Background

The present invention is concerned particularly, but not exclusively, with an aerodynamic structure which is capable of adapting or changing in shape and thus providing changeable aerodynamic performance.

Conventional movable aerodynamic structures used on aircraft comprise an aerodynamic structure which is mounted to the aircraft wing, body or engine (or the like) by means of a hinge arrangement. The movable structure can then be rotated about the hinge to change the overall aerodynamic performance.

Moveable structures on aircraft include flaps, ailerons, spoilers, tail wings and various other components arranged, in use, to guide or control airflow over an aircraft structure. Ailerons, as one example, are coupled to the main wing structure by means of hinge arrangements allowing the aileron to be rotated about a pivot to change the flow direction of air.

Actuators, such as electric motors, hydraulic pumps, worm gears or the like, are used to pivot and move the moveable structures about the hinge thereby changing the aerodynamic performance and characteristics of the structure. This allows for controlled aircraft flight by movement of the structure.

For example, an aircraft flap is conventionally mounted to the trailing edge of a wing by means of a series of hinges located along the length of the wing. The flap is coupled to a series of actuators which, when activated, cause the flap to rotate changing the aerodynamic performance of the wing and increasing lift. Such arrangements have been used for decades in aircraft design and are robust, reliable and generally provide adequate aerodynamic performance.

However, the present inventor has identified an alternative approach to moveable aerodynamic structures which provides a structure with a continuous surface which can adapt in shape so as to change the aerodynamic performance of component. The invention provides a highly adaptable surface without a complex internal structure or actuation arrangement thereby additionally improving reliability and offering a low maintenance solution which is of importance in allowing for the economical operation of aircraft. Summary of the Invention

Aspects of the invention are set out in the accompanying claims.

Viewed from a first aspect there is provided a deformable aerospace structure, the structure comprising a first layer and a second layer spaced from the first layer and defining a space therebetween, the space comprising one or more reinforcement elements extending between the first layer and the second layer, wherein the ends or portions of the reinforcement element(s) proximate to the first layer are connected thereto and ends or portions of the reinforcement element(s) proximate to the second layer are moveable with respect to ends or portions of adjacent reinforcement element(s) proximate to the second layer.

By allowing the points at which the reinforcement elements meet the second layer to be moveable relative to eachother there is provided a structure which is flexible and can be deformed whilst maintaining a smooth continuous surface on an opposing side of the structure (for example an airflow facing surface). The reinforcement elements, combined with the way they are coupled or connected to each of the first and second layers, advantageously provides a desired level of structural strength to be provided whilst simultaneously allowing for the curvature of the structure when actuated with a suitable actuator.

The term deformable is intended to refer to a structure which can change in shape and in particular to bend or flex so are to form a generally curved, concave or convex shape.

The reinforcement elements may be any suitable member and may, for example, be a plurality of discrete and individual elements extending between the two layers. The elements may be arranged at an angle with respect to the two surfaces which is less than 90 degrees.

The elements may be arranged at the same angle or at different angles to provide for different characteristics along the structure. Advantageously the reinforcement element(s) may be in the form of a plurality of adjacent members each alternating in direction and extending from the first layer to the second layer.

Alternatively the reinforcement member may be in the form of a continuous member configured to alternate between the first and second layers along its length. Thus, instead of a plurality of individual elements a single element can be formed, for example corrugated, and located between the two layers. This reduces the number of connections and simplifies construction and manufacturing by minimising the components.

The second layer may advantageously be in the form of one or more elastic elements connecting adjacent reinforcement elements together. The elastic elements may then permit the relative movement of adjacent reinforcement elements at the second layer. As described above, relative movement of these points allows for curvature of the structure.

For example, the elastic elements could be in the form of elastic or metal springs.

Advantageously, the second layer may be formed of a continuous elastomeric layer encapsulating the ends or portions of the reinforcement elements proximate thereto. Thus, the ends (or portions is the reinforcement element is a corrugated arrangement) of each of the reinforcement elements is secured within the elastomeric layer. Because of the elastomeric properties not only is the reinforcement element secured but it is also advantageously permitted to move by virtue of the flexibility of the material.

