Searching Z8RC.com for the best match.........

Tuesday, March 29, 2011

Yak vs. Yak - Round 1

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


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

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

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

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

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

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

.....

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

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

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

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

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

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

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

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

...more to come...

Latest standings xls (soming soon):

Saturday, March 26, 2011

Spektrum DX8 Review

UPDATE:  Also see: Half of DX8 users report "unresolved" problems

UPDATE:  Also see: Head to Head: Aurora 9 vs Spektrum DX8



UPDATE: March 27, 2011.  While conducting an Aurora 9 vs Spektrum comparison, the DX8 dropped a link and destroyed the Z-8 all time fav Pitts Special.  Level flight, left to right pass, 40% power cruise, aprox 100 feet away and 100 feet high, the beautiful little RWB starburst Pitts popped up then slow rolled over to the left, no control whatsoever as the Spektrum radio system nosed it straight down into the dirt.  Likely an airborne receiver reboot with too little altitude to affect a complete reboot.
This my third model crash under an eerily similar, uncontrolled flight profile.  I call it the "Spektrum rock'n roll over"  Interestingly, the first two were with OrangeRx brand DSM2-compatible receivers.   However, that model (crashed twice from Spektrum loss of control) was my 4S 850W+ F8F Bearcat, which was probably too susceptible to brown out.  After doing more research on the topic of Spektrum brownouts, I learned that only 3S and lower powered models may be used safely with Spektrum radio systems.  With 4S+, you MUST buy a dedicated third party BEC, as 4S+ ESCs without a dedicated switching BEC cannot be used with Spektrum radio systems.  I apologize for incorrectly attributing these crashes to OrangeRx, when in fact they were due to my lack of homework understanding the inherently unsafe design of all Spektrum radio systems when used with such a setup.

For now, my entire Spektrum fleet is grounded.  Since I don't want to lose too much flying until I can replace all of my Spektrum Rx equipped planes and helis, I will be installing a high quality switching BEC before another one of my Spektrum aircraft endangers itself, and others, by taking off.

The high cost of this faulty radio line continues to mount, even as I hurry to phase out all Spektrum equipment from my RC collection.  In fairness to Spektrum, they are clear in their AR9000 Rx literature that you may sacrifice control of your model due to a known design defect:
"QuickConnect™ With Brownout Detection
Your AR9000 features QuickConnect with Brownout Detection.
• Should an interruption of power occur (brownout), the system will reconnect immediately when power is restored (QuickConnect).
• The LED on the receiver will flash slowly indicating a power interruption (brownout) has occurred.
• Brownouts can be caused by an inadequate power supply (weak battery or regulator), a loose connector, a bad switch, an inadequate BEC when using an Electronic speed controller, etc.
• Brownouts occur when the receiver voltage drops below 3.5 volts thus interrupting control as the servos and receiver require a minimum of 3.5 volts to operate."
Personally, I would prefer no loss of control over a by-design, brief loss of control, even when using new and very expensive Spektrum Rxs.  Uhg. 

.....
UPDATE: March 18, 2011.  After doing some quick web research on the latest unsafe DX8 defect, four bad potentiometers inducing random control inputs, bad centering, and stepped travel on all four stick axes, I found that this problem is inherent to most if not all DX8 radios.  Loads of people are writing about this problem, and perhaps 50% noted that Spektrum service could not fix the issue, likely replacing defective parts with new defective parts.  Requests for a full refund of wasted money on these defective radios reportedly go  unanswered by an unresponsive manufacturer.   I myself have never been able to get a human on the phone, and not for lack of trying--my limit is 60 minutes on hold.  So....

Having decided to throw my DX8 radio away, since it is definitely unusable, probably unserviceable, and thoroughly unreliable--all making it morally unsalable--it seemed there was little to lose by trying a user-recommended fix that was heralded as working each time it was tried.  There is obviously a risk to servicing my own radio, but what is there to lose when the thing is garbage at this point?

The user-recommended fix is to properly lubricate and clean the pots by applying a drop or two of WD-40 to the visible metal pot bearings, then working it in with stick movement.  This fixed all four of my defunct pots, initial results show smooth operation of every stick function.  Since I couldn't find a good photo tutorial on how to do this, here is my own:

Applying WD-40 proved to be ineffective in the long term, though it did seem to help in the short term.  Another user community idea was to stabilize the connector to each pots wire harness using a dot of epoxy and rerouting the wires to help relieve stress on the connector from stick motion.
.....

