Focus on: Yak-52

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Noisy, thirsty, powerful and fun, the Yak-52 is a big hit with pilots – but what does Alan Cassidy think of it?
A QUICK search of the G-INFO database shows 68 Yak-52 aircraft currently on the UK register, plus another 15 de-registered. Dates of manufacture range from 1981 to 1998, and all have been imported since 1992.

So it is impossible to deny the popularity of the type with UK pilots. The equivalent total for Pitts aircraft, which have been around roughly 20 years longer, is 180. Yaks can now be found all over the country, indeed, all over the world.

The FAI has even recognised a class of international aerobatic competition exclusively for this one type of aircraft. Such a contest is planned for this summer in Novosibirsk, Siberia, where a number of aircraft will be available to rent to anyone brave enough to make the journey.

HISTORY
The Yak-52 is a primary training aircraft. It first flew in 1976 and has had a long production run, latterly in Romania by Aerostar.

Since the early 1990s and the fall of the Soviet Union, many Yak-52s have been exported to the west. One of the first in the UK was flown here from the Moscow area in 1992 by the late Len Perry, who was a member of the British Aerobatic Team in 1995/6. Of approximately 1800 produced to date, many now fly in the United States, United Kingdom, New Zealand, Australia, South Africa and other Western countries.

A descendant of the single-seat competition aerobatic Yakovlev Yak-50, the all-metal Yak-52 is powered by a 360hp, nine-cylinder radial engine, the Vedeneyev M14P. The aircraft has inverted fuel and oil systems permitting inverted flight for as long as two minutes.

The tricycle landing gear is retractable, but it remains partially exposed in the retracted position, affording a measure of protection should the plane be forced to land ‘wheels up’. The main wheels retract forward into the slipstream, so that the airflow can assist deployment if the emergency lowering system has to be used.

WHAT’S IT FOR?
My preference is to think of it primarily as a rather complex alternative to the Super Chipmunks of the 1970s. This is the sort of thing the military here might have liked as a regular Chipmunk replacement, had the Government not forced on them the political decision to buy the Bulldog.

The Yak, of course, was laid out in a very accomplished design bureau, conforms to a military specification that required very rugged construction and predictable handling characteristics and was built as a series production aircraft in recognised Eastern-bloc aircraft factories. All of which surely explains why – in this country – the CAA has determined that, unlike its Chipmunk and Tiger Moth predecessors, the Yak-52 is ineligible for a Certificate of Airworthiness.

Consequently, those aircraft registered in the UK have only a Permit to Fly and are thus unable to be used for the aerial work of remunerated instructional flight. So, to fly one you really have to buy one. Or at least buy a share in one. And that is what most regular Yak drivers have done.

The UK answer, then, to the question “what it’s for?” is “to have fun” while spreading your carbon footprint as big as a clown’s shoes. While wearing these oversized clogs, you can pretend to be a warbird (why else all those completely unauthentic camo paint schemes?) while working as feverishly, nay strenuously, as Farmer Giles on his Massey-Ferguson. What could be better?

BASIC PRACTICALITIES
One of the reasons for the appeal of the Yak is its complete difference from any equivalent Western machine. Most noticeable of these is the radial engine, while more hidden at first is the pneumatic system used for starting, flaps, gear and brakes. Then, there is size and weight, more of which later. A certain degree of agility is required just to climb onto the wing before getting into the cockpit. There is scope to fit a stirrup-like mounting step, but few aircraft seem to have retained it. The seats are completely non-adjustable and require cushions or, preferably, a seat parachute of prodigious proportions. The sitting position is upright and, at first, the array of switches and dials is both impressive and confusing. But that is what type conversions are for, so I’ll not dwell on the ergonomics here.

The control column has the finesse of a baseball bat and you are as likely to bend it. At the top there is a hand-brake rather like that on a motorbike. It screams ‘men only’ at you in a rather macho way, but that, of course, is a bluff . Identical PTT buttons for both radio and intercom are mounted on the throttle lever. Embarrassment often follows the mixing-up of these. The propeller lever, which is anything but blue, lies sensibly beside the throttle and shares the same quadrant movement. Being able to operate throttle and prop as required without changing hands is really good.

