Author: Boran Pivcic

By me
Photos me too unless otherwise indicated, copyrighted

With a click and unwilling grunt, the imposing four blade prop slowly catches the air. Protesting now with an ever-louder series of coughs and bangs, the big engine comes to life, spewing clouds of white smoke to show its displeasure at being so rudely awoken. The characteristic whiff of petrol and grease spreads through the air as the whine of the huge supercharger builds up, almost inaudible beneath the increasing bass roar of nine cylinders. Spewing drops of oil from the single exhaust pipe, the unruly engine looks and sounds like it can barely hold itself together, like it might fall apart any second without warning.

And with its belly already smeared in oil, its fuselage stained by exhaust and its metal skin shuddering in the propwash, the big biplane doesn’t inspire much confidence in the casual observer. And yet, for all its farmyard machinery appearance, this beautifully ugly airplane still has an obvious air of competence, durability and purposefulness around it… but that really should not be very surprising; for after all it is one of aviation’s greatest legends – the fantastically charismatic, and damn near indestructible, Antonov An-2 :).

1. Future-proof:

Lumbering unhurriedly along in the lower levels – comically too in any stiff headwind – it’s hard to see at first what made the Anushka into one of the world’s great aircraft. As sophisticated as a telegraph pole, this noisy, ungainly, uneconomical biplane is a stereotypical anachronism, looked at by many with the same mix of fondness and patronization as an exhibit in a WW1 museum. Sort of like “you gave it your best shot, but it now time to move on to newer things”…

Yet, despite all its apparent crudeness, the An-2 is a true masterpiece of design. Understated, it has gone quietly about its business for more than 60 years, never blowing its trumpet even though it had a million reasons to do so. From deserts to polar wastelands, often operating in conditions that would shame most other designs, the An-2 has soldiered on without fuss or pomp, setting records for machine and man achievements that, more than anything else, show what aviation is really about :).

And therein lies the answer to the main question: what makes the An-2 great is the same thing that made the DC-3/C-47, the C-130 Hercules, and the Twin Otter great – the ability and capability to do anything and everything, to be adapted to every required role and do it brilliantly. And like the DC-3, C-130 and DHC-6, it has outlived all of its intended replacements, finding none equal even in today’s world of glass cockpits, carbon fiber and super-efficient jet engines…

But to find out the story of this amazing aircraft, to see what makes it tick so well, we first have to turn to the birds and the bees… and the badgers, mosquitoes, bears, goats and whatnot else the Soviet Ministry of Agriculture and Forestry had to deal with in the immediate aftermath of WW2. Faced again with the age-old problems of administering the USSR’s vast open areas, in 1947 the Ministry had issued a specification outlining a simple and dependable utility aircraft that could be used for this purpose. Required from the outset to operate pretty much out of open fields far from large population centers, the new aircraft had to have a demanding mixture of characteristics, not least of which was full rough-terrain STOL capability. But more critically, it also had to be almost completely self-sufficient once on the ground, and uncomplicated and intuitive enough to be maintained with a minimum of basic equipment by whatever crews could be scraped together from the local populace.

In addition, the aircraft had to be easily adaptable to a variety of secondary roles – one of the most important being cropdusting – and be easy and forgiving to fly in all conditions. And it had to be able to do all of this in a bewildering range of climates found across the former USSR, from the hot deserts and steppes of Asia, to the vast taiga of Siberia and the snow and ice of the Arctic circle…

In the spirit and general optimism surrounding the new aeronautical technologies developed and refined during WW2 – jet engines, advanced liquid-cooled V-block pistons, monoplanes, retractable gear – Oleg Antonov’s solution to this challenging requirement took a number of people by surprise. Fresh from the Yakovlev design bureau, this talented engineer – responsible in no small part for the superlative Yak-3 fighter – had quickly gained a reputation for innovation, thoroughness, and not a small amount of design boldness. So it came as a bit of shock that, tackling such a stimulative specification, he had only managed to come up with a lumbering, antiquated biplane – a design considered by many to be outdated before it had even flown…

However, like with every aircraft he had designed, Antonov had put a lot of thought into what the future An-2 should really be. Already an experienced designer, he was well aware of the problems the USSR’s great, sparsely populated open ranges presented. He had also observed the sometimes crippling effects the Russian winter – and generally the hard going – had on the sophisticated German fighters of WW2, and how the comparatively simpler Soviet aircraft seemed to suffer a great deal less, happily flying when their counterparts were grounded for days on end.

