The Skylark 2c, a unique subject for scale
By Martin Simons
In 1953 Fred Slingsby in England began production of the Type 41, Skylark 2, one of the first gliders ever to have a NACA six digit, low drag wing profile and certainly the first ‘laminar flow’ sailplane to enter production. It had a wing span of 48 feet, slightly less than the fifteen metres nominated for the (then new) ‘Standard Class’ in World Championships. The performance was very good and the type became popular with British gliding clubs and pilots. (Slingsby soon followed it with the Skylark 3, with over three metres additional span.)
Rudolf Kaiser’s Ka 6 won the Standard Class design prize in 1958, and with it Heinz Huth twice won the St Class World Championships. The Skylark 2 already began to seem out of date.
A group of aircraft engineers at the Bristol Gliding Club, led by Dennis Corrick, decided that the Skylark 2 could be considerably improved. A wind tunnel model was made to test the ideas before construction was begun. Taking an existing ‘2, they went through a program of modifications that produced the new version of the Skylark 2..
This interesting extract is from information passed by Martin Corrick, the son of the developer Dennis Corrick:-
"As far as I'm aware, my father did all the design work on the modifications himself - and indeed most of the actual modifications too, though other members of the syndicate helped with the practical work. We took out the front windows of our Victorian house in order to get the fuselage into the front room for the work to be done, and the project dominated family life for a considerable time. When the modifications were completed, the aircraft had to undergo a complete set of flight trials; these were overseen by Ken Brown, a member of the syndicate, who was a flight test observer at BAC. "
The following report is from Ken Brown, one of the syndicate of eight involved with the modifications:-
"We took delivery of the ordinary Skylark 2 in February 1957 at Nympsfield, and immediately entered it for the Nationals at Lasham that year. We were allocated the competition number 33. While we were debating how we were going to mask up these very curvatious numbers, the artist Peter Scott and of Wild Fowl fame, was in the workshop and just took the paint brush and paint pot and drew on the distinctive stylish threes which have stayed with the glider all its life. Throughout its life the glider was always referred to as Thirty Three.
That year, Bernie Palfreyman won a day prize at the Nationals, which was to be a set of photographs of the glider taken by Charles Brown, who was a very famous aviation photographer at that time. Lack of opportunity meant that the flight could not be done until 1959, by which time Bernie had returned to Canada, so I flew the glider. It was the photographs of the Skylark flying at 70mph to keep up with the Prentice which had Chas. in it, which showed Denis how the glider was nose down, with the elevator down and the trim up at that speed. Denis thought that all three should be more or less lined up to reduce the drag. It was that that started him on designing the mods to turn the glider into what he thought should be designated the Skylark 4 (Slingsby had already marketed the 3).
Denis not only designed the mods, but he also set out the plan to implement them in two stages over the winters of 1960/61 and 61/62 and organised the supply of all the hardware. But before the work started, he built a scale model which he had tested in the wind tunnel at Filton. (Holding a pretty senior position at Filton, he had influence in these things). Fred Slingsby took a great interest in the glider and gave it the the official designation 2c. Although the brochure which Denis produced showed the glider with a cheek line and a large 4 painted on the side, in fact these were never applied to the full scale glider. Most of the actual work of modifying it was done by Denis and Ted Chubb, who was a stress engineer. Gordon Fisher and I assisted in a rather minor way. The Flight tests after each stage of the Modification were done by Denis, and it was he who negotiated the experimental CofA. The only thing which prevented the granting of a full CofA was the need to calibrate the static side of the airspeed system. This was not done until 1972, by which time Denis had left the syndicate, so it fell to me to do those measurements.
In the 1960s, glider radios were short ranged, unreliable devices. However we had one and Bob Perrott decided the call sign should be Merlin - a merlin is a soaring bird, and Merlin was a wizard - so he thought it was appropriate. The radio was Merlin, but the glider was Thirty Three.
There was one interlude in the re-gaining of the full CofA which caused us a little problem and because of this, for a long time it flew on an experimental C of A, carrying the word EXPERIMENTAL on the side of the fuselage as required by the regulations. Denis being an engineer had wanted to get an accurate measurement of the centre of gravity of the glider. So he had weighed it with each of the pilots in the syndicate sitting in it in turn, and made sure that the resulting CofG was within Slingsby's limits. The flight tests were OK, but the spin required the full recovery action. When I came to weigh it later, the CofG came out behind the aft limit. But then, I had weighed it in the conventional way, assuming a standard CofG position for the pilot. (just as Sling had). So although Denis's CofG was accurate, it did not correspond to the CofG which Sling had used to define the limitations. We had to remove the elevator mass balance which Denis had installed, and that sorted the problem out.
We sold the glider to Harry Johnson in about 1974, and he was very pleased with it and kept it until he gave up gliding. By that time there was little demand for wooden gliders with old fashioned performance and he could not find a buyer. It languished in its trailer for some years until Mike Cummings took it over and made a splendid job of refurbishing it, and in fact added the cheek line and 4 designation as on Denis's brochure."
The most significant change was to reduce the wing rigging angle on the fuselage by four degrees. This ensured that the fuselage was aligned with the airflow at high airspeeds, and so generated less parasitic drag. The low speed performance for soaring was hardly affected. A slight adjustment of the elevator neutral angle was required to maintain trimming balance.
The only noticeable change in handling was that the fuselage was more tail down when landing, so the tail skid touched before the main landing wheel, resulting in a hard landing if one held off in the traditional way. Since the main wheel was also set further into the fuselage, and further forward, this further exacerbated the hard landing, but not enough to trouble anyone. The wing span was increased to the full 15 metres by adding Hoerner tips. Other details included a much improved wing root fairing, smaller and better faired skids, and sealing of control line hinges and all other gaps and leakages.
It was considered that the Merlin was capable of keeping up with the bigger Skylark 3 in competition flying. The Merlin remained in use for many years at Brisol but, when plastic sailplanes arrived, older, wooden gliders were often neglected and the Merlin remained out of use for over twenty years, slowly deteriorating in storage.
It was rescued from this sad fate by Tony Cummins. He was able to negotiate for possession of the glider and worked hard for several years to bring it back to first class condition and full airworthiness. It is now as good as new, beautifully finished in its bright yellow colour and still carrying the contest number, 33, on the vertical tail. After some early test flights in 2005, Tony brought it to the Vintage Glider Club rally at Camphill in June-July 2005. In mediocre soaring conditions he showed the Merlin to be as good now as ever it was before, capable of keeping up with the best of its generation.