A hybrid airship is an aircraft that combines characteristics of lighter-than-air (LTA), airship technology with heavier-than-air (HTA) technology, either fixed-wing or rotary-wing. A rotastat is a rotorcraft/airship hybrid typically intended for heavy lift applications, while a dynastat is a dynamic lift airship typically intended for long-range cruising. No production designs have been built, but several manned and unmanned prototypes have flown.
The term "hybrid airship" has also been used to describe an airship combining elements of different types of airships.
- 1 Characteristics
- 2 Design principles
- 3 History
- 4 Current efforts
- 5 List of hybrid airships and projects
- 6 See also
- 7 References
- 8 External links
- 9 External links
Conventional airships have low operating costs because they need no engine power to remain airborne, but are limited in several ways, including low payload/volume ratios and low speeds. Additionally, ground handling of an airship can be difficult. Because it is floating, in even a light breeze it is susceptible to wind buffeting.
The hybrid airship combines the airship's aerostatic lift, from a lighter-than-air gas such as helium, with the heavier-than-air craft's dynamic lift from movement through the air. Such a hybrid craft is still heavier than air, which makes it similar in some ways to a conventional aircraft. The dynamic lift may be provided by helicopter-like rotary wings (the rotatstat), or a lift-producing shape similar to a lifting body combined with horizontal thrust (the dynastat), or a combination of the two.
Hybrid airships are intended to fill the middle ground between the low operating cost and low speeds of traditional airships and the higher speed but higher fuel consumption of heavier-than-air craft. By combining dynamic and buoyant lift, hybrids are intended to provide improved airspeed, air-cargo payload capacity and (in some types) hovering capability compared to a pure airship, while having longer endurance and greater lifting capacity compared to a pure HTA type.
Hybrid aircraft technology is claimed to allow a wider range of flight-performance optimizations ranging from significantly heavier than air to near buoyant. This perception of uncommon dynamic flight range when coupled with an appropriate landing system is claimed to allow ultra heavy and affordable airlift transportation.
Hybrid airship efforts, like airship efforts in general, have been called into question from both economic and technology viability perspectives. The hybrid approach has been described as the "worst of both worlds".
Compared to a conventional airship, the hybrid can be made smaller and does not need to carry ballast for altitude control, while compared to a heavier-than-air craft the hybrid requires either a smaller rotor or a shorter runway.
Where the dynastat is seen as more promising in the longer-distance passenger and freight roles, the rotastat is anticipated to be more suitable as a "flying crane" able to lift heavy external loads for shorter distances.
Some airships employ thrust vectoring, typically using pivoted ducted fan propulsors, to provide additional lift when the engine thrust is no longer needed for forward propulsion. Once airspeed is gained, the craft can use body lift to help carry a load greater than its aerostatic lift capacity alone. However, such airships are not usually regarded as hybrids.
The dynastat obtains additional lift by flying through the air. Configurations studied have included deltoid (triangular), lenticular (circular) or flattened hulls, or adding a fixed wing.
Some early airships were fitted with wing planes with the intention of providing additional dynamic lift. However the added lift of planes can be less efficient than simply increasing the volume of the airship. At low air speeds, of 60 mph (97 km/h) or less, the increase in lift obtained by the use of planes on an airship would require a disproportionate increase in engine power and fuel consumption compared to increasing the size of the gas bags. Moreover the attachment of flying surfaces to the airship envelope would require significant structural strengthening and accompanying weight gain.
Conventional airships often make use of aerodynamic lift by using their elevators to set a nose-up attitude so that the main body of the airship provides some lift as it flies along; however, this is typically done to counteract minor out-of-trim conditions and it is as likely that the nose may need to be pointed down to reduce lift.
Some Hybrid designs, such as the Hybrid Air Vehicles HAV-3, use a flattened or multi-lobe hull to increase the aerodynamic lift obtainable. The aerodynamic approach is similar to that of a lifting body aircraft, although airspeeds are much lower. Attainable dynamic-lift-to-drag ratios are significantly below those of efficient fixed wings, in part because induced drag increases with decreasing aspect ratio. As a result, the lift comes at a higher drag penalty than using wings. On the other hand, compared to a helicopter the dynastat has better fuel efficiency within a given speed range.
Another issue arises during take off and landing, when in calmer conditions the airspeed may be too low to provide sufficient aerodynamic lift. For this reason the dynastat is often conceived of as a STOL rather than VTOL aircraft, requiring a shorter runway than a conventional airplane.
The rotastat obtains additional lift from powered rotors similar to a helicopter. Single-, twin- and four-rotor designs have been studied.
Early examples in the inter-war period included designs by Oehmichen and Zodiac. These used the rotors for vertical control only, with additional powered propellers for forward flight, as in the gyrocopter.
In more recent times the experimental Piasecki PA-97 "Helistat" attached four helicopter airframes to a helium blimp while the SkyHook JHL-40 remains a project. Typically aerostatic lift is sufficient to support the weight of the craft itself, while when a load is carried the rotors provide additional lift as required.
Solomon Andrews built two airships in the period during and shortly after the American Civil War. The first of these, Aereon, used three individual cigar shaped balloons rigged together in a flat plane; the second, Aereon #2, employed a single "lemon-shaped" balloon. Andrews' Aereons were propelled by angling the balloons upward and dropping ballast, whereupon the balloons were used as a low aspect ratio wing to glide forward; the process was then reversed, the balloons being angled downward and large quantities of lifting gas being vented to glide forward on descent.
