 26. Flow along the arc LS proceeds to the stagnation point S. at which a pressure centre exists. Because of the existence of the cenke of pressure at the point S. a backwards flow is created, denoted by the arrow 28, which is superimposed upon the main flow downwards. A flow backwards, as shown by the arrow 28, about the vertical centre-plane will produce vortexes 30L and 30R as shown in Figure 3(b) in plan view which counteract the secondary vortexes 18L and 1 8R shown in Figure 2(b) and thereby at least partially nullify the adverse effects of the secondary flow vortexes 18L and 18R. The broken circle 22 shows the area of the propeller arc in a horizontal plane. The effect of the vortexes 30L and 30R is both to reduce the spread of the air flow from the circle 22, thereby reducing the divergence of the discharge stream from the vertical and also to reduce loss of energy from swirl in the discharge stream.

A wing section can be formed by the arcs LS and S I on the underside and the circular arc LT, 10, shown by broken line in Figure 3(a) at the upper surface. Other sections can be devised which also have a stagnation point in the underside but are more appropriate for horizontal flight, with a flap or, by change of pitch of the aircraft, without a flap.

Figure 4 shows another wing section that has a stagnation point in the underside, at the point of inflexion 15. The barrier shown in Figure 4 is'the underside of a wing 21, the upper side of which is a quadrant of a circle.

A propeller 23 with its axis in a horizontal plane through a cusp point (or point of inflexion) 15 is shown to discharge air against the underside of the wing 21 so that the air is deflected downwards. The diameter of the propeller 23 is equal to the breadth of the wing 21, so the horizontal flow shown by the half-arrow I represents the flow at the boundary of the air stream that passes through the propeller 23. The downward deflection of the air stream from the propeller 23 by the wing 21 produces a reaction force on the wing. The vertical component of the reaction force provides a lift force on the wing 21 whilst the horizontal component acts to counteract the thrust of the propeller 23.

The wing 21 deflects air like a fishtail (or fan), air being deflected to the sides as well as downwards. A greater lift force is achieved if sideways flow is controlled. Side panels 25L and 25R for controlling sideways flow are shown in a canopy wing so formed in Figure 5. The side panels 25L, 25R are inclined at 60 degrees to the horizontal plane as shown in a front view of the canopy wing in Figure 6. The side panels are aligned with the axial direction of flow through the propeller 23. Thus, any horizontal line in a side panel is parallel with the axis of the propeller. The area swept by the propeller 23 is shown in Figure 6 as the propeller arc 27.

The upper part of the leading edge 29 of the wing 21 deflects the stream of air downwards from the top to produce a vortex flow about each of its tips, 31L, SIR, as shown in Figure 7. The vortexes, 33L and 33R, about the tips are of a radius equal to one-half the span of the upper part of the leading edge 29 and will therefore produce pressure centres, 35L and 35R, at the midpoint of each side panel 25L, 25R, the midpoints being coincident with extremities of the line 15 along the underside of the wing through the point of inflexion 15 shown in Figure 4. These pressure centres, 35L and 35R, produce radial pressure fields, 37L and 37R, and consequently vortex flows 391, and 39R, as counterparts of the vortex flows 33L and 33R, about tips 41L and 41R of a trailing edge 17 of the wing. The perpendiculars 43L and 43R to the side panels 25L, 25R through the pressure centres 35L and 35R meet in the horizontal plane of the trailing edge 17 on its centre-line and air is displaced substantially vertically downwards between the vortexes 39L and 39R shown about the trailing edge tips 41L and 41R. A substantial proportion of the propeller thrust is therefore converted into a litt force (over 70 percent has been measured in private tests on a reaction wing like that described).

