Abstract:
The invention is a hovercraft with multiple lift chambers which are operable independently of each other. Independently-operable pivot arm assemblies connect each lift chamber to the hovercraft main body, and his gives the hovercraft the ability to travel over uneven surfaces, traverse obstacles that would block conventional hovercrafts, and climb or descend even severe inclines. The hovercraft also includes side thrusters which allow it to maintain its vertical position on an incline while traveling laterally across the incline.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    Not Applicable. 
       BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The invention is in the area of hovercrafts. 
         [0004]    2. Description of the Related Art 
         [0005]    The prior art discloses various hovercrafts; however, none of these prior art devices exhibit the features of the present invention—that is, multiple, independently-operable lift chambers which enable the inventive hovercraft to surmount and overcome obstacles that block conventional hovercrafts. 
         [0006]    U.S. Pat. No. 7,931,239 to Pedersen discloses a hovercraft with two pairs of counter-rotating fans to generate lift. However, Pedersen&#39;s device has only a single lift chamber—not multiple, independently-operable lift chambers as in the invention. 
         [0007]    U.S. Pat. No. 7,748,486 to Mantych discloses a landing gear for a hovercraft. Self-leveling legs are used to accommodate landing the hovercraft on a sloped surface. However, the legs do not allow the lift chamber to be raised or lowered with respect to the hovercraft main body, as in the invention, nor does Mantych disclose multiple, independently-operable lift chambers. 
         [0008]    U.S. Design Pat. No. D564,046 to Hetman shows two air cushions for a toy hovercraft—but there is no disclosure that the toy actually operates—that is, blows air through the cushions to generate lift. And in any case, Hetman&#39;s air cushions are not movable, much less movable independently of each other as in the invention. 
         [0009]    U.S. Design Pat. No. D543,928 to Sanders, Jr. shows a hovercraft with a stacked rotor thruster and winglets. The Sanders, Jr. device does not show multiple, independently-operable lift chambers, as in the invention. 
         [0010]    U.S. Pat. No. 5,592,894 to Johnson discloses a “spidercraft” with four large tires and ground effect wings for planing over rough seas or rolling over rough terrain. However, it is definitely not a hovercraft, and uses significantly different technology than a hovercraft. There are no multiple, independently-operable lift chambers, as in the invention. Moreover, in his specification Johnson discusses hovercraft only in the context of pointing out their disadvantages—disadvantages that Johnson contends his spidercraft device overcomes. 
         [0011]    U.S. Pat. No. 5,522,470 to Stiegler discloses a hovercraft with two engines to drive forward movement and a trim compensator to direct the driving air jets and steer the hovercraft. However, there is only one fan to generate lift, and only one lift chamber—not multiple, independently-operable lift chambers as in the invention. 
         [0012]    U.S. Pat. No. 5,560,443 to DuBose discloses a hovercraft with a segmented skirt to reduce plowing. DuBose&#39;s device has only a single lift chamber, which is very different from the invention&#39;s multiple, independently-operable lift chambers. 
         [0013]    U.S. Pat. No. 5,377,775 to Rush discloses a combination hovercraft-motorcycle with wheels in front of and in back of the hovercraft section. However, in Rush&#39;s device the wheels are continuously operated, and cannot be raised and lowered to go in and out of service as in the invention. Also, Rush&#39;s hovercraft section has only a single lift chamber—not multiple, independently-operable lift chambers. 
         [0014]    U.S. Published Appl. No. 2004/0094662 by Sanders, Jr. discloses a hovercraft with the capability of taking off and landing vertically (VTOL). Sanders Jr.&#39;s device has only a single lift chamber—not multiple, independently-operable lift chambers as in the invention. 
         [0015]    U.S. Pat. No. 6,619,220 to Ducote discloses a hybrid SES (surface effect ship)/hovercraft having a retractable flexible skirt, so that the device can operate as a high speed SES on open water and as a hovercraft on land. Ducote&#39;s device has only a single lift chamber, which is very different from the invention&#39;s multiple, independently-operable lift chambers. 
         [0016]    U.S. Design Pat. No. D646,198 to Desberg shows a hovercraft with a single thruster to propel the craft forward, and steering vanes to control the direction of the thrust. The Desberg device does not show multiple, independently-operable lift chambers, as in the invention. 
         [0017]    U.S. Pat. No. 6,260,796 to Klingensmith discloses a multi-thrustered hovercraft—but it does not disclose or suggest not multiple, independently-operable lift chambers as in the invention. Instead, Klingensmith&#39;s multiple thrusters are just used for controlling the movement and direction of the hovercraft more effectively. 