At the ends of the reinforcement elements proximate to the first layer each adjacent element may be connected to the inner surface of the first layer at a common point or along a common line i.e. at the same position. This provides a V or apex structure which provides rigidity and strength to the first layer and reinforcement layer.

Thus, providing a difference in the way adjacent ends of each reinforcement element are connected together results in a difference in the stiffness of each side of the structure; namely the first layer has a greater stiffness than the second layer. Specifically, the stiffness between adjacent points at which the reinforcement elements connect to the first layer may be greater than the stiffness between adjacent points at which the reinforcement elements connect to the second layer.

In an aerospace application, the first layer may comprise an airflow facing outer surface and a reinforcement element facing inner surface. The airflow facing outer surface may then become part of a continuous aerodynamic surface, such as a spoiler, flat or the like.

The structure may be formed of any suitable combination of materials whilst retaining the stiffness requirements described above. For example, the first layer and the reinforcement elements may be formed from a carbon fibre reinforced plastic or aluminium material and the second layer may be formed from a continuous rubber or silicone elastomer layer.

Advantageously the reinforcement element may be is in the form of a corrugated member alternating between the first and second layers along its length and defining a plurality of generally V shaped sections. The one or more V shaped sections may incorporate a supplemental reinforcement member arranged perpendicularly with respect to the first layer and second later and having a first end extending into an elastomeric layer forming the second layer and a second end extending into an elastomeric material arranged within the base of the V shaped section proximate to the first layer. Such an arrangement provides enhanced stiffness within the structure.

Viewed from another aspect there is provided a deformable fluid directing structure, the fluid directing structure comprising a first layer and a support layer spaced from the first layer and defining a space therebetween, the space comprising one or more reinforcement elements extending between the first layer and the support layer, wherein the ends or portions of the reinforcement element(s) proximate to the first layer are connected thereto and ends or portions of the reinforcement element(s) proximate to the support layer are encapsulated within an elastomeric layer.

Advantageously, the Young’s Modulus of Elasticity (E) of the elastomeric layer may be between between 80 and 120 MPa, between 90 and 110 MPa or greater than 100MPa.

Viewed from a still further aspect there is provided a deformable structure for an aircraft component, the structure comprising a first airflow facing layer and a second opposing layer defining a space between the first and second layers, wherein the modulus of elasticity of the first airflow facing layer is greater than the modulus of elasticity of the second layer.

Advantageously the space comprises a reinforcing or support layer such as a corrugated metallic or carbon fibre layer which transfers the shear loads between the airflow facing layer and the second layer. This triple layer arrangement advantageously allows the structure to change in shape whilst allow allowing the loads caused by air impinging on the structure to be transferred to the second layer. The reinforcement layer may itself be a continuous layer or material with an intermediate modulus of elasticity between the airflow facing layer and the second layer. In effect a laminate structure is provided with a different modulus of elasticity for each of the three (or more) layers (decreasing from the airflow side to the second internal side i.e. internal to the aircraft structure).

In the case of a rubber being used for the second layer, the material properties allow the layer to stretch. The relative thicknesses of each of the layers may be suitably selected to accommodate the desired loads for the structure and the amount of curvature needed.

Viewed from yet another aspect there is provided an aircraft, aircraft engine or wind turbine blade comprising a deformable aerospace structure as described herein.

Drawings

Aspects of the invention will now be described, by way of example only, with reference to the accompanying figures in which:

Figures 1 A and 1 B show a schematic of an example moveable structure of an aircraft wing;

Figure 2 shows a cross-section through a structure according to an invention described herein;

Figure 3 shows a flap and spoiler arrangement in an un-deployed flap state;

Figure 4 shows a flap and spoiler arrangement in a deployed flap state;

Figure 5 shows force diagrams for the structure described herein;

Figure 6 shows a cross-section through a prototype arrangement of adaptive structure described herein; and

Figure 7A and 7B show two alternative arrangements of an invention described herein.

