UAV recovery system

An unmanned aerial vehicle (UAV) recovery system comprises a base and a pneumatic capture net, including a set of upwardly extending, flexible, inflatable tubes, supported by a capture net support assembly. Drag forces are exerted on a UAV by the set of tubes when the UAV flies into them. In some examples the recovery system includes a plurality of decelerators, each decelerator having a supply of a restraint strap, connected to the pneumatic net, which can be pulled from the decelerator upon the application of a sufficient force so that movement of the pneumatic net is resistible by forces exertable by the decelerators on the pneumatic net.

BACKGROUND OF THE INVENTION

Unmanned aerial vehicles (UAVs), also known as remotely operated aircraft, are used for many different military and commercial applications. These applications include reconnaissance, surveillance and security; communication relay; area mapping; monitoring erosion and environmental changes; agricultural, farming and commercial fishing purposes; fire detection and damage assessment; surveillance of borders, harbors and canals; convoy, road and population protection; and natural resources and wildlife management.

Some UAVs are launched using pneumatic tube launchers to eliminate the need for long runways. UAVs may fly autonomously along a preprogrammed flight path that is modifiable from a ground control station while in flight. It is common to use Differential GPS to provide enhanced accuracy for ensuring that the UAV flies to within inches of the desired location for recovery.

One of the problems with UAVs is how to successfully, that is with no or minimal damage to the aircraft, recover or capture them at the end of a flight if a runway or a runway-like surface, such as a road, is not available. This is a significant problem when the UAV is to land on a boat or ship, such as a helicopter landing pad on a ship. It is also problem in remote or otherwise unimproved areas in the field. Several different recovery systems have been developed to recover the UAV without destroying it. One is to use a horizontal line and a hook on the UAV similar to that used on aircraft carriers with piloted aircraft. Another system uses nets to capture the UAV. Another system, described in U.S. Pat. No. 7,059,564, uses a vertically extending recovery line; a wing of the UAV hits the recovery line which catches the tip of the wing and spins the UAV around until it comes to rest.

BRIEF SUMMARY OF THE INVENTION

An example of an unmanned aerial vehicle (UAV) recovery system comprises a base, a capture net support assembly and a pneumatic capture net. The base is supportable by a support surface. The pneumatic capture net is supported by the capture net support assembly. The pneumatic capture net comprises a set of tubes. The tubes are flexible inflatable tubes placeable in deflated and inflated states. The tubes extend upwardly away from the base when in the inflated state. The set of tubes has a width and a height, the width and height defining an impact area into which a UAV can be directed. Drag forces are exerted on a UAV by the set of tubes when the UAV flies into the impact area of the set of tubes. In some examples the recovery system further comprises a plurality of decelerators, each decelerator comprising a supply of a restraint strap that can be pulled from the decelerator upon the application of a sufficient force. Each restraint strap is connected to the pneumatic net so that movement of the pneumatic net is resistible by forces exertable by the decelerators on the pneumatic net. In some examples the recovery system further comprises a trigger assembly, the trigger assembly comprising a trigger net and a trigger line coupled to the trigger net, the trigger net being positioned at the impact area. In some examples a decelerators is placeable in a locked condition, at which the restraint strap for that decelerator is prevented from being pulled from the decelerator, and an unlocked, use condition. Such decelerator comprises a releasable lock element operably connected to the trigger line so that engagement of the UAV with the trigger net places the decelerator in the unlocked, use condition.

A method for recovering an unmanned aerial vehicle (UAV) after a flight is carried out as follows. A UAV recovery system is set up at a recovery site, the UAV recovery system comprising a base, a capture net support assembly, and a pneumatic capture net. The pneumatic net comprises a set of inflatable, flexible, compliant tubes. The setting up step comprises placing the base on a support surface at the recovery site and erecting the pneumatic capture net adjacent to the base. The pneumatic capture net erecting step comprises supporting the pneumatic net adjacent to the base using the capture net support assembly and inflating the set of tubes of the pneumatic net to place the tubes in an inflated, use state extending upwardly away from the base. A UAV is directed into the pneumatic net along a final flight path, the UAV having wings with forward edges. A drag force is created on the UAV by engagement of at least the forward edges of the wings with at least some of the tubes as the UAV moves along a terminal segment of the final flight path. In some examples the drag force creating step comprises resisting movement of the pneumatic net using decelerators operably connected to the pneumatic net. Some examples further comprise temporarily preventing a decelerators from releasing line from the decelerator, sensing when a UAV engages the pneumatic net, and then permitting such decelerator to release line from the decelerator.

