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Sunday, July 24, 2011

Hobby King Yak-54 Review after the Hundred Dollar Matchmaker

With a 15" prop in the cards for my Monster Yak 54 from Hobby King, I picked up a nicely made $90 E-Flite Power 46 to spin it.  The stock 3740 motor, my ST Triple .10, and the Power 32 all proved too weak to haul this Russian beast on anything resembling vertical ascent.  Ivana 3D's Hubble Space Telescope cowl really needs a reachy 15" prop to generate enough unblocked thrust for prop dangling.

Turns out, the Power 46 is a perfect match.  Even with only 770Kv, the plane is finally able to pull off a hover with plenty of margin for error, and the airplane's balance (after one small trick) couldn't be better - inverted flight remains absolutely level without trim change or any stick movement.  With a 4S 5000mAh, 3D flight times are only 4-6 mins, but sport flying time is well over 10 mins due to the fantastic cruise efficiency of turning a big, slow prop.
The motor's fit is about perfect using the method show above.  In order to balance the plane and strengthen its hold on this 10 oz chunk of copper, I elected to slice an inch off of the HKY54's thick wooden motor mount.  There are two potential firewalls in the stock mount's design, so now I'm using only the rear one.  This is a match made in heaven.  Balance is superb and the 19.8oz battery's roomy home has just enough shifting range to change the CG from nicely nose-heavy to unnervingly nose-light.  The lower moment elevator has noticeably more authority.  Yay!

Even with the 1" set-back, prop clearance is fine.
The stock spinner provides an 1/8" clearance and a perfect fit,
but I want to be more conservative on cooling so I used an
FW 190 front mounted spinner for the tests.
Excellent flying results, full report to follow:

This Monster has been amazing with the big 46 in the house.  Balance is exceptional, making it the most poised flyer of the foamie Yak fleet.  It's size has a lot to do with it's composure in the air, the momentum of 80+ oz penetrating atmosphere lends almost enough credibility to forget, for a moment, it is a foamie.

The plane tears straight ahead with enough speed to generate a loud, telltale foam hiss.  So solid, in fact, is the top speed, that I dumped the 15x8 for a 16x4, next flight (update: the 16x4 sports slightly better hovering power but might not worth the general speed loss [and noise spike] during pattern aerobatics).  With the 15x6 on the nose, hovers are not a problem down to about 15V, when pullout authority gets shaky.  I'm hoping the downshift to 16x4 alters the tradespace from pattern to 3D.

Even with the lowest T:W in this group, the Monster shines.  And with the power off, this big bison is superb!  The first thing that leaps out at you is the glide, it is uncanny slow.  This beautiful hunk of Russian utility looks weird as hell hanging darn near motionless in the delirious burning blue.
Reason:  Wing Cube Loading.  WCL is a better gauge of floatability between two differently scaled planes, due to different dimensionality between overall scale (which is 3D) and Wing Area (which is 2D).  For example, a typical 250 sq inch plane does not have 1/2 the span of a 500 sq inch plane, but rather has about 2/3rds the span.  So wing loading doesn't capture the full story when comparing planes of different scale.  For that, you need to divide again by the scale to get a normalized, unit-less wing loading per scale unit. That is Wing Cube Loading (WCL).  There is a nice calculator here.

The WCL of the mega-Yak is impressive, even with a mega-motor and battery to match.  Specifically: 7.8.  Compare to the wonderfully floaty and fleet-footed 41" Great Planes Yak-54, which has a WCL of 7.0, but the Monster is relatively huuuuuge in the air, making the big mama-jama appear to disregard gravity at times.  It's WCL beats the Great Planes 55M by a tenth, which in turn bests the Carbon Z foamie's last place finish of 8.0.  Of the foamies, the Art Tech Yak wins the WCL war with a cool 7.2. 

The WCL calculator page linked above suggests these values for WCL:

Gliders ~ under 4
Trainers ~ 6 to 7
Aerobatic ~ 9 to 10
Scale ~ 12 to 13
Racers ~ 15 and over

By that estimation, all of our Yaks are in the extreme aerobatic range, with the Monster in the middle.  That's how it feels in the air, too, shockingly light for it's empirical heft.  The rock stable, long ratio, lumbering glides this beast is capable of is inspiring to witness in person.

Aerobatic capability, as expected for a plane so light on its feet is tremendous, limited only by a pound or two less thrust than ideal for a physics-shunning degree of aerial freedom, which, while way too much to ask from mere mortal aircraft, is present in all the other Yaks in this line up.  Nevertheless, giant loops are not an issue, and look crack-a-grin scale as the plane slows a little on the upside.  C8's have the same feeling of both power and mass as the airplane nimbly flips and accelerates down the diagonals.  Knife edge passes on middle-rates are perfect, as the power and slightly inhibited (85%) rudder travel meet to produce a perfect horizontal line, and coupling is amazingly absent for a foamie proably due to the massive carbon rod.

