Slingsby T-50 Skylark 4
Although developed from the later versions of the Skylark 3, the Skylark 4, with its new and shallower fuselage with the pilot sitting in a semi-reclining position, and its new outer wings and ailerons giving a wing span of exactly 18m (59ft 0.5in), was almost a new design. It was developed through the Slingsby T47, a verison of the Skylark 3 projected in December 1958 with a span of 20m (65ft 7in) created by increasing the span of the constant chord centre section; the wing area was now 193.45sq ft and the aspect ratio 22.2. The Skylark 4 has the wings faired directly into the top fo the fuselage without the built up pylon-type structure behind the cockpit of the Mks 3 and 2, the height of the wing being 9in lower than the Mk3's. The wing is very similar to that of the 3G but has modified wing roots, and the main spar has been strengthened to avoid the Mk 3's tendency for the wing tips to be deflected downwards at high speed.
The prototype Skylark 4 first flew in February 1961 and altogether 63 Mk 4s were built, plus three more constructed in New Zealand by Mr Fred Dunn from kits supplied by Slingsby. The Mk 4 was successful in competitions, and scored two notable successes in 1963 when examples of this version won both the US and Canadian National Championships.
Structurally the Mk 4 was very similar to the Mk 3, with a light rear spar carrying the ply-covered ailerons, the wing being plywood-covered to the rear spar and with a fabric-covered trailing edge; the air brakes in both upper and lower surfaces are on the 50% chord line. The wooden fuselage is a semi-monocoque of elliptical cross section with a glassfibre-covered nose and plywood covering for the remainder. The pilot sits under a moulded Perspex canopy that is larger than the Mk 3's, and likewise hinges sideways to open. Landing gear consists of a non-retractable Dunlop monowheel with rim brake, a rubber-sprung nose skid and a tail bumper. The fin and tailplane are plywood-covered and the rudder and elevators fabric-covered, with a trim tab in the starboard elevator.
The Royal Air Force operated 4 (known as the Swallow T. Mk. 1) in its air cadet training program. Altogether 192 Skylark Mks 1-4 were built.
Span: 59 ft 0.5 in / 18 m
Length: 25ft 1 in
Height: 5ft 3in
Wing area: 173 sqft
Aspect ratio: 20.5
Empty weight: 570 lb
Max weight: 830 lb
Mex speed: 135 mph
Max aero-tow speed: 80 mph
Min sinking speed: 1.74 ft/sec at 43mph
Best glide ratio: 36:1 at 47 mph
No. of Seats: 1