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

THE KRANICH
  
  On its first appearance, in 1935, Hans Jacobs’ Kranich was described as a two-seat Rhoensperber, and so, in essentials, it was. Except that the whole thing was bigger with two seats instead of one, the Kranich ws aerodynamically ДальшеMore>>> and structurally very similar to the popular Sperber. The prototype was flown with open cockpits, but enclosed canopies were also fitted and became standard. There was space for radio and oxygen, and either cockpit could be curtained off for blind flying practice.
  The seats were set in tandem to reduce frontal cross-sectional area, and on most previous two-seat sailplanes this had meant placing the rear seat underneath the wing, which gave the instructor a good view to each side and downward, although he could see little upward and the pupil in front tended to obscure most of the view in that direction. In the Kranich, the wing was joined to the fuselage at shoulder level and the instructor’s cockpit was placed between the two main fuselage frames with his head and shoulders above the wing. There was a good view upward but very little in any other direction. Some instructors would fly with the rear canopy removed altogether. This gave them a better field of vision but it could become noisy and draughty at high airspeeds.
  To get the balance right, the wing required a few degrees of sweepback, rendering construction more difficult. The root fittings had to be ‘joggled’ slightly to mate up the spar ends where they were joined together by steel pins. To avoid a double bend in the mainspars, at the ‘gull’ bend, they were made straight in plan form, which meant that over the constant chord central panels of the wing, they were not parallel to the leading and trailing edges. Each rib was different from its neighbor.
  The fuselage was the usual semi-monocoque structure of plywood skin over laminated wooden hoops. The cross-section was the common ‘pointed pear' shape, rather deeper than usual since space was allowed for seat-type parachutes. To lighten control loads on the stick, early Kranichs were fitted retrospectively with aileron servo tabs and both elevator and rudder had aerodynamic balances ahead of the hinge line. Aluminium fences of triangular shape were fitted in the gaps between these horns and the fixed surfaces, to prevent air leaking through the gap when the controls were deflected. These proved dangerous since they could easily become distorted and bent, jamming the controls, and after an accident all such fence plates were removed from German sailplanes. All controls were cable operated. Small hinged spoilers were fitted on the upper surface of the wings.
  The Kranich underwent some re-design in 1940. The structure was strengthened, and large, effective airbrakes were fitted. The aerodynamic balances on the elevators and rudder were removed and so were the aileron servo tabs. To prevent binding at the hinges, the ailerons were divided into sections. The front cockpit was enlarged slightly and adjustable rudder pedals were fitted. A trim tab was added to the elevators, which were completely redesigned. The result of all these changes was a somewhat heavier but very much more practical sailplane.
  Various special versions of the Kranich were built for experiments. One had the entire front fuselage redesigned with a position for a pilot to lie prone. Another which was used for a famous wave flight over Zell am See, to 11410 metres by Erich Kloeckner in 1940, had large-capacity oxygen bottles installed in the wings plus increased dihedral. Kloeckner’s record was not officially accepted since it was made in wartime but it was not surpassed till 1950.
  The Kranich's performance was at least as good as most contemporary single-seaters, and it quickly achieved an outstanding reputation. The world two-seater distance record was taken by a Kranich in 1937, and the following year a two-seat duration record of 50 hours 15 minutes was set. Erwin Ziller, before the war, broke both the solo and the two-seat records for altitude in the Kranich, with climbs of 6838 and 3304 metres respectively.
  During the war until the end of 1944, official German records indicate that 1312 Kranichs were built by one contractor alone. Kranichs continued in use as trainers. It has been claimed that Kranichs were used on the Russian Front to carry fuel to a Panzer unit surrounded by Soviet troops, the rear cockpit being gutted to make room for oil drums. The Kranichs were reputedly towed within reach of the trapped tanks and then glided silently to land close to them. If this story is true the Kranich is probably the only sporting sailplane type ever used in action during war.
  After 1945, Kranichs for some years dominated two-seater competitions and broke almost all two-seat records. Production did not continue in Germany, but more Kranichs were built in Spain and in other countries.
  A very few Kranichs remained in service in 1980. The Kranich 3, first flown in 1950, was Hans Jacobs' last sailplane design, and was entirely different from the earlier type. Although impressive, it never achieved the success and reputation of its forerunner.
  The performance figures and weights quoted below come from W. Spilger’s report in 1937 of the DFS flight tests.

