DG Flugzeugbau GmbH / Passion, Power + Performance

The DG-1000S: The Challenger

 

Two-Seater from DG Flugzeugbau:

This article was published in the German Aerokurier 01/2001
All photos were made by Gerhard Marzinzik.

There is now a competitor in the Two-Seater Class.

DG Flugzeugbau offers an attractive alternative in this

competition class with a 20 m Two-Seater.

In it's 18 m version the DG-1000 is suitable for aerobatics and instruction.

 

 

Relief has arrived. After more than ten years of the DG-500 there is now a new two-seater from DG Flugzeugbau, the DG-1000. With a 20 m span the composite two-seater fits exactly into the competition definition of the Two-Seater Class. It will be good for the competition scene where the "Discus Only Culture" practically changed the class to a monotype. It will add plurality and
attractiveness.

The aim of the DG chief designer Wilhelm Dirks was set high. Before deciding to develop a new two-seater much research was to  see if and how much performance could be improved in this class. DG would undertake such a great new project not only to just improve the handling qualities, but a definite performance improvement should take place. The result was convincing. Two and a half years ago the decision was reached to develop and build the DG-100

Good Performance

The wing profile (HQ51) was developed at the German Center for Air and Space in Braunschweig (DLR) by Dr. Karl-Heinz Horstmann and Dipl. Ing. Hans Köster and was tested in the wind tunnel in Stuttgart. On paper the calculations showed a best L/D of 46.5 for the 20 m version at maximum gross weight. Minimum sink with pilot only should be about 0.51 m/s. In addition the polar showed the typical downward bend of most newer sailplane types only at the higher speed range. This means that the DG-1000 will stay with the laminar flow very well.

Comparison flights conducted within the company took place and, according to Wilhelm Dirks, confirmed the planned performance. After the first few flights in July Wilhelm Dirks was convinced that the profile also has little performance degradation due to bug impacts. On the first flight on July 27th, 2000 there was a fine, misty rain.

The fuselage-wing fillets were optimized for minimal drag by Professor Loek M. Boermans of Delft University. The winglets were also designed at Delft. The tail profiles came from the DLR..

As is usual these days the outer wing ends bend up (15 degrees) , are pulled back and have high winglets. All design features that improve the slow flight and thermalling characteristics. Unusual, but effective for reducing drag is the use of a fairly rough nobby tape on the underside of the wings.

The distinct upward bend in the wing helps ground handling. Only the small wheels at the outer end of the inner wing touch the ground when a wing is put down. Even the ailerons which extend almost to the tip and is connected to the inner aileron for both up and down movement, do not drag on the ground.

The division of the wing panels at 8,6 m half span make it easy to attach the outer wing panels with their winglets. Advantage of this division: the 1,4 m "bent" pieces and the straight main wing are easily stored in a trailer. But one must still heave the main wings parts, heavy as is usual in two-seaters, when assembling. All connections are automatic.

The exchange 18 m outer panels are connected just like the other tips by box-beam connection, and safetied with a spring driven pin.

In the 18 m version the DG-1000 becomes a trainer as well as an aerobatic sailplane. For use primarily as a trainer a (cheaper) club version with a tandem gear of the DG-505 is in planning.

The fuselage of the DG-1000 is derived primarily from the DG-505. The main modification is the landing gear. It consists of one main wheel that is retracted behind the pilots seat and swings quite far forward when extended. Because of the position in front of the c/g a smaller front wheel is not necessary, even when landing on rough ground.

When starting on a soft grass runway at Karlsruhe there was no tendency to drop to the front of the fuselage.

The forward position of the main wheel, with hydraulic disc brakes, naturally shifts weight to the tail wheel. But with an empty cockpit the tail can be lifted easily to attach or detach a dolly. No special tool is necessary.

The rudder also received a new profile. A piece of the super sailplane "eta" is incorporated here. It is as high as that on the DG-505, but is slimmer. The elevator can be attached without acrobatics, the pilots are helped by the automatic connection and the location of the safety pin on the rudder fin.

The rudder fin contains two mass balancing containers. There is the usual fin tank to balance the c/g with water ballast. Filling is through the aft fuselage. The amount can be judged by the marking on the visible scale.

To balance the c/g for heavy cockpit loads there is a glass faced weight box in the tail fin. The trim position is immediately visible. With two pilots weight can be added to achieve a rearward c/g. Maximum load is nine one-kg metal blocks. This makes it possible to fly with optimum c/g regardless of cockpit occupancy.

A comfortable, but high cockpit

After these preparations the high landing gear makes it necessary to "climb" in. However, if one first sits in the cockpit side it's easy to get in. The split, side-opening canopy leaves ample room.

