January 31, 2006 marked the maiden flight of the P-791 experimental hybrid airship. Developed by Lockheed Martin’s Advanced Development Programs aka Skunk Works, the P-791 hybrid airship was flight tested at Lockheed Martin’s flight test facility on the Palmdale Air Force Plant 42.
The United States Department of Defense is interested in the development of an airship capable of transporting heavy loads, 500-1000 tons of cargo, up to 12,000 nautical miles. Such designs have been announced by DARPA ( Defense Advanced Research Projects Agency ). The Walrus HULA ( Hybrid Ultra Large Aircraft ) is an example of such an aircraft. A small scale version of the Walrus is scheduled to fly this year with a 40,000 pounds payload.
Skunk Works managed to test fly the P-791 two years earlier. Although just a testbed for future development, P-791 successors can be used in the future for a number of applications such as delivery of fighting units in a theater of operations or as a weapons/sensor/communications platform capable of operating for long periods of time. The test flight was just a short traffic circuit around the Palmdale Air Force Plant 42 airport and Lockheed did not want to comment the flight.
Airships have great potential for transporting cargo but their use has declined after a series of accidents, one of the most famous of which was the 1937 Hindenburg disaster. Another reason for their decline is the delicate ground handling and relatively high vulnerability to meteorological conditions.The P-791 is an independent research and development program initiated by Skunk Works to better understand the capabilities and to try to solve the numerous problems faced by operating large airships.
A hybrid airship derives most of its lift by being filled with a lighter-than-air gas such as helium. Overall, it is heavier than air and gains the final 20% or so of lift by flying like an aircraft, but with slow takeoff and landing speeds that allow operations from short unprepared strips. One of the design features of the P-791 is the way the airship is built to gain span to produce lift: the entire construction is formed out of three pressurized lobes joined together. Four air cushions are placed on the outer lobes. These air cushions are used as landing gear and present a few advantages: the craft can taxi, land and take off in a conventional manner, pressure can be used to spread landing loads and also the flow can be reversed thus anchoring the craft to the ground to enable cargo loading and unloading in windy conditions.
Four propellers are clearly visible on the craft, two at the tail and two on the sides that are capable of pivoting. It has been suggested that these are used to control the craft at low speeds. Another important aspect of the P-791 is the striking similarity with the British SkyKitten, called SkyCat. Both use the same concepts and there have been voices stating that the two programs were related. In any case, on January 31, 2006 Chief Test Pilot Eric P. Hansen flew for the first time this amazing hybrid airship prototype. Designed to be the best of two worlds by retaining the high speed of conventional aircraft and lifting capacity of aerostatic aircraft, critics say the hybrid airships represent 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. Up until now, no hybrid airship design has ever been developed past the initial experimental stages. Maybe the future will be brighter for the Skunk Works design.