The Slingsby Type 6 - Kirby Kite
by Martin Simons
In 1935 it seemed to Slingsby that the expanding British gliding clubs and private owner groups would soon be needing something better than the Grunau Baby which he had just started to be built under licence from Edmund Schneider. He guessed it would be unwise to produce a really advanced sailplane at this stage He probably looked at the Hjordis, the special sailplane designed by Mungo Buxton which he was building for Philip Wills and recognised that it was not going to be a sailplane for the average pilot and would never be produced in quantity.
He also recognised his own limitations. For stressing and advanced aerodynamic calculations he relied on expert consultants. He felt capable of re-working and developing an existing well proven design, as he had done when converting the Falcon 1 into the two seater Falcon 3 but he was not ready to begin something totally new from scratch.
There were several obvious ways of improving the Grunau Baby and with little cunning it would be possible to use many of the components, wooden and metal, in the new type, saving on rigging and workshop time. While retaining the main aerodynamic features of the wing including the profiles and the basic planform, it could be extended in span to 14.2 metres. This would involve only the addition of an extra rib bay on each side, stretching the outer wing panel and so improving the performance at small cost.
Gull wings were very fashionable and improved stability in circling flight compared with wings which had no dihedral at all. They also looked very graceful and had sales appeal. They cost a little more to build but the spars of a strutted sailplane were not very' elaborate so the extra complication was not likely to cause serious problems.
Finally, the fuselage could be given streamlined form instead of the hexagonal box section of the Grunauu type The Kirby Kite took shape in Slingsby's mind. The prefix Kirby, came from the village where the factory was now established, Kirbymoorside.
There was some urgency. The British Gliding Association was to hold a major competition at Sutton Bank at the end of August 1935. The Hjordis would be there and so would several Grunau Babies from Slingsby's and other factories. If the Kite also could be ready and made a good impression, orders would come in.
Having made the decision there followed a period of frantic work over a fourteen week period. Supervising the workmen building primary gliders, Falcons and Grunau Babies in the factory took most of Slingsby's days, with many details of the Hyordis also to be elucidated on the shop floor.
Design work on the Type 6 was done mostly in the evenings after normal working hours, Slingsby employing a teenager, Thoby Fisher, to help. A general arrangement layout diagram was completed and construction began, using full-sized lofted templates, long before the detailed drawings were completed. The design was not finalised until some time after the prototype had done what was required of it at Sutton Bank
Wherever possible, Grunau Baby parts were used in the wing and tail. It was comparatively easy to transfer ideas and components from the older design to the new. The rudder was taken straight from a Grunau Baby. The tailplane and elevator were treated in much the same fashion but the tips were rounded slightly.
The wing like that of the GB, had single main spar, with plywood skinned D nose to resist torsion. Aft of the spar the ribs were braced laterally with linen tapes. The ailerons incorporated the nearly elliptical taper of the GB with change of section and washout but the additional rib bay near the tips gave the curved outline a slightly more pointed shape. There were very few' refinements. The gaps along the hinge line of elevator and ailerons, 30 mm wide, were sealed only by strips of doped fabric. The rudder hinge was not shrouded even in this elementary, way.
The fuselage in cross section was round backed with a pointed keel. The outline of each frame was made up of a semi circle above the datum line. Below', two circular arcs intersected at the keel. The low wing mounting pylon required only small extensions of the three main frames.
The whole fuselage was skinned in plywood, forming a monocoque shell over a light framework of longerons and cross frames. The cockpit was open but an elementary wooden 'dog collar' type of canopy was fitted, leaving the pilot's head exposed to the airflow without any windscreen. A pad was provided at the junction of the wings as a headrest. As in the Grunau Baby, the seating position was upright.
Everything worked out remarkably well. The Kite did its first successful test flights a few days before the BGA competition started and was entered in Class 1, the 'high performance' category, along with several Grunau Babies (one built by Slingsby), Scud 2s, she Hjordis and the German Rhönbussard. 'Sling', as he was now known, made the first brief flights but handed over to John C Neilan for the contest proper.
Neilan's first competition flight was a triumph for him and for Slingsby. He was launched over the Sutton Bank slope by winch to 400 ft and quickly found a thermal which took him above the hill lift to 3,300 ft. He headed off immediately downwind, eastwards towards the coast. More thermals and glides took him close to Bridlington with plenty of height so he turned south and with another thermal to help, eventually landed at Garton. The distance was 87 km. and it proved to be the longest cross country flight of the entire competition.
