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Thursday, July 28, 2011

Parkzone UM Pole Cat BNF Flight Review

Nice looking little plane, but the beauty 
of this bugger is more than skin deep
pole·cat (n).  A chiefly nocturnal European carnivorous mammal (Mustela putorius) of the weasel family that ejects a malodorous fluid to mark its territory and ward off enemies.

Hmmm, ok, well, uhm, with that out of the way...

Great News!  The PZ UM Pole Cat is not one of those smelly fanged rodent thingamajigs.  But whatever it is, it comes as close to hitting it's quasi-advertised mark as any Horizon Hobby micro I've tested since the magical Hobbyzone Champ RTF landed in stores.  Having bounced off Mach 2 for much of my life, personally, I find it both more relaxing and more challenging to fly slow than fast, at least as it pertains to this hobby.  Nevertheless, the Pole Cat is an undeniably endearing little punk with both attitude and character.  It is swift and stable in pitch and yaw, and very quick to roll--more on that later.  You get what you are promised: a little speed and a lot of fun.
The PZ UM Pole Cat doesn't have a 
lot in common with its 1:1 namesake
The purpose-built nature of the Pole Cat is the best UM design effort to date.  Not because it is complex, because it is simple.  The airframe is aerodynamically suited to task, which is, presumably, to accommodate bulimic mice that want to pylon race.  The wing employs a molded airfoil cross section, thankfully.  The base material is $1 ice chest style Styrofoam, weak at best, but there are no exposed PCB servos or delicate plastic gears to drag over pavement, everything is tucked inside the fuselage.  Even the pushrods to the tail surfaces are mounted above the horizontal stabilizer to avoid constant scrape-age.

The only drawback to this terrific simplicity is single channel aileron counter-motion, without the possibility of scheduling flaperons or spoilerons, but that is a small price to pay for HH finally getting the basic layout right.  The real jackpot is a lack of parasite drag from servos and wires and rods and horns--from top to bottom--this stinky-ass euro-kitten is squeaky clean.
The shiny chin and leading edges are from aftermarket 
scotch tape.  Guess I've dinged-up too much foam in my life.
The plane looks and feels almost too simple, I keep wanting to open a hatch or see a servo swing, but there is literally nothing to see here so move along.  The battery sticks to the CG.  That's it.  Well alright, the landing gear pinches out too, for those who want to hurry up and crash-land.
The PC uses a standard 130x70mm Champ prop.  
The motor is well sealed--is it really any any 
bigger, or just geared to spin a bit faster?  The answer
lies on the parts list: it's the same tired, unreliable 
brushed tin can used in most HH micros
This sleek Cat looks an awful lot like an Edge 540 or Extra 300, with a near-straight wing leading edge and small forward sweep of the mean chord. However, it doesn't fly like either one, at least not as set up.  The Edge/Extra design genre is awfully slippery and well suited to any race format that turns rotten dinosaurs into some optimum combination of knots and G, Red Bull style. But where those fiendishly aerobatic designs deviate from the Pole Cat is in the amount of say they give the pilot.

The Pole Cat is different because it doesn't allow you explore the limits and quirks of its inherent stability, there's not enough control surface to get silly.  One glance at the hind end of the Pole Cat reveals an apparent lack of control surface area, and an even more disturbing lack of travel.  It voluntarily leaves the Edge and Extra's huge barn door rudders and big aerodynamic balance horns at the airshow.It takes a highly symmetrical airframe and extracts as much low drag straight line slippery speed as it can break loose.

In the air, the most critical concerns are alleviated with comfortable elevator authority at or near full rates (low rate settings need not reduce elevator travel a heckuva lot).  Rudder authority is minimal.  But straight line speed doesn't demand a lot of yawing and tumbling and assorted Jedi mind trickery, so the design pays dividends.  That said, flat out speed is not outrageous, out of control, or even very spooky, but it is a step above its micro siblings.  It zips.

The result of the plane's go fast first philosophy is better built-in stability than most flying micrometers.   This plane changes heading using its lateral axis, alone.  Kicking the rudder only yaws the plane a little, with no secondary axis coupling.  Holding full rudder for what seems like an inordinate amount of time doesn't change the flight path very much.  In contrast, the Cat rolls effortlessly on the longitudinal axis, and again, with no secondary coupling due to the perfect mid-mount wing.  Neither sideways stick does much in the way of redirecting mass and energy away from the crowd.  That leaves pitch.  The lateral axis is the only effective pivot point capable of altering your flight path.   Roll to place the straight-up lift vector on the new flight path target, then pull to align the nose with destiny.