UPDATE: March 18, 2011 - Today I realized that, what I thought were OrangeRx defects and servo defects, were actually due to the dirt poor quality of the DX8 radio.  I have video documentation of yet another incredibly dangerous flaw in the DX8 radio hardware uploading to youtube right now, but I wanted to quickly issue this ***** WARNING ***** to all Spektrum DX8 users to stop using this acutely hazardous radio even before it finishes uploading.  A quick web search confirms that as many as 2/3rds of all DX8s have developed similar control failures.  My faulty and defective DX8 was responsible for two crashed models that I erroneously attributed to OrangeRx failures.  I must apologize to OrangeRx and those who may have held off buying these products due to my erroneous attribution of Spektrum's horrific quality to OrangeRx receivers, which are likely fine.  The only problem I can be sure of at this point is my own poor taste in radios.  I will link the video here as soon as possible:

..... UPDATE: January 26, 2011 - I'm downgrading my rating on this radio to an F. After only a few months of solid but careful use, and waiting for busy schedules and the weather to align today, the radio failed. Some purchases seem to fight with you in perpetuity, and this DX8 has been one of them from my perspective. In my experience, most of those sorts of nagging bad deals were bargain priced equipment I wished I'd skipped in favor of higher-end equipment, but this DX8 is just the opposite--premium priced with inferior component quality, unrelenting nanny-state annoyances, in-your-face ergonomic blunders, often plain stupid and needlessly complex daily operation, software logic errors, and a demanding, needy support system that just has to know all your private information before offering relief from their own incompetence. Wish I could grade it lower. Bad reviews for this radio are all over the web, bottom line: it is acutely dangerous product and it has horrible quality control.  Horizon cust service can't keep up with all the safety problems and have gone into hiding. ..... Original review follows:
September 12, 2010: DX8 has arrived.  I will add to this review over time, as the radio reveals its strengths and weaknesses.
 
First Impressions:
First things first - the radio ships with a very serious flaw: the main roller bar is too smooth and does not have sufficient traction to make your selections easily.  Unlike the 6i, in order to spin the 8's roller positively, you have to apply almost enough down force to press it, often hitting "enter" by accident..  This flaw alone nearly rules the radio out for me.  I suspect this has to do with how much "print" one has on the meat of their thumb, but assuming all thumbs are created equal is a mistake in itself.  My thumb slips to the point where I can't turn the wheel predictably on most attempts.  I have no problem at all with my other Spektrum radio rollers.
A second major flaw quickly appears with the very smooth, thin hexagonal sticks. Again, the material is simply too slippery and the stick grips (a kind choice of words for something resembling polished Teflon) do not give sufficient tactile friction to maintain positive control.  
How could such a major release have two glaring errors in the most basic functionality of the radio?   Here's an idea: don't get creative with main controls that work perfectly well, it's only down hill from perfect. 
The poor ergonomics of the two main controls (sticks and roller) are inexcusable.  In fact, even my bundled BlitzRC radio ($30 for the 2.4 Ghz transmitter and 6ch receiver) has a much better (excellent, actually) adjustable length, knurled round metal stick grip.  And so the solution to the second  flaw is quite simple, swap the stick stalks with any $15 transmitter.  Presto, fabulous.  Unfortunately, now my BlitzRC TX sticks slip like a pig on ice skates .
If you don't mind the constant headache of frustrating data entry, and after you change-out the sticks, the DX8 is a load of fun.  There is a whole lot to like:
Two things that will immediately jump out at the DX6i crowd are the three-position rate adjustment switches and flap switch. Three-position flaps are wonderful, now you can have no-flap, combat flap and landing flap, separate takeoff and landing flap setting, or set inverted wing camber with flaps beyond "up."  More coolness is the time to motor down function--you can specify any amount time for the flap "motors" to run the flaps up and down.  Any elevator pitch interconnect or other mix is blended at the same rate.  This is an excellent feature to avoid over-speeds and abrupt pitch and trim changes.
With the primary controls' three-position rate adjustments, you can finally introduce expo with one click and travel adjustment with the other, or run them in any three-combination you please.  Setup is a tad easier than the DX6i, as switch assignment selection is an option in the same screen that tailors travel and expo, not buried in a different global menu, but that is a double edge sword as the task of assigning more than one axis to one switch is now multiplied.  More chance for user error, and Spektrum made quite a few software errors themselves (see below).
Speaking of global settings, another major annoyance is the requirement to turn the radio off to use it.  That's right, half the model's settings come up by default, to get to the other half, you have to cycle the power off then on again while holding the roller down.  Unbelievable.  Awful idea.
Unfortunately, there are a lot of model-specific settings buried in the "turn me off" menu, requiring you to cycle power off then on to change your current model's setup, such as trainer switch operation.  This is a major shortcoming, since you must unbind the currently selected model to adjust it. This is unsafe, as you cannot verify the new bind without re-opening most airplanes and verifying a steady bind light.  The DX8 software forces people to routinely unbind, possibly causing the loss of a model, or worse, injuring themselves or bystanders.  This is one of many very serious safety problems we'll see with the DX8 in this review, and one that could be hard to fix in future releases since it involves hardware (to get to the hidden menus) as well as software.  Just awful!
My guess is that the need to turn the radio off and give up your bind is to keep people from adjusting certain key settings with the model in the air.  I did that occasionally too, it can save an airplane if you accidentally set something way off.  So to save you from yourself, they kill you.  Nanny-state run amok, and another reason to dislike the radio.  Not promising for the rest of the review.  
Telemetry: It's hard to imagine a less convenient telemetry module than the DX8's TM1000, and the (not) included sensors.  In its most basic form, a voltage readout, the DX8 telemetry setup actually requires soldering a custom connector (extra parts to mate to your battery-connector are required). Personally, I don't mind conceiving and soldering-up a custom sit-between to wedge the DX8's bare wire voltage module between my battery connector and ESC connector, but to most people, this is entirely unacceptable and essentially a useless solution.  Plus, soldering a double EC3 bridge isn't without trickiness, you need a jig to act as a third hand.   And what if I want a voltage readout from another plane?  How do I move a soldered sensor from model to model in the field?  This absurdity alone gives the DX8 telemetry pack an F.
 
