Active hook for in-air operations

Abstract

Disclosed herein are components, systems, and methods for providing stability to an in-air drogue in free flight and in capture, and improving high bandwidth placement of the drogue relative to a probe on a trailing aircraft to improve the ability to connect the two devices. An example system aspect includes a lead aircraft, a tether attached to the lead aircraft, an active hook attached to the tether, and a trailing aircraft configured to connect to the active hook. The active hook can be configured with control mechanisms, one or more control paddles, onboard batteries, and an external support structure, useful for achieving connection with the trailing aircraft.

Description

ACTIVE HOOK FOR IN-AIR OPERATIONSBACKGROUNDTechnical Field

[0001] Aspects of the present disclosure relate to components, systems, and methods for providing stability to an in-air drogue in free flight and in capture, and improving high bandwidth placement of the drogue relative to a probe on a trailing aircraft to improve the ability to connect the two devices.Background

[0002] In-air drogues can be used in a variety of in-air operations, such as air-to-air refueling, air-to-air charging, or air-to-air towing. However, typical in-air drogues can be unstable and can be limited in their ability to navigate for proper placement on a probe of a trailing aircraft.SUMMARY

[0003] In aspects presented herein, components, systems, and methods can provide stability to an in-air drogue in free flight and in capture, and can improve high bandwidth placement of the drogue relative to a probe on a trailing aircraft to improve the ability to connect the two devices.

[0004] In an aspect, an example system for aircraft towing using an active hook is described. The example system includes a lead aircraft, a tether attached to the lead aircraft, an active hook attached to the tether, and a trailing aircraft configured to connect to the active hook using a probe. The active hook can be configured with control mechanisms, one or more control paddles, onboard batteries, and an external support structure, useful for achieving connection with the trailing aircraft.

[0005] Further features and advantages, as well as the structure and operation of various aspects, are described in detail below with reference to the accompanying drawings. It is noted that the specific aspects described herein are not intended to be limiting. Such aspects are presented herein for illustrative purposes only. Additional aspects will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate aspects of the present disclosure and, together with the description, further serve to explain the principles of the disclosure and to enable a person skilled in the pertinent art to make and use the disclosure.

[0007] FIG. 1 is a schematic of towing an aircraft using an active hook, according to some aspects of the present disclosure.

[0008] FIG. 2 is a schematic of a sequential towing process using an active hook, according to some aspects of the present disclosure.

[0009] FIG. 3 is a side view illustrating proper alignment of an active hook on an aircraft probe, according to some aspects of the present disclosure.

[0010] FIGs. 4A-4B are a front and side view of control paddles on an active hook, according to some aspects of the present disclosure.

[0011] FIGs. 5A-5B are side views of flat-back airfoils on an active hook’s control paddles, according to some aspects of the present disclosure.

[0012] FIGs. 6A-6B are an assembly and perspective view of an external support structure for an active hook, according to some aspects of the present disclosure.

[0013] FIG. 7 is a detail view of a gurney flap on an active hook, according to some aspects of the present disclosure.

[0014] FIG. 8 is a side view of an active hook having a sting with a spring-break, according to some aspects of the present disclosure.

[0015] FIG. 9 is a side view of charging batteries using an active hook, according to some aspects of the present disclosure.

[0016] FIG. 10 is a flowchart of a method for capturing an aircraft probe using an active hook, according to some aspects of the present disclosure.

[0017] FIG. 11 is a block diagram of an example computer system useful for implementing various aspects.

[0018] In the drawings, like reference numbers generally indicate identical or similar elements. Additionally, generally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears.

[0019] Aspects of the present disclosure will be described with reference to the accompanying drawings.DETAILED DESCRIPTION

[0020] Provided herein are apparatus, device, system, method and / or computer-readable medium aspects, and / or combinations and sub-combinations thereof for providing stability to an in-air drogue in free flight and in capture, and improving high bandwidth placement of the drogue relative to a probe on a trailing aircraft to improve the ability to connect the two devices.

[0021] FIG. 1 is an exemplary schematic 100 of towing an aircraft 102 using an active hook 103, according to some aspects of the present disclosure. FIG. 1 includes a lead aircraft 101, trailing aircraft 102, active hook 103, a tether 104, and a wake 105.

[0022] Lead aircraft 101 can be powered by battery electric propulsion. In others aspects, lead aircraft 101 can be powered by some other means of propulsion with some other means of energy storage. For example, lead aircraft 101 can include a turboprop engine. Lead aircraft 101 can be configured to provide towing or energy transfer (e.g., charging, fuel transfer, etc.) for other aircraft, such as trailing aircraft 102, via tether 104 and active hook 103. One end of tether 104 can be fastened to lead aircraft 101 and the other end of tether 104 can be fastened to active hook 103. Lead aircraft 101 can include a winch to deploy or reel in active hook 103, attached via tether 104. In some aspects, lead aircraft 101 can include a squirting device on its tail to provide de-icing fluid to tether 104, active hook 103, and trailing aircraft 102.

