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Monday, September 12, 2011

E-Flite Carbon-Z Yak 54 Flight Review (Yak vs. Yak, Round 3)

Updated with grades.

Update: After a long bout with high winds, flight results are typing up.

My full in-flight review of the Carbon Z Yak-54 and Great Planes Yak-55M is set to take off, as Yak vs. Yak enters a knock-down drag-out Round 3.As part of this Round, I will post the numerical standings to rack and stack all of the Yak's considering both their price and performance.

Great Planes Yak-55M (after 80 flights) vs. E-Flite's Yak-54 (new)
The GP Yak-55M's wheel spats are not shown. The GPY55M color
scheme is Monokote with painted fiberglass cowl.  The CZY54 color scheme
is painted with colored ABS pants.  Please note the "E-flite" logo is printed
on the fuselage centerline and the Carbon Z's wing is mounted
distinctly below that logo--we'll come back to that later.

Carbon Z Yak 54 PNP
Great Planes Yak 55M

BNF = $400
Unknown BL 25 1000 Kv
4 x MG Digital Servos
60A E-Flite Pro ESC
4S 2800mAh E-Flite Lipo
AR600 Rx
Car Charger
Sub Total = $431 
+$15 Misc parts and glue
+$10 Tower club membership
-$50 Tower club discount on $300+
-$15 Tower club discount on $100+
Tower club free shipping x 2
= $400
(for Power 25) 537W Continuous, 705W Max
143W/lb Continuous, 188W/lb Max
925W Continuous, 1480W Max
279W/lb Continuous, 447W/lb Max
60 oz w/batt
53 oz w/batt
525 sq in
505 sq in
16.5 oz/sq ft
15.1 oz/sq ft
Foam, carbon fiber, wood reinforcement
Wood, carbon fiber, Monokote

First Impressions:

The GPY55M reflects the CZY54 in its Monokote finish.  
The two planes are surprisingly similar in overall size.
If I'm not careful, an Ultra Micro Yak could be on the way.
The real Y54 engine cooling louvers look just like E-Flite's
orientation, which denies their Carbon Z cooling airflow to
the motor, and adds to the danger of it's over-amp'ed motor.
The real Yak's louvers are designed to catch air from a Russian
engine that spins opposite direction. Great Planes designers reversed
the louvers for proper motor cooling to their model.
For the scaling exercise above, I lined up main spars then adjusted the
overall plan view until the leading edge of the horizontal stabilizers aligned.
While neither plane is true to the original design, the Carbon Z, with it's
sleek fuselage and more square, low aspect ratio wing bears almost
no resemblance to the uniquely stubby Yak-54 and its highly tapered wing. 
The lack of resemblance to their Yak brethren stems from
the fact that both planes look a lot more like Extra 260s in the plan view.  
The Extra 260 image is perfectly scale on both sides, above,
but the camera perspective is not exactly top-centered.  The 
Carbon Z "Yak's" low wing mount is also true to an Extra 2X0 core design.
The GPY55M maintains the real 55M's center mounted wing.
A 3-view design comparison to the Yak-55M.  A true Yak-55 wing
leading edge notches slightly  into the cowl, same for a Yak-54.
Although not properly proportioned in the top view, Great Planes maintained a very strong resemblance to the Yak-55M in the side and front view, to include an exact center-mount wing to replicate the perfect aerobatic symmetry for which Yak's have become famous.  We saw stunning 3 axis symmetry during our aerobatic tests.
E-Flite wisely did not include a 3-view of the "Yak-54" in the manual or on the box.  But they did make the mistake of including a decent profile on the side of the box.  The Carbon Z "Yak-54" is an near Carbon Zopy of an Extra 200-series trainer, to include the low biased wing and very accurate Extra 200 landing gear and wheel pants.

The Carbon Z "Yak" bears essentially no resemblance nor shares any of the key design attributes with the uniquely pudgy Yak-54.  The Yak-54 has a highly tapered wing with a pretty high aspect ratio for pitch instability, spin ability, and fuel efficiency.  It absolutely does not have a low biased wing mount, it is a wonderfully symmetrical aerobatic trainer.  The Carbon Z "Yak" suffers from exactly the same light to moderate aerobatic roll coupling as an Extra 200-series aircraft.  Now we know why.  The 54 never sported full wheel pants, only spats on a single US import, maybe two.   The inclusion of taught, enclosed wheel pants is a strange design choice by E-flite, and again displays a splitting image of Extra 260 wheel pants.

Dollars to doughnuts says this Carbon Z airplane was conceived, born and developed as an Extra 200-series aerobat, then touched up in the final hour to re-brand it as a more trendy Russian Yak, but without the proper flight characteristics. Was it too similar to their Extra 300 flying-brick?  Leave it to Horizon Hobby to build any airplane they want then call it something completely different; another HH scam aimed at the aviation novice.

