Slingsby Type 9 King Kite

 

In 1935, more and more glider pilots were becoming experienced enough to try cross-country flying, whereas before it had been reserved for the very few, and most pilots had been content to fly only in slope lift. Whereas hill soaring required slow speed gliders with low sinking speeds, cross-country flying would require gliders with good performance throughout a wide speed range.

Although excellent profiles which produced low drag at high speed had been developed in the wind tunnels at Göttingen before 1930, gliders for slope soaring had usually been designed with very high lift wing sections which also produced a rapid increase in drag with

increase of speed. The Hans Jacobs designed Rhönadier had one of these wing profiles, the Göttingen 652, but it had to be admitted that even this profile was performing quite well at speed after a Rhönadler had been among the four sailplanes to reach Brno (Brunn), 502 km from the Wasserkuppe during the tremendous weather of the 1935 Rhön Contest. (These were the first 500km flights carried out in the world.) It was thus demonstrated that a high lift profiled wing could be induced to go fast if loading was increased. This was further exploited with the Göttingen profiles ~ 535 (Rhönbussard, Rhönsperber, Kranich 2; 549 - Reiher, Weihe, Meise, Kranich 3, Mg I 9a; and the 532 section Condors 2,3, and 4. The latter three two-seaters were capable of world distance and speed performances into the 1950s.

Thus, one way to give sailplanes with the old Göttingen wing sections wider speed ranges, was to increase their wing loading. The second way, which was used for the King Kite in 1936, was to use the fastest known wing profile for gliders, which gave very low drag with increased speed and great speed changes for minimal changes of angle of attack, and to try to slow it up with flaps to give the sailplane thermalling capability. This second way was to be tried for the first time in Britain with the King Kite.

 

During the previous year 1935, Mungo Buxton had designed the Hjordis for P.A. Wills and it was built at Slingsby Sailplanes. This sailplane was designed to the Rhönadler philosophy using the same Göttingen 652 wing section, which Mungo Buxton had evidently great faith in, as he had soared a Scud 2 with such a section to 8,24Oft in a thunderstorm during the previous year. The Rhönadler was then the best sailplane in Britain and the Hjordis was designed to be an improvement on that, with increased cleanliness of design, a higher aspect ratio wing and an increase in wing loading from 2.79ib/ft to 3.88ib/ft. For the King Kite of 1936, it was decided to bypass the superb well proven G6ttingen 532, 535, 549 fast profiles to use an American NACA profile with a 21% thickness to chord ratio at its root. It seems that this profile had only just been produced in the NACA wind tunnels and it had already revealed dubious low speed characteristics on much higher loaded aeroplanes. However, it was felt that it ought to be safe for much lighter wing loaded gliders. It must be said that the King Kite was the first to use it but that German Akafliegs tried it afterwards. e.g. Hanover AFH-4, Stuttgart Fs 18, Aachen FVA 11 "Eifel" and then, after the war, the Arsenal 4-111 and Jaskolka (which was a very successful sailplane) used it. Also many aeroplanes, especially aerobatic aeroplanes, use it even today. There are some profiles, which stall first at their leading edges. There are others which stall at their trailing edges first. Those, which stall at their trailing edges first, fall out of the air like pianos. Those, which stall first at their leading edges, usually have gentle stalls, and a quick recovery. It is thought that the King Kite's NACA 230 profile had one of the latter stall profiles. 

The Design Team

 Although Mungo Buxton had designed the Hjordis during the year before, he was in 1936 busy carving out a career for himself in the Royal Air Force. He thus set about trying to find a young designer capable of the King Kite project. He seems especially to have searched among the graduates from Cambridge University (perhaps because Mungo came from Norfolk. Most of the boys simply thought that they were just not up to the task, but at last, after a considerable search, a brilliant young Mechanical Engineering Honours Degree Graduate called Peter Shaw said that he would like to have a try, although he had never worked on aircraft before. He at once set about trying to discover as much about gliding as possible in the shortest possible time. 

 

The Design Office

 


G-AAAC

This was in a small cabinet offshoot of Slingsby Sailplanes. In it were two drawing boards side by side. One was for Peter Shaw as Chief Designer; the other was for John Sproule as Chief Draughtsman. Fred Slingsby had no drawing board but undoubtedly came into the office to influence the design. He perhaps would have said "Its got to have a gulled wing this year, they are all the rage." or "Put the wing on the fuselage at a high angle of incidence," although why this was done is not apparent to the writer (C.Wills) as it was then necessary to get the tail up really high to start the machine flying. Mungo Buxton probably originally came in with a sketch of the plan view, and was heard to say when asked about the profile “I should try the NACA 23021" It was this profile that proved the failing of the design no matter how brilliantly the young Peter Shaw could do.