An aircraft that has two reaction wings of the type described above is shown from the front in Figure 8. This particular aircraft has a fuselage 45 of trapezoidal cross section, the top, bottom and sides being brought to a point at the nose 47, as shown in Figure 9, and into the plane of the top of the fuselage at the tail to form a trailing edge 49 (see Figure 10) having a span equal to the width of the top of the fuselage. A power unit 51 is located, at low level, in the fuselage 45 and a power train 53 is employed to drive the propellers (shown in broken line) from it. The wings may be linked structurally and this can be done by a number of aerofoil sections to form a wing for horizontal flight. In the basic aircraft illustrated, the power train 53 to the propellers is accommodated between the wings inside a horizontal number 55 of aerodynamic cross-section. Vertical transmission from the power unit is within a vertical tail fin 57. A cockpit 59 is located in front of the power plant. Figure 10 shows an aircraft of the same kind as that of Figures 8 and 9 with the addition of a further propeller, 61, for propulsion and control purposes, driven from the same power train, 53. This propeller 61 pitches the nose 47 of the aircraft down for forward flight. In Figure 11, which is a larger scale, the aircraft is being shown in forward flight.

A more efficient aircraft in forward flight can be achieved by varying the wing geometry. The wing shown in vertical section in Figure 4 has a pointed nose, but the wing section can be built up without affecting the shape of the underside and the wing can be jointed for articulation. A thickened wing is shown in Figure 12. This wing section has a rounded nose 63 and a flap 65 at the tail that is hinged at the point of inflexion 15 in the underside. Articulation enables adaptation of the wing to form an aerofoil section for forward flight, as shown in Figure 13. The pitch of the wing can also be adjusted for higher efficiency in forward flight by pitching the nose of the aircraft downwards, when the propeller 23 becomes inclined to the vertical plane as shown in Figure 14. If desired, the propeller 23 can be swung back into the vertical plane, for improved flight efficiency, as shown in Figure 15, by movement in the direction of the arrow 67.

Alternatively, the fuselage can be horizontal in forward flight and the fuselage pitched upwards in vertical flight. Such an aircraft is shown in Figure 16, Figure 16(a) being a vertical section through the fuselage showing the aircraft in horizontal flight and Figure 16(b) a section showing the aircraft in vertical flight. The pitch of the aircraft is varied by means of a rotor 69 mounted in the tail section. One half of such an aircraft is shown in horizontal flight in Figure l 7. In this aircraft, adapted for efficiency in horizontal flight, only one side panel 25R is used with each canopy wing, the side panel 25R being mounted on the side of the fuselage 45. On the open side the top section of the canopy is extended in the form of a tapered wing 71, thereby increasing the wing span of the aircraft. The flap section of the canopy wing is also extended, in width. On the open side, this assists in deflecting flow from the propeller downwards in vertical flight whilst on the closed side it has no effect on the flow from the propeller in vertical flight.

Figure 18 shows one side of the aircraft in vertical flight. Figure 19 shows a canopy wing 21 with two propellers, 23L and 23R side by side. Figure 19(a) is a view from the front in which the direction of rotation of the propellers is shown by arrows 73L and 73R, the propellers being counter-rotating. The relationship between the vertices of the trapezium seen when the wing is viewed from the front and the centres of the propellers is shown by broken lines, the lines being inclined at a orb (30 degrees or 60 degrees) to the horizontal and therefore forming a triangular grid. The point 75, at which the lines 77L and 77R through the respective propeller centres and tips of the trailing edge, 41 L and 41R7 intersect provides a centre about which the flow can be divided and therefore a location for a common power plant to drive both propellers. A Pairing can be used in this position to divide the flow efficiently on the centre-line of the wing. In Figure 1 9(b) it can be seen that one of the side panels 25R is cut back to improve flow over the wing in horizontal flight and reduce weight. The performance of the wing is slightly less satisfactory in vertical flight. The relative importance of efficiency in horizontal flight to that in vertical flight is a fundamental design consideration for an aircraft of this kind. A perspective view of the wing is shown in Figure 1 9(c).

In Figure 20 an aircraft with two wings 21a and 21b, each wing having a twin unit 23L, 23R as described with reference to Figure 19, is shown. The wings are attached to the fuselage by full side panels but the wing tips have side panels that are cut back. The fuselage is as described previously with reference to the aircraft shown in Figure 16.

The arrangement shown in Figure 20 provides an aircraft which has a relatively low height with respect to the wing span.

