Rotor-controlled coupling unit for aerial refueling

Abstract

Coupling unit (1) for one end of a refueling hose (3) or a cable of a tow plane (5) for coupling another aircraft, comprising a rotor (7) with at least two rotor blades projecting radially from a rotor axis of rotation, which can be set into rotational motion about the rotor axis of rotation by aerodynamic flow, and comprising a first actuator unit coupled to the rotor (7), wherein the first actuator unit is designed to adjust an inclination of a rotor plane formed by an orbit of the blade tips of the rotor blades, such that a deflection of a normal vector of the rotor plane from the direction of the aerodynamic flow causes a force perpendicular to the aerodynamic flow on the coupling unit (1).

Description

[0001] The invention relates to a coupling unit for one end of a refueling hose or a rope of a tow plane for coupling another aircraft, as well as a tow plane with a coupling unit and with a winch and with a control unit.

[0002] For air-to-air refueling of aircraft or for capturing and towing rocket sub-stages, actuated coupling devices (also known as "Actuated Coupling Devices," abbreviated "ACD") can be used at the end of a tow rope or refueling hose. Actuation allows the coupling device to compensate, within certain limits, for positional deviations from a target position, such as that of the aircraft being coupled. This generally reduces the workload for the pilots of the aircraft being coupled, as well as the technical demands placed on the aircraft during formation for refueling, and allows the coupling process to be established more quickly.

[0003] Such docking units are known from the prior art, for example from the publication: Krause, Stefan and Cain, Sebastian and Funke, Alexander and Ferrändiz, Mario and Gonzälez, Joaquin. (2022) “Overview of a planned flight test operation for a scaled in-air capturing demonstration”. European Conference for Aeronautics and Space Sciences (EUCASS 2022), 27 June - 1 July 2022, Lille, France. This publication describes an actuated docking unit. As in the Fig. As shown, this coupling unit can consist of two aerodynamically effective components: First, a cone to generate a certain amount of drag, which stabilizes the coupling unit in the air and tensions a flexible refueling hose or a cable with such a coupling unit at its end; and second, stator surfaces or control surfaces, which comprise airfoil profiles and can be individually controlled so that the coupling unit can be positioned laterally and vertically in the direction of flight and any possible roll movements of the coupling unit are prevented. The control surfaces are always located in a plane that, as far as possible, passes through the center of gravity of the coupling unit in order to avoid deflection moments. A winch in the towing aircraft can be used to winch the refueling hose (or cable) with the coupling unit at its end to achieve positioning of the coupling unit in the direction of flight.

[0004] In addition to the actuators and corresponding avionics for their control, the coupling unit can be equipped with sensors and radio telemetry to detect the positions of the aircraft in the formation and, if necessary, to command them.

[0005] In this context, US 2023 / 0 242 270 A1 relates to a method for compensating for aerodynamic radial loads applied to a drogue coupling of a hose and an active air-to-air refueling system, comprising the steps of: deploying a refueling hose from a tanker aircraft, wherein the drogue coupling is located at a distal end of the hose and the drogue coupling is connected to a hose end control unit comprising at least three fins extending outwards into the air flowing over the hose end control unit; measuring the acceleration of the control unit at the hose end and / or the drogue coupling, thereby generating an acceleration signal with data representing the detected acceleration; determining at least one angle of incidence for at least one of the three fins based on the acceleration signal; and rotating at least one of the three fins by the at least one angle of incidence.

[0006] CN 1 18 419 273 A further relates to a self-sustaining, steerable attitude stabilization funnel for aerial refueling and a control method for it. The conical sleeve consists of a conical head, a control mechanism, a conical column, and a stabilizing parachute. The control mechanism comprises a rotating sleeve, an actuating circuit, a lifting unit, and a motion unit. Energy is generated by the rotation of the rotating sleeve without requiring an additional power supply to meet the energy requirements of the control mechanism for operating the actuating circuit. The lift generated by the lifting wing changes periodically with the periodic change in the angle of attack. These periodic changes in lift are used to actively maneuver the refueling device and to achieve stable control of its relative position.

[0007] US Patent 2010 / 0237196A1 also relates to a refueling funnel that can be connected to a refueling hose extending from a tanker aircraft. The funnel may include an active stabilization system that effectively stabilizes the refueling funnel via control surfaces when the funnel is brought into an airflow.

