Aerodynamic profile body for aircraft

Description

[0001] The invention relates to an aerodynamic profile body for aircraft with an aerodynamically flowable surface.

[0002] For the purposes of the present invention, the term "aerodynamic profile body" refers to those elements of an aircraft (for example, airplanes, commercial aircraft, transport aircraft, and helicopters) that are arranged projecting from the fuselage of the aircraft and, during normal use of the aircraft, are exposed to an external airflow, thereby generating aerodynamic forces on the aircraft. Aerodynamic profile bodies of an aircraft include, in particular, wings or airfoils of a wing structure, as well as empennage (for example, horizontal stabilizers, vertical stabilizers, or ailerons). In the case of empennage, the aerodynamic force is generated only when the control surface is deflected outwards from the neutral position, when the empennage is exposed to an external airflow.As a rule, the aerodynamic profile bodies of an aircraft are exposed to the flow of the outer layer of air during the movement of the aircraft through the airspace.

[0003] The airfoil surfaces of such aerodynamic profiles, i.e., the outer, aerodynamically exposed surface, generally possess a laminar boundary layer. However, in modern commercial aircraft, this transitions early into turbulent boundary layers. Such a turbulent boundary layer exhibits significantly higher frictional drag than a laminar boundary layer. Shape deviations in the airfoil surfaces, such as gaps, steps, and waviness in the contour, promote the instability of the boundary layer, leading to an early transition from a laminar to a turbulent boundary layer.

[0004] If shape deviations cannot be avoided, a step of up to 0.5 mm or 0.6 mm can be tolerated, depending on the application. Avoiding shape deviations larger than the permissible values ​​in the leading edge of the aerodynamic airfoil leads to a later transition of the flow from a laminar to a turbulent boundary layer, thus extending the area of ​​laminar flow around the airfoil. Because a laminar boundary layer has lower frictional drag during flight than a turbulent boundary layer, maintaining a laminar boundary layer for as long as possible can save fuel and thus make the operation of the aircraft more economical and environmentally efficient.

[0005] Such a natural laminar flow requires, in addition to a disturbance-free surface on the aerodynamic profile body, where ripples, steps and gaps as well as heads of connecting elements in the surface are largely avoided, a suitable pressure distribution in order to avoid a premature transition of the laminar boundary layer flow to a turbulent boundary layer flow.

[0006] In addition, hybrid laminar flow control is also known, in which the boundary layer is drawn off in the leading edge region of the aerodynamic profile through a pore size or slotted aerodynamic surface, allowing a fresh boundary layer to continuously form. This active suction can maintain a laminar boundary layer even under certain conditions where natural laminar flow is no longer possible.

[0007] In addition to these flow-related aspects of an aerodynamic airfoil, which concern fundamental aerodynamic properties of the airfoil within the aircraft, maintenance-related aspects also come to the fore from an economic and ecological perspective, particularly regarding the repairability and replaceability of individual aircraft components. Due to the fact that the leading edge of an aerodynamic airfoil is an exposed area susceptible to impact damage, the aircraft design must consider the replaceability of this leading edge, especially the leading edge of the airfoil.Especially in light of the use of fiber composite materials as outer and load-bearing layers of a leading edge of an aerodynamic airfoil, it must be ensured that such a leading edge can be replaced by maintenance personnel in a normal maintenance cycle (usually overnight) and, moreover, that after completion of the replacement of the aerodynamic airfoil with the new leading edge, it also exhibits laminar flow characteristics.

[0008] WO 2013 / 000447 A1 discloses a method for connecting a wing leading edge to the wing upper shell, in which the upper shell is slid under the leading edge in the connection area, and the two elements are then joined in the overlap area using bolts that pass through the outer surface. The connection area lies in a groove below the aerodynamic surface and is sealed with a filler compound after the bolts are inserted, thus creating a smooth and undisturbed aerodynamic surface. A disadvantage of this method is that it requires a particularly high level of effort for the precise application of the filler compound.Since commercially available fillers shrink considerably both during curing and at low ambient temperatures, such as those encountered during the cruise flight of commercial aircraft, deviations from the desired contour occur under flight conditions, which can disrupt the maintenance of laminar flow. Furthermore, practical experience has shown that when replacing the component, the bolts under the filler must first be exposed, which significantly increases the time required for replacing the leading edge.

