Abstract:
A landing system for an air vehicle with vertical takeoff and landing capability is provided that comprises a set of selectively pressurizeable upper and lower air chambers surrounded by a connecting curtain assembly. The upper and lower air chambers are each continuous having elongated right and left cylindrical center sections interconnected by semicircular sections at each end. The landing system is connected to the air vehicle by a catenary system connected to the upper air chamber. The landing system can adjust pressure in each individual set of landing chambers such that the attitude of the vehicle can be adjusted to clear uneven ground or assist with loading and offloading. The system is capable of absorbing energy during vertical landings. After landing, the system is capable of providing suction between the air vehicle and the ground to stabilize the air vehicle.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to air cushioned landing systems for flight vehicles and more particularly to a multi-chamber landing system for use with an air vehicle. 
     BACKGROUND OF THE INVENTION 
     Air cushioned landing systems have previously been proposed for air vehicles. These prior art systems were designed for rolling takeoff and landing following the principals of a hovercraft by allowing the vehicle to accelerate during take-off and decrease speed during landing. However, the prior art systems are of limited utility for large vertical takeoff and landing vehicles because they are not weight efficient and suffer from an inability to absorb and redistribute energy during takeoff and landing. Vertical takeoff and landing flight vehicles have specific requirements for a landing system. The landing system should actively absorb energy during vertical impact. The system should also provide suction to increase the vehicle&#39;s stability while on the ground and reduce friction while the vehicle is taxiing. Finally, the system should have the ability to adjust the attitude of the vehicle to enable the vehicle to clear uneven ground and other obstacles while taxiing and to assist with the loading and offloading of cargo. Prior art landing systems for flight vehicles do not meet these requirements. 
     Therefore, there remains a need in the art for and an improved air cushion landing system that addresses the above deficiencies and is particularly well suited for use on an air vehicle designed for vertical takeoff and landings. 
     SUMMARY OF THE INVENTION 
     The landing system of the present invention solves the problems of the prior art by providing an air cushion landing system that comprises a set of selectively pressurizeable upper and lower air chambers surrounded by a connecting curtain assembly. The upper and lower air chambers are each continuous having elongated right and left cylindrical center sections interconnected by semicircular sections at each end. The air chambers may also take the shape of an elongated torus. The landing system is connected to the air vehicle by a catenary system connected to the upper air chamber. Typically, the landing system will include a series of sets of landing chambers. 
     The upper air chamber includes a top surface which is essentially sealed with an air impermeable barrier and the upper and lower air chambers are otherwise configured such that there is a space or third chamber defined by the interior walls of the air chambers and the ground when the air vehicle is in contact with the ground. The application of suction to this third air chamber allows the vehicle to adhere to the ground during cargo and/or passenger unloading. This ability is particularly important for vehicles with lighter-than-air characteristics. The application of pressurized air to the third chamber reduces ground friction allowing the air vehicle to taxi. Pressure in the upper and lower air chambers can be adjusted to absorb energy on vertical landing. When arranged sequentially, pressure can be adjusted in each individual set of landing chambers such that the attitude of the vehicle can be adjusted to clear uneven ground or assist with loading and offloading. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of an exemplary air vehicle incorporating the landing system of the present invention. 
         FIG. 2  is a front view of the exemplary air vehicle of  FIG. 1  incorporating the landing system of the present invention. 
         FIG. 3  is a perspective view of the landing system of the present invention. 
         FIG. 4  is a cross sectional view of the landing system of  FIG. 3  taken along the line  4 - 4  in  FIG. 3 . 
         FIG. 5   a  is a partially exploded perspective view of the landing system of  FIG. 3 . 
         FIG. 5   b  is a partially exploded perspective view of the upper and lower air chambers of the landing system shown in  FIG. 3 . 
         FIG. 6  is an exploded perspective view of the landing system of  FIG. 3 . 
         FIG. 7  is a partial cutaway view of the upper air chamber of the landing system of  FIG. 3  showing in an exemplary inner bulkhead. 
