DG-808E - the uncompromised Motor glider with Electro-Power?
“Soaring - the Silent Flight.” We all know this is not quite correct when we speed through the air with our sailplanes at close to red line. But nobody complains about that. Unfortunately there is still a steady opposition by many of our fellow citizens when we start with an engine and generate some noise. Although especially the DG-808B is extremely quiet and ecologically friendly, restrictions are imposed because of other noisier aircraft and we are all affected.
I wanted to have a flying holiday in Samedan in the Engadin (Switzerland). No dice.
Reason: "We don't want any motor gliders with retractable props."
No amount of arguing and proof of meeting the most stringent standards helped, they just didn't want it. There are also soaring sites which permit only winch starts and exclude motor gliders. They also don't give a motor glider with a gasoline engine a chance, but would permit an electric motor, according to the government licensing authorities we consulted.
If one relates these facts to our customers, especially in the USA, they just shake their heads and can't understand it. Just as an aside, and it's not much help, because we live here and have to deal with our bureaucracy.
These considerations prompted the idea of an electric sailplane. It's not that unrealistic if you look at the development of model aircraft. When I was active in that "sport" more than 20 years ago we could only smile condescendingly about the colleagues on the “humming front” . Their aircraft were made out of lightweight balsa wood and at the same time the carrier for heavy battery packs. Sometimes they broke up in the air if stressed a bit too much.
And today: At the Aero exhibition large helicopter models flew inside the hangar with electric propulsion and performed perfect aerobatics. It was amazing! Our considerations brought us to the conclusion that in principle three electric propulsions would be possible:
- 1. Pure solar energy for hours of flight as long as there is sunshine.
- 2. A very light aircraft with a battery powered electric motor at a competitive price.
- 3. A high-performance sailplane without any compromise and the required batteries.
In particular:
1. The pure solar energy propulsion:
Such an airplane already exists and won the “Berlinger Award 1996” of the city of Ulm. 
The “Icare 2” aircraft is able to load a built in battery by solar power, to start with it and at about 2 m/sec reach 450m altitude. It can stay there as long as there is reasonable sunlight, shut down the motor if there are thermals while the battery is being recharged. Is this an ideal solution?
Even in the eyes of the “father” of this idea, Prof. R. Voith-Nitschmann of the Stuttgart University the “Icare 2” is not an attempt at an everyday airplane, but a pure technology carrier. It was to test if such an airplane is possible without regard of the aerodynamic design or the production cost. The result was an airplane of extremely light construction, which had all horizontal surfaces covered in expensive solar cells, and which was very expensive. It had a maximum speed of 120 km/h and is therefore not very attractive for normal soaring flight. At a span of 25 m it only weighs 270 kg.
Today's solar cells are about 16 to 17% efficient, and are very expensive. If these cells could improve their efficiency by several multiples and because of this were mass-produced . . . who knows what would be possible.
2. An Ultra Light:
Such an airplane also already exists, the “Electro-Silent”, an ultra light sailplane equipped with a 13 kw electric motor. Also a relatively large two-blade prop, which folds to retract and brings fairly good performance. Its first flight took place in Aachen August 1997. The performance was quite impressive for such a small airplane as reported in “Fliegermagazin” by Jochen Ewald. One did not expect to achieve a climb rate of 2.4 m/s, and in comparison an accompanying “normal” motor glider (Samburo) did not climb any faster. The battery lasted for a climb to about 500 m, but after that any “assistance to get home” is no longer possible.
On the other hand one could start by winch, and gain another 500 m with the help of the motor to get home. This would allow only a radius of about 15 km from the airfield. But at least one could gain some height in unlandable territory in the mountains in order to find a landable area in the next valley, or one could in most of Germany reach an airfield in that distance, without risking an out landing. Even if the airfield is “PPR” it would still be a comfortable landing spot. And a GPS would show the way to the nearest field.
The construction is simple and robust. One can exclude starting problems with this motor. There is almost no maintenance. One needs only a specially developed charger to get optimum performance from the battery. A load cycle off a normal plug is about two hours.