With this in mind, it soon became apparent to Antonov that these new technologies the world was on about would simply not cut it in the Soviet backwoods (at least not just yet). Leaving aside the extremes of the weather, where would one find a qualified mechanic for a liquid-cooled V12 in a remote village in Siberia or on the wind-swept plains of Kazakhstan? Or the workshops and materials to repair a high-loading monoplane wing or a retractable gear leg when you’re operating out of a forest clearing on the rim of the Arctic circle?

The way forward therefore was backwards. What Antonov saw as the key to making the An-2 work – and with 20/20 hindsight we can agree he was spot on – was to use older tried-and-tested technologies to make the aircraft so dependable and simple that there wouldn’t be anything on it to break… and if it did, it could be fixed with a spanner and some tape.

But the resulting design – first flying, to considerable chaffing, on 31 August 1947 – was anything but a mere collection of bits the Wright brothers could have used; indeed, the An-2 still stands today as a shining example of intelligent, purpose-built and minimalistic design. Far from being just another biplane, it is brimming with solutions and ideas that show just how much thought, planning and old-fashioned common sense went into its design…

2. Go Ugly Early:

For starters, there’s its trademark biplane layout. While this does pay a high price in drag – with the An-2 pegged at just 140 knots, despite the 1000 HP up front – it reaps huge benefits in the low-end of the speed range. The large wing area – 71.5 m2 (770 ft2) – means that enough lift can be generated down to very low speeds, which, combined with its clever airfoil shape, gives the An-2 a comically low minimum flight speed of just 49 knots! 😀 (for reference, that’s also the clean configuration stall speed of the Cessna 172)

Slowing down further from this speed, the unknowing pilot would find himself/herself quite surprised by the An-2’s stubborn refusal to stall (though I feel the novice pilot would be very appreciative of this feature 🙂 ). Indeed, should the aircraft for whatever reason find itself at such a low speed in level flight, the spring-loaded leading edge slats on the upper wing would extend, keeping the airflow glued to the wing, and the whole thing would simply descend gracefully under full control at a “parachutists rate” and just 30 knots of forward speed :D. The big, chunky landing gear would absorb the impact and, more often than not, the crew would just walk away with very little damage to the aircraft… as a consequence the aircraft – uniquely – has no concrete published stall speed in The Book* (and I’ve checked this).

* however, the whole stalling issue is a minefield. The popular idea is that the stall is caused by a lack of speed. This is not so – a stall is caused by a disruption to the airflow around the wing. Low speed does indeed cause a stall – because to maintain level flight the aircraft has to continually increase the Angle of Attack as it slows down, until it becomes so large that the airflow separates from the upper surface of the wing and lift is lost. However, you can stall an aircraft going at full speed, in a climb, dive, turn, loop, you name it. You just have to pull on the commands with such force that the aircraft rotates so quickly in a short period of time that airflow breaks off the upper surface. So the An-2 can stall – but in level flight its aerodynamics allow it to be flown in such a manner that the airflow sticks to the wing at all times.

But its low speed capability is best evident in the takeoff run, which is a spectacle that can best be described as – interesting. On most aircraft, the takeoff is a visually striking event, with the charge down the runway, the purposeful rotation and powerful climb-out… the An-2 though just slowly accelerates – with the inevitable misfire or two – and after two hundred meters starts slowly going up, no rotation, and rumbles away like it’s not in any sort of hurry…

The third factor contributing to the An-2’s low speed prowess is the wing loading – or simply put, how much weight does each unit of wing area have to support in flight. Normally, this is used as a measure of aircraft handling, with the lower the value, the more docile and easier to fly the aircraft is.

And despite looking like a jolly mass of airplane, the An-2 weighs just 5.5 tons at MTOW, which is spread over the aforementioned 71.5 m2 of wing area. This gives a wing loading of 77 kg/m2, which compares very favorably to the 87 kg/m2 of the Cessna 182T – and is not that far above the the 172R’s loading of 70 kg/m2, which pretty much ticks the “easy handling” box :).

Another interesting side-effect of the this biplane configuration may not be readily apparent to us at our big airports, but is probably much appreciated in the areas where the An-2 is “at home” – namely, neither wing has a very large span, which means the Anushka can happily operate in tight, confined areas outside normal airports and airfields. The comparatively narrow main gear span too means that its turning circle is quite small (for an aircraft its size anyway), which helps in maneuvering on the ground.

The engines too were given a good deal of thought, even though Antonov was not really spoiled for choice in this department. Jets were still just getting off the ground, it’d be years before the first turboprops left the drawing boards, and V-blocks were just too complicated and frail for a lifetime of torture – and dubious maintenance practices – they’d be subjected to. So, the only remaining option was to go radial :).

