YAK 18T flight test

YAK 18T

 

Yak-18tImproved relations between East and West has benefited several sectors of aviation. Almost overnight, we’ve gained access to everything from long-lost warbirds and contemporary military trainers, through commuter liners and heavy-lift transports, to attractively-priced lightplanes.

If you can call the Yak 18T ‘light’.

A four-seat tourer-cum-aerobatic trainer, the 18T was designed by Yuri Yankyevich and first flew in 1967. More than a thousand have been produced and delivered, mainly to Eastern Bloc countries. The manufacturing licence was subsequently bought by TechnoAvia in Moscow. Their mercurial Chief Engineer Slava Kondratjev previously designed the Yak 55 for Yakovlev and later the incredible SU26 for Sukhoi. TechnoAvia already has several exciting new designs on the board including a DH Beaver replacement, the Finest, which should fly in 1994.

However, any manufacturing company needs cash, particularly in the start-up phase, no development or certification costs to amortise, it was put straight back into production by TechnoAvia, deliberately priced to attract foreign currency into the company.

One of the earliest Brits to spot the ‘Russian opportunity’ was aerobatic display pilot and business entrepreneur Richard Goods, several of whose aircraft have already graced the pages and covers of Pilot. Goods is the European TechnoAvia distributor and recently imported the first of what he hopes will be a long line of brand-new 18Ts for the European marketplace.

If the description ‘four-seat tourer with a radial engine’ conjures up an image of a blunt-nosed Cherokee, you’re in for a surprise the first time you encounter the 18T.

Finished in the new Russian national colours of red, white and blue, it’s more akin to an overfed Harvard with a training wheel. The bulbous red fibreglass spinner is above shoulder height, while the big, broad wooden propeller blades could double as book-shelves. A large diameter cowling covers the nine-cylinder supercharged Vedeneyev 360hp M-14P radial engine, whose cooling shutters have substantial anti-flutter springs.

At 271/2 feet long and 361/2 feet span, the Yak is nearly four feet longer and a foot wider than a Piper Warrior, yet conveys an impression of much greater bulk. From most angles an attractive, if somewhat dated design, it stands tall on its undercarriage, towering above pilot and passengers. A high, sturdy step on each inner-wing trailing edge provides access to the cabin.

 

The walk-around reveals traditional construction methods, riveted alloy panels forming the main structure. The rudder, double-braced tailplane and elevator are fabric covered, with a large, powerful anti-collision light atop the fin and just a single aerial breaking the lines of the main fuselage. The split elevator has an adjustable trim-tab on each side, while the rudder carries only a fixed tab. I would have expected such a powerful beast to have an adjustable device on the rudder, as I later discovered, it would be beneficial.YAK-18T_large

The wing centre-section is of metal construction and carries both an oil radiator in the starboard wing-root and a large metal single-position plain flap-cum airbrake across its span, plus the inward-retracting main gear legs. Just forward of the starboard leg is an access hatch secured by three Camlock fasteners. Releasing these causes a hinged tray carrying the aircraft battery to drop down, until arrested by two cables. Just two catches release the battery from the tray for service, charging or replacement: obviously a military specification, and a considerable improvement on access over just about every other civilian tourer I have yet encountered. There is an external power connector behind a small access door near the port wing-root.

The wing dihedral starts at the break point just outboard of the main undercarriage. The outer wing panels are fabric-covered and can be removed, leaving the aircraft standing on its wheels for ease of servicing. The port wing carries a long barber’s-pole-striped pitot tube, the stall warning vane, and a large-diameter landing light. The Frieze ailerons are also fabric-covered, while tie-down rings are provided near each wingtip. Each wing contains a 95 litre (21 imperial gallon) fuel tank, of which four litres are unusable.