         [0018]    U.S. Pat. No. 6,200,069 to Miller discloses a hovercraft that converts into a fixed work platform when it is in a desired position over water. As with the other devices discussed above, Miller&#39;s device has only a single lift chamber—not multiple, independently-operable lift chambers as in the invention. 
         [0019]    U.S. Pat. No. 4,984,754 to Yarrington discloses a hovercraft with a heli-rotor at its uppermost point for propelling the craft. However, Yarrington&#39;s device has only a single lift chamber—not multiple, independently-operable lift chambers as in the invention. 
         [0020]    U.S. Pat. No. 5,105,898 to Bixel, Jr. discloses a hovercraft ground effect vehicle that is capable of sustained flight. Bixel Jr.&#39;s device is not really a hovercraft but instead operates on ground effect principles. It does not have a lift chamber—much less multiple, independently-operable lift chambers as in the invention. 
         [0021]    U.S. Pat. No. 4,718,501 to Lawler discloses a self-trailering hovercraft with wheels that can be lowered to the ground. However, Lawler&#39;s device has only a single lift chamber, which is very different from the invention&#39;s multiple, independently-operable lift chambers. 
         [0022]    In sum, none of the prior art hovercrafts disclose or suggest the unique features and capabilities seen in the invention. 
       SUMMARY OF THE INVENTION 
       [0023]    The invention is a hovercraft with multiple lift chambers which are operable independently of each other. This gives the inventive hovercraft the ability to travel over uneven surfaces, traverse obstacles that would block conventional hovercrafts, and climb or descend even severe inclines. 
         [0024]    When the hovercraft approaches an obstacle—for example, a vertically-faced ridge or abutment—the forward chamber can be independently raised by hydraulic, motor, compressed, air, manual, or other suitable means, until it clears the obstacle. The other chambers, meanwhile, hover over the lower ground surface—i.e., the ground surface before the obstacle. The hovercraft is then moved forward until the second chamber encounters the obstacle. The second chamber is raised until it clears the obstacle; the hovercraft is moved further forward; and so on until the hovercraft has progressively “stepped” over the obstacle. 
         [0025]    The inventive hovercraft can also travel across an incline laterally without losing its vertical position (i.e., its “height”) on the incline. The hovercraft&#39;s unique ability of being able to maintain its vertical position while traveling laterally on an incline is due to its two side thrusters, one located at the bow and the other at the stern of the craft. The side thrusters can swivel, so that their thrust offsets the force of gravity acting on the hovercraft which would otherwise cause the craft to fall down the incline as it travels laterally across it. The side thrusters can also be tilted downward to create additional lift off the ground surface for the craft, when desired. 
         [0026]    The inventive hovercraft is propelled forward by two other main thrusters. These main thrusters can be turned through a 360 degree range. If the main thrusters are turned 180 degrees, this allows the craft to go backwards. The main thrusters can also be turned 90 degrees, i.e., so their thrust is directed downward, to create additional lift off the ground surface if desired. Each thruster can tilt/swivel independently of each other, thus allowing the craft to perform very tight maneuvers when required. 
         [0027]    In addition, the forward lift chamber and the rear lift chamber house wheels that are retractable. On a solid, relatively even surface such as a road, the retractable wheels can be lowered to the ground and the craft driven as a road vehicle. The forward and rear chambers may also house retractable hydrofoils that are retractable, so that on a relatively even water surface, the retractable hydrofoils can be lowered to the water and the craft driven as a hydrofoil. This saves fuel and extends the range of the hovercraft. 
         [0028]    The inventive hovercraft is thus completely versatile over all terrains—even those that include significant inclines or declines, as well as obstacles. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1  is a perspective view illustrating the main components of the hovercraft. 
           [0030]      FIG. 2  is a bottom view of the hovercraft, showing the interior of the lift chambers and the wheel assemblies. 
           [0031]      FIG. 3  is a side view of the hovercraft, with the wheels in the extended/down position. 
           [0032]      FIG. 4  is a front view of the hovercraft, corresponding to the wheels-down position shown in  FIG. 3 . 
           [0033]      FIG. 5  is a top view of the hovercraft. 
           [0034]      FIG. 6  is another perspective view of the hovercraft, with the main body, main and side thrusters, and frame omitted. 
           [0035]      FIG. 7  is a top view of the embodiment shown in  FIG. 5 . 
           [0036]      FIG. 8  is a side view of the embodiment shown in  FIG. 5 . 
           [0037]      FIG. 9  is a front view of the embodiment shown in  FIG. 5 . 
