In the world of aviation, there are some instances where you find yourself asking “how the heck does that fly?”
The PZL M-15 Belphegor is one of those instances.
This jet-powered biplane was manufactured in Poland during the Cold War, with the intention of becoming an agricultural aircraft to replace designs that dated back to World War II and earlier. However, the result was something far stranger than you
might imagine, and it’s surprising that such a weird little aircraft doesn’t have more notoriety.
Demand for the PZL M-15 Belphegor came from the Soviet Union’s requirement for a new agricultural plane that could be used on the vast farms of the USSR, including the kolkhoz collectives, and state-owned sovkhoz. At the time, the USSR’s primary forms of agricultural aviation were a motley crew of designs that dated back to and beyond the Second World War, including early Antonov’s such as the An-2. The aircraft formed part of a large scale fleet of agricultural aircraft which would be constructed by Polish builder WSK PZL-Mielec (Polskie Zakłady Lotnicze – Polish Aviation Works), which would eventually include the M-15, but also the 106 Kruk of 1973 and the M-18 Dromader. Poland was selected for the task as it had previously created agricultural versions of the An-2 known as the An-2R, built under license before being exported back to Russia.
Unlike previous designs, The Council for Mutual Economic Assistance (Comecon) demanded that the new aircraft be powered by a jet engine so as to be faster and more efficient than turboprop equivalents. As such, PZL created a flying laboratory known as Lala-1 (Latające Laboratorium 1 – Flying Laboratory 1) to test the effects of a jet engine on a biplane design, Lala-1 comprising of the forward section of an An-2, together with its wings, while the rear section was removed and replaced with a frame in which was housed an Ivchenko-Progress AI-25 jet engine (as used on the tri-engined Yakovlev Yak-40 and the single-engined Aero L-39 Albatros fighter-trainer). Lala-1 also sported
equipment for agricultural uses, including crop dusting tanks and dispensers. Once testing had found that marrying a jet engine to a biplane design was feasible, design of the M-15 itself began throughout late 1972.
The M-15’s final design is based on a twin-boom sesquiplane platform, with the AI-25 engine mounted above the crew cabin. A sesquiplane design, which is arguably the most common biplane design, means that the lower wings have a shorter wingspan than the upper wings, reducing interference drag between the wings while retaining the aircraft’s structural advantage. The aircraft was designed to be flown single-handedly, though there was space in the somewhat cramped cabin for two other passengers. Between the wings either side of the fuselage, the aircraft carried two tanks which could contain up to 2,900L of either liquid or dry chemicals for pest control and fertilisation. These chemicals were dispensed from tubes on the lower wings, these wings being made of laminate so as to avoid corrosion.
In terms of performance, the M-15 was not only the world’s only jet powered biplane, but it also has the distinction of being the slowest mass-produced jet aircraft! With only 3,306lbf being output from the aircraft’s underpowered AI-25 engine, the aircraft could
attain a top speed of 124mph, but that’s only if you dared go that fast. Cruising speed could be anywhere between 87 and 103mph, which made it slower than the An-2 it was planned to replace, which could travel at a cruising speed of 160mph. While its rate of climb was better than the An-2, it was still a very tepid performance, and its maximum range of only 248 miles meant that one really had to clutch at straws when it came harvest time, especially if the field you intended to dust was either very large or some distance away which, when you consider the size of Russian collective farms, is not too much of a stretch.
At the same time, PZL, probably aware of how hopeless this aircraft was going to be, had just unveiled a slew of far superior turboprop designs which could outrun and outmanoeuvre the M-15. The first to arrive was the PZL-106 Kruk (Raven), which was launched in 1976 as a competitor to the likes of the Piper PA-25 Pawnee. This was joined the same year by the PZL-Mielec M-18 Dromader, a license built version of the Rockwell Thrush Commander from the USA. Both these aircraft could fly at well over 130mph, climb faster and had a greater range, as well as being much more efficient in terms of fuel.
Small wonder then that when the M-15 was launched in 1976 alongside its turboprop brethren, the aircraft was largely overlooked following the first few sales. Comecon had predicted approximately 3,000 orders, but this was quashed following the response of early operators, who noted the aircraft as being slow, highly inefficient, not having a sufficient range and was incredibly noisy, resulting in it garnering the nickname Belphegor, the name given to a noisy demon who is also one of the seven princes of Hell.
Eventually, only 175 of these aircraft, including two prototypes, were built before production ceased in 1981, with sales never extending outside the USSR. While the aircraft was exhibited at the 1976 Paris Air Show, hoping to woo potential foreign buyers with its strange design, most people saw it as a bit of a joke, a comedy plane which
looked like it had been designed by a 10 year old boy who’d just consumed 8 tonnes of sweets!
Today, it is unknown how many of these aircraft are still airworthy or, more to the point, how many even exist. Most disappeared off into the wilds of the Soviet countryside and were never heard from again, though it is likely that not many will remain in regular service these days. While parts for the engine can be sourced from the much more successful Yak-40, other spares would be very hard to come by, especially when you consider the aircraft’s specialist nature. Several have been preserved in varying states of intactness, but overall this very obscure little Polish plane has been lost to the sands of time, an aircraft which, to be perfectly honest, could never have been anything more than a one-off prototype, being far too complicated, expensive and inefficient for the role it was designed to fill.
The fact that it went into mass-production alone is a miracle in itself!