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.