Flight Test

It was awkward to say that I was maintaining a reasonable height above the ground. Difficult in fact, as there was little contrast in the dull lighting over a landscape, now covered in snow, with a heavier darkening grey cloudbase. I was skirting features in the 500ft bubble from vessels, vehicles, structures and beings. The Met forecast for my destination, still over an hour away, was not living up to expectation. I was guiding a Yak-50 which was, in the early 1990s, one of the most desirable single-seat aerobatic aircraft available. I was bringing her to a new home in England from Lithuania… in the middle of winter.

Nearly 20 years earlier at the 1976 Kiev aerobatic championships, the Russian team had swept the board with machines like this one. It truly ousted the Pitts and Zlins of the day, and my turn to ferry one on behalf of Yak UK had come. I grabbed the opportunity, despite the season. One hundred hours in its dual-control, heavier, nosewheelequipped sibling, the Yak-52 had left me wanting to get my hands on a 50. They share the same engine and prop, but the 50’s max take-off weight is 905kg, within three kilos of the 52’s empty weight. With 310kg less to haul, that reduction of weight alone promised to enhance performance, particularly vertical penetration.

Straight and level was nowhere near her métier (aerobatics), but that would come. I had a Lithuanian licence in my pocket and experience of this route, good battery strength in my Garmin GPS III velcroed onto the instrument panel, and a supposed workable forecast at my destination.

In economic cruise setting, 6/60 on prop and power, burning an estimated 45 litres an hour. Engine and oil temperatures were fine with both oil and cylinder gills fully closed, maintaining both cylinder head and oil temperatures despite the ambient conditions. In fact, it was probably just a walk in the park for an aircraft designed for Russian weather conditions. The pneumatic pressure used for the engine start, retractable undercarriage and brakes, was more than adequate with the engine driven pump topping up the system.

When I had crossed the Polish border and started talking to Berlin Information, I had good reception. Nobody else was on frequency and ‘my’ female controller started a conversation, noting that I obviously wasn’t either Lithuanian, as was the 50’s registration, or Russian… with my accent. I admitted to being English and in the unusual ensuing RT exchange, she asked why on Earth I was flying today… nobody else was. I had been asking myself that. This was a projected two-hour leg to Braunschweig but I still had not reached my point of no return, having sufficient fuel to turn tail and retrace my steps to Szczecin (Stettin). Prior to that, I had been stuck for three days in Gdansk, the Polish port which, in winter, is seemingly permanently gripped in a cold, clutching fog. I had no desire to retrace my steps or divert, always striving to go forward as a ferry pilot. But I realised I had to be prepared. The landscape was flat, hardly a hillock anywhere, and I had been edging lower with the cloud base. As a consequence, I’d started to weave around settlements, first to the left, then the right and so on, so as to average out the track divergences and not drift too far to one side of the track.

Far left The radial cowl gills in their fully open position, and on the bottom of the cowling, the oil cooler.

My chatty controller gave me an update on the weather at my destination, which was still workable, but my actual current visibility certainly looked greyer until, yes, a small section ahead was in a paler light. Looking upward, the layer of cloud had thinned and there was a hint of blue sky above that, way beyond that, cirrus, beckoning me onwards and upwards.

As I passed 1,000ft I dropped my shoulders and relaxed. I now had ‘pure clear blue’ above, and those cold, malevolent moisture laden Cu were now off to the left and no longer baring my way.

I thanked Berlin Info and soon was safely back on terra firma. The Yak hadn’t missed a beat. Refuelled and re-oiled after the taxi to the hangar, I ran the engine up and held the oil dilution switch on. This cold weather practice ‘dilutes’ the engine oil with a measured amount of fuel to prevent it from thickening to a cold porridge-like mass, which almost solidifies in the freezing night air. It would at least give me a fighting chance of starting the engine in the morning using my preciously limited pneumatics.

That evening, cossetted in my hotel room, I raised a glass and toasted my chattering friend from Berlin Information. Another couple of hours of a 12-hour journey ticked off and, being back in the West again speaking ‘meine slecht Deutsch’ and, while I wasn’t in my own backyard yet, I certainly felt comfortable with the lovely Yak. It’s not the warmest of cockpits with no heater, but the engine allows some heat to trickle backwards to the cockpit.

The thought had crossed my mind to do some aeros, pull a bit of ‘G’ to force blood to the extremities, but with a full ferry tank there is no way any sensible being is going to compromise his charge for the sake of comfort. Incidentally the ferry tank, which doubles the capacity, was awkward to fill, as the pressure in the pipes would trigger the nozzle’s autostop. It was a reason to always refuel the tanks yourself, just in case a refueller got bored, not knowing the awkwardness of the system.