On each of the three gear legs is a small, forward-facing white light, about an inch in diameter. These are provided as an indicator for the benefit of the quaintly-named ‘flight dispatcher’, who can see immediately if a night-flying student pilot has remembered to select undercarriage down before giving him landing clearance. (Don’t think it will catch on over here, though). In addition to the cockpit undercarriage-position indicator, three small mechanical plungers protrude, one from the top surface of each wing and one just in front of the windscreen, to act as a belt-and-braces method of checking the undercarriage position. The two main wheels seem relatively thin (5.00 x 500) for what is touted as a rough-field aircraft. Long anti-static wicks trail from each main wheel assembly.

The civilian 18T conveys its military heritage from the first glance inside the spacious cockpit. Each door is individually jettisonable via a prominent red handle below the panel. The aircraft can be flown with both doors removed for aerial photography or other work. The fore-and-aft adjustable front seats are fairly Spartan affairs, consisting of exposed tubes partially covered in grey cloth and a blue cushion, though they are acceptably comfortable in use. From the top tube of each seat unroll two shoulder straps, with a release cable routing down to a locking handle on the lower inner frame. The four-point harness seemed a bit fiddly initially, but no doubt practice makes perfect. Neither a central fifth g-strap not second aerobatic security strap is provided. The hinged rudder pedals are simple, sturdy affairs with leather stirrups, but no brake pedals. The pedal assemblies are adjustable.

Rear passengers have a wide bench seat behind which, taking up much of the baggage compartment, sits a large yellow-painted auxiliary fuel tank. This holds 95 litres which drain automatically into the wing-tanks. Future models will do away with this intrusion, as the wings will be modified to hold a total of 330 litres (73 imperial gallons).

The cockpit trim and rear seat materials, colour and finish standards are reminiscent of an early 1960s aeroplane, i.e. slightly plasticky and with an almost home-made look, but durable nonetheless. The rear side windows boast sliding curtains, which are also fitted above the two front seats. Two smoked plastic sun visors hinge down from the top of the screens, adding to the 1960s impression. (Who said nostalgia ain’t what it used to be?).

The panel top roll is a stitched black leather affair, under which are a row of cylindrical lights, part of the triple panel lighting circuits. On top, a pull-cord arrangement unrolls a miniature window-blind in front of the pilot’s screen to facilitate IMC training. A special fitment holds the cord-end ball in the extended position. The front windows are a collection four flat panels, with no attempt at curvature, looking at first glance like those on Concorde when its nose is drooped. The outer pair are angled at forty-five degrees and have their lower halves hinged to provide a clear vision panel. The Yak is also the first light aircraft I have flown which is equipped with a two-speed, self-parking windscreen wiper (but no washers!).

The panel is a large grey expanse of metal with ample space for even the biggest instruments. Unlike Western layouts, it is dominated centre-stage by a huge electrically-driven and non-toppling artificial horizon. There are two long rows of switches, one under each yoke. Their functions, plus the instrument markings, are shown in orthodox Roman characters where possible (though Cyrillic letters are used if no equivalent exists, as with the ADF switch). Most flight instruments such as the ASI, VSI and altimeter are calibrated in metric units; UK certification rules will doubtless want these changed to more familiar imperial gauges on future examples.

The 18T as tested is equipped with a gyro-magnetic compass that is not only adjustable for north or south hemispheres, but also individual latitudes within either one. Space precludes the fullest description of all the unusual instruments and gauges, but suffice to say that the operation of some is so simple you wonder why other designs haven’t got the same thing, while others appear so needlessly complicated (to Western flyers) that it will take careful study of the extremely detailed flight manual to understand their operation and function.

In the former category, for example, is the single fuel gauge and its associated selector switch. Ordinarily, it shows the total number of litres in both tanks on the outer scale. Select either tank on the switch, and the contents of that tank reads on the inner scale. Only after the auxiliary fuselage tank has drained automatically into the wing tanks does the total begin to reduce from maximum. The fuel is controlled by a prominent red T-handle on the panel left of the quadrant. Push for On, pull for Off – very simple, very safe. Likewise the combined single ammeter/voltmeter. Press its switch for amps, release for volts.

