Aircraft

Abstract

An aircraft (10, fig 1) comprising:a starboard and port swept wing (14A, 14B) , comprising an integrated payload fuselage (20);inner wing sections (26A): a rear spar 40 disposed close to a trailing ed

Description

The present invention relates to an aircraft. BACKGROUND TO THE INVENTION A V-shaped aircraft has been devised previously by the inventor, which has been disclosed in his patent applications (including for example DE102014201040A1 and NL2034242B1) and in a number of published papers on the concept. Proof-of-concept prototypes of the V-shaped aircraft have been made. V-shaped aircraft are characterised by a highly-swept inner wing which incorporates a payload fuselage, and an outer wing extending with a lower sweep angle, for extending the wingspan beyond that of the inner wing and generating lift. Unlike in conventional aircraft, the inner wing accommodates the payload fuselage and therefore must be shaped to withstand internal pressurisation, as well as being aerodynamic in shape. This creates a tension between design constraints, as the ideal wing shape for aerodynamics is an aerofoil shape, whilst the ideal shape for pressurisation is a near circular cross section. Some previously-proposed designs use the ‘oval-fuselage concept’, in which a large part of the outer shape of the aerofoil and the shape of the pressurised section are the same. That is to say, there is a single skin that acts as an outer surface for the aircraft and also as the enclosure for the pressurised section. In particular, the pressurised section is formed by a rear spar, and three curved portions which cover the top, front and bottom of the wing. The curved portions are each substantially arcuate, that is to say, as a circular arc. Each of the curved portions may have a different radius of curvature. The outer surface of the wing is formed by these three curved portions, and a rear fairing that is disposed behind the rear spar. The rear fairing has an upper curved portion, a lower curved portion and a portion parallel to the rear wall (see Figure 15). This minimises the number of parts used and the corresponding weight of the aircraft. An efficient pressurisation structure is achieved using circular arcs for enclosure of the pressurised cabin. In the oval-fuselage concept, a cabin can be defined within the fuselage by a floor beam and a ceiling beam which are loaded in compression, and a front wall and a rear spar loaded in tension. None of the beams experience significant bending due to the pressurization of the circular arcs, which results in an efficient and light structure. A remarkable feature of the oval fuselage geometry is that the exterior shape is quite similar to the geometry of at least the front (near the leading edge) and middle region of conventional wing sections. In the centre region of blended wing body aircraft, where the lift coefficients are low and there is a certain amount of design freedom forthewing sections, the oval fuselage parameterization could be applied well to serve both as the interior shape to enclose the pressurized region, and as the exterior profile shape. Current V-shaped aircraft concepts have relatively low twist on the wings, which allows for fairly uniform wing design across the aircraft. A wing generally has ‘twist’ in order to modify the distribution of lift along the wing. The inner wing of a V-shaped aircraft is thick to accommodate the fuselage and has a high sweep angle. It also has low local lift coefficients and large chord lengths. However, the shape, and in particular the twist of the inner wing still has a substantial effect on the aerodynamic performance of the aircraft, as it influences the lift distribution over the aircraft. Advantageously, the unique shape of the planform on the V-shaped aircraft allows for an efficient elliptical lift distribution without the need for strong wing twist on the inner wing. The low required twist means the front and middle regions of the aerofoils can be kept substantially constant across the span of the aircraft. This allows the region near the front of the inner wing to be substantially tubular or ovular. The twist and chord of the wings can then be set by adjusting only the rear fairing. The reduced need for wing twist in V-shaped aircraft means the wing can accommodate a relatively uniform fuselage shape, and the required wing twist and chord can be adjusted simply by modifying the design of the rear fairing. The above sets out the broad design context for current V- shaped aircraft concepts. However, to better understand the invention, the various shortcomings of current concepts are now discussed. In V-shaped aircraft, unlike in conventional aircraft, the design of the wings is constrained by pressurisation requirements. Current versions of the oval fuselage concept that enclose the pressure cabin on V-shaped aircraft do not allow the incidence angle of the front and middle section of the aerofoil to be set independently from the orientation of the cabin floor and the overall layout of the aircraft. Modification can only be done by modifying the rear fairing geometry. The angle of incidence is the angle between a chord line of the wing and a reference axis. Herein, the reference axis is an axis across the floor of the cabin. In current designs of V-shaped aircraft, the incidence angles on the inner wing are constrained to a relatively low value by the current oval fuselage concept. In conventional aircraft, the angle of the wing could just be rotated relative to the fuselage of the plane, but in flying wing designs this is not possible. This means that the angle of attack of the entire aircraft needs to be relatively high to achieve necessary lift, for example during landing. A higher angle of attack during landing reduces clearance of outer wing tips to the ground. To compensate for this, and ensure clearance, current designs have very long landing gear. This has the disadvantage of adding significant structural weight and requiring additional space in which to stow the landing gear. An increased angle of attack is not just required during landing, but during all flight conditions, including cruising flight, in order to generate suitable lift. Previous studies have shown the angle of attack during cruising flight to be between 4 and 5 degrees. This angle of attack causes decreased cabin comfort and may cause difficulties for inflight cabin service, because the floor of the cabin is significantly off the horizontal. Previous simulations (see Figure 14) have shown that pressure isobars are concentrated towards the rear of the wings, and in