  Technical data:
   1936 production Kranich: Span, 18.00 m. Wing area. 22.68 sq m. Aspect ratio 14.3. Empty weight. 255 kg. Flying weight, 465 kg. Wing loading, 20.5 kg/sq m. Aerofoils, Goettingen 535 at root and mid-span, tapering to a thin symmetrical tip. Best glide ratio, 1 : 22.5 at 68.5 km/h. Minimum sinking speed, 0.75 m/sec at 51.5 km/h. Sink at 100 km/h, 1.56 m/sec.
   1940 production Kranich, as for 1936 version but empty weight 285 kg.

M.Hardy. Gliders & Sailplanes of the world

DPS Kranich

  Although the first two-seater glider had been produced by Anthony Fokker as far back as 1922, it was not until the mid-1930s that the high performance two-seater sailplane with a performance that compared favourably with its single-seater counterparts began to emerge, and the DFS Kranich (or Crane), which first flew in the autumn of 1935, was the real forerunner of this new breed of two-seater which could be used for competition flying and long distance soaring as well as dual-control training. Prior to the new fashion set by the Kranich most two-seaters were built similarly to, and had similar handling and performance characteristics to single-seater secondary training gliders such as the Grunau Baby and Slingsby Kirby Cadet, which represented a half-way stage between primary trainers like the Dagling and SG 38 and true sailplanes. Designed by Ing Hans Jacobs and built by Ing Luck, the Kranich prototype was developed from an earlier Jacobs design, the Rhonsperber high performance singleseater which was probably the most successful of the prewar German sailplanes, breaking many records in its day. After successful flight trials, the Kranich was put into production by Karl Schweyer A.G. at Mannheim, since the DFS did not manufacture aircraft of its own design except for prototypes, and altogether 400 Kranichs were built in Germany. The type was also built under licence in Sweden, Poland, Yugoslavia, Czechoslovakia and Spain. As late as 1952 Kranichs captured the first three places in the two-seater class in the World Gliding Championships held at Madrid and the type had previously set up more world records and many national ones. The two pilots sit in tandem under a long and narrow framed canopy with individual detachable sections, dual control being provided, and an unusual feature is a small transparent panel in each wing root to provide downward visibility for the instructor in the rear seat located behind the wing spar. Construction is of wood and fabric, the fuselage being of plywood. The mid-set gull wings were fitted with spoilers in the initial production version - use of these had been pioneered in the Rhonsperber - but the strengthened Kranich 2 was fitted with air brakes. Take-offs were made on a double wheel unit that was jettisoned when airborne, and there was a long ash skid under the forward fuselage for landing. A Kranich 3 was recently used to flight test a special wing section for the Akaflieg Braunschweig SB-11, this wing section, of 1.5m span and 0.75m chord, being mounted on a steel tube framework on the tip of the nose in front of the cockpit, and having two large endplate surfaces on each side of it.
  After the war 40 Kranich 3s were built by Focke-Wulf GmbH, the prototype of this series, registered D-3002, first flying on 28 May 1952. The Kranich 3 was different in several important respects from the prewar versions; it had a new wing in the low-mid instead of mid position, with dihedral from the roots and straight taper instead of the gull wing with compound taper of prewar aircraft; aspect ratio was now 15.6. A longer forward fuselage was featured with the canopy top now flush with the fuselage top line; length was now 30ft 6V«in. In the early 1970s a
powered version of this veteran design was produced by Eduard Schappert in Germany, who modified one of the Kranich 3s built postwar by Focke-Wulf GmbH to have a 35hp Fichtel & Sachs SA-2-440 engine mounted on a retractable pylon aft of the rear seat, and driving a two-blade tractor propeller. A fuel tank of glassfibre in the fuselage held 1.87 Imp gallons, and this variant was designated Kranich 3M. It had a maximum speed of 87mph with the engine on, a cruising speed of 62mph, a take-off run of 985ft and a maximum range of 74 miles.


Data: Kranich 2
Span: 59 ft 0 3/4 in
Length: 25 ft 3 1/4 in
Wing area: 244.4 sq ft
Aspect ratio: 14.3
Empty weight: 562 lb
Max weight: 959 lb
Max speed: 133 mph
Min sinking speed: 2.3 ft/sec
Best glide ratio: 23.6:1