But one must recognize that flying the “Silent” is quite a compromise. The gross weight of 300 kg including pilot allows only the most sparing construction. The cockpit is only an “aerodynamic pilot dress”. No trace of a safety cockpit. Performance at the 12 m span is as expected, best L/d 31. But, perhaps for some after work fun still interesting.
But is a price of Euro 50,000 justified? That is a decision for each customer. Jochen Ewald found the concept interesting.
In the meantime we have to see, that obviously there is no market for this glider in Germany. The importer only sold 4 units.
3. The Sailplane without Compromise:
As a manufacturer of high-performance sailplanes we were naturally interested in the question of practicality of the concept of an electric-powered sailplane without sacrificing performance. Some basic considerations:
- First we had to investigate the technical problems. Is it at all possible to achieve an acceptable start height with a sailplane like the DG-800 without exceeding the gross weight limits?
- Then a cost estimate had to be calculated.
- And last but not least a marketing study had to show that such a sailplane was acceptable to customers.
Our preliminary investigation brings some answers: 
On the technical side there is first of all the choice of an appropriate propulsion system, especially the energy storage method. One has to consider that the energy density of a Ni-Cad battery is only 1/200 of the density of gasoline, about 30 w/hr per kg. As an example: The DG-808C has a tank capacity of 22 liters of gasoline - approximately 16 kg. The equivalent weight of a Ni-Cad battery to store the same energy would be about 3,200 kg, which clashes somewhat with the gross permissible weight of the sailplane of 525 kg. So that does not work. On the other hand, a battery pack of 60 kg would be the equivalent of about 0.4 l of gasoline (300 g). Not very impressive.
This raises the question of another battery type. There are Nickel-Metalhydrid, Lithium-Ion, and Zink-Air batteries, but they are either poor performers or too expensive. Fuel cells out of space technology are a possible alternative in the distant future. At the moment they are “priceless”. There is a possibility that future batteries achieve a great efficiency increase, which seems possible with solar cells. But here physical constants hinder development. If one uses conventional batteries an efficiency of motor and battery of 60 to 65 % is possible. At an empty weight of a DG-800 without an engine of about 260 kg, adding about 80 kg for an electric motor and batteries and a normal pilot weight, a climb rate of about 2 m/s to 550 m is theoretically possible. A “long range version” with a 23 kw motor and enough batteries to come up to the maximum weight of 525 kg would bring the maximum attainable start altitude to about 1189 m, and after an aero tow or winch start a return flight of about 60 km would be possible.
A second set of batteries in the luggage compartment would make a second start possible. It's technically possible.
After retracting the prop you would have a full featured sailplane.
However, not much more can be done without an explosive cost increase.
Now to the question of costs: It's fairly certain that an electric sailplane like the DG-800E would only be slightly cheaper then a DG-808B. In the “long range” version the costs would be about equal to the DG-808B. This makes sense if one considers that the basic sailplane is identical and only the cost of the motor and the battery has to be exchanged for the gasoline engine. The transmission to the prop by belt is very similar. But it simply could not be done for less than Euro 90,000 sales price.
Now the market:
We are certainly a company that takes environmental concerns seriously and tries to offer products with this in mind. That is why the DG-808C is so quiet. As an active pilot myself I have a personal interest to fly as quietly as possible. But no one would expect us to produce something that cannot be sold at least while covering it's development and production costs - which means a reasonable production run. Government subsidies cannot be counted on. We would need customers who would seriously consider such a sailplane.
Now a question to you:
How do you, our potential customers, rate the chances of such a sailplane?
Would you be prepared to pay an equivalent price for an electric sailplane as for the classic DG-808B? Would you make a deposit on one, if the deposit bore interest and would be guaranteed fully refundable if for some reason production would not proceed?
We look forward to your comments with great anticipation.
- friedel weber - 
translated by Albin Schreiter, CDN
Here is one of several answers to our question.