Better solution: Quanum's 16 gram voltage telemetry module plugs into any battery's balance connector, making it model-independent and portable; it installs quickly without any soldering.  As a result of using the balance port, the voltage readout on the main display shows each battery cell's voltage, as well and total voltage, allowing you to identify a weak cell within a battery before it bites you.  The unit shown is included in Quanum's $60 telemetry package, or it costs $30 for each additional self-binding telemetry transmitter in case you wish to leave it in a plane.  It has a wired plug to pick up the optional temperature probe with amp sensor ($20).  This is a much more mature solution that can live in multiple airplanes, cars, or boats, or simply append to any 2 to 6 cell battery, or move between many devices quickly and easily.  Oh, and it beeps, but it can't buzz :)
The temperature sensor is straight forward, you wrap it around some hot thing and plug it into the T1000.  It works well. An RPM sensor is supported, but not supplied.  Cheap. With the telemetry grade of "F" out of the way, once you spend A FEW HOURS getting everything installed and soldered (luckily I had two spare EC3 connectors on hand), the module works.  Unfortunately, the display mechanization is not good.  Not only is the DX8's back-lit (nice) screen on the bottom of the radio, a very difficult position to use for telemetry data (especially with a neck strap, which blocks the screen with or without telemetry data displayed),  the main telemetry screen is different from the flight screen so you can't view trim position and telemetry at the same time.  The good news is that the DX8's trim display is so small, it's virtually unusable during flight anyway.  The telemetry screen does have a nice, large font. Overall, you are better off buying a $60 Quanum Telemetry pack that mounts high on your transmitter's antenna for easy viewing and has a voltage relay that is not hardwired to a given model.  DX8 telemetry is a serious disappointment compared to inexpensive, more convenient and more usable solutions.  Too bad the TM1000's telemetry receiver is built-into the radio, that perpetually adds cost for those who prefer more mature solutions.
In Flight: After flying with the radio for quite a few sessions, I'm sorry to have to move the DX8 to my AVOID list until the beta testers (early buyers) are finished with it.  For the most part the radio flies excellent, very responsive and precise.  The fine trim increments more than fix the too-course trim problem of the DX6i and DX5e, which almost always left a high-throw model climbing or diving without a small enough trim click in-between.  Features are improved as well, with up to 6 Mixes and three-position rates.
Switches are numerous and have a lot more adjustment stops the the Dx6 and 7, but the toggles still feel cheap.  I have a broken rate switch on both my 6i and 5e (they won't budge).  And after only a couple of weeks use, my DX8's aileron rate switch has rotated about 70 degrees--it is now more of a left-right movement than up-down and won't easily rotate back.  Cheap, again. Much has been advertised about the easy to use software.  I find the "operating system" less intuitive and needlessly complex, but generally more useful.  For example, good luck calling up different models without consulting the manual.  Model selection is hidden and there is a secret switch combination to unlock it.  But hey, that is good because if your radio is stolen, a thief won't be able to use it because the system is so counter-intuitive.   Another example: instead of navigating to different mixes in a menus labeled: Mix 1, 2, etc., there is only one Mix screen.  You have to "know" that hidden underneath the words "AIL>RUD" are the rest of your mixing options.  Huh?  Why not call the field "Mix 1" to give you a clue there are more mixes underlying that field?  I had to go find the manual after being unable to find any more mixes in the field.  I don't appreciate losing flying time for impossible to decipher software, it's hard enough to find time to fly. Another software nagging annoyance occurs in the Expo setup.  As you set up your rates, you have to remember to assign each control to the rate switch you want to use.  This is in contrast to previous DXs, where you can universally assign, say, RUD, AIL, and ELEV to a single switch, independent of the rate settings themselves.  If you set the DX8 up without the proper switch assignment, you can't correct the problem by re-assigning your throws and rates to a different switch because changing the switch clears the setup.  Yuck!  And, surprise, it is way too easy to miss that a switch automatically reverted to the default setting when changing assignments, until your model is in the air and your rates don't work the way you planned.  Vibration is an interesting feature.  I'm not sure if I like it--it is a bit too intrusive to physically shake the radio while flying, especially if one isn't wearing a neck strap.  As a minimum, I recommend turning the radio-unattended warning to the audible warning tone only, to avoid the default vibration from "walking" itself off a table top or car bumper whenever you are not watching--another nanny error--break the radio to correct the customer.  I switched mine to "tone only."  Next thing I knew, it was vibrating like crazy balanced (a bit too precariously) on my car trunk.  