Hybrid airship

A hybrid airship is an aircraft that combines characteristics of heavier-than-air, (HTA), (fixed-wing aircraft or helicopter) and lighter than air, (LTA), technology. Examples include helicopter/airship hybrids intended for heavy lift applications and dynamic lift airships intended for long-range cruising. No production vehicles have been built, but several manned and unmanned prototypes have flown and successfully demonstrated the concept.

The term has also been used to describe an airship combining elements of different types of airships.

Background

Traditional airships have low operating costs but are limited in several ways, including low payload/volume ratios and low speeds. Additionally, ground handling of airships has historically presented great difficulty. When a purely LTA ship comes in for a landing, it is nearly neutrally buoyant and is very susceptible to wind buffeting. In even a slight breeze, a truck or many ground crew members are required to secure the ship to a mooring mast.

Heavier-than-air aircraft, while addressing these difficulties, require the use of power to generate lift, and airplanes also require runways, while helicopters need even more power to hover. Hybrid airship designs are intended to fill the middle ground between the low operating cost and low speeds of traditional airships and higher speed, but more expensive heavier-than-air aircraft. In addition, by combining dynamic and buoyant lift, hybrids may be able to provide otherwise unattainable air-cargo payload capacity and/or a hovering capability. Such a design is intended to be the "best of both worlds" combination: the high speed of aerodynamic craft and the lifting capacity of aerostatic craft. However, critics of the hybrid approach have labeled it as being the "worst of both worlds" declaring 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.

Most modern airships, for instance the Zeppelin NT, use some combination of vectored thrust and buoyancy. However, for these designs, almost all of the load is carried via buoyancy and vectored thrust is used primarily for maneuvering. To date, there is no formal distinction between hybrid airships and airships with vectored thrust. However, most people in the field usually define a hybrid airship as one that carries at least 40% of the weight of the loaded ship by aerodynamic means.

Concept

With hybrid designs, as much as 40% of its total lift is created by aerodynamics. So, when on the ground, it is much heavier than a purely static lift design and can presumably taxi around like an airplane. Hover-cushion landing systems (replacing wheels), possessing a suck down mode have addressed the ground handling problems of airships, potentially resulting in remote operations in areas of the world previously inaccessible to airships and conventional aircraft. The aerodynamic approach is very similar to that of a conventional lifting body aircraft. The hybrid aircraft technology has a wide range of flight performance behaviors ranging from heavier than air to near buoyant characterizations. This uncommon dynamic flight range when coupled with an air cushion landing system has reinvigorated the LTA community and those seeking ultra heavy and affordable airlift transportation options.

History

No hybrid aircraft design has ever been developed past the initial experimental stages despite many such designs having been proposed over the years, though recent advances may indicate that the technology has matured.

In 1905, Alberto Santos-Dumont, made what is likely the first attempt at a hybrid aircraft. His "Number 14" combined an airship envelope with an airplane frame. At that time, Santos-Dumont was the world's most accomplished aviator. All of his previous flights had been made in purely aerostatically lifted airships. The Number 14 proved unworkable. Later, Santos-Dumont would remove the envelope and successfully use the recristened "14-bis" (meaning "14-again") to make the first public flight of any heavier-than-air aircraft in the world.

One example of hybrid aircraft 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.

The SkyCat vehicular technology is a hybrid aircraft amalgamation; a scale version at 12 metres called "SkyKitten", flew in 2000. ATG, the UK company who fashioned the small unmanned aerial vehicle, borrowed from Lockheed Martins Aerocraft designsFact|date=September 2008, is now defunct.

The U.S. Defense Advanced Research Projects Agency, DARPA, initiated the WALRUS program in 2005, a technology development initiative focused on ultra heavy air lift technology explorations. The program was terminated in 2007.

In 2006, Lockheed Martin's P-791 manned flight test of the SkyCat technology indicated substantial progress of the technology, and presently several development efforts are underway.

Current and proposed designs

The Hybrid Aircraft Corporation has trademarked the SkyCat and SkyFreighter (cargo variant) names for such vehicles and is involved in design and development efforts.

The Aeroscraft, a design proposed by Worldwide Aeros Corp is also a hybrid airship that uses a lifting body shape, vectored thrust, as well as buoyancy control. Aeros was a beneficiary of the WALRUS program.

World SkyCat Ltd, in Britain, is also pursuing a design in the heritage of the SkyKitten.

Treatment in fiction

H.G. Wells' novel Tono-Bungay features the protagonists working on hybrid airship designs with arguable lack of success.

External links

* [http://www.cnn.com/2007/TECH/10/23/new.airships/] CNN Article on Hybrid Airships