Aeronautics and astronautics – Aircraft – lighter-than-air – Airships
Reexamination Certificate
1999-12-21
2001-09-25
Swiatek, Robert P. (Department: 3643)
Aeronautics and astronautics
Aircraft, lighter-than-air
Airships
C244S025000, C244S125000
Reexamination Certificate
active
06293493
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the field of aircraft and, in particular, to the design of a pressure stabilized gasbag having an aerodynamic shape for a semi-buoyant vehicle.
2. Description of Related Art
There are basically two main types of fully lighter-than-air vehicles; the ridged type or as it is more commonly called the “dirigible” and the non-rigid type or “blimp”. Blimps basically comprise a single or multi-number of non-rigid gasbags wherein internal inflation pressure is used to form the external shape of the vehicle. A typical example of this design is found in U.S. Pat. No. 4,265,418 “Elongated Inflatable Structures For Flying Device Bodies” by M. Eymard the shape of the vehicle. The other basic type of lighter-than-air vehicle is the rigid design wherein an internal support structure is covered with a flexible material that serves as the outer skin. The vehicle may consist of a single gas chamber wherein the outer skin serves as the “gasbag” or can have numerous internal gasbags. An example of this concept can be found in U.S. Pat. No. 4,591,112 “Vectored Thrust Airship” by F. N. Piasecki, et al. However, both examples require that they be simultaneously loaded and unloaded in order to prevent the vehicle from “flying off.” In fact, such vehicles must be tethered when on the ground during such operations. A particular limitation of the non-rigid design is that the cargo compartment and propulsion system must be mounted on the gondola attached to the bottom of the vehicle. Catenary cables typically support the gondola or curtains attached to the top of the gasbag. This dirigible design allows most if not all these components to be mounted within the main body of the vehicle; although most all incorporate a gondola of some sort. However, when the vehicle is extremely large their costs become prohibitive because the complexity of the internal structure. A problem with both designs is that, as fuel is consumed, the vehicle becomes lighter.
These two examples are true lighter-than-air vehicles in that the gas filled balloon generates all the lift. However, having the external contour of the vehicle in an aerodynamic lift producing shape can reduce the overall size of such vehicles and generally cost, for any given payload. Such aircraft are not totally buoyant and take off in a manner similar to a conventional aircraft. In such designs, it is common practice to use a rigid internal frame (the dirigible concept) in order to maintain the proper contour. For example U.S. Pat. No. 3,486,719 “Airship” by J. R., Fitzpatick, Jr. While the Fitzpatick, Jr. design uses a rigid skin, most use a flexible gasbag with an internal frame structure. Of course there are non-ridged designs such as disclosed in U.S. Pat. No. 2,778,585 “Dynamic Lift Airship” by D. B. Tschudy. D. B. Tschudy's design includes a multi-lobe gasbag with a general aerodynamic shape, formed by catenary cables extending between the upper and lower surfaces of the vehicle.
However, there are problems with such vehicles, especially when they are very large. The generation of dynamic lift from the gasbag of the vehicle creates bending in the gasbag, which is much greater than found in conventional fully buoyant vehicles. Secondly, the lift-generating gasbag is much more aerodynamically unstable and therefore requires much larger tail surfaces than conventional vehicles, which in turn creates even greater loads on the gasbag. These two factors would tend to point toward the use of a rigid internal structure. However, it has been found that designing a rigid internal structure that's light enough and simple enough to produce at a reasonable cost does not appear to be feasible at the present time. Thus a pressure-stabilized gasbag appears to provide the only viable solution. However, providing a gasbag design capable of absorbing flight loads, especially those introduced by the vertical and horizontal stabilizers has proven difficult.
Prior art approaches such as disclosed by D. B. Tschudy use a metal support structure at the rear of the vehicle gasbag to absorb and distribute loads induced by the horizontal and vertical stabilizers into the gasbag. However, it is a complicated assembly. The three main lobes terminate in the same plane and the support structure includes three connected cup shaped caps that attach to the ends of the three lobes. While such an approach provides some benefit, it would have insufficient effect in very large aircraft. What is needed is gasbag design that allows for the introduction and gradual distribution of these tail assembly loads into the gasbag without unduly effecting its aerodynamic shape. Additionally, the gasbag should provide for the closest possible alignment of the center of buoyancy with the center of gravity of the vehicle. None of the prior art addresses these issues.
Thus, it is a primary object of the invention to provide a non-rigid partially buoyant vehicle having an aerodynamic shape.
It is another primary object of the invention to provide a non-rigid partially buoyant vehicle that allows for the efficient distribution of tail assembly loads into the gasbag structure.
It is a further object of the invention to provide a non-rigid partially buoyant vehicle that provided close alignment of the center of buoyancy and the center of gravity of the vehicle.
SUMMARY OF THE INVENTION
The invention is a non-rigid semi-buoyant vehicle. In detail, the invention includes a pressure stabilized gasbag having a longitudinal, vertical and horizontal axis, top and bottom surfaces and front and rear ends and an aerodynamic shape capable of producing lift. First and second catenary curtains are attached to the top and bottom surfaces between the sides of the gasbag. These, first and second catenary curtains are positioned on either side of the longitudinal axis and extend from the front end along a first portion, preferably 20 to 22 percent of the overall length of the gasbag measured from the front end thereof.
The first and second catenary curtains then transition to an Y shaped portion aft of the first portion of the gasbag and extend over a second portion, preferably to 47 to 50 percent of the overall length of the gasbag. The arms of each of the Y shaped curtains are attached to the top surface and the leg attaches to the bottom surface. Each of the Y shaped portions of the first and second catenary curtains then transition to pairs of vertical catenary curtains (four curtains in total) aft of the second portion and extend over a third portion of the gasbag to the rear end. The termination is accomplished by increasing the depth of the arms of the Y until a V is formed. Thereafter, the vertex of the V is moved apart until the arms are vertical. The pairs of the vertical catenary curtains are attached by their top and bottom ends to the top and bottom surfaces, respectively, of the gasbag.
Secondary vertical catenary are positioned on either side of each of the pairs of vertical catenary curtains and extend from the rear end of the gasbag forward therefrom over a portion of the length of the third portion of the gasbag, preferably about 30 to 33 percent of the overall length of the gasbag. The secondary catenary curtains are attached at their top and bottom ends to the top and bottom surfaces of the gasbag. The pairs of vertical catenary curtains extending over the third portion include angled catenary curtains extending outward and rearward at an acute angle thereto and joined to the front ends of the secondary vertical catenary curtains. Additionally, angled catenary curtains extend from the side walls of the gasbag to the ends of the most outward positioned secondary vertical catenary curtains.
Preferably, the rear end of the gasbag extending outward from longitudinal axis along the horizontal axis on each side thereof has a forward sweep. The preferred angle is approximately 20 degrees. A vertically extending flexible beam is attached to each of the pairs of catenary curtains and secondary catenary curtains in proximity t
Eichstedt David B.
Kalisz John B.
Morehead John P.
Lockheed Martin Corporation
Schruhl Robert A.
Swiatek Robert P.
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