Other features, aspects and advantages of the present invention can be seen on review the figures, the detailed description, and the claims which follow.

DETAILED DESCRIPTION OF THE INVENTION

The following description will typically be with reference to specific structural embodiments and methods. It is to be understood that there is no intention to limit the invention to the specifically disclosed embodiments and methods but that the invention may be practiced using other features, elements, methods and embodiments. Preferred embodiments are described to illustrate the present invention, not to limit its scope, which is defined by the claims. Those of ordinary skill in the art will recognize a variety of equivalent variations on the description that follows. Like elements in various embodiments are commonly referred to with like reference numerals.

The present invention relates to the use of a set of inflatable, upwardly extending tubes creating a pneumatic capture assembly such that when a UAV flies into the pneumatic capture assembly, the tubes bend over the wings to decelerate the UAV in a controlled manner causing the aircraft to safely stop. The invention provides enhanced UAV survivability as well as ground crew safety.

An example of a UAV recovery system10is described below with reference toFIGS. 1-5C. System10includes broadly a base12, supported a support surface14, such as the ground or the deck of a ship, a pneumatic capture assembly in the form of a pneumatic capture net16supported at one end of the base by a capture net support assembly18.

The base12of the UAV recovery system10is made of a layer of individually inflatable base plenums20. Each base plenum20is fluidly coupled to an air supply unit (air compressor)22through an air supply conduit24and a base manifold26. The base acts as a pneumatic catch pad. A ground cloth, also called a ground tarp and typically made of nylon, not shown, can be used between the base12and the support surface14to help protect the base from being punctured by objects, such as glass, sharp rocks, sticks and debris, on the support surface.FIG. 1illustrates the use of a cover or sheet28covering the upper layer of base plenums20. Although not shown in the figures, base12has loop at each corner and two places along each side. These loops are attached to sandbags to secure the base to support surface14. Other techniques for maintaining base12in place, such as the use of ground stakes, may also be used.

The base plenums20are preferably fastened to one another using, for example, hook and loop fasteners. Use of separate base plenums permits the removal or replacement of an individual base plenum if the base plenum has become damaged, or for other reasons. In this example the base plenums are 28 feet long and 2 feet in diameter and create a base having a width of about 24 feet, a depth of 28 feet and a height of 2 feet. The forward ends30of base plenums20are cone shaped and act as an entrance ramp to help upwardly deflect portions of a UAV that are too low.

Pneumatic capture net16is positioned, in this example, about 4 feet in front of base12. Pneumatic capture net16preferably includes a row of flexible, compliant, inflatable tubes32which extend upwardly from a tube manifold34. The tubes32are supplied with air from an air supply unit, such as air compressor22, through the tube manifold34. The connection of air compressor22with tube manifold34is not shown in the figures for clarity of illustration. The upper ends of the tubes32are physically secured to and fluidly connected to a top connector conduit36. The top connector conduit36permits air to flow from the top end of one tube32into the top end of one or more other tubes32upon UAV impact. Other arrangements of inflatable tubes are also possible. The top connector conduit36is connected to an upper strap38and a series of vertical straps40, straps38and40being components of support assembly18. The tube manifold34, top connector conduit36and the row of tubes32are typically collectively referred to as the pneumatic capture net16. The tubes, plenums, manifolds and conduits are typically made of sturdy materials such as rip stop nylon.

Support assembly18also includes a tripod42, having, in this example, a height of about 22 feet, at either end of the pneumatic net16. Each tripod42is secured in place by two earth anchors44. The capture net support assembly18comprises, in this example, tripods42, upper strap38and vertical straps40. Each end of the upper strap38is connected to a restraint strap46which extends over a pulley, not shown, at the upper tip of each tripod42. Each restraint strap46extends downwardly to a side decelerator48. The side decelerators are secured to a base board50. The base board50is secured to the support surface14in a manner appropriate to the support surface. For example, when the system10is being placed in a field and the support surface14is the earth, the base board50can be is secured in place using conventional ground spikes or ground anchors.

Base restraint lines or straps52extend from the tube manifold34to a row of front decelerators54. The front decelerators54are also secured to the base board50. As shown inFIG. 1, a number of base restraint lines52may be connected to one another to form a common base restraint line53which is connected to and wound onto a front decelerator54.

