In The Anniversary Year For DG Sailplanes
The following article was first printed in the December 1998 issue of the Aerokurier
and is reprinted here with the kind permission of the Publisher.
Two-Seaters enjoy a market revival. In the model series of the DG Sailplanes this lead to the several variations of the DG-500, which pretty well covers the market. In the anniversary year “25 Years DG Sailplanes” a modern successor, the DG-1000 appears.
The new Two-Seater of DG Flugzeugbau in Bruchsal is entirely a child of the times. Swept back and upward pointing wingtips continue the modern wing geometry first seen in Schempp-Hirth sailplanes and now spread through the entire series of the Swabian manufacturer. It makes for good handling, and especially excellent thermalling behavior.
After about ten years of production of the DG-505 with straight wings the DG-1000 will replace it. In various models the DG-1000 will not lag behind it’s predecessor 500. The 1000 is planned in two wingspans of 18 M and 20 M. This will ensure optimal conditions for both instructing and cross-country / contest flying.
The performance requirements for the new two-seater were ambitious.In the opinion of the Chief Designer Dipl.Ing. Wilhelm Dirks studies showed that it should be possible to develop and build a sailplane that exceeds the performance of two-seaters with 20 m spans. In the spring of 1997 this gave DG-Flugzeugbau the impetus to start the DG-1000 project.
Besides excellent behavior good performance was also the aim of the development. The projected data are very promising. Best L/D with a wing loading of 42.8 kg/m2 (20 m version with maximum take-off weight) should be 46.5. Minimum sink with a wing loading of 28 kg/m2 (20 m version with 80 kg crew weight) should be 0.51 m/s.
The good behavior and performance should be the result of a new wing and tail plane. The fuselage of the DG-500, with modifications in the landing gear and cockpit area, will live on in the DG-1000.
A laminar profile by Horstmann/Quast of the German Center for Air and Space (DLR) in Braunschweig was selected as the wing profile. There were two choices. The alternative promised the best possible performance in slow flight, but this had to be bought with lesser performance in the higher speed areas. Wilhelm Dirks also suspected that there might be problematic behavior in slow flight. That is why it was decided to use a profile that promised minimal reduction in the area of best glide angle, but which showed considerably better performance in the area above 160 km/h. Harmless stall characteristics and little sensitivity to bug and rain degradation seem to be assured.
The profile selection was guided by what can be achieved in praxis. Wilhelm Dirks says: “We believe that the minimal advantage of the first profile could not be achieved in real flight situations, but the harmless stall characteristics and minimal sensitivity to bugs and rain are extremely important.”
A number of scientific institutes were involved in the development of the wing. The profile developed in Braunschweig was tested in the wind tunnel in Stuttgart. Professor Loek M. Boermans of the Technical University in Delft optimized the wing root to fuselage section and calculated the winglets. Wilhelm Dirks designed the basic wing geometry for the best possible lift distribution by using a 4-section trapezoid. Winglets further improve the slow flight characteristics. For best thermal behavior the outer sections of the wing of the 20 m variant are bent upwards. This wing geometry has proven to bring stability while thermalling.
The upward bend of the outer wing played a role in the development of good ground handling. The angle is so large that the down going tip cannot drag on the ground. Says Wilhelm Dirks: “This ensures that the danger of a ground loop is no greater that in a sailplane with conventional wings”.
As in the DG-505 ORION the wing is divided at half span of 8.6 m. For the 18 m version the basic span of 17.2 m is extended by wing tips of 0.4 m. The extend to mini winglets. This provides a useful training sailplane with docile flight characteristics and a good roll rate. The 18 m version of the DG-1000 will be licensed as fully aerobatic.
With wing tip extensions of 1.40 m, into which the ailerons are extended, the 20 m version of the DG-1000 for cross country flying and contests, is created. These wing tips can be had with integrated winglets. All connections are automatic, as expected in a DG sailplane.
The tail surfaces are also new developments. The elevator follows the trend of the times with a double trapezoid shape. With this elaborate planform the necessary, but in drag elements detrimental, part of the steering units has been optimized for good performance. The slim, high rudder shows it’s relationship to the 500. Its as high but has a greater aspect ratio which makes the fuselage 10 cm shorter. Both elevator and rudder get new profiles.
Drag is saved on the fuselage, too. A new retractable gear with a further forward moving wheel (similar to ASH 25 and fs-31) eliminates the need for a forward extra wheel as in the DG-500. The 1000 will stand higher and has more ground clearance.