The first choice, beginning the An-2’s “third cousin removed” relationship with Wright Engines of the US, fell on the Shvetsov ASh-21 (or more accurately, AŠ-21), a 7-cyl radial producing about 780 HP. In essence, this was a single-row version of the company’s twin-row 14-cyl ASh-82, an engine based on the knowledge, experience – and a fair number of structural parts – of the M-25, a Soviet license-built Wright R-1820 Cylcone 9, one of the great radials of WW2. Finding out that the An-2 prototypes could do with a bit more poke, the engine was changed on the production versions to the ASh-62, which was – again – a distant relation of the R-1820, being based on the same M-25. Quite a bit more potent than both the ASh-21 and the Cyclone, the ASh-62 was able to produce 1000 HP out of nine cylinders, which was deemed enough for the new aircraft.

While selection of the ASh-62 would have been a foregone conclusion based on its rated power alone, it did have several other beneficial – and I’m inclined to believe intended – consequences, which would have fit right in with Oleg Antonov’s vision for the An-2. Like the Cyclone on which they are based, the ASh-62 and 82 were as common as trees, powering a number of famous aircraft such as the Polikarpov I-16, the Lisunov Li-2, Tupolev Tu-2 and all the Lavochkin fighters – aircraft common to virtually every corner of the USSR. Indeed, both engines were intended to remain in widespread service for years to come, so finding someone qualified to repair one was sufficiently likely even in the most remote of airfields.

And despite the fact that the ASh-62 and 82 were different engines only partially based on the Cyclone, they still carried part of the R-1820‘s DNA – or more specifically, its technologies and lessons learned, most of which the hard way. And when it’s chosen to power the B-17, DC-2, DC-3, the Dauntless divebomber, the Wildcat and many others, it definitely must be good :D.

3. The Devil is in the Details:

But if anything, it was the little things that really showed how much thought was invested into the basic An-2 concept. The cockpit for example is very airy and roomy, while extensive glazing provides a good view in all directions – something especially important if you were slated to spend most of your life rumbling at low levels, never mind the slow speed.

Out back, the main cabin is similarly utilitarian – but for the An-2, this is a compliment if anything :). Almost perfectly rectangular in cross-section, it can be – and was 😀 – adapted to countless applications, while its comparatively high floor strength means you can load up a lot of cargo without undue worry. Other interesting touches also include cabin walls lined with glass-wool to reduce noise – which can be considerable, it must be said – and, on some passenger models, even a toilet!

Underneath the skin though, away from criticizing eyes, the An-2 starts to show off its true colors – starts to show off just how cleverly it was really designed. For example:

• despite its dated biplane format – which would have probably suggested otherwise – the An-2 is built almost entirely of metal. The entire fuselage structure is a stressed-skin semi-monocoque – as seen on passenger airliners – rather than the simple frame used on similar aircraft (including many light aircraft of all sorts still produced today). As mentioned in a previous post, in the semi-monocoque construction the loads exerted on the fuselage in flight are spread between both the basic structure and its metal shell. This was a boon for pressurized airliners, because it provided a light, yet durable and strong airframe, which could easily absorb the stress created by pressurization. In the unpressurized An-2’s case, this structure can absorb significant forces – for example during a hard landing – and distribute them evenly over the entire airframe (including the skin), reducing stress on specific components
  
• on the other hand, all the flying controls – rudder, elevators, flaps, ailerons – as well as the entire wing aft of the main spar, were – fabric covered. An odd pair with the advanced metal structure, this common WW2 solution was (cleverly) chosen for practical reasons: the “hybrid” wing allowed the leading edge – and ergo the spar, the wing’s most important element – to be protected from frontal impact. At the same time, any damage caused by debris thrown at the wing and the controls by the wheels – which was sure to happen on a daily basis – would be easy and inexpensive to repair out in the field (one of the reasons you may often see An-2s with control surfaces painted in a scheme completely different from the rest of the aircraft)
• but the feature that shows most of all just how pessimistic – or realistic – Oleg Antonov was about the ground infrastructure the An-2 would have available is the refueling system. Nothing as old-fashioned as a man climbing on a ladder and pouring fuel into the tanks, the Anushka instead uses a powerful on-board pump that draws fuel from any fuel canister and flushes it into the tanks :). The whole procedure consists in simply rolling a barrel of fuel up the aircraft, dropping a special hose into the barrel and turning the pump on – and presto!

