YAK 11 flight test

YAK 11

Its not every day that you get the chance to fly a direct descendant of a Russian World War II fighter plane. And, after 9,000 hours or so of rebuilding what started out as a pile of scrap, Mark Jefferies of Yak UK is justifiably protective of his pristine beauty, so I felt very honoured when he gave me the opportunity to have a fly of his C11. Even better was the news that we would be joined by a second C11 which would be turning up for the photo shoot.

Up close

The C11 cuts an impressive figure parked alongside the Cherokees and Cessna’s on a typical flight line. The aeroplane has a beefy and brutish fuselage with uncharacteristically thin wings and tail surfaces, its WWII heritage is unmistakable. The construction is a mixture of steel tubing and metal skinning for the forward fuselage, with fabric covering aft of the mainplane. The wings and tail surfaces are skinned in metal and the ailerons, rudder and elevator panels revert to fabric. The Yak sits on a wide-tracked, inwardly-retracting undercarriage and a small, non-retracting tailwheel. The brakes have been modified from the standard pneumatic drums to a set of hydraulic Cleveland discs which originated in a Cessna 421 – the aircraft is based on an 800 metre strip and discretion is always the better part of valour.

The Yak 11’s 700 horse power, seven cylinder ASH 21 radial is hidden behind a tight fitting cowling with a cooling gill arrangement which will be familiar to anyone who has seen a Yak 52 from the front. Access to the cockpit is easy – simply climb up the trailing edge of the wing and push in the knob at the front bottom corner of the forward or aft canopy. The cockpit interior is relatively large for a military machine and, not surprisingly, devoid of luxury, although the seats themselves are comfortable. Cyrillic script makes everything alien to a westerner, although CAA-approved labels take care of the important bits. Needless to say that a thorough check out is a necessity before you could even contemplate starting the engine, let alone taking this thing into the air.

Strapping in is one of the easiest bits of the conversion course but be careful

with the canopy – if you have flown a Yak 52 it would be easy to reach for the toggle above your head to close it. Unfortunately all that will do is release the canopy’s securing pins and allow the whole caboodle to fall of the back of the fuselage. Not good. Instead use the little knob at the forward corner and make sure that it is fully home before you try to take off. The canopies are allowed to be opened in flight, though.

Engine starting

The engine is turned over pneumatically. An ingenious priming device means that you don’t have to get someone to pull the prop through while you hit the plunger, as on typical radials (although the pull-through to clear the bottom cylinders of oil still has to be done if the aeroplane has been left standing for a few hours). Instead an internal priming cylinder is charged with fuel using a lever on the lower right of the cockpit before hitting the firing button on the left of the instrument panel. The venturi effect of blowing air over the top of the priming cylinder sucks just the right amount of fuel to be carried into each cylinder in turn. This mixture is ignited by a shower of sparks and the engine bursts into life, accompanied by a satisfying puff of smoke from the exhaust stubs. Not as easy as a light aircraft engine, but straightforward once you have done it a few times.

Anyway, successfully lighting a radial is a pretty cool thing to do….

Taxying the Yak C11 is a doodle after all that starting palaver. The aeroplane feels heavy on the ground but the toe brakes fitted to Mark’s aeroplane make steering easier. Power checks and pre take-off drills are pretty standard but, as in the newer Yaks, you do have to make sure that cowl flaps are open. There are two types of Yak pilots – the ones who have taken off with the cowl flaps closed, and the ones who haven’t yet but will do so in the future.

Lining up at Little Gransden the aircraft was allowed to run forwards a few feet to make sure that the automatic tailwheel lock had engaged with aft stick before full power was applied. The aeroplane didn’t swing particularly and the lack of action outside allowed a prolonged check of Ts and Ps before it was time to rotate. This Yak seemed reluctant to break free of the ground, instead wobbling alternately on the main wheels before lift off was finally achieved with a firm pull on the stick at 90 knots. Once airborne the gear was raised and the power brought back to 75% with the throttle and rpm lever for a leisurely climb at 135 knots. The VSI will show 1,600fpm at max weight and max power. The cylinder head is less willing to climb towards the red line than with Vedeneyev-powered aeroplanes like the Yaks and Sukhoi.s familiar to western pilots. I was immediately impressed by the 11’s control lightness and harmony, spot on at low speeds, although the ailerons harden up considerably at higher velocity. Surprisingly, the roll rate was less than a Yak 52, perhaps 90 degrees per second at cruising speed compared to 120 degrees per second for the ’52. With hands off the aircraft exhibits positive stability in all directions – a good weapons platform.