particular in the centre of the V-shaped aircraft. This can increase pressure drag, and is another problem with current concepts. Finally, previous studies have demonstrated that significant rear loading would be necessary in profile sections of V-shaped aircraft to reduce the overall angle of attack (see Figure 15). Rear loading is increased concave curvature at a rear section of the aerofoil to increase lift. However, rear loading moves the optimum location for the centre of gravity of the aircraft backwards, closer to the neutral point. This reduces the static margin (distance between centre of gravity and neutral point), which is required for longitudinal stability of the aircraft. Increased rear loading also has the disadvantage of reducing available volume in the rear fairing, which can otherwise be used to store, for example, fuel (see Figure 16). It is an object of the present invention to reduce or substantially obviate the aforementioned problems. STATEMENT OF INVENTION According to the present invention there is provided an aircraft comprising: a starboard swept wing and a port swept wing, each swept wing having an inner wing section comprising an integrated payload fuselage and an outer wing section for extending the wingspan and providing lift; each inner wing section comprising: a rear spar disposed close to a trailing edge of the inner wing section to carry loads along the inner wing section; a wing surface, in which the wing surface is substantially shaped as an aerofoil, and in which the wing surface comprises a rear fairing disposed behind the rear spar, and near to the trailing edge, and in which the wing surface comprises an upper curved portion which has a substantially arcuate cross section, a front curved portion which has a substantially arcuate cross section, and a lower wing surface, the upper curved portion meeting the rear spar at a rear of the upper curved portion, and the upper curved portion meeting the front curved portion at a front of the upper curved portion, the front curved portion meeting the lower wing surface at a front of the lower wing surface; a cabin structure in the inner wing, in which the cabin structure comprises one or more floor beams and a rear wall defined by the rear spar, in which the lower wing surface comprises a front lower curved portion, in which the front lower curved portion is substantially arcuate in profile and extends from a front edge of the floor beam(s) of the cabin structure towards the rear wall; and in which the lower wing surface of each inner wing extends below a first line, the first line being a line along the rear wall of the cabin structure where a projection of the arcuate front lower curved portion of the wing surface meets the rear wall, and in which a rear lower portion of the lower wing surface meets the front lower portion and continues the lower wing surface to a second line, which is spaced from and below the first line. In the present invention, the incidence angle (that is, the vertical angle between the chord of the wing and the floor of the cabin) is increased by having the cabin at an angle relative to the aerofoil of the wing. This allows for additional adjustment of the cabin angle since the whole wing is modified to obtain the incidence angle, rather than only the rear fairing as has been done in previous concepts. Compared to previous designs, the aircraft can be pitched at a relatively low angle of attack, both in flight and during take-off and landing. The present invention requires a lower angle of attack than in previous concepts. The wing is essentially tilted upwards relative to the cabin floor, therefore during landing, a lower angle of attack can be used to create the required amount of lift. A decreased angle of attack is particularly advantageous on V-shaped aircraft, as it increases the clearance of the wingtips to the ground and therefore means the landing gear can be shortened. Reducing the length of the landing gear could lead to a weight saving on the order of tonnes for a full-size concept. Shorter landing gear are also simpler to integrate and store, which is a significant challenge in present concepts. There are a number of other advantages associated with the relative angle of the wing surface and cabin structure. Raising the front of the aerofoil in the Flying V centre wing region is likely to have a positive impact on the isobar locations reducing their concentration at the rear kink and therefore decreasing pressure drag. Also, it can be expected that shifting the isobars further to the front in the centre wing region will reduce transonic drag due to a higher efficient sweep angle in that region. The front part of the lower wing surface is arcuate. A continuation of that arc would intersect with the rear wall of the cabin at the first line. However, the lower wing surface is in fact disposed below this first line. Hence the lower wing surface, which is a circular arc at the front of the wing, transitions into a different curve in its rear section. In many embodiments, the first line corresponds with the point where the floor beam of the cabin meets the rear wall. Hence an extension is provided below the rear wall to meet the lower surface of the wing (the “rear spar extension”). Arcuate as used herein is used to mean shaped as an arc of a circle, i.e., part of a circumference of a circle. The curved portions can efficiently withstand the forces of the pressurised area without significant extra weight for reinforcement. The inner wing may have a greater sweep angle than the outer wing. In particular the sweep angle of each inner wing section may be greater than 60°. The higher sweep angle of the inner wing section allows the inner wing section to be relatively thick while minimising transonic drag. A rear spar extension may be disposed below the rear wall. The rear spar extension may extend from the rear wall and join with the wing surface. The rear spar extension may extend from the floor beam(s) of the cabin and join with the wing surface. An ‘oval fuselage’ concept is previously known. A previous oval fuselage concept had four curved arcs which formed the outer surface of the wing, viewed in a perpendicular-to-streamwise cross section of a blended wing design. The cross section of the oval fuselage was therefore symmetrical. The oval fuselage concept has not been fully integrated into a Flying V aircraft before. The present invention adapts the oval fuselage concept to use in a streamwise cross section of the aircraft, and is therefore no longer symmetrical. In the present invention, the oval fuselage is at an angle to the cabin