Whilst the aircraft described previously have a fuselage of trapezoidal cross-section, this is not necessary. Figure 21 shows an aircraft in front view that has a circular fuselage 45 with two reaction wings each with a single propeller. This provides an aircraft with relatively high wings and the stability associated with this.

A reaction wing is a turning vane, for turning flow from a propeller through an acute angle, and, in the case of a vane with a hinged flap, provides a means of diverting the flow from a propeller between substantially vertical and horizontal directions. A reaction wing unit as previously described may be used as a sailplane for control and propulsion.

Two units like those shown in Figure 21 are shown in Figure 21 as a sailplane. The units shown in Figure 22 have hinged flaps like those described with reference to Figures 12 and 13 and by individual control of the flaps is capable of both applying a large measure of control of an aircraft by varying the liforce on each side of the sailplane and of providing thrust for forward propulsion.

The units can be used with other kinds of lifting means such as the propeller and aperture arrangement mentioned by the applicant in the copending GO application number 0214514.2.

Claims

Claims 1. A propulsion arrangement for an aircraft, the propulsion

arrangement comprising a propeller and a static wing, wherein the propeller is arranged to discharge and direct a stream of air onto substantially only an underside of the static wing.
2. A propulsion arrangement according to Claim 1, wherein the static wing comprises a wing which has two parts, a first fixed part and a second part which is movable with respect to the first part.
3. A propulsion arrangement according to Claim 2, wherein first fixed part is hinged to the second part.
4. A propulsion arrangement according to any preceding claim, wherein the arrangement comprises a plurality of propellers, which cooperate with the static wing or a plurality of static wings.
5. A propulsion arrangement according to any preceding claim, wherein the propulsion arrangement is arranged so that the boundary of the discharge stream of the propeller is depressed by a part of the wing adjacent the leading edge of the wing.
6. A propulsion arrangement according to Claim 5, wherein the boundary of the stream substantially coincides with the foremost part of the leading edge of the wing.
7. A propulsion arrangement according to Claim 6, wherein the lower part of the discharge stream also acts on the wing due to the arrangement.
8. A propulsion arrangement according to any preceding claim, wherein the wing is trapezoidal when viewed flow-wise from the front.
9. A propulsion arrangement according to any of Claims 1 to 7, wherein the wing has two parts, a first part which is parallel to a horizontal plane though the fuselage and a second part which is arranged below the first part, and at an angle of between 55 and 65 degrees to the plane of the first part.
10. A propulsion arrangement according to Claim 9, wherein a third part is also arranged at an angle of between 55 and 65 degrees to the plane of the one part.
l l. A propulsion arrangement according to any preceding claim, wherein the wing comprises two parts; the first part comprising the leading edge and the second part comprising the trailing edge, the first part meeting the second part at a point of inflection, and an angle of between 10 degrees and 40 degrees exists between a vertical line through the point of inflection and the line along the surface of the underside of the second part, when viewed in section.
12. A propulsion arrangement according to Claim 11, wherein the angle is about 25 degrees.
13. A propulsion arrangement according to any preceding claim, wherein the static wing is enclosed on one side by a bounding surface aligned with the direction of motion in forward flight.

S
14. A propulsion arrangement according to any of Claims I to 13, wherein the static wing is enclosed on two sides by a bounding surface aligned with the direction of motion in forward flight.
15. A propulsion arrangement according to any preceding claim, wherein two counter-rotating propellers are used. l
16. A wing for an aircraft, which is arranged for horizontal flight and for vertical flight, wherein the wing is arranged to divert air transverse in only one direction to the substantially horizontal flow from a propeller.
17. A wing according to Claim 16, wherein, when adapted as a turning vane for vertical flight, the wing has a stagnation point in the underside which enables the flow to be diverted downwards sharply without excessive energy losses and maintains the lift force produced by the wing in substantially the same position in both horizontal and vertical flight to facilitate transition between the two modes of flight.
18. An aircraft comprises a propulsion arrangement unit in accordance with any of Claims 1 to 15 and/or a wing in accordance with any of Claims 16 or 17.