Photo File – Rubik’s Tube: Rubik R-18c Kanya, HA-RUF

By me
All photos as credited

I’ve always said that only good things can happen when you use your off time from flying airplanes to – photograph airplanes. For me, this was very much the case recently when my itchy photo finger led me into neighboring Hungary in search of interesting indigenous and Eastern Block flying machinery. And while almost every airfield there is a gold mine in one way or another, my travels that day had taken me straight to Budaörs Airfield (LHBS) just outside Budapest, a well-known GA center in its own right – but doubly more interesting as the home of the Goldtimer Foundation. An eclectic group of enthusiast dedicated to preserving the country’s rich aviation heritage, it is most famous for its flagship, the world’s sole airworthy Lisunov Li-2 – a Soviet license built version of the early C-47 that had needed so many alternations (1400+ by some counts) to survive life in the Union that it pretty much became a standalone type.

But while the Big Li has always been the foundation’s party piece, the rest of its six-strong fleet also boasts much to write home about – in particular my target for the day, the home-grown (and extremely rare) Rubik R-18c Kánya STOL utility aircraft… 🙂

Rarity: check. STOL credentials: check. Russian radial: check. Yellow paint: check. Everything’s here!

Last of the Mohicans

While it may lack the pedigree and heritage of similar designs East or West, the R-18 nevertheless ticks many Achtung, Skyhawk! boxes right from the start – not least of all for its interesting origins. Designed in 1944, the R-18 was penned by Ernő Rubik (father of the same Ernő Rubik who would much later design the eponymous cube) and was intended to fill the niche for a cheap-and-cheerful STOL utility aircraft that could also double as an effective glider tug. Despite nowadays being known solely due to Junior’s successes, Rubik Senior was at the time already a prolific aircraft designer*, and was thus intimately familiar with the challenges of producing a rugged and dependable working aircraft on a tight budget. Though the R-18 was never a direct copy (being much smaller for starters), to make it work Rubik had from the outset used the superlative Fieseler Fi-156 Storch as inspiration, adopting its solutions such as large fixed slots along the wing leading edge, wide-span drooping ailerons, a mixed wood/metal construction to save on strategic materials – and a tall landing gear that could both cope with the realities of rough field operations and provide sufficient drag to allow for steep approaches. Unlike its idol however, the R-18 would not have folding wings, a powerful engine with a constant speed propeller, provisions for light armament or quite the same insane level of STOL performance – all compromises made to simplify design and construction and keep production costs manageable.

* what’s more, Rubik Sr. would continue at it even after the war, turning his attention now to gliders (on which he had actually made his name before the war). The most successful of these new designs was the R-26 Góbé of 1961, a simple all-metal two-seater with a moderate 14 meter wingspan. Though production had ended in the late 60s after 115 examples were made, the design would come back to favor again in the late 80s, when a modernized version – the R-26SU Góbé 82 – was put into production by a Hungarian automobile plant. Despite this unorthodox return and the availability of the Let L-13 Blanik, a further 78 examples would be completed and sold, a large proportion of which continue to happily fly to this day.

In spite of its down-to-earth design goals, the R-18 – now named Kánya (“kite”, a species of hawk) – would not see the light of day until the end of the war. The German occupation in May of 1944 and the arrival of the Red Army in September had had a catastrophic effect on the country’s aviation industry, which made producing even such a simple and basic no-frills aircraft a very tall order indeed. In the event, the first Kánya – the R-18a, carrying the serial E-524** and military ID 1-002 – would be completed only in 1948, flying for the first time on 18 May 1949.

** like many Hungarian light aircraft, the R-18 family was produced by the state-owned Sportáru Termelő Nemzeti Vállalatnál aircraft factory at Esztergom (now LHEM) in northern Hungary. This was reflected in their serials: E-524 may sound exotic, but it simply meant 1-002 was the 524th aircraft produced at Esztergom so far.

The very first R-18, showing the original cabin shape and doors (photo from: http://www.avia-info.hu)

In its original guise, the R-18a was a pretty clean three-seater (two in the front, one in the back), powered by a Czechoslovak Walter Major 4-I engine which developed a modest 130 HP from four inline cylinders, and spun an unremarkable two-blade fixed pitch propeller. Interestingly, Rubik had envisioned the Kánya to be powered by a British-made inline engine (such as the 135-150 HP Blackburn Cirrus Major), but the post-war political situation in Hungary had quickly sent that idea down the tubes.

