Just another Airship „Made in Germany“?
by Karl Ludwig Busemeyer, GEFA-FLUG GmbH, Aachen, Germany, october 2000
Introduction
With hotair airship no. 20 in the order books and the certification of a fourseater version „Made in Germany“ almost a year ago is the reason for the AIRSHIP JOURNAL to ask association member Karl Ludwig (Mucky) Busemeyer, managing director of GEFA-FLUG, designer and testpilot to write down his experiences with airships, how his company developed the new fourseater – no. 5 is under construction – and where he thinks the future market for these beauties will be. Mucky has spend around twenty five years in the lighter than air sceene and has designed, build and flown probably more different hotair airships, than anybody else. Last but not least he received the „Santos Dumont Airship Gold Medal“ for his outstanding work, one of the highest awards of the „Federation Aeronautique Internationale“.
Backround and History
Along with the general renaissance of the hotair balloon, some 25 years ago, a new type of airship entered the sceene using hot air as its lifting medium. In the mid 70s Cameron Balloons started selling these aircraft for sport and aerial advertising purposes. In general these early hotair airships were elongated dirigible hot air balloons. Shape and stability were solely dependent on the static hotair pressure like in ordinary hotair balloons. They are relatively simple to build and operate, because many technical features are derived from hotair balloon (or special shape) technology. The burner unit is positioned, as in a hotair balloon, under the open belly of the airship envelope. Due to the low natural envelope pressure, the use of these airships is extremely dependent on superb weather and virtually restricted to windless conditions. Horizontal manoeuvrability is realised by a rudder; the rate of climb and descent is dependent on burner input.
At the beginning of the 80s Thunder & Colt Balloons produced the first pressurised hotair airship. With the help of a fan system and later with the propeller slip stream the pressure is maintained and controlled inside the airship envelope. The burner unit now works inside the entirely closed envelope. By using ordinary hotair balloon fabric early pressure airships could not stand high pressures. With the introduction of high tenacity nylon fabrics the pressure nowadays is around three times higher than in the unpressurised airship type. Maximum pressure so far is around 1.5 mbar. In the mid 80s Cameron Balloons also brought a superpressure airship type on the market, followed by Lindstrand in the mid 90s.
Situation Today
The majority of today´s hotair airships are pressure airships. Volumes vary between 1.600 m³ for a single seater and up to 3.400 m³ for two a seater with some extra payload. Most of the engines in use are two stroke varying from 30-50hp. The resulting speed is around 15 kts. Average flight time varies from 45 to 70 minutes with standard airships. Depending on local circumstances and crew skills; todays hot air airships can be operated at ground wind speeds of 6 to 8 kts. This means that hotair airships are as weather dependent as special shapes. Altogether about 100 of both types have been sold world wide. In 1988 the first world-championships were held thereby promoting airship technology and pilot skills. So far the main market for hotair airships has been aerial advertising. There is, however, a steadily increasing market with environmental monitoring and research around the world. Due to the fact that hotair airships are still technically underdeveloped and therefore dependent on suitable weather, they have not as yet been widely accepted and used for these markets.
The German entry
Since the mid 70s GEFA-FLUG a Ltd company based in Aachen has been developing airships. The first years were spent with the operation of remote controlled airships. Since 1985 experiences gained with big remote-controlled systems were used to develop manned systems. Together with Thunder & Colt the first AS 80 GD was built in 1990 using an upgraded Thunder & Colt twoseater gondola combined with an envelope designed and build entirely by GEFA-FLUG. This envelope type is more streamlined than existing hot air airships. The general manoeuvrability has also been improved over the years. Pitch control is possible with the help of a V-form twin burner arrangement and the resulting heat distribution in the envelope fore and aft. To improve the trimming of the ship and to avoid hot air from sloshing backwards and forwards the ship is divided into two parts (front and rear) with the help of a fabric membrane-system. In turbulent air the flight characteristics are now much improved compared with ordinary hotair airships. In addition the maximum speed is higher due to their slimer fineness ratio against traditional hot air airships.
Quite a few airships including the AS 80 GD and later the AS 105 GD have since then been successfully used for various purposes in so far twenty countries. The highlight of GEFA-FLUG´s development work is a three / four-seater (depending on climatic conditions) hotair airship with a volume of 3.000 m³. The development of this airship has been partly government funded. The AS 105 GD has been certified under JAR 21 by the LBA after a five years development programm. At the time of writing airship SN 0019 is under construction with SN 0020 and 0021 in the orderbook.