structure, and as explained the lower wing surface is only in part arcuate. Each inner wing may comprise a pressurised structure. The wing surface may form a portion of the pressurised structure. The pressurised structure of the inner wing may comprise a lower curved portion which is substantially arcuate in profile. Therefore, in this embodiment, the front lower curved portion is part of a larger curved portion extending all the way to the rear wall of the cabin. An arc of the lower curved portion may have a secant which is coincident with one of the floor beams of the cabin. The lower curved portion may be formed by the wing surface at the front of the wing, but it will be distinct from the lower wing surface near the rear wall. In other words, in this embodiment there is a void between the pressurised compartment and the lower wing surface, at least near the back of the cabin. Note that the “rear wall” of the cabin is “rear” in the sense that it runs along the back (trailing edge) of the wing. From the point of view of a passenger in the cabin, the “rear wall” will actually be a side wall of the cabin, facing broadly inwards of the aircraft, towards the other wing. The lower curved portion may be a boundary of the pressurised structure. That is to say, the pressurised structure may comprise the lower curved portion. The lower curved portion may be substantially arcuate in profile. The arc is still a suitably strong shape to withstand the pressure difference, without requiring heavy reinforcement. The lower curved portion may extend from the lower edge of the rear wall of the cabin structure. Therefore, the lower curved portion can join with the rear wall, which may also form part of the pressurised structure. The lower curved portion may extend from the lower edge of the rear wall of the cabin structure to a front edge of the floor beam. A majority of the lower curved portion may be formed by the wing surface. However, the wing surface may be distinct from the lower curved portion near the lower edge of the rear wall of the cabin structure. It is advantageous for the majority of the lower curved portion to have a dual purpose of containing the pressure as well as being an aerodynamic surface for the wing so that weight is minimised. However, separate surfaces for the cabin and the wing surface may be required near the lower edge of the rear wall of the cabin structure to accommodate the relative angle of the cabin structure and the wing surface. The wing surface may join with the rear wall. An arc of the lower curved portion may have a secant which is coincident with the floor beam of the cabin. An arc of a circle is a strong structural cross section as the stress is not concentrated at a particular point. Therefore, this is an optimal shape for the lower curved portion and enables it to withstand pressure. In another embodiment, the pressurised structure may be formed by the wing surface near the lower edge of the rear wall of the cabin structure. The pressurised structure may be formed by a skin of the wing. That is to say, there may be no separate lower curved portion having an arcuate shape and separate wing surface near the lower edge of the rear wall. Instead, there may be one skin that functions as a pressurised structure and as a wing surface. The wing surface may not be arcuate along its whole length. The pressurised structure may comprise the rear wall or rear spar. That is to say, the rear spar supports or forms a rear bulkhead to withstand the pressure forces. The pressurised structure may have a front curved portion. The pressurised structure may have an upper curved portion. The cabin structure may have a front wall. The front wall may be disposed near a leading edge of the wing. The cabin structure may have a ceiling. The front curved portion may extend from an upper edge of the front wall to a lower edge of the front wall. The upper edge of the front wall may be where the front wall joins the ceiling. The lower edge of the front wall may be where the front wall joins the floor beam. The upper edge of the front wall may join with the wing surface. The upper edge of the front wall may be raised relative to an upper edge of the rear wall. The front wall may have a greater height (above the floor beam) than the rear wall. The front wall may be at an angle to the rear wall. The front wall may be substantially flat. The rear wall may be substantially flat. An arc of the front curved portion of the wing surface may have a secant which is coincident with the front wall of the cabin structure. The upper curved portion of the wing surface may extend from an upper edge of the front wall to an upper edge of the rear wall. The upper edge of the front wall may be where the front wall joins the ceiling. Conversely, the lower edge of the front wall may be where floor beam joins the front wall. The upper edge of the rear wall may be where the rear wall joins the ceiling. An arc of the upper curved portion of the wing surface may have a secant which is coincident with the ceiling of the cabin structure. The rear fairing may join with a lower edge of the rear spar extension or a lower edge of the rear wall. The rear fairing may join with the lower wing surface near the lower edge of the rear spar extension or the lower edge of the rear wall. The rear fairing may join with a top of the rear wall. The rear fairing may have a different shape in different sections of the aircraft. For example, it may have a certain amount of twist along the length of the wing. The front wall may be or may be attached to a front spar, tension strut or other structural reinforcement. The front wall may be a front spar. The ceiling may be a ceiling beam, ceiling rib, ceiling reinforcement, or other structural reinforcement. The ceiling of the cabin structure may be sloped relative to the floor beam of the cabin structure. The ceiling of the cabin structure may join with the wing surface. The ceiling of the cabin structure may join with the wing surface at a first edge and / or a second edge. The ceiling of the cabin structure may be substantially flat. The pressurised structure may comprise or consist of the rear wall, the front curved portion, the lower curved portion and the upper curved portion. The curved portions of the structure are a strong shape that can withstand pressure forces. The rear spar is conventionally load bearing and so a rear wall close to it can withstand pressure forces or can be reinforced without undue burden in order to bear additional pressure loads. The pressurised structure may comprise or consist of the rear wall, the front curved portion, a