[0008] US 2013 / 0 168 497 A1 further relates to a refueling device for use in in-flight refueling between a tanker aircraft and a receiving aircraft, comprising a selectively steerable body and a control system. The selectively steerable body is configured to be towed by a tanker aircraft via a fuel hose, at least during in-flight refueling, and includes a boom element with a boom axis configured to transfer fuel from the fuel hose along the boom axis to a receiving aircraft during in-flight refueling.The control system is configured to selectively steer the body into an engagement position that is spaced apart from the receiver aircraft, align the boom axis in an engagement position that enables an engagement position at the spaced position, and then move the boom element along the boom axis towards the receiver aircraft to enable fuel transfer between them.

[0009] CN 1 15 196 026 A further relates to an active control sleeve for a flexible refueling line. This sleeve comprises a conical body, a control device, and a grid fin, with a plurality of control devices evenly distributed on the outer conical surface of the sleeve body. Several grid fins are controlled at their angle of incidence to generate an aerodynamic force in a desired direction, thereby suppressing disturbances and moving the funnel into position.

[0010] These state-of-the-art solutions often present the following disadvantages or challenges: Typically, at least four such stator surfaces are required for positioning the coupling unit. Simultaneously controlling the coupling unit's position and preventing roll movements relative to the towed aircraft necessitates that the required control commands be mixed and distributed across the stator surfaces. Prioritizing roll stabilization is essential, as the tendency for undesired roll movements around the longitudinal axis is quite high. However, the stator surfaces inherently exhibit saturating actuator behavior.

[0011] Arranging rudders in a single plane increases the risk of unwanted moments occurring, the lever arm of which is determined by the distance of the rudder plane to the center of gravity.

[0012] The air resistance generated by the cone is primarily dependent on the aerodynamic airspeed and therefore cannot be adjusted in any other way.

[0013] Providing power to the coupling unit is difficult. Either a battery can be integrated, which, however, results in an undesirable ground loop, or alternatively, a power cable can be integrated into the refueling hose or the tow rope.

[0014] Communication between the winch in the tow plane and the coupling unit is necessary to position the coupling unit in the direction of flight. Relocating the winch from the tow plane to the coupling unit with an additional cable or refueling hose is not advisable due to the required installation space and the associated increase in weight. This communication can be implemented as a data link, which may be susceptible to interference and / or detection, or as a long cable integrated into the refueling hose or tow rope, thus increasing the complexity of these otherwise simple components.

[0015] The object of the invention is to improve such a coupling unit while retaining the basic functions of the coupling unit of coupling another aircraft and the positioning to be carried out for this purpose.

[0016] The invention is defined by the features of the independent claims. Advantageous further developments and embodiments are the subject of the dependent claims.

[0017] A first aspect of the invention relates to a coupling unit for one end of a refueling hose or a cable of a tow plane for coupling another aircraft, comprising a rotor with at least two rotor blades projecting radially from a rotor axis of rotation, which can be set into rotational motion about the rotor axis of rotation by aerodynamic flow, and comprising a first actuator unit coupled to the rotor, wherein the first actuator unit is designed to adjust an inclination of a rotor plane established by an orbit of the blade tips of the rotor blades, such that a deflection of a normal vector of the rotor plane from the direction of the aerodynamic flow generates a force perpendicular to the aerodynamic flow on the coupling unit.

[0018] The rotor with its rotor blades is driven by the oncoming air at the aerodynamic speed of the towed aircraft during flight, similar to the rotor of a stationary wind turbine for generating electrical energy for the regular power grid and similar to a helicopter in autorotation.

[0019] The oncoming air flows through the rotor plane and drives the rotor blades, resulting in a self-stabilizing rotational speed within the rotor. This rotational speed depends on the density and velocity of the oncoming air, as well as the aerodynamic properties of the rotor blades, particularly their angle of attack. As the rotational speed of the rotor blades increases, their aerodynamic drag against their circumferential speed also increases, creating a stabilizing effect and allowing a steady rotational speed to be established in equilibrium.

