Heinonen HK-1

The Heinonen HK-1 Keltiäinen is a Finnish single-seat, single-engined sport aircraft of the 1950s. Three examples were built. The first was used by its designer to set a class distance record in 1957 that stood for 18 years before being beaten.

Design and development
Juhani Heinonen, an aeronautical engineer who had previously worked for the Valmet aircraft factory at Tampere, and then for Finnair, designed a single-seat, single engined aerobatic sport aircraft, the Heinonen HK-1. It was a low winged monoplane of all-wooden construction, powered by a Walter Mikron air-cooled inline engine rated at 65 hp driving a two-bladed propeller. Split flaps were fitted to the wings, while the aircraft had a fixed tailwheel undercarriage, with a steerable tailwheel but no brakes. The pilot sat under a sliding perspex canopy. A prototype was built at the glider school at Jämi, first flying in August 1954.

Operational history
The HK-1 was displayed at the 1955 and 1957 Ypenburg airshows. On 10 July 1957, Heinonen flew the HK-1, fitted with an additional ventral fuel tank, non-stop between Madrid, Spain and Turku in Finland, covering a distance of 2844 km in 17 hours 1 minute, setting a class world distance record for aircraft of less than 500 kg take-off weight. For this flight, Heinonen was awarded a Louis Blériot medal by the Fédération Aéronautique Internationale. This record was not broken until 2 July 1975.

The aircraft is now preserved at the Finnish Aviation Museum near Helsinki Airport.