Hybrid airship

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Hybrid airship has two meanings. First, it can be an airship combining elements of different types of airships. It can also be used to describe 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. This article focuses on hybrids that combine heavier-than-air and lighter-than-air technologies.

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 a 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.

Using the above definition, no practical human-carrying hybrid airships have been built to date. However, many designs have been proposed and some prototypes built.

[edit] Concept

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.

With hybrid designs, as much as 40% of its total lift is created by aerodymics. So, when on the ground, it is much heavier than a purely aerodynamic design and can presumably taxi around like an airplane. Such operation should make it simpler and cheaper than strictly LTA ships. The aerodynamic approach is very similar to that of a lifting body aircraft. However lifting bodies have no aerostatic (buoyant) component.

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. However, hybrid designs are not without their detractors. 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 though 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.

[edit] History

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 flown.

In 1905, Alberto Santos-Dumont, made what is likely the first attempt at a hybrid airship. 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 aircraft in the world.

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.

The SkyCat airship design was a hybrid.

[edit] Current designs

The WALRUS airship designs, the Ohio Airships Dynastat design and the Lockheed-Martin P-791 are all hybrids.

[edit] Treatment in fiction

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