 

John Sproule, with already some experience of working on gliders at Slingsby Sailplanes, tried to help Peter Shaw as much as possible. It was during this year 1936 that John Sproule had designed the first Kirby Cadet (or Kadet) during a time when Fred Slingsby was hors de combat through being ill with flu, and so John had a free hand on this one.

 

It was resolved to build three prototypes to take part in the next year's international contest on the Wasserkuppe as a major part of the British entry. The disadvantage of building three prototypes simultaneously was that any mistakes made would occur three times! But Fred Slingsby believed that his luck, which had held out so far, would continue.


G-GAAB launces at the Wasserkuppe

The Product 

It was truly a remarkable machine with a tremendous speed range through a small change of trim. The fuselage, as was that of the Hjordis, was so shaped that there was little increase in drag with change of flying attitude (like the Bocian). Controls were light and harmonious and the cockpit was large enough to offer the pilot comfort for long flights, and this was very rare in those days. Its thermalling speed was about 5mph faster than that of the Rhönsperber. Philip Wills, who test-flew it, announced that it clearly had a great future. However its designer already had the worry that its C of G was at the aft limit and this had not been helped, when it was found necessary to stiffen the rear fuselage with a thicker plywood skin, because the tailplane had vibrated.  

The Spin Test 

Philip Wills put it into a spin one way and it had come out. He then spun it the other way and it started to spin like a wild animal. Repeated attempts failed to stop it and the pilot, having jettisoned its canopy, resolved to bail out. This he tried three times, throwing himself out downwards into the centre of the spin. However, centrifugal force flung him outwards and slammed him back into the machine. His final effort surpassed all others, as he was by now very low. The machine caught him a tremendous blow, which was luckily taken by a silver cigarette case in his breast pocket, and he was again flung back into the cockpit. However, the force of the blow had stopped the machine spinning. It was flying, but upside down, at 30Oft! He was able to pull the machine round in the second half of a loop and land on the green grass which he was never so glad to be able to lie on, alive but shaken.  

The Remedy 

"The spin could clearly be cured with a larger rudder." Thus the pre-war King Kite was fitted with a series of three rudders, each one of larger area than the previous one and the aircraft's C of G went still further back. There are some who say still now that the reason for the severe wing drop was that the Slingsby workers had installed the wing tip sections and wash-out, upside down. Those who have worked on the new King Kite say that this was absolutely impossible, because:  

1)     The Slingsby workers were not that bad!

2)     Aerodynamic wash-out was ensured by the tip profile being symmetrical and this should have caused it to stall well after the root profile. Geometric washout was assured by some 3 degrees according to the drawings and it must have been built with this. 

Dudley Hiscox, one of the British Team, also mentioned on the Wasserkuppe flying a King Kite, that it was very nearly a very good glider. "One just had to fly it slowly with a little down flap and it never spun." Down flap would have washed out the entire outer portion of the wings and it should have made it sate. It seems incomprehensible to us now that it was ever flown slowly or thermalled without down flap. As it sometimes spun, and sometimes did not, depending on the pilot, it seems probable that it was the pilot's weight effecting the aft C of G position and the dubious NACA 230 wing section that caused the spin problem. 

 

Flying

 In spite of the above problem, plans went ahead to send this wonder glider with the British Team to the Wasserkuppe and the three King Kites received their C of As in May 1937 about six weeks before the contest.

G-GAAB was to be flown by John Neilan and Joan Price - BGA 302 contest No. 16. 

G-AAAC to be flown by Fit. Lt. P.M. Watt and G.O. Smith - BGA 303 contest No. 17. 

G-GAAD to be flown by Fit. Lt. P.M. Watt and Dudley Hiscox - 13GA 304 contest No. 18. 

In spite of bad weather, it had been possible for each pilot to familiarise himself with the aircraft's flying characteristics in England and “Willie" Watt had managed a fine flight around Sutton Bank at great altitude. Nevertheless, conditions would be different in Germany from the difficult Wasserkuppe site with bungee launch starts and thermalling at incredibly low altitudes. 

The King Kite had no change of sound to indicate speed, no different "feel" to its controls at different speeds and all there was to gauge its speed was its unfamiliar nose-down attitude to the horizon, if there was one, and a small change of flying attitude meant a tremendous change of speed. From a bungee launch start, there would be next to no time to familiarise oneself with the machine or the new site. This is what may have caught Willie Watt out. 