The E-Flite Carbon Z Yak-54 only wishes it was as rigid and well behaved with one wing pointed at mother China.  But the Carbon Z is also, erroneously, a low wing design, so while it is the only other sizable foamie in this line-up, it is not designed for symmetrical aerobatics like true Yak.  One more area of superiority over the Carbon Z is servo quality, the Monster's metal gear servos center very well (or any centering error is lost at scale), providing a much more satisfying precision aerobatic experience.

Tumbling maneuvers are a load of fun, as the massive foam rudder audibly swings in the air.  The travel on this 54's barn door is so physically lengthy, that yaw kick is noticeably more blunt than the other two axises.  But once again, after this big horkin' Yak makes up its mind to zumba, the resulting maneuver quality generally hangs with the best in class.  Increasing the receiver voltage to 6.5V, and thus boosting servo speed, with a LiFe Rx battery is definitely in this plane's future.

Just when you think you've extracted the last rabbit from the big Yak's hat, ailevons twist the fun meter even more.  With independent servos on both sides of the elevator, this Yak can tango in ways most can't.  Mixing both in the same direction as aileron gives the little tornado maker an extra crank during rolls.  And of all the Yaks in the showdown, this one does the most perfect wings level 360 turn, with nearly full rudder, plus some opposite direction aileron and thus ailevon.  The plane doesn't seem to care a whit when airflow hits it dead in the cheek instead of the lips.  Wow.

Traffic Pattern Stalls aren't that easy to induce, as the plane would much rather climb, but once a wing shudders, the resulting dip is very manageable.  With power on, a slight wing rock settles into straight-ahead motion.  Not bad at all.  A fully developed power off stall falls, chin up, on about a 70 degree downward glide path.  The resulting down-elevator is only exceeded in flightpath-down, nose-up attitude by the rock stable Great Planes Yak-55M sink-o-matic.

Spins and inverted spins are easily accomplished, but I need to futher explore the baset inverted flat spin stick and throttle locations.  I'm confident the controls can be tuned for beautiful upside down auto-rotations.

Landing this Mastodon is the most fun of all the planes in the line up.  First, the balance of this plane is perfect, if not slightly more nose-weighty than the more edge-of-control Yakobats (ATY54 & GP55M with a way aft CG dialed up), it still has a very lethargic but predictable tendency to lower it's tail as it slows down.  The difference is that the tail gets a little droopy on an easy to establish glide path, not in an incorrigible desire to hold level flight as airspeed bleeds.  A little power blows the tail right back up, and on down the tracks this runaway train lumbers.  The result is almost an auto flare.  As you starve the motor of the last 20%, the plane rounds out and touches down wonderfully independently.  You watch this big Turkey Buzzard gracefully alight, more than actively land it.

The last tasty treat the plane bestows is a loud 747 landing chirp as the tires meet the ground, spin up, and squish under the plane's weight.  Luv it.

Ok, this is a bit of a hard grade.  The plane is cheap, big, wonderfully scale, and a beautiful sight in the air.  It is surprisingly refined aerobat, if not a bit sluggish to initiate controlled insanity like the other Yaks can conjure up as fast as you can think it.  It won't Yak as shipped, you need to replace the motor and prop to defy gravity.  That said, it is certainly aerobatic out of the box.  Better get a massive battery to help weight down the wimp motor in a stock nose.

Additionally, the difficulty finding a motor that can really toss this baby around adds to a feeling of mass in the air, even though the plane is quite nimble.  It's Jackie Gleason doing the Soft Shoe (kids out there have no idea what I'm talking about, so here).  The flip side of the Yak's aerobatic development time are to-scale visuals like no other plane in this field.  The bat has more than enough grunt to execute any scale maneuver and then some, but not so much that it presents itself as an airspeed-constant toy on rails no matter what the task.  A real joy to guide.  I'd classify it as a "scale unlimited" aircraft, unlike the rest of these Yakobats which are just plain "unlimited."

Value: A-
(incredible at $200 as shipped for 59", but needs $110 motor and prop to 3D.  Proves foam can make sense.)

Build Quality/Durability: C
(more carbon and ply than the Carbon Z somewhat offset a foam composition)

Performance: B-
(only hampered by normal servo speed across long travels and a rational T:W)

Overall: C+
(a 28oz T-bone at a fast food price, smothered in a Peppercorn Bearnaise)
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