Inside the cockpit there is little change from the DG-505. The front pilot positions his legs around the instrument panel and has a seating position almost like a single seater. The co-pilot or instructor sits more erect, and his seating position can be adjusted both in height and back position as in the 500 series. There are no obstacles to an emergency exit. The canopies are ejected by pulling two levers.
The controls of the DG-1000 are well positioned, and the control travel is convenient. The rudder pedals are adjustable. New is the "Piggott Hook" to prevent the accidental deployment of the dive brakes, as well as a parking brake position for the main wheel. Braking is by full extension of the dive brake handle.

The start in aero tow - the tow hook is located in the fuselage point and the winch hook under the second seat stick - was without problems right from the ground roll on. The ailerons become effective quickly and the sailplane rolls easily on the large main wheel. The two-seater follows the tow plane in a stable manner, and only small control deflections are necessary for correction. The wheel can be retracted while on tow, and, considering the large wheel, with little effort. Visibility is good.

The good first impression continues into free flight. The DG-1000 stays stable, both in straight flight and banked flight. Trim is effective from minimal airspeed up to about 180 km/h.  

No problems in slow flight

The first flight was in the 20 m span. In this configuration the two-seater gave definite stall warning. With a low horizon the shaking of the elevator left no doubt about the transition to stalled flight. Relaxing the stick restored normal flight. If the stall warning was ignored  and the airspeed reduced further, the DG-1000 became unstable and the ailerons lost effectiveness until a wing dropped. Restoring normal flight was routine and resulted in only little height loss.

Stall in thermalling flight was similar. In straight flight at 580 kg gross weight the wing dropped at about 70 k/h and in 30 degree bank at about 3 km/h above that.

The 18 m version showed the same benign slow flight characteristics, but would not go quite as slow as the 20 m version. The border airspeeds were slightly higher due to the higher wing loading.

Unfortunately I could not test the thermal flight characteristics on this November day. However, a 45 degree to 45 degree change at about 4.5 seconds at 90 k/h showed that this large sailplane is still quite maneuverable and not at all slow to react.

Initiating turns and corrections in turns, such as rough thermals require, showed very well balanced aileron and rudder forces. There was a marked difference in the aileron forces between the two versions because the 18 m version handled almost like a single seater. This is where span has it's price. On the other hand, the visibility over the bent-up and rear tapering wings is excellent and adds to the optic flight enjoyment.

Adjustable vents ensure comfort in the cockpit. Besides the nose vent there are adjustable outlets in the right cockpit wall for both front and rear seats.

The dive brakes require only minimum effort, and with the wheel out steep approaches with sink rates of 4 to 5 m/s can be achieved. Full deployment of the dive brakes cause a slight downward movement of the nose leading to an increase in airspeed easily corrected. One can also side slip the DG-1000. The winglets did not interfere.

Approach and landing of the 1000 pose no particular problems. The flaps can regulate the descent rate. Touch down can be at minimum speed as a two point landing. The wheel brake ensures good roll out. Because of the good ground clearance and the bent up wing tips even landings on rough ground should not result in a ground loop.  

My over-all impression:

In both span variants the DG-1000 presents a good impression.
It is a well designed sailplane with good flight characteristics,
and is suitable even for narrow thermals.
It's performance potential will no doubt become obvious in the coming season. 

 
 

The Piggott-Hook

The DG-1000 from DG Flugzeugbau in Bruchsal will have a new, important safety feature as standard equipment, the Piggott-Hook. This hook prevents the dive brake / spoilers from opening accidentally while starting if they were inadvertently not properly locked at the start.

One can see the details of this safety feature when the canopy is opened. It's an asymmetrically toothed piece of metal next to the dive brake handle, and a corresponding hook on the dive brake handle. A spring will pull the lever towards the cockpit side so that still open dive brake handle will catch on the hook. This prevents further opening of the dive brakes. The "unlocking" for the event that the dive brakes should be used will be automatic because the handle will have to be pulled away from the cockpit side. Locking the dive brakes normally can be done in the usual manner.

The parking brake by fully extended flaps functions in the same manner. Only the teeth point in the opposite direction

Gerhard Marzinzik
translated by Albin Schreiter, CDN

Other Articles of Interest:

 


DG-1000 - the development

 

DG-1000 - Impressions and Comments

 

Derek Piggott flies the DG-1000

 

DG-1000 Trim Box

 

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

 

DG-1000 T - the sustainer version

 

DG-1000 hums

DG-1001TE - the Electro Sustainer

DG-1001 Club - the version for the USAF

 


 

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