           [0038]      FIG. 10  is a side view of the hovercraft, illustrating the mechanisms which raise and lower the pivot arm assemblies and lift chambers. 
           [0039]      FIG. 11  illustrates the components that control the movements of the hovercraft. 
           [0040]      FIG. 12  shows the hovercraft approaching an obstacle that must be surmounted. 
           [0041]      FIG. 13  shows the hovercraft with the first lift chamber having surmounted the obstacle. 
           [0042]      FIG. 14  shows the hovercraft with the second lift chamber in the process of surmounting the obstacle. 
           [0043]      FIG. 15  shows the hovercraft with the first and second lift chambers having surmounted the obstacle. 
           [0044]      FIG. 16  shows the hovercraft with the first, second, and third lift chambers having surmounted the obstacle. 
           [0045]      FIG. 17  is a front view of the hovercraft traveling laterally across an inclined surface. 
           [0046]      FIG. 18  is a front view of a hovercraft embodiment with extendable/retractable hydrofoils. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0047]    The following provides a list of the reference characters used in the drawings:
         10 . Hovercraft     11 . Main body     12 . First lift chamber     13 . Second lift chamber     14 . Third lift chamber     15 . Blower     16 . Flexible skirt     17 . First pivot arm assembly     18 . Second pivot arm assembly     19 . Third pivot arm assembly     20 . Spring     21 . Linkage     22 . Main thrusters     23 . Frame     24 . Side thrusters     25 . Air duct     26 . Wheel assembly     27 . Wheel extension/retraction motor     28 . Stanchion     29 . Pivot arm motor     30 . Threaded rod     31 . Threaded fitting     32 . Obstacle     33 . Incline     34 . Central processor     35 . First accelerometer     36 . Second accelerometer     37 . Third accelerometer     38 . First gyroscope     39 . Second gyroscope     40 . Third gyroscope     41 . GPS     42 . Control module     43 . Power source     44 . Software     45 . Hydrofoil assembly     46 . Hydrofoil extension/retraction motor       
 
         [0085]      FIG. 1  is a perspective view illustrating the main components of the invention. The hovercraft  10  has a main body  11 , to which first lift chamber  12 , second lift chamber  13 , and third lift chamber  14  are attached. Each lift chamber has a blower  15  located thereon, and blower  15  uses blades turned by a motor to blow air down into the bottom of the lift chamber in order to generate lift. Blower  15  is shown as a “black box”, as it is a conventional blower seen in hovercrafts. Each lift chamber also has a flexible skirt  16  around the lower circumference thereof, in order to help seal the bottom of the lift chamber against the ground or other operating surface, and thus help seal in the air blown down into the bottom of the lift chamber by blower  15 . 
         [0086]    First lift chamber  12 , second lift chamber  13 , and third lift chamber  14  are attached to main body  11  by first pivot arm assembly  17 , second pivot arm assembly  18 , and third pivot arm assembly  19  respectively. Each pivot arm assembly is rotatably attached to main body  11 , such that it can pivot up or down thus raising or lowering its attached lift chamber. Springs  18  are connected between the pivot arm assemblies and lift chambers, which allows the lift chambers to move up and down when encountering unevenness in the ground or other operating surface while the spring keeps tension against the surface. Linkages  21  also connect the pivot arm assemblies to the lift chambers, serving to further control and stabilize lift chamber movement. Springs  20  and linkages  21  are provided with swivel end fittings, so that first lift chamber  12 , second lift chamber  13 , and third lift chamber  14  are still able to swivel when uneven operating surface conditions are encountered. That is, the lift chambers can rotate so that their back end is higher or lower than their front end, and/or one side is higher or lower than the other side, in a manner similar to the movement indicated by the illustrative arrows in  FIG. 6 . 
         [0087]    Main thrusters  22  are attached to main body  11  by a frame  23 . The main thrusters operate via motor-driven blades, and provide forward movement for hovercraft  10 . Main thrusters  22  are rotatable on their mountings, to provide thrust in other directions including pointed up to provide additional lift, or pointing down if desired. Main thrusters  22  can also be rotated 180 degrees, in order to provide reverse thrust and move hovercraft  10  backward. Said another way, although the main thrusters in this view are pointed to provide forward movement as indicated by the illustrative arrow, they can be rotated 180 degrees to provide backward movement, in the direction opposite from the arrow. 
