The PZL Milec M-15 was a strange agricultural aircraft developed in the USSR. The aircraft was designed and built in Poland for Soviet agricultural use. Mainly crop spraying and dusting over the vast expansive farms of the USSR.
The aircraft was designed in the early 1970s as a replacement for the Antonov An-2 – a large single-engine biplane which first took to the air in 1947. The M-15 brief called for a modern and efficient aircraft which must be jet-powered. The two chief designers of the aircraft at PZL were Kazimierz Gocyła and Riamir Izmailov.
They came up with a biplane configuration for the M-15, and in doing so inadvertently designed the only jet-powered biplane ever built. In 1972 the first prototype took to the skies. It was built using many components from the AN-2, including the forward section and the wings. It was powered by a single Ivchenko-Progress AI-25 turbofan engine mounted above the fuselage.
Over the next four years, two more prototypes were built and tested, as were the compressed-air powered agricultural spraying systems. In 1976 the design was finalised and the finished aircraft was revealed at the Paris Air Show of that year. It soon gained the unfortunate nickname “Belphegor” due to its strange appearance and awkward design. Belphegor was an ugly mythical demon who is said to have specialised in tricking people into thinking they had devised an invention which would make them rich.
The M-15’s nickname proved to be extremely accurate. The Soviets had originally planned to order up to 3,000 of the aircraft, but soon after it entered normal service its deficiencies became apparent. It was uneconomical, and the jet engine was more difficult and expensive to repair than a comparable propeller-engined aircraft. In the end the Soviets cancelled all orders after just 175 had been built.
The PZL Mielec M-15 Belphegor did make the history books though. Not only was it the first and only jet-powered biplane. It is also the only jet-powered agricultural aircraft ever built, and the slowest jet ever built. Top speed was just 124 mph, while the normal cruising speed was around 95 mph.
In the end, the aircraft which the M-15 had been brought in to replace, the old Antonov An-2, outlasted it. In fact the An-2 remained in production until 2002, with over 18,000 built!