I like it.  It is fun.  And what more do you really need from a 1-cell torpedo?

Well, I'll answer that.  A little more top end speed would be nice.   Don't blame the airframe, blame the wimp can motor and gum stick battery.  That said, the plane is clearly faster than the other HH micros, and it manages to poop just enough goose juice to deliver some real fun.   The plane's achieved top speed with so little oomph proves that sexy isn't the same as dirty.  At 35g with a 150 mAh in the bomb bay, the Pole Kitten packs a meow instead of a roar, but it also lugs half the mass and fewer strap hangers then the brushless  Sbach, with similar airframe dimensions:
Get off me!
In the end, this plane simply works.  The sleek, simple exterior, the faster gearing, the stability in the air--even the $100 price tag is better than Horizon's usual Ultra Micro value proposition.  If this plane sold for $59, I could give it an A+.  At the $100 price point it gets:

Appearance: B+
Cute plane; color scheme seems stale.

Flight Performance: A
Nicely aligned with its fun theme.

Build Quality/Durability: C-
Molded Styrofoam airfoil; embedded electrics; crap motor--still a foam plane.

Value:  C-
Less face it, at $100 this pipsqueak is overpriced.

Overall Grade:
Fun factor rules in the end; you'll want to fly it a lot.

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)

Wattflyer Moderator, rcers

Known child pornographer clown
Update 3: Moderators at underage-child web front Wattflyer.com are again bad mouthing this site for whistle-blowing the secret links on Don Simm's sham RC forums.  You might want to de-register before the fallout.

Update 2: Looks like the "The Wolfe" (played by Harvey Keitel) paid a little visit to Don Simm's wattflyer to "fix" my signature, maliciously altered by the adolescent-moderator rcers, by deleting it altogether (visit the scene of the crime).  Gee Don, when you have to sanitize your website to keep the feds away from shutting you down for linking to underage child websites, that's when you know your moderators are professional.  Clown act. 

I'm considering changing the Z8RC banner from "Advanced Radio Control" to "No Links to Child Porn."  Let me sleep on it. 

Update:  Z8RC just got a defensive email from Don Simms of Watt Flyer.  No apology, no rebuke of his moderator's adolescent abuse of his own members, no statement that he will take action to uphold their own privacy policy.  Amazing.

If you post on Wattflyer, please understand that their moderators are childish and they have been given free reign to secretly edit members posts without their knowledge or consent, fully condoned by the site owner Don Simms.  

Kids, these days....

Here is a quote of my reply to Don Simms regarding the blog article I originally linked only from the wattflyer signature that his own moderator had previous edited (other z8rc visitors wouldn't see it):


Re: WattFlyer RC Electric Flight Forums - Discuss radio control eflight Contact Us Form - Moderator abuse
...
To:Don Sims <don07tncav@gmail.com>

A well deserved joke (got email laughs from Wattflyer members, btw) after rcers' violation of your own ignored privacy policy.  But I've toned that down. I don't want a joke to pull my blog down to your level even if justified. 

But thanks for the reply, apparently you approve of your moderators changing member signatures.  I'll be sure to and that to my blog - that I got an email response from Don Simms official condoning of rcers repeated adolescent meddling with Wattflyer member signatures, without their knowing or consent.

It's a shame the low maturity level of site owners like you can't see when they owe their members an apology, and fire their own mistakes.  But I've grown to expect that from kids these days.




End update, blog article follows:


I found out a disturbing fact today:  Wattfyler moderator rcers has been redirecting my Wattflyer signature to an underage child website. When I called him on it, of course he banned me for his own atrocious behavior. Gee, like I didn't know that would happen. I would never consider remaining a member of a site like Wattflyer, where the moderators think its funny to maliciously edit member posts to their adolescent liking,  managing to exploit children at the same time.

Wattflyer.com is a disgrace to the RC community.   Done with those lawbreakers.

Saturday, July 23, 2011

Parkzone UM F4U Corsair Flight Review

Update: Jiggy Gets a Heart Transplant

Update:  Nano Corsair video link added.