Later though, back home in England, clear of snow and fuelled within aerobatic limits, the Yak 50 and I were unleashed, flying many displays together.

A happy reacquaintance

Twenty-five years later, the same Yak 50 from that flight would cross my path again for this flight test. Now in the ownership of Richard Ellingworth, G-BVVO is the first Yak-50 to move onto an LAA Permit to Fly. Seeing the three-bladed MT propeller and an infuriated cartoon Cossack painted on the chequerboard engine cowlings, you could say I was a smidgeon more than rather happy…

Although the aircraft is of metal construction, the generously sized control surfaces are fabric covered. The Frise ailerons have large deflections, with control forces assisted by outboard ‘elephant ears’, thin plates that protrude beyond the wingtip, forward of the ailerons’ hinge line. The roll rate is estimated around the 180° a second mark, but both the reaction of positive and negative flicks is swifter, but your hand / eye coordination soon adapts to the timing and tempo of control needed to arrest the roll. There are no flaps, but the elevators have a greater downward deflection aiding inverted flight, while the rudder has an aerodynamic and mass balance, with a small manually adjusted trim tab.

The nine-cylinder, air-cooled Vedeneyev M-14 P radial develops 360hp at 2,950rpm and weighs in at a sumoweight of 485lb. It is a big step up from our general aviation aircraft engines, both in terms of power and fuel burn. The powerplant of choice for many of Russia’s series of world-class aerobatic machines, it has been further modified over the years to produce 400hp, as the PF version, and the R variant is reputed to generate 451hp. Fuel consumption is but one of the lesser considerations in the scheme of maintaining and operating such a capable aircraft.

Radial engines have to be rotated to check that no oil has pooled in a lower cylinder or cylinders before attempting a start. With the rotary mag switch confirmed off, the prop can be pulled through – you should not feel resistance over and above normal compression. On no account should you push the prop backwards, as the oil will merely retreat through an open valve giving the impression that any problem has been solved, only to reappear when rotated in the correct direction, risking an hydraulic lock and bent con-rod should a start be attempted.

From the cockpit the prop turns in an anti-clockwise direction, just like the Gipsy Major, needing left rudder at slow speeds, at every instance of power increase, and right rudder beyond the cruise in high-speed dives.

A one hour’s aerobatic detail, including 15-minute warm up for a cold engine, transit at 7:70 (7 being measured in mmHg and 70% the prop), and a full 8:82 for aeros, plus return to base and a cooling shut down, will burn around 60 litres of fuel. But be aware, as the book figure the full power 8:82 is an astonishing, and costly, 115 litres an hour. Oil capacity is 18 litres of Straight 100 and Richard reckons on half a litre an hour in cruise, and probably double that per aeros session, but sessions are generally in the order of half an hour. Minimum oil contents shouldn’t be let drop below 10 on the dipstick.

Having climbed up onto the left wing there is a latch on the vertical canopy frame to release the canopy lock. If you have done this before you will know the force required to free the depressed lever is high, and once released the astonishing speed at which the canopy wants to rush back, unless restrained by your right hand. Holding onto the front canopy frame and a leg swung into the cockpit, standing on confirms a fair amount of the planet ahead is hidden. The view is fighter-like and approaching 360°, with just the shoulder straps of the five-point harness preventing you from turning to see the tail surfaces.

The main instrument panel stands slightly proud of the edges, with knurled nuts top left and right that undo to allow the whole panel to swing down on a lower hinge, giving access to its back. Check they are tight! Taking time to become reaccustomed to my surroundings, several things are of note – all of the instruments are traditional and have metric values, some are colour-coded and a few have Cyrillic lettering.

Centrally positioned is an artificial horizon, an instrument which is head and shoulders above any Western equivalent. Comprised of a background sphere that may be used in any attitude, it does not topple or tumble, well, I have not seen it do so even during lomcevaks, in fact aerobatics may be flown using it. However, as canny and as novel as these are, forces imparted to yaw can certainly be felt through the seat of your pants, the slip ball admonishes the unaware pilot, quantifying the balance needed. To the left is an ASI, running from zero to 450kph, it has no colour coding to indicate stall, normal operation or Vne, but those values are placarded alongside. Beneath is a clock with two inner faces, including a stopwatch facility for aerobatic sequences. The altimeter is standard.

The centrally placed fuel gauge requires some careful understanding. A scale of vertical lights, downwards from 55 litres in five litre steps to a redline of 12. Victor Oscar has a ferry tank, so the indications on the fuel gauge should be doubled, and precise amounts have been pencilled in beside the lit scale. It should be noted that excess fuel above a prescribed limit of 55 litres prevents any aerobatics.

