The PZL M-15 was a jet-powered biplane designed and manufactured by the Polish aircraft company WSK PZL-Mielec for agricultural aviation. In reference to both its strange looks and relatively loud jet engine, the aircraft was nicknamed Belphegor, after the noisy demon. Development of the M-15 can be traced back to a Soviet requirement for a modern agricultural aircraft to succeed the Antonov An-2; it was at the insistence of Soviet officials that jet propulsion would power the type. WSK Mielec's design team recognised the value of the An-2's biplane configuration to the role and set about developing an initial experimental aircraft, the Lala-1, for Latające Laboratorium 1 ("Flying Laboratory 1") to explore the use of a jet engine with such a configuration. On 20 May 1973, the first M-15 prototype performed its maiden flight; even during the test flight phase, it was apparent that there were several drawbacks to the aircraft, including its poor handling, limited range, and high operating costs. While production commenced in 1976, these problems remained unresolved and meant that the M-15 was noticeably inferior in several respects to the An-2. During 1981, production was terminated in favour of procuring more An-2s; a total of 175 M-15s were built against the many thousands which had once been planned. The PZL M-15 Belphegor was a metal twin-boom sesquiplane. It was intended to be routinely operated by a single pilot, but also had provisions for two additional crew to serve as technicians when deemed necessary. Portions of the lower wings and the chemicals tanks were composed of a laminate to avoid corrosion. The upper and lower wings were connected with two thick columns which housed the chemical tanks. It was outfitted with a fixed tricycle landing gear arrangement. The M-15 was a relatively heavy aircraft, and has been described as being the heaviest biplane to ever be produced. For the crop-dusting mission, the M-15 could accommodate a payload of just under three tons of pesticides within two sizable pylons that separated its two wings; chemical dispersal was achieved via compressed air. This storage system was relatively unorthodox, the conventional An-2 simply stored these in a single tank housed within the fuselage in a space that could be reused for various other cargoes if not fitted. As such, the arrangement adopted upon the M-15 allowed for no such flexibility and severely limited alternative uses for the aircraft. To avoid the engine exhaust interfering with the dispersal system during release, the engine had to be positioned in a relatively elevated location on top of the fuselage; this was also beneficial to minimise the engine's ingestion of debris, which was a particular problem when operating from austere airstrips. For more details on development, fligght testing and production, click here.