Seems you have to set it for each model, by first turning the radio off to find that menu.  UHG!!   Radio operation is generally poorly thought out compared to previous DX radios, it requires more time and careful diligence to program properly, and it hides more things in the spirit of consolidating menu items which were sometimes preferable.  Even the back-light's operation was not thought through, hitting one of the two buttons to make it light up clears the timer, eliminating a key reason to light it up and again, making the radio hazardous to your model collection.  However, with the increased time and manual manipulation, come more setup combos and potential permutations.   The DX8's own battery is a 2000 mAh 4 AA cell NiMH pack that will barely last a long morning and failed far too quickly, needing to be replaced.  It hardly works in extremely cold weather anyway, common to large sections of the USA, lasting perhaps 10 mins after a full night's charge.  All NiMH batteries have trouble in such an environment.  Another huge miss for the U.S. market; a failure to do even the most basic research about your customer.  (Disastrous) Bugs and Defects: Unfortunately, today a dangerous software error almost caused the lost of an airplane.  The problem occurred while bound to my 3-channel BL Beaver project.  I noticed that I couldn't seem to trim-out what appeared to be an ever-increasing rolling tendency to the right.  The right roll was slowly getting worse over time.   Eventually, I wasn't unable to trim left anymore; the trim hit the far limit.  At this point, I had to hold significant left stick in to keep the plane flying level.  I brought the plane around the flag pole and touched down uneventfully, with the control stick close to the left stop at touchdown.  Phew! Upon investigation, I quickly discovered this near-mishap was a DX8 software logic error: Since I don't like flying 3-channel airplanes with a stick missing, I mix RUD to AIL.  That way I can use either stick to turn (rudder stick used primarily during taxi), and since the mix is additive, the effect is much like flying a 4-channel plane at least from a control input perspective.  Unfortunately, the Spektrum DX8 software mixes the channels improperly.  I checked the mix on the ground, of course, but I neglected to test the trim direction which is erroneously reversed.  Note, if you turn the associated "Trim" field (in the Mix settings) from "Inh" to "Act" then no trim is available.  Please see my youtube clip for documentation:
DX8 SOFTWARE DEFECT
This is an awfully dangerous software glitch. For now, don't use this radio.  Beta testing seems to be ongoing. Yet another serious bug surfaces when I mix AIL to RUD using the preset Mix, and assign it to the Flap switch, it is the same as assigning it to "On."  There is no way to turn off the mix.  All other switch assignments seem to work fine, unfortunately, I want the rudder to help out only when the flaps are down, not all the time. Update: all of the DX8 mixes are faulty, and some occasionally stop working.  It seems to depend on the order you program your radio as to which mixes work properly or continue to function.  Complete mess.  Lastly, the AR8000 receiver hates to bind properly.  When yout first bind using the TM1000bind button, you may get a solid bind light. After that it is always flashing.  I guess this mitigates the bind problems caused by Spektrums new software that forces you to turn the radio off, and lose your bind, to adjust certain settings, since binding never occurs properly in the first place.  Again, this is an acutely dangerous flaw that Spektrum is surely aware of, but wantonly released their dangerous product to the general public, anyway. On a good note, the radio is extremely precise in the air.  The trim works in very fine increments rather than previous, too coarse Spektrum DX radios that are unable to properly trim any high-throw plane.  The rubber hand grips feel good, a nice touch.  The back light works well, I hope there is a way to make it stay lit longer, but haven't found it yet.  The timer options are great, and can be set to tick only when throttle is applied (warning - check youtube [http://www.youtube.com/watch?v=C45Izp5qxX0] for a serious software error that can easily crash your airplane/heli with an un-commanded full nose down input at timer expiration). Conclusion This radio almost caused the loss of one of my airplanes within the first few uses.  There are more people reporting losing models due to odd or hazardous radio behavior.  The ability for users to upgrade the firmware (as long as you give Spektrum a host of your private information which they may sell) seems to have encouraged Spektrum to release a half-baked product.  The latest software release, 1.02, is reported to add a whole new set of very dangerous bugs that weren't in the original release.  Spektrum seems to be flailing in both technical and managerial  incompetence. For now, absolutely avoid the DX8.  The main controls ergonomic interface is poor, the nanny software is inconvenient and in some cases poorly or incorrectly implemented, and early bugs appear to be dangerous indeed.   After the beta testers (we early adopters) absorb the initial casualties, then decide if the ergonomic flaws and high price are worth the new features and improved responsiveness. z8rc rating for the DX8 package: D 
B+ and higher =  Highly Recommended
D+ and lower = Avoid