[0009] From DE 10 2014 102 117 A1, a method is known in which the wing leading edge is attached using a mounting bracket arranged on the front spar of the wing box, without having to extend the outer wing upper shell under the wing leading edge. Here, too, connecting elements are guided through the outer surface of the wing leading edge to attach it to the first leg of the mounting bracket. The connecting elements are then covered by an outer metal layer of the wing leading edge. A disadvantage of this method is that replacing the wing leading edge requires access to the interior of the leading edge, as the replacement is achieved by loosening the attachment of the second leg of the mounting bracket to the front spar or by loosening internal screws securing the first leg. However, access to the interior is not readily available, particularly in the case of empennage.

[0010] A similar connection concept is also known from DE 10 2015 105 298 A1, in which, however, the mounting bracket is integrally connected to the leading edge and thus no connecting elements need to pass through the surface of the leading edge. The remaining gap between the two joined components (joining gap) is still to be filled with a filler compound. This connection principle also relies on placing connecting elements inside the wing to avoid disturbing the outer surface.

[0011] From EP 2 445 785 A1, a connection between a wing leading edge and a wing box is known, in which the connecting elements, which are guided through the outer surface within a recessed groove, are subsequently covered flush with the aerodynamic contour by a metal sheet. Manufacturing tolerances are to be compensated for by the thickness of the adhesive compound. A disadvantage of this is that a gap remains in the edge regions of the metal sheet in the groove, which must be sealed with a filler compound if disturbances to the maintenance of laminar boundary layer flow are to be avoided.

[0012] WO 2010 / 001008 A1 discloses the fairing of an engine inlet, for which a leading edge is to be arranged on the annular fairing. This leading edge is screwed to the fairing structure. To prevent disturbances in the outer flow surface, a cover is glued over the entire area of ​​the connection.

[0013] US patent 4,888,451 A also discloses the connection between two elements of a wing body, in which a covering element, which is not a cover film, is used in the area of ​​the connection arrangement to cover the bolts. This covers a small gap, while a gap remains at the outer flow surface that is not covered.

[0014] US 5,106,037 A and US 5,014,934 A disclose a cover that is arranged in the area of ​​the connection of two elements of a wing body and extends both from one wing body and towards the other wing body.

[0015] It is therefore an object of the present invention to provide an improved aerodynamic airfoil body for aircraft in which the leading edge is interchangeable and easy to replace without the need for access from the inside, and furthermore promotes a laminar boundary layer flow.

[0016] The problem is solved according to the invention with the aerodynamic profile body according to claim 1. Advantageous embodiments of the invention are found in the corresponding dependent claims.

[0017] According to claim 1, an aerodynamic airfoil for aircraft is proposed, which has an outer surface exposed to aerodynamic flow. During normal use of the aircraft in flight, the outer surface is exposed to the surrounding airflow and can thus exert aerodynamic forces on the aircraft. In the case of a wing as the aerodynamic airfoil, a lift force can be generated by the airflow over the outer surface.

[0018] By definition, an aerodynamic airfoil body comprises a main body, which includes a main body support structure and an outer layer arranged on the main body support structure as part of the aerodynamically flowable surface. Such a main body of the aerodynamic airfoil body can be, for example, the wing box of an airfoil or the tail box of a tail assembly. The main body has a support structure, for example, in the form of ribs and spars, which is preferably made of a fiber-reinforced composite material. An outer layer, also called the outer skin or outer shell, is applied to the support structure of the main body as part of the aerodynamically flowable surface.

[0019] Furthermore, the generic aerodynamic airfoil body has at least one leading-edge body, which includes a leading-edge support structure and a leading-edge outer layer applied to this support structure as part of the aerodynamically flowable surface. The leading-edge body is the front part of the aerodynamic airfoil body, located in front of the main body in the direction of flight and thus occupying an exposed position. The leading-edge support structure can also be made of a fiber-reinforced composite material, and can likewise consist of ribs and spars. Truss structures, which provide the necessary stability for the leading edge, are also conceivable.The leading edge outer layer is applied to this supporting structure and thus forms part of the aerodynamically flowable surface, whereby a perforation may be present in the leading edge outer layer in order to be able to draw off the boundary layer flow at the outer layer and thus achieve a hybrid laminar flow.

