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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 In Christian demonology, Belphegor (or Beelphegor, he, בַּעַל-פְּעוֹר ''Báʿal-pəʿór'' - Lord of the Gap) is a demon. In later Kabbalah Belphegor is a demon who helps people make discoveries. He seduces people by suggesting to ...
'', after the noisy demon. Development of the M-15 can be traced back to a
Soviet The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, ...
requirement for a modern agricultural aircraft to succeed the
Antonov An-2 The Antonov An-2 ("kukuruznik"—corn crop duster; USAF/DoD reporting name Type 22, NATO reporting name Colt) is a Soviet mass-produced single-engine biplane utility/agricultural aircraft designed and manufactured by the Antonov Design Bure ...
; it was at the insistence of Soviet officials that
jet propulsion Jet propulsion is the propulsion of an object in one direction, produced by ejecting a jet of fluid in the opposite direction. By Newton's third law, the moving body is propelled in the opposite direction to the jet. Reaction engines operating o ...
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 ("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 The maiden flight, also known as first flight, of an aircraft is the first occasion on which it leaves the ground under its own power. The same term is also used for the first launch of rockets. The maiden flight of a new aircraft type is alwa ...
; 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.


Development


Origins

By 1970, the
Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen national ...
was formulating a new requirement for an agricultural aircraft that it intended to use above the very large areas of Soviet farms, the
kolkhoz A kolkhoz ( rus, колхо́з, a=ru-kolkhoz.ogg, p=kɐlˈxos) was a form of collective farm in the Soviet Union. Kolkhozes existed along with state farms or sovkhoz., a contraction of советское хозяйство, soviet ownership or ...
collectives, and state-owned
sovkhoz A sovkhoz ( rus, совхо́з, p=sɐfˈxos, a=ru-sovkhoz.ogg, abbreviated from ''советское хозяйство'', "sovetskoye khozyaystvo (sovkhoz)"; ) was a form of state-owned farm in the Soviet Union. It is usually contrasted wit ...
. It was explicitly stated in the requirement that the envisioned aircraft was to be both more efficient and modern than the existing Antonov An-2SKh and An-2R, of which tens of thousands had been produced primarily to perform this role. During 1971, following an agreement between the Soviet Union and Poland on the matter, the Polish aircraft manufacturer WSK Mielec set about developing its own original response to the requirement. By this point, Poland had already produced the agricultural Antonov An-2R under licence for export back to the
USSR The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen nationa ...
, while agricultural planes had become a Polish specialization within the
Comecon The Council for Mutual Economic Assistance (, ; English abbreviation COMECON, CMEA, CEMA, or CAME) was an economic organization from 1949 to 1991 under the leadership of the Soviet Union that comprised the countries of the Eastern Bloc along wi ...
. WSK Mielec's design team was headed by two engineers, Kazimierz Gocyła and Riamir Izmailov. The designers recognised that it would be highly desirable to retain many of the characteristics of the successful An-2, while also improving upon them where feasible. As such, there was a reported desire to incorporate state-of-the-art technologies and to make the aircraft into a symbol of the rapid progress of development. According to aviation author Krzysztof Luto, the highly unusual decision to adopt
jet engine A jet engine is a type of reaction engine discharging a fast-moving jet of heated gas (usually air) that generates thrust by jet propulsion. While this broad definition can include rocket, Pump-jet, water jet, and hybrid propulsion, the term ...
propulsion for the prospective aircraft had been at the insistence of Soviet officials, who also actively participated in the design process. Accordingly, the design team were compelled to use such an engine due to political factors rather than practical ones. Recognising the favourable qualities of the An-2, it was decided to adopt some similar design features, such as its biplane configuration that gave favourable lift characteristics.


Flight testing

It was recognised from the onset that use of a jet engine for a relatively slow agricultural biplane posed several problems that would need to be addressed, including unforgiving handling and maintenance issues. In order to better explore these problems, an experimental airplane ''Lala-1'', for ("Flying Laboratory 1"), was constructed in Poland. Performing its first flight on 10 February 1972, this aircraft comprised the whole forward section of an An-2, together with its wings, while the rear part was cut off and replaced with a frame construction that housed a single
Ivchenko-Progress AI-25 The Ivchenko AI-25 is a family of military and civilian twin-shaft medium bypass turbofan engines developed by Ivchenko OKB of the Soviet Union. It was the first bypass engine ever used on short haul aircraft in the USSR. The engine is still ...
turbofan The turbofan or fanjet is a type of airbreathing jet engine that is widely used in aircraft engine, aircraft propulsion. The word "turbofan" is a portmanteau of "turbine" and "fan": the ''turbo'' portion refers to a gas turbine engine which ac ...
engine (as used on the tri-engined
Yakovlev Yak-40 The Yakovlev Yak-40 (russian: Яковлев Як-40; NATO reporting name: Codling) is a regional jet designed by Yakovlev. The trijet's maiden flight was in 1966, and it was in production from 1967 to 1981. Introduced in September 1968, the Ya ...
and the single-engined
Aero L-39 Albatros The Aero L-39 Albatros is a high-performance jet trainer designed and produced in Czechoslovakia by Aero Vodochody. It is the most widely used jet trainer in the world; in addition to performing basic and advanced pilot training, it has also fl ...
fighter-trainer). The Lala-1 was equipped with agricultural devices; experiences and data gathered from its test flights greatly influenced the design of the M-15. On 30 May 1973, the first variant of the M-15 conducted its
maiden flight The maiden flight, also known as first flight, of an aircraft is the first occasion on which it leaves the ground under its own power. The same term is also used for the first launch of rockets. The maiden flight of a new aircraft type is alwa ...
; it was followed by the second prototype on 9 January 1974. During the following years, both aircraft were intensively tested, and were joined by a pre-production series. Even at this stage of the project, the aircraft's performance was being criticised and constantly compared unfavourably with its An-2 predecessor. The M-15 was publicly displayed at the
Paris Air Show The Paris Air Show (french: Salon international de l'aéronautique et de l'espace de Paris-Le Bourget, Salon du Bourget) is a trade fair and air show held in odd years at Paris–Le Bourget Airport in north Paris, France. Organized by the French ...
of 1976; it has been claimed that it was at this event that the aircraft received its popular nickname of "Belphegor", a result of its strange appearance and noisy jet engine propulsion.


