A single-seat sports-plane, the Finnish HK-1 was designed by Mr. Juhani Heinoven and built by the Jami Soaring School. First flight was in August 1954. Engine is a 65-h.p. Waiter Mikron; span 22 ft 6 in.; loaded weight (aerobatic) 795 lb.; max. speed 135 m.p.h.; range 430 miles.

HEINONEN HK-1. Dipl.-Ing. Juhani Heinonen worked on the design of the trim HK-1 (OH-HKA) single-seat ultralight during his time off as a member of the Valmet O/Y (government-sponsored aircraft factory) design team. He assisted in the design of the new air force advanced trainer, the Valmet VH-2 Vihuri (Squall).
The HK-1 was built at the Central Gliding School at Jarnijarvi and Dipl.-Ing. Heinonen flew it for the first time in August 1954. The HK-1 is a cantilever monoplane of wooden construction with plywood sheet covering. The 65-h.p . Waiter Mikron III was recovered from a wrecked Praga Air Baby, and drives a 5-ft. diameter two-blade wooden airscrew. The main undercarriage is fixed (sprung steel) and the tailwheel is steerable.
Salient features: Straight lines to the wings, fuselage and tail assembly give the HK-1 a businesslike air, while the deep canopy presents a slightly humped-back appearance in side view.
Photograph shows the designer "prop.-swinging" in unconventional manner at Tampere.

HEINONEN HK-1. Data: Heinonen HK-1 (OH-HKA). Power: 65-h.p. Waiter Mikron III four-cylinder inverted inline. Accommodation: single-seat. Dimensions: span 22 It. 6 in.; length 19 ft. 0 1/4 in.; height 6 ft. 10 1/2 in.; wing area 75 sq.ft. Weights: empty 550 lb .; loaded (aerobatic 795 lb., (normal) 880 lb . Performance: maximum speed 135 m.p .h . at sea-level; cruising 115m.p.h .: landing 47 m.p.h.; range 430 miles.