Landing device for VTOL aircraft

Abstract

The invention described here belongs to the technical field of VTOT aircraft. According to the present invention, such an aircraft type requires a retractable main landing gear integrated into the fuselage, which can be closed within the fuselage during flight. Two further devices, serving as support points during landing, are located at the two wingtips. These represent the extendable leading edge of the downward-pointing wingtips, which are extended linearly downwards along a track during landing. The load-bearing component at the leading edge of the wingtip is connected to the wing spar to transfer forces generated by loading to the fuselage. The device also performs an aerodynamically stabilizing function and reduces drag.

Description

[0001] The invention shown relates to a VTOL aircraft.

[0002] International publication WO 2020 / 190 223 A1 describes a VTOL aircraft consisting of a multirotor layout and a tilting fuselage. The VTOL aircraft takes off and lands vertically and rotates its fuselage during flight so that the rotor axes are parallel to the ground.

[0003] In US application No. US 2017 / 0 137 111 A1, an aircraft wing consists of a rigid wing and a wingtip. The wingtip can be folded during ground operations to reduce the wingspan, while it is unfolded during flight.

[0004] The CN 1 17 141 768 A shows an unmanned aerial vehicle with tilting winglets.

[0005] The landing gear enables an aircraft to reach takeoff speed, absorb shocks from uneven ground, and achieve a stable stance.

[0006] The vast majority of landing gears are tricycles, with a main landing gear with at least one wheel centered on the left and right sides of the aircraft, and a tail or nose gear with at least one wheel centered either at the very rear or the very front. This design distributes the load evenly and ensures secure positioning.

[0007] The wheels of the two main landing gears are mounted on a strut, which contains all the necessary components to absorb the rolling and landing shocks, as well as a device for effective damping of the spring movement. These struts can be mounted in a rigid bracket (a so-called monopod landing gear structure) or guided and made movable by several support struts, which are also articulated (a so-called tripod landing gear structure).

[0008] Landing gears can also be divided into retractable and non-retractable. While in the first half of the 20th century, most landing gears were non-retractable, today retractable landing gears, which are retracted for the duration of the flight after takeoff (possibly with a cover) and extended again for landing, are the norm to reduce drag. Aircraft with high cruise speeds exclusively have retractable landing gears.

[0009] However, due to the high complexity of the many moving individual components, these are expensive and heavier. A non-retractable landing gear, on the other hand, is less complicated, cheaper to manufacture and test, and more robust at the same weight.

[0010] This is a major hurdle for vertical-take-off-landing (VTOL) aircraft, especially zero-emission aircraft, which are being developed by many companies thanks to advances in propulsion technologies, as well as energy storage options in the form of batteries and other alternative fuel sources. This is why most companies use non-retractable landing gear, especially since most VTOL aircraft intended for civil use fly at lower maximum speeds (<100 m / s), where the additional drag is a minor problem in this flight regime.

[0011] However, non-retractable landing gear, where the wheels are fixed and their position remains unchanged throughout the flight, is associated with significantly high aerodynamic drag, which negatively impacts top speed and range. This is unacceptable, especially given the still relatively low energy density of alternative energy sources (batteries, hydrogen).

[0012] In addition, a non-retractable landing gear not only increases frontal drag, but also has a negative effect on the aerodynamic stability and thus the controllability of the aircraft.

[0013] The VTOL aircraft shown here is designed for high speeds (high subsonic speeds), which does not allow for the omission of retractable landing gear.

[0014] At the same time, due to the need for the greatest possible usable volume, including for passengers and fuel (and / or rechargeable batteries and hydrogen tanks), it is not possible to accommodate such a landing gear without compromise in the aircraft structure.

[0015] To circumvent this problem, the Boeing 777-300ER, among many other aircraft models, has a retractable main landing gear that stows inside the wings to provide more usable space in the fuselage. A nose gear is mounted at the front, consistent with the tricycle design. However, this design unavoidably requires a more complex wing structure and limited usable space for fuel storage.

[0016] With respect to the invention shown, this problem is circumvented by providing a VTOL aircraft having the features of independent claim 1. Advantageous designs of this VTOL aircraft build thereon in dependent claims 2 to 9.

