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

THE WRENS

  The Crested Wren was flown by its designer-builder, Corporal W. L. Manuel, in 1931. It was cheap and easy to build. Its performance was comparable to that of the Grunau Baby which appeared in the same year. Manuel devised a simple mass-production method of making wing ribs without the usual elaborate jigs. Plywood blanks were cut and shaped together in a block, sandwich fashion, like the balsa ribs of a model aeroplane, then the plywood webs were edged with thin spruce capping strips. The ailerons were extensively cross-braced to improve stiffness but were not geared differentially and no wing washout was used.
  The fuselage had a tall pylon to carry the wing above the pilot’s head. The upward view was very restricted, especially since the slight sweepback of the wing brought the leading edge forward at the root. The Wren was unstable and without any means of trimming for different cockpit loadings. The control cables to the tail were external for most of their length and a single bracing wire ran from the open bungee hook on the extreme nose, to the wing strut fitting.
  Manuel himself built two more Wrens, each incorporating improvements. The Willow Wren had a redesigned elevator and internal control cables; the Blue Wren of 1934 had wing washout to cure the spinning tendencies of the earlier model, and the ailerons were covered with oak veneer. Amateur groups built their own versions from the Willow Wren plans. The Golden Wren had extra stiffening in the fuselage, extended ailerons of lobate planform and an enclosed cockpit, and the White Wren had dihedral. Both had a wide transparent leading edge section to give the pilot a view to the inside of turns.
  A Willow Wren was built in Australia by F. M. Hamilton and flew regularly in the Sydney area from 1935 till 1937 when it was written off after a spinning accident. Another was built in New Zealand at about the same period. The Blue Wren, after a couple of years in England, was exported to South Africa.
  In February of 1935 Manuel and his associates advertised the Dunstable Kestrel. The Kestrel was similar to the Blue Wren but was strengthened and had minor detailed improvements such as a deeper landing skid and differential ailerons. Apparently only one factory-built model ever saw the light. Manuel sold sets of drawings and several Kestrels were built from these, one in England by W. E. Godson and at least one in the USA. Another three were Australian-built. In England the Willow Wren, restored by Manuel himself, still survives. The Golden Wren flew a good deal in the immediate post-war period but was eventually condemned because of glue deterioration. Godson was killed in his Kestrel when he span in at the British National Competitions at Camphill in 1939. The Australian Kestrels still existed in 1980, though they were not airworthy.

  Technical data:
   Crested Wren: Span, 12.19m. Wing area, 13.94 sqm. Aspect ratio, 10.66. Empty weight, 97.5 kg. Flying weight, 165.5 kg. Wing loading, 11.87 kg/sq m. Aerofoil, root, Goettingen 549. tip, thin symmetrical. Stalling speed, 40 km/h.
   Golden Wren: Span, 12.19 m. Wing area. 14.03 sq m. Aspect ratio, 10.60. Empty weight, 108.8 kg. Flying weight, 176.9 kg. Wing loading, 12.60 kg/sq m. Stalling speed 43.5 km/h.
   Kestrel: Span, 12.19 m. Wing area, 13.94 sqm. Aspect ratio, 10.66. Empty weight, 111.1 kg. Flying weight, 179.1 kg. Wing loading, 12.84 kg/sq m. Stalling speed, 45.1 km/h.