Czerwinski CW-5
Страна: Польша
Год: 1931

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


  By 1930 some government interest and support for gliding was developing in Poland and a specification was issued for a high-performance single-seat sailplane. Waclaw Czerwinski designed the CW-5 to meet this requirement. It was originally intended to use the Goettingen 652, a thick, strongly cambered aerofoil, but wind tunnel tests on a model of the sailplane showed that this profile fell short of expectations. Czerwinski redesigned the sailplane, using a less cambered profile designed by the Warsaw Aerodynamic Institute.
  The result was the CW-5 bis. It flew first in the summer of 1931. The wing had a parallel chord over most of the span with elliptically tapered tips. The mainspar and plywood-covered leading edge formed the usual torsion-resistant box beam, whilst a second spar aft stiffened the ribs. The ailerons, hinged to a diagonal spar, narrowed almost to zero chord at their root ends, to reduce the additional vortex drag caused, when deflected, by the sharp change of wing profile with normal ailerons. A slight ‘gull'-type dihedral was incorporated, with large ‘V’ struts.
  The fuselage was suspended below the wing on a narrow pylon, with an open cockpit. To keep the all-moving tailplane clear of the ground, it was placed on two pylons above the fuselage, ahead of the fin. German designers facing the same ground clearance problem usually fitted the tailplane part of the way up the fin or on a stumpy sub-fin. Czerwinski’s solution was unique.
  Subsequent models of the CW-5 were fitted with better cockpit covers and the 1934 version had a fully enclosed transparent canopy. This did not blend smoothly into the narrow pylon. The instruments were mounted in separate housings outside the cockpit on the front fuselage decking, the pilot having to look through his windscreen to see them. The CW-5 bis/35, of 1935, had a completely redesigned fuselage with much cleaner aerodynamic form.
  A still further improved version, the CW-5 bis/WOS, was built by the Military Gliding School under the direction of Michal Blaicher. This was one of the five sailplanes taken to the 1937 International Competition on the Wasserkuppe. Flown by Zabski, it achieved the best altitude of the whole contest, 3293 metres. Blaicher later designed the B-38.
  Altogether, about 20 CW-5 bis were built. Blaicher’s military group built several more. The type was in direct rivalry with the SG series designed by Szeczepan Grzeszczyk, capturing and recapturing most of the Polish National Records for both men and women during the period 1933 to 37.

  Technical data:
   CW-5 bis/34: Span. 17.80 m. Wing area, 17.40 sqm. Aspect ratio. 18.20. Empty weight. 144 kg. Flying weight. 224 kg. Wing loading. 12.9 kg/sq m.
   CW-5 bis/37 WOS: As for CW-5 bis/34 but empty weight 170 kg.
The prototype CW-5 bis in 1933. The windscreen was enlarged after early tests.
The CW-5 bis/34 flying over typical Polish strip cultivated fields during 1934.
The CW-5 bis/34. The rather awkward compromise of the enclosed canopy fitted to a sailplane which originally had been designed with an open cockpit, is evident. The unusual tailplane mounting is well shown. On the upper part of the rudder, the type designation CW-5 bis/34 was marked in a rather ugly lettering style and above it a laurel wreath emblem.
The CW-5 bis/35 had a much-improved fuselage. The example shown here, registered SP-754, had all plywood surfaces painted red with clear dope and varnish on fabric areas. The nosecap was either white or natural aluminium. The Polish national colors, red and white, were much favored for sailplanes.
CW-5 bis