[0017] The invention shown here is a VTOL aircraft (1) which has a centrally mounted retractable landing gear (3) with a cover (6) on the fuselage (similar to the main landing gear on most gliders). However, this includes a double wheel (4) with a spring mechanism and connecting kinematics (5) which is used for attachment to a structural component of the aircraft. This structural component supports and transfers the load acting on the main landing gear to the fuselage of the aircraft. This landing gear is mounted close to the aircraft's center of gravity, thereby supporting the majority of its weight. This also places it close to the reinforced structure of the fuselage, which absorbs loads at the wing roots and from the engines installed in the fuselage, while at the same time eliminating the need for a separate structural component for the landing gear.This landing gear is intended to enable the main landing gear to be designed with a single double wheel, while still reliably and safely transferring the loads encountered during ground operations to the aircraft fuselage. This results in lower costs and weight for the landing gear. Furthermore, the volume required for fuel storage is saved in the fuselage. Due to, for example, the low energy density per unit volume specific to hydrogen, a larger usable volume is a significant advantage, especially with regard to future viability.

[0018] To ensure a stable stand on the ground, two additional contact points with the ground are required, which are located to the left and right behind the aircraft's center of gravity.

[0019] These represent the wing tips pointing downwards (2a), (2b), which are located behind the center of gravity of the aircraft due to the strong sweep of the wings.

[0020] As a structural component that carries part of the overall weight of the aircraft, the wingtips also have an aerodynamically shaped outer surface that provides minimal frontal drag.

[0021] To provide additional aerodynamic stability, the outer surface of the aircraft has an aerodynamic profile (e.g. a traditional NACA wing profile, or a custom profile tested in advance for this purpose, which generates the desired stabilizing forces).

[0022] Due to the positive wing dihedral and the >90° angle of the wingtips relative to the wings, the wingtips are not vertical relative to the horizontal plane. This results in an arrangement comparable to the V-tail configuration of a conventional aircraft, eliminating the need for an additional tail to generate stabilizing momentum, with the trade-off of increased weight.

[0023] This slightly slanted position away from the aircraft's center of gravity (similar to a chair with legs slightly slanted away from the center of gravity) also provides greater stability on the ground.

[0024] Due to its high-speed design, the wingspan is small, which also reduces the momentum of the force generated by the extended wingtip load acting on the reinforced structure in the fuselage and wings. This force is transferred to the fuselage via the aforementioned reinforced structure in the wing.

[0025] This reinforced structure in the wing runs through its reinforced leading edge (7) and extends to the pressure point, which represents the sum of all forces acting on the wing in a flow field around this point. This structure extends in the same way to the wing tips.

[0026] The reinforced leading edge structure of the winglets is divided into two parts: the reinforced movable nose profile (9) and the reinforced winglet structure along the path of travel (15). The reinforced winglet structure along the path of travel (15) is firmly integrated into the wingtip (13) and has a positive fit rail (11) extending the entire length of the reinforced winglet structure (15). The reinforced movable nose profile (9) has a negative fit, which can move freely in only one dimension. This results in a linear extension and retraction movement.

[0027] In the current invention, the reinforced movable nose profile (9) is moved linearly along the positive rail shape (11) by the rotation of a threaded rod. The mechanical drive is provided by a gear motor, which is located in an extension of the reinforced structure (8) and covered by the cover (14).

[0028] Thus, the threaded rod (10) extending from the gear motor serves, in addition to the reinforced winglet structure along the movement path (15) and the positive rail form (11) located thereon, as an additional device which transfers loads from the reinforced movable nose profile (9) to the reinforced leading edge of the wing (7).

[0029] Instead of a gear motor with a threaded rod, a hydraulic mechanism can also be used.

[0030] The leading edge (9) can be extended downwards by approximately two-thirds of the track length along component (15), thus significantly increasing the aircraft's ground clearance, allowing sufficient space for additional devices, such as flaps, beneath the fuselage. The winglet itself (13) can thus remain much smaller, saving weight.

[0031] When retracted, the reinforced movable nose profile (9) fits seamlessly between the reinforced winglet structure along the movement path (15) and the reinforced extension with the movement mechanism (8), resulting in a closed body that uncompromisingly meets all aerodynamic requirements.

[0032] (2a), (2b) performs the functions of a landing gear and stabilization on the yaw (Z) and roll (Y) axes during horizontal flight. Additionally, the remaining winglet structure (13) performs the function of a winglet to reduce the induced drag caused by lift forces on the wings. A winglet often involves many compromises. However, in this case, the benefits are largely profitable due to the many advantages achieved.

[0033] While (2a) and (2b) only carry a fraction of the total weight of the aircraft, the tip (12) of the reinforced movable nose profile (9) is shaped in such a way that the ground contact is not exerted at a point but along the length of the edge, thus avoiding point loading.

