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Sunday, May 29, 2011

LiFe Saver

A flawless GP Yak-55m replacement airframe flew its father's guts today, these GP ARFs are works of art.  This one was everybit the vision of perfection, same or better than the last one.  I'm still amazed at the value, after the standard email coupons (-$25) and club discounts (on sale for $159), this big 55 oz'er came from Towerhobby for $134 with free shipping. Not as good a deal as the first airframe, but nevertheless encapsulating many man-months of stunning perfection for around a fourth of a second tier business executive's hourly rate.
Perhaps foolishly, I properly soldered the E-flight 60A "Pro" ESC adn reused it.  It is solid overkill for a 45A plane, plus, I have a trick up my sleeve to avert Horizon Hobby's next, even more creative lethal defect...
Since I fly primarily park flyers, I hadn't previously used an independent RX battery, as few extra ounces makes a big difference to a 20-30 oz airplane.  But with my reborne Yak-55m still carrying a certain-to-fail E-flight ESC, I decided to add a 6.6V LiFe battery to operate the Rx and servos.   I still have motor battery SPC and the ESC BEC as Rx and Rx + servo backups, respectively. 
I choose a 2.2 oz 1300  6.6V LiFe battery to power the 55 (now 57.2) oz Yak-55m.  In addition to relieving the motor battery from having to power the aircraft electronics, increasing flight times and recovering perhaps half the battery weight in the form of extended flight time, aerobatics also benefit from faster servo movement.

Flight tests were flawless.  I'm gong to use this method a lot in the future.

Saturday, May 28, 2011

First Giveaway: 3x Spectrum AR500 5ch Rx

As I just got back, I'll give this one more week then award on May 15 2011.


Since I switched to Hitec Aurora, I have a lot of Spektrum stuff to unload.  First up, I'll be giving away a package of three Spektrum AR500 5 channel Receivers.  To become eligible to win:
  1. Leave a comment on this post from any account ID that is not anonymous. 
  2. In your comment, quote a link to any external www page where you have left a link back to any page on this blog.  Enter as many times as you like, but you must leave a unique link for each comment entry.
  3. Check back after April 30, 2011.
  4. I will use random.org to choose and document a random number between 1 and the total number of entries.
  5. The person who left that comment number wins--e.g. a random drawing of the number 10 awards the 10th comment, below.
  6. I will show the winning # in this post along with the random.org drawing documentation.
  7. The winner must email me a mailing address at z8machine@yahoo.com.  Your address information will remain private and never shared with anyone.
  8. I will reply to your email with a code word.
  9. Post that code word in another comment here from the same user ID as the winning comment number.
  10. You win!  Z8RC will mail your prize via USPS Priority Mail with Delivery Confirmation.
The winning comment number is:  #1!   
Please email z8machine@yahoo.com a shipping address and I will send you a codeword to post as a comment here, to confirm your ID.

Thursday, May 19, 2011

Blind confusion, improper terminolgy, and the on-going 3D RC debate

It strikes me that more than other hobbies, RC enthusiasts tend to make a lot of crap up.  From amateur hour motor testers, creating huge databases of statical noise derived from unsound methods and their subsequent outer space conclusions, to vocal rank amateurs produced by our "there-is-no-wrong-answer" "school" systems, the shear volume of wrong stuff posted on the usual-suspect message boards is quite impressive.  Yes, there is no shortage of posts and blogs and RC forums universally aspiring to make us all dumber.

One on-going cyber debate is what "3D" aerobatics really means.  It's such a waste of time, I thought I would do the world a favor by wasting a few minutes of my own time to save the minutes of billions.  Here is the proper, aerodynamically sound definition of 3D as it applies to the unscrupulous world of the big RC forum crazies:

3D maneuvering, as commonly used to describe a class of radio control airplanes, simply denotes predictable control at AOAs above critical.  Simple as that.

To underpin a useless term with a few useful definitions and assumptions, we have:

Definitions
  • AOA = the angle between the wing chord line and relative wind resulting primarily from the aircraft's flight path.  I say "primarily" because the high speed air column created by the motor is often used to create blown wing lift or to enhance control surface effectiveness, this effectively creates a different AOA near the wing root than the rest of the wing experiences from flight path alone.
  • Critical AOA = the AOA above which the wing stalls, thereby producing less lift than at a lower AOA, at positive or negative angles of attack.
  • Predictable control = repeatable.
Assumptions
  • Since the wing is stalled for all or part of 3D maneuvering, any true 3D aircraft must have a T:W greater than 1:1 (or achieve it at some point during the flight).
  • "Wing" refers to the main wing(s), not the prop blades.
  • Prop-driven aircraft with greater than 1:1 Thrust:Weight are technically a rotary-wing aircraft, as well as a fixed-wing aircraft.
  • All helicopters fit the proper definition of 3D, since carrying a stalled fixed wing is not technically different than having no fixed wing.  Some helicopters are advertised as 3D helis, but such a distinction  from other helis is not proper since it boils down to a matter of degree.  Any craft that can hover is performing a staple 3D maneuver.