The next day was not so successful. Neilan, without goggles or flying helmet, was sucked into a cloud and soaked with rain. The total lack of windscreen proved a serious matter. On emerging, still finding it hard to see where he was going he had to land hastily in a small field. To avoid hitting the upwind hedge he ground looped the sailplane, tearing the skid off and damaging a wing tip on an inconvenient tree.
It did not take Slingsby long to put things back in place and Neilan was in the air again next day. The total flying time recorded by the Kite during the competitions was under ten hours. Neilan carried off the Wakefield Trophy for his flight to the coast.
Slingsby's judgement of the market was correct and a fairly steady stream of orders came in. The prototype was sold in November, without alteration, to Frank Charles, a champion speedway rider well known at Wembley Stadium. He had never flown before but to the astonishment of his friends in the Barrow in Furness Gliding Club and the rest of the gliding movement in Britain, he taught himself to fly within two months. Immediately after taking delivery he made a two ground slides and two low hops in the Kite. Without any further practice, in January 1936 he had himself bungee launched off the top of the hill above Ireleth, gliding down safely to land 800 feet below on the beach. He retrieved the Kite, which he called Cutty Sark, using a trailer he had built himself, and repeated the exercise. On his next flight a few days later, equipped with a variomeler he found himself in a thermal and circled up in it for a flight of nearly half an hour. By the end of January he was making soaring flights up to an hour's duration and by February was essaying his first cross country flights. Whatever else might be said about Charles's exceptional talent he had certainty demonstrated that the Kirby Kite was not difficult to fly.
The second Kite was built for Dudley Hiscox, a member of the London Gliding Club. The nose was lengthened to create more room for tall pilots. Taking a lead from the later models of the Grunau Baby now appearing in Germany a better cockpit canopy was designed, incorporating a small and very necessary windscreen. Slingsby did not immediately learn all the lessons of Neilan's field landing incident. The Type 6 lacked spoilers. If owners required these, as most eventually did, a retrospective modification was necessary.
Later models of the Kite had larger rudders of a graceful curved outline. This not only improved the appearance but gave the controls a more balanced feel.
A feature of the Kite which could have been improved was the junction of the wing to the fuselage. By bringing the wing down in the centre to just above the pilot's shoulders and mounting it on a narrow pylon, an awkward constriction between the top of the fuselage and the wing root was created for the air flow. There is little doubt that the performance was reduced slightly by this but the point was not considered seriously at the time.
A rival to the Kite, produced by the small Dunstable firm, Dart Aircraft Ltd., was the Cambridge sailplane. This also used essentially the same, slightly stretched, wing as the Grunau Baby but without any gull bend. The streamlined fuselage of the Cambridge retained the tall pylon which kept the wing roots out of the disturbed air aft of the cockpit. Only a couple were built. Philip Wills indicated that the control response and harmony of the Cambridge was better than the Kite which he classed as only fair. At the time it was almost impossible to arrive at accurate performance figures without extensive flight tests, but it is probable that the Cambridge would have gained a point or two over the Kite if the comparison had been made.
Early in 1936 a minor controversy arose about the structural weight of the production Kirby Kites. Slingsby claimed 248 lbs (112 kg) empty. In an article Philip Wills quoted 270 lbs (122 kg). Llewellyn Barker stated forcefully that he had weighed a Kite and found it scaled 313 lbs (142 Kg). Slingsby responded by taking a new Kite to an official weighbridge which presented him with a certificate reading 252 ths (114 kg), which included instruments. Barker was unconvinced and prepared to bet £3 on his own figures, Whether Slingsby ever took him up on the wager is not recorded. In much more recent times a carefully restored Kirby Kite was found to weight 280 lbs (127 kg) while another no less well preserved, scales 360 lbs (163 kg.). There is little doubt that quite large variations arise between wooden sailplanes coming out of the same factory so all the claimed weights and wing loadings, and the associated performance figures claimed, must be regarded with some suspicion. In flight, providing the centre of gravity with the pilot on board was correct, the total weight probably made very little difference.
Two Kites competed in the 1936 National Competitions at Camphill. The weather was disappointing and although Hiscox won a prize for the greatest total hours by any individual, there were no especially notable flights by the Kites. By the end of the year, nevertheless nine had been completed. In 1937 the total reached seventeen, by which time most all the leading British gliding clubs and several private owner groups possessed one. Among the individual private owners was Amy Johnson.
Almost all were finished in clear dope and varnish all over, but one, belonging to a syndicate at Dunstable was painted grey and another at the Midland Gliding Club on Long Mynd in Shropshire, had the plywood surfaces yellow with clear doped fabric.