The engine is completely impractical when compared to anything used for basic training in modern times. Starting procedures are tortuous, while fuel and oil consumption are prodigious. For many, this just adds to the attraction. Taxying using differential pneumatic braking is an art slowly acquired. Getting airborne is relatively mundane, as long as you remember to apply left rudder to counter the slipstream.

This propeller goes round ‘the other way’ if you usually fly American. Once stabilised, the Yak climbs at close to 1400 feet per minute and will comfortably transit level at 120-130 knots. Overall fuel consumption is going to work out at around 90 litres per hour over a general handling sortie.

The airborne visibility is amazingly similar to that of a Chipmunk: virtually nothing downwards because of the wing position. For landing, there is a large barn-door flap that has no intermediate positions. I never use it. The Yak is more responsive and precise with the flap up at the fl are.

PERFORMANCE
At 2200lb empty weight, the Yak-52 is, err, how can I say this... heavy? Twice the weight of an empty Pitts S-2A, for example, but with only 80% more power. Sledgehammers and nuts come to mind. However, we are a warbird farmer and we are having fun.

Despite the weight, it is quite responsive and capable as an aerobatic aircraft. Many UK pilots have flown it in domestic aerobatic competitions and the international Yak-52 category sits a little above our Intermediate level, while staying more simple than Advanced. It is stressed to +7 and -5 gs.

At a fast cruise speed, about 140 knots, the Yak rolls (to the right) at about 180 degrees per second. But getting full deflection takes, for me, the use of both hands. I measure this by seeing how long it takes to complete two full revolutions while flying level. This is actually about four-and-a half seconds, but the heavy aileron control forces limit the speed with which I can apply full deflection. The heavy metal wing also has some inertia; 180° per second is thus my estimate of the peak rate of roll.

Russian tachometers measure in percentages of maximum engine speed. Perhaps this is because the engine drives the propeller through an epicyclic gearbox and an absolute figure in revolutions per minute would thus apply correctly to one item and not the other. Whatever the reason, percentages are easy to remember.

The maximum continuous engine speed for the M14P is 82% which actually means a little over 2400rpm for the engine core. However, 100% is allowed for take-off and for other short bursts. I used this to find the maximum level speed of the Yak, which ran out at 151 knots (280kph on the metric ASI). From this speed, the zoom climb with two pilots aboard and two-thirds fuel is around 1300 feet.

HANDLING
I have already alluded to the fact that the ailerons are pretty heavy. In fact, they might be heavier. For ab-initio training, the Russians fit additional springs into the aileron control system to add more ‘feel’. Read ‘more resistance’. I can’t imagine what the Yak feels like with these additions, but aerobatic rolling would be pointless in that configuration.

Elevator control forces are also quite high, but manageable in the context. It is very unlikely that the airframe would be over-stressed as getting close to the g limit requires a lot of force. The rudder is counter-balanced aerodynamically and is relatively light. Of the three primary controls, the ailerons are the one which would most benefit from some extra mechanical advantage.

Control forces are just one aspect of handling. The others are inertia and balance. The Achilles heel of the Yak, as coincidentally with the Chipmunk, is the balance.

Both these aeroplanes were designed as tandem-seat military trainers. Both training organisations clearly decided that the student should have the best view out of the front and so made this the ‘solo’ cockpit; the instructor sits behind. While this gives the student the benefit of being at the sharp end, it has a major drawback. The aircraft is simply too stable for optimum aerobatic handling when flown solo.

Consider the aeroplane with a pilot in the front and an instructor/passenger in the back. The latter might weigh 220lb and is sitting in a seat considerably aft of the centre of gravity. In this configuration, the aircraft must be flyable with the CG inside the aft limit of the envelope.

Now remove the man from the back seat and the CG rushes forward as quick as a young bull in search of a herd of cows.

This increases stability, but really too much, making any figure that requires rapid yawing quite difficult to perform quickly and accurately. In particular, this affects stall turns and spins.