The canopy affords a good lookout and the aeroplane feels natural in the air, not the viceful monster that you might imagine a WWII-derived Russian fighter might be. I was certainly aware of the high wing loading, though. The Yak 11 was going places quickly once the nose was lowered, and the wings cut through turbulence like a knife through butter as I turned towards Duxford for our rendezvous.

Cruising for a bruising

With the throttle left wide open the C11 records an impressive speed, 225kt TAS at 1,000 feet, for an equally impressive fuel burn, for the wrong reasons, of 50 gallons per hour. At 75% power the speed and fuel burn drops to a respectable 200 knots and 33gph, and the aeroplane becomes frugal at 140 knots, using just 16gph. It is no surprise that with the headset off the noise is pretty stupendous as sound insulation is nowhere to be seen on the inside of this aeroplane. Outside is a different matter, though – the Yak C11 is surprisingly quiet from the ground.

Aerobatics in the Yak 11 are a joy. Once you get the thing heading downhill the speed builds quickly, and loops 2,000 feet in diameter are easy to accomplish. The speed washes off quickly in the vertical and energy management is much more important than in higher powered warbirds such as the Spitfire. Having 700 horse power bolted onto an aeroplane which was designed for over 1,200 has an obvious result. Nevertheless, for the average PPL the Yak 11’s performance would seem impressive in any case.

The stall is interesting, to say the least. The aeroplane exhibited a pronounced starboard wing drop in all configurations and power settings, the severity of the wing drop dependent on the power applied. I would not be surprised if the flow over the wing is pretty much laminar – it is either flying or it isn’t and there isn’t much in the way of warning buffet when the G break is about to happen. Equally interesting is the aeroplane’s ability to flick into a steep, mind-numbing spin. Spin recovery is predictable, though, and the aeroplane always comes out cleanly within 90 degrees of rotation.

In the circuit the Yak C11 is typically difficult to slow down and it takes a while to get the airspeed low enough to meet the gear and flap limits of 163 and 135 knots respectively, even when the throttle is fully closed.

The best approach to make is a curved one as the visibility over the nose is poor – non-existent from the rear seat. I can imagine that Russian instructors had to be made of stern stuff when allowing their students to fly from the front seat. There’s not much for the rear seater to do on short finals other than close his eyes and say a prayer. The landing flare needs to be positive but, once on the ground, the aeroplane stays put. Directional control is adequate all the way down to a walking pace. The brakes are very powerful and the stick needs to be brought back to prevent a noseover before any large pressure is applied. The original pneumatic brakes are more forgiving than Cleveland discs but less effective.

An affordable warbird

Eddie Coventry’s Yak C11 (our platform for the photo shoot) is for sale at the moment for £170,000, comparing favourably with Harvard prices – and that’s only half the aeroplane that the Yak 11 is. You get the buzz normally associated with aeroplanes such as Spitfires and Mustangs for between half and a third the purchase price and a quarter of the operating cost. A figure of around £250 per hour excluding hangerage would seem reasonable for a well utilised aeroplane. Spares are not too much of a problem – there are several small inventories in the UK and more overseas, especially in Russia and the USA.

For about half the purchase price and the same hourly charge as a Yak 11 you could run a JP3 on a UK permit and go a little faster in the process. You may not get to the opportunity to put your JP3 on the display circuit as there are plenty out there already, but if displays aren’t your bag you would probably be better off in the jet.

What about converting a Yak 11 back to its more agile ancestor the Yak 3? Don’t try it, someone just did. The job took over five years at the Yak factory and the cost was rumoured to be more than the original purchase price of the aeroplane. Could a PPL fly a Yak 11? No problem, but expect to spend as much as 10 hours converting onto the type depending on total flying hours and tailwheel experience.