    Tuesday, May 17, 2011

    Another Horizon Hobby quality defect destroys a classic

    Radio control flight is unbearable fun peppered with heart ache.

    Yesterday, my triple-redundant Optima Rx lost the ability to control what was quickly becoming my all time favorite machine, my gorgeous 50" Great Planes Yak-55m.  Puzzled, at how an Rx with an SPC connection, a dedicated BEC, a Pro ESC with switching BEC, all powered by a parallel double-battery system could lose power, I embarked on the necessary accident investigation that would make the NTSB proud.

    Horizon Hobby's junk kills a gorgeous, high quality Great Planes ARF
    Amazingly, the only single point of failure in the system failed, or maybe I should say, "predictably."  The setup?  Twin 4S batteries on a parallel cord Y-d into the ESC, from the ESC connector, a BEC and an SPC connector tee'd off to feed the Rx link and servo power, respectively, as well feeding the switching BEC on a 60A E-flight Pro ESC.  This all drove a Power 32 spinning a 3-blade MAS at (what I should have been) a rather conservative 45A max, measured, static draw solution.  This plane flew awesome, with phenomenal low speed manners and absolutely exhilarating high speed Doppler passes. Even if the copper-brick Power 32 was a little meaty for the plane.


    During one of those high speed Doppler passes, perhaps 10 secs into an eye-poppingly stable, full power scream, the motor simply stopped.  No smoke, no squeal or shriek, no fanfare at all, just quiet with no change in flight path.  I thought I found a way to burnout the monstrous Power 32 with a puny 55 oz plane, so I turned to land; cake setup for a dead stick.  My gorgeous, perfectly behaved, always eager to please 55m disagreed, and proceeded forward, arrow-straight.  Dead.  In the air. 

    I collected the carnage, and was still unclear as to the cause of this mishap until I began salvaging parts.

    The culprit?

    A cold-soldered E-flight EC3 joint that separated the ground wire from the 60A "Pro" ESC's factory connector under less than a 45A load.  The black wire that slipped out of the ESC side of this EC3 looked brand new, perfectly round and solid, and beautifully tinned, much like the gold bullet from which it separated:

    Once again, Horizon Hobby's disregard for quality and rotten workmanship ate a fabulous model.  This is the lastest in fairly long line of E-Flight ESCs that have burned up on me in various ways, starting with my first experience with a Horizon model, the over-Amp'd and under-performing 25A ESC in their T-28 Trojan.  Horizon Hobby holds the world record for new an imaginative ways to find catastrophic, absolutely lethal failure modes.  Time after time, their stuff fails.  Buy nothing from HH, the  company absolutely, positively sucks.   Through blind luck, Horizon Hobby's gross negligence did not kill a human being yesterday.  Thank God for a fairly large world.

    E-flight Pro ESCs moved to AVOID.

    Friday, May 13, 2011

    Art-Tech Yak 54 Review

    Update:  please see: http://z8rc.blogspot.com/2011/02/fixing-art-tech-yak-54.html

    Update: March 20, 2011 - The AT Yak 54's lack of precision, as noted below, was later discovered to be attributable to all 4 of 4 defective DX8  potentiometers.  I apologize to Art-Tech, I mistakenly blamed them for Horizon Hobby's FUBAR radio.  The ATY54 is simply exceptional for the $; fix the grade to A+.

    After owning several (with another on the shelf, unopened) gorgeous Art-Tech Pitts S2B biplanes, I had to try their very reasonably priced Yak 54 RTF.  Warning: for those who go to auto races to see cars crash, there is no disappointment here.  Like their Pitts S2, the A-T Yak 54 is a terrific flier.
    One badass machine; the plane isn't half bad either.

    Unfortunately, the OrangeRx receiver I stubbornly re-tried, wasn't nearly as good as the plane.  The rx caused major binding/unbinding/trim/re-trim issues throughout the flight, but bottom line first:

    The Yak flew wonderfully when the Rx wasn't freaking out.

    Kit Quality and Value:

    A-T's Yak isn't setting new records in foam quality, best described as beer cooler Styrofoam, but they are setting records in the important area of value.  Both their Yak 54 and the PittsS2B run about $150 in RTF form (with a surprisingly nice 8-AA Tactic 4ch Tx and 6ch Rx).  Declining the radio/Rx gets you down to about $130, ready for your own, painfully expensive Rx.  The A-T package dutifully adds a quality 1300 mAh 3-cell to your collection, and you'll need to find another plug for the 0.3 to 1.0 Amp dial-a-rate Lipo charger.   I love these chargers: you plug the battery in; it charges.  Imagine that.  No needless gadgetry supplied, required, or desired.  13 minutes of anti-gravity indicates approx 1min/100 mAh ordered up from the engine room.