         FIG. 8   a  is a block diagram showing the air chamber inflation system of the landing system of the present invention. 
         FIG. 8   b  is a block diagram showing the air chamber deflation system of the landing system of the present invention. 
         FIG. 9   a  is a perspective view of the landing system of the present invention during taxi, partially cutaway to reveal a third air chamber bounded by the interior walls of the upper and lower air chambers when the air vehicle is on the ground. 
         FIG. 9   b  is a perspective view of the landing system of the present invention during suction, partially cutaway to reveal a third air chamber bounded by the interior walls of the upper and lower air chambers when the air vehicle is on the ground. 
         FIG. 10  is a schematic diagram of a dampening system for regulating pressure within the upper air chamber to ensure energy absorption upon air vehicle touchdown (landing). 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to  FIGS. 1-2 , the present invention  10  is a landing system for an air vehicle  1  with vertical takeoff and landing capabilities. The landing system  10  is designed to support landing, takeoff, taxiing, and ground stability through suction. The landing system is capable of absorbing ground impact during all modes of flight and ground taxiing operations. The landing system  10  of the present invention also supports landing on rough or uneven ground conditions and provides landing surface suction while stationary in order to secure the vehicle to the ground to resist the effects of wind conditions and any increased positive buoyancy (static lift) created by the unloading of cargo and/or passengers. Typically, the landing system will include a series of sets of landing chambers distributed to equally absorb the force of the vehicle during landing. 
     Referring now to  FIGS. 3-6 , and particularly to  FIGS. 5-6 , the landing system of the present invention  10  comprises a set of pressurized upper and lower air chambers  12  and  14 , respectively. The air chambers  12  and  14  are load bearing and are able to absorb the ground impact upon touchdown of the vehicle and are also able to support the vehicle&#39;s weight when parked. The upper  12  and lower  14  air chambers are in the form of an elongated torus, as shown in  FIG. 5   b  each is continuous having elongated right  16  and left  18  cylindrical center sections interconnected by semicircular sections  20  at each end. The upper chamber of the landing system  12  is connected by a catenary system attached to the air vehicle. The upper chamber has a series of patches  22  through which connectors are woven. These connecters serve as attachment points between the air vehicle and the landing system. 
     Both chambers are made from lightweight high density fabric  24  designed to withstand pressure and weather conditions. Suitable fabrics from which the air chambers may be constructed include any coated or laminated ultraviolet (“UV”) fabric such as polyester, nylon, vectran, or other fabrics known in the art. It is desirable that the fabric be coated on both sides with a UV light blocking coating for protection from degradation caused by UV light. Suitable UV light blocking coatings for fabrics are known in the art. 
     Referring to  FIG. 6 , in addition to the upper and lower air chambers  12  and  14 , the landing system of the present invention  10  includes a top cover  26 . The top cover  26  is bonded to a top surface  28  of the upper chamber  12 , intermediate the top surface and the under carriage of the air vehicle  1 . A debris shield  30  is similarly bonded to a bottom surface  32  of the upper air chamber. Likewise, the lower air chamber  14  also includes a debris shield  34  bonded to a top surface  36  of the lower air chamber  14 . When assembled, the debris shields sit one on top the other. The debris shields further include a plurality of air chamber ports  55 . Thus, when fully assembled the upper and lower air chambers sit directly one on top the other with the debris shields sandwiched in-between. 
     The top cover  26  and debris shields  30  and  34  are made of fabric material  24 , in the exemplary embodiment. It is desirable that a bottom surface  38  of the lower chamber  14  be coated with an abrasion resistant coating  40  to reduce wear on the bottom surface of the lower air chamber  14  during landings, takeoffs and taxiing maneuvers. Various polyurethane materials make suitable abrasion resistant coatings known to those of skill in the art. 
     With continued reference to  FIGS. 3-6 , an upper curtain  42  is bonded to an exterior radial surface  46  of the upper chamber  12 . Likewise, a lower curtain  44  is bonded to an exterior radial surface  48  of lower air chamber  14 . The upper and lower curtains  42  and  44  run continuously around the perimeter of the upper and lower air chambers  12  and  14 . The curtains are interconnected by tension cords  50  to both bind the upper and lower air chambers together and allow a degree of flexing between the upper and lower air chambers so as to prevent overstressing of the chambers. 