It seems to be a typical one:
Betreff: Electric Flight
Von: "William Mcnair"
Hi Mr. Weber,
Firstly, your web site is most impressive; it is refreshing to see a glider manufacturer actually trying to promote his sailplanes, and pay attention to his customers!
I wish you and your employees continued success.
Electric sailplanes - hmmm.....
OK, my first glider was a DG202/17; great ship, and with no ballast ideal for scraping on weak days - terrible with wet wings though!
However, due to the lack of gliding clubs, and launches mid week, when I saw a DG-400, I knew that was what I needed. I came into gliding from Sailing, and had no qualms about using an engine to get more soaring out of a given day or week. In fact I think the engine really allows gliding to fulfill it's primary objective of freedom of the air; to go where one wants, explore the sky and visit areas unexplored due to lack of launch facilities.
The only problem with the 400 was the wing (age was showing the design to be dated), and the lack of wing area when one considers the extra weight of the engine; I missed the low wing loading of the 202.
Then came the perfect ship, the 800. Unbelievable. OK, my Rotax engine is Fred Flintstone technology, but it is tried and tested, and works (noise is not too big a problem where I live). The airframe is super. With the big wings, I now have the old scraping ability back, the new section almost ignores rain, and the flaperons give outstanding control. The coordination is excellent; the 400 always felt best at 15mt.
Having said all this I have now placed a order for, not an ASH26, Ventus, or LS, but a B version of the 800.
The above preamble is useful to my comments on the Electric idea.
For a self launcher to be attractive to me it must satisfy the following criteria:
1. Primarily be a good sailplane. I took up gliding to soar, not run engines, so a touring motor glider, with the engine running most of the time is "out".
So, I want a modern wing, 18mt minimum. I would like 20mt (I often fly in weak weather), but no manufacturer can do this.
Included in this are things like cockpit comfort and safety, vision from the cockpit, build quality, ease of rigging and taping, and good gel aging (if there is such a thing).
2. Be reliable and have good after sales service. There are now plenty of self launching sailplanes available; where are they all on their learning curve, and can one get things fixed easily?
3. Have a good engine on performance. If the engine quits, I want to be as high as possible as quick as possible, to give myself lots of options. Also I require the ability to transit controlled airspace engine on, en-route to soaring areas.
4. Be able to taxi on the ground at ATC airfields.
Before you think I am anti conventional gliding, I should say that I am actively involved in the sport: I Instruct, Tow, Inspect and act as an Official Observer.
The true fun though is getting away on my own in my DG.
I would love an electric version of the 800 if it would give me the same things that my 800A, and hopefully my 800B will, but in silence.
However, it would need to:
1. Not have a weight penalty.
2. Have the endurance similar to the 800, as well as being able to taxi without burning up a lot of battery time.
3. Provide a strong rate of climb; at least as good as the 800A.
4. Have a similar price.
Maybe I have got the wrong idea from your web site.
Perhaps you are thinking of a "turbo" type self retrieve, instead of a self launcher. This would not interest me. I feel if one adds the complexity of an engine one may as well go the full way and make it self launch able.
I think there is a danger of falling between two stools; the pure glider, and the self launcher.
For me, and this is only my personal view - I have not researched the subject - I would either go for a pure glider or a real self launcher with no compromise on either the strong climb rate or endurance.
Oddly the attraction of the engine for me is the ability to take off unaided. OK, it is great to self retrieve, but to be able to take off when and where one wants opens up the soaring flight. Having said that if I add an engine I want it to do everything!
The electric engine is a good idea, but if it requires you to compromise on the wonderful independence and safety which the combustion engine offers, I feel that the idea although attractive may be ahead of current technology (no pun intended).
However, I am not familiar with the technology involved, and it may be out there already or waiting in the wings to appear in a few years time.
If you can pull this one out of the bag I would be most impressed.
Wishing you the seasons greetings and a safe and prosperous new year.
William McNair
Further Development
One can easily see that, because of the above results, we decided not to proceed with the development. Why would we offer our customers a product inferior to the DG-808C for a comparable price? Who would buy it?