Monday, March 21, 2011

Yak vs. Yak

The Yak-54 more than meets my "classic" criteria to own, and the Art-Tech Yak 54 was such a great flier (after it became clear the flaws I noted were attributable to poor Spektrum DX8 radio quality) it convinced me to do a new Z8RC series called, "Yak vs. Yak."

I'll increment aircraft size as I go, and I reserve the right to sneak in a Yak-55 if/when it makes sense.  Next up will be the Great Planes 41" Yak-54 with it's admirable (estimated) wing  loading for a 356 sq in model.


But as the chart below shows, the ATY54 and Z8ATY54 are no slouches either, and that certainly shows in the air. I'm still deciding on the best power system for the GPY54; I've estimated a few trades below:

GP Yak-54 (ST .10)
GP Yak-54 (ST 400 on 2s)
AT Yak-54 (Stock)
Z8 AT Yak-54 (ST .10)
Airframe Weight
12.00
12.00


Servo Weight
2.10
2.10


ESC Weight
1.20
1.10


Motor Weight
2.20
1.80


Mount/Misc Weight
0.60
0.40


Prop Weight
0.80
0.80


Batt Weight
4.05
2.00


Wing Area
356.00
356.00
297.00
297.00
Installed Thrust
44.00
30.00
21.00
44.00
Fly Weight (oz)
22.95
20.20
19.00
20.00
T:W Ratio
1.92
1.49
1.11
2.20
Wing Loading (oz/sqft)
9.28
8.17
9.21
9.70

If the wind ever stops blowing 25 mph, I will also re-evalute the AT Y54's performance with a self-serviced DX8 radio. I thought the Yak's lack of precision was due to Art-Tech servo arm slip (corrected review), but as usual, AT provided exceptional flying qualities for the money.  The random lack of precision that I experienced was due to a FUBAR Spektrum DX8.

