P-791
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The P-791 is an experimental aerostatic/aerodynamic hybrid airship developed by Lockheed-Martin Corporation. The first flight of the P-791 was made on 31 January 2006 at the company's flight test facility on the Palmdale Air Force Plant 42. According to press reports, the designation "P-791" has no particular meaning.
[edit] Hybrid airship design
The P-791 is an example of a hybrid airship. In such designs, part of the weight of the craft and its payload are supported by aerostatic (buoyant) lift and the remainder is supported by aerodynamic lift.
The combination of aerodynamic and aerostatic lift is an attempt to create a craft that is a "best of both worlds" combination with the high speed of aerodynamic craft and the lifting capacity of aerostatic craft. Critics of the hybrid approach have labeled it as being the "worst of both worlds" in that such craft require a runway for take-off and landing, are difficult to control and protect on the ground, and have relatively poor aerodynamic performance.
Proponents of hybrid designs claim that these shortcomings can be overcome through advanced technologies. In particular, it has been proposed that the use of various buoyancy control mechanisms can minimize or in some cases eliminate the need for a runway. However, to date, no effective buoyancy control mechanism has ever been demonstrated on a hybrid airship.
No hybrid airship design has ever been developed past the initial experimental stages. And, in spite of the fact that many such designs have been proposed over the years, very few proposed designs have ever flown. One example of hybrid airship design that did take flight was the Aereon 26. The development of this aircraft was documented in the book "The Deltoid Pumpkinseed" by John McPhee.
[edit] WALRUS
Although Lockheed-Martin is developing a design for the DARPA project WALRUS, the company claims that the P-791 is unrelated to WALRUS. Nonetheless, the design represents an approach that may well be applicable to WALRUS. Some believe that Lockheed-Martin has used the secret P-791 program as a way to get a "head-start" on Worldwide Aeros Corporation, the other Phase I WALRUS competitor.
As of April 2006, the WALRUS program appears to have been cancelled.
[edit] Potential SkyCat controversy
The company has released no details about the design of the aircraft. However, from a distance, the P-791 appears to be essentially identical in design to the SkyCat design unsuccessfully promoted for many years by the now financially troubled British company Advanced Technologies Group (ATG). Press reports have also confirmed that the P-791 incorporates some of the most unique design features of the SkyCat, specifically the use of hover/suction skirts as "landing gear."
Industry observers have noted that individuals once closely associated with ATG later worked on the WALRUS project at Lockheed-Martin.
