Slingsby T-51 Dart
This high performance Standard Class single-seater was the last Slingsby type of conventional all-wood construction and the last to be designed under Mr F.N. Slingsby's direction.
The Dart was originally designed to Standard Class rules and the prototype Dart 15 first flew on 26 November 1963 and the Dart 15 – known as the 15R when fitted with a retractable monowheel - was the initial Standard Class version with 15m span shoulder wings, which were cantilever single spar spruce structures with a birch plywood leading edge torsion box and a fabric-covered rear portion; there were air brakes at the 50% chord line and the plain ailerons were plywood-covered. The wing spars were initially entirely of wood, but were later changed to box spars of mixed wood and light alloy construction with Redux bonding when this type of spar was introduced into the Dart 17 in 1965. Wing root fillets like those on the Dart 17 were also fitted at this time and later production Dart 15s had an all metal tailplane.
Altogether 50 Dart 15s were built, plus five more constructed from kits supplied by Slingsby, four of these being built by Mr Fred Dunn in New Zealand; the price of a Dart 15 in July 1964 was £1,425.
This verison scored a number of competition successes: one flown by G. Burton gained 5th place in the Open Class at the 1965 World Championships at South Cerney, Gloucestershire, and the Dart 17 prototype, flown by H. C. N.
Goodhart, took 7th place in this event. The Dart 15 was awarded the OSTIV Design Prize at these 1965 Championships. In League One of the 1967 British Championships, Darts came 1st and 2nd and took eight more of the first 20 places. In 1965 Dick Georgeson of New Zealand set a world Out & Return record of 730.6 km./ 453.98 miles in a Dart 15.
But the Dart 15 in its wooden-sparred form was really too heavy and did not really have the performance for soaring in average British conditions, and this led to the Dart 17 - or 17R with retractable monowheel - with the span increased to 17m, this now being the Open Class version; the prototype 17 first flew in November 1964 and the price of a 17R was £1,950 in August 1966. Altogether 44 Dart 17s and 17Rs were built, plus four more built from kits in New Zealand by Fred Dunn. There was also one Dart 15/17, G-ATOE, which had detachable wing tips for changing the span from 15 to 17m, and two examples of the Dart 15W were built, this being a special version for the British team in the 1968 World Championships in Poland. The 15W had a new Wortmann wing section instead of the previous NACA 64-series aerofoils, a revised canopy shape and cockpit interior; the 15W first flew at Lasham on 29 March 1968 and after the Championships both 15Ws were convertred to Dart 17Ws with the 17m span wing, first flying in this form on 3 May 1969, and both were later fitted with retractable monowheels, in which form they were designated Dart17WR.
Slingsby T51 Dart 17
Most Dart 15s and 17s had the retractable wheel, which became available as an optional fitting at the end of 1965, and this allowed a change of wing incidence, thus avoiding the Dart's tail-high attitude when flying at high speeds. All-metal tailplanes were also fitted to the later production Dart 17s. With the original wooden spar wing, flexure was caused when the Dart 17's air brakes were extended, and so to reduce this a new box spar with light alloy booms
Redux-bonded to wooden webs was introduced, the first Dart 17 with this spar being rolled out in April 1965. At the same time the aileron span was increased by 11.75in, and new wing root trailing edge fillets were added to reduce drag. On the Dart 15 the new spar resulted in a saving of 45lb in tare weight over the wooden-sparred version. The Dart's fuselage is a semi-monocoque spruce structure of elliptical cross section, the cockpit section being covered with glassfibre and the remainder with birch plywood. The pilot sits in a semi-reclining seat under a sideways hinging moulded Perspex canopy with clear vision panels, and the cockpit is very similar in size and general arrangement to the Skylark 4's. The fuselage is shallower than the letter's because the flying controls run along the sides of the cockpit instead of under the pilot's seat. The fin and rudder are of spruce with glassfibre leading edges, the rudder being fabric-covered, and the light alloy stressed skin tailplane, previously wooden, is an all-moving surface with anti-balance tabs. As well as the monowheel, which has an expanding brake, there is a short forward skid under the nose and a tail bumper fairing.
A total of 81 Darts were built.
T51 Dart 17 R
Wing span: 17 m / 55ft 9.25 in
Wing area: 13.87 sq.m / 149.3 sq.ft
Aspect ratio: 20.4
Length: 25 ft 5 in
Empty Weight: 243 kg / 535 lb
Payload: 88kg / 195lb
Gross Weight: 730lb / 331kg
Wing Load: 4.89lb/sq.ft / 23.86kg/sq.m
Max speed: 136 mph (in smooth air)
L/DMax: 37 at 87 kph / 47 kt / 54 mph
No. of Seats: 1
MinSink: 0.58 m/s / 1.97 fps/ 1.13kt at 46 mph