[0023] Trailing aircraft 102 can connect to one or more lead aircraft 101 over the course of its flight. Trailing aircraft 102 can connect to one or more lead aircraft 101, sequentially. Trailing aircraft 102 can connect to one or more lead aircraft 101, via active hook 103, using a probe on its nose. Trailing aircraft 102 can be a glider or can be configured to fly under a power source. Trailing aircraft 102 can be configured to be towed or to gain energy (e.g., by charging, fuel transfer, etc.) by one or more lead aircraft 101, via active hook 103. For example, trailing aircraft 102 can be an electric vertical take-off and landing (eVTOL) aircraft configured to be towed by lead aircraft 101. Trailing aircraft 102 can include a squirting device in its nose, to port fluid through active hook 103 such that it is delivered near the upwind extent of active hook 103.

[0024] Trailing aircraft 102 can include a differential GPS system, such as a real time- kinematic GPS, with a moving base station, to track active hook 103. Trailing aircraft 102 can also track active hook 103 using one or more onboard cameras, one or more widebandrelative position sensors, or one or more time-of-flight sensors. Trailing aircraft 102 can track active hook 103 using a combination of tracking data. For example, trailing aircraft 102 can track active hook 103 using a combination of differential GPS and imagery. An inertial-guided model can be constructed using information from any position sensors to back-calculate position information to provide for accurate tracking.

[0025] Active hook 103 can be configured to perform the control required to place active hook 103, and thus tether 104, on the nose of trailing aircraft 102. Active hook 103 can include a plurality of control mechanisms, such as a position tracker, a turn coordinator, actuators, controllers, sensors, and / or an actuator allocator. The actuator allocator can be considered a control in which available actuator authority (i.e., deflection) is allocated between non-parallel axes of control according to their relative priority in the control loop. In other words, the actuator allocator can compute, with a fixed number of control surfaces, a maximum force and moment available on any axis of active hook 103. Using this information, a choice can be made, with an optimization routine or calculation, for an ideal output of actuator commands that appropriately manages forces and moments on active hook 103. In this way, the actuator allocator can assemble a hierarchy of needs of output of a controller. In aspects using this actuator allocator, the feasible control envelope can improve significantly. In some aspects, the actuator allocator can prioritize roll above all other axes. In some aspects, the actuator allocator can prioritize vertical and horizontal displacement over non-roll axes of control.

[0026] Active hook 103’s control mechanisms can provide for one or more flying modes. For example, the flying modes can include a stable flying configuration. The flying modes can also include a capture configuration, where active hook 103 flies in the middle of a capturing window, such that trailing aircraft 102 can approach from a side where visibility is good. It may be desirable for trailing aircraft 102 to approach active hook 103 from an angle that is not directly behind active hook 103 to allow for better information to be gathered, either by an autopilot or a human pilot, on the relative location and closing speed between active hook 103 and trailing aircraft 102. Approaching from this angle can also allow for better system safety, such that excessive closing speeds of aircraft do not lead to an inadvertent contact.

[0027] Once formation has been established between active hook 103 and trailing aircraft 102 in capture configuration, trailing aircraft 102 can activate its tracking control, such asdescribed above. The flying modes can also include a final closure configuration. Activation of tracking control can trigger final closure configuration. In final closure configuration, active hook 103 can actuate to locate itself along an axis predominantly along the direction of airflow, in front of trailing aircraft 102. In this configuration, trailing aircraft 102 can validate accurate tracking performance of active hook 103, and can better ascertain the remaining amount of closing distance. To provide for safe operation, active hook 103 can switch back to stable flying configuration if trailing aircraft 102 overflies active hook 103. In some aspects of such overflight scenarios, a winch of lead aircraft 101 can be configured to retract tether 104.

[0028] When tracking (e.g., positional feedback) is activated in active hook 103 and / or in trailing aircraft 102, some or all attitude gains (e.g., pitch, roll, yaw) can be set for higher bandwidth control. Tracking can also be enabled to detach active hook 103 from trailing aircraft 102, to reduce risk of mechanical interaction upon release. When tracking is disabled in active hook 103 and / or in trailing aircraft 102, it can be necessary to provide gains that result in stable flight at a full range of tether lengths and airspeeds.

[0029] Active hook 103’s turn coordinator can be used to roll active hook 103 during steering turns. For example, in aerial refueling operations and in typical air traffic management, aircraft can be requested to turn by Air Traffic Control. In such cases, aircraft roll to create the requested angular rate. The turn coordinator can be used to better achieve proper alignment between active hook 103 and trailing aircraft 102. In such aspects, a sustained angular rate about the yaw axis feeds into a commanded roll angle, where active hook 103 rolls to approximately match the average roll angle of trailing aircraft 102 through the turn. Such a turn coordinator may be active only when tracking has been activated.

[0030] Active hook 103’s control mechanisms can also be configured with a control law that delivers a closed loop performance that mimics the behavior of trailing aircraft 102 when flying through a gust or other disturbance. For example, active hook 103’s control mechanisms can deliver a vertical acceleration at a delayed time and with a feedback- controlled extent after passing through a sharp-edged gust, in accordance with performance by trailing aircraft 102.

[0031] Active hook 103 can also include one or more onboard batteries. The one or more onboard batteries can power the sensing, computation, and actuation of active hook 103. In some aspects, the one or more onboard batteries can be recharged when active hook 103 isretracted into lead aircraft 101. In other aspects, the one or more onboard batteries can be recharged when active hook 103 is captured on a probe of trailing aircraft 102 and when power is not conveyed to active hook 103 over tether 104. Active hook 103 can also be configured to charge batteries on trailing aircraft 102.

