DG Flugzeugbau GmbH / Passion, Power + Performance

DG-1001TE - How to get home - quietly and safely!

 

A. Concept

Many of you know that after having thought about it at great length we were quite sceptical about electric motors, in particular in connection with self-launchers. The power provided by even the heavier batteries is still not enough, compared to the tank of a combustion engine, even with the new lithium polymer batteries.

However, what about an electric turbo?
This has totally different requirements:

It becomes apparent that designing an electric turbo can be made a reality with far fewer compromises than needed on self-launchers at the moment.

We also wanted to concentrate on a further vital aspect:

B. The safety of an electric motor.

You may think there is nothing unsafe about an electric motor.
Unfortunately you are wrong!

To keep the electric currents at controllable levels you have to use relatively high DC voltages of more than 200 Volt. A DC voltage electric shock of that magnitude however is significantly more dangerous than e.g. from a mains socket in your house. In the latter case the hand is pulled away immediately due to the pulsating voltage - the muscles contract in an uncontrolled but fairly hefty manner - with direct voltage you may "get stuck" until...

Of course all leads are well insulated, but if the batteries are stored in the wing then long leads are inevitable. What would happen if during a heavy field landing the wing swings forward and the uninsulated cable ends get in contact with conducting carbon fibre structures? I don't even want to think about that!

I also don't want to think about what happens to a defective cell if by coincidence the monitoring of exactly this cell is defective. I am not going to elaborate any further, but explain the essential requirements we came up with from the beginning:

If these requirements can be met then this power source can be called the "safest electric motor for gliders".

C. The power source

There was another vital requirement.

This requirement meant that high efficiency was excluded from the start as this would have cost enormous amounts in development. Instead the aim was to use mostly industry-standard parts.

This was partly achieved, but motor, inverter and charger had to be designed specifically after all.

We also found during the development process that the available space and load allowance compared to the required battery is much better in the DG-1001 than in the "LS10-ste" which had been the original plan. This is why as a first step we have are developing the two-seater with an electric motor, and the LS10 will follow once a new generation of batteries is available.

Another point is that the development cycle of new batteries is significantly shorter than the development cycle of a new glider.

This way we can maintain an up-to-date system for years to come and are not restricted to one battery type.

D. The motor control

It is almost a company tradition that DG again do their own thing in this respect.

We will therefore have the well-known DEI-NT. As is tradition at DG Flugzeugbau, to operate the motor you simply have to switch it on, everything else happens automatically.

E. Application

The idea was that everything you can do with the DG-1001S or the DG-1001T should also be possible and legal with the DG-1001TE. The empty weight will not be much higher than that of the 1000T with a full tank, and there is also the option for an electric launch support if you are towed by a weak tug.

F. Availability

In spring 2009 the development is in full swing - the picture above has of course been fudged a little! At the AERO you'll only see the announcement - our "star" there will be the DG-1000M.

We expect to start serial production in the spring/summer of 2010, however we need the government's approval first ("ZIM", a grant programme designed specifically for SMEs).

- friedel weber -
- translation by Claudia Buengen -
 

The Development continues

We stopped the further development of the DG-1001TE after the AERO 2009, because we wanted to ensure the governmental aid for this project.

Meanwhile, German chancellor Angela Merkel and German finance minister Peer Steinbrueck met each other and officially decided to support the development program of an innovative sailplane manufacturer close to Karlsruhe!

Well, its not that much but it helps to keep the development costs manageable so as to remain the subsequent price for the system affordable.

We assume that the price for the DG-1001TE will be 10.000 Euro higher compared to a classical Turbo version - rather less.

Today's strategy is to develop an electro-turbo propulsion that fits exactly into the motor box of the DG-1001T, in order to achieve a simple and practical feasibility study.

Next steps will be done when the DG-1001TE is flying and when we gain the accurate performance data from practical experience.

Motortest of the DG-1001TE on the Ground

Here you can see Jelmer Wassenaar, the "Father" of the DG-1001TE, testing the system.

Using the propellor of the DG-1001T the motor runs with 2.700 rpm on the ground. That means about 15% more power as the piston engine has. The climb performance probably will be quite higher but exact measurements will be required.

This rpm constantly remains during a time period of 20 minutes. After that the performance decreases quite fast, until the system cuts the power to save the batteries.

Within these 20 minutes - practically 2 x 10 minutes! - the gliders has reached a sufficient altitude to fly 100 km at least. So the goal we set at the beginning of the development has been achieved.

Now we are very excited to see the Maiden Flight within in next days.

Here is a video showing the very simple process of extracting and retracting the engine:

Testing on the Ground

Maiden Flight of the DG-1000TE

by Jelmer Wassennaar

When I started my career at DG-Flugzeugbau in October 2009, the DG-1001TE was still in the stage of a concept. Only the idea and a rough theoretical part was done.

In the first setup we planned to develop a special electric motor and a special power inverter together with a partner company. However, after a while it was clear that this joint venture would not work.

So first of all we started to look for a motor and power inverter combination which was able to use our DG-1001T propeller. Via Germany and China we finally found a very experienced company in Slovenia. Together we finally made the decision to modify the existing system according to the needs of the DG-1001TE. Now we were able to start the system integration.

At the same time, our project partner Utz Schicke started to develop a management system for the DG-1001TE's power plant based on the well know DEI-NT. The multifunctional DEI-NT should also be able to care for other systems e.g. battery-management, temperatures, charging and the power inverter.

On May 7th we finally did it. I performed the "TE’s" maiden flight due to better conditions in Nahstätten, the home airfield of Holger Back, our managing director.

With a mass of 625kg I took of at 12:45 behind the Dimona (pilot: Jochen Back, who will fly the glider during the German Nationals).

The engine extracts automatically by switching the "Ignition Switch" on the DEI-NT. Everything is based on our well known and very simple engine management. A starter button is not installed any more. After full extraction the engine starts by pushing the throttle forward.
You cleary recognize the strong power of the electric motor. Also the vibrations and noise level is much lower than in a comparable DG-1001T. Especially the noise level in the high frequencies is very low. The result is a very gentle "humming" in a very comfortable frequency on the ground.
The power inverter smoothly increases the motor speed and keeps it at the adjusted rpms.
By flying faster the power inverter converts the motor into a generator. The power inverter now generates DC power and recharges the batteries.

The sink rate with the extracted motor is much better than the DG-1001T's sink rate due to the better aerodynamics and drag. So it was possible to keep on climbing in weak thermals although the engine was extracted.

The best climb rate was not measurable precisely due to turbulences. But an average climb rate of at least 1,5m/s and more is possible.

Our aim to create a maintenace friendly, reliable and easy to handle electric power unit seems to be fully achieved.

Jelmer Wassenaar

Flyer of the DG-1001TE

 

Related topics and articles:

 


DG-1000 - Development

DG-1001 - the new DG-1000

 

DG-1000 - Impressions and Trial Flight

 

DG-1000 - A flight report by Derek Piggott

 

The DG-1001 trim box

 

Aerobatic Test flights of the DG-1000S/18m

DG-1000 is humming

 

Aerotow with the turbo engine running

DG-1001M - the Self-Launcher

 

 

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