Each side and front decelerator48and54contains a length of the corresponding line or strap46and53and provides a restraining or drag force preventing the free release of the line or strap from the decelerator. Base restraint lines52,53are used to stabilize the lower portion of the pneumatic net16while restraint straps46are used to stabilize the upper portion of the pneumatic net16. In one example the decelerator is similar to a large fishing reel having a spool, on which the line or strap is wound, with an adjustable disc brake type of friction drag restraining free rotation of the spool. Therefore, the restraining force is provided by both the friction drag and, to a lesser extent, by the inertia of the spool and line wound thereon. Decelerators with other types of drag systems including pneumatic and fluid drag systems may also be used.

It has been found that the use of the pneumatic capture net16connected to decelerators48,54provide for the effective capture of UAVs. The tubes32of the pneumatic net16have a tendency to flatten out on impact so that the braking force on the UAV is spread out over an extended wing surface area. In some examples adjustable drag decelerators are used to permit the amount of braking force provided by the decelerators to be adjusted or selected. The selection of the braking force typically will depend upon the operating conditions, including the type, size and weight of the UAV, wind speed and direction, whether the UAV and its contents are fragile, and the expected impact velocity. In some examples different drag forces can be set on the decelerators in a manner similar to that available on fishing reels. Although not presently used, one or more of the tubes32, the tube manifold34and the top connector conduit36can include a pressure relief valve to permit any overpressure therein to be exhausted to atmosphere. The one or more pressure relief valves could be adjustable so as to when they open.

One of the problems created by using the relative large diameter pneumatic tubes32is that they are affected by wind. It has been found that in windy conditions the wind forces can be sufficient so that the restraint straps46connected to the side decelerators48are pulled out from the side decelerators48permitting the upper portion of the pneumatic net16to be deflected from its normally upright state. That is, wind forces can be sufficient to overcome the drag forces exerted by the side decelerators48on the restraint straps46to effectively blow over the pneumatic net16. If a gust of wind causes that to occur during a UAV capture, it could result in the UAV not being safely captured but rather damaged or destroyed. In response to this problem, system10includes a trigger assembly56. The trigger assembly56includes broadly a trigger net58secured to pneumatic net16, a trigger or unlock line60connected to an extending downwardly from each end corner of the pneumatic net to a trigger lock, not shown, associated with the underlying side decelerator48. Each trigger lock is made as a part of a side decelerator48to operate in a manner discussed below. In this example the trigger net58includes first and second parallel, spaced apart lines66secured to tubes32; in other examples a single line or a meshwork of lines could be used. The side decelerators48are each placeable in an unlocked, use state, in which strap46can be pulled from side decelerator48by applying sufficient tension force, and a locked state, in which strap46is effectively prevented from being pulled from side decelerator48.

The trigger lock portion of side decelerator48is designed so that under normal circumstances the trigger line60can remain in tension between the side decelerator48and the pneumatic net16so to maintain the side decelerator48in the locked state. That is, the forces exerted on the trigger lock portion of the side decelerator48by trigger line60as a result of the wind on the pneumatic net16are not sufficient to cause the trigger lock portion of the side decelerator48to unlock the decelerator48, which would permit the restraint strap46to be pulled from the decelerator. Therefore, normal wind forces will create insufficient forces to place the side decelerators48in the unlocked, use states, which would allow restraint strap46to be pulled out from the side decelerator48. This is particularly true because system10is typically oriented so that the UAV heads into the wind during recovery. Such a wind heading will generally not tend to create large tension forces on the trigger line60between the pneumatic net16and the trigger lock portion of the side decelerator48. However, when the UAV contacts the pneumatic capture net16and the trigger net58, a sufficient tension force is exerted by the pneumatic net16on the trigger line60to cause the trigger lock portion of the side decelerator48to permit strap46to extend the from side decelerator48, under tension, during the capture of the UAV. Therefore, only when a UAV strikes the pneumatic capture net16will the side decelerator48permit the strap46to be pulled from the side decelerator. Also, upon UAV impact base restraint lines52are pulled from the front decelerators54. The impact force of the UAV is then effectively absorbed by the pneumatic net16and the side and front decelerators48,54.

In this example it has not been found necessary to include releasable lock elements associated with the front decelerators54connected to the tube manifold34because the wind forces at the lower end of the pneumatic net16are not typically sufficient to cause the tube manifold to be moved about by the wind to any significant extent. However, in appropriate situations one or more of the front decelerators54secured to the tube manifold34may also have releasable lock elements to help prevent undesirable movement of the pneumatic net16prior to impact by a UAV.

In some examples trigger line60could be connected directly to trigger net58instead of indirectly to trigger net58through pneumatic capture net16. Also, in some examples the inflatable tubes constituting pneumatic capture net16may be constructed and connected in such a manner that no separate trigger net would be used but rather the pneumatic capture net would act as the trigger net.

