Waco F series
The Waco F series is a series of American-built general aviation and military biplane trainers of the 1930s from the Waco Aircraft Company. Development. The Waco 'F' series of biplanes supplanted and then replaced the earlier 'O' series of 1927/33. The 'F' series had an airframe which was smaller and about lighter than the 'O' series, while continuing to provide accommodation for three persons in tandem open cockpits. A similar performance to the earlier model was obtained on the power of smaller and more economical engines. The initial models were the INF ( Kinner engine), KNF ( Kinner ) and the RNF ( Warner Scarab), all of which had externally braced tailwheel undercarriages. Many further sub-models followed with more powerful engines of up to . The most powerful in the range was the ZPF of 1936/37, intended for executive use. Operational history. The 'F' series was popular with private owner pilots for sporting and other uses and continued in production through the late 1930s. The tandem cockpit UPF-7 was adopted by the Civilian Pilot Training Program and continued in production until 1942 by which time over 600 had been built. The 1934 model YMF was substantially redesigned with a longer  and wider fuselage, larger rudder and other structural changes, and put into production in March 1986 by WACO Classic Aircraft of Lansing, Michigan as the YMF-5. Over 150 YMF-5s were completed as of 2017 with new examples being built to specific orders. The WACO Aircraft Company of Ohio Inc had built three replicas by December 2011, which they designated MF. Considerable numbers of 'F' series biplanes, both original and newly built, remain in service. Variants. Listed in approximate chronological order (per Simpson, 2001, p. 573) Note: from 1936 Waco added year suffixes to designations—e.g. YPF-6, YPF-7, with the numeral  being the last digit of the model year.