In 1938, the Estonian aviation engineers Voldemar Post, Rein Tooma and Otto Org, previously responsible for the PON-1 trainer, designed and built the PTO-4 training aircraft.[1] It was a two-seat low-winged monoplane powered by a De Havilland Gypsy of 120 hp, with a fixed undercarriage that could be fitted with wheels or skis.[2] The aircraft could fly at a maximum speed of 245 km per hour and had a ceiling of 5,000 meters.[3] On 12 October 1938, the PTO-4 was taken into service of the Air Force.[4]
The Estonian Air Force received two PTO-4s (serial numbers 161 and 162), one with an open cockpit and the other an enclosed cockpit.[1] Six examples were in civil use,[5] of which five were used by the Eesti Aeroklubi (EAK), a flying club controlled by the Estonian Military.[1]
Four examples surviving from the Soviet occupation of Estonia (1940–41) were operated by the German Luftwaffe, being operated by a unit manned by Estonian volunteers (initially called Sonderstaffel Buschmann and later 1./SAGr.127) based at Reval-Ülemiste airfield. They were operated as training and liaison aircraft as well for coastal patrol over the shores of the Baltic.[6]
Germany