Instead of the mechanical actuation of the lock elements associated with the decelerators, the actuation could be accomplished using electrically actuated release lock elements. Such a release lock element could be operated using signals provided over wires or in a wireless manner. The trigger for sending the signal could be, for example, the initial contact with the trigger net or through the use of a proximity or other type of noncontact sensor. The signal could also be sent by an operator at, or remote from, the site.

The upper strap38and the vertical straps40, in this example, may be made of lengths of one-inch nylon strap sewn at their junctions. The junctions of the vertical straps and the top connector conduit36are preferably strong connections, typically sewn or other reinforced connections when straps and the tubes are both fabric-based materials. Trigger lines60of trigger net58are, in this example, sewn to manifold34.

To prevent damage to the UAV, it is important that the maximum deceleration be limited to an amount the UAV, and any payload carried by the UAV, can withstand. That is, an aircraft flying into a set of rigid poles would no doubt be quickly stopped but would also be destroyed. The successful capture or recovery of the UAV requires a controlled deceleration of the UAV thereby limiting the decelerating forces exerted by the pneumatic net16on the UAV. Upon impact with the pneumatic capture net16, an initial drag force on the UAV is created by the forward edges of the wings engaging the tubes32as the UAV moves along a terminal segment of the final flight path. This causes the tubes32to deform and create an initial drag force on the UAV. As the UAV continues its forward movement, while decelerating, the pneumatic net16pulls on the trigger lines60connected to the side decelerators48, and the tube manifold34of the pneumatic capture net16pulls on the straps46connected to the front decelerators54. Doing so permits movement of the pneumatic capture net16while dissipating the inertial force of the UAV through the drag provided by engagement of the tubes32by the wings of the UAV, and by the side and front decelerators48and54. At the end of the capture, the UAV, together with portion the pneumatic and trigger nets16and58, come to rest on the base12.

To capture the UAV, the UAV is typically directed to fly into the center of the pneumatic net16. In some cases, all or part of the UAV may be lower than desired. Recognizing this, the UAV recovery system may include an entrance ramp at the front end of the base12. The entrance ramp, such as that created by cone shaped ends30of plenums20, preferably has a low friction surface to help redirect a low-flying UAV to a more appropriate height. In some examples the entrance ramp may be placed in front of pneumatic capture net16or on both sides of the pneumatic capture net. In the latter case the entrance ramp may need to be configured to accommodate the base restraint lines52and front decelerators54by, for example, providing appropriately positioned cutouts.

Once the UAV has been brought to rest, the air supply units can be turned off or down to a lower pressure to permit the UAV to be removed from the trigger net, the pneumatic net, and the various straps and lines. After recovering the UAV, the air supply unit or units, such as air compressor22, can be once again used to inflate the pneumatic net16, and, if necessary, the base12, for the recovery of any additional UAVs. When there are no more UAVs to be recovered, the base plenums20, tubes32, conduits24, manifolds26,34, and any other inflatable components, are deflated. The air compressor22is detached from the manifolds, the various lines are detached from their associated components, the tripods42are collapsed and the base board50is disconnected from the support surface14. The extensive use of collapsible components permits some or all of the components to be folded into a relatively compact volume for ease of transport and storage.

Some examples of the UAV recovery system10are easily transported to a recovery site when deflated. When not in use, the deflated the UAV recovery system can be stored in a compact package. Assume an example of a UAV recovery system having12base plenums20each 28 feet long and 2 feet wide; a 22 feet tall by 24 feet wide pneumatic capture net16including17pneumatic tubes, each tube having a diameter of about 4-6 inches. This equipment, when folded and deflated, along with the associated equipment, can typically fit into relatively small containers to facilitate both transport and storage. Minimizing storage space is especially important in situations where storage space is limited, such as on a ship. The ability to be quickly set up, taken down and placed in a suitably small size configuration for transport and storage are important advantages achieved by the present invention.

One example of a method for recovering a UAV after a flight is carried out as follows. Once at the recovery site, the UAV recovery system10can be quickly set up. The base12, support assembly18, pneumatic net16and trigger assembly56are arranged in the appropriate direction relative to the final flight path. One or more air supply units22are connected to the conduits and manifolds so that the inflatable components can be inflated. The front and side decelerators54and48are adjusted to apply the appropriate drag force on the base restraint lines52and the restraint straps46. While an entrance ramp may be incorporated as part of the inflatable plenums20, in some situations it may be desired to have a non-inflatable, but typically foldable, entrance ramp. Typically the UAV is pre-programmed to fly to the recovery site at the end of the mission. In some situations it may be desirable to have someone at the recovery site with the ability to make minor corrections to the final flight path of the UAV to help the UAV contact the pneumatic net16at the center of the impact area, the impact area being defined by the pneumatic net. A local Differential GPS transmitter is typically used at the recovery site to help ensure the UAV impacts the pneumatic net at or close to the desired center position.

