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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
Watts
/lb
(for Power 25) 537W Continuous, 705W Max
143W/lb Continuous, 188W/lb Max
925W Continuous, 1480W Max
279W/lb Continuous, 447W/lb Max
Span
48”
51”
Fuse
48.5”
47”
Wt
60 oz w/batt
53 oz w/batt
WA
525 sq in
505 sq in
WL
16.5 oz/sq ft
15.1 oz/sq ft
Bld
Foam, carbon fiber, wood reinforcement
Wood, carbon fiber, Monokote
Vid

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:   http://z8rc.blogspot.com/2011/07/hundred-dollar-matchmaker.html  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
Airplane
Prop
Amps
Watts
RPM
GP Yak-55M
Rimfire 32
12x6 APC
35.7
561
10120
12x8x3-blade MAS
54.9
814
8560
13x6 MAS K
54.1
807
9020
EF CZ Yak-54
Generic BL25
12x5.25 Stock
55.1*
810
11890
13x6 MAS K
88.1**
1240
10010

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.

Sunday, September 11, 2011

Parkzone Sukhoi SU-26XP Flight Review

I've heard mixed reviews at best about the little PZ Sukhoi, which immediately piques my interest. If most people don't like a plane, that can be an indicator of a fine intermediate-to-advanced flyer.

The mini SU-26XP didn't let me down. Although there is plenty of room for improvement, there is a lot of fun to be had driving this little aerobat.

On the Ground:

The plane has a nice high-vis color scheme.  Top-bottom contrast is limited, due to the use of the same colors which tend to blend at range.  The biggest different is use of yellow on the top of the fuselage and horizontal stabilizer.  Overall, I like the scheme and it works "ok" in the air, though top/bottom orientation is more challenging than it should be. 
This airplane is a classic mid-wing aerobat with a molded symmetrical airfoil, theoretically giving it the same or very similar flight characteristics whether upside right or upside down.  That works too. The wings are about 40% tapered with no washout for simplicity and symmetry.  All of the control surfaces are oversize, with large aerdynamic horns on the elevator and rudder for greater effect and less servo demand. 
Nice big control surfaces, but a non-adjustable rudder control arm hurts the best knife edge flyer in the HH micro line-up.
The ailerons are huge, consuming about 40% of the wing chord, making them very effective at high and low speed.  They do not extend to the wing root, so they aren't blown by the motor when airspeed approaches static in harriers and hovers, perhaps adding to the difficulty the SU-26XP has trying to pull these maneuvers off.
The landing gear struts are nicely rounded, like the real airplane--a nice touch.  They are easily removed for a little less drag when hand-launching and ditching over grass.

For $100, the plane seems like less of a ripoff than most Horizon Hobby micros, but I would like to see it selling for more like $49 to see it better compete with other Chinese imports in its utility range. There aren't many other microbats on the market, but much larger aerbats sell for a similar amount of money.  We flown and reviewed several of these top notch performers in their price category.  They need a little more space, but not much and are more resistant to wind.  For example, this 30" span balsa and ply Yak-54 PnP is $60, or $90 with a 6Ch Tx and Rx:
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=13451
This Katana requires a receiver and an ESC, but it's also a big 45" span balsa and ply model for $119:
http://www.tiger.com.tw/product/4351-F00-03.html
This 36" Pitts is $79 as a PNP, $100 as an RTF:
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=11227
This AT Yak-54 is a Z8RC value favorite with a 36" span and a 4Ch RTF price of $99:
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=10350
As dominant as the models above are when compared to the capabilities of the PZ Micro Sukhoi, I was unable to find anything on the market that directly competes--a tiny, scale indoor/outdoor aerobat.

There are some flat foamies that are in the same size category, like this TechOne Piaget or Yak-54 (both airframes run $24):

But these planes both have the exact same exterior dimensions.  I mean come on, there is nothing Piaget (whatever that is) or Yak about either one of them, they are flat foam flying thingies with different printed color schemes and slightly different die cut profiles.

Part of the problem with going small is Rx size, some of these micros are under 1 oz total flying weight.  It seems that until someone comes out with a decent, 4ch bind-able truly micro Rx, besides Horizon Hobby, it looks like they have a monopoly on the scale UM market.  HH has license to release wildly over-priced and under-performing model after model, and the Su-26XP is no exception.  It contains about 2 cents of foam, reflects about $5 of foreign slave labor, a few dollars in common electronics and a 5 cent brushed can motor. 

Just to let some enterprising company know, if they came out with a high quality scale UM foam series that was bindable to any radio standard or even a proprietary one, I would pay a few hundred bucks or more for better quality than HH disposable junk without thinking twice about it.  An optional tailored hard shell case instead a giant foam box would be a huge bonus; obviously portability is the idea here.