[0020] A normal vector to the rotor plane is an abstract construct used to describe the geometric relationships at the rotor relative to the oncoming airflow. The normal vector denotes a direction perpendicular to an imaginary plane in which the rotor blade tips rotate. By precisely aligning the rotor plane with the direction of the aerodynamic flow, a force can be generated on the coupling unit that acts perpendicular to the aerodynamic flow. This force is, in particular, a component of the rotor's aerodynamic drag.

[0021] This component is zero when the normal vector perfectly coincides with the direction of the aerodynamic flow. In this case, the aerodynamic drag lies exactly in the direction of the aerodynamic flow. However, if the rotor plane is tilted by the first actuator unit such that the normal vector to the rotor plane forms a non-zero angle with the direction of the aerodynamic flow, then the direction of the aerodynamic drag will also deviate from the direction of the aerodynamic flow by a non-zero angle, and the rotor's aerodynamic drag can be decomposed into a component in the direction of the aerodynamic flow and a component perpendicular to it.

[0022] The direction in which this component of aerodynamic drag is directed in the plane perpendicular to the aerodynamic flow depends on which axis or linear combination of axes of a coordinate system fixed to the coupling unit the rotor plane is tilted.

[0023] The first actuator unit and the second actuator unit (mentioned below) are preferably controlled by a control unit of the coupling unit. The control unit controls the respective actuator unit according to a desired positioning of the coupling unit relative to the towed aircraft.

[0024] This advantageously creates the possibility of using the first actuator unit to generate a force on the coupling unit, adjustable in direction and magnitude, by changing the orientation of the rotor plane at the coupling unit. This force lies in a plane perpendicular to the aerodynamic control of the coupling unit and thus of the towed aircraft, in order to align the coupling unit with the position in this plane relative to the other aircraft to be coupled to the coupling unit. The rotating mass of the rotor also generates a stabilizing spin.

[0025] Furthermore, if, as described above, a cone, such as the conical element described below, is provided at the end of the coupling unit—a common use, for example, in aerial refueling to center the refueling nozzle of the other aircraft—the function of the conical element can be reduced to guiding the coupling component (such as a refueling nozzle) of the other aircraft to be coupled to the coupling unit and protecting it from the rotor. For this purpose, a much lighter and more delicate design can be used than a typical cone from the prior art.

[0026] According to an advantageous embodiment, the coupling unit further comprises a stator which includes at least two aerodynamic working surfaces which are coupled to a second actuator unit, wherein the second actuator unit is designed to adjust an aerodynamic angle of attack of the aerodynamic working surfaces.

[0027] By using a rotor adjustable in its rotor plane in combination with a stator, particularly one in a stator plane essentially parallel to the rotor plane, two control planes arranged one behind the other are created. The second control plane, comprising the stator, serves primarily to compensate for unwanted torques introduced by the rotor. Distributing the control of position and torque across two control planes simplifies the control problem for each plane and increases control authority.

[0028] According to a further advantageous embodiment, the coupling unit further comprises an electric generator which is coupled or can be coupled to the rotor in order to convert a rotary motion of the rotor relative to the rest of the coupling unit into a rotary motion in the electric generator for generating electrical energy.

[0029] By coupling the rotor to a generator, the drive power of the airflow can be used to generate energy. This eliminates the need for a power supply from the towed aircraft or the need to carry potentially large batteries, thus reducing the system weight. The self-sufficient power supply allows the coupling unit to be used completely independently of the towed aircraft.

[0030] According to a further advantageous embodiment, the first actuator unit is connected to a swashplate and is designed to adjust an inclination of the swashplate to the cyclic pitching of the rotor blades in order to adjust the orbit of the radially outer blade tips of the rotor blades by means of a flapping angle profile of the rotor blades.

[0031] The preferred method is to generate the tilt of the rotor plane using a swashplate and cyclic rotor blade pitch control. By changing the orientation of the swashplate using control rods of the coupling unit, the pitch angle of each rotor blade, and thus generally also the aerodynamic angle of attack of each rotor blade, is cyclically adjusted over the rotation. Changing the aerodynamic angle of attack alters the aerodynamic drag in a rotational plane and the aerodynamic lift of each rotor blade, inducing a flapping motion of the respective rotor blade and thus adjusting the rotor plane. Such a control system is well-known in helicopter technology.By using a bearingless and hingeless rotor, the phase delay of the control input can be reduced, and a higher bandwidth can be achieved when transmitting control commands to the physical effects on the rotor. Such bearingless and hingeless rotors are also well-known from helicopter technology.

