The world’s only jet-powered agricultural aircraft. Designed and manufactured at WSK Mielec on order from the USSR, which was seeking a successor to the An-2 in the role of an agricultural aircraft. Because Soviet agriculture was dominated by large-scale farming, solutions were needed to increase the chemical payload as well as the width and uniformity of dusting. The creation of the new aircraft was intended to be part of an agricultural modernisation programme promoted by the new USSR leadership of Leonid I. Brezhnev and Alexei N. Kosygin, who came to power in the second half of the 1960s.
Designers from various aircraft factories, the Institute of Aviation, and Soviet engineers participated in the design and testing, led by engineer Riamir Adamovich Izmailov, whose I-711 project was selected for further development. The Polish lead designer was engineer Kazimierz Gocyla. The formal basis was the protocol of 26 April 1971 on cooperation in the serial production of aviation products in Poland, and the intergovernmental agreement on the development and production of new aviation products in Poland, signed on 1 December 1971. In order to test the biplane configuration with a jet engine adopted in the design, a flying laboratory called Lala-1 was built at the Institute of Aviation: the forward fuselage with wings of an An-2 aircraft was mated with an AI-25 engine and a new tail assembly mounted on a new uncovered truss structure. Curiously, the aircraft was registered as a military machine.
Testing showed that the use of jet propulsion did not adversely affect the spraying/dusting characteristics, nor did it harm crops. The prototype was first flown on 9 January 1974 (pilot: Tadeusz Golebiewski). Serial production began in 1976 and ended in 1981. A total of 175 units were built, including 10 in the dual-control version. Most of the aircraft went to the USSR. Five aircraft underwent operational trials at the Aerial Application Services Plant, and several flew in the GDR. In 1977, the M-15 was demonstrated at the Paris Air Show, where it was given the name “Belphegor”, which was later officially registered. However, wider operational use did not materialise due to high fuel consumption (which, especially in light of the 1970s oil crisis, significantly increased operating costs), long turn-around times, and high requirements for chemical quality and technical servicing that were difficult to meet under Soviet conditions.
A problem turned out to be the proper flushing of the equipment, as water sources were lacking at operational airstrips. Many USSR pilots feared that using an aircraft with twice the application efficiency of the An-2SCh/An-2R would lead to staff reductions and the reassignment of some pilots to lower-paid duties. One of the drawbacks attributed to the M-15 was of a systemic-economic nature: the fuel for the turbojet engine — aviation kerosene — unlike the petrol used in the “Anteks” (An-2s), could not be sold on the black market for use in cars…
The aircraft is of all-metal construction in a twin-boom biplane layout with twin rudders. The biplane configuration allowed the separation of wing high-lift devices (upper wing) from the agricultural equipment (lower wing), and the twin-boom tail arrangement provided unobstructed exhaust gas flow and avoided interference with chemical distribution by the jet wash. The single-seat cockpit offers excellent visibility (no engine or propeller in front!), is ventilated (using engine bleed air) and heated; according to pilots, it provided exceptional comfort for an agricultural aircraft. There was capacity for 2 mechanics during ferry flights. The undercarriage is a fixed tricycle type with a nosewheel. The powerplant is an AI-25 turbofan engine. This choice was partly driven by the fact that piston and turboprop engines available in the USSR did not provide sufficient power for an aircraft intended to carry a greater payload than the An-2. It was assumed that selecting a powerplant known from the Yak-40 regional airliner, operating USSR domestic routes, would facilitate technical servicing. The operating costs of the fuel-hungry engine were expected to be relatively low, given the then-low prices of aviation kerosene and the engine’s fairly long service life. The engine was mounted in the upper part of the fuselage; its height and the proximity of the cockpit below and ahead were intended to protect against foreign object ingestion under the typical operational airstrip conditions of agricultural aviation. At the rear of the fuselage, a trolley with a starter-loader unit — the AI-9 auxiliary power unit — was carried.
[…] there is no comparison to the other agricultural aircraft I flew, such as the Thrush Commander S-2R or M-18 Dromader. Getting into those aircraft was almost like getting into a tractor, while the M-15 — that was an office! — Jerzy Zieborak*
The design incorporated a number of innovative solutions, particularly in the agricultural equipment. Two laminate chemical tanks of 1,450 l each were installed between the wings. The agricultural equipment provided exceptionally uniform lateral distribution and a large working width. In the dry-material equipment, built into the wings, compressed air from the engine compressor (so-called bleed air) was used to transport chemicals from the tanks, as well as to drive the turbopump and atomisers in the liquid version.
The M-15 at the Polish Aviation Museum was assembled from parts of two aircraft with serial numbers 1S006-01 and 1S006-03 — two of the three test aircraft built in 1976–77, after the completion of eight prototypes. 1S006-01 was used for static tests, and 1S006-03 for testing modified agricultural equipment. The aircraft assembled from these two units was donated to the Aviation Museum in Krakow by WSK “PZL-Mielec” in 1981.
| year of production | 1976 |
| wingspan | 22.33 m |
| length | 12.72 m |
| height | 5.34 m |
| wing area | 67.9 m2 |
| empty weight | 3270 kg |
| take-off weight | 5750 kg |
| cruise speed | 200 km/h |
| working speed | 160–175 km/h |
| max speed | 200 km/h |
| service ceiling | 4500 m |
| range | 480 km |
| take-off/landing run | 260/270 m |
| working width | up to 60 m |
| fuel consumption | 550–700 l/h |
| powerplant | AI-25 turbofan (bypass) engine with a thrust of 14.7 kN (1,500 kgf) |