[0020] A connecting arrangement attaches, or allows for the attachment of, at least one leading edge body to the main body. For this purpose, connecting elements in the area of ​​the connecting arrangement are passed from the outside through the aerodynamically open surface and engage with counterparts located inside the profile body for fastening. Such connecting elements can be, for example, screws that engage with a thread located inside the profile body, thus forming a positive and / or non-positive connection. Alternatively, bolts that engage with a corresponding positive-locking counterpart are also conceivable. The connecting elements primarily connect and fix the leading edge body to the main body by means of a positive-locking connection.

[0021] Due to this connection arrangement, as known from the prior art, the head ends of the connecting elements lie in the aerodynamically flowable surface, thus preventing disturbances in the laminar flow of the boundary layer. Furthermore, a joining gap exists in the aerodynamically flowable surface, formed by the arrangement of the leading-edge body on the main body between the leading-edge outer layer and the main body outer layer, and forming a step with respect to the boundary layer flow at which a laminar boundary layer transitions into a turbulent boundary layer.

[0022] It is now provided that in the area of ​​the connection arrangement a rigid cover film is applied to the outer aerodynamically flowable surface, wherein the connecting elements passing through the aerodynamically flowable surface are concealed by the rigid cover film and wherein the rigid cover film extends over the joining gap between the part of the aerodynamically flowable surface of the main body and the part of the aerodynamically flowable surface of the leading edge body.

[0023] The rigid cover film thus covers the connection assembly with its connecting elements, as well as the joint gap between the leading edge outer layer and the main body outer layer, thereby eliminating disturbances in the aerodynamically flowable surface of the airfoil body. It has been shown that a rigid cover film, which covers both the connecting elements and the joint gap, promotes a natural laminar boundary layer flow and largely prevents premature transition to a turbulent boundary layer flow.

[0024] The rigid cover film is designed such that it forms part of the aerodynamically flowable surface of the airfoil body in the area of ​​the connection. The rigid cover film therefore has a joining side and an outer side, with the joining side of the rigid cover film being attached, for example, by means of an adhesive, to the outer surface of the airfoil body in the area of ​​the connection, while the outer side forms part of the outer flowable surface of the airfoil body on the opposite side.

[0025] According to the invention, the connection arrangement has a wedge-shaped insert whose outwardly facing surface is chamfered inwards towards the profile body in the direction of the joining gap. Such a wedge-shaped insert is advantageous whenever either the leading edge outer layer is guided beneath the main body outer layer, or vice versa, in order to achieve an overlap of the leading edge outer layer with the main body outer layer in the area of ​​the connection arrangement. The connecting elements are then guided through both the leading edge outer layer and the main body outer layer, thus forming a positive fit between these two elements for attaching the leading edge to the main body. The wedge-shaped insert reduces the joining gap that arises from the lowering of one of the outer layers beneath the other.By chamfering the wedge-shaped insert inwards towards the profile body, manufacturing tolerances can be compensated for, allowing the rigid cover film to cover the joint gap without forming ripples or steps, thus ensuring reliable laminar flow. At the joint gap between the wedge-shaped insert and the outer layer of the corresponding body element (main body or leading edge body), a step is therefore created on the outward-facing surface, which is then covered by the rigid cover film.

[0026] According to the invention, it is further provided that the rigid cover film, with an outer edge of the section spanning the joint gap, presses against the outwardly facing surface of the wedge-shaped insert with a bearing force. This ensures that thickness tolerances of the leading edge outer layer or the main body outer layer, as well as manufacturing tolerances in the step height of the wedge-shaped insert, can be compensated for by the interaction of the curvature-induced prestress of the rigid cover film and the inclined bearing surface (outwardly facing surface) of the wedge-shaped insert. The curvature-induced prestress of the rigid cover film ensures that the rigid cover film does not already rest on the edge facing the gap, which would cause the rigid cover film to be pushed upwards at this edge and no longer lie flat at the outer edge (rear edge).

[0027] The present invention makes it possible to promote laminar boundary layer flow despite a connection arrangement where connecting elements must pass through the outer flow surface, while maintaining external access to the connection arrangement. This allows the leading edge to be replaced without requiring access to the interior of the airfoil body or the leading edge itself. This is particularly important for control surface bodies, as these typically lack interior access. Furthermore, the present invention eliminates the need for filler materials, such as those used in the prior art for the joining gap, thus simplifying leading edge replacement. Moreover, the present invention can be easily combined with boundary layer suction at the leading edge, enabling reliable hybrid laminar flow control.