Another interesting feature on the An-2 is its use of a pneumatic system instead of a hydraulic one normally used in the West. Common to virtually all Soviet light aircraft before or since, the pneumatic system works and functions exactly like a hydraulic one, but uses air as the working medium instead of hydraulic fluid. While this may appear to be an insignificant change – and even a complication – it does have a number of advantages when used in the conditions the An-2 was designed for:

• first and foremost is its lower weight when compared to the hydraulic system. Because the air in the installations is at very high pressure, smaller diameter pipes are necessary to produce the same force, which drives the overall weight of the system down
  
• the system can also be easily replenished. The An-2 for example has an air line fitted to a special compressor in the engine bay, which can refill all of its pneumatic systems – the brakes, tailwheel lock, shock-absorbers and even the tires – which are normally charged from an 8 liter compressed air cylinder. This has a raft of benefits, the greatest being that it negates the need to carry reserve hydraulic liquid around. Also, the pneumatic system is replenished without human intervention – apart from opening the air line – which also means one time-consuming task less for the mechanics
  
• the last major benefit is that air is much more forgiving that hydraulic fluid (which is usually a special synthetic oil) in temperature ranges as diverse as the ones the An-2 would see – especially at low temperatures, where the viscosity of the oil increases and the system loses power (not to mention the possibility of the oil freezing)
  

The pneumatic system does have some disadvantages however, the biggest being the inherent hazards of handling compressed air cylinders – but this pretty much applies to any compressed gas or liquid. The other major disadvantage is that the pneumatic system is much more coarse when it comes to metering out the force to be applied, which can lead to imprecise system performance and usage. However, this is only a small setback as far as the An-2 is concerned: considering its most important pneumatic system – the brakes – you either have to stop so quickly that just slam the brakes full on, or you have a long enough runway on which the An-2’s STOL characteristics mean that stopping distance isn’t an issue :D.

4. Revenge of the Write-Offs:

Naturally, with a design as thought-out as this one, it was only a matter of time before the humble Anushka outgrew its original specification – and before Oleg Antonov started catching breath for the last laugh. And while transport and cropdusting had indeed remained among its primary missions even to this day, the aircraft’s durability, adaptability and stunning range of capability had immediately lent it to a host of other – and often diametrically opposed – duties.

To cater for these, a number of versions and sub-versions were developed, which progressively grew in number until only the most fastidious An-2 fans could even being to count them all up. Further complicating the matter is that in 1960, the majority of An-2 production was moved from the Ukraine to PZL-Mielec in Poland (along with production of the ASh-62 to PZL-Kalisz), which would eventually cause some linguistic problems as aircraft with different roles were allocated the same designations. And cataloging Chinese production – where it was known as the Shijiazhuang/Nanchang Y-5 – is a similarly herculean task. However, in the interests of a balanced post, I’ll post a link to the full list on Wikipedia (and for once, a list made from a reliable source) and single out a couple of the most interesting ones:

• An-2A – developed to intercept US reconnaissance balloons (now there’s a novel usage), this interesting version was equipped with a dorsal gun turret and a more powerful, turbocharged version of the ASh-62 engine
• An-2E – two ekranoplan (wing-in-ground-effect) versions sharing the same designation. Though Boeing had touted loudly a few years ago about its innovative Pelican concept – which would have been a massive transporter “flying” a few feet above the water – the original technology was developed in the USSR in the 60s by famous scientist Rostislav Alekseyev, who had also developed the Alekseyev KM, a humongous 10-engine ekranoplan that even today remains one of the largest flying objects ever built… despite the fact that it’s currently at the bottom of the Caspian Sea
  
• An-2F – among the three versions to use this designation, by far the most fascinating was a proposed VTOL version, with an AM-9 turbojet in the rear fuselage
• An-2PD-5 – an executive version provided with a bar and pantry 😀
• An-2PRTV – modified as a TV broadcast relay for the Polish Radio and Television Company
• An-2RT – a single An-2 converted to receive and record telemetry from test missiles
• An-2V – in the first use of that designation, a floatplane 😀 (photo @ Airliners.net)
  
• An-6 Meteo – a high altitude weather reconnaissance aircraft that had even taken an altitude record for its class at 36,902 ft
• Y-5C – one up from the An-2V, the Y-5C is actually an amphibian 🙂 (photo @ Airliners.net)
  

What can be considered to be the ultimate development of the An-2 though – a development that actually worked, sort of – was saved for last: the An-3. Re-engined in the 80s with a 1433 HP Glushenkov TVD-20 turboprop, the An-3 was intended as a cheap, off-the-shelf replacement for the vast fleets of ageing An-2SKh cropdusters, as well an alternative to the ultimately failed Myasischev M-15 Belphegor, the world’s only jet powered cropduster :). Fitted also with a squared-off vertical stabilizer and a thoroughly updated and modernized cockpit, the An-3 prototypes had in a short time set an impressive six payload-to-altitude world records for their class – but in the end, with the breakup of the USSR looming very close, these had counted for very little and the An-3 became just another commercial failure. The design resurfaced again in the mid-90s as the An-3T, but this time as a retrofit of existing, surplus low-time An-2s – with just marginally more success…

