DG-1001T - our Two Seater with Turbo Engine

A. Concept

In the course of developing the DG-1000 into a whole product family, introduction of a variant with wing flaps was planned as the next step , together with the self-launching DG-1000M.

But to our surprise, ongoing discussions with prospective customers revealed the strong interest in an inexpensive auxiliary engine to allow safe return to the home base during a cross country flight. Particularly clubs are interested in this return capability to intensify cross country training and cross country flying without the risk of out landings. Their established launching capabilities by winch or tow would not justify the higher cost of the self-launch capability.

We listened carefully to our customers and changed our planning. The next addition to the DG-1000 family is the DG-1000/DG1001 Turbo, the variant with the auxiliary engine for return flights.

B. The Power Plant

We did an extensive market research for existing modern auxiliary power plants, not to invent the wheel again. Of course we had investigated different solutions, in particular the use of four stroke engines.

Two-stroke engines are less optimal than four stroke engines in terms of fuel efficiency and emission characteristics, but this is in our case not of significant importance. However, air cooled two-stroke engines excel by unbeatable simplicity. We don't need a coolant or an oil system and save the associated two pumps. We also avoid cold-start problems and oil leakage when retracting the engine.
A four stroke engine would therefore be much more expensive.

A Cart engine built in Switzerland was offered to us, which would have been a good fit. But after the manufacturer became insolvent, we lost this little 4-stroke engine as an option.

Therefore we selected the well-proven Solo engine again; a two-cylinder two-stroke engine, used in a similar configuration in our LS8-st. This engine is paired with a comparably large two-blade propeller, a custom design by our specialist Dieter Schmidt. It provides a much better efficiency than a smaller and faster turning two blade propeller, or as an even smaller four-blade propeller.

The efficiency of a propeller typically increases with its diameter. But also the engine frontal area becomes less influential with increasing propeller diameter. A small propeller which blows mostly over the engine has obviously more drag and less efficiency.

Have you ever seen the inside of a propeller?
Please click on the picture!

C. Engine Control

It is already “corporate tradition” that DG seeks for an optimum solution. The DEI in the DG-808C provides already outstanding comfortable engine control, contributing to improved safety. In the DG-1001 Turbo we go even a step further. The following list itemizes the actions required by the pilot to start the engine:

1. Ignition On

The DEI in the DG-1001 Turbo is always on, even in glider configuration (we report on this feature in another report). Therefore after switching the ignition on, the following sequence happens automatically:

The electric fuel pump and the extension spindle actuator start concurrently
The engine doors open and the engine is extended
The fuel valve is always open
When the engine is fully extended, the starter works, which knob you have hold down
The primer injects the exact cold-start fuel quantity
The motor starts and develops full power

2. Next step

Sorry, there is no next step! This was already everything needed!
At DG Flugzeugbau we call this:

“On-and-Go”

Stopping and retracting the engine is similarly “complicated”:

Switching the ignition off will bring engine and propeller to a full stop.

The propeller stopper is extended into the propeller plane
The propeller turns slowly until it reaches the propeller stopper
The spindle actuator retracts the engine
The engine compartment doors close

Again here is switching the ignition off the only required action, everything else happens fully automatic. In case of a malfunction allows a manual system to retract the engine without the need for any electronic support.

Such a sophisticated control system is not only a convenience for the pilot. It is even more an important safety improvement. An immediate response of the engine is typically needed at low altitudes, when the pilot is exhausted from unsuccessful search for thermal lift. In this stressful situation any single mistake with a conventional engine control system can prevent the engine from immediate starting and result in a dangerous situation for the pilot. Auxiliary engines are usually much less frequently used compared to engines of self-launching gliders. Particularly club pilots tend to be less fluent and trained in the usage of the auxiliary engine systems. The operation of the engine must therefore be as simple as ever possible.

We do not like an experience with the DG-1001T, as pilots with a competing type of glider have had, as they landed in a lake in southern France having forgotten to switch on the ignition....

D. Usage Spectrum

The DG-1001S is already known for its universal talent for cross country flying, pilot training and aerobatics. "Simple Aerobatic" such as Loop, Turn, Spin with positive g-forces are allowed also with the DG-1001T.

Furthermore the DG-1001T is certified also with 18m wing tips. So it remains also suitable for glider education and in this configuration the complete aerobatic program is allowed too.

Theoretically we also could offer a "DG-1001T Club" with fixed gear and fixed 18m wing tips. But practically that will not make any sense.

Last but not least a turbo engine can be used to support an aero tow behind a motor glider or a microlight aircraft.

- friedel weber - Translation: Manfred Koethe

Maiden Flight of the DG-1000T - Febr. 3rd, 2004

The maiden flight of the DG-1000 turbo-version was completed unspectacular, because we already knew the excellent flight characteristics of the glider.

We only wanted to test the function of the new power plant, and everything went well.

