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Back in the summer of 2018, a sudden and quite powerful urge to photograph something really rare and interesting had seen me head for Budaörs Airfield (LHBS) in neighboring Hungary, where I had arranged to fly on the Goldtimer Foundation‘s stunning Rubik R-18c Kánya. An indigenous STOL design created by Rubik Ernő Sr – father of the same Rubik Ernő who would much later go on to design the eponymous cube – it was the last airworthy survivor of just nine made ever, making for a proper, full-on Achtung, Skyhawk! nerdout.
Fast forward to the summer of 2021, and the very same “eastern itch” had returned once again. Deciding, as before, to scratch it while the weather was still fine, I set off for Budaörs once again, intent on getting some air time on another Goldtimer classic, the magnificent and charismatic Polikarpov Po-2 biplane…
For an aircraft that would go on to be produced in more than 40,000 examples and achieve so much in both peace and war, the Po-2 had an almost disappointingly straightforward birth. Gotten right straight out of the box, it was designed in 1926 by a young Nikolai Polikarpov (then aged just 34) and intended to be a cheap, simple, no-frills STOL utility aircraft that could be used for anything from basic flight training to crop dusting to reconnaissance and even combat. Flying for the first time on 24 June 1927, it would be designated as the U-2 in the Soviet system of the time (U – uchebnyy, trainer), and would quickly replace the successful but outdated U-1 – itself another Polikarpov design, reverse-engineered from an Avro 504K captured in 1919 during the Russian Civil War. The familiar Po-2 designation would appear only in 1944, and then as a tribute to its designer, who had died from cancer in July of the same year, aged just 52.
An entirely conventional wood-and-fabric affair, the U-2 would be made mostly out of plywood and pine (as common as trees, literally, in the USSR), with key components – such as the engine mounts, wing struts, bits of the cockpit frame and the landing gear – made either out of aluminium in the early versions, or significantly cheaper steel in the later models. Power was provided by the newly developed Shvetsov M-11 five cylinder radial, which produced 125 HP for take-off and 115 continuously in the most commonly used D and K versions – though the 160/140 HP M-11FR was also used on occasion.
However, what the U-2 could do with that power depended entirely on what it was actually meant to be, since each version – and there were many – had its own particular set of masses and speeds. Standard trainers were usually around 650 kg | 1,430 lbs empty and around 1,000 kg | 2,200 lbs at maximum take off mass, which made for a 150 km/h | 81 kts maximum speed, 130 km/h | 70 kts in a realistic cruise, and a ceiling of around 12,500 ft. WW II combat versions on the other hand weighed in at 750 kg | 1,650 lbs empty and up to 1,400 kg | 3,900 lbs full when bombs were carried, which resulted in a top speed of just 130 km/h | 70 kts, a 100 km/h | 54 kts cruise and a drop in ceiling down to some 10,000 ft. Take off performance had suffered as well, with the “heavies” reportedly needing a 50% longer take off run – though this needs to be put into perspective, since the standard trainers took barely 100 m to get airborne.
Despite a slow and pretty chaotic start to production in 1928 – sources quote missing diagrams, mismatching components, inadequate calculations, as well as understaffing and general improvisation at the factory level – the U-2 would find itself in widespread service already by 1930, starting first of all with the USSR’s major flight schools. Unsurprisingly, a number of “early days” issues were found along the way, including leaking fuel systems (w/ inevitable in-flight fires), main gear failures, cracks in parts of the fuselage structure and frequent engine overheating – though many of these would be cured in 1932 with the second production series, which also saw the addition of larger fuel & oil tanks, expanded cockpit equipment and a few extra amenities for the crew. But despite these problems, pilots spoke highly of their vice-free handling, particularly its low speed agility and a degree of longitudinal stability that was unmatched by anything else at the time (which made them highly spin resistant and easy to recover). Post-1932 examples were, however, rated slightly worse in general handling on account of their 20-30 kg | 45-65 lbs increase in empty mass – a not insignificant 5%.