[0032] Active hook 103 can include discrete control surfaces for creation of aerodynamic forces to place it in front of trailing aircraft 102. Active hook 103’s control surfaces can include lifting surfaces configured to actively fly active hook 103 above wake 105 of lead aircraft 101, and at an altitude at which shed ice or material from tether 104 or lead aircraft 101 would pass below active hook 103. Active hook 103’s control surfaces can be manipulated by the control mechanisms. An example aspect of active hook 103’s control surfaces are further described with reference to FIGs. 4-7.

[0033] Active hook 103 can include indicator lights on its aft surface to indicate the location of active hook 103 relative to the center or edges of the active window. In other aspects, the relative location of active hook 103 can be communicated, through a radio telemetry link or another means, to trailing aircraft 102 for display to the pilot. In some aspects, communication of the relative location of active hook 103 to trailing aircraft 102 can be used for the control law of trailing aircraft 102. An aircraft, such as lead aircraft 101, can be configured to carry more than one active hook 103, so that redundancy exists if a primary active hook 103 is not operational.

[0034] Active hook 103 can be configured to provide for a sequential capture. In the sequential capture, active hook 103 first captures trailing aircraft 102 at any rotation angle. Then, when tension is applied to the connection, the rotation between active hook 103 and trailing aircraft 102 can be aligned.

[0035] Active hook 103 can be configured to connect trailing aircraft 102 and tether 104 using a latch. The latch can include a reusable tension release mechanism, such as a balldetent pin. The ball-detent pin can release active hook 103 at a tension that is lower than the breaking strength of tether 104 or any other components located on tether 104 or lead aircraft 101. The latch can also include a low- force spring that recesses the latching mechanism when active hook 103 is moved onto a probe of trailing aircraft 102, but leaves the latching mechanism in place when active hook 103 is moved off of the probe. Accordingly, only small forces relative to the aerodynamic drag of active hook 103 are experienced by active hook 103 in the process of latching.

[0036] Tether 104 can be a rope, hose, mechanical tether, or electromechanical tether. In other aspects, tether 104 can be rubberized. In icy conditions, ice may accumulate on tether 104. Although, in some aspects, a rubberized tether 104 or a tether 104 coated with a low- adhesion and / or low absorption coating, such as a plastic coating, can reduce the ability of ice to adhere to tether 104 and the size of shed ice when flying in icy conditions. Such aspects can also result in reduction of the mass of water or ice that may be absorbed into tether 104. Tether 104 can also be configured to be non-conductive. Tether 104 can include a resettable tension release latch, such that active hook 103 can disconnect from probe 302 before tether 104 or any other components malfunction or fail.

[0037] Wake 105 is an illustration of one possible direction of the wake of lead aircraft 101. In some aspects, tether 104 can be long enough to allow for active hook 103 to be flown over wake 105 of lead aircraft 101. In other aspects, active hook 103 can be flown below wake 105 of trailing aircraft 102.

[0038] FIG. 2 is an exemplary schematic 200 of a sequential towing process using active hook 103, according to some aspects of the present disclosure. FIG. 2 can include one or more lead aircraft 101 (e.g., 101-a, 101-b, etc.), trailing aircraft 102, one or more active hooks 103 (e.g., 103-a, 103-b, etc.), and one or more tethers 104 (e.g., 104-a, 104-b, etc.).

[0039] In some aspects, lead aircraft 101-a can be connected to tether 104-a. Tether 104-a can be connected to active hook 103-a. Trailing aircraft 102 can connect to lead aircraft 101-a for the first tow via active hook 103-a. This first aircraft towing system can enable a first tow of trailing aircraft 102. Trailing aircraft 102 can disconnect from active hook 103- a and can continue flying. Then, at some point in time in a continued aspect, a second lead aircraft, 101-b, can enable a second tow of trailing aircraft 102. Lead aircraft 101-b can be connected to tether 104-b. Tether 104-b can be connected to active hook 103-b. Trailing aircraft 102 can connect to second lead aircraft 101-b for the second tow via active hook 103-b.

[0040] In some aspects, lead aircraft 101-b can be the same as lead aircraft 101-a. For example, trailing aircraft 102 can connect to lead aircraft 101-a, via active hook 103-a, for a first tow. Trailing aircraft 102 can disconnect from active hook 103-a and can perform a task, such as landing and then taking off again. Trailing aircraft 102 can then reconnect to lead aircraft 101-a, via active hook 103-a, for a second tow. This aspect is particularly useful when trailing aircraft 102 is an eVTOL aircraft being towed and / or charged by leadaircraft 101-a, and when trailing aircraft 102 does not recharge upon a landing between first and second tows.

[0041] FIG. 3 is an exemplary side view 300 illustrating proper alignment of active hook 103 on an aircraft probe 304, according to some aspects of the present disclosure. Exemplary view 300 depicts a configuration of active hook 103, where the aerodynamic center and center of mass are in a position allowing for ideal placement of active hook 103 on probe 304 of trailing aircraft 102. FIG. 3 includes tether 104, drogue 302, probe 304, center of mass 306, a first location 308, a second location 310, a third location 312, and a fourth location 314.

