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A hybrid airship is an aircraft that combines characteristics of lighter-than-air (LTA), aerostat technology with heavier-than-air (HTA) technology, either fixed-wing or rotary-wing. 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 "hybrid airship" 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 lands, being nearly neutrally buoyant, it is 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 aircraft. 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 or Skyship 600, 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.

Concept

The idea behind the hybrid airship is to combine lift from a lighter-than-air gas such as helium with lift from aerodynamic forces. Such a craft is still heavier than air, which makes it similar in some ways to a regular aircraft. The rest of the lift comes from vertical thrusters such as helicopter-like rotors, or a lift-producing shape (like a wing) combined with horizontal thrust, or a combination of the two.^[1] 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.

Engineering Perspective

The viability of "hybrid" airships has always been questionable from the engineering perspective. As discussed by renowned aeronautical engineer Charles P. Burgess, Chapter XI "Common Airship Fallacies" in his 1927 book Airship Design, The use of planes to give dynamic lift to airships has been a favorite idea with inventors for the past thirty years; and some early airships, notably Santos-Dumont's No. 10, built in 1903, were actually fitted with such planes. An airship with lifting planes may be regarded as a combination of airship and airplane, and a consideration of the characteristics of such a craft shows that it combines the disadvantages, and loses the merits of both types in a peculiarly complete manner."

After discussing the peculiar shortfalls of airships deriving significant lift from aerodynamics with regard to takeoff and landing, Burgess continues, focusing on the crux of the matter: "Even if the difficulties of starting and landing the combination craft could be overcome, it would still be inefficient in flight. For every 1,000 lbs. lift carried by the planes, approximately 60 lbs. resistance must be overcome by the thrust of the propellers. On the other hand, a 5,000,000 cu. ft. airship flying at 60 mph experiences only about 20 lbs. resistance per 1,000 lbs lift, and the relative resistance decreases with increasing size and diminishing speed. It is apparent, therefore, that the increase in lift obtained by the use of planes on an airship would require a disproportionate increase in engine power and fuel consumption."

It is interesting to note that Burgess' example comparison is actual wings operating at a dynamic-lift-to-drag ratio of 1000/60 = 16.7:1, typical of efficient wings, whereas the static-lift-to-drag ratio of 1000/20 = 50:1. Thus, simply increasing the displacement of the airship is 3.0 times more efficient than adding wings.

Meanwhile, current proposals intend to use a flattened or multi-lobe hulls to create aerodynamic lift. Professional papers on the subject (e.g. "Hybrids - The Airship Messiah?" by Crichner and Nicolai, of Lockheed's Skunk Works) show attainable dynamic-lift-to-drag ratios that can be significantly below that of efficient wings. Thus such aircraft will be even less efficient than airships equipped with lifting planes, and thus significantly less efficient than an airship deriving its lift entirely from aerostatic lift.

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.^{[citation needed]}

The idea of a tri-lobe airship belongs to Solomon Andrews when he first flew the Aereon back in 1863.^[6] The ship he hoped to use for military and commercial was a triple-hulled, gravity powered airship.^[6] When the war was over though it took away the need to fund for a controllable reconnaissance airship vehicle.^[6] "Undaunted, Andrews built a single hull airship that moved sideways. To explain how the craft flew, he published a booklet subtitled "Without Eccentricity, There Is No Progression."."^[6]

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.

In the timespan of 1923 to 1935 the US Navy operated four rigid airships: Shenandoah, Los Angeles, Akron, and the Macon. "The loss of three of them to accidents—only Los Angeles retired without mishap—coupled with the loss of the Hindenburg several years later, sounded the death knell for large airship operations."."^[3]

The 1986 Piasecki PA-97 Helistat combined four helicopters with a blimp in an attempt to create a heavy-lift vehicle for forestry work.

The Aereon 26 was an aircraft which made its first flight in 1971. It was a small-scale prototype of the hybrid Airship Aereon Dynairship and part of the "TIGER" project. But it was never built due to lack of market for a hybrid airship.^[2]

The SkyCat or "Sky Catamaran" vehicular technology is a hybrid aircraft amalgamation; a scale version at 12 meters called "SkyKitten", built by the Advanced Technologies Group Ltd, flew in 2000.

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, although the only program to provide serious funding is the US Army LEMV one awarded last year to Northrop Grumman and Hybrid Air Vehicles.

Current and proposed designs

The Millennium Airship Corporation has Patented their ITAMMS thrust management system and are currently developing a heavy hybrid lift system.^[3]

Hybrid Air Vehicles has the first of three HAV 304's under final construction in the USA. First flight is scheduled for later this year as part of the 517 million dollar US Army LEMV program. Surveillance, remote control and ground station equipment will be supplied by HAV's partner Northrop Grumman. In addition Hybrid Air Vehicles has signed a provisional contract with Canada's Discovery Air to build up to 45 HAV's for oil, gas and mining operations in Northern Canada. The contract, which the companies hope to have finalised by 2012, is potently worth $3.3 billion with each airship costing $40 million and the first delivery expected in 2014.^[4]^[5]^[6]

"In 2008, Boeing announced it was teaming up with SkyHook to develop a heavy duty lifting vehicle. Part blimp, part helicopter, the SkyHook JHL-40 aircraft is capable of transporting a 40-ton sling load up to 200 miles."^[2]^[4]

An Australian-based company is working on a project to develop an air crane called the SkyLifter, a "vertical pick-up and delivery aircraft" being capable of lifting up to 150 tons.^[2]

"Northrop Grumman has been awarded a US$517 million contract to develop the massive airship and present it for military assessment in just 18 months. The company is developing the LEMV to plug straight into the Army's existing ground command centers and will provide flight and ground control operations. According to the company release, the LEMV will "operate within national and international airspace" from "austere operating locations using beyond-line-of-sight command and control."^[5]