None of this, however, had managed to detract from the type’s enormous potential. During the course of my research for this piece, I’d managed to identify 34 separate versions introduced between 1932 and the end of Soviet production in 1952 – though the realities of flying (and fighting) in the Union inescapably suggest that there may have been many more, undocumented, unaccounted for and nowadays lost to time. Apart from the “bread & butter” training model, the two historically most notable are:
- U-2AP / Po-2AP: the single-seat agricultural version that gave the type it’s Kukuruzhnik (maize worker) nickname. Produced in more than 9,000 examples, the AP had the front cockpit moved 25 cm forward and a 250 kg hopper installed in place of the rear seat, which could be used either for conventional crop dusting or aerial seeding. Other changes included strengthening the upper wing so it could accommodate a top-mounted fuel tank like the DeHavilland DH-82 Tiger Moth (as there was no longer sufficient space in its usual spot between the engine and cockpit), and moving the rear wing struts slightly to better cope with the new load distribution
- U-2LSh: the most common combat model, used mostly for nuisance raids on German positions. The standard fixed weapon fit included just a single swiveling 7.62 mm ShKAS gun in the rear cockpit, while up to 120 kg of ordnance could be carried under the lower wing (usually two 50 kg FAB-50 bombs or four RS-82 82mm unguided rockets). The upgraded U-2LNB could carry a combat load of up to 200 kg, and was equipped with aiming spotlights to enable operations even in the dark – while the very similar U-2PTO was more of the same, but adapted to carry napalm canisters and other incendiary mixtures. These two versions would become famous as the main aircraft of the all-female 588th Night Bomber Regiment – the famous Night Witches – who would use them to great effect all the way from the Don Basin in 1942 to the Red Army’s storming of Berlin in 1945. Because of their resulting infamy, Po-2s of all sorts would become known to German troops as the Nähmaschine (sewing machine) due to the very characteristic tapping sound of the M-11 engine
While 1952 would mark the end of official production in the USSR, it would not be the end of the Po-2 itself; indeed, low-key assembly from spares in smaller factories and even by flying clubs would continue all the way until 1959, a full 31 years after its entry into service. What’s more, it would also be made under license in Poland as the CSS-13 (Centralne Studium Samolotów, Central Aircraft Study), initially at the WSK-Mielec plant near Rzeszow (1949-1950) and then the WSK-Okęcie works in Warsaw (1952-1955). Polish sources report that these differed slightly from the originals, sporting different ailerons, an elevator trim tab, upgraded main gear and various minor alterations to the structure; it is also mentioned that these changes had already been included in plans received from Moscow in 1947.
Unlike the originals, the CSS-13 would be produced in only two versions:
- the stock trainer
- and the CSS S-13, an air ambulance version with enclosed cockpits for the pilot, medical orderly and a single stretched that was roughly similar to the Union’s own U-2S / Po-2S. A single S-13 would be modified into the CSS-13P, a three-seat passenger model with two seats in the back, similar in concept to the original U-2SP
The actual production figures for the CSS are hard to nail down with precision, since they differ from source to source; but the most credible I’ve seen goes with 550 made in total, 180 at Mielec and 370 at Okęcie. Of the latter, 320 were the basic version and 50 were S-13s – though some sources mention that nine regular models had at some point been converted into ambulances, which would bring the tally up to 311-59.
Nikolai vs Ernő
But, despite its undeniable qualities as an airplane, the Po-2’s postwar association with Hungary came about not because of its capability – but squarely because of politics. At the heart of the matter was the Soviet system of planned economies, whose goal in the early 50s was to assert control over the newly-formed Eastern Bloc, and then use its considerable resources to help rebuild the USSR’s war-torn economy. To do this, emphasis would be put more on heavy industry than consumer goods, which necessitated using the existing infrastructure of the Bloc to its fullest and without regard for long-term consequences. This essentially resulted in each country mass producing only a limited variety of products – usually things they’d been good at before the war – which were then exported for use by both the USSR and the rest of the Bloc. At the same time, high tech and R&D would be consolidated to Russia proper, denying smaller countries the means of potentially outpacing Soviet plans and becoming less dependent and subservient to the Union’s whims.