Originally pitched to the reformed Hungarian Air Force, 1-002 would quickly be made redundant by large numbers of readily available aircraft coming from the USSR (most notably the Polikarpov Po-2), which left Rubik with only one option – to go civilian. To this end, 1-002 would be transferred to the civil register, becoming HA-RUA the same year. Unfortunately, not long afterwards it would be involved in the type’s very first accident, when it stalled at low altitude and sideslipped into the ground during a glider tow demonstration. Even though the damage was repairable, the aircraft was not rebuilt and was instead re-purposed as a training aid for apprentice mechanics.

Based on experiences from military test flights and civilian trials, Rubik then developed the slightly improved R-18b, whose primary claim to fame was a redesigned fuselage around the rear seat, allowing the second passenger a bit more breathing room. As was the case with the A, only one B model would be made, wearing the serial E-552 and registered HA-RUB. Like its predecessor, it would meet its end during a glider tow exercise on 25 September 1954, ending up severely damaged in a corn field after running out of fuel.

Mostly identical to the A model from the outside, the B could only be recognized by slightly different contours of the fuselage just aft of the wing (photo from: Airwar.ru)

Having been convinced all along that there was more to come out of the basic design, at the very beginning of the 50s Rubik began work on a more extensive update, which would debut in 1952 as the R-18c. Compared to the B model, the C – in the form of the “prototype” HA-RUC (s/n E-761) – packed a more powerful six cylinder Walter Minor 6-III developing 160 HP, as well as a cut down and extensively glazed rear fuselage. The new powerplant was initially delivered with a two-blade Avia V410 variable pitch metal propeller – but unspecified problems with its reliability had quickly seen the switch back to a classic fixed pitch wooden unit manufactured right at Esztergom. Having caught some flak due to comfort issues with the A and B models’ rear seat, Rubik would soon dump it completely and replace it with a 120 l fuel tank to augment the two standard 60 l tanks located in each wing root.

In this tweaked form – which one source calls R-18c/1 – the C would become the first, and last, R-18 to enter any form of series production, with just six further examples completed between 1952 and 1953 (registered HA-RUD through HA-RUI). The reasons for such a short production run vary from one source to the other; but staff at Budaörs had told me that the R-18 was simply a casualty of Eastern Block politics of the time, which prioritized the import of aircraft from large factories abroad over small-scale indigenous production. Thus, like the original A model, the Kánya as a whole was simply swept away by a tidal wave of Polikarpovs, Yakovlevs and Zlins rolling in in their hundreds.

Visually the most curious of the lot, the C model can be identified by the long nose, large cowl flaps on the right side (not visible here) and the cut-down rear fuselage. Other changes included larger doors, which significantly improved the view downwards (photo from: airwar.ru)

To add insult to injury, the Minor engines would prove to be quite problematic and failure prone in Hungarian service, leading to a disproportionate number of incidents and write-offs; indeed, some sources claim that by 1966 – when the type was withdrawn from service – only two aircraft had remained intact. This rate of attrition had between 1955 and 1958 prompted a fleet-wide re-engine program, in which the Minor was thrown out in favor of the Shvetsov M-11 five cylinder radial used on the Po-2 (and manufactured by WSK-Kalisz in Poland), developing either 125 HP in the D model – or a more substantial 160 HP in the FR variant. Unlike the home-grown props used with the Minor, both M-11 variants would be bundled with the “factory default” WD-450, also made by WSK.

Interestingly, there was only one other structural mod attempted – and that was fitting skis to HA-RUE (s/n E-763). The aircraft was subsequently based at Budaörs, but I had been unable to find any photos of it in this configuration.

Kite flying

One of the two lucky ones to survive into their old age, the foundation’s example goes by the name HA-RUF, and was the first Kánya to be produced in 1953 (wearing the serial E-778). A standard R-18c (or R-18c/1 according to some), it sports the more powerful M-11FR engine, and had flown for the first time (again) on 1 October 2012, following an on-off restoration that took more than 20 years. Painted in accurate period colors that really make it stand out on the apron, it would immediately after enter the Goldtimer fleet, where it would happily open its doors to wandering aircraft geeks… 😀

While it is far from flattering, a head on view of the R-18 best shows its “Inspired by Storch” design. As well as providing adequate shock absorption, the tall main gear also ensures ample propeller ground clearance. However, the entire gear system is at the same time one of the Kánya’s biggest weak spots: fractures of the main gear attachment points have been reported throughout its service life – and the freely castoring tailwheel, coupled with the soft suspension, means that ending up in a nasty ground loop doesn’t require much effort