lower portion of the wing surface and the upper curved portion. Likewise, the upper curved portion may join with an upper edge of the rear fairing. The join may be smooth so the curved portion and an upper curve of the rear fairing form a part of the continuous wing surface. The lower curved portion may join the front curved portion. The inner wing section may have comparatively little rear loading compared to prior art designs. This is advantageous as less rear loading leads to less drag and increases the static margin for longitudinal stability. More lift is generated at the front of the inner wing due to a higher incidence of the profile sections and reduced rear loading. The centre of pressure is therefore further in front of the neutral point of the design, which results in less trim drag, relative to previous concepts. The aircraft may comprise a starboard transition region where the starboard inner wing section meets the starboard outer wing section and a port transition region where the port inner wing section meets the port outer wing section. According to a second aspect of the invention, there may be provided a method of constructing an aircraft, comprising the steps of: (a) constructing a front portion of an inner wing, the front portion of the inner wing comprising a pressurised structure and a rear spar, the rear spar disposed close to a trailing edge of the inner wing; (b) constructing a rear fairing; and (c) joining the rear fairing to the inner wing at the rear spar. Advantageously, this allows for modular construction of the aircraft. This can facilitate simpler and cheaper construction, in particular by simplifying the logistical challenges such as transporting sections of the aircraft. The method may be applied to construct a wing according to the first aspect of the invention. The rear spar extension does not prevent the aircraft from being constructed in this way. The rear fairing may have a different shape in different sections of the aircraft, whilst the pressure cabin, which is the more expensive and complicated part, may have a constant cross section and take the same shape over large sections of the aircraft. Therefore, it is useful to be able to construct these parts separately. Arcuate in profile is used herein to mean that a cross section shows that the shape is a part of the circumference of a circle. Rear loading is used herein to mean the curvature on a lower surface of the rear fairing. BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made by way of example only to the accompanying drawings, in which: Figure 1 is a perspective view of an aircraft, with a cross section identified; Figure 2 is the cross section of an inner wing which is part of the aircraft shown in Figure 1; Figure 3 is the cross section of the inner wing identified in Figure 1, with the rear loading marked, and the volume of the rear fairing marked; Figure 4 is the cross section of the inner wing represented in Figure 1, with the thicknesses of the structure shown; Figure 5 shows a method of manufacturing the present invention; Figure 6 is an overlay of the cross section of a previous concept with the cross section of the present invention identified in Figure 1; Figure 7 is an overlay of the required angle of attack in a previous concept and the required angle of attack in the present invention; Figure 8 is a section of the aircraft of Figure 1, with multiple cross sections indicated; Figure 9 is a rear view of the section of the aircraft shown in Figure 9, with cross sections indicated; Figure 10 is a starboard section of the aircraft, showing the effect of less rear loading on the centre of pressure; Figure 11 is an alternative embodiment of the invention; Figure 12 is an alternative embodiment of the invention; Figure 13 is an alternative embodiment of the invention; Figure 14 is a starboard section of a previous concept, showing pressure isobars across the wing area; Figure 15 is a cross section of a wing in a previous concept, with rear loading indicated; Figure 16 is a cross section of the wing in the previous concept shown in Figure 13, with the volume of the rear fairing marked; and Figure 17 is a three-dimensional view of the cross section of a previous concept. DESCRIPTION OF PREFERRED EMBODIMENTS Referring firstly to Figure 1, an aircraft 10 is shown. The aircraft 10 comprises a central region 12, a starboard wing indicated at 14A and a port wing indicated at 14B. The wings 14 extend from the central region 12. The wings 14 enclose an integrated payload fuselage, part of which is indicated at 20. Each wing 14A, 14B has a leading edge 18A, 18B and a trailing edge 22A, 22B. For brevity, the starboard wing, in particular a cross section of the starboard wing is described fully. The port wing is symmetrical to the starboard wing and will comprise identical features. Symmetrical I identical features labelled on the starboard wing as xA will be labelled on the port wing as xB. It will be appreciated that in embodiments, the aircraft may not be completely symmetrical, for example different equipment may be provided on either side. However most embodiments are likely to be roughly symmetrical in their main features. The starboard wing 14A is disposed extending from the central region 12. The wing 14A extends substantially horizontally. The wing 14A comprises an inner wing section 26A that attaches to the central region 12. The wing 14 comprises an outer wing section 30A which extends from the inner wing section 26A. The inner wing section 26A has a positive sweep angle. Preferably, the inner wing section 26A has a sweep angle of over 60 degrees. The outer wing section 30A also has a positive sweep angle. The sweep angle of the outer wing section 30A is less than the sweep angle of the inner wing section 26A. The wing 14A comprises a transition region 23A where the inner wing 26A is joined to the outer wing 30A. I.e. the transition region 23A is the area of wing close to the “kink” (the change in sweep angle). In the transition region, the thickness of the wing will also taper from the relatively thick inner wing section 26A to the thin outer wing section 30A. Each wing section 26A, 30A has a leading edge. In this embodiment the leading edge 18A extends along the inner wing section 26A and the outer wing section 30A. The leading edge 18A runs in a straight line along the front of the inner wing section 26A. There is then a discontinuity in the transition region 23A where the leading edge 18A transitions to a significantly smaller sweep angle in the outer wing section 30A. The outer wing section 30A provides an increased wingspan of