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Tuesday, March 29, 2011

Yak vs. Yak - Round 1

The Round 1 bell approaches, with the simply outstanding Art-Tech ready to take on the Great Planes  Electrify EP E-Performance Series Yak-54 ARF 41".  That is quite a name! I like to call it the "Yak." 


As expected, the quality of the GP ARF is amazing.  Everything was built and covered with precision; the plane falls together.  I've built a few GP ARFs, but I'm still not up to their 4-6 hour estimate.  Allow a full day, plus time off for glue/paint drying. But overall, the airplane is a delight just to take in.

This Y54 is a one piece build.  The main spar is a single, composite beam running from wing tip to wing tip, formed with ply, balsa, and carbon fiber.  The two finished wing-halves interlock inside the fuselage in a plywood clasped Gorilla Glue sandwich.  I ziptied mine while it dried overnight.  If you use the recommended 30 min epoxy, GP's 4-6 hour total build estimate could still happen, but I think epoxy is too heavy to use en mass on a 41" aerobat designed for ultimate slow flight agility.  Other than that central critical wing joint, the plane goes together quite quickly.

The main tasks are: glue the main spar, hing all flight controls, trim away covering and drop in servos, assemble the tail, bolt on the landing gear, glue the magnets to the main hatch and cowl, and mount your choice of engine.  In fairness to GP, I've seen several of those tasks required by RTF, RxR, PNP or BNF models, too, they certainly deliver the ARF promise when viewed in that context.

This is what comes in the kit, in later photos I'll show the completed aircraft:

 
Every time I assemble on of these mini works of art, I marvel at the price tag.  I paid $105 for the ARF, minus Towerhobby's usual 20% email discount  for club members, or $84 with no tax.  It should be illegal to work slaves this hard, but I'm secretly glad it's not.  It would take me at least 3 months to assemble a kit to this level of execution, and I doubt it would come out half as nice.

I'm excited to get this baby up, the Yak as shown above (and reinforced) weighs a mere 15.0 ozs.    With 7-8 more oz to go (motor, ESC, battery), the final wing loading should come in below GP's estimate.  With the enormous movable rudder surface, oversize elevator and huge full wing ailerons, the AT could face a real knife fight.

.....

Weight came in slightly above my hopes at 27.4 oz RTF. Wing loading is still plenty low for a 41" model at 11 oz/sqft. In addition to an oz or two of reinforcement, I accepted another two ounces or so to put a .10 motor/battery/ESC under the hood instead of a 400 system. I'm glad I did, (1) because power is outrageous, resulting in effortless, nearly silent half power hovers. But more importantly (2), I don't think I could have balanced the plane with a lighter motor and battery, especially after opting to mount the tail plane servos next to the control surfaces, in the very rear of the fuse for tied-in responsiveness.

The GP Yak 54 now has several flights under its belt. I'm overjoyed! It took a flight or two to verify the ideal power system config, but the current ST .10, 2000-2500mAh 3-cell, 40A ESC, and 11x3.8 (or Z83D scissor) prop is a magical combination in the air.  A 12" prop with a 3D pitch would tear even harder upward, but given a roughly 2:1 T:W as is, it doesn't seem worth the hit to battery life.  The plane feels lighter than air, almost like it can float without power.  The .10 is still an airy choice at just 2.2 oz motor weight; this plane can dance.  

If I had to do it again, I would arrange the checkerboard in
rectangular stripes.  The flowing pattern still tends to blend, but
the stock color scheme is definitely too similar on top and bottom.
Possibly with better planning and shoved forward guts, a 400 motor and the lighter associated total weight, would have no problem hovering this plane closer to full throttle. It's certainly another valid build path that would yield noticeably more float in exchange for noticeably more strained verticals. In the 400-choosers' defense, .10 power on this plane probably produces one of the highest T:W Yak-54s your're likely to find at any price.

When the monster power goes silent, the GPY54's glide characteristics are awesome.  With 50% throttle level flight trim set, the nose rises ever so slightly with the prop windmilling until the fainest shudder resets the pitch attitude by a a degree or less and sticks there.  The plane comes down like a para-sail, catching the wind as it floats in slow motion, settling into a steady, 4-5 degree glide path.  The plane lands itself hands-off, just a little steep, very slow, without bounce.   Plunk and roll is always available, if nothing else.

I tried to limit nose intake area with a large spinner.
 Ding, Ding, Ding...

The Art-Tech Yak is a formidable opponent.  I know, many are thinking itss a $130 RTF foamy, it can't be any good.  Well, with a lighter than stock .10 brushless, and a carbon main wing spar and tail box, this AT Yak rocks.  Example: the fastest, perfectly axial rolls I've every seen in nearly 35 years of flying and watching everything I could.  No, make that twice as fast.  It's a miracle it doesn't come undone.  But,  there is more to Yaking it up than transforming ino a blurred Tasmanian Devil.  I've compiled a few subjective scores in the Yak v. Yak table, above.  These scores are highly scientific, I assigned them subjectively--a valid method when truth is not only measured but defined by the tester.

The ATY54 is amazingly capable plane for the money and (lack of) time invested.  I love flying it.
Ironically the ATY54's lightness is its only enemy.  Light wind bounces it around some, and the lack of anything resembling a real Reynold's Number means you have to actively fly the plane along the lines all the time.  With the CG way back at nearly 45% chord (!), the plane is amazingly controllable and lively.  Anytime you reduce the power below an elevator blowing 40% or so, the tail falls and the plane begs to howl at the Moon.  Harriers are not flown, they "happen."

This makes the ATY54 a hoot to fly, but a bit of a handful to land.  You have to push the plane down glide path, balancing lift, the tendency to seek more lift as power comes out, with the component of thrust vectored against gravity.   To flare, just stop pushing the plane lower.  If you miss smearing wheels onto the pavement on the tangent of the first natural round-out, add ~15% power to extend your  time over target and fore-go the impending belly-flop.

...more to come...

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