[0028] An aircraft within the meaning of the present invention is, in particular, a self-propelled aircraft or airplane. Such motorized aircraft generate thrust independently through at least one engine arranged on the aircraft, e.g., a motor or turbine with propeller or jet engines. Such an aircraft within the meaning of the present invention can, for example, be a commercial airliner. Commercial airliners generally have a maximum takeoff weight of more than 50 tons and / or a maximum speed of more than 600 km / h.

[0029] The rigid cover film can be glued onto the area of ​​the connection assembly. An adhesive must be selected that possesses sufficient strength, particularly with regard to the potential flight speeds of the vehicle, and that can withstand the significant temperature differences between ground and air operation. Furthermore, the adhesive should be chosen so that the rigid cover film can be detached from the surface in the area of ​​the connection assembly by applying a sufficient force (e.g., shear or peel force).

[0030] According to one embodiment, the rigid cover film in the section spanning the joint gap has a warping-induced prestress in the direction of the aerodynamically exposed surface. This prestress in the direction of the aerodynamically exposed surface presses the rigid cover film onto the surface behind it when spanning the joint gap, thereby creating a smooth transition in the outer flow surface through the rigid cover film in the area of ​​the joint gap.

[0031] According to one embodiment, the rigid cover film is a metal film, in particular a steel, titanium or aluminum film, or a rigid plastic film.

[0032] According to one embodiment, the rigid cover film has a thickness of less than 0.6 mm, preferably no more than 0.25 mm, and particularly preferably between 0.125 mm and 0.1 mm. This ensures that the rigid cover film applied to the outer surface remains within permissible values ​​for a laminar flow surface, thus preventing the formation of steps or edges that could promote a transition to a turbulent boundary layer. Optionally, the outer edges or margins perpendicular to the flow direction may be chamfered.

[0033] According to one embodiment, the outer layer of the main body and the outer layer of the leading edge overlap in the area of ​​the connection arrangement, so that the connecting elements pass through both the outer layer of the main body and the outer layer of the leading edge. Preferably, the outer layer of the main body is positioned beneath the outer layer of the leading edge, with the leading edge layer thus resting on the outer surface of the main body's outer layer with an inwardly facing joining surface. The outer layer of the main body is, in turn, arranged with an inwardly facing joining surface on an element of the main body's supporting structure, resulting in a secure connection.

[0034] The invention is explained in more detail using the attached figures as examples. They show: Figure 1: Schematic representation of a section of an aerodynamic profile body in the area of ​​the connection arrangement; Figure 2: Exploded view of the Figure 1 Figure 3: Detail of the joining gap.

[0035] Figure 1 and 2 Figure 1 shows a section of an aerodynamic profile body 10 in the area of ​​the connection arrangement 40 between the main body 20 and the leading edge body 30. The main body 20 has an internal main body support structure 21, which in the exemplary embodiment of the Figure 1 and 2 The main body 20 is shown only as a front beam. However, the main body 20 typically has further elements that form the main body support structure 21. Furthermore, the main body 20 has an outer main body layer 22 attached to the front beam 21, which in the exemplary embodiment of the Figure 1 and 2the outer shell of the main body 20. The main body outer layer 22 has an outer surface 23, which forms part of the aerodynamically flowable surface of the entire profile body 10.

[0036] Furthermore, the profile body 10 has a leading edge 30 attached to the main body 20, which, similar to the main body 20, has a leading edge support structure 31 and a leading edge outer layer 32. It is in the Figure 1 and 2 It is indicated that the leading-edge support structure 31 is designed as a truss or corrugated sheet, with the outer layer 32 arranged on this support structure 31 of the leading edge 30. Of course, other support structure designs and designs without boundary layer extraction are also conceivable.

[0037] The outer layer 32 of the leading edge 30 can be perforated and / or slotted, allowing the boundary layer flow at the outer surface 33 of the outer layer 32 to be drawn off by a suction device (not shown), thus enabling the continuous formation of a new boundary layer flow. This allows for hybrid laminarization consisting of active boundary layer suction and natural laminar retention. In combination with a truss-like or corrugated leading edge support structure, chambers are formed within the support structure. These chambers are subject to negative pressure and are operatively connected to the perforation of the outer layer, allowing the boundary layer to be drawn off.