INTO HISTORY

As the end of the Second World War approached the Russian government announced plans for a new two-seater to replace its obsolete fighter trainers, the Yak 7 and U12. Part of the requirement for the new aeroplane was that it should have the same handling qualities as the fighter aircraft then in use. Yakolev’s initially simple answer to this was to convert one of its most successful fighter aircraft, the small but agile Yak 3, into a two-seater. The Yak 3’s big V engine was replaced with a lower powered radial and the forward fuselage was altered quite a bit to accept this change, but otherwise the original design was hardly altered. The new aeroplane flew for the first time in November 1945 and was a success although the government delayed signing an order straight away. Yakolev’s response was to fiffle and refine the basic aeroplane until a deal was finally struck a year later. By this time the aircraft featured an increased wingspan over the Yak 3, , non-retractable tailwheel and an increase in max take off weight. The max level speed had dropped to 250mph, down quite a way from the 300mph prototype, and the name had changed to Yak 11.

In addition to the 3,800 aeroplanes eventually built by Yakovlev (big numbers you’ll agree) a further 700 were built as C11s under license in Czechoslovakia. The aeroplanes made their way into the majority of the Warsaw Pack countries in the role of advanced fighter trainer until the early 1960s. The Yak 11’s ability to carry a 12.7mm machine gun in the nose plus two 220lb bombs made it desirable as a light attach aircraft and many third world countries used it as such. Egypt was one of these and this is where both Mark Jefferies’ and Eddie Coventry’s aeroplanes originate. Both aircraft were bought from French aeroplane trader Jean Salis before being extensively restored. The saga of Mark’s own rebuild would make a feature length story in itself, the aeroplane finally being unveiled to the public at the 1994 PFA Rally at Cranfield where it won the prize for Concours de Elegance. And deservedly so.

THE BIG REBUILD

When Mark Jefferies purchased his Yak C11 from Jean SallisSalis in 1991 the aeroplane was something not much better than a pile of scrap metal – a £60,000 pile of scrap metal to be exact. The original aircraft had started life at the Let factory in Czechoslovakia in 1956 and saw service with the Czech Air Force before moving onto serve with the Egyptians (another Yak C11 force landed in Cyprus on its way to Egypt and impounded by the British, eventually ending up on the English register as G-AYAK). For the Jefferies Yak, years of dereliction followed before Jean Salis secured its purchase along with 41 other aeroplanes of varying degradation. Mark spent three years and 9,000 hours of labour restoring his aeroplane, accumulating a telephone bill along the way that would even make British Telecom blush. Many parts had to be made from scratch using the rusted originals as patterns and some Yak 50/52 components also made their way into the project. Vintage Engine Technology, also based at Little Gransden with Yak UK, took care of the engine rebuild. Considering the engine’s age surprisingly little remedial work was necessary once a new set of cylinders had been sourced. The aeroplane is now immaculate in every respect and its Concours de Elegance prize at the ’94 PFA Rally was no surprise to the people who have seen it at close hand. Mark Jefferies is now rebuilding a C11 for a German customer with an even higher specification.

YAK 11 SPECIFICATIONS

Vne 323kt
70% 195kt
Stall 83kt
Wing span 9.53 metres
Length 8.56 metres
Max T/O weight 2,470kg
T/O run 575 metres
Length 8.56 metres
Engine Ash 21, 700 hp

and another flight test report

YAK-11

Standfirst
Although it may look like ‘a Russian Harvard’, Dave Unwin soon discovered that the Yak-11 is a much more potent aircraft than its capitalist counterpart.