All that said, the Su-27 XP is fun to fly and somewhat portable, at least while it lasts.  And it is "only" marked up about 20x to $100, a welcome relief from HH's usual 40x markup for their cheaply made, foam planes.


In the Air:

As I suspected, the S-26XP is a good aerobat.  A lot of people seem to think it is too unstable or unforgiving, but I found it very manageable, even mildly forgiving.  There are a few things it does very well.  Let's start with those. 

The one thing the micro Su does best, better than all other UMs, is knife edge flight.  Unfortunately, you have to have a programmable radio to do it, as it requires setting 120% rudder deflection, as the plane's physical control horn travel adjust is non-existent: there is only one hole (shown above).  With 20% more rudder, the Su knifes very well indeed, and rudder control at 90 degrees of bank is almost uncoupled.  It can even pull off a knife edge loop, though you have to be pretty high for the cheap brushed motor to reel-in the fall on the backside.

Another thing the plane does well is slow flight, though you have to stay right on top of it.  In this area, I need to distinguish between capability and effort level:  It has the capability to fly very slow, but it takes a lot of effort. In my last review, we saw the opposite, the triangular Stryker 180 flies slow rather effortlessly (just needs a ton of trim) but its slow flight capability is a more limited than the Su.

Flying the Su at high alpha requires attention.  Fortunately, neither the rudder not the monster ailerons washout, give you the ability to stay on top of the airplane as the wings or tips stall.  Even though the plane can be prone to sliding off to one side on a whim, you can upright it with timely control inputs.  This is especially helpful is slow turns, when the plane is most likely to want to roll over.  With steady but predictable guidance, the plane turns out to be an excellent nose high slow flyer.  The huge battery position allowance of the velcro lined belly, makes this trait even better and facilitates a lot of fun.

The best way to fly slow is to lighten up the plane with a lighter, smaller, more powerful and longer lasting (as in, time between buying new replacements) Hyperion or Turnigy 1S battery.  The induced 150mAh 1S is poorly constructed, heavy, and low voltage, resulting in a significantly lower thrust:weight ratio than is really necessary.   I flew my UM Su with a 138mAh Turnigy 1S with noticeably higher flight performance.

Here is my second flight, using the better 138mAh battery.  Not a lot going on but general flight characteristics testing.  Decent, beautifully uncoupled knife edge at 2:20:
The neat thing about flying the plane slowly is the ability to force a stalled wing back to level with the enormous ailerons.  At about 40% of the total wing area, the ailerons are so big they work all the time, even to right a stalled wing.  Working after a stall is the best definition of 3D capable.

If the Su had more power, it would be a fantastic 3D machine, but as sold the wimpy five cent 8.5mm brushed can motor and gearbox are barely adequate for aggressive conventional aerobatics.  A brushed motor is in this airframe's near future.

Aside from the loser power system and monster ailerons, the rudder is extremely effective but too throw limited to overcome the plane's lack of blowing power.  Knife edge flight is outstanding, but only possible with a computer radio set to 120% rudder throw.  Oddly, there is no physical throw adjustment with the stock control horn.  The plane can't balance on the prop as a result.

Elevator effectiveness is fine.

Float is adequate but not satisfying with the supplied 150mAh battery.  It is much better with a lighter Turnigy 138mAh.  Wing loading is a touch high for the planes unstated mission.  Adding a brushed motor could weigh the plane down even more, but I think it could still be an awfully fun flyer given enough power and vastly improved tail surface blowing.

In stock form the Su-26XP is a ton of fun, but it falls short in the power and throw dept to fulfill any hope one might have of 3D'ing it.  It just can't must the power and throws to match the raw capability of the airframe.  That said, the airframe seems to have a bad wrap as a poor flyer, nothing could be farther from the truth, the form flies great, but is let down by the Parkzone guts.  The ultra-cheap power system and tail throws limit the Su to more conservative maneuvering to keep out of 3D trouble.

Appearance: B
Nice looking airplane.  Top/bottom color scheme is too similar in tone.

Airframe: A
Great raw ability.  Needs more throw or blow--no surface throw adjustments.

Power System: D
Let down by 5 cent brushed motor.  Decent battery life.

Build Quality/Durability: C-
As good as Parkzone gets - below avg.

Value:  C+
Not as pricey as most HH micros at $99.

Overall Grade: B+
Very nice handling plane.  Ripoff motor.

Monday, September 5, 2011

Parkzone UM F-27Q Stryker 180 Flight Review

UPDATE:  Video added of top speed, low speed and stalls

UPDATE:  Video added.