On the other hand, for some reason each yoke sports two PTT buttons, one on each horn. The left-hand one opens the air-ground transmission circuit while the right-hand one activates the cockpit intercom. Not only does this encourage two hands on the yoke (not recognised as good piloting practice), but it requires the pilot to remove his hand from the throttle to talk to his companion. While just about acceptable in normal operation, during the photo-formating it proved to be a real pain.

The pneumatically-operated brakes work through a pull-handle on the back of each yoke. The P2 position has an override button to allow an instructor to release the brakes if he feels they are being used too enthusiastically by the student. The park brake consists of a further small button under the yoke. Pull the lever, press the button and the Yak is arrested. In common with many military-originated aircraft, the 18T has no nose-wheel steering. To initiate a turn on the ground requires differential braking by pressing the appropriate rudder pedal, then squeezing the brake lever.

The pitch trimmer is a small handle not unlike a window-winder, set on the left-hand cockpit wall. It is low-geared, taking five turns from full aft to full nose-down trim. No position indicator is provided other than a light, one of an array of six on the panel, which indicates neutral trim. Once out of neutral the light is extinguished. If the light is out when commencing the starting procedure, you have to wind the handle to establish the neutral datum before setting the desired trim. Other annunciation lights in the same block show Fuel low, Gen. fail, while further along the panel is a set of just two red lights. These augment the stall warner by flashing Slow and Stall as the aircraft approaches the stalling speed.

The undercarriage lever is set low down on the left-hand end of the panel, almost out of reach when one is belted in securely. It has to be pressed firmly before it can be operated, and inadvertent selection is prevented by a slide-across safety bar. The two-position, Up and Down, flap lever is situated, with the cowl gills control, the carb heat, the oil cooler selector and the throttle friction lever, on the central quadrant. The prop lever actuates a microswitch which, at anything less than full throttle in fully fine setting, causes the landing gear warning light to illuminate.

The overall impression is of a well-engineered, but somewhat haphazardly laid-out cockpit – an impression later confirmed in the air.

Starting the Yak is relatively simple, requiring a few pumps of the primer (which can be selected to fee Line or Cylinder), after which the starter button is unlocked by turning its outer ring until two red dots are in alignment. With master switch and almost all the double row of switches selected On, the starter is pressed, and after two or three blades have passed the vertical, the magneto switch is turned anticlockwise to 1+2. As with most big radials, the resulting cough and splutter can be cured by the judicious pumping of the throttle to get all nine cylinders on line. The engine then idles at around thirty per cent.

Thirty per cent of what?, you may ask.

Another Eastern Block idiosyncrasy is that the rpm gauge doesn’t measure revs per minute. Set well over to the right of the main panel, almost directly in front of the P2 seat, it is calibrated in percentage of crankshaft speed; 99 per cent equates to 2,900 rpm. Initially unfamiliar, and therefore possibly daunting to those more used to Western convention, after a while it becomes no different to flying by reference to the actual revs of the engine. The same comment applies to the metric manifold gauge immediately above it.

The big radial requires to be thoroughly warm before flight, allowing plenty of time for cockpit checks, avionics settings and the like. For really cold climates the engine oil can be diluted from inside the cockpit by means of a button next to the starter. This feeds neat petrol into the sump, up to twelve per cent dilution being allowed. The Russian-built radio gives good r/t clarity, as does the intercom – once you remember to press the correct button!

I think, however, I would substitute the present I/c system in favour of one which is either permanently on or is voice-actuated, though I personally dislike the latter.

Taxying requires a degree of initial concentration, at least until the braking system is mastered for turning, and the pre-flight run-up only differs slightly from that of a Lycoming or Continental. Long vortices corkscrewed dramatically off the prop-tips during the run-up, caused by the damp air on the foggy day of our test.

With the ground tending towards boggy, the heavy Yak required a fair bit of power to get it rolling and I was conscious of the prop-wash behind me. Lined up on White Waltham’s runway 25, I got the distinct impression that the wheels were dragging in the soft ground on take-off, though the Yak was airborne in a respectably short time. Lift-off occurred at 130kph and required an immediate firm push forward to overcome the initial pitch-up characteristic – which I had been alerted to while studying the Flight Manual the previous evening.