A lot of people probably think I hate Horizon Hobby products. That's not true, I hate products that suck, and Horizon Hobby's value proposition generally sucks bad. As much as I wanted to like the little UM Corsair, it proved to be no exception to the "Horizon Hobby sucks" rule of thumb.  For the record, HH has plenty of representation on my highly recommended list, to the right.....
On the ground:
First the good news:  as you open the box, the little Corsair looks great, it has a few extra details over previous UM models from HH.  Also showing movement in the the right direction, Horizon has been listening to me (I say "me" with certainty, because this blog is the only source of much needed criticism on planet Earth-- all the other "glowing" internet reviews are bought and paid for by HH directly or indirectly; nothing more than thinly veiled advertising stunts) and this model is a bit more robust than their previous offerings.  It has a molded airfoil cross section wing unlike the usual, ultra-cheap stamped out or die cut flat-foil foam wing, as well as a molded tailplane.  For their willingness to take constructive criticism and improve, I give HH kudos.
Now the bad news: Unfortunately, HH still has a ways to go on build quality, the Corsair is still pretty flimsy overall. It still ships with exposed PCB, exterior mounted, very weak micro servos under the wings--the predicted durability of the wing servos alone is well below sea level.  An unfortunate artifact of Horizon trying to improve their lowly UM airframe durability is excessive weight, the UM Corsair weighs in at a portly 1.5 oz.

The antique brushed motor has an uphill battle to fight, and it is certainly not a winner. The little motor and gear box are overtaxed with the new 3-blade 110x80 prop. 4:50 minutes into my very first test run to determine typical flight time (50% throttle until LVC), the main reduction gear stripped to the point of chronic slipping. Subsequently, advancing the throttle above 40% produced nothing but pathetic screams, screeches, and wails. A new nylon reduction gear from an extra gearbox I had laying around in my misc micro parts drawer fixed the problem, for now.  PZ should not interface a hot brass motor pinion with a cheap nylon reduction gear when there is zero cooling airflow, due to the solid motor facade decal.

In order to keep heat under control on future runs, I sliced out a small inner circle from the engine sticker to expose the micro gearbox and motor to some cooling airflow, as shown behind the prop hub below:
Horizon continues to release seemingly untested, failure prone junk at premium price tags.  My UM Corsair was dead before it ever got airborne.  If the BBB doesn't lock Horizon Hobby's doors and fumigate the building, I'll keep hammering on their peculiar brand of gross negligence until they are shamed into competence.

Thrust from the 5 cent, brushed, 8.5mm can motor and the 3-blade prop is poor. Full throttle produced a whopping 0.7 oz of thrust, making the UM Corsair the most underpowered PZ UM yet with a 0.47 Thrust-to-Weight ratio.  Even the Hobby Zone Champ would clobber the UM F4U in a two circle rate fight, with its more respectable 0.77 T:W.

This UM F4U is way too pathetic to wear the venerable, 2800hp, 440 mph, twin-radial engine "Corsair" badge, so from this point on I'm going to call it Jiggy.  Switching out the prop to a 130x70 increased Jiggy's ultra micro horsepower substantially to 1.0 oz, resulting in a greatly improved T:W of 0.67.  That's about 42% more power with longer legs.  Still, it is nothing to brag about.  The only problem with the larger prop is the reason for a real Corsair's inverted gull wing configuration in the first place, on takeoff the prop tips begin to graze pavement as the tail rises under power.
A 130mm 2-blade results in 42% more installed thrust,
a welcome boost to anemic performance
I don't blame HH for wanting the scale look of a big honkin' 3-blade paddle. I do blame them for not understanding the very basics of aerodynamic propulsion.  A 3-blade absorbs more power per unit diameter, which is exactly why the original twin-radial Wasp used a 3, and later 4-blade propeller.  HH including their same, tired brushed motor to drive a decent size 3-blade was a plan doomed to fail upon conception. 

In order to make their wimp motor viable, HH reduced the diameter of their standard 13 cm prop offering to just 11 cm, apparently not understanding the consequences of installation error.  I'm sure their 11cm 3-blade test prop produced reasonable power compared to the old 13 cm 2-blade on the test stand, but Jiggy has a large, scale radial cowl.  The installation losses in such a configuration become unacceptably high as a percentage of total thrust as diameter decreases, because only a small portion of each paddle digs unblocked air.  The solution, of course, is to account for airframe installation losses in the design phase, but unfortunately, RC toy makers like Horizon are cluedo when it comes to deep-dive design, they just copy pictures.  I recommend that all HH toy designers read my blog article on this topic, before beginning another similarly doomed project. 
The decals look pretty nice, partly because I had to apply them.
The next glaring problem is value.  At $110 as a BNF, this 16" span mini pig costs way too much.  Even its  high-priced big brother (44") is a better value, and sports adequate performance.  Of course you can't fly a much larger plane in your front yard, but that's a small consolation prize for putting up with HH's rip-off price tag for mediocre performance with junk component quality.