An Attempt to Compare: Hotair Versus Helium Airships
Operating gas airships is very expensive. Gas airships do need quite a big crew even when not in use they do cost almost the same (permanent watch, hangar, helium, crew, etc.) Helium airships therefore are only cost effective if they can be operated during a high number of months per year. This is where the hotair airship has a big advantage over the helium one. When not in use it costs hardly anything because it is stored in a trailer and neither hangar, watch nor care are necessary. The second big advantage is carrying the hotair airship to the place of operation. The helium airship normally flies to this place which can be quite expensive, depending on the distance to the field of operation – the hot air airship, however, is transported by road including its four crew members. More crew is not necessary because the hotair airship will only be inflated and operated in good flying weather when a large crew is not necessary. The crew of a helium airship must always be big enough to encounter bad weather periods as well. Crew size of a helium airship varies therefore between 10 and 20 depending on the type and size of the ship.
Of course there are disadvantages as well. In fact, the disadvantages are quite remarkable. Hotair airships need much more volume to create the same amount of lift and payload. But it is possible to reduce weight on existing hotair airships. In future, fabrics will be improved and hotair airships will be flown with higher temperatures and will obtain more lift per volume than now. With stronger fabrics the envelope pressure can be higher as well, resulting in a stiffer envelope. The difference in lift compared to the helium ship will be minimised, hot air however will of course never reach the lifting capacity of helium! There will also be another limitation for hotair airships. As they will always be inflated on the launch field (and not in a hangar!) the weather resistance will always be lower than with helium airships. As mentioned above at present we expect a ground wind of around 6 to 8 kts.
With a professional crew and using an advanced airship like the AS 105 GD it is possible to stretch this groundwind limit up to 10 or 12 kts. It might be possible to extend this limit even up to 15 kts. More is not realistic because too much effort, manpower and high-tech equipment is neccessary to inflate the big envelopes in higher wind speeds, thus making flight operations then too expensive.
On the other hand, a simple and cheap aircraft can never have a performance as high as an expensive one. However the efficiency can be good in both cases, as long as both aircrafts do not compete in the same market niche. The fourseater hotair airship AS 105 GD costs less than 100.000 pounds ready to fly. A four-seater helium airship like the ABC A 60 + is five to six times more expensive to buy. It seems however likely that there will be a market share for both of them, but in (slightly) different market places.
Hotair Airships: General Characteristics
Relatively cheap to operate and still economic even for only a few hours per day.
Low transportation costs, hotair airships travel on the road, not through the air.
Weather dependent, inflation only possible in low wind speeds. There is however no need for a big engine, nor a big crew.
For flight operations no airfield is neccessary, hotair airships take off and land vertically.
Small payload limits flight time. Flights will only cover local area
Passenger flying with twinseaters is not cost effective. That might change however with a
sponsored fourseater airship.
First Market For Hotair Airships: Aerial Advertising
The main market for hotair airships today is the traditional airship market with aerial advertising. Normally these airships are operated by companies which operate hot air balloons as well. One can still describe a hotair airship as a powered, steerable hotair balloon. Many technical features are the same: without engine, a hotair airship can be flown like a hotair balloon. The big advantage over the hotair balloon is, however, the engine and the ability to hover over a defined area. Hotair airships are thermically sensitive vehicles like hotair balloons and like other lighter than air aircraft. Hotair airships are flown for a couple of hours after sunrise and before sunset when there is hardly any thermal activity.
There is a good market in visiting fairs, exhibitions, open air and sporting events, etc. in the evenings. Another possibility are patroling flights over motorways and trunk roads during traffic jams in the early morning and evening. In wintertime hotair airships can be operated over ski resorts and can visit big winter games. All the above flight profiles are ideal for hotair airships; they are much better suited for these purposes than hotair balloons which are exclusively „wind toys“. As mentioned earlier, it does not cost much to carry the hotair airship to its operational theatre.