The best climb speed is 170kph. We had no difficulty in catching the camera ship, the ex-Goode Aerobatic Bonanza, which had taken off ten seconds ahead of us. Immediately noticeable was the fair amount of ‘boot’ I needed to maintain balanced flight against the engine torque and p-factor.

Although most of the photographic sortie was performed at eighty per cent crankshaft speed, the cruise setting once we were waved away was a more relaxed 59 per cent, with the manifold pressure showing 6 on its dial (actually 600mm of mercury). The trick is to fly at almost equal settings on the two gauges, i.e. 80/80, 60/6. This is easily achieved as the throttle and prop levers are well-matched in their gearing and functional effect, and can, for most phases of flight, be treated almost as one. At 6,000 feet the 59 per cent setting is producing 150hp, giving a surprisingly economical fuel consumption of only eleven gallons an hour at 205kph (110 knots).

One apparently normal characteristic of the M14 radial is a rather irritating harmonic, rather like an unsynchronised twin. In cruise, both prop and throttle levers were vibrating sufficiently to cause their handles to become blurred. Further oddities manifested themselves, like the way the large, 28-volt artificial horizon operates. In roll, its little aeroplane symbol operates in reverse sense, i.e. backwards to western eyes, though the pitch indication is normal. The Yak’s AH is completely untoppleable, allowing aerobatic to be flown confidently ‘on the gauges’ in the event of there being little or no horizon. However, since, with its associated inverters and circuitry, it not only costs a packet but weighs around seventy pounds, Richard Goode is contemplating substituting the lighter electric western versions if purchasers prefer these.

I had been expecting such a large aeroplane to be a heavy old bird, and was most pleasantly surprised at how light and responsive the ailerons and elevator were, though the rudder was heavier. The yoke is well geared in roll; full aileron requires only about forty degrees deflection either way, unlike (say) a Cessna 150 Aerobat, where the gearing is so low you have to twine your arms to execute a full-throw roll.

For such a big machine the Yak rolls rapidly but, although classed as aerobatic, the test aircraft had no inverted oil system, thus no negative manoeuvres were permitted. Even the vertical entry and bridge over a stall turn produced some mild flickering of the oil pressure gauge, while rolls had to be executed with a slight ‘barrelly’ element. An inverted oil system is a possible option (at £1,500), which will allow buyers better use of the +6.4/3.2g limitations.

In the section entitled Advanced Flying, the already authoritarian style of the Yak’s comprehensive Flight Manual (translated into occasionally quaint – English) goes really over the top, describing in great detail exactly how to execute each aerobatic manoeuvre, even telling the reader where to look (‘During the spin the pilot should direct his look to the side of the spin, 25-30 deg below horizon’). One can almost imagine some poor Russian student pilot flying the Yak with one hand while reading the manual with the other!

The stall is particularly docile, occurring (depending on all-up weight and power settings) at between 100kph (54 knots) and 123kph (65 knots) and is signalled by a horn, flashing lights and a pre-stall buffet. Roll authority remains present throughout, and the final nose drop and recovery takes all of 100 meters to execute it done smartly. The Yak is also cleared for spinning. Behaviour in the spin is normal with no tendencies to bite, though a properly-executed three-turn spin and recovery consumes some 2,300 feet loss of height.

Returning to the circuit, the Yak can dangle both gear and flap at anything below cruise speed of 200kph; the resulting drag requiring additional power to maintain height. The approach is made at 150kph, and I found full aft trim was needed with just two occupants. If high, the throttle can be closed almost completely (but watch the sink rate), aiming to cross the threshold at 140kph and flaring in the approved manner to a touch-down around 115kph. In the last stages of final approach and flare, the airfield disappears under the nose. The pilot must look peripherally to judge the height, and keep directionally straight. Elevator authority remains excellent, even below touchdown speeds.