While the invention is susceptible to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings and are herein described in detail. It should be understood however that drawings and detailed description attached hereto are not intended to limit the invention to the particular form disclosed but rather the invention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the claimed invention. As used in this specification, the words “comprises”, “comprising”, and similar words, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean“including, but not limited to”.

It will be recognised that the features of the aspects of the invention(s) described herein can conveniently and interchangeably be used in any suitable combination. It will also be recognised that the invention covers not only individual embodiments but also combinations of the embodiments that have been discussed herein. Detailed Description

The present invention is concerned with a deformable or morphing structure with an aerodynamic profile. This may include, but is not limited to, a flap, trailing edge, leading edge, spoiler, air inlet or the like. Specifically, the invention provides such a structure where a minimum number of actuators are desire and, importantly, where no hinges are present.

The structure described herein provides a deformable aerospace structure which advantageously:

Can transfer loads (with no buckling or large deformations are acceptable when loaded under aerodynamic or structural loads);

Will not fail due to high internal stresses (mostly caused by the bending stresses when forced into desired shape); and

Is flexible (can be morphed into the desired shape. Large deformations are needed under actuation loads)

No suitable solutions are currently available that meet these requirements.

The invention described herein provides an arrangement in which elements and materials with a significant difference in stiffness in an axial direction are combined in a structure in such a way that the bending stiffness of the complete structure is enlarged while the maximum stress in the elements remains at an acceptable level when the structure is morphed/bended.

The invention will now be described in detail with reference to the figures.

Figures 1A and 1 B are schematic end views of an aircraft wing 1 viewed in cross-section towards the fuselage of the aircraft. The wing comprises a leading edge 2 and a trailing edge 3. Figure 1 illustrates one example of a moveable structure on a conventional aircraft. The structure shown is a flap 4 which is movable about a pivot (not shown) proximal to the trailing edge of the main wing box 5. The arrow A in figure 1 B illustrates how the flap can then be moved about the pivot. Movement causes the distal part of the flap from the pivot to move in an arc which in the case of the flap causes the airflow to change in direction (see arrow B) and to generate more lift. Figures 1A and 1 B represent just 1 location of a moveable component on an aircraft structure. Other examples include wing flaps, the tail wings, tail rudder, air inlets, spoilers and even the landing gear doors. It will be recognised that the arrangements and methods described herein can be applied to any hinged arrangement for an aircraft structure.

An example of an invention described herein will now be provided with reference to one of these movable components, namely a wing spoiler.

The location of a typical wing spoiler is shown in figures 1A and 1 B by reference S. The spoiler can serve multiple functions. For example, the spoiler may be rotated in a vertical direction to increase drag on landing or to change the aerodynamic profile to slow the aircraft in flight. The spoiler is operating by rotating the spoiler about a pivot located at its upstream edge with the trailing edge entering and disturbing the airflow to cause the desired drag.

In another arrangement the spoiler can be used to bridge the gap which is formed when the flaps shown in figures 1A and 1 B are deployed or activated.

As shown in figure 1 B the flaps 4 have been deployed to increase the lift generated by the wing. As shown in figure 1 B a gap 6 is generated at the trailing edge of the wing box as the flap is deployed and rotates away from the wing box body. This gap is generally undesirable since it is detrimental to the efficient airflow over the wing surface. To counter this a spoiler Smay be arranged so as to extent over part of the gap to increase efficiency.

However, because of the way the flap rotates and the flat structure of the spoiler there is always an unwanted gap along the trailing edge of the wing box. The invention described herein addresses this problem and provides a unique uninterrupted aerodynamic surface that can conveniently change in shape to provide a continuous aero-surface.

The composition of the structure according to an invention described herein will be explained with reference to figure 2 which is a cross-section through the structure.