 

The International Contest on the Wasserkuppe 

July 4th 

Immediately after the opening ceremony, there was a rush to get machines to the start. After a short delay, Kurt Schmidt's "Atalante" was bungee launched straight into a thermal occupied by a Buzzard. The "Atalante" climbed away to cloudbase and departed. This was followed by Hofrnann - Moazagotl and Dittmar in Sao Paulo. Then followed Watt in his King Kite as the first British launch. The King Kite immediately spun and struck the ground with one wing tip and nose, its pilot literally arriving "on his toes" as he put it. Wills then followed utterly terrified, feeling as he put it "like St George for merry England being launched over the Niagara in a barrel to create a German holiday". He alone of the British team managed to get away in his Hjordis. The remaining King Kites descended to the valley with most of the other competitors. On this day, three pilots reached Hamburg, 351km. These were Hanna Reitsch in the Reiher VA, Dittmar in Sao Paulo and Mynarski (Poland) in a PWS 101. The "Atalante" was the second prototype Mü 13 which had an ingenious feature, flaps and ailerons which could be trimmed unequally on both sides to make the machine more efficient when doing steep turns (as if a Mü 13 does not climb well enough anyway!).

 

                     

 

Date Pilot Distance

July 9th Watt - King Kite No. 18   Jena - 128km.
Neilan - King Kite No. 16 35km
July 12th Neilan - King Kite No. 16 40km
July 13th  Watt - King Kite No. 18 Cheb/Eger - 179km (to Czechoslovakia)
Joan Price - King Kite No.16 Schwurbitz - 92km
July 14th Neilan - King Kite No, 16 56km
July 16th Neilan - King Kite No. 16 Gotha - 77km
Watt - King Kite No, 18 154m

P.M. Watt finished 12th out of 27 competitors with a total of 461km flown. 

P.A. Wills finished 14th with Hjordis with a total of 402km flown. 

J. Neilan finished 21st with 208km flown. 

Dittmar, the winner, had flown 1,615km.

 

 

A feature of this contest was that from bungee launches; it was not always possible to get away on some days. Watt's performance after his bad start was most creditable considering that he had to share his machine. All pilots shared their machines except Philip Wills who owned the Hjordis. Watt's flight to Jena had consisted of 13/4 hours blind flying.

G-GAAB was ground-looped after a bungee launch in no wind, by John Neilan to prevent it going into a small wood. Its fuselage was broken in half and Slingsby, who was present, said that it would never fly again during the contest. However, it was taken to the workshop, stretched out to the length of its control cables, and repaired in just over a day by the German repair staff who were ably supplied with bottles of beer by John Sproule. That was all the payment they required. The damage occurred on the 6th of July. It is most creditable of the British Team that Willie Watt was given an almost free hand with GAAD after the "write off" of GAAC.

Thus, only two King Kites, out of the three, returned to England.

 

From the SAILPLANE. September 1937

During the contest, the King Kites had had their moments of glory. "On Friday July 9th, it won the Daily Height Gain Prize and this revealed that it could be blind flown. Fit. Lt. Watt, after landing in the valley, returned to the top and got a thermal at 3 ft per second. The flight finished at Jena, 80 miles away. During it, he made a climb to 7,644ft above the previous lowest point of the flight, which had been somewhere below the Wasserkuppe's West Slope. Although this was a greater climb than that of Späte the day before, the absolute height was not quite as much, so this prodigious climb did not earn the Chief Height Prize. It did however earn the Daily Prize, though only by a narrow margin, for Dittmar, as was determined from his barograph three days later, got within 82 feet of it. Watt's achievement was done by blind flying for 1314 hours! Once, during the climb he rose at 1000ft per minute while in his biggest thermal, Watt had the pleasure of seeing another sailplane being aerotowed home 2,00Oft below. Finally he reached Jena at 6.30pm with 4,00Oft in hand, saw an airfield and landed on it. It turned out to be a training school for the German Air Force... and he was given a most hospitable reception."