The competition:
Unfortunately, Jiggy gets blown away by much higher performing, lower priced competition:
21.5" (cubed difference = 2.5 times larger model) 4ch, 10A brushless
motor with better scale detail and higher quality internal servos.  $69 PNP
or $84 as an RTF with a solid full size 4ch 2.4Ghz Tactic Radio

Hobby King 40" F4U Corsair PNP
This 40", 5ch 20A brushless Corsair is $69 PNP
32" Hobby King F4U Corsair PNP


31" 5ch, 10A brushless for $69 PNP
In the air:
Jiggy looks the best and flies the worst of the entire UM series.

My first test flight was cut short due to increasing winds, but was plenty long to confirm that Jiggy has Ultra Micro power.  My unrealized hope was that the high wing loading of the plane would make it a little more apt in light wind.  Bzzzzzzt.  No.  The plane was helpless in 5-8 mph winds, revealing both underpower and under-control.  Flying with the 130x70 nailed on is much more satisfying way to burn dinosaurs, but the plane is still light on thrust. This Corsair wannabe is begging for a brushless upgrade--but that's assuming the basic airframe is aerodynamically sound, which it's not.

Once trimmed up, the plane is fundamentally stable in roll but not pitch, making it too inconsistent to fly enjoyably across a range of airspeeds in sport mode. It wants to dart up/down, after it does it wants to roll over on its side for lack of power, or tear for the dirt due to an abundance of weight.  The plane is too underpowered to fly in any mode other than sport, which doesn't leave a lot of options. Could be tail heavy as shipped.

You'll need to move the aileron pushrods closer to the control surface to get more throw, the plane struggles to complete an aileron roll as set-up by PZ. Unfortunately, the plane has so little oomph that large deflections are lossy in the airspeed dept, so you still need to supplement with potential energy to pull off a decent roll.  Using high deflection ailerons also risks reverse direction rolls once slow, due to the up-going wing (down aileron) stalling shortly after airspeed poops in the gutter.   Loops are best accomplished from a downhill entry with the 3-blade installed, better with the wider 2-blade, but mild aerobatics are still thoroughly unsatisfying.

Rudder deflection is very effective, but the influence of the vertical stabilizer on straight line yaw stability is pretty low. I need full right rudder to takeoff but not to counter high throttle/low speed torque in the air, possibly a wheel friction differential or airstream blockage with the tail low.  In the air, rudder control definitely helps to get the plane lumbering in the right direction, but couples heavily with pitch-down.

Oddly, the plane has rare moments of solid high alpha, low speed flight--until the flight path needs to be corrected--then it falls off the rails from a lack of helpful control surface guidance, the inability to power out of any induced drag hole, and out-of-square wing root stalls, likely due to improper washout geometry in the inverted gull's airfoil.  A quick look down the wing, from tip to root, reveals that undercambered airfoil is at its highest AoA at the gull's wrists. This is certainly a contributor to Jiggy's bottom-feeder flight characteristics, since the most severely stalled wing-section tugs far too from the fuselage, inducing yaw which quickly couples to roll as the opposite wing gets kicked into the relative wind like a seesaw, resulting in forward sweep.  It's the same inherent instability and lousy tracking that one feels from leaving the flaps down during cruise.

The cheap Rx has discrete aileron servo plugs, but the internal electronics are a Y connection instead of 5 ch, eliminating the possibility of differential, spoiler, or flap movement.  That's unfortunate:  plenty of vices to iron out; limited options.


Z8RC Verdict:
This plane is woefully outclassed by relatively high amp, brushless competition selling for less money, and is a marginal performer in the air.  I can't imagine anyone, who is aware of the competition, buying Jiggy given it's price point, tiny scale, and handicapped performance.  Along those lines, after this HH UM sucked so bad, I decided to try the BlitzRCworks 21.5" 2 or 3-cell Nano Corsair for $69.  It rocked Jiggy's world:

In the end, gave the plane my lowest passing grade, despite junk components and poor flying qualities.  While I feel violated by HH's lack of a rational value proposition for this lazy, misbehaved micro warbird, it wasn't quite as painful as usual at $110 as a BNF and $140 RTF.