[0032] According to a further advantageous embodiment, the rotor is mounted in a tiltable manner, wherein the first actuator unit is designed to tilt a mounting of the rotor together with the rotor blades and their rotor axis of rotation.

[0033] According to a further advantageous embodiment, the coupling unit further comprises a conical element for receiving an interface element of the other aircraft, wherein the conical element is connected to the rotor via a joint on a carrier unit, so that the conical element and the carrier unit can be tilted relative to each other.

[0034] Depending on the rotor system used (e.g., a swashplate with non-articulated rotor blades), the linear forces generated for positioning can be accompanied by undesirable rotational moments. Such moments also occur when using an articulated rotor, such as one with a central mechanical flapping joint, if the plane carrying a resulting force does not pass exactly through the center of gravity. These moments can lead to an undesirable change in the orientation of the coupling unit relative to the oncoming airflow. This reduces the effectively usable opening of the cone element, and any sensors used in the coupling unit may no longer be able to detect the other aircraft to be coupled. To remedy this, a device (e.g., a joint) can be provided according to this embodiment, which allows the cone element to be tilted relative to the rotor planes, so that the cone element can still be aligned with the other aircraft to be coupled.The cone element can be passively aligned by the airflow (not actuated) or actively aligned by a further actuation.

[0035] According to another advantageous embodiment, the first actuator unit is designed to perform synchronous collective control of the pitch angles of the rotor blades.

[0036] Collective control of the rotor blade pitch angles means a synchronous adjustment of the pitch angles of the rotor blades and, generally, a change in the aerodynamic pitch angles of the rotor blades, so that they generate more lift and more drag during their rotation. If all pitch angles of the rotor blades are changed synchronously, the rotor speed and the total drag of the coupling unit change.

[0037] Another aspect of the invention relates to a tow plane with a coupling unit as described above and below, with a winch and with a control unit, wherein the tow plane is designed to pull a refueling hose or a rope behind it in flight, each with the coupling unit at its end, wherein the winch is designed to adjust a length output of the refueling hose or the rope to the tow plane upon control of the control unit.

[0038] According to a further advantageous embodiment, the control unit is designed to regulate the tensile tension in the refueling hose or rope to a setpoint value by extending the refueling hose or rope away from the towing aircraft when the tensile tension is too high and retracting it towards the towing aircraft when the tensile tension is too low.

[0039] According to a further advantageous embodiment, the first actuator unit of the coupling unit is configured to perform a collective control of the pitch angles of the rotor blades, wherein the coupling unit has a control unit configured to control the collective pitch angles of the rotor blades in order to indirectly adjust a longitudinal distance of the refueling hose or cable to the tow plane by utilizing the control of the control unit of the tow aircraft.

[0040] Similar to wind turbines, collective pitch control allows the rotational speed and torque of the rotor to be varied. This changes its drag, which in turn allows the pulling force of the coupling unit on the cable / refueling hose to be adjusted. By using a winch in the tow plane, which preferably maintains a constant cable tension, the coupling unit can independently change its position in the direction of flight. Higher drag extends the refueling hose / cable, while lower drag retracts it. This further decouples the coupling unit from the tow plane and, particularly in military applications, eliminates the need for a complex data link between the tow plane and the coupling unit, at least for this purpose.

[0041] Advantages and preferred further developments of the proposed towing aircraft result from an analogous and substantive transfer of the above statements made in connection with the proposed coupling unit.

[0042] Further advantages, features, and details will become apparent from the following description, in which – possibly with reference to the drawing – at least one embodiment is described in detail. Identical, similar, and / or functionally equivalent parts are identified by the same reference numerals.

[0043] They show: Fig. 1: A towed aircraft with a coupling unit according to an embodiment of the invention. Fig. 2: A coupling unit according to an embodiment of the invention. Fig. 3: A coupling unit according to a further embodiment of the invention.

[0044] The representations in the figures are schematic and not to scale.

[0045] Fig. Figure 1 shows a towed aircraft 5, which is about to refuel another aircraft. The tail of the towed aircraft 5 is shown in the left half of the image. A refueling hose 3, at the end of which a docking unit 1 is located, is pulled behind the towed aircraft 5 by a winch 15. The right half of the image schematically shows the front of another aircraft with its refueling nozzle extended, which is about to dock with the docking unit 1 of the towed aircraft 5.