With a hiss and a roar, the Shevetsov radial burst into life and the VISh propeller dissolved into a shimmering blur. I cinched my shoulder harness tighter and began to look forward immensely to the forthcoming flight. With 700 Soviet horses champing eagerly at the bit, it promised to be quite a ride!
I met Yak UK’s Mark Jefferies at his Little Gransden base on a rather blustery day in early October, and was immediately taken with the brooding, almost brutish, look of the big Russian fighter trainer. One of the facets of the aircraft that immediately caught my attention was that the wing is quite small. Indeed, with a wing loading more than 50% higher than the Harvard’s and an extra 150 horsepower, it was fairly obvious that Aleksandr Yakovlev had designed a bit of a beast. I was also fascinated by the hardpoints under each wing, which enabled the aircraft to carry up to 100kg of ordnance either side. In military service the Yak-11 was also armed with a single 12.7mm belt-fed UBS machine-gun, located behind the engine and synchronised to fire through the propeller arc. Viewed from any angle, its World War Two fighter lineage is obvious.
Looking around the aircraft, I noticed that it appeared to be entirely conventional in both design and construction. The wings use the Clark-YH aerofoil section and are relatively thin. Essentially of all-metal construction, they are built around two spars covered with metal skins and fitted with fabric control surfaces, while the fuselage is a conventional welded steel tube structure. Except for the aft fuselage, which is fabric-covered, this is covered with metal panels. The rudder and elevators are also fabric-covered, and I was intrigued to note that although ground adjustable trim tabs were fitted to the rudder and ailerons, only the elevator trim could be adjusted in flight. I was rather surprised that an aircraft fitted with a 700hp radial did not have a rudder that could be trimmed from the cockpit, although Mark assured me that the rudder pedal loads were not excessive.
The mainwheels retract inwards, and consequently the Yak is blessed with quite a wide wheel-base. The lockable tailwheel does not retract. As delivered from the factory, and in common with many other Russian aircraft, nearly all the services are pneumatic. They are supplied with compressed air from a large main and a smaller emergency bottle, charged by an engine-driven piston compressor. However, like many Western operators, Mark has chosen to retrofit his aircraft with toe – actuated Cleveland hydraulic disc brakes.
Moving around the aircraft I noticed that it is covered by a plethora of quick release panels, which Mark delighted in quickly removing to show me how easy the aircraft is to work on. I was very impressed by this excellent feature, and I know some engineers who probably wish Cessnas and Pipers had been so thoughtfully designed. The rest of the walk-round contained no real surprises, with the possible exception of checking very closely around the spinner, as this area is prone to cracks. As with any radial engine, it is absolutely imperative that the engine is carefully pulled through by hand to preclude any possibility of the engine experiencing a hydraulic lock, something caused by oil pooling in the lower cylinders of the engine. The engine, a seven-cylinder Shvetsov ASh-21, is quite tightly cowled, with cooling controlled by the same type of cowling gills fitted to other Yaks powered by radial engines. Oil cooling is provided by a ram-air inlet fitted to the leading edge of the left wing root: this is fitted with a shutter controlled from the cockpit.
Having climbed up onto the wing root walk-way and slid the canopy back, I carefully slipped my foot into the spring-loaded step and climbed into the rear cockpit. Yes, that’s right, readers – it was the back seat for yours truly. In fact, I should make it clear from the start that, unlike a typical Today’s Pilot flight test, I did not do the take-off and landing. Mark has invested a considerable amount of time and money in restoring G-BTUB, and as the brakes and also a number of the services (such as the controls for the cooling gills, oil cooler shutter, magnetos, undercarriage and flaps) are only in the front cockpit, I would have done exactly the same if the aircraft had been mine. Furthermore, the day in question featured a boisterous, blustery crosswind which was blowing across a runway that was not exactly overlong for operating this kind of aircraft.
As soon as Mark had strapped himself into the front cockpit, he began to busy himself with bringing the big Shvetsov radial to life. As mentioned previously, it is turned over pneumatically and, I might add, quite energetically. Obviously, any pressurised air system can leak, so it is very important that the air system is only turned on just before start-up and is turned off immediately after shutdown. To ensure that there is no possibility of the engine kicking back, it is important to allow the propeller to revolve a couple of times before selecting the magnetos on. If the air supply has been severely depleted during start-up, it is imperative that the engine-driven compressor has recharged the air bottles before take-off. Failure to observe this very simple precaution could cause the undercarriage (which is also operated pneumatically) to malfunction.
On this occasion, the engine quickly burst into life with a healthy roar and we were soon making our way towards the runway, with the Shvetsov making the wonderfully liquid ‘bloop-bloop-bloop’ noise that only an idling radial can make. In common with most other large, single-engined taildraggers, the view forward from the rear seat is practically non-existent and I found myself thinking (and not for the last time) that those Russian instructors had really earned their roubles!