Though it lacks the visceral appeal of a big radial, the M-11 is nevertheless a perfectly charming little package in its own right. The exposed valve rods, a tendency to spit oil out of the exhaust, inevitable misfires on idle and that famous “sewing machine” sound all make for a delightful experience

A notable leitmotif of the R-18 is simplicity – and the use of whatever components the production team could get their hands on. The oil and rear fuel tank fillers (left and right respectively) have, for example, been salvaged from wartime German aircraft and take some getting used to – particularly for those of us brought up on the “plug & play” systems used on Cessnas and Pipers. Of further interest, the nose and cabin are the only bits of the Kánya that are made of metal; the rear fuselage, tail and wings are all wood (+ a bit of fabric)

In common with many aircraft from the Soviet sphere of influence, the R-18 uses pneumatics, rather than hydraulics, in its braking system. The upsides are a low total system weight and carefree operation in cold weather – but at the cost of very coarse metering and the need to isolate the air tank from the installation when the aircraft is at rest to prevent leaks. On the R-18, the valve for the tank is located on the floor in front of the seats – a pretty convenient solution compared to some others I’ve seen

As on any self-respecting utility aircraft, the visibility out of the cockpit is excellent in pretty much every direction, and there’s extensive glazing everywhere but on the floor. Apart from the sheer amount of air and light, I was most fascinated by the clean panel layout, which is ergonomic far beyond its 40s origins. Inevitably (and thankfully) there still are a couple of oddities: the comm radio is BELOW the pilots seat (barely visible here), the flap position indicator is above the pilot’s head – and the fuel level indicators for both wing tanks are combined into a single tube-style gauge above the passenger door. Another (welcome) curiosity are the instruments, a charming mix of German, Soviet and Hungarian gauges and switches

Despite the Kánya’s high stance, visibility over the nose is excellent, which allows for easy operation on the ground (steering by differential braking notwithstanding). An interesting detail is the vertical rod nearest the door: this is actually part of the flight control linkage and actuates the ailerons. Unlike most modern light aircraft, the R-18 uses pushrods for all flight controls, which – while adding weight – give it a very quick, precise and predictable feel. The flaps too are mechanical and are operated by a Piper-like handle between the seats

An unusual view backwards showing just how much the C model’s cut down fuselage helps with visibility. Naturally, with all this glazing the cockpit can get pretty hot on sunny days, even with the roof-mounted sliding curtain drawn all the way. An interesting peculiarity here are the yellow tubes, which actually form part of the C’s fuel system. Unlike on the A and B, fuel from the wing tanks drains first into the fuselage tank, from where it is then drawn into the engine

The proper way to spend a vacation: buckled up in a German WW2 harness, pulled along by a Russian sewing machine, valves tapping away in front of your eyes and a windscreen full of oil drops from the exhaust…

The world’s sole airworthy R-18 to the background of the world’s sole airworthy Li-2… I kind of like it here I must admit!

And finally, a bit of video… a poor attempt I admit, but I’m not one with moving pictures and the air that day was a bit turbulent. But you can still hear the Singer in the nose doing its thing – and that’s worth a thousand pro videos! 😀

Customarily, I would like to thank everyone at the Goldtimer Foundation for a beautiful flight, especially my pilot, Mr. Gabor Szakacs!

Appendix – R-18 production list:

Reg

Variant

S/N

Mfd.

Notes

HA-RUA

R-18a

E-524

1948

crashed 1949 (location unknown)

HA-RUB

R-18b

E-552

1949

crashed 1954 near Székesfehérvár

HA-RUC

R-18c

E-761

1952

crashed 1962 near Gödöllő

HA-RUD

R-18c/1

E-762

1952

crashed 1956 near Szentes

HA-RUE

R-18c/1

E-763

1952

fitted with skis; wfu 1966 and scrapped

HA-RUF

R-18c/1

E-778

1953

wfu 1966; made airworthy in 2012

HA-RUG

R-18c/1

E-779

1953

wfu 1966; preserved in museum until 2016

HA-RUH

R-18c/1

E-810

1953

crashed 1957 near Kaposvár

HA-RUI

R-18c/1

E-811

1953

wfu 1966 and scrapped

Sources:

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