[0042] Active hook 103 can be configured in a cone shape, including drogue 302, for use with in-air connection. As shown in FIG. 3, drogue 302 can be used for connection between tether 104 and probe 304. Probe 304 can be installed on the nose of an aircraft, such as trailing aircraft 102, and can be used for connection to tether 104. In such aspects, the location of the aerodynamic center, center of mass 306, and center of pressure of drogue 302 are critical. In aspects where center of mass 306 extends too far forward, contact between drogue 302 and probe 304 can occur at third location 312. Third location 312 can be considered a lateral and rearward location on drogue 302. Contact at or near third location 312 can result in an unstable rotation around the aerodynamic center for horizontal motion, towards first location 308, or the aerodynamic center for vertical motion, towards second location 310. It is also important for drogue 302 to be configured such that few appendages extend behind an aft surface, near the fourth location 314. Fourth location 314 can represent a surface of an aft ring of drogue 302.

[0043] It is possible to configure drogue 302 such that center of mass 306 moves in an aft direction. But because active hook 103 must fly when not in a captured configuration (e.g., connected to probe 304), aft motion can eventually lead to instability of active hook 103 in flight, resulting in oscillatory or divergent behavior at some or all relevant airspeeds.

[0044] FIGs. 4A-4B are an exemplary front view 400 and side view 420 of control paddles on active hook 103, according to some aspects of the present disclosure. FIGs. 4A-4B can be understood with reference to FIG. 3. One or more control paddles can be attached to drogue 302 of active hook 103 to provide direct force control of active hook 103. The one or more paddles can be placed around drogue 302, relative to the center of mass 306 and fourth location 314. The one or more control paddles can be placed on drogue 302 suchthat at least one control paddle is placed in front of center of mass 306 and at least one control paddle is placed behind center of mass 306. The one or more control paddles can be supported by dual bearings or bearings capable of carrying significant side load. The one or more control paddles can be actuated to control an attitude state of active hook 103, such as pitch.

[0045] In turbulent flight conditions, or when making a rendezvous under non-ideal conditions, active hook 103 can begin in a position other than directly in front of trailing aircraft 102’s probe 304. In such aspects, fast lateral translation is ideal. For this reason, active hook 103 can be configured with the ability to provide direct lateral translation using two or more front paddles 402 and two or more aft paddles 404. For example, active hook 103 can include four control surfaces (i.e., front paddles 402 and aft paddles 404) that, with two deflected upwards (i.e., front paddles 402) and two deflected downwards (i.e., aft paddles 404), generate a lateral force.

[0046] In some aspects, it is advantageous to make the vertical lift control authority much greater than the lateral control authority, such as with the X configuration shown in FIG. 4A. Front paddles 402 can be secured to drogue 302 of active hook 103 in a forward and upper position. The forward position can be near first location 308 of FIG. 3, forward of the center of mass 306. Front paddles 402 can be secured around the longitudinal axis of active hook 103. For example, one front paddle 402 can be positioned 60 degrees from a vertical axis, and another front paddle 402 can be positioned -60 degrees from the vertical axis. Aft paddles 404 can be secured to drogue 302 of active hook 103 in an aft and lower position, such as near fourth location 314. Aft paddles 404 can also be located near any other position aft of center of mass 306. Aft paddles 404 can be secured around the longitudinal axis of active hook 103. For example, one aft paddle 404 can be positioned 120 degrees from a vertical axis, and another aft paddle 404 can be positioned -120 degrees from the vertical axis. Because of the aft ring, such as that at fourth location 314, on active hook 103, induced effects of flow can counter the majority of impact that is created by any of the one or more control paddles operating parallel to drogue 302, in any location close to fourth location 314 in FIG. 3. For this reason, a preferable layout places the one or more control paddles orthogonal to the aft cone. Front paddles 402 and aft paddles 404 can be positioned equidistant from center of mass 306, along a longitudinal axis of drogue 302.

[0047] In some aspects, the one or more control paddles can be replaced with grid fins; particularly, in configurations involving larger scales and / or airspeeds. At small scales with moderate speeds, the Reynolds number on the one or more control paddles may only be 200,000, such that the lower Reynolds flow over a grid fin would result in an unacceptably low lift range.

[0048] In some aspects, the one or more control paddles can be arranged such that pitch control of active hook 103 is feasible.

[0049] In some aspects, the one or more control paddles can be arranged to provide perpendicular lift capability relative to the normal of a toroidal wing at the aft of active hook 103. For example, the one or more control paddles can be configured in a cross configuration or a + configuration, as opposed to a box configuration.

[0050] In some aspects, the one or more control paddles can have less than six percent camber, or can otherwise provide both significant positive and negative control authority.

[0051] In some aspects, the one or more control paddles can include one or more redundant control surfaces. For example, there can be more control paddles than required for the minimum number of axes that need control, such that in the case of a failure the excess control paddles can control active hook 103.