Banana Hobby's 59" Giant Scale foam, carbon fiber and plywood
reinforced Yak-54 is actually a Yak-54.  In RTF form it sells for
about $300.  Hobby King sells the same PNP Yak-54 (above)
for about $200, including their more expensive shipping.  Notice
the complete lack of resemblance to the E-Flite Carbon Z "Yak-54."
My next Yak vs Yak contender will actually be a Yak-54:  Banana Hobby's Giant Scale Yak-54, AKA Hobby King's Monster Yak-54.

Update, please see:  The 60" Monster Yak is a excellent foamie with deficient thrust as sold, but it's so cheap you can bring up to par for a lot less than the Carbon Z.  The Monster also has more carbon and a more rigid build.

The Build:

The Carbon Z Yak-54 (let's humor E-Flite and pretend it's a Yak) was a little bit a of surprise to put together. Those used to Horizon RTF/BNF/PNPs probably won't expect an hour or so build time; this kit requires more time than most.  The basic flow is: insert carbon fiber tubes for the main wing and horizontal stab, slide on those 4 wing halves, wire the ailerons and install the four set screws, hinge one side of the rudder (awkward fit; one hinge was loose as pre-installed), install the pushrods and clevises, and screw in the landing gear (ABS pants and wheels come installed).

The foam shipping box is a helpful prop for resting the model during construction as the foam skin is very easily dented and scratched.  It sounds silly, but closely trim your finger nails before opening the box to avoid marking the plane's delicate surface.   The fit of this model is tight, and assembly requires stressing the foam to its limit, use extreme care not to hear the dreaded "crack" by pushing too hard.  Wiggle and wait.  The riskiest connection was the rear wing roots, where the ailerons stop, the foam is not very thick and pushing the roots fully into the fuselage is an exercise in patience. 

The CZY54 has two hatches: a magnetic foam hatch on the top of the cowl to place the battery, and screw-in plastic hatch on the bottom to access the Rx and servo connections.   The ESC sits in a wide motor vent tube that diagonals out to the bottom around the leading edge.  There is no cooling airflow to the Rx, but oddly there is a foam lattice behind the cockpit that vents nothing.

E-Flite's decorative lattice design, again, bears no resemblance whatsoever 
to a Yak, and problematically weakens the un-reinforced fuselage structure.
The Carbon Z Yak fuselage has a nasty habit of breaking in two on a fault line right behind the cockpit, the pointless foam lattice, venting nothing, almost certainly exacerbates the problem.  During construction,  I thought about strengthening the CZY54 fuselage with some embedded carbon slats, but decided to test it as shipped since it is advertised to be set up by an expert.

Motor Tests:

For the purposes of this review, I tested the recommended GPY55M motor with a Castle ICE 50A ESC and a variety of propellers, against the stock CZY54 with its stock 12x5.25 prop and also a control prop.  For the control prop, I used a wide blade MAS K-series 13x6, because I think it makes an excellent 3D propeller given it's reasonably low pitch, large diameter gyroscope, extremely explosive low speed acceleration, and decent top speed.  But as you can see from the yellow results, the control prop didn't work out:

Motor Tests
GP Yak-55M
Rimfire 32
12x6 APC
12x8x3-blade MAS
13x6 MAS K
EF CZ Yak-54
Generic BL25
12x5.25 Stock
13x6 MAS K

To estimate the CZY54's generic motor limits, if you interpolate published E-Flite Power 25 limits between the 870 Kv version and the 1250 Kv version, you find the 1000 Kv limits to be 38.2A continuous, and 48.8A burst.   The CZ motor is running at 144% of the continuous limit, and 113% the absolute burst limit, right out of the box! The control prop was a bust, the motor isn't anywhere near capable of spinning it, as the results were 231% of the continuous limit, and 180% the burst limit.

The motor tests indicate quite a difference.  The GPY55M's Rimfir 32 is running awfully casually , pulling only 36A with a stronger prop than the stock 12x5.25 causing the CZY54's BL25 motor to flash signs of cardiac arrest, pulling a whopping 55A.  The CZY54's motor in stock form is operating well over the brink.

The control prop test was interesting, in a sad way.  The CZ's motor pulled 54% more power (180% pf its burst capacity) to turn the prop 11% faster, a sure indication that if the test went on for a few more seconds the motor would have smelled like chicken.