[0038] In the area of ​​the connection arrangement 40, the main body outer layer 22 is reduced towards the inside of the profile body 10 and is thus placed below the leading edge outer layer 32, as well as in the exemplary embodiment of the Figure 1 and 2also under the leading edge support structure 31. Because in the area of ​​the connection arrangement 40, the outer layer 32 lies directly against an extension of the support structure 31 of the leading edge 30 and thus forms a common unit.

[0039] A first row of connecting elements 41 is guided through the outer layer 22 of the main body, which extends under the leading edge 30, and through a leg of the front rail 21 of the main body 20 in the area of ​​the connection arrangement 40, and is attached to a counterpart 42 in the form of a thread. The thread 42 is fixed to the leg of the front rail 21, so that the connecting elements 41 can be attached to the counterpart 42 in a form-fit and force-fit manner. This allows the outer shell 22 of the main body 20 to be attached to the designated support structure and the main body 20 from the outside, without requiring access from the inside.

[0040] Furthermore, a second row of connecting elements 43 is provided, which extends through the outer layer 32 of the leading edge 30 and the outer layer 22 of the main body 20, which extends under the leading edge 30, and engages with a counterpart 44 located on the inside of the outer layer 22 of the main body 20. This allows the first row of connecting elements 41 to be securely covered, so that only the heads of the second row of connecting elements 43 remain in the outer surface 33 of the outer layer 32.

[0041] The counterpart 44 can also be a threaded assembly into which the second row of connecting elements 43 can be screwed. The threaded assembly 44 is firmly connected to the main body 20 and thus ensures a secure attachment of the front edge 30 to the main body 20.

[0042] In the area of ​​the connection arrangement 40, a rigid cover film 50, for example in the form of a metal foil, is applied to the outer surface 33. This cover film covers at least the second row of the connecting elements 43 and extends over and covers a joining gap 60 formed in the rear area between the leading edge 30 and the main body 20. The rigid cover film has an outer surface 51 that becomes part of the aerodynamically flowable surface of the profile body 10.

[0043] The main body outer layer 22 is arranged at an angle into the interior of the profile body 10 in the area of ​​the connection arrangement 40 in order to form an overlap area. To keep the joining gap 60 as small as possible, a wedge-shaped insert 70 is provided, which is intended to fill the inwardly extending chamfer 24 of the main body outer layer 22. This allows manufacturing tolerances in the thickness of the leading edge 30 and the main body 20 to be compensated for.

[0044] Figure 3 Figure 1 shows a detailed view of the area with the joining gap 60. It can be seen that the bearing surface 71 of the wedge-shaped insert 70, which represents the outwardly facing surface, is chamfered inwards and slopes downwards towards the front edge 30. This creates a step between the outer front edge layer 32 and the bearing surface 71 at the front edge 72 of the joining gap 60.

[0045] Due to a pre-tension caused by the curvature of the rigid cover film, the rear edge 52 of the rigid cover film 50 is pressed against the recessed bearing surface 71 of the wedge-shaped insert 70 with a contact force, so that a smooth and homogeneous transition is formed. The joint gap is reliably covered, and no waviness or other disturbances remain on the outer surface that could promote a transition to turbulent boundary layer flow.

[0046] In a specific application on the leading edge of an HLFC (Hybrid Laminar Flow Control) horizontal stabilizer, it is shown that a 0.125 mm thick steel strip with a radius of 150 mm, which protrudes 15 mm beyond the trailing edge of the wing leading edge skin, rests on a 30 mm long and 2° inclined sloping support surface even under the most unfavorable conditions with a line load of at least 10 N / m, even if the thickness of the leading edge varies by ± 0.15 mm and the height of the support surface by ± 0.1 mm.

[0047] The contact pressure can be increased by increasing the curvature (reducing the radius), by increasing the thickness of the steel foil, or by shortening the overhang. It should be noted that the ability to compensate for manufacturing tolerances decreases with a shorter foil overhang. The thickness of the steel foil should not exceed 0.25 mm, as the end of the steel foil creates a downward step for the airflow, which can promote a transition to turbulent boundary layer flow. Sufficiently high contact pressure cannot be achieved with excessively thin steel foils. Excessive curvature of the steel foil can result in surface waviness, which can also cause turbulent boundary layer transitions.