[0052] FIGs. 5A-5B are exemplary side views 500 and 520 of flat-back airfoils on active hook 103’s one or more control paddles, according to some aspects of the present disclosure. FIGs. 5A-5B can be understood with reference to FIGs. 4A-4B. It is critical for the one or more control paddles of FIGs. 4A-4B to generate a reasonably linear response. For this reason, the one or more control paddles can be configured in a low aspect ratio, having flat trailing edges. Accordingly, in some aspects, the one or more control paddles can be configured as 502, shown in FIG. 5A. In other aspects, the one or more control paddles can be configured as 504, shown in FIG. 5B. Typically, such flat-back airfoils can be both harder to damage and generate a much larger coefficient-of-lift to angle-of-attack ratio, up to a higher angle of attack, compared to sharp-trailing-edge airfoils.

[0053] FIGs. 6A-6B are exemplary assembly view 600 and perspective view 620 of an external support structure 602 for active hook 103, according to some aspects of the present disclosure. In a high bandwidth device such as active hook 103, it is important to have a portion of the device that is stiff, coupling one or more output actuators to one or more inertial and positional sensors within the device. In order to accomplish this, active hook103 can be designed with external support structure 602, existing outside of drogue 302. External support structure 602 can be stiffer than drogue 302, to increase the feasible bandwidth. Accordingly, external support structure 602 can provide structural support for the one or more control surfaces and to increase body vibrational modes, increasing control bandwidth. Actuators and sensors can be tightly coupled to external support structure 602. In some aspects, two or more front paddles 402 and two or more aft paddles 404 can be coupled to external support structure 602. External support structure 602 can be configured as a U-frame.

[0054] FIG. 7 is an exemplary detail view 700 of a gurney flap 702 on active hook 103, according to some aspects of the present disclosure. In general, it is ideal for active hook 103 to be as small as possible and to retain as much symmetry in its one or more control paddles as possible, to improve its linear responsiveness. Further, it is known that a large lift component from active hook 103, with angular displacement, can result in less reliable captures in tow. Accordingly, in some aspects, drogue 302 of active hook 103 can be configured with a toroidal aft wing, such as that at fourth location 314, incorporating one or more gurney flaps 702. One or more gurney flaps 702 can be installed on the top and / or bottom of drogue 302 of active hook 103, such that an aft ring, such as that at fourth location 314 of active hook 103, is the source of a significant amount of lift. For example, in such aspects, active hook 103 can be responsible for generating two-thirds of steady state lift, while the one or more control paddles can be responsible for generating variable lift.

[0055] FIG. 8 is an exemplary side view 800 of active hook 103 having a sting 802 with a spring-break 804, according to some aspects of the present disclosure. Because active hook 103 is not a low drag device, which is a necessary feature to avoid a phugoid-like longitudinal mode on tether 104, active hook 103 has a significant drag relative to its weight or lift. It is also challenging, while retaining a lightweight design, to achieve a correct placement of aerodynamic center, center of mass 306, and center of lift. Active hook 103 requires greater surface area at its aft position (e.g., fourth location 314 in FIG. 3) to meet center of mass requirements relative to the aerodynamic center, in turn allowing for better captures in drogue 302. Accordingly, active hook 103 can include sting 802 with springbreak 804 on its forward nose, as to further move center of mass 306 in the aft direction. Tether 104 can anchor through sting 102 or can anchor to the tip of sting 802.

[0056] Spring-break 804 can be used to reduce loads on the nose of trailing aircraft 102 when under tow. Spring-break 804 can also allow for retraction of active hook 103 into a position on trailing aircraft 102 that is at a different angle of attack to the local flow as compared to a rigid sting.

[0057] Sting 802 and spring-break 804 can be configured so that they remain rigidly in place on active hook 103 during a majority of free-flying loads experienced. However, sting 802 and spring-break 804 can also be configured to rotate relative to active hook 103 when tether 104 is under load at an angular displacement from the primary axis of sting 802.

[0058] Sting 802 can also be angled relative to the longitudinal axis of active hook 103, or relative to the free airstream around active hook 103, such that a pitch-up moment is induced on active hook 103. This pitch-up moment can improve an angle of inclination of active hook 103 when flying with tension on tether 104.

[0059] The forward nose of active hook 103 can also be configured with a radial clocking feature, useful when it is reeled in towards lead aircraft 101. The clocking feature can ensure that active hook 103 is stowed at a fixed and known position on the tail of lead aircraft 101, when retracted. For example, a two-surface ramp system may be incorporated.

[0060] The capture system can include an asymmetric capture mechanism for capture of active hook 103 onto the back of lead aircraft 101 when retracted. The capture system can include two grooved capture areas of different lengths, configured at an angle to the airflow such that a single groove captures prior to the other groove in all capture cases. In this configuration, active hook 103 may only be captured on-axis on reel in, but may still be loosely captured if reeled in upside down. In some aspects, the two-surface ramp system is asymmetric, with the upper ramp being shorter than the lower ramp, such that it is not possible for active hook 103 to become stuck with both clocking elements to one side of the two ramps (e.g., when rotated 90 degrees about the direction of flight and displaced a small distance laterally). An asymmetric two-surface ramp system also allows for a more compact capture mechanism than is enabled through a single ramp.