         [0088]    Side thrusters  24  are also attached to main body  11  by frame  23 . The side thrusters have motor-driven blades which provide thrust to counter the force of gravity when hovercraft  10  is traveling laterally across an inclined surface, and maintain the vertical position of hovercraft  10  on the inclined surface. Side thrusters  24  are rotatable on their mountings, so that they can provide thrust in the opposite sideways direction when pointed in that direction, and can provide additional upward thrust/lift when pointed downward. Side thrusters  24  also incorporate variable-pitch blades, and thus the blade pitch can be reversed to provide thrust in the opposite sideways direction without having to rotate the side thruster on its mounting. Side thrusters  24  are located along the front-to-rear centerline of hovercraft  10 , in order to minimize the torque steer impact on forward and reverse hovercraft movement when the side thrusters are operating. 
         [0089]      FIG. 2  is a bottom view of the hovercraft, showing the interior of the lift chambers and the wheel assemblies. Flexible skirts  16  extend around the bottom of the lift chambers, and each lift chamber contains an air duct  25  which conducts air from blower  15  into the interior of the lift chamber. Wheel assemblies  26 , each comprising two wheels and an axle therebetween, are located in the interior of first lift chamber  12  and third lift chamber  14 . Via wheel extension/retraction motors  27  or hydraulic, manual, or other suitable means, wheel assemblies  26  can be lowered to the ground or other operating surface when such surface is suitably smooth, to enable the hovercraft to ride on wheels instead of a cushion of air. Wheel assemblies  26  are retracted when not in use, also via wheel extension/retraction motors  27  or hydraulic, manual, or other suitable means. The wheels in wheel assemblies  26  are steerable, to enable the hovercraft to change direction when riding on wheels instead of air. The hovercraft may also of course be “steered” in wheels-extended mode by varying the thrust of one main thruster  22  versus the other main thruster  22 . 
         [0090]      FIG. 3  is a side view of the hovercraft. In this view, wheel assemblies  26  are in the extended/down position. 
         [0091]      FIG. 4  is a front view of the hovercraft, also with wheel assemblies  26  in the extended/down position. Note that in  FIG. 4 , side thruster  24  has been rotated 180 degrees, so it is pointed in the opposite direction from that shown in  FIGS. 1 and 3 .  FIG. 5  is a top view of the hovercraft. 
         [0092]      FIG. 6  is another perspective view of the hovercraft, with main body  11 , main thrusters  22 , side thrusters  24 , and frame  23  omitted in order to show the structure of pivot assemblies  17 ,  18 , and  19  more clearly. In the embodiment shown in this view, there are no springs on second lift chamber  13 . As discussed above, each lift chamber can rotate so that its back end is higher or lower than its front end, and/or one side is higher or lower than the other side—as indicated by the illustrative arrows next to first lift chamber  12 . 
         [0093]      FIG. 7  is a top view of the embodiment shown in  FIG. 6 , showing the three lift chambers, pivot assemblies, and linkages. 
         [0094]      FIG. 8  is a side view of the embodiment shown in  FIG. 6 , with the wheels in the retracted/up position. 
         [0095]      FIG. 9  is a front view of the embodiment shown in  FIG. 6 , also with the wheels in the retracted/up position. 
         [0096]      FIG. 10  is a side view of the hovercraft, illustrating in particular the mechanisms which raise and lower the pivot arm assemblies and thus the lift chambers. In this view, the main thrusters  22 , side thrusters  24 , and frame  23  have been omitted, in order to show the raising/lowering mechanisms more clearly. Also, in this view the wheels are in the retracted/up position. 
         [0097]    A stanchion  28  extends upward and outward from the forward edge of main body  11 . A pivot arm motor  29  is located on stanchion  28 . Threaded rod  30  is fixed at its upper end to the output shaft of pivot arm motor  29 , passes through an opening in the bottom of stanchion  28 , and then threads into and through a correspondingly threaded fitting  31  attached to first pivot arm assembly  17 . When pivot arm motor  29  turns threaded rod  30  in one direction, threaded fitting  31  moves upward on threaded rod  30 , thereby moving first pivot arm assembly  17  upward toward stanchion  28 . Conversely, when pivot arm motor  29  turns threaded rod  30  in the other direction, threaded fitting  31  moves downward on threaded rod  30 , thereby moving first pivot arm assembly  17  downward away from stanchion  28 . The upward and downward movement of threaded fitting  31 , and thus first pivot arm assembly  17 , is indicated by the arrow. Threaded fitting  31  is rotatably attached to first pivot arm assembly  17 , which prevents threaded fitting  31  from binding on threaded rod  30  as it and first pivot arm assembly  17  move upward and downward—i.e., toward and away from stanchion  28 . 