I don't usually buy airplanes that are not scale classics.  The F-27Q from Parkzone is the exactly the kind of RC proprietary plane I typically avoid.  If there had been any micro competition available on the store shelf, anything, I would have bought it instead.  Monopolies ...uhg.
The name is funny in more ways than one.  Why "180?"  Well, it comes with a brushless 180, but so do quite a few UM models without the 180 designation.  The appended number seems to  imply a different motor or in-between model scale may be offered in the future--mSR "120" style.  Or maybe it is the way they want to distinguish the micro from its big brother, since "UM" doesn't actually show up in the printed name, only on the corner logo of the box?  At any rate, a name that leaves a question mark over your head kind of sucks. 

The little Stryker is mostly cute, maybe that's what the Q stands for?  The color scheme is overdone and under-performing, a little awkward and ugly, like its big brother.  For some reason it reminds me of a pack of Sunday bicyclers in gaudy racing regalia--too many stripes, lightning bolts and bold colors.  But after all that supersonic speed implication, the motor looks like it is missing a nacelle.
The wing spans 17 inches and the airplane weighs almost 3 oz RTF.  Wing area isn't stated, it looks larger than most UMs, but the plane feels heavy.  That heavy feel is a good indicator that it'll need some speed.

On the Ground:

Ok, it's never good when the instructions require you to disassemble then reassemble a "BNF" airplane. This UM is not a BNF, as stated on the orange edged box.  The instructions call for a DX6i or better, but using the plane with a DX6i first requires taking the fuselage apart, removing the receiver form the mounting tape, carefully wiggling out two servo plugs so you can reverse them, then put the plane back together and re-tape the fuselage closed.  PITA--and what's worse, it didn't work. Now, my F-27 only mixes elevons properly when I reverse the aileron channel, not the elevator channel as stated in the manual.  So I probably didn't need to disassemble anything. Sheeeze.

The Stryker comes with a new 200 mAh 2S battery.  It's a pretty heavy battery setup, but the flying wing should be very efficient, so already I have to wonder what PZ was thinking?  The battery hatch is nice.  It is plastic instead of foam.

Another interesting thing is the inclusion of rudders.  The larger Stryker has vertical stabilizers without movable rudders.
Also in the "OMG they final learned" category are the servo covers on the bottom of the wing, protecting the delicate PCB servo gears from scrapage.

In the Air:

Launching a plane without landing gear is easy, you just give it a light toss.  Right?

Well ...maybe not if the prop spins right over your knuckles as you release it.  In an instruction manual crammed with dire Saftey Warnings and fire-prevention Cautions, wedged within a mountain of Notices and Disclaimers, Parkzone politely warns: never launch the plane with the motor running.

Clearly, a brilliant plan.  A pusher with no option but a hand launch--freaking dangerous design.  Parkzone graciously added a pinch hold, just in front of the million-RPM brushless propeller.

First dead stick toss sought grass.  Plop.  Second one.  Plop.  Trim adjustment based on two glide tests.  Third one: stall to 90 degrees of bank, pointing down, throttle up, pull up, ahh, wings rocking, whoops, up and over, upright, and, ooooooh woah, there she goes!  Simple as pie.

Or so I thought.  After landing I discovered that one of those plops cracked the nose almost all the way  through the foam, under the canopy.  The little pointy wing slat tips were rubbed off on one side by nicely manicured lawn grass.  The foam is weak. 

So if you don't mind breaking your first $160 foam frisbee the first time you dead stick it, which is Standard Operating Procedure for takeoff, the little bird is actually easier to launch after you manage to get it trimmed up.

Once plowing clean air, this little Styrofoam dentist drill goes pretty good.  The wedge design is interesting to fly.  Not exactly a drag machine, this UM flies quickly by default.  The nose is easy to control, and level flight can be dialed in with trim at a comfortable cruise pace.  The plane pulls pretty long and wide with an ability to change speed a lot faster than you can change trim, making throttle setting something you need to think about and prepare for, more than other planes.

In a straight line, dynamic stability is very good.  Static stability  is not.  The platform waggles at the slightest perturbation from a breeze.  After the plane waggles for a while you might get used to it, when it's tracking nicely you start to wonder why it's not waggling.
My kludgy Canon HD camera is arbitrarily 
limited to 10 min clips.  The horizon was straight, 
it is the camera that's tilted.
A slow speed, stabilized turn fits inside a baseball diamond; a top speed turn consumes the entire outfield.  Speeding up in a turn makes it hard to keep the nose from climbing, and vice versa.  The rudder is effective and can help guide the nose until the trim catches up to the airspeed, but I have to admit it is eerie feeding-in nose-down rudder on a 90 degree knife edge.  Slowing in a turn is a lot more dangerous, as the nose wants to fall strongly.  I have never seen an RC plane with such a wide range of required trim settings, it uses perhaps 75% of the available trim range, from full back to about half forward.