[0061] FIG. 9 is an exemplary side view 900 of charging batteries using active hook 103, according to some aspects of the present disclosure. In some aspects, active hook 103 can include an inductive charging coil 902, a plug, or some other means of charging. In some aspects, active hook 103 can be powered through use of an electrical cord, a ram air turbine, or onboard batteries. When active hook 103 is in either a stowed position or a connected-on-tow position, it can recharge onboard batteries using the charging means. When not in a charging position, active hook 103 can use its onboard batteries to power the computation and control mechanisms of active hook 103. Use of onboard batteries avoids systems difficulties that can arise when running wire to active hook 103 (e.g., use of a slip ring, stretching or flexing of material, etc.).

[0062] Active hook 103 can also be configured for other applications. For example, active hook 103 can be used in an application where the purpose of the connection between lead aircraft 101 and trailing aircraft 102 is to convey an energy carrier (e.g., fuel) from one aircraft to the other. In some aspects, de-icing operations from lead aircraft 101 or trailing aircraft 102 can be powered by electric regeneration power.

[0063] FIG. 10 is a flowchart of an exemplary method 1000 for capturing an aircraft probe using an active hook, according to some aspects of the present disclosure. It is to be appreciated that not all steps need to be performed according to the disclosure provided herein. Further, some of the steps can be performed simultaneously, or in a different order than shown in FIG. 10, as will be understood by a person of ordinary skill in the art.

[0064] Method 1000 can be implemented by lead aircraft 101, trailing aircraft 102, and active hook 103, and operations caused by computing system 1100. However, method 1000 is not limited to that example aspect. Prior to method 1000, the active hook can be reeled in on the back of the lead aircraft. In this case, method 1000 depicts only a portion of the process that occurs once the active hook is reeled out.

[0065] In 1002, an active hook can be configured in a stable flying configuration. The active hook can be secured to a lead aircraft via a tether. Stable flying configuration can allow for lower risk flight, where the lead aircraft and a trailing aircraft are not connected and are not approaching one another. In some aspects, a stable flying configuration can also be configured when a trailing aircraft has overflown the active hook.

[0066] In 1004, the active hook can be configured in a capture configuration. In capture configuration, the active hook can fly in the middle of a capturing window, such that the trailing aircraft can approach the active hook from a side where visibility is good. It may be desirable for the trailing aircraft to approach the active hook from an angle that is not directly behind the active hook, to allow for better information to be gathered, either by an autopilot or a human pilot of the trailing aircraft. The information can include relative location and closing speed between the active hook and the trailing aircraft.

[0067] In 1006, the active hook and / or the trailing aircraft can be configured for tracking. Tracking configuration can occur once formation has been established between the active hook and the trailing aircraft in capture configuration.

[0068] In 1008, the active hook can be configured in a final closure configuration. In final closure configuration, the active hook can actuate to locate itself along an axis predominantly along the direction of airflow, in front of the trailing aircraft. In this configuration, the trailing aircraft can validate accurate tracking performance of the active hook, and can better ascertain the remaining amount of closing distance.

[0069] In 1010, the active hook can capture a probe of the trailing aircraft.

[0070] Various aspects can be implemented, for example, using one or more computer systems, such as exemplary computer system 1100, shown in FIG. 11. Computer system 1100 can be used, for example, to implement a system for controlling active hook 103. For example, computer system 1100 can provide sensing, computation, and actuation of active hook 103’s control mechanisms, such as the position tracker, turn coordinator, actuators, controllers, sensors, actuator allocator, and / or onboard batteries. Computer system 1100 can be any computer capable of performing the functions described herein.

[0071] Computer system 1100 can be any well-known computer capable of performing the functions described herein.

[0072] Computer system 1100 includes one or more processors (also called central processing units, or CPUs), such as a processor 1104. Processor 1104 is connected to a communication infrastructure or bus 1106.

[0073] One or more processors 1104 may each be a graphics processing unit (GPU). In an aspect, a GPU is a processor that is a specialized electronic circuit designed to process mathematically intensive applications. The GPU may have a parallel structure that is efficient for parallel processing of large blocks of data, such as mathematically intensive data common to computer graphics applications, images, videos, etc.

[0074] Computer system 1100 also includes user input / output device(s) 1116, such as monitors, keyboards, pointing devices, etc., that communicate with communication infrastructure 1106 through user input / output interface(s) 802.

[0075] Computer system 1100 also includes a main or primary memory 1108, such as random access memory (RAM). Main memory 1108 may include one or more levels ofcache. Main memory 1108 has stored therein control logic (i.e., computer software) and / or data.

[0076] Computer system 1100 may also include one or more secondary storage devices or memory 1110. Secondary memory 1110 may include, for example, a hard disk drive 1112 and / or a removable storage device or drive 1114. Removable storage drive 1114 may be a floppy disk drive, a magnetic tape drive, a compact disk drive, an optical storage device, tape backup device, and / or any other storage device / drive.

[0077] Removable storage drive 1114 may interact with a removable storage unit 1118. Removable storage unit 1118 includes a computer usable or readable storage device having stored thereon computer software (control logic) and / or data. Removable storage unit 1118 may be a floppy disk, magnetic tape, compact disk, DVD, optical storage disk, and / any other computer data storage device. Removable storage drive 1114 reads from and / or writes to removable storage unit 1118 in a well-known manner.

