Challenger in the Luxury Class
Test report by Jochen Ewald about the DG-1000,
published in the aviation magazine "Fliegermagazin", issue 07/2001
In recent years the 20 meter two-seater class has been dominated by the Duo Discus. Now DG Flugzeugbau have undertaken to challenge the Schempp-Hirth glider with the introduction of the new DG-1000S. The DG-1000S has just gone into production and like the Duo Discus it is an unflapped glider. However, the wingspan of the DG-1000S can be reduced to 18 meters for training and aerobatic flying.
The look of the newcomer seems familiar: the fuselage configuration has largely been taken from its predecessor, the DG-500/505. Totally new, however, are the big, well-sprung retractable undercarriage situated in front of the C of G, which makes a nose wheel redundant, and the tail section. The elevator is designed in a double trapezoid shape, and the rudder fin incorporates a sophisticated trim system: A number of removable trim weights compensate for the weight of the copilot in the back seat (see photo). The trim weights can also be used to increase the cockpit load for light pilots to the required minimum in the front seat. There are special boxes for the trim weights in front of the seat under the pilot's knees.
A 7.4 liter water ballast tank in the fin can be filled to compensate for the maximum of 160 liters water ballast in the wing tanks. This way the new DG can always be flown within the best C of G range. In 20 meter mode the wing load of the two-seater ranges between 28 (single-seated) and 42.8 kg/mē, depending on the glider's weight, which varies between 415 and 750 kg.
A brand new feature is the wing profile HOK-51 by Karl-Heinz Horstmann, Braunschweig and the winglets and the wing/fuselage section by Loek M. M. Boermanns, Delft. Apart from a high performance the main focus lay on docile handling and a minimal bug/rain sensitivity.
The main wings have a span of 17.2 meters which is extended to 18 or 20 meters with two different sets of wingtips. In 20 meter mode the wings are of a quadruple trapezoid shape, the wingtips being of a higher dihedral and fitted with winglets. A small wheel at the lowest point of the main wing provides enough ground clearance (with either of the two wingtips) for aero tows on tarmac or cut grass runways even without a wing holder.
The wings weigh 90 kg each and are easily put together, with the tongue and fork type spar connection, two main pins and automatic torsion rod connections. Vertical drag pins on the rear lateral wing mountings provide the necessary rigidity for aerobatic flying. The long wingtips incorporate aileron segments which slide over the inner ailerons and move with the main ailerons in both directions. Just like on the DG-500, the locking pin of the automatic elevator connection is clearly visible when the elevator is not connected.
On the ground the DG-1000S sits on the tail wheel, to put the tail dolly on a second person has to push down on the glider's nose. Both canopies are hinged to open to the right, the front seat is quite high.
Enough Room for Tall Pilots
The spacious cockpit is big enough even for tall pilots - as you would expect from a DG glider. Once sitting in the comfortable seat pan, the pilot can easily reach the levers for undercarriage, trim (the lockout lever is mounted on the stick) and airbrakes, which are fitted on the left of the cockpit. Even though the rear pedals are not adjustable, the rear seat pan is. Height and tilt adjustment provides pilots of all heights with a comfortable seating position and excellent visibility.
The undercarriage is retracted easily and with a positive lock. Even if the airbrakes are not locked they cannot open inadvertently during the launch as a Piggott hook fitted to the airbrake lever prevents this. The canopy emergency release hooks could be placed a bit further forward.
|
|
For an aero tow the DG should be aligned with the runway direction as, for the first few meters, the tail wheel will steer the glider as if it were on rails. Right from the beginning of the ground run the aileron control is excellent, steering against a cross wind is not a problem.
Both on the rope behind the tug as well as in free flight the 18/20 meter glider is docile and stable, the controls are easy to move and well coordinated. Another well-designed feature is the ventilation system with a central vent in the front of the canopy and adjustable nozzles for both seats on the left of the cockpit. In the configuration we flew - 600 kg take-off weight, with a rearward C of G position - the DG-1000S behaves well in the stall: At 73 kph (39 kts) it starts to shudder, at 70 kph (37 kts) one wing will want to drop. If no recovery is undertaken the DG will go into a spin which can be terminated immediately with the standard recovery method - opposite rudder first, then ease the stick forward. Exactly what the instructor wants for the spin recovery training. In the 18 meter configuration the speeds are approx. 3 kph (1.5 kts) higher. Opening the airbrakes increases the stall speed in both configurations by 5 kph (2.6 kts) and allows holding the glider in a mushy stall without one wing dropping.
Fully Aerobatic in 18 Meter Mode
The roll rate in 20 meter mode is good: 5 seconds at 100 kph (54 kts). In 18 meter mode, however, it is only slightly better: 4.7 seconds at 105 kph (57 kts). At this speed rolling maneuvers at full deflection are possible without any sideslip.
Soaring flights are a joy - even in weak thermals this two-seater will make it easy for the pilots to get the best climb out of it. Unfortunately we were not able to do any aerobatic flying as the newly fitted ailerons made of more rigid carbon fiber had not yet been tested for their flutter resistance. For aerobatic flying, however, the DG - which will be fully certified for aerobatics in the 18 meter mode - would benefit from a slightly better roll rate.
Landing is easy with the very effective two-bladed Schempp-Hirth style airbrakes. They increase the optimum trim speed from 85 kph (46 kts) to 100 kph (54 kts). Sideslipping is very easy and effective. The rudder tends to stick but can be moved back with little pedal movement. Fully held off the DG-1000S will touch down on both wheels simultaneously. The hydraulic disc brake actuated with the brake lever works well, the risk of pitching is low.
A comparative test flight that DG Flugzeugbau made with a Duo Discus confirms the company's calculations: The performance of the DG-1000S at 80 kph (43 kts) is said to be slightly below that of the Duo Discus, but 1 to 2.5 points better at 140 kph (75 kts), the same as the Duo's at 160 kph (86 kts), and above that it is said to be slightly better again. On both glider types there is very little need for improvement in the flying characteristics.
So the conclusion can be drawn: "The DG-1000S has reached its target." The luxury class of the training and competition gliders has its price, though: 70,000 Euro with 18 and 20 meter tips plus VAT. A simple club version, the DG-1000C (18 meter wingspan, fixed undercarriage, no water ballast) as well as several other versions in-between are available, the most affordable being priced at 58,000 Euro.
In coming years DG Flugzeugbau will extend the model range by a 20 meter flapped version as well as a self-launching motorglider which will then replace the DG-505M/MB gliders.
- Jochen Ewald -
- translation by Claudia Buengen -