In 1905 Alberto Santos-Dumont conducted various experiments with his first airplane, the Santos-Dumont 14-bis, prior to attempting to fly it for the first time. These included hanging it from a steel cable and towing it, and subsequently hanging it beneath the envelope of a previously built airship (Number 14) - akin to learning to swim with "water wings". The combined craft was unusable, and was broken up, being referred to as "a monstrous hybrid". After these "rehearsals" were completed, Santos-Dumont made the first public demonstration of a heavier-than-air aircraft in the Europe.
In 1907 the British airship British Army Dirigible No 1 (named Nulli Secundus) first flew. It used aerodynamic surfaces for attitude control in flight, and for its first flight was also fitted with large wings amidships. The wings were intended to aid stability rather than provide lift and were removed for all subsequent flights. The use of dynamic lift by pitching the nose of the airship up or down was also recognised and practised on this airship.
In June 1907 Alberto Santos Dumont constructed his No. 16, described by l'Aérophile as an appareil mixte. This had a 99 m3 (3,500 cu ft) envelope but was too heavy to fly without supplementary lift supplied by a 4 m (13 ft) wing surface. It was tested without success on 8 June 1907.
Hybrid airship history
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.
In 1984 the AeroLift CycloCrane helistat flew briefly.
The 1986 Piasecki PA-97 Helistat experimental design combined four helicopters with a blimp in an attempt to create a heavy-lift vehicle for forestry work. It broke up at the end of its first flight possibly due to inadequate structural strength
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 Hybrid Ultra Large Aircraft program in 2005, a technology development initiative focused on ultra heavy air lift technology explorations. The program was terminated in 2007.
In 2006, the Lockheed Martin P-791 underwent manned flight tests. It was an unsuccessful candidate for the military Long Endurance Multi-intelligence Vehicle program
Northrop Grumman was awarded a US$517 million contract to develop a hybrid airship and present it for military assessment in just 18 months as part of the Long Endurance Multi-intelligence Vehicle (LEMV) program. The design was based on Hybrid Air Vehicles' design. On 14 February 2013, the Army confirmed that it had cancelled the LEMV development effort, citing technical and performance challenges, as well as the limitations imposed by constrained resources.
No hybrid aircraft design has yet been developed past the initial experimental stages.
Hybrid Air Vehicles purchased the LEMV vehicle from the US Department of Defense for $301,000, and is currently re-erecting the vehicle - now known as "Airlander" - in one of the historic airship sheds at Cardington, with plans to further develop the vehicle and make a passenger flight in 2016. One investor, Bruce Dickinson, has announced plans to "drum up publicity" by flying twice around the world nonstop.
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.
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.
List of hybrid airships and projects
- Hybrid Air Vehicles HAV-3
- Lockheed Martin P-791 - first flew 2006
- Nimbus EosXi - Italian small (7 m) delta-wing hybrid, first flying in 2006
- SkyCat - scale demonstrator by ATG flown in 2000
- Thermoplan - in development, Russia
- Walrus HULA
- AeroLift CycloCrane - flown in 1980s
- Piasecki PA-97 - flew in 1986
- SkyHook JHL-40 - in development, USA
- Kytoon - a tethered kite/balloon hybrid
- Tolip (18 February 2008), P-791 hybrid airship project, military-heat.com
- Khouty (2012).
- Zolfagharifard, Ellie (28 February 2014 (updated 1 March 2014)), "The flying bum! 300ft-long 'airship' unveiled in Britain is the world's longest aircraft", mailonline (Associated Newspapers)
- Hpanchal (30 June 2011), "High flying demand or bust?", Air Cargo World
- Farnham, Alan (29 April 2002), All hangar, no blimp
- Dick, Joseph (27 May 2011), "Helium Hokum: Why Airships Will Never Be Part of Our Transportation Infrastructure", Guest Blog (Scientific American)
- Burgess, Charles P (1927), "Chapter XI: Common Airship Fallacies" (pdf), Airship Design, Ronald Aeronautic Library, Ronald Press, pp. 289–290, "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."
- Crichner and Nicolai; "Hybrids - The Airship Messiah?" Lockheed.
- Burgess, Charles P (1927), "Chapter XI: Common Airship Fallacies" (pdf), Airship Design, Ronald Aeronautic Library, Ronald Press, pp. 289–290, "there would still remain the apparently insurmountable problems of starting and landing the combination craft"
- Solomon Andrews, The Art of Flying, 1865
- Payne, Lee, Lighter than Air: An Illustrated History of the Airship, p. 39
- Nancy Winters, Man Flies - The Story of Alberto Santos-Dumont, p. 100
- Reese, P.; The Flying Cowboy: Samuel Cody Britain's First Airman, History Press, Reprint 2008, 978-0752436593 page 87.
- Walker, P.; "Early Aviation at Farnborough Volume I: balloons, Kites and Airships", Macdonald (1971), page 198.
- Walker, P.; "Early Aviation at Farnborough Volume I: balloons, Kites and Airships", Macdonald (1971), page 170.
- "Le Nouvel Engin de Santos-Dumont". l'Aérophile (in French): 161. June 1907.
- Aereon26[dead link]
- Hybrid Airships, The Airship Association, 2012
- Grover, Sami (20 March 2014), "Lead singer for Iron Maiden to pilot hybrid airship around the world", Mother Nature Network
- Daily Mail Reporter (7 October 2010), "The giant airships which can carry entire buildings hundreds of miles", mailonline (Associated Newspapers Ltd)
- Hamilton, Tyler (14 October 2011), "Hamilton: Toronto start-up designs solar-powered hybrid aircraft", thestar.com
- Khouty, G.; "Airship Technology", 2nd Edition, CUP (2012), Chapter 19.
- Havill, C. Dewey (1974), NASA TM X-62,374 Some factors affecting the use of lighter than air systems, Ames Research Center, NASA