As you can see on the pictures, the engine has a normal starter, so you also can use the engine on the ground for testing purpose. We are convinced that such a true electrical starter system gives an substantial improvement in safety, because you do not need to fly very fast in low altitude to start the engine. Only for the case of emptied batteries you still have this option available.

The new DEI is fascinating. We call it "DEI-NT " (New Technology!). Here you can read a special report about that item.

- w-dirks -

Prototype-Testing in Lesce, Slovenia 2004

"If Friedel doesn't manage to break it then it's ready for production." That's what you can hear from Wilhelm Dirks all the time. Therefore he agreed very much with my plan to take the DG-1000 Turbo prototype to our annual vacation in Lesce-Bled; a place we visited now for the 6th time in a row.

Let me share my experience flying the DG-1000 for 2 1/2 weeks all across the Alps, with the “return to home insurance” provided by this little engine in the back. Each day I had the "problem" to find a partner to fly with me, since my wife prefers to remain firmly on the ground, as you know. However the problem always resolved naturally and led to excited comments from those flying this ship for the first time. Not only that it handles nicely, it has apparently very good glide performance and is particularly quiet.

I have never before flown any glider with such a low noise level. The whole ship provides a very solid impression, surely a good value for the money. But this is nothing new for pilots having already experience with the pure glider version DG-1000S.

New was however the engine and the pending questions about its reliability. Here again this flying vacation provided a positive experience.

The engine management with the new “DEI-NT” is very easy, as mentioned earlier. The almost fully automated system is very reliable. The simplified control procedures eliminate opportunities for mistakes almost completely. This is particularly for flying clubs an important safety improvement. The engine started immediately every time and ran smooth. The noise and vibration level was very low; noise reduction headsets became never necessary. The electric starter is another safety benefit. It allows a full check-out of the engine systems on the ground. Also, briefings including engine operation for transitioning pilots can be done safely on the ground instead in the air, another important advantage for club operations.

The engine has sufficient power to enable a safe return to the home base - even in higher altitudes of the Alps. The relatively large propeller has high efficiency, also due to the small frontal area of the engine.

Betankungseinrichtung der DG-1000 Turbo The generously dimensioned tank holds 6 US gallons (22 liters). The refueling system is similar to that of the DG-808C, however with one improvement: The DG-1000T has the fuel line connector and control switch located in the engine compartment; eventual fuel spills will not cause unpleasant odor in the cockpit. Refueling is very simple: Just connect the refueling hose, drop the open end into the fuel container and press the yellow button. The onboard pump stops automatically when the tank holds 6 US gallons (22 liters). There is hardly a way to make this simpler.

Equally reliable operated the solar generator, which is smoothly integrated into the fuselage similarly as in the DG-808C. Even with the two soaring computers and frequent trials of the engine, we had always enough electric energy available from the main battery with 12 Ah capacity. The installed second battery was actually not necessary.

We had no stress with the technology and could fully enjoy the wonderful flights with this extraordinary aircraft. Here we are circling above the Triglav, the highest mountain of Slovenia (2.850m):

Further developments and optimizations:

The Solo Engine runs smooth with no excess vibrations or rattling parts. Also it has a pretty elegant appearance. While that is not a primary argument, it is still a nice observation.

We were finally fully satisfied. Besides appearing very solid, the new engine system has all the qualities we at DG Flugzeugbau expect from a modern sustainer engine system.

The retraction mechanism has a likewise elegant design with its simplicity and reliable operation. Here is how it works:

To retract the engine, just switch of the ignition and continue to concentrate on your current thermal. In the meantime the engine pylon has tilt backwards about 30 degrees to reduce the windmilling forces. There is no need for slow flight to stop the engine, it will stop with no further intervention. The new DEI recognizes when the propeller stops and retracts the engine pylon further, bringing the propeller stopper into the propeller plane. In this configuration the propeller is turned slowly by the slipstream until it reaches the propeller stopper. If you become impatient, you can accelerate the procedure by pressing the starter button. In this case pulsed current to the starter turns the propeller until it reaches the propeller stopper in a perfect vertical orientation. Now the engine will be retracted completely without further intervention.

This procedure sounds more complicated than it is, and it requires only two sensor switches, a bit of new programming inside the DEI and the clever mechanical design of the propeller stopper. This retraction mechanism is much simpler than that of the DG-808C, and its sturdy design makes it club-proof. Please take look into the engine compartment, every technically-inspired person will probably be excited.

So, how does the new bird fly?

The most important change compared to the previous engine, we had built in, is the climb performance. With 275ft/min (1.4 m/sec) at standard atmosphere conditions, the DG-1001T climbs better than any other aircraft in this category, and a speed of 76 kts (140 km/h) in horizontal flight can be reached. In an altitude of about 500m and in summer temperatures you still can expect a climb rate of 236 ft/min (1.2 m/sec)!
The vibrations and noise level are at an acceptable level, so that noise-protecting headsets are not necessarily required.