Saturday, March 19, 2011

A Quest for Quality

I'm guessing that I'm not atypical, in that, after a few decade hiatus from the hobby, I made a dumb mistake a few years ago.  Simply put, I asked an LHS-kid to recommend a great radio.  It was a silly mistake on my part, not realizing that his idea of a high end radio and my idea would be worlds apart.

I blame myself for being so stupid.  But thinking back through the process, in my defense, even the bottom-feeder DX6i that he recommended looked like a giant leap forward from the technology I remember from back in the day:  square hammered metal box, sticks, metal antenna with frequency flag.  It worked. 

Fast forward.  Spektrum/Horizon does a super job of catering to novices.  That's ok.  Even with more full scale flying hours than most people have driving hours, I recognized that I had been out of the hobby for a while.  Horizon makes great stuff for people getting into, or back into the hobby.  Like most sharp high-volume marketeers, they do a savvy job of locking you into a low end standard.  Over time, I've realized that my initial mistake in the LHS, not doing enough research and relying on a kid with no money for a recommendation, quickly became very limiting and far worse, time consuming.

The DX8 seemed like a reasonable path forward, given Horizon's claim that there were attempting to build the best 8ch in the world.  I don't need 8chs, but the higher resolution appealed to me as I my RC skills had come back to the point where the low res DX6i wasn't precise enough.  And so, I was ready to make the next classic rookie mistake: throwing good money after bad...

The DX8 story is history on this blog.  Horizon proved too technically weak to make the leap to a high performance radio.  I don't blame them for trying.   I blame myself for buying the high side of a low quality line, something I've sworn off many times in other facets of life.  My brief life experience has taught me, over and over again, to buy the low end of a quality line when dipping a toe in the water, not vice versa.  Again, my fault for doing less than adequate homework.  Time down the drain is a bummer.

On the bright side, the full range of radios available today are amazingly inexpensive, especially for the over-the-top features.  Ironically, I don't want that.  I want fast, extremely precise, reliable control with excellent ergonomics.  That's it.  I don't see myself ever needing 8chs, but I have nothing against extra channels, either.  The extra glitz and complex features are actually a negative to me--no time nor desire for Nintendo.  But I do appreciate a great interface for staple features.

So I'm on a quest to migrate from Spektrum DSMX to a higher quality standard.  More to come...

Thursday, March 17, 2011

Quicktake - Parkzone Ultra Micro T-28

The 40" PZ T-28 has become a staple aileron trainer for the throw-money-at-it minded RC community.  Expensive but good, the T-28 has mostly excellent in-flight manners, as long as you keep the speed moderate and have a reasonably long strip.  I was curious to see how its baby brother stacked up, but hadn't got around to it until now.

First, I generally have a problem with Horizon RC models price points, they obviously don't care to be competitive.  Equally obviously, the market supports their value proposition: cater to mostly novice fliers who are light on time, heavy on cash, and happy to shun shopping around given snazzy marketing and a steady diet of venerable aircraft to add to a pretty interesting product line.

Although Horizon is viewed as distributing some of the higher-end Chinese products on the market today, they are still peddling low end stuff that continuously suffers from hit or miss QC.   I have found that Horizon's stuff, for all the savvy marketing, is every bit as cheaply constructed as less expensive stuff--and is probably built at the exact  same sweat shop.  American shoppers have proven happy to accept that compromise--I get that--three cheap models for the price of one high-end build.   It makes sense.  But when you add a premium price tag to the low side of the quality equation, Horizon's models are greeted with a tough, uphill battle right out of the box. The UM T-28 is no exception.

The 16.5" Trojan (I can't believe I said that) with its ancient brushed motor is well crafted, but suffers from the same delicate materials as its sibling micros--be extremely careful removing it from the well packed box--it is easy to permanently damage with mild handling. The paint job is really nice, and the plane looks handsome.  The T-28's trike landing gear works well, with a flexible, steerable nose gear.

Overall, the BNF T-28 is way too flimsy and small to sell in the $100 range (or $160 as a Dx5e RTF).  It's ability to absorb battle damage benefits from having no external servos, which are too common to Horizon Hobby frail micro designs, the UM Trojan's ailerons actuate from concealed control rods.  Compare to similarly priced, excellent 4ch performers which at least attempt to deliver serious foam builds:
39" span, brushless, 4ch.  $140 as RTF
 37", 4ch, brushed.  $89 as RTF
 34", 4ch, brushed.  $119 as RTF. 
Blows away the UM T-28 in stability and aerobatic capability.
30", 4ch, brushless, $79 (shipped) as PNP.