The adaptive or dynamic structure 7 comprises an upper or outer first layer 8 and an opposing lower or second layer 9. A gap or space h is defined between the two surfaces or layers. The upper layer 8 is the air-facing layer and has an upper outer surface against which air is caused to flow in flight. It is this surface which received the air pressures and therefore the associated forces. In the example shown an undulating or corrugated reinforcement or support member 10 is positioned between the two layers. This layer is arranged in a generally V-shaped cross- section with opposing apexes of the V extending to the first and second layers as shown in figure 2

The precise geometry of the corrugated member 10 will depend on the particular application for the structure including the angles of the V cross-sections, height and thickness. The material used may also be adapted depending on the structure requirements of the component.

Similarly the material used to form the first and second layers may be selected according to the anticipated forces and desired deflection.

Importantly, at the points at which the corrugated reinforcement elements meet the first layer the reinforcement element is connected or bonded to the inner surface of the first layer (reference 11). Depending on the material used this may be by an adhesive, co-curing or welding. Thus, the reinforcement element is firmly fixed or connected to the top of the reinforcement element at each (or a subset of) apex.

The first upper surface or layer may be a carbon fibre reinforced plastic (CFRP) or a metal such as aluminium or titanium. In an example of a spoiler it may for example be an aluminium layer between 1 and 1.6mm thick. Similarly the reinforcement element may be formed of CFRP or aluminium between 0.6 and 1.2mmm thick.

In the example shown in figure 2, the opposing apexes of the reinforcement elements extend into the second layer 9 as shown at the bottom of figure 2. Thus, the ends of the reinforcement elements which extend to the second layer may be encapsulated within the second layer as opposed to being bonded or connected to the layer as described above with reference to the first layer (for example by means of welding).

Importantly, the second layer shown in figure 2 is an elastomeric material such as silicone or rubber which has a Young’s modulus of elasticity of approximately 100MPa (having a thickness of 6mm. Thus, the ends or portions of the corrugated reinforcement element 10 are entirely encapsulated in a flexible (or semi-flexible) material. This conveniently allows these ends of the corrugated reinforcement element to move with respect to adjacent portions of the reinforcement element encapsulated within the second layer. This is illustrated at references 12a and 12b and the associated arrows. It will be recognised that bending or flexing the structure about the direction of arrow C will cause the portions 12a and 12b to move together. Conversely bending the panel in the opposite direction acts to move the portions 12a and 12b apart. Because of this permissible movement of adjacent portions of the reinforcement element the structure can accommodate bending forces and thereby flex and bend without fracturing or breaking.

It will also be recognised that because of the connection or bond at points 11 the structure retains structural strength. The exactly strength and rigidity of the structure will depend on the materials used, the thicknesses and the associated relative modulus of elasticity of the first layer and reinforcement elements versus the modulus of elasticity of the second layer i.e.

Modulus of elasticity of first layer combined with reinforcement layer = EFER

Modulus of elasticity of the second layer alone = Es

EFER > Es

This relationship ensures that the structure is permitted to conveniently flex whilst maintaining a continuous and uninterrupted surface of the first layer.

Another alternative embodiment is described below with reference to figures 7 A and 7B.

Figures 3 and 4 illustrate an application for the structure described herein, namely a spoiler with an adaptive surface which advantageously does not require a hinge arrangement.

Referring to figure 3 the deformable or deflectable structure 7 is located between the wing box 5 and the spoiler S. The trailing edge of the spoiler S overlaps with the leading edge of the flap 4 in normal flight to provide a continuous surface.

An actuator 13 is shown which is coupled to the spoiler S. Movement of the actuator 13 along the direction of the arrow D will cause movement of the spoiler in a downward direction. Ordinarily without the structure 7 a hinge may be required to connect the spoiler to the wing box 5 i.e. to provide a pivot about which the spoiler could rotate. However, the present invention conveniently provides not only the hinge functionality but also a smooth and continuous surface 14.

Referring to figure 4, the flap has been deployed and the actuator 13 activated to cause the spoiler to follow the rotation of the flap in a downward direction. As shown because of the way the points at which the reinforcement elements of the deflectable structure can move relative to each other the structure 7 can conveniently bend or deform into the curve 15 shown in figure 4. This allows the first upper surface 8 to bend and provide a smooth arc between the wing box and the spoiler.

