***image1***Biplanes have proved uniquely adaptable to agricultural operations, especially “crop dusting,” because of the exceptional maneuverability bestowed by the lift of their two wings and because speed is not required – or even desired.
A semi-logical extension of this fact resulted in one of the most unusual aircraft built in the jet era – the Polish PZL M-15 jet biplane. The M-15 was not only the world’s first jet biplane, but also the world’s only specially-designed jet agricultural aircraft.
The M-15 was designed in response to a Soviet requirement to replace old crop-spraying propeller-driven biplanes with 3,000 more modern and efficient agricultural aircraft for the enormous collective farms of the Warsaw Pact.
From the beginning, the Soviet side insisted on using a jet engine in a new plane. The jet biplane idea was conceived in 1971 as a joint Soviet-Polish project between the Aeronautical Institute at Warsaw and the Soviet Research Institute of Special and Utility Aviation.
Poland was chosen because – under the Warsaw Pact Comecon system – different countries were responsible for producing different types of equipment; agricultural planes were assigned to Poland.
The commercial farms in the West never considered a jet crop duster because the enormous cost of operating such an aircraft was far more than the benefits. But cost – especially fuel costs – was unimportant under Soviet communism.
As completed, the M-15 was a metal twin-boom biplane with fixed tricycle landing gear and a 3,307-pound turbofan engine mounted over the crew cab. The upper and lower wings were connected with two thick containers that carried a huge amount of chemicals – 766 gallons or 4,850 pounds.
Part of the lower wings and the chemical tanks were made of a laminate to prevent corrosion. The chemicals were sprayed with compressed air out of thin struts that went from the bottom of the tanks to the outer part of the upper wing.
The pilot was seated in the extreme nose of the aircraft with excellent visibility and two technicians could be carried in a compartment behind him.
The prototype first flew on May 20, 1973, and by 1979, the aircraft was being delivered to the using agencies. The M-15 was shown at the Paris Air Show in 1976, where the French – always sensitive to aesthetics – found it so ugly, they nicknamed it the “Belphegor,” after a grotesque character in a 1966 French horror film.
The idea of a jet biplane crop duster seemed so ridiculous that many in NATO thought the M-15 was actually intended as a chemical weapons delivery platform. That may well have been true; it would certainly explain the two extra crew members. Only 175 M-15s were built and they were only used in the USSR.