the aircraft. In this embodiment, it is the inner wing section 26A which integrates the payload fuselage 20. The outer wing section 30A is much thinner, more akin to the wing of a conventional aircraft. The payload fuselage 20 is integrated into a front part of the inner wing section 26A. In other words, the payload fuselage 20 is integrated near to the leading edge 18A, and part of the wing extends behind the payload fuselage 20 to the trailing edge 22A. The payload fuselage 20 runs broadly parallel to the leading edge 18A of the wing. The payload fuselage 20 is integrated into the inner wing section 26A for more even weight distribution and therefore reduced bending moments. The payload fuselage 20 may be pressurised for accommodation of passengers. Engine 16A is provided on the trailing edge 22A of the wing 14A, approximately halfway along the inner wing section 26A. The engine 16A may be semi-buried, i.e. may have an intake at a boundary layer close to the wing 14A. Figure 1 also indicates the position of a cross section of the aircraft which is shown in more detail in figures 2 to 6. The cross section is indicated generally at 24. The cross section 24 is through starboard wing 14A. The cross section 24 is through the inner wing section 26A. The cross section 24 is cut perpendicular to the leading edge 18A of the inner wing section 26A. Figure 2 shows the cross section 24 of the inner wing 26A of the aircraft 10, as indicated in Figure 1. The inner wing 26A has a wing surface 30 which is shown in the cross section 24. The inner wing 26A also has a cabin structure 32 which is shown in the cross section 24. The trailing edge 22A (at a rear of the wing) and approximate position of the leading edge 18A (at a front of the wing) are indicated. The cabin structure 32 has a ceiling 34, a floor 36, a first (front) wall 38 and a second (rear) wall 40. The ceiling 34, floor 36 and walls 38, 40 define the cabin structure 32. The cabin structure 32 may be used for passengers. The cabin structure 32 may be used for cargo. The cabin structure 32 has a quadrilateral cross section. The cabin structure 32 has four edges (corners in the 2D cross section). The cabin structure has a front wall upper edge 44. The cabin structure has a front wall lower edge 46. The cabin structure has a rear spar upper edge 42. The cabin structure has a rear spar lower edge 48. The ceiling 34 of the cabin structure 32 is substantially flat. The floor 36 and walls 38, 40 are also substantially flat. The ceiling 34 is not parallel to the floor 36. The ceiling 34 is instead at an angle to the floor 36. The front wall 38 is not parallel to the rear spar 40. The walls 38, 40 are at an angle to each other. The ceiling 34 slopes upwards towards a front of the wing and joins with the wing surface 30. The horizontal floor beam(s) 36 may be loaded in compression due to the pressurisation of the cabin, as is the ceiling beam(s) 34. The inner wing 26A has a pressurised structure. The pressurised structure is bounded in part by a lower curved portion 54. Lower curved portion 54 is arcuate in profile. In a profile view, a secant of lower curved portion 54 is coincident with the floor 36. The lower curved portion 54 has a front portion 54a and a trailing portion 54b. The pressurised structure is bounded in part by an upper curved portion 50. Upper curved portion 50 is arcuate in profile. In a profile view, a secant of an arc of the upper curved portion 50 is coincident with the ceiling 34. The pressurised structure is also bounded in part by a front curved portion 52. Front curved portion 52 is arcuate in profile. A secant of an arc of the front curved portion 52 is coincident with the front wall 38. The pressurised structure is also bounded in part by the rear spar 40. Hence in this embodiment the pressurised structure is formed by the rear spar 40, the upper curved portion 50, the front curved portion 52 and the lower curved portion 54. A rear fairing 62 is disposed behind the rear spar 40 of the pressurised structure. The rear fairing 62 is formed by two curved sections 58, 60 that join at the trailing edge 22A. The curved sections 58, 60 form a rear fairing 62. The rear spar 40 has a rear spar extension 56. The rear spar extension 56 of the rear spar 40 extends below the floor 36 of the cabin structure 32. The rear spar extension 56 joins the wing surface 30 at point 64 (i.e. edge in three dimensions). The rear spar extension 56 allows the cabin to be tilted at an angle relative to the reference axis through the floor of the cabin of the aircraft (i.e. the angle of incidence). The wing surface 30 is shaped as an aerofoil. Part of the wing surface 30 is formed by the upper curved portion 50 of the pressurised structure and the front curved portion 52 of the pressurised structure. The front 54a of the lower curved portion 54 forms a portion of the wing surface 30. However, not all of the lower curved portion 54 forms a portion of the wing surface 30. The wing surface 30 is distinct from the trailing portion 54b of the lower curved portion 54 close to the rear spar 40. That is to say, there are two distinct, separate surfaces at the rear spar 40 and rear spar extension 56. There is the lower curved portion 54b (of the pressurised structure) and the wing surface 30. The lower curved portion 54b joins with the floor 36 at the rear spar 40. The wing surface 30 joins with the rear spar extension 56 but not the floor 36. There is a void 104 in front of the rear spar extension 56 (i.e. closer to the leading edge). The void 104 is defined by the trailing portion 54b of the lower curved portion 54, part of the wing surface 30 and the rear spar extension 56. This additional space is created because the lower curved portion 54 and the wing surface 30 are not coincident in this region. The void 104 improves the aerodynamics of the aircraft and is not structural. Likewise, the rear fairing 62 also improves the aerodynamics rather than providing structural support. The cabin structure 32 may be non-symmetric with respect to a plane of symmetry 80 of the lower curved portion 54. The plane of symmetry 80 is also the plane of symmetry for the floor 36. The cabin structure 32 and upper curved portion 50 are non-symmetric with respect to the floor plane of symmetry 80. The rear spar 40 and front wall 38 are at an angle to each other and are not symmetric with respect to plane of symmetry 80. This differs to state-of-the-art concepts, in which the cabin structure 32, upper curved portion 50, and lower curved portion 54 are symmetric, and have a common plane of symmetry. The plane of symmetry of the ceiling and the