[0078] According to an exemplary aspect, secondary memory 1110 may include other means, instrumentalities or other approaches for allowing computer programs and / or other instructions and / or data to be accessed by computer system 1100. Such means, instrumentalities or other approaches may include, for example, a removable storage unit 1122 and an interface 1120. Examples of the removable storage unit 1122 and the interface 1120 may include a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an EPROM or PROM) and associated socket, a memory stick and USB port, a memory card and associated memory card slot, and / or any other removable storage unit and associated interface.

[0079] Computer system 1100 may further include a communication or network interface 1124. Communication interface 1124 enables computer system 1100 to communicate and interact with any combination of remote devices, remote networks, remote entities, etc. (individually and collectively referenced by reference number 1128). For example, communication interface 1124 may allow computer system 1100 to communicate with remote devices 1128 over communications path 1126, which may be wired and / or wireless, and which may include any combination of LANs, WANs, the Internet, etc. Control logic and / or data may be transmitted to and from computer system 1100 via communication path 1126.

[0080] In an aspect, a tangible, non-transitory apparatus or article of manufacture comprising a tangible, non-transitory computer useable or readable medium having control logic (software) stored thereon is also referred to herein as a computer program product or program storage device. This includes, but is not limited to, computer system 1100, main memory 1108, secondary memory 1110, and removable storage units 1118 and 1122, as well as tangible articles of manufacture embodying any combination of the foregoing. Such control logic, when executed by one or more data processing devices (such as computer system 1100), causes such data processing devices to operate as described herein.

[0081] Based on the teachings contained in this disclosure, it will be apparent to persons skilled in the relevant art(s) how to make and use aspects of this disclosure using data processing devices, computer systems and / or computer architectures other than that shown in FIG. 11. In particular, aspects can operate with software, hardware, and / or operating system implementations other than those described herein.

[0082] It is to be appreciated that the Detailed Description section, and not any other section, is intended to be used to interpret the claims. Other sections can set forth one or more but not all exemplary aspects as contemplated by the inventor(s), and thus, are not intended to limit this disclosure or the appended claims in any way.

[0083] While this disclosure describes exemplary aspects for exemplary fields and applications, it should be understood that the disclosure is not limited thereto. Other aspects and modifications thereto are possible, and are within the scope and spirit of this disclosure. For example, and without limiting the generality of this paragraph, aspects are not limited to the software, hardware, firmware, and / or entities illustrated in the figures and / or described herein. Further, aspects (whether or not explicitly described herein) have significant utility to fields and applications beyond the examples described herein.

[0084] Aspects have been described herein with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined as long as the specified functions and relationships (or equivalents thereof) are appropriately performed. Also, alternative aspects can perform functional blocks, steps, operations, methods, etc. using orderings different than those described herein.

[0085] References herein to “one aspect,” “an aspect,” “an example aspect,” or similar phrases, indicate that the aspect described can include a particular feature, structure, or characteristic, but every aspect can not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same aspect. Further, when a particular feature, structure, or characteristic is described in connection with an aspect, it would be within the knowledge of persons skilled in the relevant art(s) to incorporate such feature, structure, or characteristic into other aspects whether or not explicitly mentioned or described herein. Additionally, some aspects can be described using the expression “coupled” and “connected” along with their derivatives. These terms are not necessarily intended as synonyms for each other. For example, some aspects can be described using the terms “connected” and / or “coupled” to indicate that two or more elements are in direct physical or electrical contact with each other. The term “coupled,” however, can also mean that two or more elements are not in direct contact with each other, but yet still co-operate or interact with each other.

[0086] The breadth and scope of this disclosure should not be limited by any of the abovedescribed exemplary aspects, but should be defined only in accordance with the following claims and their equivalents.

Claims

WHAT IS CLAIMED IS:

1. A system for an active hook, comprising: a drogue; one or more control surfaces attached to the drogue; a control system attached to the one or more control surfaces, wherein the control system is configured to actuate the one or more control surfaces; and a power source attached to the control system, wherein the power source is configured to provide power to the control system.

2. A system for placement of an active hook on a probe of a trailing aircraft, comprising: an in-air entity, comprising: a lead aircraft; a tether attached to the lead aircraft by a first end; and an active hook attached to a second end of the tether; and a trailing aircraft, comprising a probe, wherein the active hook is configured to attach to the probe of the trailing aircraft.

3. The system of claim 2, wherein the in-air entity is a first in-air entity, and the system further comprises: a second in-air entity, comprising: a second lead aircraft; a second tether attached to the second lead aircraft by a first end; and a second active hook attached to a second end of the second tether, wherein the trailing aircraft is configured to attach to the first in-air entity through a connection between the active hook and the probe, to detach from the first in-air entity, and to attach to the second in-air entity through a connection between the second active hook and the probe.

4. The system of claim 2, wherein the tether is one of a rope, a hose, a mechanical tether, or an electromechanical tether.

5. The system of claim 3, wherein the second tether is one of a rope, a hose, a mechanical tether, or an electromechanical tether.

6. The system of claim 2, wherein the tether is a rubberized tether.

7. The system of claim 3, wherein the second tether is a rubberized tether.

8. The system of claim 2, wherein the tether is coated with a polymer capable of reducing adhesion of ice.

9. The system of claim 3, wherein the second tether is coated with a polymer capable of reducing adhesion of ice.

10. The system of claim 2, wherein the active hook comprises: a drogue; one or more control surfaces attached to the drogue; a control system attached to the one or more control surfaces, wherein the control system is configured to actuate the one or more control surfaces; and a power source attached to the control system, wherein the power source is configured to provide power to the control system.