At the Soaring Symposium 1999 in Braunschweig Axel Lange of Zweibrücken introduced a new project "Antares"
Mr. Lange worked for many years on the DG 800 as a development engineer under Wilhelm Dirks, and is using such a sailplane as the test bed for a propulsion system which, in the spirit of the headline of this article, can be called "as without compromise". (Is that the DG-800E?
)
Mr. Lange will use this propulsion system later in a completely new design with a 20 m span (18 m is also possible). This system is to be available in 2001.
Here is some information on this interesting project:
The newly developed special motor achieves a hard to believe 40 kw in the start phase, which gives about the same acceleration values as our motor glider. In the climb phase the performance degrades rapidly, but at an average of 2.9 m/s is still adequate. Service ceiling is about 1600 m.
No doubt this is quite an improvement on the performance of electric propulsion, but which is reached with considerable cost "without compromise". To achieve the high performance a battery charge of 250 volt is necessary! An electric shock would be fatal for a human, because he would be stuck on the direct current, whereas an alternating current would bounce back. I can imagine what would happen if there was a short circuit near a carbon fiber part. The sailplane would instantly burst into flames. Does one want this in a sailplane?
The motor itself if astonishingly simple and nearly maintenance free. However, around it a complex technology is necessary. The batteries have to be cooled by large air intakes in the wing nose and a turbine in the fuselage. For the actuation of the motor, the motor covers and the undercarriage a complete hydraulic system is necessary. The entire battery set has be monitored by an electronic system that will detect defective cells in flight and switch around them.
And lastly, a propeller with a 2m diameter needs two hinges in order to retract into the fuselage. And these parts are subject to failure. It will take extensive development and testing to bring such a system up to the standard of reliability of today's motor gliders. One can see that a great deal more expense will be necessary than anticipated in the initial project study.
Because the batteries are fixed in the wing, rigging requires additional specially developed tools. Mr. Lange unfortunately does not give out numbers of the weight of the wings, but it has to be considerable. The empty weight of the sailplane is in any case above 400 kg, which restricts competition flying especially in weak conditions. (As comparison the DG-808C weighs about 335 kg).
Climbing to 1600 m would be sufficient in flat land flying. But in alpine flying to enter wave or to return home over a mountain pass it is less than adequate.
A second start is only possible after charging the batteries for 8 hours. Fast Charge would take 2.5 hrs, but would require a suitable dc connection. Real fast charge (lass than 1 hour) is not possible with NiMH batteries. And flying from remote fields is not possible because of lack of suitable charge facilities.
For information: The total energy in the batteries is about equal to 2 l fuel. Who would buy a motor glider with a 2 l tank which, in addition can only be filled very slowly? A DG-808C tank takes 22 l.
In this connection one often hears the proposal to use fuel cells. They could be the fuel of the future, but today they are still enormously expensive, about 50,000 Euro for every kw . We will, of course, follow these developments. At this time the battery technology unfortunately does not produce acceptable performance.
This leaves minimal noise as an advantage. It must be wonderful to hear only a hum when climbing out, but is that enough to overcome the other problems?
Only the market and you can decide.
In any event, we wish Mr. Lange all the best in his new development.
The entire German manufacturing branch can use new ideas and innovations.
Von: Sessa Alberto
Dear Mr. Weber,
I read with pleasure your Newsletter and I send you mine personal considerations on glider's propulsion.
I'm really of the opinion that the future of gliders is connected to motorization for all reasons we know.
We must consider, first of all, that the engine is for the glider an "accessory" that works about 3-5% of total flight time. (Probably you have statistical data of this utilization).
If we accept this concept, we must say that actual motorizations are too complex, heavy and expensive for their use. (the cost of engine is about 20-25 % of total price of the glider).
Also actual research of electrical propulsion is, with state of the art technology, a nonsense because the weight and the cost of batteries is too much for having a productive solution.
Perhaps in the future with fuel cells at reasonable costs, electric engines could be interesting.