All of these FMS minis sell around $69 in the 
30" class, with great features. 
Note, these are all much bigger models that have true foam airfoils, many have carbon fiber and plywood reinforcement (Horizon markets as "Carbon Z"), standard size servos, and they all include a Tx/Rx.  They do not sport the T-28's (and most of the UM series') flimsy under cambered, flat foam airfoils, paper thin control surfaces, and make-shift pcb servos surface mounted with double sided tape.

On component quality, I give the PZ UM Trojan a D+, the workmanship is nice, but the Horizon Hobby overly delicate foam and tiny outdated components, like a nickel's worth of motor, is an in-your-face ripoff.  Horizon Hobby executives have to be belly laughing at the predictably sheepish acceptance of these dime store builds by their growing customer base, and even harder at the abused slaves that churn out this stuff for pennies ...to the bank, anyway.

Flying

Due to it's size, the UM Trojan is less stable than it's big brother, you need fairly still air to fly it outside without risk (largely due to the high price tag and poor build quality).  The brushed motor has  sufficient power, but is not exceptionally spirited. The stock 120mAh battery is small for the plane, probably to keep heft down, so flying times are below average in its price category.

The plane flies well.  Control surfaces are set up for intermediate skill, with high roll rate ailerons, acceptable rudder, and slightly inadequate elevator authority as setup in the box. It executes basic aerobatics reasonably well, with some roll coupling at higher speeds and significant coupling at lower speeds.  Complete aileron rolls are strained from a lack of power and no lack of drag, even though roll responsiveness is good.   Top speed becomes drag limited fairly quickly, making smart power management a key to achieving longer flying times.  Turns below half throttle require a healthy dose of up-elevator, much like its big brother.  Stall characteristics are also similar, less than forgiving, but not uncontrollable.  Getting slow in a nose high attitude slides the nose off into a required spin-prevent almost every time.  This plane needs a little speed.  Glide range is average to slightly below, but the speed is fast-- tell tale sign of higher than ideal wing loading. 

Overall, the UM T-28 is a good low wing flier with a few rough edges around a faster than average flight envelop.  It needs a little space to stretch its antiquated brushed legs.

Z8RC PZ UM T-28 Rating: C+ for quality workmanship, dirt poor component quality and out-dated motor, terrible value compared to much better flying and larger scale competition, solid intermediate airborne behavior with good aerobatic capability and somewhat shaky stall characteristics.  It would get a B with 40%-60% lower pricing.

Wednesday, March 16, 2011

Fixing the Art-tech Yak 54

Update - March 16, 2011:  New #7 fix in yellow.


The AT Yak 54 is a great flying airplane.  Even better, it's cheap.  Even worse, it's cheap.  These fixes are aimed at fixing the bad part about being cheap.  In order to preserve the good part, I've tried to keep the fixes simple and cheap, too.

Flight test confirms that these fixes make the Yak 54 an absolutely stellar flier!  The new 2:1 Thrust-to-Weight ratio, outstanding wing rigidity and lighter flying weight brings handling to the A+ level.  I couldn't be happier with this airplane, it is making a serious run for "all time favorite."  In fact, as an advanced flyer, it is definitely my favorite airplane, but you have to stay on top of it which removes some of the Sunday relaxation factor.   I'll have to think some more about giving it the official title.

The little Yak is fun, it probably has no idea what its parents went through.
First the problems, then the fixes:

1) The geared motor has plenty of torque, but lacks the umph to accelerate hard, and fails to provide a large margin of error that is desirable in a smaller scale 3D model. 
2) The plane is stuck in first gear.  1st gear isn't a bad place for a slow speed 3D model, but a more powerful motor can provide even better performance across a wide airspeed envelop.
3) It is loud.
4) The foam wing is very flexible, making precise maneuvers inconsistent and more difficult.
5) The wing cradle fits loosely, compounding the problems of #4.
6) The foam dents easily.
7) (Disregard: this turned out to be a Spektrum DX8 quality defect) The servos and linkages are not secure, introducing slop.  The aileron control arm is under the most pressure and tends to slip on the servo head.
8) The landing gear is weak and way too bouncy, including the tail wheel.
9) The spinner is for show and doesn't stay on.