HH continues to target novices who seem fine paying out their nose for chimp engineered toys stuffed with the most fragile Chinese garbage, all wrapped up in a catchy paint job and sold using their socialist-European price-fixing business model.  They obviously think their sales scheme is a winner.  It's not.

I could recommend Jiggy to people who don't expect a whole lot more than a cabinet display at a BNF price point around $40-50 retail, maybe as high as $65 in RTF form with Horizon's typical UM toy radio. 

Appearance: A-
Flight Performance: C- (HH can never say I'm not a kind person)
Durability: D- (assuming my gearbox failure was a fluke)
Value: F
Overall Grade: D-

Monday, July 18, 2011

E-Flite UMX Sbach 342 BNF Review

UPDATE:  See: http://z8rc.blogspot.com/2012/01/z8rc-umx-3sbach-342.html

E-Flite's latest UMX is the Sbach 342 mono-wing aerobat. It looks damn fun.  Is it?
The Sbach is the first in the UMX series to include side force 
generators.  There are two sets included with the model, adding 
almost a penny of extra foam at no extra charge.
In typical E-Flight fashion, they've priced the UMXS342 like an unwatchable rerun of the Twilight Zone.  For $170 you get a 4ch micro-foamie, a 180mAh 2-cell chicklet battery, 2 pairs of die cut foam slip-on side force generators, and a 12V DC charger with no AC power cord so you cannot plug it in. Plugging in the battery charger will run you another $20.  The battery uses a proprietary 2S connector, so you'll need to buy another at about $20 street price.  Total cost to operate: around $210, before adding a transmitter.
MIA
But I'm willing to fly anything for the betterment of the Human race, so let's have a look.  Trust me, I'll let you know if the little guy is worth the money.  Unlike every other review you'll find on the sleazy RC sales forums, Horizon Hobby hasn't paid me to regurgitate a mandatory glowing review. 
The Scotch tape holding the plane together looks 
like it was applied by a 5 year old.
 
Black is one of the better colors to maintain a visual in the air.  
This is a nice contrasty color scheme.
The engine bay is reminiscent of the UMX Beast.  But E-flight
has included a 180mAH battery this time, instead of 120mAh,
making the $170 price tag a few percent less ridiculous.

It would be nice to fly the Sbach indoors, but like the Beast,
it will need a very large indoor venue
There's no doubt the Sbach 342 is a nice looking microbat.  My guess is, if you knew nothing about RC, you might peg the plane's price at $30 or $40, certainly not near the $170 that it'll carve out of your wallet. But I'm immune to E-flight's utter lack of self awareness at this point.

Unlike most of E-flight's UM(X) offerings, the Sbach has a molded airfoil cross section, more similar is the lack of structural reinforcement.  The control surfaces are exceptionally over-size, with the aileron consuming almost a third of the wing area, and the elevator and rudder consuming about 2/3rds of their respective stabilizer area.  The servos are the usual exposed PCB, linear travel, Rube Goldberg specials, with the plastic gears all set to scrape pavement resulting in instant death.  I might be teachable, and fashion some sort of protector before leaping above terra firma and landing in Horizon Hobby's overpriced parts isle.

Predicted usable lifespan: less than a month in the hands of a careful expert.
The plane's weight seems reasonable for its power system, which was lifted from the solidly aerobatic UMX Beast.  The Sbach weighs with a battery at 66 grams, or a touch over 2.3 oz, that's about 0.1 oz heavier than it's Beastie brother.  The additional weight is more than accounted for by it's 50% larger stock battery, which weighs 0.5 oz. Thrust to weight ratio should be the same at 1.3 to 1, at least for the first minute of flight or so.

