Robert Stierlin is one of the few Swiss who designed, built and tested five ultra-light helicopters. This helicopter fan began his activity in 1948 and continued until May 1969 when he vas victim of a flight accident during a flight test.
Stierlin was born on the 9th of October 1926 in Toulouse (France). In 1932 together with his family he established in Geneva and some years later in Meyrin. Since childhood he was very interested in mechanic and in aviation. After the compulsory school he continued his studies at the college. He then did an apprenticeship as a mechanic and much later he became an engineer and was employed by the European Organization for Nuclear Research (CERN).
By 1948 assisted by his close friend Roger Mercier (and other helicopter fans) he started the construction of the first prototype (image 1). At that time none helicopter was yet registered in Switzerland. The Federal office of civil aviation (FOCA) was not officially informed about Stierlin's helicopter activities.
This model of standard configuration was completed in 1949. It was a single-place ultra-light powered by a 11-14/15-20 kW/hp Villiers gasoline engine. As many contemporary models it had an overhead stick which controlled the swash-plate, the collective lever and foot pedals. The helicopter never rose in the air because it was underpowered.
After this unsuccessful attempt, in the period between 1952 and 1953, Stierlin began to build his second prototype (image 2) usually known as the Merlin. This model had a two blade main rotor with stabilizer bar and was powered by a 9 cylinders 33.5/45 kW/hp Salmson engine. After a series of tests it was modified until it flew satisfactory. With it Stierlin and some of his friends learned how to fly a helicopter. Pilot checkouts in the Merlin were in fact easily accomplished. During initial familiarization of the pilot, two people, one on each side, stabilized the craft while the pilot lifted off and hoovered a few feet above the ground. As soon as the pilot had achieved the proper feel as demonstrated by several simulated take-offs, landings, hovering turns, and slow translations while still under the restraint of ground personnel, he was considered ready to fly solo. Pilots with no prior experience checked out in this method with little difficulty. The Merlin was "secretly" tested near the village of Meyrin.
In September 1954 Stierlin and Mercier won a price in France where an international competion for individual helicopters was organized. After this exploit the Merlin was exposed in some Swiss malls. For the chronicle this model was the first Swiss made helicopter to fly successfully.
Encouraged by the recognition of his design the builder of Geneva started almost contemporary the construction of his third prototype (image 3). The test flights began in 1956 with the same designer at the controls. This prototype, powered by a 48.5/65 kW/hp Continental engine, was equipped with a hydraulic control system which eliminated most of the control mechanisms. Probably this novelty was not functioning in a satisfactory way. In fact in the following models this new control system was abandoned. The demonstrations of this helicopter, which was officially registered X-HB-XVA, were observed by the rapresentatives of the FOCA in 1960. Stierlin's name became more and more popular, especially among the community of the amateur builders. Several aviation magazines published articles concerning his helicopters.
In 1962 the Swiss builder began to design and build the fourth prototype (image 4) which was completed in the winter of 1963-1964. As its predecessors it was a conventional, lightweight, low cost, one-man helicopter. At the beginning this model (very similar in general appearance to the Goodyear GA400-3 Gizmo) was equipped with a three blade main rotor, which was then however replaced with a two blade rotor with a stabilizer bar. It was powered by an outboard 29.8/40 kW/hp Johnson water-cooled two-stroke engine mounted behind the pilot. The flight tests began in July 1964, but at the beginning its builder had some problems with the cooling of the engine which were then however solved. As it predecessors it was of an extremely simple construction. It received the Swiss registration X-HB-XVB. The single place could be disassembled and transported in a Renault 4L car. Stierlin tested successfully this helicopter and flew it during some aviation meetings in Switzerland and in France. Until 1969 complessively it logged with this model about 60 hours of flight. Nowaday this model is exposed in Lucerne, in the Swiss museum of transport.
Differently from its predecessors the last helicopter built by Stierlin (image 5) was a two place very similar to the Matra-Cantinieau MC. 101, a French helicopter which flew for the first time in 1952. The Swiss inventor decided again to install an outboard engine (65.6/88 kW/hp Johnson). The construction of this model started in 1967 and was completed in the spring of 1969. The flight tests began on the 15th of May. In the late evening of the following day a friend arrived on the place. Stierlin, who was probably encouraged by the first flight test results, invited him for the first cross-country flight.
The new helicopter had however some problems with the engine's cooling system. Its builder probably underestimate the imminent danger and decided to fly again. During the following flight, at an estimate altitude of about 20 to 30 meters, the observers hear the engine's rpm dropping. It seems that Stierlin did not attemp to autorotate. Few instants later the helicopter crashed in the territory of Grilly (Ain/F) very close to the border between France and Switzerland. Unfortunately in the accident both occupants were fatally injured.
As it is written in the official accident report the pilot was not in possession of a helicopter pilot license, and the helicopter was not registered. As probable cause of the crash there is almost certainly a sudden loss of the engine power. One of the engine's pistons presented signs of damage (ecessive friction).
Robert Stierlin deserves a place of honor in Swiss helicopter history. To celebrate his memory in the village of Meyrin there is a road dedicated to him.
Michel Devaux rebuilt the helicopter after the accident. The new helicopter known as the SD 90 (or SD 100 when it was equipped with a boxer aircooled VW-Porsche engine) was registered HB-YAD between 1972 and 1989.