Aside from the performance improvement the new wheel configuration also improved the start behavior. Because of the positioning of the main wheel and tail wheel there is no tendency to oscillate when starting, or the tendency for the tail to crash down, which is especially noticeable in three wheel configurations and which launches.
The wheel housing on the DG-1000 remains behind the pilot seat. A cleverly designed movement of the gear avoids bringing the gear into the area of the copilots lower back, which is the case in a conventionally designed gear. In the design of the cockpit the latest safety designs will be incorporated.
Cockpit according to the latest safety standards
|The construction of cockpits for the single and tow-seaters is carefully coordinated. The conversion from the trainer DG-505 is made easier. In the motorized DG sailplanes the operation is concentrated on a single unit, the DEI.
Safety is written in capitals. For the single seater we now offer the emergency exit system NOAH.
Safe and useful is a further design, which makes the DG-1000 very simple to vary single seat/two seat configuration for instructional use. The rudder will contain a box for trim weights. This makes it possible to vary the C of G by simply sticking weights into box. A water tank in the rudder can also be accommodated.
It will be about six months to the first flight of the 1000. The manufacture of the prototype is well advanced. At the beginning of November the moulds were almost ready, according to Wilhelm Dirks. The maiden flight of the DG-1000 is planned for the summer. Flight testing will commence at the same time, so that the series production can commence in the year 2000.
For details of the DG-1000 please see our special report.
The new two-seater is number eight in the DG-Family, who can look back on a 25 year history. In August 1973 Glaser-Dirks Flugzeugbau commenced production of the moulds for the Standard Class DG-100
The history of DG sailplanes consists of three companies:
Dipl.Ing. Wilhelm Dirks, who in 1973 had just finished his education at the Technical University in Darmstadt, and the construction company principal Gerhard Glaser formed a company that existed until 1996. Financial problems lead to bankruptcy in 1996. Friedel Weber, a business man in the Electronic Data management area, and his wife Eva-Marie revived production as DG-Flugzeugbau based in Untergrombach. Elan in Slowenia joined as a partner in 1978.
The large canopies, in the beginning still in two pieces, became a recognizable feature of the DG sailplanes. The DG-100 became the model. It was a development of the D-38, which Wilhelm Dirks had designed and helped build at the Akaflieg in Darmstadt. In only nine months of development and building time the DG-100 prototype started in May 1974 for it’s maiden flight. A total of 327 DG-100 were built, 222 at Elan.
Late in the 70’s (1977) the 15 m class DG-200 followed. Later it was made available with 17 m wing tips (DG-200/17) and also in carbon fiber (DG-200/17C). 192 DG-200 were built.
With the DG-200/17C Glaser-Dirks Flugzeugbau had the basis for a whole new series, the self-starting sailplane with retractable engine, the DG-400. The wing span, the low weight and the high strength of the DG-200/17C made an excellent basis for motorization, which kept the good sailplane performance in spite of the extra weight. The DG-400, of which 290 were built, was used in many motor glider and normal glider records.
With the DG-400 came the development of the compact engine and retraction DEI , which concentrated the activation on one instrument, which made it very simple. It probably accounted for much of the success of the DG-400. Today it is used in all DG motor gliders.
As a follow up design to the DG-100 the DG-300 Elan in the Standard Class was introduced in 1983. The series for cross country and contest pilots was extended with the fully aerobatic “Acro” and the and the cost effective “Club”. The series 300 is still in production, and and 484 have been delivered so far.
The first example of the two-seater family, the DG-500M with a 22 m flapped wing, started in March 1987 for it’s maiden flight. Only four weeks later the new 15m class DG-600 started it’s test flight. The carbon fiber construction made a very thin and sharp wing profile (12% thickness) with excellent high speed performance possible. The DG-600 was offered right from the beginning with tips for a 17 m wing. After 112 units, some with engines, the production was stopped, because a fire had destroyed the moulds.
With the follow up model, the DG-800, which was planned as an 18 m sailplane and, like the DG-400, as a motor glider, the production palette branched off in the DG-505 family. The aerobatic DG-505 Elan Trainer with 18 m span and straight wing and the pure sailplane DG-505/22 with flapped wing arrived in 1989. In a shorter version came the DG-505/20 (1993) and finally the DG-505 Elan ORION with a straight wing in three span variations. So far a total of 196 DG-500 have been produced.
At the present time the single seat DG-800B with the Solo engine 2625, which remains in the fuselage in powered flight, the competition sailplane DG-800S and the DG-505 variations, with the exceptionally quiet 47 KW / 64 PS Solo engine (see Aerokurier 11/98) are in production.
– Gerhard Marzinzik – 1998 –
translated by Albin Schreiter, CDN