     Referring to  FIG. 7 , the upper chamber  12  may also include one or more internal dividers  52  that divide the upper chamber into semi-independent sections. The internal dividers serve as an added safety feature. In case one section of the upper chamber ruptures, the remaining sections prevent the chamber from completely collapsing. 
     Referring now  FIGS. 4 and 6 , the upper  12  and lower  14  air chambers are elongated torus-like structures and as such when assembled there exists a space interior of the air chambers that forms a third air chamber  56  when the air vehicle is in contact with the ground. The third air chamber  56  is bounded by the interior walls of the upper and lower air chambers  90  and  92 , respectively, the top cover  26  and the ground when the air vehicle is on the ground. By the use of at least one bi-directional blower assembly  80  (see  FIGS. 8   a  and  8   b ) suction can be created within the third air chamber  56  which assists the air vehicle in maintaining ground contact during high wind conditions or during passenger/cargo unloading (see  FIG. 9   b ). 
     Similarly, when the at least one blower assembly  80  is reversed, pressurized air may be blown into the third chamber  56  to assist the air vehicle in taxiing or achieving a vertical takeoff (see  FIG. 9   a ). The the top cover  26  of the upper chamber  12  includes one or more portholes  54  through which suction may be applied to the third chamber  56  by the at least one blower assembly  80  and likewise pressurized air can be blown into the chamber  56  by the at least one blower assembly  80 . The two debris shields  30  and  34  function to filter ground debris to prevent damage to the equipment during suction. 
     When the air vehicle  1  is in flight, the upper and lower air chambers  12  and  14  of the landing system  10  are deflated and retracted to reduce the air vehicle&#39;s profile thereby reducing the aerodynamic drag on the vehicle. During the landing decent, the upper and lower air chambers  12  and  14  are inflated. After landing, the volume of air in the lower chamber  14  is adjusted to closely fit the ground surface. Adjusting the air volume within the lower chamber  14  allows for maximum ground contact, i.e. creates the best seal with the ground, when the bi-directional blower assembly  80  is operating in suction mode. 
     Air Control System 
     The air control system of the landing system  10  of the present invention contains two independent blower systems. The inflation and deflation blower system ( FIGS. 8   a  and  8   b ) controls the inflation and deflation of the of the upper and lower air chambers  12  and  14  of the landing system  10  to allow expansion and retraction of the upper and lower air chambers  12  and  14  during takeoff and landing. A second, independent bi-directional blower system  80  controls pressurization and suction in the third air chamber  56 , i.e. the space in-between the upper and lower air chambers and the ground when the air vehicle has landed. 
     Referring to  FIGS. 8   a  and  8   b , a block diagram showing an exemplary embodiment of the air chamber inflation and deflation blower system  58  is shown. Those skilled in the art will understand that multiple blower systems maybe used depending upon the size and intended use of the air vehicle in which they are installed. The inflation and deflation blower assembly  58  comprises a motorized or engine driven blower motor  60  and a series of valves, i.e. external air intake valve  62 , an internal deflation valve  64 , an external air exhaust valve  66 , an internal inflation valve  68 , an upper chamber valve  70  and a lower chamber valve  72  that control the air direction in the system  58  and consequently allows for changes in air pressure inside the upper  12  and lower  14  air chambers. The blower  60  may be of any of several types including screw, Roots, Paxton, and piston type air pumps. In the exemplary embodiment, a twin screw pump is preferred. 
     The external air intake valve  62  and the external air exhaust valve  66  allow for the intake or exhaust of air from the external atmosphere. The internal deflation valve  64  and the internal inflation valve  68  control the direction of the internal air flow. The upper chamber valve  70  and lower chamber valve  72  regulate the flow of air into and out of the air chambers. The valve arrangement in the blower assembly  58  allows for a change in direction of air flow depending upon whether inflation or deflation of the upper and lower air  12  and  14  chambers is desired. 