There is little float, and with such a long undercarriage, touchdown occurs about six inches before one expects it. Once the mains contact the ground then, unless the yoke is right back, the nose-wheel drops with a thump. The natural reaction, pulling the yoke back to support the nose, causes the Yak to rear up. Executing a touch-and-go or balked landing is quite hard work. The aft trim must first be rapidly unwound to neutral, before the prop and throttle can be pushed firmly forward and the flaps brought up. That pronounced pitch-up on initial take-off is even more accentuated if the flaps are still down or the trim hasn’t reached neutral by the time lift-off occurs, which happens quickly with such a big , powerful radial pulling you aloft.

Then you must retract the undercarriage. If, like me, you secure your harness tightly for the landing, stretching down to push the u/c lever in and move it up the slot (it is quite stiff in operation) will prove….interesting. Especially as you now have your hands full of 360 horses, you are keeping the pitch attitude and climbing speed correct, and you know the aeroplane demands a firm but accurate touch on the rudder for a properly balanced climb and doesn’t take kindly to its pilot fumbling round under the dashboard. The trick is to unlock the shoulder harness as an extra ‘vital action’ before going round; but I’ll bet some pilots will forget – as I did – in the heat of the moment.

While I had no other problems in mastering the aeroplane (especially with Proteus display pilot Paul Bonhomme in the right seat to assist and advise), I would strongly recommend that anyone buying an 18T (not least a relatively low-hour pilot) should spend considerable time reading the manual, then doing several hours of concentrated circuit work. This will equip them to fully comprehend the Yak’s systems and handling traits, especially in a balked or touch-and-go landing situation.

For the final flight we took two extra passengers on board to sample the take-off performance four-up. Notwithstanding my earlier comments, the Yak still took less than half of White Waltham’s boggy eleven-hundred metre Runway 25 before I was able to lift off, so the fully-laden, short-field performance appears pretty much as advertised. Carefully judged, it should be possible to achieve quite short landings, once the aircraft has been mastered. The manual quotes 350 metres; the deceleration once the aircraft has landed was noticeable, even without brakes (which must not be used over 110kph) due to the nature of the runway.

At a basic £55,000 plus VAT, a new Yak 18T is aggressively priced; you get a lot of aeroplane for that. The overall performance and payload capacity is competent, the cruise economical and the range (especially with the modified tanks) respectable, giving over 41/2 hours flying with plenty in reserve. Overall, the standard of construction appears high, though the outmoded interior detract somewhat.

The 18Ts plus points are: it is robust, it is relatively cheap, and it’s certainly different. If you want a capable four-seater that stands out, the Yak will fit the bill admirably. Just don’t let its idiosyncrasies overwhelm you.

 

Yak 18T

Dimensions

Length                                       27 ft 6 in

Height                                       11 ft 2 in

Wing span                                 36 ft 7 in

Area                                202.36 sq. ft

 

Weights and loadings

Max auw (utility)                          3,637 lb

(aerobatic)                   3,307 lb

Empty weight                             2,683 lb

Useful load (utility)                        954 lb

(aerobatic)                 624 lb

Fuel capacity (as tested)                 62,7 imp gall

Wing loading (utility)                     17.97 lb/sq ft

(aerobatic)              16.34 lb/sq ft

Power loading (utility)                   10.10 lb/hp

(aerobatic)             9.18 lb/hp

 

Performance

Cruise @ 59% crank speed 110 kt#Max speed in level flight  156 kt

Vne                                               161 kt

Stall (clean)                                     64 kt

(with flaps and gear)                55 kt

Take-off roll (firm grass)                   370 m

Landing roll (firm grass)                     390 m

Take-off (firm grass, to 50 ft)              690 m

Landing (firm grass, from 50 ft)          790 m

Range (as tested, with reserves)          485 nm

Rate of climb at s/l                             1,082 ft/min

Service ceiling                                    18,000 ft

 

Engine :- Vedeneyev M-14P supercharged single-row air-cooled nine-cylinder radial producing 360 hp at 99 per cent crankshaft speed (2,900 rpm). UK TBO: to be determined. Propeller: B530TA-A35 constant speed, two-bladed, wood, 94.5 inches diameter.

 

 







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