         [0098]    Similarly, another stanchion  28  extends outward from the side edge of main body  11 . A pivot arm motor  29  is located on stanchion  28 . Threaded rod  30  is fixed at its upper end to the output shaft of pivot arm motor  29 , passes through an opening in the bottom of stanchion  28 , and then threads into and through a correspondingly threaded fitting  31  attached to second pivot arm assembly  18 . When pivot arm motor  29  turns threaded rod  30  in one direction, threaded fitting  31  moves upward on threaded rod  30 , thereby moving second pivot arm assembly  18  upward toward stanchion  28 . Conversely, when pivot arm motor  29  turns threaded rod  30  in the other direction, threaded fitting  31  moves downward on threaded rod  30 , thereby moving second pivot arm assembly  18  downward away from stanchion  28 . The upward and downward movement of threaded fitting  31 , and thus second pivot arm assembly  18 , is indicated by the arrow. Threaded fitting  31  is rotatably attached to second pivot arm assembly  18 , which prevents threaded fitting  31  from binding on threaded rod  30  as it and second pivot arm assembly  18  move upward and downward—i.e., toward and away from stanchion  28 . 
         [0099]    Similarly, another stanchion  28  extends upward and outward from the back edge of main body  11 . A pivot arm motor  29  is located on stanchion  28 . Threaded rod  30  is fixed at its upper end to the output shaft of pivot arm motor  29 , passes through an opening in the bottom of stanchion  28 , and then threads into and through a correspondingly threaded fitting  31  attached to third pivot arm assembly  19 . When pivot arm motor  29  turns threaded rod  30  in one direction, threaded fitting  31  moves upward on threaded rod  30 , thereby moving third pivot arm assembly  19  upward toward stanchion  28 . Conversely, when pivot arm motor  29  turns threaded rod  30  in the other direction, threaded fitting  31  moves downward on threaded rod  30 , thereby moving third pivot arm assembly  19  downward away from stanchion  28 . The upward and downward movement of threaded fitting  31 , and thus third pivot arm assembly  19 , is indicated by the arrow. Threaded fitting  31  is rotatably attached to third pivot arm assembly  19 , which prevents threaded fitting  31  from binding on threaded rod  30  as it and third pivot arm assembly  19  move upward and downward—i.e., toward and away from stanchion  28 . 
         [0100]    As shown in  FIG. 11 , main body  11  contains the components that power and control the movements of the hovercraft. A central processor  34 , which can be a microprocessor or other computer, is operatively connected to each blower  15 , each main thruster  22 , each side thruster  24 , each pivot arm motor  29 , each wheel extension/retraction motor  27 , and each hydrofoil extension/retraction motor  46 . Central processor  34  is connected to these components in the ways commonly known in the art, such that the speed and air output of each blower can be independently controlled; the speed, thrust, and rotation (i.e., the angle or direction of thrust) of each main thruster can be independently controlled; the speed, thrust, and rotation (i.e., the angle or direction of thrust) of each side thruster can be independently controlled; each pivot arm motor and thus each pivot arm assembly can be independently controlled; and each wheel extension/retraction motor can be independently controlled. 
         [0101]    It should be understood that although the aforementioned components can be independently controlled, there may be situations wherein it is desirable to run the components at a similar speed, thrust, rotation angle, etc. By way of non-limiting example, there can be situations wherein it is desirable to run a particular blower at a lower speed to generate less air output, and there may be situations wherein it is desirable to run all the blowers at the same speed to generate the same air output and lift. As another non-limiting example, there can be situations wherein it is desirable to run both side thrusters at the same speed to minimize any “torque steer” imparted to the hovercraft, and there may be situations wherein it is desirable to run one side thruster at a different speed (or rotation/thrust angle) than the other side thruster. 
         [0102]    Central processor  34  is also operatively connected, in the ways commonly known in the art, to a series of sensors that provide information about the position and change in position, velocity, and acceleration of the hovercraft. Central processor  34  is operatively connected to first accelerometer  35 , which measures the change in position of the hovercraft along the “x” axis, which for convention&#39;s sake will be considered to be a line running through the center of main body  11  from front to rear. Central processor  34  is also operatively connected to second accelerometer  36 , which measures the change in position of the hovercraft along the “y” axis, which for convention&#39;s sake will be considered to be a line running through the center of main body  11  from side to side. And central processor  34  is operatively connected to third accelerometer  37 , which measures the change in position of the hovercraft along the “z” axis, which for convention&#39;s sake will be considered to be a line running through the center of main body  11  from top to bottom. The accelerometers also measure the rate of change in position (velocity) along the respective axes, and the acceleration along the respective axes. 