1, 2, & 3)  I upgraded to my favorite brushless motor, the $24 Super Tigre .10.  The ST .10 is a great 3D motor as it has a radically higher motor power:weight ratio than any other motor in it's class.  The price is right, too.  The ST .10 and suggested mounting hardware weighs 0.6 ounces less than the stock motor, gearbox, and mount.

Installing the new motor int he Yak is super simple:
  1. Remove the four screws holding the old motor/gearbox to the firewall (the old motor is soldered to the A-T 20A ESC--bummer--you'll need to snip then re-solder the motor leads or add connectors, or change out the ESC depending on how many Amps you want). 
  2. Center the ST .10's aluminum X bracket mount on the Yak's firewall and mark the 4 mounting screw holes.
  3. Drill four 1/8" holes all the way through the front and rear plastic firewall.
  4. Buy four, 3" long, 1/8" diameter metal bolts, 8 matching washers, and 12 nuts.  If your hardware store doesn't stock the bolts separately, look for them in the wall anchor section.
  5. Looking at the front face of the motor:
    1. Insert the bolts through the aluminum X mount bracket, so you can see the head of the bolt from the front of the airplane.  
    2. Put 2 nuts on each bolt, on the back side of the X mount bracket.  Keep them loose for now.  
    3. Put a washer on each bolt after the 2 nuts.
    4. Screw the bolts into the 1/8" holes in the firewall.  Screw each one in a little at time.  To gauge the final motor position:  the base of your chosen prop adapter (or the back face of the prop) should be about 3.5" in front of the firewall.  Don't worry about the exact motor position, as this method will keep it adjustable even after the plane is fully assembled.
    5. Once the motor spacing is correct, and all evened up for a straight thrust line, put a washer and nut on the back firewall.  Use a small spot of Guerrilla Glue or some other all purpose glue to adhere the nuts/washers to the firewall (but don't glue them to the bolt).  Tighten up the back nuts.
    6. After applying a similar dab of glue to the firewall,washer, and the first nut on the bolt section between the firewall and motor, tighten up that first nut against the washer and front firewall.  Because of the 8 washers against the firewall, these 8 nuts (4 on the backside of the firewall and four on the front side) should be tightened down until the plastic flexes a little.  When these 8 nuts/washers are done and the glue is dry, you will essentially have a threaded firewall for the four bolts to anchor into.  Since the nuts are glued to the firewall, and the double-plastic firewall provides a lot of friction against the bolts turning, the thrust line will remain adjustable from the front face of the engine by turning the bolt heads individually.
    7. Tighten the 4 remaining nuts against the back of the X mount.  Again, use a dab of glue to adhere them to the X mount, but not to the bolts. 
    8. You now have a mounted motor with a field-adjustable thrust line.

4) Add two strips of foam weather stripping tape to the bottom fuselage section's wing roots.
5) Embed a carbon fiber slat (weighs 0.25 grams)  in the foam underwing.  Cut a shallow slot with a new exacto blade, widen using the end of the slat itself as a knife.  Gently tap into slot with a hammer, using a foam sheet underlay to protect the top of the wing.  Secure with foam safe thin CA glue.  Tape over with scotch tape.
6) Wrap clear mailing tape around the leading edge.  This also stiffens the wing slightly.
7)  (Disregard: this turned out to be a Spektrum DX8 quality defect) Remove servo control arms.  Add a tiny drop of epoxy to the inside of control arm where it attaches to the servo (careful not to use too much, or it might squeeze out and into the servo gears).  Update: I changed to a metal gear servo for aileron control, using the same control arm.  Roll rate in the air doubled, and it was already very  fast with full throw.  The new full throw roll rate is best described as "a blur," indicating that the stock servo was under a lot of stress, and as such, certainly not as precise as it should be.  While adjusting the pushrod lengths to calibrate the new servo, I noticed that the stock setup's servo + push rod length induced a little camber into the wing via mild flaperons.  Taking the flaperon out to create a perfectly symmetrical wing/aileron setup now allows inverted level flight with exactly neutral stick.
8) Add another piece of piano wire to reinforce the gear.  Rewire the tail wheel using slightly thicker piano wire.
9) The Parkzone Fw-190 spinner works well, or add a solid aluminum prop nut if you desire a the same CG.  The ST .10 and mount is about 0.5 oz is lighter than the stock motor and mount.

Result: Lighter plane with a 2:1 Thrust-to-Weight ratio.

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