Yak 54 – Part One

Designed as a trainer for honing the aerobatic skills of sports pilots to world-class competition level, the two-seat 26′ 9″ span Yak 54 first took to the air during December 1993, its 2120 lb hauled skyward by a lusty 360hp powerplant that would take it to a maximum speed of 170 knots for a range of just over 500 miles.

You’ll be glad to hear that the subject of this review is somewhat smaller: 74″ (1880mm) wingspan, 71″ (1803mm) long and weighing in at 11.2 lb, it’s roughly 23% scale in terms of measurement but only 0.5% of the weight! Manufactured by Extreme Flight the Yak is imported into the UK by Freestyle RC, a helpful bunch of guys who are very happy to advise on the motors, servos and set-ups that will get the best out of the models they sell.
When I first saw this kit at the shows last year I was put off a bit by the price and the level of equipment needed to complete it. Mind you, hindsight is a wonderful thing, and had I known how superbly it flies (as I do now) then I’d have made a purchase straight away. It really is very good.

The box is absolutely huge, the contents wrapped in thick plastic bags and taped to the sides to stop things shifting around. As I removed and checked the parts everything on view screamed beautiful, lightweight quality. The only problem I found was with the cowl, which had been damaged during shipping. This was immediately replaced by Freestyle, who were already aware of a packing problem and taking steps to ensure that future kits wouldn’t have an issue.

The instructions are pretty comprehensive, with text and pictures providing a lot of detail. It appeared to me that there wasn’t much to do to put the Yak together. And so, with a suitably whetted appetite for the job, I got stuck in.

First on the list are the control horns; double composite affairs that slide into pre-milled slots within their respective control surfaces. The horns are glued in with a liberal dose of epoxy, having first removed the covering from around the slots. A ball is sandwiched between each pair with a nut and bolt fixing, which makes the set-up extremely strong and very reliable. The hinges come next, Robart-type, barbed pin affairs that just need gluing into place (taking care not to stick the moving parts together). These are supplied dry-fitted on all surfaces, and a couple are modified so a little care is needed when putting them all together. The resulting hinge lines have minimal gaps, and what little is left is sealed up with tape.

The wing servos are fitted next, and here you’re directed to use metal geared units with a minimum torque rating of 100oz/in. Incidentally, during the installation I found a slight problem with one of the supplied pushrods in that the thread was just a row of circular grooves!

Rudder attachment is next, after which a small threaded brass connector must be screwed into the underside specifically to carry the tail wheel steering arm. As if to confuse, I found four of these connectors in the box, although it appeared that all were needed for the closed loop system. Alas, with no bags left to open I shrugged my shoulders and hunted for a similar item in my spares drawer. When finally fitting the tail wheel assembly (a very impressive carbon plate affair) I discovered that the aforementioned steering arm was at the wrong height to thread through the connector. This being the case, a bit of careful ‘reforming’ was necessary.

A quick trip to my local model shop hooked me up with a new Ace DS1213 servo, a quality item that has the right specification for use on the rudder. I also picked up some 3mm carbon plate to fashion a longer servo arm for extra throw. The rudder is actuated by a standard (but heavy duty) closed loop system, and by crossing the wires I achieved a nice, straight run to the control horns. When installing the closed loop I also discovered that the four brass connectors mentioned above had M2 threads, whereas the plastic ball links to fit them were M3. Result? I was unable to use them after all!

Whilst the undercarriage is aluminium (a shame in these days of carbon everything) it’s certainly robust enough for the job, bolted firmly to a hefty block in the fuselage. With threaded axles bolted on, the wheels are held in position using standard collars, the spats being fitted later.

I was spoiled for choice when it came to powering my Yak: either an O.S. 160FX or a Super Tigre T3250. The ST with its integral rear mount was around 10mm too short, so the O.S. was wrested from its slumber. The engine mount is attached securely to the bulkhead with M4 bolts (I used lock nuts throughout), whilst the engine is also secured using M4 fixings. For throttle control I used a small E Sky micro servo secured to the side of the ply engine stand-off. As for the supplied fuel tank, this looks tiny when engulfed in that massive fuselage but is perfectly positioned on its shelf just forward of the balance point.

Fitting the cowl is a simple matter of getting the engine access / cooling holes in the right place before drilling four holes for the mounting screws (I added rubber washers to these to prevent damaging the fibreglass). A 3″ spinner is recommended (not supplied in the kit), and this finishes the front end off very nicely.

Back at the other end of the model a carbon tube joiner is fed through the fuselage, and the tailplane halves slid onto it, secured with small bolts. Worthy of note is the fact that threadlock was used wherever metal meets metal across the airframe – a wise precaution! As is typical for this sort of aeroplane, the elevator servos are fixed into the rear of the fuselage then hooked up using hefty rods and ball links.

I used a JR RS77S receiver, powered by a 2s TP 1320 Li-Po battery through an Align B3X regulator that supplies 5.8V and has a 5.1V step-down, which I used for the throttle’s micro servo. A ‘whip’ aerial bolted to the top of the fuselage keeps things nice and tidy. The Yak’s all-up weight with an empty tank was just 11.2 lb (5.1kg), which is impressively low for this size of model.

The C of G is quoted as 6″ (152mm) back from the root l.e., which is exactly where the wing tube passes through the fuselage. The rearmost quoted position is just 3/4″ (19mm) back from this point. When I picked the model up carefully by the centre of the wing tube I found it to balance perfectly, with no need to add any weight or shift any components around. The instructions also suggest balancing laterally, which is tricky to do, but again I found the Yak spot-on as it stood.

As far as control throws are concerned, for high rates the instructions dictate the use of ‘bevel to bevel’ deflections; with both sides of the hinged surfaces being bevelled, that’s quite a throw! I currently have three flight modes set on my transmitter, the first has 3D rates, the second is as per the instructions and the third is just 15% of travel to give smooth, precise aerobatics. Of course most of the time I fly the Yak at the max, but it’s nice to fly gently every once in a while, especially with a model that does it all so well.

That just about takes care of the preperation process, so take a look at Part Two to see how she coped in differing flying conditions.