This advantageously increases the effectiveness of the flaps and improves aerodynamic performance. It will be recognised by those skilled in the art that any increase in aerodynamic performance can allow components and structures to be made smaller and thus save weight.

It will be recognise that operating the actuator in the opposite direction will cause an opposite arc of the deformable structure 7 and the spoiler moves in an upward direction (for example in an application where the spoiler functions to increase drag).

This is further illustrated with reference to figure 5 which illustrates the forces and nodes of one embodiment of a deformable structure described herein.

Advantageously the arrangement described herein redistributes loads in such a way that the structure can be morphed or deformed into different shapes without creating unacceptable high stresses in the materials whilst simultaneously allowing the structure to transfer the applied structural and aerodynamic loads.

Referring to Figure 5, elements 1 to 6 form the primary skin surface (the first layer). Thus, a continuous skin is provided from point a to point h with certain properties of (length, width, thickness and stiffness).

Elements 12 to 23 form a corrugated internal reinforcement layer or elements within the structure, again with properties (length, width, thickness and stiffness). Elements 7 to 11 represent the support or second layer with a much lower stiffness than the primary skin and the reinforcement layer. Here, the selected material may conveniently be rubber for example with a certain thickness t such that no buckling failure of this element is possible.

An alternative arrangement replacing the elastomer with a spring is described below with reference to figure 7.

As discussed above, the important relationship is that the total axial stiffness between adjacent apexes in the elastomer layer is much lower than the axial stiffness of the first and reinforcement elements combined.

As shown in figure 5, the structure has been deflected or deformed in an opposite direction to that shown in figure 4. The upper load diagram shows a cross-section through the structure as described herein and the lower load diagram a normal skin. The dotted lines indicate the deformed positions.

The inventor has established the following observations in developing the deformable or morphing structure

1) A first requirement will be that the deformation of the skin when loaded under an aerodynamic pressure will remain at a certain acceptable level. In figure 5 the force P1 represents the aerodynamic loading.

When the structure described herein and the normal conventional skin element are both optimized to meet this requirement and their deformation as a result of the loading P1 , the thickness of the structure described herein can be much thinner than the thickness of the normal conventional skin.

2) A second requirement will be that the stresses in the skin remain at an acceptable level when the structure is loaded with an action force. In figure 1 the actuation force is represented by the moment M1 and M 2.

When the structure described herein and the normal conventional skin element are both pushed into an equal morphed shape, the stresses in the normal skin will be much higher (and in most of the practical applications unacceptable) than the stress in the innovative structure described herein because of the difference in skin thickness.

Out of assessment 1 and 2 it has been established that the invention described herein has huge potential to contribute to the development of morphing adaptive (wing) structures.

Figure 6 shows a cross-section of a prototype deformable aerospace structure where the elastomeric layer is clearly visible at the bottom of the image. In addition further reinforcement elements are shown located with each V shaped reinforcement. The lower end of these additional reinforcement elements is encapsulated within the second layer and at an opposing end (in the apex closest to the first layer) another bead of elastomeric material is provided to receive the opposing end of the additional reinforcement. This structure provides still further strength which allowing the structure to retain its deformable properties.

Referring to figures 7 A and 7B, an alternative arrangement is described. As shown in figure 7A the structure described above is shown using an encapsulating elastomeric layer. Another way to provide the same or similar elastic properties is to use a spring 16 to define the second‘layer’. It will be recognised that the elastomeric option allows for functionality in two directions whereas the spring embodiment allows functionality in a single direction.

In an arrangement where an elastomeric or rubber layer is used the layer may incorporate spaces or apertures across its surface or its depth or allow for compression of the layer. This may then advantageously allow greater curvature of the structure i.e. a tighter bent structure or curve.

It will be recognised that an invention described herein can be applied to a variety of fluid controlling or directing components where a hinge would ordinarily be used and where a smooth surface can be advantageous.