I think that in this moment the approach to the problem should be to investigate which engine has the following characteristics:
* Light and small as possible to reduce the impact on the structure of the airframe
* Easy to install on the gliders already flying in order to reduce
cost of airport structures in a reasonable time (if engines are fitted only
on new gliders, we must wait about 20 years to have benefits on flying costs!)
* The least important problem is the cost per hour of engine
operation, because we use it only for a few hours every year.
* Also the problem of noise is not so dramatic.! If someone doesn't
want engines on gliders we shall use winches for leaving the airport. In all
other situations don't forget that now we utilize an air tow that is really noisy.
If we agree on these points, we must investigate small gas-turbines or rockets or something similar. (Do you remember the flying men that opened the Olympic Games in Los Angeles? They had a backpack that thrust them vertically for several minutes!). These are, in my opinion, the new realistic possibilities to motorize economically both new gliders and old ones.
I'm very interested to know your opinion.
Best regards, Happy New Year and Good Landings
Alberto Sessa
Betreff: Electrically powered motor glider
Dear Mr Weber!
I read your article on the glider without compromise and I liked the idea of a glider manufacturer that spends some time to hear from the potential customers, and discuss with them the new ideas.
I am a glider pilot and a student of aeronautical engineering in the Technion in Haifa in Israel, I found your article while doing some preliminary reading on solar flights for a final project I would like to make "A Solar Powered Manned Aircraft". As a glider pilot I was thinking of the possibilities of having a solar powered motor glider for a long time and now that I have been reading about it, I can see that many people are sharing the same dream as me.
Here are a few comments I have to your article.
In your article you compared the fuel/motor motor glider to the battery/electrically powered motor glider but without considering the use of solar cells. It is clear that batteries are not the most efficient energy storage system, but because they are "rechargeable" they can be refueled during flight. Considering the technical data of the DG-800 and with a rough calculation I made, based on the wing area and weight of the glider and the performance characteristics, and based on 17% efficient solar cells, you can get over 70% of the power needed for cruising. Which means that in every hour of flight you can maintain altitude using the electric power for over 40 minutes or climb at 2 m/sec for over 5 minutes (600 m). As a glider pilot I would like to glide as much as possible without using the motor, and the need for the motor is mainly for the launch or for the "getting home".
With the improved technology of solar cells (now available at 24% efficiency but for a very high price) I am sure that in a few years we will start seeing more and more solar powered motor gliders and the feasibility of manufacturing them will improve.
The new technology of "Fuel Cells" is the only technology I think you can compare with the 22l fuel tank you have in in your glider and this technology is not going to be very cheep in the next few years although the car industry is involved in it very deeply.
Both these concepts must be studied today and development should start in order to be ready once the technology is available.
Your idea of a sailplane without compromise is a little problematic because you of all, as a sailplane manufacturer, should know that any aircraft design is a compromise. This brings me to the understanding that you might have to compromise on the performance a little bit in order to get a lower noise level or a better environmental propulsion system. Or, if you don't compromise on the performance you might have to compromise on a higher price (80,000 Euro is already not very cheep for me).
Looking forward for new innovations
Ofer Gideoni
Answer:
Dear Mr. Gideoni
Thanks for your comments.
If you have read the entire article you found a short description of the ICARE-project, which is solar powered. This is a "flying compromise" only to find out if it works. You just cannot use it as a "normal" sailplane.
Of course with better technologies new possibilities will be available. But in the moment we do not have solar cell with 24% efficiency or more.
Furthermore we do not think that gliders are the best "market" for such new technologies. It is much easier first to develop in cars and when everything is stable and has become cheaper then we can adapt it for our purpose.
My consideration was if in the moment there is any necessity to develop any revolutionary new thing.
The result: In the moment it is not. But the situation may change in the near future.
Of course every glider is a compromise but I would not accept an even worse compromise in comparison to techniques of today.
And by the way: Also the technique of a conventional motor is not at all at its end. The noise-level of a DG-808B is extremely low and my be it can be reduced further.