[0034] In order to prevent the occurrence of rough wear marks and deep scratches on the tip (12), which can be caused by landing on rough surfaces, this component is preferably coated or locally made of a harder, more wear-resistant material.

[0035] The main landing gear (3), which is primarily loaded by the aircraft's own weight, extends further downward from the fuselage, ensuring the first contact with the ground during landing. Its long spring travel allows for a gentle descent of the aircraft through a steady reduction of thrust (during a vertical landing), resulting in the subsequent contact of the extended struts (9) of the landing gear (2a), (2b).

[0036] The aircraft always remains in a leveled position. Contact between the props (9) does not occur due to tilting backward, but rather due to the compression of the spring mechanism (5) of the main landing gear (3), whereby the difference (h) between the ground contact point of the main landing gear and the tip of the extended nose profile (2a), (2b) gradually approaches 0.

[0037] The vertical takeoff works the same way in reverse.

[0038] The design of the landing gear shown here, which consists of a rolling main landing gear centrally located close to the center of gravity (G) and two transversely displaced supports, also enables the Vtol aircraft to perform short takeoff and landing.

[0039] Here, the thrust is also directed downwards, so that the portion of the weight resting on the two struts (2a), (2b) at the rear is offset. Due to the short distance between the main landing gear (3) and the aircraft's center of gravity (G), only a low power (thrust) is required. Since the aircraft is equipped with devices that allow control on the lateral axis even when stationary in the air, the aircraft can be kept balanced on the main landing gear and navigated on the ground. Once the aircraft has maintained its balance on the main landing gear through its own propulsion and is taxiing, the reinforced movable nose profiles (9) of (2a) and (2b) can be retracted, minimizing the risk of wingtip contact during takeoff and forming an aerodynamic unit on the winglets (2a), (2b).

[0040] The takeoff / landing is performed as a short takeoff / landing (stole), with the main landing gear thrust being adjusted from a vertical to a tilted position, thus using part of the thrust for forward propulsion. This landing / takeoff option is technically and legally easier to implement, as it eliminates the need for a full transition from vertical to horizontal flight during flight.

[0041] Because the aircraft, as a VTOL-capable aircraft, is capable of manipulating airflows using various devices that enable control on all axes even when stationary, it can balance itself on the single support point formed by the dual wheel (4) during taxiing. Furthermore, the need to steer with this is eliminated, as there is only one point of contact with the ground (two points very close to each other due to the dual wheel). This allows the main landing gear to be further simplified, saving cost, weight, and space.

[0042] Preferred embodiments of the invention are illustrated and explained in more detail below with the aid of reference drawings. The drawings depict the following: Fig. 1 an isometric representation of the reference aircraft, according to the current invention Fig. 2 a front view of the reference aircraft Fig. 3 a top view of the reference aircraft Fig. 4 a side view of the reference aircraft Fig. 5 an enlarged view of the support device of the left wing in the extended state

[0043] Fig. Figure 1 shows a VTOL aircraft (1) in an isometric perspective. It can also be seen that the extended landing gear consists of a retractable main landing gear (3) that is covered during flight. This has a double wheel (4) that transfers the load during ground contact to the reinforced structure in the fuselage. A more detailed representation of the main landing gear (3) is shown. Fig. 2 and Fig. 3. In Fig. 1 also shows the landing gear (2a), (2b) with the extended nose profile (9), which, together with (13), form a winglet. This winglet is directly connected to the wing, with loads being transferred via the reinforced extension (8) to the reinforced structure of the wing nose (7) via the shortest possible path. This distribution of the supporting points also achieves a wide footprint, which, thanks in part to the outwardly angled orientation of the reinforced, movable nose profiles (9), allows landing on an inclined plane.

[0044] In the side view of Fig. 4. The distribution of the reference components along the length of the aircraft (1) is shown. It can be seen that the main landing gear (3) is attached to the reinforced structure of the fuselage immediately in front of the aircraft's center of gravity (G), thus carrying the most load. Likewise, it can be seen that (2a) and consequently (2b) have a much greater distance between themselves and the center of gravity (G), which means they carry a much smaller proportion of the total weight. The center of pressure on the winglets (P) is also far from (G), resulting in a stabilizing momentum during forward flight.