*************** SAFETY WARNING ***************
As shipped, the E-Flight Carbon Z Yak-54 pulled 55A and  810W in our ground tests using a 25C 4S battery.  E-Flite has declined to publish the motor's safety specifications.  The included motor is listed as a generic "BL25 1000 Kv outrunner," almost certainly a lower quality offering than a branded E-flite Power 25.  A Power 25 BL 870 Kv motor, the closest product to the generic  BL25 1000 Kv outrunner is rated at 32A continuous load.  That equates to a MASSIVE 71% over-amp of the included motor.  E-Flite also sells a 1250 Kv racing version of their Power 25, which is rated to 50A continuous.  If you interpolate the two using 1000 Kv, and ignore the reduced quality from a genuine Power 25, you get a maximum continuous rating of 38A for the included motor.  This equates to a 44% over-amperage of the included generic motor.  Until E-Flite publishes specs allowing 55A continuous load, assume the Carbon Z Yak to be a defective product.  Do not select full throttle for more than few-second bursts, and do not operate the airplane in the vicinity of people.   
*************** SAFETY WARNING ***************

There are two reasons the CZY54 motor is flailing, (1) the BL 25 is too small for 3D performance given the size and weight of the plane, and (2) the prop E-Flite selected is way to big for the motor.  Essentially they are bundling undersized, cheap components, then severely shortening the product's lifecycle in order to squeeze enough performance out of them.  Consider that the 1250 Kv version of the E-Flite Power 25 recommends using an 8" prop maximum, due to the high Kv rating of the motor.   The 870 Kv Power 25 recommends a 11x8 to 14x7.  So this 1000 Kv BL25 should be turning a 11" prop, maximum.  The 13" test was a disaster.  The problem with using a right-sized 11" prop, is that the airplane and cowl are really to big to accept an 11" prop--probably because the plane is really an Extra 200 with a kludged round cowl.  The motor is simply too small (or cheap) to both  produce enough thrust and have a reasonable life cycle.

Perhaps most disappointing, the CZY54 is slightly heavier overall even with the smaller high Kv motor installed.   E-Flite likelly felt compelled to use a cheaper, smaller motor to make up for a heavy airframe build.
The Great Planes Yak-55M kit is an ARF, advertised as "a few hours" to airborne.  Realistically, this kit isn't that far from the Carbon Z: you have to install the landing gear, insert the carbon tube, slide on the wings and glue the elevator, then hinge the tail.  The main difference is that you have to install the Rimfire engine onto it's pre-fit mount, and screw four servos into their pre-cut bays.

The upside to the last sentence worth of work is that you can choose much higher quality components and still fit into the same budget, and you get to choose your level of tacky decal indulgence.  As we'll see in the flying tests, a set of quality digital metal gear servos and a dead-serious motor makes a world of difference in the air, especially in the 3D realm of extreme throws, where a tiny servo centering miss can mean a big rolling tendency.

As I've come to expect, Great Planes ARF kit was flawess, and the resulting balsa and plywood drum measured up perfectly square, within a 32nd of an inch or so.  This is one of the easier ARFs I've built, as the huge ailerons are pre-hinged and the kit doesn't have that many parts.  If you worked steadily, a half a day is realistic, maybe as little as 3 hours if you've built a GP ARF before.
Flight Tests:

Since I've already characterized the GP55M in a previous Round, I will only critique the CZY54 here.

Once airborne, the first thing a CZY54 flier discovers is how efficient the plane is at converting 4-cell power into noise--the plane is louder than some nitro powered models.  I'm not sure why, maybe its the plastic mount transmitting maximum sound waveage to the foam frame, or maybe its the small prop, high RPM approach; whatever the reason, be prepared to find an isolated field unless you want the whale eye from testy neighbors or annoyed park visitors.

The next thing you notice is the spotty tracking.  There are three reasons for this - the primary culprit is slack in the servo movement and inconsistent centering--each time you return the sticks to neutral, the servos pick a slightly new center position.  Compounding the poor quality servo centering, is the very high throws generated by the CZY54.  The CZ has the best throws of all the planes tested, but oddly, it does not generated the best rates in the air.  But still, a tiny servo centering miss induces a healthy roll around the affected axis, causing trim trim trim and re-trim, each and every time the plane reestablishes a platform.  The last reason is the foam build.  As much as E-flite would love to re-brand cheap foam construction as "Carbon Z", the plane is a foamie and it flies like one.  Most foamies have carbon fiber and/or wood reinforcement these days, including the Art-Tech Yak-54 tested here.  And if a foamie doesn't have carbon fiber reinforcement, it only costs about $6 for a nice stretch of carbon - a sharp knife and a few dots of foam safe CA will embed it right into the foam in a few minutes time.  Presto - "Carbon Z."

Amazingly light and thin, this Dave Brown CF tape is extremely stiff when embedded like an I-Beam in foam.
In fact, one problem with the CZY54 is a lack of carbon reinforcement, especially in the fuselage which is traditionally flimsy.  I recommend embedding some extra carbon along the length of the fuse, to keep the plane from flexing and/or breaking.

