Abstract:
An aircraft is provided having an inflatable parafoil canopy wing and a suspended fuselage. The wing is constructed such that, when inflated, it has an airfoil configuration having leading and trailing edges, thereby producing lift by interaction with air encountered by the leading edge. A central compartment confines a buoyant gas which causes the total volume of the wing to be varied in response to the degree of inflation with the buoyant gas. With sufficient inflation, the aircraft is capable of vertical take-off and landing (VTOL).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to parafoil aircraft, and more particularly concerns parafoil aircraft having a parafoil canopy that is inflated with lighter-than-air gas to a degree that provides vertical takeoff and landing (VTOL) capability. 
     2. Description of the Prior Art 
     A parafoil is a flexible structure made of lightweight fabric or similar material having a shape similar to an airplane wing or airfoil. 
     Aircraft using parafoils to generate lift are well known. Inflatable parafoils are also known. U.S. Pat. Nos. 4,934,630; 4,860,970; 4,557,439 and 4,424,945 describe parafoils that are inflated during flight by air rammed into apertures generally located at the leading edge of the parafoil. They do not use lighter-than-air gas for inflation, and they do not have VTOL capability. 
     U.S. Pat. No. 5,620,153 describes a parafoil canopy which is inflated with buoyant gas such as heated air or helium so as to provide at least partial lift. It does not describe a VTOL aircraft. 
     U.S. Pat. No. 5,005,783 describes a variable geometry airship that is essentially a dirigible balloon equipped with retractable inflatable wings so that it can also be flown like an airplane. 
     U.S. Pat. No. 5,090,637 discloses a helium purification system for lighter-than-air aircraft aimed mainly at removing oxygen and nitrogen when mixed with the helium in the aerostat to improve lift. The catalytic system described generates heat as a by-product which generates additional lift by heating the lift gas. It does not describe controlled variation of the displacement volume of the aircraft itself as a means for controlling lift, nor does it describe a parafoil aircraft in general or a VTOL parafoil aircraft in particular. 
     It may be seen that the prior art does not describe a VTOL parafoil aircraft wherein buoyancy is controlled by varying the outer envelope volume of the parafoil by use of a lighter-than-air inflating gas. A further drawback of current parafoil wings is that as horizontal speed increases, the parafoil canopy will lag further and further behind the suspended passenger module, and tends to function more as a drag chute than an airfoil wing. Like a drag chute, present parafoils tend to develop a downwardly directed concavity in their undersurface during flight. Such concavity entraps air and causes considerable drag. 
     It is accordingly a primary object of this invention to provide a parafoil aircraft with VTOL and hovering capability. 
     Another object of the present invention is to provide a parafoil wing capable of maintaining a streamlined shape and smooth surface with low drag and high aerodynamic efficiency suitable for cruising at higher speeds. 
     A further object of this invention is to provide a VTOL aircraft that can be manufactured easily and inexpensively and can be operated simply, safely and economically. 
     These objects and other objects and advantages of the invention will be apparent from the following description. 
     SUMMARY OF THE INVENTION 
     The above and other beneficial objects and advantages are accomplished in accordance with the present invention by an aircraft comprising a parafoil wing which, when fully inflated with buoyant gas, will generate sufficient lift to permit vertical takeoff, and when partially deflated will enable the aircraft to hover or make a slow and controlled vertical descent and landing. 
     The buoyant gas is deployed in three sets of independently inflatable compartments, namely, an upper compartment disposed on the entire upper surface of the parafoil, a lower compartment disposed on the entire lower surface, and a control, third variably inflatable compartment between the two. The upper and lower compartments are kept constantly tautly inflated so as to present a smooth external surface to the parafoil and give it a more defined and less deformable airfoil shape. 
     Chordwise stiffening ribs are placed at regular intervals from the leading edge to the trailing edge to prevent or diminish concave deformity of the undersurface, thereby diminishing drag and improving lift. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing forming a part of this specification and in which similar numerals of reference indicate corresponding parts in all the figures of the drawing: 
     FIG. 1 is a top view of an embodiment of the aircraft of the present invention, with portions broken away to reveal interior details. 
     FIG. 2 is a front view along line  2 - 2 ′ of FIG.  1 . 
     FIG. 3 is a sectional view taken in the direction of the arrows along line  3 - 3 ′ of FIG.  1 . 
     FIG. 4 is a sectional view along line  4 - 4 ′ of FIG.  1 . 
     FIG. 5 is a sectional view along line  5 - 5 ′ of FIG.  1 . 
     FIG. 6 is a view similar to FIG. 5 showing the aircraft during vertical ascent. 
     FIG. 7 is a view similar to FIG. 5 showing the aircraft during vertical descent. 
     FIG. 8 is a view similar to FIG. 5 showing the aircraft during forward flight. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIGS. 1-8, an aircraft  51  of the present invention is shown comprised of fuselage  36  suspended below an inflatable parafoil  10 . Said fuselage has a passenger seat or module  41 , an engine  29 , gas handling components, and control features. 