         [0103]    Central processor  34  is also operatively connected to first gyroscope  38 , which measures the roll angle of the hovercraft—i.e., its angle of rotation about the roll (“x”) axis running from front to rear of the hovercraft; to second gyroscope  39 , which measures the pitch angle of the hovercraft—i.e., its angle of rotation up or down about the pitch (“y”) axis running from side to side of the hovercraft; and to third gyroscope  40 , which measures the yaw angle of the hovercraft—i.e., its angle of rotation left or right about the yaw (“z”) axis running from top to bottom of the hovercraft. 
         [0104]    Central processor  34  receives the feedback from these accelerometers and gyroscopes, and thus can tell the position of the hovercraft at any given time as well as the change in that position occurring from various forces acting on the hovercraft, including gravity when the hovercraft is traveling up, down, or laterally across an incline. Central processor  34  also accounts for the shifts in the hovercraft&#39;s center of gravity that result from the raising and lowering of the lift chambers. Central processor  34  can optionally be operatively connected to a Global Positioning System (GPS), which can detect the position and change in position of the hovercraft, and which can substitute for or supplement the feedback from the gyroscopes and accelerometers. 
         [0105]    A control module  42  is connected to central processor  34 , and via central processor  34  the hovercraft operator can increase or decrease the speed of blowers  15 ; increase or decrease the thrust of main thrusters  22  and side thrusters  24  and rotate them to change their thrust angle; operate pivot arm motors  29  to raise or lower pivot arm assemblies  17 ,  18 , and  19 ; and extend or retract wheel assemblies  26  or hydrofoil assemblies  45 ; The hovercraft operator can operate these components independently if desired or operate them in conjunction with one another, as discussed above. 
         [0106]    Main body  11  also contains a power source  43  which is used to power the various components of the hovercraft. All the power connections are not shown in  FIG. 11 , but it should be understood that power source  43  is operatively connected to central processor  34  and all other control or sensor components that require power, as well as to the blowers, main and side thrusters, pivot arm motors, wheel extension/retraction motors, and hydrofoil extension/retraction motors. 
         [0107]    Software  44  resides on central processor  34 . This software is of the kind known in the aircraft control art, particularly the helicopter control art, but has not been previously used to control hovercrafts. For example, circuit boards and software are available from KapteinKUK, also known as KKmulticopter; and also from MultiWii, an open source software project. Absent any input from the operator, the software will use the inputs from accelerometers  35 - 37  and gyroscopes  38 - 40  (and optionally from GPS  41 ) and automatically operate main thrusters  22  and side thrusters  24  to counteract any forces acting on the hovercraft from gravity or any other source, and keep the hovercraft in a steady position even if it is, for example, on an uphill or downhill slope. When the hovercraft operator signals via control module  42  that forward, backward, and/or side thrust is desired to move or steer the hovercraft in a certain direction, software  44  will execute those operator commands, while also taking into account any forces acting on the hovercraft from sources other than the operator. Thus the hovercraft moves in the direction desired by the operator in a smooth, accurate, and stable manner. 
         [0108]    A notable achievement of the invention is that when the hovercraft is proceeding down a road, hovering above the road, and the road then turns or curves, the inventive hovercraft avoids the “slip” that conventional hovercrafts experience when the operator wishes to change the yaw angle—i.e., steer—to follow the turning or curving road. This slip is due to the forward momentum of the hovercraft in the original direction, which serves to impede a smooth and accurate change in that original direction. Specifically, the hovercraft&#39;s forward momentum causes it to understeer, and swing wide of (go past) the turn or curve in the road. The inventive hovercraft avoids this problem, because its accelerometers and gyroscopes detect the slip and the central processor automatically adjusts for it—for example, by applying more power to the main/forward thruster that is on the outside of the curve, and/or by pointing the side thrusters toward the outside of the curve, to counteract the hovercraft&#39;s forward momentum. This improved control applies of course not just when the hovercraft is traveling over a road, but also when the hovercraft is traveling over any surface and the operator wishes to change direction in a smooth, accurate, and stable manner. 
         [0109]      FIGS. 12-16  illustrate how the hovercraft surmounts an obstacle that is encountered. The hovercraft&#39;s direction of travel is indicated by the arrow in these figures. The mechanisms that raise and lower the pivot arm assemblies are not shown in these figures; however, it is apparent from  FIG. 10  and the foregoing description how the pivot arm assemblies are raised and lowered. Also, for ease of illustration, the full length of obstacle  32  is not shown in  FIGS. 12-14 , but will be apparent from  FIGS. 15 and 16 . 