High rate, slow speed turns reveal some of the mini-Stryker's most endearing flight characteristics.  The flying wing is very resistant to stalling.  There is no discrete elevator to twist the wing on its lateral axis beyond critical Angle of Attack.  The wing itself must generate the force to go beyond critical, and once approaching critical AoA, any twisting moment needed to increase AoA is naturally reduced--result: great stall resistance!  The elevons tend to wash out and loose effectiveness before they can lift the nose into no man's land.  Burying the elevator stick more than halfway into your lap while reducing throttle results in very forgiving high alpha slow flight.  To wallow around just beneath the stall, the plane's elevons tend to stay more effective than the rudders.  Rudder airflow is partially asked by the wing at high angles of attack.

Bottom line on stall characteristics: as long as you increase back stick pressure smoothly (so the wing doesn't go ballastic to near-zero airspeed), the little Styker might wallow and waggle, but it will never quit flying.

The crank is a little reminiscent of flying an F-16.  As long as you maintain some speed in a turn, the nose continues to rate very strongly as vorticies roll off the steep strakes, up and over the the central area of the wing and lifting fuse.  The conventional main-wing sweep funnels span-wise flow to the tip vortex.  The result is a nose track that keeps on giving.  Important safety tip: don't get into a low speed dual with a cranked arrow unless you're sitting in one.  This thing is just plain fun to turn aggressively long after you think you can't.

Here is a video of the mini Stryker's top speed (impressive), bottom speed (pretty darn good), and full aft stick stalls (tame):
0:09 mins: Normal, Nerve-Racking Launch
1:17 mins: Full rate Aileron Rolls (note coupling)
4:45 mins: Bottom Speed, accelerating to:
5:45 mins: Top Speed 
6:00 mins: Loops
8:00 mins: Full Aft Stick Stall
Loops are bigger than one would expect for no elevator arm, and aileron rolls are not axial, they are surprisingly coupled--might need a control throw adjustment.  Pulling too hard on the nose occasionally couples to roll, especially when the plane is pointing away from gravity.  This plane isn't gonig to win any pattern competitions, but it is inherently stable in level flight.

Spin rate varies upon the spin mode, but all conventional modes have one thing in common, the ground comes up fast.  The Stryker has a conventional spin mode that resembles Barrel Rolls in the vertical.  Placing the sticks in various corners produces widely different spin traits, from spiraling down to winding up like a pinwheel.

If you enter a conventional spin with pro-spin aileron, then reverse direction and invert the elevator, the plane can be coaxed into a very rapid, pinwheel-like flat spin.  While a conventional spin leaves one wing flying (below critical angle of attack) around the other wing that is stalled (below critical angle of attack) causing auto-rotation, the aerodynamic driver of the pinwheel effect is less clear. The plane appears to rotate about  the front of the nose, with both wings subscribing the same flat arc around it.  The rate of fall is much slower than a convention spin mode.  My pinwheel spins aren't quiiiiite as tight as the Parkzone demo video, which appears to rotate around a point closer to the canopy.  I don't know why. 

Flight times are great with the included 200mAh battery, 15 minutes or more, but the plane is too heavy.  Again, a big swing and a miss on stock battery selection.  Maybe the designers were going for top speed and/or high speed stability, not realizing that weight slows the airplane and it is plenty stable flat out.  Slow speed handling quirks would benefit greatly form lightening the load.

The last thing worth covering is the small size for the huge speed envelope.  This little buzz saw can get hard to see in a hurry.  This is complicated by the flying wing design, which is inherently difficult to orient, and an ineffective color scheme in the air.
Overall, the UM Stryker is a design exercise in extremes.  It goes extremely fast, it spins extremely tight, it's slow speed nose tracking is extremely effective, and the foam nose is extremely weak.  What the daredevil does not do well is find middle ground.  Tooling around at a comfortable pace is not this plane's forte.  Still, it is relatively easy to fly, as long as you keep it in sight.

Appearance: B
It's ok.

Flight Performance: A-
Nice turning performance.  Some wing waggle.  Huge speed envelope.

Build Quality/Durability: C
Weak nose.  Finally included external servo covers.  Prop exposed on landing.

Value:  D+
Way too expensive for a UM boomerang.  Should be more like $79 BNF.

Overall Grade: B+
A- but too expensive.  Quirky, but fun.  Trim hard, trim often.  Find a BIG park.
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