Second Market: Environmental Monitoring
Hotair airships are very suitable for another market, general survey and environmental research projects. Historically balloons and airships have always been used for these purposes. There were several airship expeditions in the 1920s and 30s. Men like Roald Amundsen, Umberto Nobile and Dr. Hugo Eckener with airships like Norge, Italia and Graf Zeppelin are still very well remembered. Airship enthusiasts since then have promoted the use of airships for environmental purposes. In fact GEFA-FLUG can proof that hotair airships are very suitable for environmental survey and research projects, exspecially where relatively small areas are to be surveyed. Hotair airships can really take off and land vertically, they only need small launch fields (like hotair balloons) which can always be found close to the flying area. This means it is inexpensive to get hotair airships to these areas and no expensive flight time is lost in getting there. (as would be with a helium airship)
GEFA-FLUG: Operational Experiences
Since the early 80s GEFA-FLUG has successfully used various hotair airship systems in around twenty countries for various purposes. How succsessful airship operations can be is proved by the fact, that GEFA-FLUG since 1991 operates two airships for Adler, an international fashion company. Each year they fly around 180 days. The programm consists of a mixture between advertising and environmental monitoring paid by the sponsor as his contribution for a better environment. There were quite a few monitoring projects all over the world like aerial photogrammetry of archaeological sites. An early example in 1982/83 was a four month survey of Mohenjo Daro, a 5000 year old ancient city in Pakistan. Comparable projects have since then been undertaken in Oman, Syria, Greece, Turkey, Yugoslavia, Egypt, Spain, Israel and Tanzania to mention just a few. Other projects have been the photo-documentation of the world famous castles of Neuschwanstein, or the survey of the Rhine and Danube valleys in Austria and Germany together with biologists and other scientists of the World Wide Fund for Nature. All these projects can be summed up as „low range monitoring“. Low range monitoring or low range measurement, of course, provide a very high degree of accuracy.
One highlight under all these projects was the 1994 expedition to the most northern point of Europe, to fly around Vadsö, the old mooring station of the Amundsen and Nobile expeditions 1926/28 in North-Norway. The mooring mast is still there and is a technical monument to-day. Several thousand postcards, which had been sold before the flight, were carried on board of the Adler airship to support the Pestalozzi Kinderdorf charity. The widow of General Nobile was Patron of this airship expedition. It was the first time for more than 60 years that an airship had flown the Arctic skies from the europeen part of the planet.
Another highlight was the expedition „Serengeti shall never die“, to commemorate the 40th anniversary of famous german professor Grzimek´s flight-expedition in Tanzania in 1958, where he and his son Michael counted masses of big animals in the Serengeti National Park. The Grzimeks used a light airplane, the GEFA-FLUG team however uesd the Adler airship, which proved to be an excellent stable camera plattform for a german TV team to monitor masses of wildebeests and zebras, without annoying them too much. The project was extremly well covered by the europeen media, the film was repeated twenty time in various europeen channels and on top of that the project raised quite some financial support for two charity organisations.
AS 105 GD Technical Development: Possibilities and Limitations
When GEFA-FLUG started developing manned hotair airships in 1985, there was a big potential for the development (and there is still quite a bit left!). Nobody so far had done much research on hotair airships in a traditional scientific way. Development work had more consisted of the output of practical operation and „from a pilots´s point of view“.
In early 1994 GEFA-FLUG accumulated a research and development budget of 500.000 pounds, which was partly government funded by the Ministery of Commerce of Northrhine-Westfalia. The programm run over a period of five years. The target was to get a “hi-tech“ hotair airship type certified and to sell it in a small series. The airship should be a fourseater. For the scientific part of the project various Aachen Technical University departments were engaged. The market of these airships are, of course, the traditional airship market and the above mentioned environmental monitoring market. Another objective was to create an airship which costs less than 100.000 pounds.
Target Definitions
Inflation possible in up to 12 kt ground wind.
Maximum flight speed up to 20 kts and more.
Stable flight characteristics in turbulent air (though using sloshing hotair as lifting medium)
Flight time longer than two hours.
Crew, including pilot, not more than four people.
One vehicle plus one trailer for transport of airship and crew.
Increase of envelope life time up to (and more than) 300 hours.
Selling price less than 100.000 pounds
Achieving The Target
To achieve the above mentioned parameters quite some scientific work was necessary:
Investigation on aerodynamic parameters (envelope, stabilizers, ruddersystem) in the Aachen Technical University windtunnel.
Measurement of aerostatic parameters and heat distribution of hotair airship envelopes with the help of testflights and loads of temperature sensors engaged.
Reasearch on envelope fabrics and sewing technologies.
Research on possibilities and limitations of weight reduction of envelope and gondola.
Flight experiments and computer simulations on aerodynamic – correlated with aerostatic – parameters of hotair airship envelopes undertaken by the Technical University Aachen to provide massive feedback for the complete research and development programm.
Outcome: Hotair Airship AS 105 GD
Total length 41 m
Diameter 12.5 m
Volume 3.000 m³
Max flight time (single pilot, max. propane) up to 4.0 hrs
Engine 65 hp Rotax
Max take-off weight 900 kg
Max flight speed 40 km/h
Crew pilot plus up to three passengers