upper curved portion is shown at 82. It can be seen that planes 80 and 82 are not coincident in this concept. Construction lines 84 are shown to the centre 86 of the arc 54. Likewise, construction lines 88 are shown to the centre 90 of the arc 50. Figure 3 shows the rear loading of the present invention, as a thickened line. The rear fairing 62 has been described previously. The rear loading is the curvature of the lower curved section 58 of the rear fairing 62. In the present invention, less curvature is required when compared to previous concepts. Less rear loading moves the centre of pressure further in front of the neutral point, which results in less trim drag, and increases longitudinal stability. Figure 3 also shows the available volume in the rear fairing 62, which is shaded with lines across the available volume. The rear spar extension 56 of the present invention, together with the reduced rear loading of the lower curved section 58, relative to previous concepts, mean there is more available volume in the rear portion of the wing. This additional volume can be used to accommodate fuel or be used as storage for cargo. Figure 4 shows the embodiment represented in Figures 2 and 3, but with the thicknesses of the wing surface 30 and the floor 36 shown. The cross section of the inner wing section is shown at 24. The lower curved portion 54 meets the rear spar 40 at point A (line A in three dimensions). The lower curved portion 54 has an inner surface 15A and an outer surface 15B. Line A is where the outer surface 15B meets the rear spar 40. The wing surface 30 extends below line A. The rear spar extension is shown at 56. Additionally, the void 104 can be seen. In contrast to other embodiments of the invention described in detail later, the lower curved portion 54 of the pressurised structure is separate from the lower wing surface. Figure 5 shows a manufacturing concept for the invention. The wing comprises the pressurised structure 92, and a rearfairing 62. The pressurised structure 92 comprises the cabin structure 32. The pressurised structure 92 (front portion) and the cabin structure 32 can be constructed separately and then joined during manufacture. A two-part construction is appropriate for this concept as the pressurised structure 92 is an expensive and complex part, which therefore ideally has a constant cross section over various concepts and may be the same shape over large sections of the plane. The rear fairing 62, however, is preferably a different shape in different sections of the plane. For example, the shape of the rear fairing 62 may be different in the central region of the aircraft, compared to the shape of the rear fairing 62 in the transition region. Therefore, it is advantageous if these two parts can be constructed separately. Figure 6 is an overlay of the state of the art and the present invention. The state of the art is shown in dotted lines. The present invention is shown in solid lines. This shows the relative local incidence angles of the two concepts. As defined previously, the angle of incidence is the angle between a chord line of the wing and a reference axis 95 of the fuselage (i.e. across a floor of the cabin). The reference axis is shown at 95 by a dashed construction line. The chord line of the previous concept is shown at 94, which the incidence angle is measured to. The chord line of the present invention is shown at 96 which the incidence angle is measured to. The floor 36 of the cabin structure 32 is used as a common reference point, i.e. the two concepts are oriented so they both have the floor horizontal. Figure 7 is an overlay of the previous concept and present invention showing the required angle of attack. The angle of attack is the angle between the airflow and a chord of the aerofoil. The aircraft 10 of the present invention during landing. This is overlaid with an aircraft 100 according to previous concepts. The landing gear is indicated at 98. The ground is indicated at 102. The illustration shows the advantage of the present invention, in particular that by designing the aircraft to change the cabin structure angle with respect to the wing surface, the angle of attack can be decreased and therefore the required length of the landing gear 98 can be reduced. It should be appreciated that though dimensions and angles are indicated in Figures 7 and 8, and in the following example, this is only illustrating the potential weight saving available to a standard size of aircraft and the example and the present invention are not limited to any particular size or dimension. With reference to Figures 6 and 7, the effect of the change in the incidence angle on the landing gear height is quantified in an example. Firstly, the change in incidence angle in a streamwise plane is calculated from the change in incidence angle in the cross section perpendicular to the leading edge of the inner wing. On current Flying V (V shaped aircraft) designs, the sweep angle of the inner wing (26A) is around <p = 64°. Using simple trigonometric relations, the change in incidence angle of the streamwise profile Aa, can be approximated with the following relationship Acq = Acq cos cp = 5° ■ cos64° = 2.2° where Acq = 5° is the change of incidence angle in the original cut perpendicular to the leading edge of the inner wing. Raising the streamwise incidence angle of the individual profile sections by -2.2° will allow the aircraft to lower its overall angle of attack by a similar amount, while keeping similar aerodynamic conditions, such as a similar overall lift distribution and similar local lift coefficients. The effect of this change of angle on the change of the wing tip clearance distance can therefore be calculated. During landing, a -2.2° lower angle of attack of the aircraft corresponds to an increased clearance of the outer wingtip to the ground of AyWT « Aoqd = 2.2° ■ -25 m= 0.96 m where d = 25m has been used to approximate the distance from the landing gear to the wingtip. Outer wing tip clearance is the main factor that dictates landing gear height. The present invention leads to a possibility to reduce landing gear length by ~1 m, keeping the outer wing clearance the same. For reference, in previous studies and without the present invention, the main landing gear length for the Flying V had been estimated to have a height as high as 5m and an overall weight of 12 tonnes. Therefore, a ~1 m reduction in landing gear length would be a highly significant improvement to the overall design of the aircraft. It shall also be noted that the present invention can be applied in conjunction with other improvements such