Another CZY54 quality issue is the finish.  It is way too easy to mark up and dent, in fact, it came with a few significant blemishes. Terrible.  Those who like their planes pristine should rule foam out, due to the short honeymoon.

Perhaps next most obvious trait, after the harsh drone and the lackluster tracking is the nose heavy CG as shipped.  Pull the power out and this puppy craves dirt.  Inverted flight wants more than its fair share of down elevator.  The lead nose is a bit of a burden throughout most maneuvers.   Add medium wing-loading, too little forward speed, and copious up-elevator and the CZY54 produces substantial, un-commanded roll coupled with yaw--the plane wants to spin.

Contrast that unrefined behavior with the GPY55M, which turns idle power and full back stick into a stabilized down-elevator, falling straight down with no wing rock, yaw, or roll.  The nose stays up high, pegged on the horizon.  Add power, and it flies straight out of its impending 80 degree alpha pancake.  Yummy.

Lack of precision is the CZ's nemesis.   It can't pull off a outside loop on rails.  Even a straight inside loop can deviate a bit off the entry line, even in dead calm wind.  Knife edge flight tucks heavily away from the canopy.   Wing rock develops and eventually becomes severe at high AoAs.

The smaller, but better balanced ATY54 foamy, pumped with a $24 ST .10 motor for a true 2:1 T:W ratio, a slat or two of carbon, and perhaps few cheap digital servos, would arguably dance around the unruly inertia of the E-flite CZ Yak, all for about $200 and 20 decibels less.

Predictably, the non-Yak design doesn't generate the telltale Yak tail-droop as air speed disappears.  Yak's properly balanced, are reluctant to seek trimmed airspeed following a power reduction, like more traditional aircraft designs.  They balance, and fly controllably, so far back on the chord line (happily at 45% in some Yaks), that the tail needs rushing air to stay up and push the nose down.  This is inherently efficient because weight you'd need to haul anyway, the elevator, does its job via gravity rather than generating lots of aerodynamic down force at slower speeds, when maximizing lift matters most.  The result is a plane that wants to stay high as power comes out, with much less aerodynamic baggage at slow speeds.  The CZY54 has no such tendency, nor efficiency.
All symmetric mid-wings, except the Carbon Z
Like most aerobats, the Yak can use some power to land out of a stabilized approach.  The tendency to dive, traditionally, after power comes out make it less tricky to dead-stick.  It isn't hard to spot land in the middle of on my tree-lined runway--well, no harder than other RC planes--which are all a handful when the winds pick up.

Does the CZ Yak fly well?  Sure  ...for a foamie.  But make no mistake, it is a foam plane, and as such it lacks the precision and aerodynamic power of a good balsa and ply build.  And it's not close.  Additionally, foam planes are delicate compared to plastic covered wood.  Crashes that are easily survived by a balsa and ply model will pulverize a foam air frame. 

Within one CZ flight, it became crystal clear that Yak vs. Yak had become race between the bubbly GPY54 Tasmanian floater and the gravity defying GPY55M big balsa scalpel.  Both of which can strip naked and don a lampshade as fast as you can switch to blurred rates.

It is interesting to note the differences between the 51" GPY55M, which is the most magical aerobat I own, and the similarly dimensioned, similarly thrusty CZY54.  Looking at the two on the ground, one would expect subtle nuance to rule any kind of fly-off, but the difference in the air is night and day.

E-Flite Carbon-Z Yak 54:

Appearance: B
Low wing Extra 260 with a round cowl.  Gorgeous color scheme.

Airframe: B
Foamie.  Relatively imprecise.  Flex.  Huge throws, medium effect.

Power System: C
Good thrust.  Over-amp'ed motor.  98% efficient electricity to noise.

Build Quality/Durability: C-
Nice execution.  Plastic motor mount.  Bad servo centering.  Weak fuse, no carbon.

Value:  C-
3D price tag.  Better components than most foamie RTFs.  

Overall Grade: C+ 
Great foamie.  Punishing opportunity cost.  Out of its league, here.

Great Planes Yak-55M:

Appearance: A-
Beautiful high contrast scheme.  Perfect covering.  Tiny 2" wheels.

Airframe: A+
Incredibly docile.  Ripping Dopplers.  Most precise plane I've flown.

Power System: B+
Heavy motor needs aft battery. 2:1 T:W. 5 mins w/3000mAh 4S.

Build Quality/Durability: A
As good as ARFs get.  Ox airframe.  Canopy latch could be better.

Value:  A+
Pure theft from China.  Tower coupons for -15% +free shipping.

Overall Grade: A++
Only A++ I've ever given.  Does everything better than anything.

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