An-3T in flight @ Airliners.net

An-3T in flight 2 @ Airliners.net

An-3T cockpit @ Airliners.net

5. The A(n)-Team:

In the end though, the above list generally an academic affair, since the majority of An-2 versions could be adapted to do everything the other ones could. So you had passenger versions dropping skydivers, cropdusters hauling cargo, transports cropdusting… some towed gliders (A.net photo), some flew to the poles (A.net photo), some became firebombers (A.net photo)… some became lorries (A.net photo) :D… generally, the list would go on for awhile.

And then there were the Croatian Air Force examples :). With the start of the ex-Yugoslav civil wars in 1991, the nascent CroAF, faced with a complete lack of aircraft, had decided to turn everything with wings into a combat aircraft. This may seem like an exaggeration, but Air Tractors fitted with a gunsight and bomb racks, UTVA-75 trainers with shoulder-held rocket launchers under the wings and Cessna 172s dropping hand grenades from the cockpit were a common sight in the early days of the war. Among them were numbers of An-2s which were mostly used as “heavy bombers”, armed with so-called “boiler bombs” – gas cylinders filled with explosives and anything that could act as shrapnel: forks, razor blades, knives… – dropped out of open doors by the crews. Operating mostly during the Siege of Vukovar, by day and night, these aircraft would fly low-level attack and resupply missions in the face of formidable Yugoslav SA-6 surface-to-air missiles and defending MiG-21 and 29 fighters. In what is perhaps the greatest irony associated with the An-2, they were virtually invulnerable in this role! 😀 Intentionally flying at barely 40-50 knots, they were so slow that they ended up below the detection threshold of every fire control radar, which then wouldn’t even show their echo on the screen. The defending fighters had an even greater problem, flying at speeds of 200-300 knots and trying to intercept a target moving slower then a car at tree-top height. However, when the Yugoslav National Army modified the SA-6’s radar to lower the detection threshold, the An-2s started suffering heavy losses and were withdrawn from the role.

All in all, not a bad showing for an “ancient, rustic biplane” :). And while time had ran the An-2 over as a commercial transport long ago – it not being the cheapest aircraft to operate, and Western certification being nigh impossible to obtain – they remained in regular production in Poland up till 1991, by which time many more modern designs came and went. Indeed, low-key production from spares continued until 2001, making for an enviable production run of 54 years – beaten only by the Hercules and the record-holding Beech Bonanza (coincidentally first flying the same year as the An-2 🙂 ). During that time more than 18,000 were produced – with some estimates as high as 20,000 – although the true number may never be known without accurate figures from license (and off-license) production in China.

But what really puts the shine on these numbers – what I’m tempted to say even eclipses the production achievements of any other aircraft – is that the An-2 went through an entire half century fundamentally unchanged from the first post-war versions. There were no new engines, no avionics upgrades, no lavish new features or wild performance increases – just the simple, basic, utilitarian 40s design, rumbling calmly about its business for 60 years in conditions and situations few, if any, other aircraft will see in their lifetime.

And this, if anything else, is a great, lasting testament to the brilliance of its design and the genius of the men who had worked on it :). Anachronism? Hardly!

6. Specifications, references and more photos:

Given the large disparity in performance figures found in various sources, I tried to stick to the ones that appeared to know what they’re talking about :D. One such website – an excellent resource for all things An-2 – is An-2 Flyers, from which I’ve taken most of the specs (unfortunately, due to the design of their site, I’m unable to link to the performance page directly, but you can find the button to it near the bottom on the left hand side of the page).

Other sources included:

• Airliners.net and its An-2 Aircraft Data Page
• Wikipedia An-2 entry for data referenced to Yefim Gordon’s & Dmitry Komissarov’s “Antonov An-2” book (trustworthy, Yefim Gordon especially, being a very authoritative expert on Soviet aircraft)
• Agplane.nl’s An-2 POH (in PDF)
  
• Warbird Alley’s An-2 page
• Utility Aircraft’s An-2 Aircraft Report

And to finish with a flourish, a small selection of – in my opinion – the best An-2 photos on Airliners.net :):

UR-BJP by Anton Dovbush / EW-40931 by Vladimir Tonkih / RA-01104 by Sergey Ryabtsev / 15 yellow by Sergy / RA-29329 by Igor Dvurekov / D-FONL by Willem Honders / D-FONL by Ramon Berk / RA-35032 by Anton Harisov