[0046] Fig. Figure 2 shows coupling unit 1, as in the situation of Fig. 1, in cross-section. The refueling hose 3 serves to transfer fuel from the towed aircraft 5 to the other aircraft during flight in order to refuel the other aircraft. For this purpose, the end of the refueling hose 3 passes through a hollow shaft of the coupling unit 1. An electric generator 11 is arranged in the front part of the coupling unit 1 to achieve an even weight distribution in the coupling unit 1. The generator 11 is connected to a rotor 7, which rotates about an imaginary rotor axis of rotation, which essentially passes through the hollow shaft, when the coupling unit 1 is in a situation as shown in Fig. Figure 1 shows the rotor exposed to an aerodynamic flow. This flow drives the rotor 7, which rotates and drives the electric generator 11, which serves as the power supply for the coupling unit 1. Should the required drag exceed the power demand of the coupling unit 1's avionics, the generator 11 can dissipate the excess energy as heat, for example, by heating heat sinks to the airflow. The rotor 7 has individual rotor blades, which are collectively and cyclically adjusted in their aerodynamic angle of attack over a complete revolution using a swashplate. A first actuator unit uses control rods to adjust the position and inclination of the swashplate. By collectively adjusting the angles of attack of the rotor blades, the drag of the entire rotor 7 is readjusted, and the aerodynamic drag of the coupling unit 1 can thus be adjusted as a whole.Furthermore, if a pulling force on the refueling hose 3 is controlled at the winch 15 of the towed aircraft 5, then a separate control unit of the coupling unit 1, which changes the collective blade angle of the rotor blades, can command the extension or retraction of the refueling hose 3 at the towed aircraft 5 without requiring explicit data transmission via an electronic communication protocol. However, this collective adjustment of the rotor blades, particularly in combination with the force control at the winch 15, does not need to be implemented; it is sufficient for a controlled movement of the coupling unit 1 in a plane perpendicular to the aerodynamic flow direction if the rotor plane of the rotor 7 can be tilted.This allows a component of the rotor 7's drag force to be generated that lies perpendicular to the aerodynamic flow direction in this plane by intentionally tilting the force vector of the aerodynamic drag. This force component of the aerodynamic drag causes the coupling unit 1 to move in precisely this plane. The coupling unit 1 is thus able to independently adjust its position within this plane, within certain limits, to allow the docking of the other aircraft to the coupling unit 1. Specifically, the docking takes place at a conical element 13, which, due to its funnel-shaped design, can compensate for certain positional deviations from the refueling port of the other aircraft.However, if, as in the example, an optional electric generator 11 is provided, which is not strictly necessary for the basic operation of the position control of the coupling unit 1 as long as an energy supply to the first actuator unit can be ensured by other means, the torque must be compensated by the generator 11. For this purpose, a stator 9 is provided, which is arranged behind the rotor 7. Here, non-rotating stator blades in the form of fins are provided, functioning as aerodynamic surfaces, the aerodynamic angle of attack of which can be adjusted by a second actuator unit. If these have a non-zero aerodynamic angle of attack, they generate local lift, which, due to the special arrangement of the stator blades, can produce a rolling moment that is directed exactly opposite to the torque of the generator 11, so that, by means of control, it can be achieved that no net rolling moment acts on the coupling unit 1.This ensures a constant roll angle. Near the stator plane, the avionics with the control unit of coupling unit 1, which controls the first and second actuator units, are located for even weight distribution.

[0047] Fig.Figure 3 shows an alternative coupling unit 1 from above. The coupling unit 1 is arranged, as previously described, at the end of a refueling hose 3. The rotor 7 and the stator 9 are also visible. Since the rotor 7 generates moments in addition to the positioning force, which could tilt the coupling unit 1 relative to the aerodynamic flow, the cone element 13 and the rest of the coupling unit 1 are freed from this tilt by a joint and can align themselves freely in the airflow. Thus, the cone element 13 is connected to the front part of the coupling unit 1 via a joint. The cone element 13 is designed so that it can align itself around the joint in the direction of flight due to air resistance. The jointless rotor 7 generates moments and forces through the cyclical tilting of the swashplate, which allow for lateral or vertical positioning of the coupling unit 1.