The UAV first contacts the pneumatic capture net16, and the associated trigger net58, as shown inFIG. 5A. Upon contact, the trigger lines60connecting the trigger net58to the side decelerators48are released by the trigger locks of the side decelerators to allow the restraint straps46to be pulled from the side decelerators48, subject to an appropriate drag force on straps46. Upon this contact, an initial drag force on the UAV is created by the forward edges of the wings engaging the tubes32of the pneumatic capture net16as the UAV moves along a terminal segment of the final flight path. Soon after the initial engagement, the pneumatic capture net16begins pulling the base restraint lines52and the restraint lines46against the drag forces created by the front and side decelerators54and48. SeeFIGS. 5B and 5C. The UAV then comes to rest, together with the pneumatic net16and the trigger net58, on the pneumatic base12. Once the UAV has been brought to rest, the air compressor22can be turned off or down to a lower pressure to assist the removal of the UAV from the pneumatic net16and the trigger net58. After recovering the UAV, the air compressor22can be once again used to inflate the tubes32for the recovery of any additional UAVs. When there are no more UAVs to be recovered, the inflatable components are deflated; the air supply units22are detached allowing the inflatable components to be folded into a relatively compact volume for ease of transport and storage.

In one testing situation in an open field, the UAV recovery system10ofFIGS. 1-5Cwas set up as follows. A ground cloth or tarp was placed on the support surface14and then the base plenums20were placed upon the ground cloth and secured to one another using hook and loop fasteners. The tripods42were secured in place using the earth anchors44. The air supply units22were used to inflate the base plenums20. Base board50was secured to the ground in the field using anchor elements driven into the ground with the decelerators54and48secured to base board50. The base restraint lines52were connected to the front decelerators54. Trigger lines60extending from the lower outside corners of pneumatic capture net16were connected to the lock elements of the side decelerators48. The restraint straps46extending from the upper strap38were directed over the pulleys at the tops of the tripods42and to the side decelerators48. The pneumatic net16was connected to the air compressor22and inflated. The tension on each of the lines52,46extending from the decelerators54,48was adjusted. After recovery of one or more UAVs, the UAV recovery system ofFIGS. 1-5Cwas taken down, including deflating the components, detaching the air supply units from the inflatable components, folding up the inflatable components, and placing all components into containers for transport and storage.

The UAV recovery system example ofFIGS. 1-5Cshould be suitable for a UAV having a wingspan of about 10-18 feet and a weight of about 60 to 200 pounds. The use of decelerators54,48with adjustable drags allows the restraining force of the system to be adjusted primarily according to the weight of the UAV, as well as other considerations associated with the operating environment and considerations associated with the content and construction of the UAV.

An alternative example of a UAV recovery system10can find particular utility when used as a semipermanent installation. In this example a pneumatic capture net16is supported along more than one edge of base12by support assemblies18. Therefore, assuming base12has 4 sides, 2, 3 or 4 pneumatic capture nets16can be used, one along each side, as shown inFIG. 6. Assuming a pneumatic capture net16is used along each of the 4 sides, support assemblies18would typically use 4 tripods42to support the 4 pneumatic capture nets16. In such a semipermanent installation, base12would typically be larger than in the prior example, such as 36′×36′. Base12could also be made with 3 sides or with 5 or more sides. In addition, cone shaped ends30can be provided at both ends of plenums20. Similar cone shaped structures can be made to extend from the edges of the outermost plenums20so that the entire base12has cone shaped deflector structures along its periphery. This example allows for optimal recovery approach regardless of wind direction.

The above descriptions may have used terms such as above, below, top, bottom, over, under, et cetera. These terms may be used in the description and claims to aid understanding of the invention and not used in a limiting sense.

While the present invention is disclosed by reference to the preferred embodiments and examples detailed above, it is to be understood that these examples are intended in an illustrative rather than in a limiting sense. It is contemplated that modifications and combinations will occur to those skilled in the art, which modifications and combinations will be within the spirit of the invention and the scope of the following claims. For example, the base need not be inflatable but rather a separate air duct system could be used to supply compressed air from the air compressor to the pneumatic net.

Any and all patents, patent applications and printed publications referred to above are incorporated by reference.