Tuesday July 13th 

"The longest flight made by a British pilot was put up by Watt, who landed his King Kite 111 miles away at Cheb/ German Eger, in Czechoslovakia. He started at about 1 p.m. and landed at 5.25. For the last hour, he said, the sky was overcast but, before that, he had encountered two large areas of clear sky. The first, he got round, but had to go through the second, being saved by a small cloud, which however disappeared before he got to it. Some of the thermals he used were very rough but got rougher and bigger towards evening. Approaching his destination, Watt saw people running all over the market place. Then suddenly, everyone stopped dead: they were all looking up at him. Still 2,00Oft up, he saw an aerodrome, so he thought that it would be the best place to land on. An hour later, he had induced them to telephone his whereabouts to the Wasserkuppe, and someone called the Captain gave him a lift to the town. The retrieving team reached the frontier at 3 am, passed through the German side but had to wait two hours for the Czech side to open. All had an excellent breakfast at the hotel for 9d each (less than 5 new pence!). The hangar on the airfield would not officially open to 8 am. Return to the Wasserkuppe was achieved by 2 p.m. where the King Kite was handed over to Hiscox and the team went to bed. " 

Friday July 16th. 

Watt did 96 miles, and might have gone further had not his start been delayed due to a trolley damaging a wing leading edge. He found the thermals narrow and rough, got up under a cloud, but afterwards found thermals in clear air. While doing one of his quick darts from one thermal to the next, he shot through a small one being used by a Swiss pilot, who forthwith tried to follow him (in either a Moswey 2 prototype, S. 18 prototype or Spyr 3,) but could not catch up and had to land. Watt found a slow rising thermal over Sangershausen, and finally a weak one over Alistadt, before landing himself. His course was first N.E. then S.E. Clouds blowing from the Harz Mountains were melting over the plains below. There was a thunderstorm in the direction of Dresden, and this, he thinks, caused the lack of thermals in this region towards the end of the flight, perhaps owing to compensating down currents surrounding the storm ". 

On these flights the King Kite showed ability to climb in weak thermals and also to fly fast, using modern "Dolphin Technique".

During its test flying previous to this on York Airfield, Hugh Bergel said that he once saw the King Kite beat its Avro 504K towplane back to the airfield. It was so fast.

P.M. Watt went to the International Contest with very little gliding experience but with thousands of hours of power flying in the RAF. His average speeds during cross-countries were high and destinations were sometimes arrived at with great heights. Then, there was his disaster on the first day (July 4th) when his King Kite spun off a bungee launch. Willy Watt did not fly again until July 9th, after two more flying days.

On July 14th, Neilan shook the spectators by going into spin, and coming out of it unnervingly low down, but it was not he who was unnerved, as he went off 35 miles cross-country afterwards.

On Friday 16th, Neilan went 48 miles to Gotha, just getting into the aerodrome by 1Oft. GGAAC, BGA 303, was crashed on the Wasserkuppe on 4.7.37 and was never repaired. 

 

1938 British National Contest 

This was held at London Gliding Club, Dunstable during the first half of July. On Monday July 11th, P.M. Watt flew a King Kite 87 miles to Wydmondham while Nicholson flew his Rhönsperber 106 miles to Lowestoft. 

On Sunday 17th, Watt flew the King Kite on a crosswind goal flight of 91 miles to Ramsgate in Kent. These two flights assured his second place in the contest to Nicholson. The Rhönadler flown by Fox came third. 

 

1939 National Contests

 

These were held at the Derby & Lancashire Gliding Club, Camphill, just 7 weeks before the outbreak of war, For some reason, although a King Kite was entered by Slingsby, it never arrived and Willy Watt flew a Petrel (that owned now by Ron Davidson), which was the opposite extreme to the King Kite. The Petrel does not have much speed range, and the King Kite was the fastest glider flying in Britain. 

Just seven weeks after this, during the first week of the war, Willy Watt was killed in a Hamden bomber while engaged in a blind flying experiment, possibly taking off on a beam in the dark and being directed through a hangar. No doubt Willy's blind flying in the King Kite should have helped him as he was now one of the foremost blind flying experts in the RAF. 

During 1937, Fred Slingsby had been on the Wasserkuppe during the International Contest and had been quite overcome with the aerodynamic excellence of the Reiher V.1. Thus he decided that his designs during 1938/39 should have Reiher Type noses... i.e. the Gull 1, Petrel, Gull 3 and at least one of the remaining two King Kites had their noses altered accordingly. (In 1945, the Weihe and Meise cockpit canopies induced Fred Slingsby to change his designs to resemble those, for better visibility than the previous Reiher style canopies). 

 

Wartime Service

 

One or both King Kites were impressed by the Military. G-GAAD was on the strength of John Furlong's ATC Gliding School and was taken by his school on an expedition in 1945 to Newcastle together with the Gull 2 two-seater, which was also in his school's service. GßGAAD was camouflaged at that time. 