         [0110]    Specifically,  FIG. 12  shows hovercraft  10  approaching obstacle  32 . First pivot arm assembly  17 , second pivot arm assembly  18 , and third pivot arm assembly  19 —and accordingly, first lift chamber  12 , second lift chamber  13 , and third lift chamber  14 —are all in the lowered/down position typically used when hovercraft  10  is traveling across a relatively smooth, obstacle-free surface. Optionally, side thrusters  24  are rotated to point downward, thus supplying extra lift (upward thrust) to the hovercraft. As hovercraft  10  approaches obstacle  32 , first pivot arm assembly  17  is raised until the bottom of flexible skirt  16  on first lift chamber  12  clears the front edge of obstacle  32 . Hovercraft  10  is then moved forward until the position shown in  FIG. 13  is achieved—i.e., first lift chamber  12  having surmounted obstacle  32 . It can be appreciated that the hovercraft&#39;s center of gravity shifts as the lift chambers are raised and lowered, and at this point, the hovercraft&#39;s center of gravity is behind second lift chamber  13 . 
         [0111]    As hovercraft  10  continues further toward obstacle  32 , second pivot arm assembly  18  begins to be raised, as shown in  FIG. 14 . When the bottom of flexible skirt  16  on second lift chamber  13  clears the front edge of obstacle  32 , hovercraft  10  is then moved forward until the position shown in  FIG. 15  is achieved—i.e., first lift chamber  12  and second lift chamber  13  both having surmounted obstacle  32 . At this point, the hovercraft&#39;s center of gravity has shifted forward, and is now on first lift chamber  12  and second lift chamber  13 . 
         [0112]    As hovercraft  10  continues further toward obstacle  32 , third pivot arm assembly  19  is similarly raised until the bottom of flexible skirt  16  on third lift chamber  14  clears the front edge of obstacle  32 . Hovercraft  10  is then moved forward until the position shown in  FIG. 16  is achieved—i.e., first lift chamber  12 , second lift chamber  13 , and third lift chamber  14  all having surmounted obstacle  32 . Side thrusters  24  are rotated back to a side-pointing position in  FIGS. 14 and 15 .  FIG. 16  shows first pivot arm assembly  17 , second pivot arm assembly  18 , and third pivot arm assembly  19  in the raised/up position; however, it can be appreciated that once all the lift chambers have surmounted the obstacle, the pivot arm assemblies can be lowered which would effectively raise the height of main body  11  from the ground or other operating surface. 
         [0113]    If the obstacle continues, such as in a situation where there is a permanent change in ground elevation, then hovercraft  10  can continue moving forward with the pivot arm assemblies in the raised/up position, or the pivot arm assemblies can be lowered before proceeding. If the obstacle is a wall, short ridge, or other impediment that does not continue, then for hovercraft  10  to climb down from the obstacle, the steps are basically reversed. That is, hovercraft  10  is progressively moved forward while first pivot arm assembly  17 , second pivot arm assembly  18 , and third pivot arm assembly  19  are each lowered in turn, until hovercraft  10  is resting on the surface past obstacle  32 . 
         [0114]      FIG. 17  is a front view of the hovercraft traveling laterally across an incline  33 . That is, hovercraft  10  is coming towards the viewer in this figure. Side thruster  24  is pointed to the downside of hovercraft  10 —that is, down the incline—in order to provide countering thrust to offset the natural force of gravity which would otherwise cause hovercraft  10  to slide down incline  33  as hovercraft  10  travels laterally across incline  33 . Said another way, the counterthrust from side thruster  24  allows hovercraft  10  to maintain its vertical position on incline  33  as it travels laterally across incline  33 . It should be noted that side thruster  24  can be rotated to a different degree than that shown in this view—for example, to point more directly or less directly at the lower portion of incline  33  or level ground which may be at the bottom of incline  33 . 
         [0115]    Although only the side thruster  24  at the fore of hovercraft  10  can be seen in this view, it should be understood that the side thruster  24  at the rear of hovercraft  24  can also provide counterthrust against the force of gravity. In sum, one or both side thrusters can be employed, at varying degrees of power/thrust, depending on the severity of incline  33 . If only one side thruster  24  is employed, or if both side thrusters  24  are employed but at different thrust levels, that will rotate hovercraft  10  somewhat about its center, which will impart a steering effect as hovercraft  10  moves laterally across incline  33 . 
         [0116]    Also, in this view one of the main thrusters  22  is rotated to point downward toward the surface of incline  33 , which has the effect of pulling that side of hovercraft  10  toward the surface of incline  33  thus helping to prevent blower air from escaping under flexible skirt  16 . 
