DFS Weihe
Страна: Германия
Год: 1938

M.Simons The World's Vintage Sailplanes 1908-45

M.Simons The World's Vintage Sailplanes 1908-45


  By 1938, Hans Jacobs had completed more than ten years as a sailplane designer. His Reiher was the best production sailplane in the world but was too expensive. He had learned a great deal during its development, and these lessons were now incorporated in his new venture, the Weihe. (The Weihe is a large bird of prey, a member of the kite family, quite common in some parts of Germany.) Baltic pine and birch ply were the most readily available materials, and mild steel was used for all fittings. The Weihe was to be cheap, easy to fly and safe for club pilots, yet capable of advanced performance, strong and stable enough for cloud flying in rough air, and practical to operate from the typical, rough and sometimes sloping ground of club hill soaring sites as well as from flat aerodromes.
  The span was larger than most contemporary club single seaters but nevertheless smaller than the Reiher. The aspect ratio, the single most important factor for reducing drag at low speeds, was as high as Jacobs could make it without excessive cost. For the sake of strength and stiffness, the wing was strongly tapered, allowing a deep mainspar at the root, but Jacobs avoided the very sharp taper of the Rhoenadler wing, which was, aerodynamically, going too far. The aerofoil was the Goettingen 549, changing to the less cambered NACA M-12 at the tip, with washout. The Weihe had a tank capable of carrying 20 kg of water ballast.
  The ailerons were long and fairly broad, making them somewhat heavy on the stick. The rate of roll was adequate but not very rapid. A dihedral angle of 2 degrees, increased slightly on the production aircraft, combined with large fin and rudder areas, gave good stability in turns. At high speeds the ailerons became progressively heavier, a common feature on sailplanes, the cause being the torsional flexibility of the wing.
  Airbrakes were fitted, fairly well back on the wing, and of the type developed by the DFS. In normal flight the brake paddles remained flush with the wing surface in shallow recesses. On opening, the upper paddle came out of its recess and moved forward to an angle of about 45 degrees to the airflow, whilst the lower paddle moved down and back, the loads on the upper and lower sides balancing one another so the pilot could open the brakes at any airspeed without strain. Fully open the Weihe brakes were much less effective than the vertical, parallel-ruler type developed by Huetter for Schempp Hirth.
  All the wing bending and torsional loads were taken by the box-section mainspar combined with the plywood-covered 'D' nose, with the plywood laid diagonally to increase the torsional strength. There was no rear spar, the ailerons being hinged to specially strengthened wing ribs and, at their inner end, supported by a plywood-covered box that also housed the airbrake mechanism. At the root, the customary heavy diagonal spar and triangular torsion box, were omitted. Instead, a short stub spar was built inside the ‘D‘ nose, and this carried the front fitting where the wing joined the fuselage. Behind the mainspar, there was no connection between wing and fuselage. A gap existed all the way back to the trailing edge from the mainspar connection point. Pilots who knew a little of aerodynamics always made sure this was taped up before flight. Each wing was attached to the fuselage at two points, the front, torsion or drag fitting, and at the lower flange of the mainspar. The upper spar flanges were joined directly to one another, on the centre line. The main pins were mounted in tubular slides and could never be lost or misplaced. They were connected by toggles and pushrods and locked by the ‘over centre' movement of the toggle handles. Ailerons had to be separately connected but the airbrake linkage was automatic. Three men could rig a Weihe in a few minutes.
  The fuselage of the Weihe had a low neck or pylon for the wing mounting. Jacobs believed that shoulder or mid-wing mounting positions were not only more difficult to engineer but also in circling flight could cause flow breakdown over the wing roots. There would almost always be some sideslip or crossflow in this region, and he thought it better to leave the upper surface of the wing clear of obstructions. There was no attempt to fair the wing root junction, except for a small extension of the wing mount pylon upward near the trailing edge to carry the lines down to the rear fuselage.
  The cockpit was roomy and comfortable, with space for oxygen gear and other equipment behind the seat. The simple transparent canopy had two large windows, big enough for the pilot to get an eye outside to look straight ahead in conditions of rain or icing. The landing skid was sprung by a long row of tennis balls, a two wheeled drop-off dolly being used for ground handling and taking off.
  Two prototypes flew in the 1938 Rhoen competitions. The Weihe was adopted by the NSFK as their standard high performance sailplane and quantity production began. During the war years, about 280 Weihes were built by Jacobs' own Schweyer works and more at other factories in and outside Germany. Most of these remained in service until captured by the Allied forces in 1945. Many were then destroyed, but a few were ‘exported’, and some were used by the British service gliding clubs during the occupation.
  The Weihe remained at this time the best available sailplane in the world. In Spain, France and Sweden, production began again and in Yugoslavia about 35 were also built, these having improved brakes of the Schempp Hirth type and ‘blown’ cockpit canopies. In 1952, the Focke Wulf Company in Germany produced the Weihe 50, which had some detailed improvements, a Perspex bubble canopy and in some cases, ailerons of reduced span. These proved as effective as the older, larger ones. Some had landing wheels.
  It is impossible to mention all the outstanding flights made in Weihes. The most famous of all Weihes was that used by Per Axel Persson to set the world gain-of-height record at 8050 metres in 1947 at Orebro in Sweden. Persson went on to win the World Championships in 1948 in this aircraft, and it was flown again to victory by Billy Nilsson at the 1950 World Championships. It still survived in 1980.
  Also outstanding were the great duration flights made in Germany during the war. Vergens, in 1942, soared for 45 hours 28 minutes over the sand dunes in East Prussia and the following year Ernst Jachtmann stayed aloft for 55 hours 51 minutes. In 1980 a number of Weihes remained in service.

  Technical data:
  Weihe: Span, 18.00 m. Wing area, 18.20 sqm. Aspect ratio. 17.8. Empty weight, 215 kg. Maximum flying weight, 335 kg. Wing loading, maximum 18.41 kg/sq m. Aerofoils, root, Goettingen 549 and wingtip, M-12. Best glide ratio, 1:29. Maximum permitted speed 170 km/h.
The Weihe on the ground at Thun in 1979 with the external rudder lock in place and the wingtip weighted down with a parachute. The great length of the aileron is evident, with two control horns on each side, to reduce the tendency of the aileron to twist under aerodynamic loads. The way in which the rear fuselage fairs into the trailing edge of the wing is interesting.
Taken at High Wycombe in 1971, this photograph shows, left to right, the nose of a Weihe, the Cantilever Gull or Kirby Gull 3, the Dunstable-based Minimoa and at the far end of the line, the Kirby Tutor.
D-11-184 was the first DFS Weihe. The wings on this prototype had slightly less dihedral than production models. All DFS Weihes had slightly shorter noses and smaller cockpit canopies than the Jacobs-Schweyer version which was produced later in larger numbers. Again, the swastika had been retouched on the original negative.
A Weihe soaring in England in post-war times. The Weihe had a well-balanced appearance in the air, and was aerodynamically tidy without a greatly complicated structure. For some years it was easily the best available sailplane for competition flying and broke all the major world solo records as well as many national records.
A Weihe in the USA with drop-off dolly wheels. The usual canvas skid covers had been removed, exposing the skid springing. Many sailplanes, including the Weihe, employed tennis balls trapped between skid and fuselage keel, instead of the simple rubber rings on less refined aircraft.