[0048] Although the invention has been further illustrated and explained in detail by means of preferred embodiments, the invention is not limited by the disclosed examples, and other variations can be derived from them by a person skilled in the art without departing from the scope of protection of the invention. It is therefore clear that a multitude of possible variations exist. It is also clear that the embodiments mentioned as examples are truly only examples and are not to be understood in any way as limiting, for example, the scope of protection, the possible applications, or the configuration of the invention.Rather, the preceding description and the description of the figures enable the person skilled in the art to implement the exemplary embodiments in concrete terms, whereby the person skilled in the art, with knowledge of the disclosed inventive concept, can make various changes, for example with regard to the function or the arrangement of individual elements mentioned in an exemplary embodiment, without leaving the scope of protection defined by the claims and their legal equivalents, such as further explanations in the description. Reference symbol list 1 coupling unit 3 Refueling hose 5 Towed aircraft 7 Rotor 9 Stator 11 Generator 13 Cone element 15 winds

Claims

[1] Coupling unit (1) for one end of a refueling hose (3) or a cable of a tow plane (5) for coupling another aircraft, comprising a rotor (7) with at least two rotor blades extending radially from a rotor axis of rotation, which can be set into rotational motion about the rotor axis of rotation by an aerodynamic flow, and comprising a first actuator unit coupled to the rotor (7), wherein the first actuator unit is designed to adjust an inclination of a rotor plane formed by an orbit of the tips of the rotor blades, such that a deflection of a normal vector of the rotor plane from the direction of the aerodynamic flow causes a force perpendicular to the aerodynamic flow on the coupling unit (1). [2] Coupling unit (1) according to claim 1, further comprising a stator (9) which includes at least two aerodynamic working surfaces which are coupled to a second actuator unit, wherein the second actuator unit is designed to adjust an aerodynamic angle of attack of the aerodynamic working surfaces. [3] Coupling unit (1) according to one of the preceding claims, comprising an electric generator (11) which is coupled or can be coupled to the rotor (7) in order to convert a rotary motion of the rotor (7) relative to the rest of the coupling unit (1) into a rotary motion in the electric generator (11) for generating electrical energy. [4] Coupling unit (1) according to one of claims 1 to 3, wherein the first actuator unit is connected to a swashplate and is designed to adjust an inclination of the swashplate to the cyclic pitch adjustment of the rotor blades in order to adjust the orbit of the rotor blades by means of a flap angle profile of the rotor blades. [5] Coupling unit (1) according to one of claims 1 to 3, wherein the rotor (7) is mounted in a tiltable manner, wherein the first actuator unit is designed to tilt a mounting of the rotor (7) together with the rotor blades and their rotor axis of rotation. [6] Coupling unit (1) according to one of the preceding claims, further comprising a cone element (13) for receiving an interface element of the further aircraft, wherein the cone element (13) is connected to the rotor (7) by a joint on a carrier unit, so that the cone element (13) and the carrier unit can be tilted relative to each other. [7] Coupling unit (1) according to one of the preceding claims, wherein the first actuator unit is configured to perform synchronous collective control of the pitch angles of the rotor blades. [8] Towing aircraft (5) with a coupling unit (1) according to one of the preceding claims and with a winch (15) and with a control unit, wherein the towing aircraft (5) is configured to pull a refueling hose (3) or a rope behind it in flight with the coupling unit (1) at its end, wherein the winch (15) is configured to adjust a length output of the refueling hose (3) or the rope to the towing aircraft (5) upon control of the control unit. [9] Towing aircraft (5) according to claim 8, wherein the control unit is configured to regulate a tensile tension in the refueling hose (3) or in the rope to a setpoint value by extending the refueling hose (3) or the rope away from the towing aircraft (5) when the tensile tension is too high and retracting it towards the towing aircraft (5) when the tensile tension is too low. [10] Towing aircraft (5) according to claim 9, wherein the first actuator unit of the coupling unit (1) is configured to perform a collective control of the pitch angles of the rotor blades, wherein the coupling unit (1) has a control unit configured to control the collective control of the pitch angles of the rotor blades in order to indirectly adjust a longitudinal distance of the refueling hose (3) or the cable to the towing aircraft (5) by utilizing the control of the control unit of the towing aircraft (5).

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