         [0117]      FIG. 18  is a front view of a hovercraft embodiment with extendable/retractable hydrofoil assemblies  45  located at the bottom of first lift chamber  12  and third lift chamber  14 , in the interior thereof. Via hydrofoil extension/retraction motors  46  or hydraulic, manual, or other suitable means, hydrofoil assemblies  45  can be lowered to a water surface when such surface is suitably smooth, to enable the hovercraft to ride on the hydrofoils instead of a cushion of air. Hydrofoil assemblies  45  are retracted when not in use, also via hydrofoil extension/retraction motors  46  or hydraulic, manual, or other suitable means. The hydrofoils in hydrofoil assemblies  45  are steerable, to enable the hovercraft to change direction when riding on hydrofoils instead of air. The hovercraft may also of course be “steered” in hydrofoils-extended mode by varying the thrust of one main thruster  22  versus the other main thruster  22 . 
         [0118]    While the above descriptions contain many specificities, these shall not be construed as limitations on the scope of the invention, but rather as exemplifications of embodiments thereof. Many other variations are possible without departing from the spirit of the invention. Examples of just a few of the possible variations follow: 
         [0119]    The raising and lowering of the lift chambers can be initiated and controlled by the hovercraft operator, or can be automatically initiated and controlled by the central processor via sensors connected thereto that detect when the hovercraft is approaching an obstacle, detect the height and breadth of the obstacle. The central processor can then determine and execute the appropriate lift chambers movements based on the sensor information. 
         [0120]    The hovercraft can optionally include devices to provide driving power to the wheel assemblies, to substitute for or supplement the driving thrust provided by the main thrusters. 
         [0121]    The power source can employ any suitable power technology—by way of non-limiting example, battery, solar, other electric, internal combustion or other fossil fuel, steam, nuclear, etc. can be used. 
         [0122]    It should be understood that relays and other electrical circuitry are included as necessary for the power and control connections between components, as known in the prior art. 
         [0123]    The size and scale of the hovercraft can be different than that shown—i.e., it can be large enough to carry a person or multiple persons, as well as cargo. 
         [0124]    The power and control connections between components can be wired or wireless, using any suitable known technology. 
         [0125]    It should understood that the position of each pivot arm assembly and its associated lift chamber relative to the hovercraft main body can change as the hovercraft proceeds to surmount an obstacle—and to accomplish this, the pivot arm assemblies are raised or lowered accordingly, using the raising/lowering mechanisms shown in  FIG. 10  and described above. Said another way, while for clarity the raising/lowering mechanisms are not shown in  FIGS. 12-16 , it should be understood that the raising/lowering mechanisms are effecting the position changes of the pivot arm assemblies in those figures. 
         [0126]    The hovercraft can have more or fewer lift chambers, as long as there are sufficient independently-operable lift chambers to allow the hovercraft to surmount an obstacle. 
         [0127]    The hovercraft can contain both wheel assemblies and hydrofoil assemblies, instead of one or the other as shown in the figures. In the case of wheel assemblies and hydrofoil assemblies both being present, they can be extended and retracted independently depending on the desired running condition. 
         [0128]    The main and side thrusters can be mounted in different locations than those shown—by way of non-limiting example, they can be mounted on an extension to the main body instead of on the main body or a frame connected thereto. 
         [0129]    The pivot arm assemblies can have different configurations and constructions than those shown in the figures. In addition, the action of the second (center) pivot arm can be “tied” to the action of the first (front) pivot arm assembly and/or the third (rear) pivot arm assembly via additional brackets, such that moving the first and/or third pivot arm (and their respective lift chambers) in one direction causes the second pivot arm assembly (and its lift chamber) to move in the opposite direction. In other words, raising the first and/or third pivot arm causes the second pivot arm assembly to lower, and vice-versa. 
         [0130]    The hydrofoils can be differently-shaped and differently-sized than those shown in  FIG. 18 . As a non-limiting example, the hydrofoils can be the fully-submerged type rather than the surface-piercing type that is shown. 
         [0131]    The flexible skirts can be retracted when the wheels or hydrofoils are deployed, to ensure that they would not scrape against the running surface. 
         [0132]    Different means to raise and lower the pivot arm assemblies and thus the lift chambers can be used—as non-limiting examples, hydraulic or pneumatic/compressed air means can be used instead of the electric motor-driven mechanisms shown in  FIG. 10 . The pivot arm assemblies and lift chambers can even be manually lifted by the operator or an assistant. 
         [0133]    While the central processor and the software residing thereon allows for automatic control of the functions discussed above, it should be understood that the functions done by the control processor and software can also be done manually—i.e., by human control. 
         [0134]    Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.