as high-lift devices, and / or improved outer wing positioning to reduce the landing gear length even further. Figure 8 is a perspective view of part of the inner section 26A. Central region 12 is shown. Leading edge 18A is indicated. Multiple cross sections 24A through the starboard wing 14A are shown. Multiple cross sections 24B are also shown through the port wing 14B. Each cross section 24 is perpendicular to a leading edge of the aircraft. Additionally, each cross section 24 may also be perpendicular to the rear spar. The rear fairing behind the rear spar 40 is not shown in this figure. Figure 9 is a view from the rear of the aircraft 10, showing the cross sections 24A on the starboard wing 14A, and cross sections 24B on the port wing 14B. This shows the structure of the rear spar 40 and rear spar extension 56. Figure 10 shows the starboard wing 14A, with the neutral point indicated at 66, and the current centre of pressure indicated at 68. The centre of pressure in previous concepts is indicated at 70. Figures 11 to 13 are alternative embodiments of the present invention. The thicknesses of the floor and wing skin are shown. The thickness of the rear fairing is not shown. Figure 11 is an alternative embodiment of the present invention. The cross section is indicated at 124. The thickness of a wing skin, which has a wing surface 130, is shown in this embodiment. The leading edge 118A and the trailing edge 122A are shown, as in previous embodiments. The wing also has a cabin structure 132. The cabin structure 132 has a ceiling 134, a floor 136, front wall 138 and rear wall or rear spar 140. The cabin structure 132 includes a front wall lower edge 146 and a rear spar lower edge 148. In this embodiment, the pressurised structure is bounded by a lower portion of the wing skin rather than a separate lower curved portion. The wing has a lower wing skin 111. The lower wing skin 111 extends from the front wall lower edge 146 towards the rear spar lower edge 148. The lower wing skin 111 has a thickness and therefore has an inner surface 111 A, and an outer surface 111B. Close to the front wall 138, the lower wing skin 111 is arcuate in profile. That is to say, the lower wing skin comprises a front lower curved portion 117 which is substantially arcuate in profile. Closer to the rear spar 140, the outer surface 111B of the lower wing skin 111 no longer follows the arcuate path of the front lower curved portion 117, and instead extends below a projection of the initial arcuate path. The projection is an arcuate continuation of the initial arcuate path of the front lower curved portion 117. The projection of the continuation of the initial arcuate path on the rear spar 140 is shown at line A (point A in the cross section). In particular, the projection is the continuation of the arcuate path of the outer surface 111B of the lower wing skin 111. An inner surface 111A of the lower wing skin 111 does follow the arcuate path in this embodiment. Therefore, in this embodiment, a lower wing skin 111 functions as both the pressurised structure and the wing surface. The outer surface 111B of the lower wing skin changes in curvature so it can form a continuous surface with the rear fairing, rather than forming an edge at the rear spar. This is in contrast to previous concepts, in which the outer surface 111B of the lower wing skin 111 would be arcuate across the whole wing, and therefore meet line A. The lower wing skin 111 thickens towards the rear spar and therefore the outer surface 111B and inner surface 111A diverge. The lower wing skin 111 then joins with the floor 136 close to the rear spar 140. The rear spar 140 does have a rear spar extension 156, but it is essentially obscured by the thickness of the outer wing skin 111. As such, no ‘void’ is formed in front of the rear spar in this embodiment. Figure 12 is another embodiment of the present invention. The cross section is indicated at 224. This embodiment is substantially similar to the embodiment shown in Figure 11, however the position of the floor beam 236 relative to the wing surface 230 is different. The cabin structure is indicated at 232. The leading edge is shown at218A, and the trailing edge at 222A. In this embodiment, the floor 236 is lower relative to the embodiment shown in Figure 11. Line A is still the projection of the continuation of the initial arcuate path of an inner surface 211A of the front lower curved portion 217. However, in this embodiment, line A is in the centre of a height of the floor beam 236, as opposed to in the Figure 11 embodiment, when line A was at a lower surface of the floor beam 236. Figure 13 is another embodiment of the present invention. Again, this is similar to the embodiments shown in Figures 11 and 12, however in this embodiment, the floor beam 336 is tilted. As in previous embodiments, the cross section is indicated at 324, the cabin structure at 332, and the wing surface at 330. The leading edge is shown at 318A, and the trailing edge at 322A. In this embodiment, the floor is indicated at 336, and slopes ‘downwards’ from a front of the wing, near the leading edge 318A to the rear of the wing, near the trailing edge 322A. There is also an additional structure, indicated at 313. The additional structure 313 is substantially wedge shaped. The additional structure 313 is disposed above the floor 336. The additional structure 313 is thicker closer to the rear spar 340, i.e. closer to the trailing edge 322A. The additional structure 313 is thinner at the front end, near to the leading edge 318A. Line A in this embodiment is the projection of the continuation of the initial arcuate path of the inner surface 311A of the front lower curved portion 317, as in previous embodiments. However, in this embodiment, point A is at the top of the floor 336, and at the bottom of the additional structure 313. Figure 14 shows pressure isobars on the starboard wing 14A. In particular, it shows increased concentration of isobars to the rear of the central portion 12. Figures 15 and 16 show previous concepts, as has been discussed in the background. Figure 17 shows the 3-dimensional structure of a previous concept. The layout of the beams is similar to that in the present concept. The floor beams are disposed across the wing. The surface of the wing is supported by a serious of frames disposed around the cross section of the wing. The embodiments described above are provided by way of example only, and various changes and modifications will be apparent to persons skilled in the art without departing from the scope of the present invention as defined by the appended claims.