With such simple systems (even the flaps are left ‘up’ for take-off, although it is important to ensure the cooling gills are open) we were soon ready for take-off. Mark lined us up with the centre of the grass runway, rolled forward a couple of yards with the stick fully aft to ensure that the automatic tailwheel lock had engaged and then slowly and smoothly brought the engine up to full power. Acceleration was good without being outstanding, and as the speed increased through 50kts a positive push forward on the stick raised the tailwheel, which improved the forward visibility tremendously. As the needle of the ASI swept through 95kts the Yak rather reluctantly left the ground and we climbed away at what initially appeared to me to be quite a shallow angle. With a noise like a peevish python, the pneumatics hissed into life as Mark selected the undercarriage up, brought the power back to 75% and passed control to me.
I swung the Yak skyward in a graceful, sweeping curve and was almost immediately impressed both by the harmony of control and also the surprisingly light control forces. The elevators and ailerons were pleasantly light and, as Mark had mentioned during the pre-flight briefing, even the rudder pedal loads were quite low.
Aircraft like this just beg to be aerobatted and as soon as we had several thousand feet tucked safely under our belts Mark and I took turns in rolling and looping the Yak above the Cambridgeshire countryside. If I say so myself, even my very first attempt at rolling the Yak was perfectly satisfactory, although to be honest my first loop was perhaps not quite as tidy! The barrel roll was entered at about 200kts and worked out great. However, even using Mark’s recommended speed of 220kts for the loop, it did get a bit slow at the top. Although the speed builds rapidly as soon as the nose is below the horizon, it does rather bleed energy just as quickly in the climb. The Vne is a hearty 323kts and even Va is usefully high at 240kts. However, I did notice that the previously pleasantly light ailerons firmed up considerably above 200kts, although this was hardly surprising.
During the briefing, Mark had emphasised that negative G was to be avoided at all costs, and I was quite surprised to learn that although its positive G limit is a reasonable +4.25, it is not approved for even -1! However, these limitations are not structural, but exist because any negative ‘G’ would interrupt the oil supply. This would be less than satisfactory as the oil pressure is used as servo power for the boost controller. Consequently, an interruption in the oil supply could cause the engine to shut down!
An exploration of the stall regime was illuminating as, particularly with the undercarriage and flaps retracted, it was actually quite vicious and was accompanied by a pronounced wing drop and almost no pre-stall buffet. Although it mostly dropped the left wing (an effect caused, I believe, by the radial engine and large diameter prop) on one occasion it caught me out by dropping the other wing, despite the fact that I took extra care to ensure the slip ball was centralised. With the undercarriage and flaps extended the stall was noticeably less ferocious. More buffet could be felt though the stick and the actual G break occurred about ten knots slower than the clean stall, at just above 70. Mark then took control to demonstrate a two-turn spin, and I was suitably impressed, both at the rate of rotation and the speed of the recovery.
I would have loved to have flown the Yak for another couple of hours and really got comfortable with it, although its prodigious thirst (as high as 50 gph at full throttle and low level) means that the two wing tanks and small fuselage collector tank can be emptied of their combined 79 gallons quite quickly. However, to be fair, when flown at economy cruise settings and higher altitudes figures for both range and endurance improve dramatically. In fact endurance in excess of four hours or a range of around 700 miles can be achieved.
Roaring back towards Little Gransden at 75% power saw the ASI indicating just over 200kts, for a fuel flow of around 33 gph. With its relatively high wing loading, the ride is pleasantly firm and in no time at all we were racing in fast and low to put on a show for Today’s Pilot photographer Steve Fletcher. After a suitably satisfying beat-up it was time to think about landing, but, unlike its namesake, this particular ‘Moose’ is quite a slippery beast and showed no real inclination to slow down. Luckily, the undercarriage extension speed is a reasonably high 164kts, and as the ASI dipped below this, the now-familiar hiss indicated that Mark had selected the undercarriage ‘down’, soon confirmed by the red-and-white striped ‘barber poles’ protruding above the wing. As the airspeed continued to reduce to below 136kts another angry hiss from the seething serpent confirmed that the flaps were on their way down. The flaps are actually pretty unsophisticated, as they are of the simple split type and only offer two positions – ‘up’ and ‘landing’ (45 degrees).
By now I was nothing more than an interested spectator, and watched fascinated as Mark swept the Yak around in a classic curving ‘constant aspect’ approach. This method is the best way to fly an approach in aircraft of this type, as the view of the nose really is quite poor. With its relatively high wing-loading, the Yak really isn’t the kind of aircraft that you want to get slow on the approach, and I noted that Mark was careful to keep the air speed at about 105kts until we crossed the hedge. At this point the speed bled back to 100kts, with a planned threshold speed of 90-95kts. A smooth steady flare and the Yak sat down promptly and showed no inclination to try and fly again. At the end of the landing run, Mark retracted the flaps and unlocked the tailwheel before taxiing carefully back to the parking area. As the big propeller slowly wound down to a stop, I slid back my canopy and began unstrapping myself from the seat and parachute.
I enjoyed my flight in the Yak immensely, and would love to own one. It has good handling, a powerful engine, and charisma by the bucket-load. As a typical early 1950s piston-engined intermediate and advanced trainer, the type can be loosely compared to the ubiquitous North American T-6 ‘Harvard’ although, in my opinion it is a much better aircraft in practically every respect. Indeed, if anyone ever gets round to setting up an air combat school equipped with a Yak-11 and a T-6, let me give you one piece of advice – make sure you get to fly the Yak!