On the right is a manifold gauge measured in mm of Hg – static on the ground reads 7.4, and above is the propeller rpm, measured in percentage terms.

Once airborne, these two are happiest having a ‘square’ manifold: prop % rpm setting such as 6:60, 7:70 and 8:80. As in all conditions with a constant speed prop, when increasing power, keep the prop ahead by changing it first, before upping the manifold pressure with the throttle lever. When reducing power, the throttle comes back first to be followed by a reduction of the prop’s rpm. There is a Becker 8:33 bottom right and a matching transponder bottom left, and a horizontal row of long fingered, guarded switches across the panel’s lower edge.

To the far right of the panel is a grouping of the large, and bright red, landing gear emergency valve, the guarded auxiliary air replenishment pump, the black-handled carb heat, the oil cooler shut off for post-flight operation, and the fuel primer. It is important to understand how to operate the latter in order to obtain a successful start. Prior to the start this has to be selected for the initial priming, first to the right, to pump fuel into the cylinders, then turned to the left to send fuel to the manifold. There is no accelerator pump connected to the throttle so once a cold start engine catches, you can encourage it with judicious pumping to keep it from stopping.

In full view on top of the panel is a G meter to record our airframe limits of +9 and -6, and an inverted slip ball, just biding its time to help in balanced upside-down flight. I think the only time I took note of the latter was when checking the inverted stall speed. Decelerating at the standard pace of a knot per second and remaining in balance, the aircraft shudders as the nose drops towards the ground at a tad over 135kph / 73kt. Interestingly, this is 30kph / 18kt, higher than the erect stall.

A wide, circular wiggle of the stick shows the control throws to be large and to have no cockpit restrictions. The one gotcha can be headset leads, possibly fouling the stick-mounted brake lever, having floated up and over during a negative G manoeuvre. Drop your left hand to the cockpit floor and there is a red tap to turn anti-clockwise on for the pneumatics, confirmed with a deep groan as the air fills the lines, its associated pressure gauge being right beside the presently downward sloping undercarriage selector on the lower left of the panel. There is a locking bar to slide to the left before raising those wheels into the wings.

Above The 50 has a purposeful stance, and the open canopy invites attention.

Right On the left side of the cockpit, the trim wheel for pitch, yellowhandled throttle, and prop in fine pitch. It's wise to check the friction locks for cowl cooling gill controls.

Below An extremely workmanlike instrument panel layout, including very heavy duty artificial horizon and ticker-tape fuel gauge.

Below On the formation break, with a skyscape that's perfect for the Yak-50 to explore.

The pilot is aligned perfectly with the trailing edge of the wing, which means when you’re drawing a nice straight vertical line while rolling, your visual references are more easily anticipated, rather than surprising you from behind a rotating wing.

That long stick, which will help with roll force leverage, also has a bicycle type lever for the brakes. Squeeze it, and you’ll get a pneumatic version of a serpent’s hiss. Leather stirrups on the rudder bar keep your feet on the pedals under negative G. Keep the bar neutral when squeezing the brake lever, both left and right wheels are braked. Should you wish to turn when rolling slowly forward, then a push on the appropriate rudder pedal and the brake encourages the turn. A backward squeeze on the lever, and engage a pawl, sets the parking brake. An initial gotcha for those not briefed, or forgetful, is that with the stick held back the tailwheel is locked – extremely handy for both take-off and landing of course. When taxying, S-turns are an absolute necessity, and the throttle is sensitive. Combine this with the pneumatic brakes and, you realise practice is required for smooth, elegant, ground manoeuvring.

One final observation regarding the stick in the 50. Should an intended erect spin recovery be called upon, simply move the stick fully forward to the middle of the lower edge of the instrument panel with absolutely no lateral aileron input. Sometimes, you'll find a reference dot on the panel as a reminder. I remember playing with erect spins using both power and outspin aileron to raise the nose to both accelerate the rotation and also encourage the nose to rise and sit just beneath the horizon. Absolutely wonderful, but perhaps not everybody’s cup of tea…

The throttle, with its yellow grip, and the prop lever, falls nicely into my left hand. Ahead are two smaller levers for opening the cowl’s nine ‘shutters’ for control of the oil and the cylinder head temperatures. There is a knurled friction knob beneath these two to lock your selected position –important as the mechanical advantage on the shutters is to make them close, an easy route to a cooked engine.