Here is an additional page with the

Technical Data for the DG-1001T

...and here the final Type Certificat of the EASA

dg1000-musterzulassung.pdf

Utilization of the DG-1001T Fuselage for the DG-1001S

If you like to purchase a DG-1001T but in the moment your financial possibilities are good for an sailplane "only", we can deliver a DG-1001 to you which is prepared for an engine installation later.

The fuselage of this "DG-1001S" will be strengthened and the engine bay doors will be mounted already. All the other work can be done by us later.

We already issued a special Technical Note.

DG-1000 above our factory

A short report from our aerobatics expert Alwin Guentert -

Aerobatic with built in Motor

A flight was made on the 2nd September 2005 in the DG1000T, serial number 10-28T1, registration D-KITT with built in and retracted motor.
T/off : 16:57 GMT from EDTC by aerotow Landing: 17:20 GMT in EDTC
Pilot : A. Guentert (pilot weight with parachute 79kg), middle CofG position

Following aerobatic maneuvers were flown after release at 2200m agl.

Looping
Stalled Turn left and right
Roll left and right
Roll over top
Stationary Inverted flight with negative pull up upto -3.5g
Half snap roll from straight and level flight to inverted flight with positive pull out turn.
Half negative snap roll from inverted flight to straight and level flight

G-forces between +6.0 and -3.5 were registered during these maneuver.
No problems whatsoever were encountered during the flight and there was no indication that the motor changed its position or that the motor cover opened.

Translation: Frank Pennauer

The following mail came from Mr. Gaida, an engineer, who for himself has developed a Turbo-System into his DG-300, which obviously is working fine.

Hallo Mr. Weber,

Let me thank you first for your Pilot- Info web site. There is always something interesting in it. And please don't stroke me off the distribution list, even if I am a nuisance at times.
I am certain , that you are aware of the advantages of the planes that you are producing, but you might be interested to hear the opinion about them from one of your customers.

My daughter reaches the age of 14 this year, and although I did not anticipate to ever sell my DG300, this made me consider the purchase of a Two Seat Glider.

I therefore have contacted the two manufactures who produce such a plane to provide me with information material. It might have been a coincidence but the person I contacted in your company provided such information immediately. But the person I contacted in the other company asked me to call back at another time as he was too busy at this moment.

I now have flown both planes sufficiently to be able to make a comparison. In my case, the plane in question would only be a two seat glider with a 20m wingspan and powered by an auxiliary engine.
I would prefer a self launch two seat glider but unfortunately no such plane is on the market at this time..

1. The Other Turbo

I flew the Other Turbo first. A brand new plane of the latest development.

At this point I am not quoting a large paragraph, because two of our readers commented that it was not necessary for me to publish negative reports about products of our competitors. Considering that two of our readers wrote to us might also represent the opinion of the other 200 German speaking readers. Therefore I am not quoting, the paragraph with the derogatory remarks about the "Other Turbo".

The letter of Mr Gaida continues:

DG-1000 Turbo

DG was considerate enough to let us fly with their plane. The rigging of the plane was completely without problems. The following sentence you can leave out if you wish. But it would be desirable for a better solution to be found for the elevator connection and airbrake lever. At least the airbrake lever changes would be simple.
The rear seat is also very comfortable, in any case quite a bit more comfortable than in the DG-500.

What I was very enthused about, was the fact, that one could use the turbo during the aerotow to assist the climb rate. We brought our 80hp Scheibe Motorfalke along in order to see how it would be capable to tow the DG1000. The result was it performed excellently.
Considering that the approximate total weight of the 3 pilots (tow plane and Glider) was 250kg, with very warm weather (30C) and taking off from grass the tow performance was better than with a single seat glider without turbo assistance.

Off tow, the Turbo achieved a climb rate between 1.3 - 1.5 m/s, even with the high pilot weight and warm weather . I consider this safety. The operation of the turbo was simple and problem free.

The control coordination is "DG". One has to "fly" the plane. But one gets used to this within a few minutes. What is excellent is the high maneuverability of the DG1000, specifically over the longitudinal axis (ailerons).
What I also liked were all the shortcomings that I criticized on the other plane.

The fact that the DG-1000 can be flown by the pilot in command from the front or the rear seat is another great feature. As this is particularly important thinking that some of the pilots in our club cannot fly by themselves anymore for health reasons, I find this feature top class. Also, if one takes up guests one has the possibility - although not being an instructor- to sit in the rear seat.

It is also excellent that the DG-1000 is fully aerobatic. But this would not be the reason for myself to decide to buy the DG-1000 as I only fly aerobatic maneuvers very seldom, but to know one can kick it around a bit, is assuring.

I would have only one wish, a shorter delivery time!

With best greetings

Dr.-Ing., Dipl.-Ing.
Gregor Gaida
Engineering Office