Yakovlev Yak-18T

                          

The Yakovlev Yak-18T is a four seat fully aerobatic utility aircraft. Introduced to train Aeroflot Pilots, it has gained some popularity as a sportplane both inside and outside the former USSR. It is powered by a 268-298 kW (360-400 hp) Vedeneyev M14P radial engine, and is designed for stresses of +6.48/-3.24 g.
The 18T was designed in the late 60's, as a civilian aircraft. The aircraft has a nosewheel, is a 4 (or 5) seater, and has a 9-cylinder 360 hp radial. The Yak-18T shares systems with the Yak-50/52 family. These aircraft all have the 265 kW (355 hp) Vedneyev M14 nine cylinder radial engine as well as the same underlying compressed-air system for engine starting, brakes, undercarriage and flaps. 

The propeller, avionics and other parts are also shared. The Yak-18T, like all Russian aircraft used for training, is aerobatic.Compared with other four-seat light aircraft such as the Cessna 172 or the Piper PA-28, the Yak-18T is only a little wider and longer but it is much heavier and is equipped with a considerably more powerful engine. The Yak-18T prototype had its first flight in mid-1967 and subsequently the type was placed in series production in Smolensk.
The Yak-18T went on to become the standard basic trainer with Aeroflot flight schools, while small numbers also entered service with the Soviet Air Force as liaison and communications aircraft. After approximately 700 were built, many for Aeroflot, production ceased in the late 1980s, to be resumed in 1993.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.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.

DIMENSION:-->

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.

Niriha Khajanchi [ MBA Aviation ] Project Manager www.AeroSoftCorp.com Web Site : www.asiaticair.co.in www.asiaticair.in