The Yakovlev Yak-11, NATO codename ‘Moose’, was developed from the Yak-3 fighter as a two-seat intermediate and advanced trainer. It first flew in 1945 and entered production the following year. That the type fulfilled its design criteria admirably is probably best indicated by the fact that by the time production ended, Yakovlev had built almost 4,000, and export sales had been made to 18 countries. Several hundred aircraft were also built under licence by LET of Poland and Czechoslovakia’s Strojviny Privni Petiletsky. Licence-built aircraft were designated C-11, although they retained their NATO code name. Mark’s aircraft, G-BTUB, is actually a C-11 and was built in 1956 at Czechoslovakia’s LET factory. After service with the Czech air force, it was sold to Egypt and served with the Egyptian air force before being struck off charge. It was recovered from the Egyptian desert in the mid-1980s by the French aircraft dealer Jean Salis, who sold the aircraft to Mark in 1991. Mark restored the airframe at Little Gransden, and Vintage Engine Technology, also based at Little Gransden, rebuilt the Shnetsov Ash-21 engine. After a huge amount of time and money, G-BTUB won the Concours d’Elegance prize at the 1994 PFA Rally.
Mark is really enthusiastic about the aircraft. He told me: “Although a Yak – 11 is a bit more money than a Harvard, it is a lot more aircraft. In fact, the only aircraft that sits between a Harvard and a Mustang is the Yak – 11”.

YAK 11
Dimensions
Length 27ft 10in 8.2m
Height 10ft 5in 3.19m
Wingspan 30ft 10in 9.4m
Wing Area 166 sq ft 15.4m2

Weights and Loadings
Empty weight 4,037lb 1,833kg
Max AUW 5,468lb 2,482kg
Useful load 1,431lb 649kg
Wing loading 32.9lb/sq ft 161kg/m2
Power loading 7.8lb/hp 3.83kg/kW
Fuel capacity 79 Imp gal 360 lit
Design G Loading +4.25/ 0G

Performance
Vne 323kts 598km/h
Cruise 200kts 370km/h
Stall 73kts 135km/h
Climb rate 1,600ft/min 8.1m/s
Service ceiling 26,000ft 7,925m
Range 690nm 1,280km

Engine
Shvetsov Ash-21 air-cooled seven cylinder radial, producing 700hp (522kW) at 2,300rpm.
Propeller
VIS-111-V20 metal two-blade constant speed

An outstanding feature of the Yak-11 is the number of fuselage panels that can be removed within five minutes. This greatly facilitates maintenance.







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