As far as aviation was concerned, this meant that most of the big, fast stuff – fighters, bombers, heavy transports and airliners – would be designed and produced almost exclusively in the USSR, with satellite states left holding the other end of the market. With their history of large-scale light aircraft manufacture, Poland and Czechoslovakia (and, to a lesser extent, Romania) would take the lead by virtue of having the necessary infrastructure and experience already in place, and thus end up supplying the entire Bloc with training, touring, utility and light transport aircraft, as well as gliders and light utility helicopters. These could be either homegrown – such as the Zlín Z-26 family, and later also the Z-42, PZL-104 Wilga, M-18 Dromader, Let L-13 Blaník, L-200 Morava and the L-410 Turbolet – or in-demand designs from Russian manufacturers such as the Mil Mi-1, and from the 60s onward the Mi-2, Antonov An-2 and Yakovlev Yak-52*.
* indeed, virtually all series production of the Mi-2 and An-2 was undertaken in Poland (by PZL-Świdnik and PZL-Mielec respectively), as was the case with the Yak-52 and Romania’s Fabrica de Avioane Usoare (FCAv) at Bacău
For this system to continue to work to the USSR’s benefit, independent designs from “third countries” would need to be put into a disadvantageous position – particularly if they stood a chance of competing with the superstars – by using the greater output of those big factories to offer better availability, commonality and support. This would also help keep production centralized, controlled and running without interruption to keep up the illusion of progress. The rapid rise of Yugoslavia’s “dissident” aviation industry following the 1948 Tito-Stalin Split – which would eventually go on to design and produce everything from basic trainers to trans-sonic attack jets – was a potent reminder of the “dangers” of letting smaller states flex their potential and use it to slip from under Moscow’s control.
In Hungary, Rubik’s R-18 – which was a more modern aircraft running on the same engine and designed to do pretty much the same things – was thus pushed aside to make way for the Po-2, 20 of which would be acquired in CSS-13 form in 1954, all sourced brand new from Okęcie.
Known sometimes as the CSS-13 Pacsirta (skylark), these would be delivered in two batches – serial numbers 0421-0425 and 0438-0451 – and would initially serve with the Hungarian Home Defense Association (Magyar Honvédelmi Szövetség, MHSz). Modeled on the USSR’s DOSAAF, the MHSz was a volunteer paramilitary organization that used various sporting activities – land, water and air – to train Hungary’s youth in a number of military skills that would come in handy in case of a capitalist invasion (a persistent boogeyman in socialist society). Like many similar organizations elsewhere in the Bloc, it used full-on military markings and nomenclature – so its CSS-13s, used by the air arm for basic training and flying competition, carried military codes based on the last two digits of their serial numbers.
Following the Hungarian Revolution of 1956, they would be handed over to the nation’s flying clubs (minus 22/0422 and 39/0439, lost in accidents), where they would be used for roles as diverse as training, taxi flights, glider towing and occasionally even skydiving. A number would even be converted into agricultural models using the same 250 kg hopper as the Po-2AS, but without its other structural modifications; these would be phased out already in 1960 due to the availability of more efficient machines such as the An-2 – and later the purpose built Zlín Z-37 (flying for the first time in 1963) and even the Kamov Ka-26 helicopter (flying in 1965).