Before we fly this whirling dervish, E-Flight's stratospheric pricing mandates a look at the broader market:

This gorgeous 39" span Hobby King Sbach 342 runs:

Quantity Product description Price Weight

Sbach 342 1000mm Balsa (ARF)
$85.99 2299

TURNIGY Basic 25A v3.1 Speed Controller $15.01 45

Turnigy 1300mAh 3S 25C Lipo Pack $19.98 350

HK-933MG Digital MG Servo 2.0k.. $33.44 140

Spin-40-4 - Spinner 40diam / 4mm shaft $3.42 29

Turnigy Park450 Brushless Outrunner 890k.. $13.05 119

Turnigy balancer & Charger 2S-3S $4.49 99

OrangeRx Spektrum DSM2 6Ch 2.4Ghz Rx $5.99 39
Total: $181.37 3120g








 Air Parcel (UNITED STATES) - $36.54
Your Total $208.38




Let's see that's 3120g vs. 66g.  In pre-built balsa and plywood, not foam.  In standard 3S, not proprietary 2S.  And in 6ch, not 4ch, with dual ailerons, not a Y-connection.  With a brushless 28mm, not a toy 8mm.  Has E-Flite gone bonkers?  Crooked scotch tape?  Really? 

This Extra 330 is $119 sold as an RTF, 
plus you get this great looking girl
Hey, is that an AC Adapter?
Flight review here, soon.  Here is a pretty lousy video of my Sbach's maiden voyage.  Unlike most of the maiden videos on the web, this actually is the maiden flight.  
Given how nose heavy E-Flite shipped their UMX Beast, I decided to use the Beast's 120mAH battery, it balance at the 25% chord mark.  The plane was perfectly balanced in the air with the lighter battery. 

The 120mAh battery flown in the video had been laying around a while and obviously wasn't fully charged.  Subsequent flights last about 8 mins with the 120mAh and as long as 12 mins with the included 180mAh.  The plane flies better on the smaller battery and unlike the draggy UMX Beast, the Sbach does not need the additional battery capacity.  It's another E-Flite miss on included standard equipment due to an unsophisticated understanding of basic aerodynamic trades.  It's not a big deal, the plane flies fine with the heavier nose and may be more suitable for the targeted amateur demographic, but the plane will be a stretch for beginners so if that was E-Flite's idea it makes little sense.

The UMX Sbach flew terrific right out of the box and is definitely suitable for intermediate fliers.  It takes a bit of rudder attention to keep the plane pointed where you want it to go, and it can hang on the motor, but the plane is very docile for an ultimate aerobat and can be slowed down a lot on about 45% power.  I started with 50% travel/50% expo for my initial low rates, but could have went with 60%/60% while retaining a bit of under-control.  100% throw is not outrageous, but rolls are quick.

What look like snap rolls (i.e. rudder induced auto-rotation) in the E-flight demo video (at 1:13) are actually quick and easy full rate aileron rolls.  Obviously, there is significant roll coupling due to the off-axis low wing.  But that only detracts from purists issuing grades, not from the fun of flying.

The 342 performed basic loop and rool aerobatics without issue, with the exception of roll coupling  from the asymmetrical wing placement (not on the thrust line or the longitudinal axis).  Full rate rolls are very fast, and loops can be very tight until the wings stall and roll out.  Inverted flight is good, with light down elevator required with the lighter battery, and moderate down input with the heavier battery.

Knife edge flight cannot be maintained in the base configuration, but is easily sustained with the SFGs on the wing tips.  The SFGs have a stabilizing effect in general, and make the plane a little lazier which some will find both more relaxing.

3D type maneuvers, including hovers are a challenge for such a tiny Reynolds Number, but the Sbach is as controllable on the prop as any micro I've flown.  Unfortunately, it stretches it's legs quite a bit and consumes a lot of airspace for a tiny plane, which will make ultra calm winds of indoor venues more difficult to enjoy.

The mini Pitts M12 Beast has the same big airspace footprint, is more toss-able, but not nearly as precise.   It is better on a knife edge, but not once the SFGs are attached.  The Beast is easier to slow down, and seems to have lower wing loading even if it is more nose heavy.

Slow speed flight is very possible with the Sbach, but will be more exploitable with considerable experience balancing high AoA with high power with required rudder--as torque becomes a dominant influence at lower airspeeds.  It's not a big wing floater, it hangs on the prop to go slow.

Thrust is copious.  No need for more, and that is saying a lot in my book.  At the same time, the nose is not too heavy and flight times are good at 8-12 minutes depending on a combination of battery size and throttle management.  The prop seems like a good choice, but I have a few GWS props in mind that might translate some of that long flight time into more performance.

Landing is about as easy as a micro gets due to the high alpha margin for error, fairly docile flight characteristics, and a well balanced glide especially with the 120mAh battery.