[0045] While the stability of a tricycle setup can be utilized, this design of the ground contact points offers another crucial advantage, which is even more advantageous for a Vtol of this type. Since a nose gear is virtually eliminated, an engine can be installed in the fuselage instead, providing part of the thrust during vertical flight. This engine would otherwise have to be installed closer to the aircraft's center of gravity, which would require it to carry more weight and thus be more powerful (heavier). This would be a compromise, with the disadvantages of higher costs and increased weight.

[0046] Fig. Figure 5 shows a detailed view of the left wingtip with its winglet (2a) in the extended state. All statements made regarding (2a) also apply to (2b) in the same way.

[0047] The movable reinforced nose profile (9) of the winglet perfectly complements the reinforced rigid extension (8), as well as the reinforced winglet structure along the movement path (15) and the positive rail shape (11), achieving a seamless transition to the rest of the winglet structure (13).

[0048] The rail form is positioned centrally on the flat surface of (15). This allows the rail to run as far along (15) as possible without extending outside the streamlined shape of the landing gear (2a), whereby the rail can also be kept as dimensionally large as possible (width, height). This is desirable in order to keep the tolerances as small as possible so that no play occurs between these components (9), (11) and (15). Since, when fully extended, only a fraction of the total length of the positive rail form (11) is in contact with the reinforced movable nose profile (9), it is desirable for it to be dimensionally as large as possible so that it is able to easily transfer loads occurring from the reinforced movable nose profile (9) to the reinforced winglet structure along the movement path (15) and subsequently to the reinforced nose structure of the wing (7).

[0049] The cross-section of the rail is shaped like an isosceles trapezoid, with its short lower side connected to the surface of the reinforced winglet structure along the path of travel (15). The parallel, opposite side is longer and forms the upper side of the rail, which is visible when the reinforced movable nose profile (9) is extended. This limits its freedom of movement in only one dimension.

[0050] The limits of this dimension are physically formed at the top by the reinforced rigid extension (8) in which the actuating mechanism is installed. There is no physical limit downwards. A limit is created by the actuating mechanism. In the case of the invention shown here, this is a gear motor with a threaded rod (10), whose speed, in the resulting downward direction of movement, determines the final extension distance. This must be studied in advance and programmed in such a way that the desired extension distance is achieved without exceeding a limit at which the contact area of ​​the reinforced extendable nose profile (9) with the threaded rod (10), the positive rail form (11) and the reinforced winglet structure along the movement path (15) is not too small.

[0051] Since the reinforced nose profile (9) does not contain expensive electronic components or other mechanically complex structures, it is a cost-effective part to manufacture. Furthermore, the actuating mechanism allows it to be easily detached from the overall device (2a) when needed. Replacing it is therefore very practical and convenient.

[0052] Another advantage is the shape of the remaining winglet structure (13), whose lower edge slopes upwards toward the rear, away from the ground. This minimizes the risk of this component being damaged by rough ground irregularities during landing.

[0053] The convergent shape of the remaining winglet (13) also serves to reduce the pressure drag of the landing gear (2a), (2b). Furthermore, these are intended to reduce the formation of air vortices caused by downward flow at the wing tips, thus increasing efficiency during forward flight.

[0054] In a further developed version of the Vtol aircraft adapted for supersonic flight, which embodies the invention discussed here, devices (2a) and (2b) additionally offer the potential to utilize the shape of the wave lift for the aircraft.

[0055] The following basic advantages can be noted with regard to the present invention with focus on the main landing gear (3): 1. By having only one main landing gear mounted transversely and centrally to the fuselage, stronger and fewer individual components are required. This results in lower costs and weight per unit of load carried. 2. Less usable volume is lost in the fuselage due to the retracted landing gear. This can be used for energy storage, which (e.g., in a purely electric design) can dissipate the power needed during takeoff and / or extend the effective range of the aircraft.

[0056] In the context of the hybrid VTOL aircraft shown here, the ability to install an engine for vertical flight further from the center of gravity thanks to the absence of a nose gear is an important advantage, contributing to weight and cost reduction. Weight reduction is particularly essential in the VTOL category, which is achieved by the entire landing gear (2a), (2b), (3).

[0057] In the same way, the following advantages of the invention (2a), (2b) can be noted: 1. By creating a wide base in relation to the low center of gravity, the aircraft achieves high stability. 2. The mechanism which allows the reinforced nose edge (9) to extend and retract is very simple and cheaper in terms of manufacturing and maintenance costs than a conventional retractable landing gear. 3. When retracted, an aerodynamic shape is still achieved, similar to what is otherwise the case with complex retractable landing gear with a cover. 4. (2a) and (2b) additionally provide passive aerodynamic stabilization of the aircraft on the yaw and roll axes, thus eliminating the need for further separate devices of this type, which also results in lower weight and costs. 5. By positioning these devices (2a) and (2b) at the wingtips of an aircraft, an additional reduction of the induced drag during horizontal flight is achieved.