Production

During 1976, serial production of the M-15 commenced. At one stage, Soviet agriculture planners had intended to order as many as 3,000 aircraft to meet its needs; however, operations of the M-15 under real world circumstances proved to be a largely disappointing experience. As an inherent consequence of adopting a jet engine, it was not an economical aircraft to operate, being inferior in this aspect to the An-2 that the M-15 had been envisioned to succeed. In contrast, the M-15 could only achieve a range of 215 nautical miles, half that of the An-2, largely due to its jet engine and relatively high weight. Maintenance was also more intensive, a factor which was compounded by the typically austere nature of agricultural airstrips. The aircraft was also expensive, both to construct and to operate. Furthermore, pilots would commonly need additional training for handling jet-powered aircraft, which was a further complication for any transition to the M-15. Production of the aircraft was terminated without ceremony during 1981, by which point only 175 aircraft had been completed. The M-15 was only ever operated inside the USSR, despite the type having been made available to potential export customers. Taking its envisioned role was the preexisting An-2, which continued to be used in the agricultural role into the twenty-first century. Of those M-15s that were produced, very few remained operational by 1995, its operators having rarely found the aircraft to be satisfactory.Simpson 1995, p. 315. It is believed that the M-15 is the world's only jet
agricultural aircraft An agricultural aircraft is an aircraft that has been built or converted for agricultural use – usually aerial application of pesticides (crop dusting) or fertilizer (aerial topdressing); in these roles they are referred to as "crop duster ...
(i.e., the world's only jet
cropduster Aerial application, or what is informally referred to as crop dusting, involves spraying crops with crop protection products from an agricultural aircraft. Planting certain types of seed are also included in aerial application. The specific sp ...
), as well as the world's only jet
biplane A biplane is a fixed-wing aircraft with two main wings stacked one above the other. The first powered, controlled aeroplane to fly, the Wright Flyer, used a biplane wing arrangement, as did many aircraft in the early years of aviation. While ...
and the world's slowest jet aircraft, at least amongst aircraft that have been put in mass production.


Design

The PZL M-15 Belphegor was a metal
twin-boom A twin-boom aircraft is characterised by two longitudinal booms (extended nacelle-like bodies). The booms may contain ancillary items such as fuel tanks and/or provide a supporting structure for other items. Typically, twin tailbooms support ...
sesquiplane A biplane is a fixed-wing aircraft with two main wings stacked one above the other. The first powered, controlled aeroplane to fly, the Wright Flyer, used a biplane wing arrangement, as did many aircraft in the early years of aviation. While a ...
. 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 Lamination is the technique/process of manufacturing a material in multiple layers, so that the composite material achieves improved strength, stability, sound insulation, appearance, or other properties from the use of the differing materials ...
to avoid
corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...
. 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 Tricycle gear is a type of aircraft undercarriage, or ''landing gear'', arranged in a tricycle fashion. The tricycle arrangement has a single nose wheel in the front, and two or more main wheels slightly aft of the center of gravity. Tricycle g ...
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
pesticide Pesticides are substances that are meant to control pests. This includes herbicide, insecticide, nematicide, molluscicide, piscicide, avicide, rodenticide, bactericide, insect repellent, animal repellent, microbicide, fungicide, and lampri ...
s within two sizable pylons that separated its two wings; chemical dispersal was achieved via
compressed air Compressed air is air kept under a pressure that is greater than atmospheric pressure. Compressed air is an important medium for transfer of energy in industrial processes, and is used for power tools such as air hammers, drills, wrenches, and o ...
. 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.


Specifications (M-15)


References


Citations


Bibliography

* ''Aviation Week & Space Technology''. McGraw-Hill, 1982. Volume 116, Issues 22-26. * Gunston, Bill. ''The Illustrated Encyclopedia of Commercial Aircraft''. Exeter Books, 1980. . * Taylor, John W. R. ''Jane's All The World's Aircraft 1976–77''. London: Jane's Yearbooks, 1976. . * Simpson, R. W. ''Airlife's General Aviation: A Guide to Postwar General Aviation Manufacturers and Their Aircraft''. Airlife, 1995. . {{PZL aircraft 1970s Polish agricultural aircraft
M15 M15 or M-15 may refer to: In science * Messier 15 (M15), a globular cluster in the constellation Pegasus In firearms and military equipment * M15 mine, a United States anti-tank mine * M15 rifle, a variant of the M14, a United States military rif ...
Poland–Soviet Union relations Sesquiplanes Single-engined jet aircraft Aircraft first flown in 1973 Twin-tail aircraft