     With reference to  FIG. 8   a , during inflation of the upper  12  and lower  14  air chambers, the external air intake valve  62  is open, the internal deflation valve  64  is closed, and the internal inflation valve  68  is open, while the external air exhaust valve  66  is closed. Both the upper chamber valve  70  and the lower chamber valve  72  are open which causes the upper  12  and lower  14  air chambers to inflate with air. Upon landing, both the upper  12  and lower  14  air chambers are fully inflated to absorb impact load caused by landing. After landing, air may be released from the lower chamber  14  via valve  72  to allow it to better form to the ground surface. Valves  70  and  72  may be open or closed independently as desired, to independently inflate or deflate the upper or lower air chambers  12  and  14 . 
     Air inlets and outlets  74  and  76  are in fluid communication with the upper and lower air chambers  12  and  14 , respectively. Means for connecting the air inlets and outlets with the upper and lower chambers are known to those of skill in the art. 
     With reference to  FIG. 8   b , during deflation, the external air intake valve  62  is closed, the internal deflation valve  64  is open, while and internal inflation valve  68  is closed, and the external air exhaust valve  66  is open. In this sequence of valve events, air is drawn from the upper and lower chambers  12  and  14  to allow for rapid deflation and retraction of the chambers. 
     Referring now to  FIGS. 9   a  and  9   b , at least one bidirectional air blower assembly  80  controls the internal pressure in the third air chamber  56 , i.e. the interior space in-between the upper  12  and lower  14  air chambers when the vehicle is on the ground. A variety of bi-directional air blowers are known to those skilled in the art. 
     Referring to  FIG. 9   a , in friction reduction mode, i.e. taxiing, the blower assembly  80  takes in external air and forces the airflow out through the air chamber ports  55  (see  FIG. 6 ). The pressure in the center chamber  56  is positive during the friction-reduction function, i.e. pressurized air is blown into the chamber  56  and such that the air escapes from underneath the lower air chamber  14 , creating slight additional positive buoyancy. This pressurized air outflow works as an air jet which allows the vehicle to taxi or be towed. Referring now to  FIG. 9   b , the opposite occurs during suction operation. The selectively reversible air blower pulls air out from the air chambers thereby creating a negative pressure in the center chamber  56  between the landing system and the ground surface. 
     During landing, a dampening system regulates pressure within the upper air chamber to ensure energy absorption and a safe touchdown. The dampening system also regulates the internal chamber pressure to keep pressure within acceptable structural limits. Referring to  FIG. 10 , during descent and as a precautionary measure during takeoff, an impact energy dissipater controller  90  uses the vehicle&#39;s inertial navigational system  88  to maintain appropriate pressure by opening and closing the internal inflation  68  and deflation  64  air valves. Appropriate pressure levels are maintained by a pressure regulator  92  and a pressure feedback sensor  94 . 
     Referring to  FIG. 3 , as a backup safety system to prevent overload of the upper air chamber  12 , a dampening system may contain safety valves  84  which open when the internal air chamber pressure exceeds the set maximum allowed pressure. The safety valves  84  close when the pressure returns to an acceptable level. 
     Referring to  FIG. 8   a , the control system may also contain compressed air reserve tanks  98  used to inflate the load bearing upper chamber during landing in cases where there is a loss of power causing the inflation/deflation air blowers to fail. The compressed air reserves are comprised of lightweight carbon fiber (or other lightweight composite) wrapped tanks filled with compressed air or other gas that may be used to inflate the load bearing chambers. 
     The foregoing detailed description and appended drawings are intended as a description of the presently preferred embodiment of the invention and are not intended to represent the only forms in which the present invention may be constructed and/or utilized. Those skilled in the art will understand that modifications and alternative embodiments of the present invention, which do not depart from the spirit and scope of the foregoing specification and drawings, and of the claims appended below, are possible and practical. It is intended that the claims cover all such modifications and alternative embodiments.