I agree that fuel cells could give additional possibilities, but in the moment a "normal glider pilot" cannot buy such a ship - it would be extremely expensive!
Always happy landings
Friedel Weber
Fuel cells as an alternative to batteries?
Nowadays the use of fuel cells to provide electricity is not only used in space stations. The car industry is also doing wide-ranging and expensive research in this sector. The plan is to release the first "zero emissions" car with this technology to the market in 2004.
"The fuel cell technology is the most promising of all alternative engine concepts", claim DaimlerChrysler.
At the same time however the hype that car manufacturers generated about battery-powered vehicles has all but died down. An expert from the design department of a big car manufacturer in California told me that this was not considered a way forward anymore and therefore all research in this field had been stopped for the time being.
So what about using fuel cells for gliders?
For this technology you need three things:
- Fuel (gaseous or liquid hydrogen, or methanol)
- a fuel cell to generate current
- an electric motor
The fuel cell remains the most difficult and most expensive component to build. Current developments show that costs of approx. $1,000 per kilowatt are realistic. Once serial production has started it is hoped that the costs will go down to approx. $100/KW, but at the moment this is just wishful thinking. At the moment it is in fact rather questionable whether these costs can ever be achieved, as a fuel cell consists partly of platinum, which is not available at low cost on the world market.
A fuel cell for the required 40 KW electric energy would currently be priced at approx. 46,000 Euro, and nobody can say whether this will eventually get cheaper or not.
In addition to that the following would be required: the cost for the methanol tank, the electric motor and the whole development costs One further problem is that the complete unit would probably weigh roughly 500 kg.
At the moment fuel cells will therefore only be used for very specific purposes and only be available more widely if the car industry starts production in a big way.
So for now this will remain just a nice idea - unfortunately.
A price of roughly € 10.000 for the battery pack appears to be practicable in our days – using a Lithium-Polymer Technology – the same as in all mobile phones. This more sophisticated solution – compared to a Lithium-Ion Cell – has two advantages.
It’s lighter in weight whilst granting the same electrical energy and is not kept under pressure. It does not require a steel frame or case. This is the reason for the smaller weight. Further on the angular outer layout of the battery enables a better fit within an airplane. This appears to be another advantage – compared to the Li-Ion battery.
We are closely monitoring the battery development. Right now we are still standing by our opinion regarding the advantages of combustion engines compared to the disadvantages of electric solutions. The development does not pay off as long as the costs for an electrified airplane exceeds those of a standard version.
But as you noticed - the development is nowhere close to an end. Time – maybe in the short future – will make an electrified
version more reasonable .
- friedel weber - beginning 2004 -
The End for Lange Flugzeugbau GmbH
The company Lange Flugzeugbau GmbH, based in Zweibrücken, Germany, filed for insolvency on 26th July 2007.
We had known about the financial problems in the company for a long time. The whole concept of the glider "Antares" with its highly complex systems was just very, very new and obviously not quite ready yet.
This insolvency is a real tragedy -
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with regards to the concept of electrically-propelled flight
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for the customers, whose investments in this glider will lose a lot in value
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for the suppliers, whose invoices have not been paid
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for the investors, who had been persuaded by the fascinating concept
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and above all for the German and European tax payers, who see millions of their money go down the drain here.
I personally am very saddened by the way this all went. The conclusion will have to be:
"Lange Flugzeugbau was ahead of its time" - but unfortunately time didn't catch up.
In discussion groups there already was a rumor, we would take over the assets of Lange Flugzeugbau. So here our own thoughts about this:
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We still don't see a profitable way of implementing electric motors in gliders.
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Furthermore, experts warn against the massive potential fire hazard caused by lithium cells.
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Using different cells however won't produce the power that the "Antares" has shown to be possible.
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We simply don't want to expose our customers to the risk of using Li cells.
In brief:
It's not all as simple as we would like it to be!
Translation by Claudia Buengen
In the meantime Axel Lange himself had bought the assets with a company founded in 2005.
He still is going to engage himself for his idea of electro flying.