[0058] The reduction in the overall weight of an aircraft is achieved without significant compromises in structure and handling. Rather, this is due to the combination of a landing gear with an aerodynamic stabilizing surface and winglet, which contribute to the advantages of the VTOL aircraft (1). Solutions in the aviation industry that aim to minimize the weight of an aircraft are of particular importance, as this is a key indicator of competitiveness in this market. This is especially true for vertical take-off aircraft, which have a highly restrictive take-off weight. This rapidly growing industry will therefore benefit the most from solutions of this kind in the future. List of reference symbols 1 VTOL aircraft 2a, 2b Winglets as landing gear supplementing the main landing gear 3 Main landing gear 4 double wheels 5 simplified representation of the spring mechanism 6 Main landing gear cover 7 reinforced wing nose structure 8 reinforced rigid extension in which the actuating mechanism is installed (here a gear motor) 9 Support as a reinforced nose profile with negative rail shape, which can move linearly up and down 10 Adjustment mechanism, which is driven by the movement mechanism and moves the reinforced nose profile 11 positive rail shape 12 hardened tip of the extendable reinforced nose profile 13 remaining winglet 14 Gear motor cover 15 reinforced structure of the winglet along the movement path of the nose profile G Center of gravity of the aircraft P Pressure point of the winglet d Distance between the aircraft's center of gravity and the center of pressure of its winglets

Claims

[1] Vtol aircraft (1), characterized by at least one retractable landing gear (2a), (2b), wherein said landing gear (2a), (2b) each comprises an extendable reinforced nose profile (9) which can be extended / retracted linearly along a rail (11), and wherein the landing gear (2a), (2b) each forms a downward-facing winglet (9, 13, 15) at the wingtips of the aircraft, wherein said rail (11), a reinforced structure of the winglet along the movement path (15), and a reinforced rigid extension (8) in which the movement mechanism is installed serve as structural components and transfer the loads exerted on the reinforced movable nose profile (9) to the reinforced structure of the wing nose (7), which is connected to a fuselage. [2] Vtol aircraft (1) according to claim 1 characterized bythat the landing device (2a), (2b) can be divided into two areas; a structurally reinforced, load-bearing area and a shape-complementing area which does not bear any loads. [3] Vtol aircraft (1) according to claim 2 characterized by in that the load-bearing region comprises a reinforced movable nose profile (9) whose movement path runs linearly over the positive rail shape (11), along the reinforced structure of the winglet (15) and is controlled by means of a movement mechanism located in the reinforced rigid extension (8). [4] Vtol aircraft (1) according to all previous claims 1 to 3 characterized bythat loads occurring on the reinforced movable nose profile (9) are transmitted via the reinforced structure of the winglet (15), the positive rail shape (11), and the adjustment mechanism (10) to the reinforced rigid extension in which the actuating mechanism is located and / or to the reinforced structure of the wing nose. [5] Vtol aircraft (1) according to claim 1 characterized by that the loading device (2a), (2b) has an aerodynamically shaped outer surface. [6] Vtol aircraft (1) according to claim 1 characterized by that the landing gear (2a), (2b) assumes a stabilizing force on the yaw and / or roll axis by selecting a suitable aerodynamic profile, which achieves a reduction in the yaw and / or roll instability of the aircraft due to the pressure point of the winglet (P) being located behind the center of gravity of the aircraft (G). [7] Vtol aircraft (1) according to claims 1 and 5 characterized bythat landing device (2a), (2b) on the respective wing acts as a winglet (9, 13, 15), which reduces the drag induced by lift force. [8] Vtol aircraft (1) according to claims 5 to 7 characterized by that the landing device (2a), (2b) in the retracted state of the reinforced movable nose profile (9) forms a seamless transition to the reinforced rigid extension (8) and to the reinforced structure of the winglet (15), whereby an aerodynamic shape is achieved without a cover. [9] Vtol aircraft (1) according to claim 4 characterized by that the actuating mechanism is located in the reinforced rigid extension (8), whereby the reinforced movable nose profile (9) can be replaced with little effort in the event of damage or wear.

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