During 1949, the RAFGSA was formed and the King Kite was used by them at Detling until it was "struck off charge" through glue failure in 1952. Its military number was VD 207, Its BGA No was 304. 

 

Postwar 

G-GAAB took part in the Cambridge University Gliding Camp on the Long Mynd during June 1946. It was a week of tremendous cumulonimbus clouds. 

On the 26th June, the King Kite G-GAAB (BGA 302) broke up in cloud causing a fatal accident to its (RAF?) pilot. The official reason for this accident was "Glue failure". Unless the pilot was Willy Watt, it seems to us now that it would have been dangerous to take a machine that picked up speed very quickly, and had no speed-limiting airbrakes, into a cumulonimbus cloud (if it was one) and that it might not have had to have glue failure to have come to pieces in those circumstances. However, who are we to challenge the official pronouncements of the day? The Rhönadler had also been condemned through glue failure earlier that year just after it had gained the height prize at the Easter Meeting by being taken to over 7,000 ft in cloud. The Condor 2 was also struck off charge because of glue failure. These machines had not been kept well during the war. 

The above led to the BGA's pronouncement that there had to be new gliders for the British Gliding Movement (the Eon Olympia etc). 

The NACA 230 series profile has been given the blame for the King Kite's basic failing. Afterwards, these profiles were used for the following sailplanes: 

 

  •        Akaflieg Stuttgart's “Wippsterz"   NACA 2318, 2315 and 4312, designed in 1937. 
  •        Fs 18.                                           NACA 23012, to 23018. After a very successful 1938Rhdn Contest. Crashed 1938. 
  •        Akaflieg Hannover AFH-4              NACA 23014 to 23012. Broke up in cloud during the 1938 Rhön Contest. 
  •        AFH 10                                         NACA 23012 (?) at Farnborough in 1945. 
  •        Akaflieg Aachen FVA 11 "Eifel"     NACA 23015 throughout its span. Damaged during the 1939 Rhon Contest. It was not repaired before outbreak of war and did not survive the war.
  •        WLM-1   NACA 23013. Built in 1947 and was intended to be trainer for the Swiss airforce’s Vampire jet fighters. As such, it was an aerobatic high performance sailplane                                                       
  •        Jarlaud for the World Championships in 1950. Two prototypes were built and both still exist, one of them being airworthy in 1990. 
  •        Jaskolka. 1951 designed in Poland. NACA 23012A. This was a very successful sailplane which held many World Records.

 

The NACA 23 series profiles have been used on several light, and aerobatic, aeroplanes with great success. David Jones says that his Tempete has the most gentle stall. Could it be that such a profile is used for aerobatic aeroplanes to give sudden, clean, stalls with good acceleration? In such a case, it would be a mistake to use it for a non-aerobatic sailplane, which is often flown at just above stalling speed.

 

As can be seen from the above, only the Yppsterz", "Eifel" and "Arsenal" used anything approaching the depth of profile in ratio to chord (21 per cent) root profile of the King Kite. 

 

The new King Kite 

Dr. Wortmann finally delivered us from the NACA profiles, although their 6 series was highly beneficial to sailplanes. The new King Kite has one of the Wortmann profiles. 

The flight handling quality of this sailplane is so superb that had it had anything approaching it in 1936, it would in Chris Wills's opinion, have easily been the best in the world. 

On two occasions, it was compared in flight with the Rhönbussard. The King Kite was not only better at low speed in climb, but could out fly the Bussard in straight flight at every speed. In fact, it could fly around the whole sky while the Bussard was still almost in one place. Such perhaps is the advantage of the King Kite's modern wing profile, although this may be a "slower" profile than its original 1936 one. 

The claimed 1:35 max. L/D for the new King Kite is in Chris Wills's opinion well possible and this must make it among the best wooden gliders ever designed in spite of its relatively small span compared with some of them. 

We are very indebted to David Jones, Thoby Fisher and Dr. Wortman for having brought back to us such a sailplane, which apart from its rudder, certainly looks like a King Kite. 

Let us spare a last glance back to 1936; to the little cabinet offshoot of Slingsby Sailplanes with the two drawing boards set side by side, at which sat Peter Shaw and John Sproule. What they achieved there was an original design of such brilliance that, had they not been led astray by experts, who knew no better at that time, they would have created a sailplane that would have put Britain ahead of the world. We wonder whether a Cambridge Mechanical Engineering Honours Graduate, who had never worked on aircraft before, could do so well today? It is said that the good die young". And so it was with Peter Shaw, who was no relation to Major Shaw, Slingsby Sailplane's sponsor and benefactor.