11. The system of claim 3, wherein the second active hook comprises: a drogue; one or more control surfaces attached to the drogue; a control system attached to the one or more control surfaces, wherein the control system is configured to actuate the one or more control surfaces; and a power source attached to the control system, wherein the power source is configured to provide power to the control system.

12. The system of any one of claims 1-11, wherein the active hook or the second active hook further comprise at least one indicator light.

13. The system of any one of claims 1-11, wherein the active hook or the second active hook further comprise a toroidal aft wing.

14. The system of claim 13, wherein the toroidal aft wing comprises a gurney flap.

15. The system of claim 1, 10, or 11, wherein the drogue comprises a spring-release sting, and wherein the spring-release sting is capable of rotating.

16. The system of claim 15, wherein the spring-release sting is angled relative to a longitudinal axis of the active hook or the second active hook in order to induce a pitch-up moment on the active hook or the second active hook.

17. The system of any one of claims 2-11, wherein the active hook or the second active hook further comprises an asymmetric capture mechanism configured to capture a back of the lead aircraft or the second lead aircraft when in a reeled-in position, and wherein the asymmetric capture mechanism comprises two grooved capture areas of different lengths.

18. The system of any one of claims 2-11, wherein the lead aircraft or the second lead aircraft comprises a squirter configured to spray de-icing fluid in an aft direction.

19. The system of any one of claims 2-11, wherein the trailing aircraft comprises a squirter configured to deliver de-icing fluid through the active hook or the second active hook.

20. The system of any one of claims 2-11, wherein the active hook or the second active hook comprises a latch, and wherein the latch is configured to connect to the trailing aircraft.

21. The system of claim 20, wherein the latch is a reusable tension release mechanism.

22. The system of claim 20, wherein the latch is a low-force spring.

23. The system of claim 1, 10, or 11, wherein the one or more control surfaces are one or more control paddles configured to create aerodynamic forces.

24. The system of claim 1, 10, or 11, wherein the one or more control surfaces are configured to generate pitch control of the first active hook or the second active hook.

25. The system of claim 1, 10, or 11, wherein the one or more control surfaces comprise: at least two front paddles; and at least two aft paddles, wherein the two front paddles are positioned in front of a center of mass of the active hook or the second active hook, and wherein the two aft paddles are positioned behind the center of mass of the active hook or the second active hook.

26. The system of claim 1, 10, or 11, wherein the one or more control surfaces comprise four paddles configured in one of an X configuration or a cross configuration.

27. The system of claim 1, 10, or 11, wherein the one or more control surfaces are flat-back airfoils.

28. The system of claim 1, 10, or 11, wherein the one or more control surfaces have less than a six percent camber.

29. The system of claim 1, 10, or 11, further comprising an external support structure, wherein the external support structure is stiffer than the drogue, and wherein at least one of the one or more control surfaces, the control system, and the power source are attached to the external support structure.

30. The system of claim 1, 10, or 11, wherein the power source is an onboard battery, and wherein the onboard battery can be charged when in a reeled-in position or when in a capture position.

31. The system of claim 1, 10, or 11, wherein the control system includes a controller and at least one actuator, and wherein the control system is configured to actuate the active hook or the second active hook to at least one flight configuration useful when capturing a probe on a trailing aircraft.

32. The system of claim 1, 10, or 11, wherein the control system includes a turn coordinator, and wherein the turn coordinator is configured to control a turn rate and a roll angle of the active hook or the second active hook.

33. The system of claim 1, 10, or 11, wherein the control system includes a controller, at least one actuator, and an actuator allocator.

34. The system of claim 33, wherein the actuator allocator is configured to prioritize roll movement over all other axes.

35. The system of claim 33, wherein the actuator allocator is configured to prioritize vertical and horizontal displacement over non-roll axes of control.

36. The system of claim 10 or 11, wherein the control system is configured to mimic behavior of the trailing aircraft.

37. The system of claim 1, 10, or 11, wherein the control system includes a position tracker.

38. The system of claim 37, wherein attitude gains are set for higher bandwidth control when the position tracker is activated.

39. The system of any one of claims 2-11, wherein the lead aircraft or the second lead aircraft comprise a position tracker, and wherein the position tracker is at least one of a differential GPS system, a wideband relative position sensor, a time-of-flight sensor, and an onboard camera.

0. A method for improving placement of an active hook on a probe of a trailing aircraft, comprising: configuring, by at least one control system, an active hook in a stable flying configuration, wherein the active hook is attached to a lead aircraft via a tether; configuring, by the at least one control system, the active hook in a capture configuration, wherein a trailing aircraft configured to attach to the active hook can approach the active hook in the capture configuration; configuring, by the at least one control system, the active hook in a tracking configuration, wherein at least one of the active hook and the trailing aircraft can track their position relative to the other in the tracking configuration; configuring, by the at least one control system, the active hook in a final closure configuration, wherein the active hook locates itself along an axis of the direction of airflow in front of the trailing aircraft in the final closure configuration; and capturing, by the at least one control system, a probe of the trailing aircraft using the active hook.

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