Kirby Kites were used by many pilots for the Silver C badge flights. Six competed at the Nationals in 1937 although they were no longer classed as high performance sailplanes. Even so, two of the best flights were made by Kites, 125 km by J.E. Simpson to the coast at Withernsea, and 128 km by K. Lingford to Easington. Production continued until 1939, by which time 25 had been completed.
An interesting variation about which nothing more is known, was the Kite built with the NACA 4416 wing profile, tapering at the tip to NACA 2412. This, apparently flown in 1937 or early 1938 might have been a trial of NACA sections before applying them to the Type 12 Gull, which flew in April '35.
One early production Kite was shipped to South Africa, where Philip Wills, during a business visit to that country, demonstrated it and where it remained after he left. Others were exported to Canada, Rhodesia, another to South Africa and one or two found their way to the USA , One, registered NC28800, was built from plans with a very' neat fully enclosed cockpit, by Herman Kursawe in the USA and flown there successfully.
In 1940 most gliders and sailptanes in Britain were impressed into service with the RAF. To find out if wooden aircraft could be detected by radar sailptanes of several types were flown over the English Channel from Christchurch in 1940. They were tossed out to sea by Avro 504 tugs, released at 10,000 ft and flown back towards the land while the radar operators at Worth Matravers near Swanage attempted to detect them. It was established that they did show up on the screens. They all had steel pushrods and cables driving the controls.
After these early tests, a Kirby Kite was stripped of its covering and so far as possible all the control drives were replaced with wooden pushrods. Further tests showed that it could be detected, though not easily. By this time, the danger of a glider borne invasion of England had receded and attention was turning in the other direction. A large programme was launched to work out operational methods and to train military glider pilots. A small fleet of sailplanes, mostly Kirby Kites, was assembled at Ringway aerodrome.
One of the first exercises from this base, described by Lawrence Wright who was there as an observer, was a simulated attack on a railway viaduct near Macclesfield. A Kite and Rhönbussard played the role of military troop carrying gliders. Painted in the standard camouflage of dark green and dark earth they floated to the objective silently and landed safety, after which imaginary airborne troops stormed out of them and destroyed the objective. The local Home Guard never noticed.
After some doubt about a suitable airfield for further work, the Number 1 Glider Training Squadron moved to Haddenham in Buckinghamshire, where five Kirby Kites, duly camouflaged, arrived on Jan 1st 1941. Others came later, a total of fourteen being on the Squadrons books. Experiments and demonstrations for high echelon officers were organised with Tiger Moth tugs. A Hurricane fighter was used to discover lf gliders were easy to short down They were sitting targets while on tow but off it they proved hard to catch in the gun sights. If unable to see the fighter approaching they could hear it and take evasive action.
Time trials were done to see how rapidly it would he possible to launch a large fleet of troop carriers. The Kites were supposed to be towed off in rapid sequence, released, and then to land quickly so that they could be launched again without delay, simulating a continuous stream of larger craft. A similar trick is used in the theatre sometimes, when a few 'extras are made to simulate an amy, marching on at stage left and off stage right, running round behind the scenery to re-emerge stage left. This went wrong at Haddenham when some of the undisciplined pilots, former gliding club members, found thermals and refused to come down.
Inevitably, in the slightly longer run, not many of the 1 GTS Kites survived. Those that did were mostly allocated to the Air Training Corps, though they were little used since soaring was not permitted in wartime.
As the war drew to a close, Slingsby looked again at the Type 6, and decided that a modernised version would be worth developing. It was allocated the Type number 23. The wing was unchanged except that spoilers were fitted as standard. The fuselage was redesigned with a landing wheel and a taller fuselage pylon, eliminating the aerodynamic trap under the wing root. The pilot's headrest now was lower than the leading edge. The new sailplane flew in December 1945 but did not enter production. The gain in performance over the old Type 6 was not great enough to justify the additional cost, and Slingsby was sure something better could be achieved. The eventual outcome was the Type 26, Kite 2. The Type 23 was sold to the Cambridge Gliding Club in 1946 but soon thereafter was re-sold to the USA..
Some six or seven Kirby Kites still survive The prototype, owned once by Frank Charles, is stilt extant, although at the time of writing it is in a very sad condition at Dunstable and awaiting restoration. It was flying regularly until the late sixties. The remainder are highly prized by their owners, maintained in excellent condition and flown whenever possible. All have been fitted with spoilers and some have enclosed transparent canopies improvised by their owners at some time. The one with wooden controls rods which was used for the radar trials, painted again in wartime camouflage, is displayed at the Museum of Army Flying at Middle Wallop in Hampshire (picture above). Another has been restored by Michael and Tony Maufe to its original clear varnish and dope condition.