     Said parafoil, fabricated of strong, lightweight airtight material, has a leading edge  12 , trailing edge  13 , right edge  14 , left edge  15 , upper layer  16 , lower layer  21 , upper intermediate layer  17 , and lower intermediate layer  18 . Upper layer  16  and upper intermediate layer  17  enclose upper lift compartment  19 , designed to be inflated with lighter-than-air gas such as helium. Compartment  19  is configured such that, when inflated, it causes upper layer  16  to constitute the upper surface of the airfoil. 
     Lower intermediate layer  18  and lower layer  21  enclose lift compartment  22  designed to be inflated with lighter-than-air gas such as helium, and are configured so that, when fully inflated, lower layer  21  constitutes the lower surface of the airfoil. To achieve the desired structural shape and rigidity, lift compartments  19  and  22  are divided by partitions  23  into an array of parallel individual chambers  31  extending longitudinally between said leading and trailing edges. This rigidity is augmented by stiffening ribs  49  integrated into the structure of partitions  23 . The front and rear ends of stiffening ribs  49  are preferably secured to front and rear shroud lines  37 . 
     Upper intermediate layer  17  and lower intermediate layer  18  enclose central compartment  24  which is likewise designed to be filled with lighter-than-air gas. Means are provided for heating and cooling the gas in central compartment  24 . The gas expands when it is heated, thereby increasing the volume of compartment  24 , and increasing the total displacement volume of the parafoil  10 . This results in increased buoyancy and lift. When the gas is cooled, it contracts, thereby reducing the volume of compartment  24  and decreasing the total displacement volume of the parafoil  10 , resulting in decreased buoyancy and lift. 
     Various means can be used to heat and cool the lift gas. For example, the gas could be ducted past the hot external surfaces of the exhaust manifold, cylinders and cylinder heads of the engine, and ducted back to the parafoil, thus utilizing heat that would otherwise be wasted. 
     The embodiment illustrated in the accompanying drawings uses an electric heater  30  with a ducted fan  25  and heating elements  26  disposed within the parafoil  10  itself as shown in FIGS. 1,  3 ,  5 ,  6 ,  7  and  8 . The ducted fan  25  is powered by electric generator  28  coupled to engine  29 , and may be switched on or off by the operator at will. The heating elements  26  can be turned on only when the fan  25  is running, for safety purposes. 
     The embodiment uses the most medially located chamber  31  of upper lift compartment  19  to house the heater  30 . Chamber  31  opens to central compartment  24  near both leading and trailing edge to permit free circulation of the lift gas between chamber  31  and compartment  24 , especially when ducted fan  25  is in operation. 
     To the rear of heater  30 , chamber  31  is further divided into upper gas passage  32  and lower gas passage  33  by a horizontal partition  34  at whose front edge is disposed a two-way valve  35 . Said valve can be swiveled upward to shut off upper gas passage  32 , as shown in FIG. 6, or downward to shut off lower gas passage  33 , as shown in FIG. 7, or adjusted to a half-way position to keep both passages  32  and  33  open, as shown in FIGS. 5 and 8. 
     The fuselage  36  is suspended beneath the parafoil  10  by shroud lines  37 , and risers  38 . Disposed on the fuselage  36  are an engine  29  with propeller  40 , a pilot&#39;s seat  41 , aircraft type steering assembly  42  and landing wheels  43 . Coupled to the engine  29  are an electric generator  28  and a gas compressor  44  with associated lift gas storage tank  45  and gas line  46  for transferring gas from the storage tank  45  to the parafoil  10  and from the parafoil  10  to the storage tank  45  after being compressed by compressor  44 . 
     To operate the aircraft, upper and lower compartments  19  and  22 , respectively, are fully inflated with a suitable lift gas, such as helium. Lift gas storage tank  45  is filled with compressed lift gas, and central compartment  24  is inflated until the aircraft attains near neutral buoyancy, preferably making allowances for the loss of the weight of fuel as the fuel is being consumed by said engine during the operation of the aircraft. 
     To take off vertically, gas heater fan  25  and heating element  26  are turned on. Two-way valve  35  is swiveled to the upward position and lift gas is then heated and circulated into central compartment  24  as shown by the arrows in FIG.  6 . The expanding heated gas increases the volume of compartment  24  until the buoyancy of parafoil  10  exceeds the weight of the aircraft to the point where vertical take off is attained. Additional buoyancy can also be gained by releasing helium lift gas from storage tank  45  through gas line  46  into central compartment  24  for added displacement volume. 
     When the desired altitude is reached, the propeller  40  is engaged for horizontal flight. As forward speed increases, the aircraft gains increased aerodynamic lift. It will then be possible, if desired, to partially deflate central compartment  24  and still maintain flight altitude through a combination of aerodynamic lift and buoyant lift. This may be particularly advantageous because it avoids any unwanted increase in altitude and may reduce drag by making the airfoil  10  less bulky and more streamlined in shape. Such status prepares the aircraft for landing procedures. Additional measures can be made to reduce drag during horizontal flight, namely shortening the front risers  381  and lengthening the rear risers  382 . Such expedient, as shown in FIG. 8, has the effect of reducing the parafoil&#39;s angle of attack, thus reducing aerodynamic drag. Stiffening ribs  49  associated with partitions  23  serve to reduce the formation of a deep concavity in the undersurface of the parafoil  10 , reducing the entrapment of air therein and thereby reducing drag. 