The UMX Sbach 342 is a great little airplane.  What a shame that it is so painful to purchase, especially when there is so much fabulous full size competition in it's price range.  Final grades are pretty easy:

Value: D+ (high price tag, lower priced competition, but great micro performance)
Build Quality/Durability: D (a bit more beefy than other unsatisfactory E-Flite micros)
Performance: A (more like an A- but with bonus points for great handling SFGs)
Overall: B+ (Recommended-  if you are stupid enough to break out $200)

Yes.  It is damn fun.

On Washout


Chris wrote;
"I don't have a good understanding of washout, its relationship to tip stalling and how the seemingly common practice of altering the default position of ailerons and flaps helps matters."

The Wiki definition that you quoted is close to accurate.  The bottom line is that washout strives to make the wing tips stall after the wing root stalls.  When a wing tip stalls first, the wing drops hard and the airplane could begin to spin (a spin is a fully developed flight condition where one wing is completely stalled and the other wing is not, so the un-stalled wing is literally flying circles around the stalled wing).  Since airplanes often fly near the limits of a stall when close to the ground (e.g. the landing phase), a wing dropping hard or a spin at low altitude can be especially undesirable.  

One way to build-in aerodynamic washout is by repositioning the ailerons (assuming they are near the tips).  By deflecting  both ailerons up a little, you effectively change the airfoil cross section near the tips so the tips produces less lift than the roots with the ailerons in their default position (trailing edge slightly up).  

This really isn’t a pure solution, because it is not designed in from the beginning, meaning that you sacrificing some of the design lift of the wing, and consequently, you are carrying a bit more structure than is required to build the wing since it isn’t producing as much lift as intended.  The end result is that you’ll experience higher landing speeds and require a faster cruise than the aircraft as designed.  Basically, you are flying with wingtip spoilers deployed, all the time.  

With real washout, designed from the ground up, the total lift of the wing will still be appropriate for the aircraft even with the washout built-in.

“What are the symptoms?”

The symptoms of no washout are different from plane to plane, depending mostly upon airfoil type.  A low performance airfoil, which is flat on the bottom and curved on top, or heavily asymmetrical, experiences a very sharp loss of lift upon stalling.  So low performance aircraft like Cubs and Champs and most high wing trainers, are more vulnerable to tip stalls, since the loss of lift is more dramatic once stalled. 
So a high wing trainer, with a flat bottom airfoil and without washout, would be expected to drop a wing hard as a stall develops, and maybe spin, because it is very rare indeed that both wing tips are experiencing absolutely identical flight conditions and that the aircraft is flying perfectly straight and true.  

An aerobat with a symmetrical airfoil (exact same curvature on the bottom as the top) and still without washout, loses lift more gradually as the wing stalls—it does all go away at once.  So a high performance aircraft doesn’t care as much about washout.

“What's the source of the problem? How does one fix/mitigate it? The PZ 109 has a reputation for tip stalling on approach. Is this a washout problem or something else?”

Hopefully the text above covered most of those q’s.   I’d have to look at the PZ 109, but it sounds like a fundamental design flaw that might be mitigated with some washout.  

Plane most susceptible to tip stalls are planes with asymmetric (low performance) airfoils with the most even lift distribution from root to tip.  IOWs, if you look at the total amount of lift produced by the wing and then chart the distribution of that lift from root to tip, a tip-stall prone aircraft will produce a lot of lift near the tip.  An aircraft that is not prone to tip stalls will produce proportionately more lift near the root, and less at the tip.
This can be done lots of ways, not just with washout.  For example, with taper.  If you taper the wing, the tip’s contribution to total lift is relatively small compared to the root, so even the tip does stall first, it’s not as big a deal because in relative terms, not that much of your total lift is at risk.
Another way is with aspect ratio.  A very long thin wing, with the same wing area as a very short and stubby wing, has wing tips that are farther away from the fuselage, making tip stalls more of a problem.

So in general..

Aircraft that are more vulnerable to tip stalls:
  • ·         Use low performance airfoils (flat bottom or similar)
  • ·         Have little or no taper , like a simple rectangular wing plan form
  • ·         Have relatively high aspect ratios, or long thin wings
  • ·         Benefit the most form incorporating some washout
Aircraft that are less vulnerable to tip stalls:
  • ·         Have high performance, very symmetrical airfoils
  • ·         May have tapered wings, or a smaller chord at the tip
  • ·         May have stubby, low aspect ratio wings
  • ·         Benefit less from washout
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