[0048] Insufficient contact pressure can cause the steel foil to vibrate and oscillate in the airflow. An unnecessarily high contact pressure, resulting from excessive curvature of the foil and / or excessive stiffness (thickness), can cause the adhesive to peel away.

[0049] Due to the enormous temperature differences between ground and air operation, thermal deformations can occur during cruise flight due to the different materials used. These deformations may need to be compensated for during manufacturing. In this process, the structure is not manufactured in its final contour, but rather pre-deformed in the opposite direction to the expected thermal deformation. As the ambient temperature decreases, the pre-deformation diminishes due to thermal behavior. This is particularly important when the airfoil is made from a composite of metallic and fiber-reinforced materials, as these materials have fundamentally different coefficients of thermal expansion. Reference symbol list

[0050] 10 Profile body 20 Main body 21 Main body support structure 22 Main body outer layer 23 Outer surface of the main body outer layer 24 Bevel of the main body outer layer 30 Leading edge body 31 Leading edge support structure 32 Leading edge outer layer 33 Outer surface of the leading edge outer layer 40 Connection arrangement 41 First row of connecting elements 42 Counterpart of the first row of connecting elements 43 Second row of connecting elements 44 Counterpart of the second row of connecting elements 50 Rigid cover film 51 Outer surface of the rigid cover film 52 Rear edge of the rigid cover film 60 Joining gap 70 Wedge-shaped inserts 71 Bearing surface of the wedge-shaped insert (outer surface) 72 Front edge of the wedge-shaped insert

Claims

1. An aerodynamic profile body (10) for aircraft, having a surface over which air can flow aerodynamically, comprising: - a main body (20) comprising a main body support structure (21) and a main body outer layer (22) disposed on the main body support structure (21) as part of the surface over which air can flow aerodynamically, - at least one leading-edge body (30) having a leading-edge support structure (31) and a leading-edge outer layer (32) applied to the leading-edge support structure (31) as part of the surface over which air can flow aerodynamically, and - a connecting assembly (40), by means of which the at least one leading-edge body (30) is or can be mount to the main body (20) by passing connecting elements from the outside through the surface over which air can flow aerodynamically in the region of the connecting assembly (40) and engaging them with counterparts located inside the profile body (10) for fastening, wherein - in the region of the connecting assembly (40), a rigid cover foil (50) is applied to the surface over which air can flow aerodynamically, - the connecting elements passed through the surface over which air can flow aerodynamically are covered by the rigid cover foil (50), and - the rigid cover foil (50) extends across a joint gap (60) between the portion of the surface over which air can flow aerodynamically of the main body (20) and the portion of the surface over which air can flow aerodynamically of the leading-edge body (30), characterized in - that the connecting assembly (40) has a wedge-shaped insert (70), the outward-facing surface (71) of which is chamfered inward toward the profile body (10) in the direction of the joint gap (60) when the wedge-shaped insert is positioned on the profile body, and - that the rigid cover foil (50) presses against the outward-facing surface (71) of the wedge-shaped insert (70) with a contact force via an outer edge (52) of the section spanning the joint gap (60).

2. Aerodynamic profile body (10) according to claim 1, characterized in that the rigid covering foil (50) has, in the section spanning the joint gap (60), a curvature-induced preload in the direction of the surface over which airflow can flow aerodynamically.

3. Aerodynamic profile body (10) according to claim 1 or 2, characterized in that the rigid covering foil (50) is a metal foil, in particular a steel, titanium, or aluminum foil, or a rigid plastic foil.

4. An aerodynamic profile body (10) according to one of the preceding claims, characterized in that the rigid covering foil (50) has a thickness of less than 0.6 mm, preferably less than 0.25 mm, and most preferably between 0.125 mm and 0.1 mm.

5. An aerodynamic profile body (10) according to one of the preceding claims, characterized in that, in the region of the connecting assembly (40), the main body outer layer (22) and the leading edge outer layer (32) overlap such that the connecting elements pass through both the main body outer layer (22) and the leading edge outer layer (32).