Starting this beast is a little different from the norm, check air tap is on, high pressure indicated, throttle cracked open, cylinders and manifold primed, stick back, and park brake on. With the magnetos on, lift the starter guard with your left thumb, check and call ‘clear prop’ and press the air start. It will winge audibly as the first blade teeters through a compression, but then will burst into an uncertain rumble, while white smoke whirls around. Give a few more prompting pushes on the manifold primer to let her keep firing into a more regular disposition of steady revolutions if needed. Check oil pressure, and watch for the slow rise of the cylinder head and oil temperatures. With the gills closed on a cold autumnal day it takes around 15 minutes to reach operating temperature.

Into wind and with the cylinder shutters opened and locked, but the oil cooler flap closed as the oil temperature is not yet very high, power and prop cycling checks are completed with the prop lever fully forward in fine at 70% on the manifold pressure gauge. Check the rotary mags first and cycle the prop. This is where the plugs may be cleaned further as the prop is cycled, the manifold pressure rising to work harder as the blades thrash at a coarse angle of attack. Back to fine pitch and an idle check. A scan around the cockpit with eyes on the pneumatics, trimmer, full control deflections, straps secure and then a thumbs up as I hold for Patrick to depart in the photo-ship.

Today my departure is a hoot. Once you have the confidence to feed in power and rudder to control power, slipstream, torque, asymmetric blade effect and the gyroscopic forces, you can be off the ground in 100m. The undercarriage lever, its restraining slider slid to the left, pushed in and up and the bolt returned across. It’s probably accompanied by a rush of air but with the roar of all nine cylinders firing I don’t hear it. The uphill attitude is wild and we’re managing 2,250ft per min – just keep your left foot pressed onto the rudder bar to hold the extended climb in balance.

I haven’t giggled so much since getting airborne in the rotary engined Bristol Scout, and chasing Steve Slater in his J3 Cub… The 50 similarly, gave me a surfeit of speed, power and manoeuvrability over the camera ship, and I delighted in reefing her around. Photos complete, once I was happy I knew my location, having recognised the imposingly tall aerial to the south of Sibson, at last, I had some time to play.

The 50 stalls cleanly from the glide at 88kph, 48kt, and can reach 162kt straight and level; Vne is 232kt. But they are trivial details – this machine is all about aerobatics. I have always enjoyed aeros, it was the reason I learned to fly, and the 50 rates as the most capable aerobatic machine I have got to know. Power on 8 / 82 and belts retightened. It wasn’t just the restraints, but I felt connected through the seat of my pants and her character through the stick. Flinging through the footless halls of air with excess power to climb and roll, to loop, Derry turn and Cuban. To balance the forces and encourage precision at the slowest of speeds, to exchange height for blissful performance and capability, to bridge from the vertical against the engine at a speed only just on the scale rather than stall turn. A slow, slow languid roll to the left, an abruptly quartered four pointer to the right. A wing over converting sweeping downward speed and energy to height and clearing the path for a stretched and arcing barrel roll. The first positive flick for a leaping salmon from the inverted at the top of the loop, to arrest and continue the downward pitching path. Up again in delirious mirth drawing a straight vertical before introducing a slowly rolling application to our right, speed decaying past the max allowed flick speed of 200 km/hr and at 180 the gentlest of sensitive pitching forward of the stick sliding along the right fuselage wall and a full left boot… and there you can feel the air detaching as the gyroscopics take hold. The nose traces the horizon while the wings slowly roll at the lowest of negative G.

All too soon it is time to go home. Looking along that beautiful long nose housing the Vedeneyev may be intimidating as it hides the world at slow speed on the approach. However, any lateral nose wander from the direction you are pointing with varying power or application of unbalanced aileron, is magnified, prompting corrective rudder. Under 200kph, 108kt, you can lower the undercarriage. The curved approach starts at 81kt, reducing to 73kt and rounding out at 100kph, 54kt. The three-point landing roll is a short 150m. Fortunately I did not disgrace myself!

“How did you like her?” asked Richard when I had shut down. A laugh and a smile on my behalf said it all. “It was brilliant, truly brilliant.”

Thanks, Richard, for your infectious enthusiasm and generosity in loaning this marvellously capable Yak 50. And thanks Sibson for the friendship and help in allowing us to carry out the shoot from your delightful airfield. ■

YAK-50 SPECS SPECIFICATIONS

General characteristics

Length 25ft 5in

Wingspan 31ft 3in

Wing area 161sq/ft

Empty weight 1,624lb

MTOW 2,120lb

Useful load 496lb

Wing Loading 13.1 lb/ sq/ft

Power loading 5.9lb/hp

Engine M14 P 360 hp 9 cylinder radial

Performance

Vne 240kt

Cruise speed @ 75% 151kt

Stall speed 48kt

Rate of Climb 2,250’min

Take off ground roll

328ft

Landing roll 492ft

Range (without out ferry tank)150 nm

G limits +9G/-6G