"For heavier payloads, hydrogen-fuelled high-altitude UAVs are a possibility. AeroVironment is close to flying its Global Observer, which is designed to carry a 400-lb. payload to 60,000 ft. for seven days. Boeing plans to fly its Phantom Eye demonstrator in January 2011, with the goal of staying aloft for up to 100 hr. to demonstrate technology for a hydrogen-fueled UAV that would operate for 10 days with a 1,000-lb. payload, and seven days with 2,000 lb."^[7]

A Canadian start-up, Solar Ship Inc, is developing solar powered hybrid airships that can run on solar power alone. The idea is to create a viable platform that can travel anywhere in the world delivering cold medical supplies and other necessitates to locations in Africa and Northern Canada without needing any kind of fuel or infrastructure. The hope is that technology developments in solar cells and the large surface area provided by the hybrid airship are enough to make a practical solar powered aircraft. Some key features of the Solarship are that it can fly on aerodynamic lift alone without any lifting gas, and the solar cells along with the large volume of the envelope allow the hybrid airship to be reconfigured into a mobile shelter that can recharge batteries and other equipment.^[7]^[8]

References

[1] Hybrid airship - Encyclopedia
[2] New hybrid airships prepare to take flight - CNN.com
[3] Gordon, Walter O. "Back to the Future: airships and the revolution in strategic airlift." Air Force Journal of Logistics 29.3/4 (2005): 47-58. Academic Search Complete. EBSCO. Web. 27 Sept. 2011.
[4] Carter, Russell A. "Blade Runner: Boeing to Develop a 40-Ton-Capacity, Heavy-Lift Hybrid Aircraft." Engineering & Mining Journal (00958948) 209.6 (2008): 58-60. Academic Search Complete. EBSCO. Web. 27 Sept. 2011.
[5] Northrop Grumman to build football field-sized hybrid airship
[6] Wallace, Lane. "Dirigible Dreams." Atlantic Monthly (10727825) 305.3 (2010): 27. Academic Search Complete. EBSCO. Web. 27 Sept. 2011.
[7] Warwick, Graham. "Rise of the Airship. (Cover story)." Aviation Week & Space Technology 172.25 (2010): 42

External links

New hybrid airships prepare to take flight - CNN.com
"Some factors affecting the use of lighter than air systems", by C. Dewey Havill at NASA.

[1] P-791 hybrid airship project

[2] Aereon26

[3] ITAMMS

[4] Futuristic 'airships' planned for North at CBC.

[5] UK group secures commercial airship deal at the Financial Times

[6] telegraph.co.uk, World's largest aircraft unveiled and hailed 'game changer, 28 Feb. 2014

[7] ttp://www.thestar.com/business/article/1069861--hamilton-toronto-start-up-designs-solar-powered-hybrid-aircraft

[8] ttp://www.solarship.com/

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@@ Line 14: / Line 14: @@
 ==Concept==
 The idea behind the hybrid airship is to combine lift from a lighter-than-air gas such as helium with lift from aerodynamic forces.  Such a craft is still heavier than air, which makes it similar in some ways to a regular aircraft. The rest of the lift comes from vertical thrusters such as helicopter-like rotors, or a lift-producing shape (like a wing) combined with horizontal thrust, or a combination of the two.<ref>[http://www.military-heat.com/91/p791-hybrid-airship-project/ P-791 hybrid airship project]</ref> <!--[[Hovercraft|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.
+==Engineering Perspective==
+The viability of "hybrid" airships has always been questionable from the engineering perspective.  As discussed by renowned aeronautical engineer Charles P. Burgess, Chapter XI "Common Airship Fallacies" in his 1927 book ''Airship Design'', The use of planes to give dynamic lift to airships has been a favorite idea with inventors for the past thirty years; and some early airships, notably Santos-Dumont's No. 10, built in 1903, were actually fitted with such planes.  An airship with lifting planes may be regarded as a combination of airship and airplane, and a consideration of the characteristics of such a craft shows that it combines the disadvantages, and loses the merits of both types in a peculiarly complete manner."
+After discussing the peculiar shortfalls of airships deriving significant lift from aerodynamics with regard to takeoff and landing, Burgess continues, focusing on the crux of the matter:  "Even if the difficulties of starting and landing the combination craft could be overcome, it would still be inefficient in flight.  For every 1,000 lbs. lift carried by the planes, approximately 60 lbs. resistance must be overcome by the thrust of the propellers.  On the other hand, a 5,000,000 cu. ft. airship flying at 60 mph experiences only about 20 lbs. resistance per 1,000 lbs lift, and the relative resistance decreases with increasing size and diminishing speed.  It is apparent, therefore, that the increase in lift obtained by the use of planes on an airship would require a disproportionate increase in engine power and fuel consumption."
+It is interesting to note that Burgess' example comparison is actual wings operating at a dynamic-lift-to-drag ratio of 1000/60 = 16.7:1, typical of efficient wings, whereas the static-lift-to-drag ratio of 1000/20 = 50:1.  Thus, simply increasing the displacement of the airship is 3.0 times more efficient than adding wings.
+Meanwhile, current proposals intend to use a flattened or multi-lobe hulls to create aerodynamic lift.  Professional papers on the subject (e.g. "Hybrids - The Airship Messiah?" by Crichner and Nicolai, of Lockheed's Skunk Works) show attainable dynamic-lift-to-drag ratios that can be significantly below that of efficient wings.  Thus such aircraft will be even less efficient than airships equipped with lifting planes, and thus significantly less efficient than an airship deriving its lift entirely from aerostatic lift.
 ==History==