By the mid 60s though, the rest of the 13s were beginning to feel the pressure as well. Having lost two more of their number – HA-PAM/0424 in a crash on 11 January 1959 and HA-PAV/0450 to a fire on the ground on 04 October 1960 – they would also come under attack by fresh designs from Russia and Czechoslovakia (such as the Yak-12A and Z-226) which, while more complex and expensive to run, came handsomely backed by a USSR keen to keep its hand in Hungary’s economy. Couple all of this to the 13s dwindling service hours and the costs of a possible lifetime extension, and the writing was very much on the wall: between 1966 and 1968, the entire fleet would be withdrawn and destroyed on the orders of the MHSz, with only HA-PAU/0443 and HA-PAO/0448 managing to escape the scrap man’s axe…
Life of PAO
Whereas PAU would eventually end up in the Museum of Military Aviation at Szolnok (LHSN) wearing period military colors, PAO would go on to lead a pretty exciting life. Having been used post-1956 as a glider tug at Dunaújváros Airfield (LHDV), it was supposed to be scrapped in 1968 along with the rest of the fleet; however, the airfield managed, Géza Jávor, and the airfield’s chief technician, Ráczkevy Béla, managed to covertly disassemble the aircraft and hide it in a nearby shed, hoping to keep it safe until it could be restored at some future date (this was actually quite a gutsy move in the climate of the time).
That future date would eventually come about in the early 80s, when PAO would finally be taken outside to see the light of day, and trucked some 150 km away to Kaposújlak Air Base (LHKV). There were two reasons for this move: one, it was the home to a major aircraft overhaul center operated by the Ministry of Agriculture’s Aviation Service (Mezőgazdasági és Élelmezésügyi Minisztérium Repülőgép, MEM-RSz) – and two, it was the workplace of Császár Károly, the base commander who had already made his name with restorations of vintage Hungarian wooden gliders, including the Rubik R-07b Vöcsök in 1981 and the Rubik R-11b Cimbora in 1982. With PAO having escaped certain death in such a dramatic fashion – and having been disassembled properly rather than just torn apart – restoring it to airworthy state was a complete no-brainer.
Led by Mr. Császár under the auspices of the MEM-RSz (the formal owner of the aircraft at the time), the restoration was completed in April 1984, just in time for it to be shown to the nation at the May Day parade in Budapest. Though it is nowadays, I believe, the youngest Po-2 in the skies, at the time it was the only airworthy example in the world, and as such was a common sight at airshows not just in Hungary, but further abroad as well; in 1985 it would even make it all the way to Switzerland and back, no mean feat at Po-2 cruising speeds!
It was at one such event – the Budaörs Airshow of 06 June 1986 – that Mr. Császár would, sadly, suffer a fatal heart attack near the end of his display routine. Having apparently already been trimmed for landing, PAO had managed to get down on its own near the western edge of the field, overrunning the airfield boundary and coming to a stop in what, at the time, was a small swamp. The Po-2’s low landing speed precluded serious damage, with just the main wheels and legs sheared off. Not long after Mr. Császár’s funeral, PAO would be airlifted out of the swamp by a Hungarian Air Force Mi-8 and quickly returned to airworthy condition.
From that point onward, PAO would finally settle into a routine of well deserved stability, continuing (with a break or to) to run pleasure flights and impress crowds at airshows to this day. Indeed, the only significant post-1986 event was the end of socialism in Hungary and the subsequent dissolution of the state-run MEM-RSz in 1989. Now in need of a new home, PAO and HA-RUF – the R-18 that had started this entry – would soon pass to the Museum of Transportation in Budapest, which would then loan them long term to the Goldtimer Foundation following its formation in 1992.
This was, thus, the situation that greeted my when I arrived at Budaörs on a beautiful September afternoon, hungry for more noise and vibration than the Q400 could provide… 😀
As always, I would like to extend my sincerest thanks to Goldtimer Foundation members Mr. Krauth Peter and Mr. Janos Zoltán – the former for a fantastic flight, and the latter for sharing so much about PAO’s history!
- Airwar.ru – U-1 and U-2 history, M-11 history (in Russian)
- All-aero – Po-2 page
- Avia-info.hu – Hungarian CSS-13 histories and HA-PAO history (in Hungarian)
- History.net – Red Mule article
- Polish Aviation Museum – Po-2LNB entry
- Russian Aviation Museum – Po-2AP entry
- Samoloty Polskie – CSS-13 entry (in Polish)