     To hover in the air, the operator adjusts the aircraft buoyancy to neutral, using thermal buoyancy control or lift gas augmentation or compression (and storage) as needed, or through a combination of both methods. Once neutral buoyancy is attained, the aircraft can be stopped safely in mid-air without undue loss of altitude. 
     To land vertically, the operator gradually deflates the volume of compartment  24  by either of three methods or any combination thereof. In a first deflation method, if the temperature of the lift gas in compartment  24  is higher than that of the outside atmosphere, the operator may elect to reduce the volume of compartment  24  by cooling the lift gas. This is done by switching off heating element  26  but keeping the fan  25  running. Two-way valve  35  is placed in low position so as to make the lift gas flow through upper gas passage  32 . The upper wall of gas passage  32  is made of heat conductive material so that, when the lift gas passes through passage  32 , heat is conducted to the outside atmosphere through said upper wall, thereby cooling the lift gas. Valves  35  and  48  are operated electrically via electrical conductors that penetrate layers of the parafoil in an airtight manner. 
     Another method for deflating compartment  24  is by drawing lift gas from chamber  24  through gas line  46  into gas compressor  44 , where it is compressed and placed into the storage tank  45 . The volume of compartment  24  is thus reduced. 
     In an emergency, if the aforesaid deflation methods fail, helium can be vented out into the atmosphere through emergency vent  48  to achieve a safe vertical landing. However, the resultant loss of helium makes this method too uneconomical for routine use. 
     In an alternative embodiment of the aircraft of the present invention, the parafoil  10  is made so that the combined volumes of upper and lower lift compartments  19  and  22 , respectively, are sufficiently large so that when these compartments are fully inflated with lift gas such as helium, the parafoil aircraft attains near neutral buoyancy. Inflation and deflation of central compartment  24  will then be mainly used to control ascent or descent of the vehicle. This opens up various choices. For instance, less expensive lift gas such as hydrogen from a tank can be piped up through gas line  46  to inflate central compartment  24  as needed for ascent, and then simply vented out through vent  48  as needed for descent. This eliminates the need for an on-board compressor. 
     A further embodiment of the aircraft would use air to inflate compartment  24 . The air can be heated to expand it and make it lighter than the surrounding atmosphere for ascent, and cooled or vented out as needed for descent. This also eliminates the need for an on-board compressor. 
     The reason for using upper and lower arrays of lift chambers, separate from central compartment  24 , is to ensure that the outer surface of parafoil  10  can be made smooth and taut at all times regardless of the degree of inflation or deflation of central compartment  24 . This makes it possible for parafoil  10  to present an aerodynamically streamlined interface with the surrounding atmosphere and to maintain its airfoil shape when the aircraft is in flight even when central compartment  24  is being deflated. Otherwise, dimpling and deformity of the parafoil may occur, with attendant increased drag and loss of aerodynamic efficiency. 
     Steering of the aircraft in forward flight is accomplished in a manner similar to that employed with other parafoil aircraft. In general, the pilot achieves a right turn by shifting his weight to the right, and similarly turns left by shifting his weight to the left. Climbing may be achieved by increasing propeller speed, and descent may be achieved by diminishing propeller speed. 
     In the specific embodiment illustrated in the drawings, the fuselage  36  is suspended to the parafoil  10  by risers  38  which are connected to the shroud lines  37 . The risers  38  are four in number, the right front riser, the left front riser, the right rear riser, and the left rear riser, each connected to the corresponding shroud lines  37 . To shift the weight to the right, the pilot pulls down on the right front and right rear risers. To shift such weight to the left, the pilot pulls down on the left front and left rear risers. To increase the angle of attack of the parafoil, the pilot pulls down on the rear risers (both left and right), and to decrease the angle of attack he pulls down on both front risers. Pulling down on the risers is facilitated by powered winches, preferably coupled to an aircraft type steering wheel. Turning of the wheel to the right pulls down the right side risers, turning the wheel to the left pulls down the left side risers, pushing forward on the wheel pulls down the front risers, and pulling back on the wheel pulls down on the rear risers, so that piloting this aircraft will be somewhat similar to piloting other aircraft. Alternatively, a joystick may be used instead of a steering wheel. 
     The exemplified embodiment of aircraft of this invention is capable of flying into headwinds of 50 to 90 miles per hour. It can handle sidewinds of similar magnitude by partially heading into the wind, as other aircraft do. However, like other parafoil aircraft, it is intended for use only in fair weather with light breezes, and mostly for recreational flying. It is, however, useful in traveling to otherwise inaccessible places. 
     While particular examples of the present invention have been shown and described, it is apparent that changes and modifications may be made therein without departing from the invention in its broadest aspects. The aim of the appended claims, therefore, is to cover all such changes and modifications as fall within the true spirit and scope of the invention.