Claims

1. An aircraft comprising:a starboard swept wing and a port swept wing, each swept wing having an inner wing section comprising an integrated payload fuselage and an outer wing section for extending the wingspan and providing lift;each inner wing section comprising:a rear spar disposed close to a trailing edge of the inner wing section to carry loads along the inner wing section;a wing surface, in which the wing surface is substantially shaped as an aerofoil, and in which the wing surface comprises a rear fairing disposed behind the rear spar, and near to the trailing edge, and in which the wing surface comprises an upper curved portion which has a substantially arcuate cross section, a front curved portion which has a substantially arcuate cross section, and a lower wing surface,the upper curved portion meeting the rear spar at a rear of the upper curved portion, and the upper curved portion meeting the front curved portion at a front of the upper curved portion,the front curved portion meeting the lower wing surface at a front of the lower wing surface,a cabin structure in the inner wing, in which the cabin structure comprises one or more floor beams and a rear wall defined by the rear spar;in which the lower wing surface comprises a front lower curved portion, in which the front lower curved portion is substantially arcuate in profile and extends from a front edge of the floor beam(s) of the cabin structure towards the rear wall; andin which the lower wing surface of each inner wing extends below a first line, the first line being a line along the rear wall of the cabin structure where a projection of the arcuate front lower curved portion of the wing surface meets the rear wall, and in which a rear lower portion of thelower wing surface meets the front lower portion and continues the lower wing surface to a second line, which is spaced from and below the first line.

2. An aircraft as claimed in claim 1, in which each inner wing has a greater sweep angle than the outer wing, and in which the sweep angle of each inner wing section is greater than 60°.

3. An aircraft as claimed in claim 1 or claim 2, in which a rear spar extension is disposed below the rear wall, in which the rear spar extension extends from a base of the rear wall and joins with the wing surface.

4. An aircraft as claimed in any preceding claim, in which each inner wing comprises a pressurised structure.

5. An aircraft as claimed in claim 4, in which the wing surface forms a portion of the pressurised structure.

6. An aircraft as claimed in claim 4 or claim 5, in which the pressurised structure of the inner wing comprises a lower curved portion, which is substantially arcuate in profile, and in which an arc of the lower curved portion has a secant which is coincident with one of the floor beams of the cabin and in which the lower curved portion is distinct from the lower wing surface near the rear wall.

7. An aircraft as claimed in any one of claims 4 to 6, in which the lower curved portion is a boundary of the pressurised structure.

8. An aircraft as claimed in any one of claims 4 to 7, in which a part of the pressurised structure is formed by the wing surface near the lower edge of the rear wall of the cabin structure.

9. An aircraft as claimed in any one of claims 4 to 8, in which the pressurised structure comprises the rear wall or a surface close to the rear wall, for forming a rear bulkhead.

10. An aircraft as claimed in any preceding claim, in which the cabin structure has a front wall and / or the cabin structure has a ceiling.

11. An aircraft as claimed in claim 10, in which the front curved portion extends from an upper edge of the front wall to a lower edge of the front wall.

12. An aircraft as claimed in claim 10 or claim 11, in which an arc of the front curved portion of the wing surface has a secant which is coincident with the front wall of the cabin structure.

13. An aircraft as claimed in any one of claims 10 to 12, in which the upper curved portion of the wing surface extends from an upper edge of the front wall to an upper edge of the rear wall.

14. An aircraft as claimed in any one of claims 10 to 13, in which an arc of the upper curved portion of the wing surface has a secant which is coincident with the ceiling of the cabin structure.

15. An aircraft as claimed in any previous claim, when dependent on claim 3, in which the rear fairing joins with a lower edge of the rear spar extension or a lower edge of the rear wall.

16. An aircraft as claimed in any previous claim, in which the rear fairing joins with the lower wing surface near the lower edge of the rear spar extension or the lower edge of the rear wall.

17. An aircraft as claimed in any previous claim, in which the rear fairing joins with the top of the rear wall.

18. An aircraft as claimed in any previous claim, when dependent on claim 10, in which the front wall is or is attached to a front spar, tension strut or other structural reinforcement.

19. An aircraft as claimed in any previous claim, when dependent on claim 10 in which the ceiling is a ceiling beam, ceiling rib, ceiling reinforcement, or other structural reinforcement.

20. An aircraft as claimed in any previous claim, when dependent on claim 10, in which the ceiling of the cabin structure is sloped relative to the floor beam of the cabin structure, such that the ceiling of the cabin structure joins with the wing surface.

21. An aircraft as claimed in any previous claim, when dependent on claim 4, in which the pressurised structure comprises or consists of the rear wall, the front curved portion, the lower curved portion and the upper curved portion.

22. An aircraft as claimed in any previous claim, when dependent on claim 4, in which the pressurised structure comprises or consists of the rear wall, the front curved portion, the lower wing surface and the upper curved portion.

23. An aircraft as claimed in any previous claim, in which the upper curved portion joins with an upper edge of the rear fairing and / or in which the front lower wing surface joins the front curved portion.

24. An aircraft as claimed in any previous claim, in which the joins between any of the curved portions are smooth to form a continuous surface.

25. A method of constructing an aircraft comprising the steps of:a) constructing a front portion of an inner wing, the front portion of the inner wing comprising a pressurised structure and a rear spar, the rear spar disposed close to a trailing edge of the inner wing;b) constructing a rear fairing; andc) joining the rear fairing to the inner wing at the rear spar.

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