    What a great way to log some cheap, high quality airtime.  As far as expected durability, well, there are two things to consider--neither is good:  1) The foam dents very easily and 2) it isn't the strongest structure you can get on the far side of $100.  That said, it is RTF.  A $100-range balsa and ply super-strong structure will come in ARF form, and the "A" stands for "After a lot of work and money."

    The Yak was packed very well and assembled with reasonable care.  Basic construction is a two-piece fuselage (top is removable with a single screw), a one-piece wing that drops into a molded cradle while the top fuse is open, lightly tighten one nylon wing bolt to pin the wing in the middle, add the one-piece horizontal and single-piece vertical stab.  The aileron hinges are pre-taped and the tail surfaces use molded foam hinges.  I elected to tape the rudder hinge with scotch tape, since the tail wheel transfers the plane's weight directly to the hinge.  Speaking of the hard plastic tail wheel--this is the one poorly executed part of the plane--you'll want to pick up a rubber-tire wheel and some piano wire to bend your own.  Mine took less that 10 minutes to form and replace using a needle nose and regular pliers--but I've bent a lot of tail wire.  I secured the bottom-rudder-into-fuselage tab with 2-dots of Guerrilla glue for a little more tailwheel strength.  The vertical stabilizer is a bit fussy to pin with the supplied nylon sandwich braces and screws.  I glued the final taper of the fuselage halves to the sides of the small, slide-in vertical stab, for fear of the huge movable rudder not having a whole lot to cling to.

    I guess there is one more poorly executed part: the spinner.  The rubber cap spinner didn't last my first run-up, plan on getting another.  I wound up painting a Parkzone Fw-190 spinner; a perfect fit.

    The Yak looks big, but the 39" Beaver, 41" Edge and 48" Cub are bigger.
    Airborne

    This is a pilot's airplane. It is light, maneuverable, and highly predictable.  Art Tech selected a solid power solution for the plane: a gear-reduced brushless in-runner with gobs of torque for the small size and reasonably light weight.  This setup lets your turn a big honkin' prop at relatively slow speeds.  Hovering is not a problem, but power delivery feels measured at times.

    The gear & motor noise is great, specially if you like a lot of noise and your neighbors do too.  In a high speed dive, the whirling Yak starts to sound like a three way cross between the punctuated snarl of an old Allison V12, a high speed blender crushing ice, and an 70's pickup truck dragging a loose roll of chain-link fence over to uncle Billy's double-wide.  Like it or hate it, it delivers.

    Traditional aerobatics are no problem for the Yak, but it is hard to resist the urge to square corners.  Carving graceful lines in the sky requires tediously tracing your imagination, rather than the natural result of a smooth trade between G and airspeed.  High load, high precision maneuvering, like established knife edge flight, is an area the where the Yak's Styrofoam becomes needy.  I'm not exactly sure where the line falls between me sucking and the foam bending, but there is a blurry area somewhere in the shades of gray.  I think I can add some fiber rigidity on the cheap.  Thank God for the feather wing loading, this thing has a lot of potential.

    The RTF's aft CG is especially pleasing and a little challenging.  The designer was quite serious or just a little bit stupid.  This tail is totally alive and it needs forced air to function.  Blowing the tail up with throttle sets the plane level with the horizon, the tires tear into the pavement resulting in pretty good top end speed.  Unzipping the sky rapidly in the horizontal is always one stick bump from inserting a 90 degree corner.  Fun.  A little darty.  Fun.

    Suffocate the tail with idle power, and the license plate droops while the 54 gasps for air.  The resulting high-alpha flight keeps the plane from doing the expected, simple search for airspeed.  Instead, the Yak holds altitude with a slow pitch up until the wings give up the ghost without rocking.  The lack of wing loading keeps it airy.  At the point the clever little plane runs out of airspeed and interesting new ideas, it begrudgingly sets a reasonable glide attitude; only because it is falling like a brown leaf in late October.  The high AoA glide path progresses in the general direction of the pilot's toes, only slightly steeper than the Shuttle getting ready to swap ends at Edwards AFB.  Adding a teaspoon of power to avoid the impending belly-flop transitions to horizontalish flight, better aligning the wind with the nose, followed by a touch of eagerness to raise the nose back to blue.  Pulling the power out again resumes the sink and the plane hunts for a place to pancake.

    Add 30% power, keep it there, and you are ready to spot  land.   Alternating blender buttons between "aerate" and "puree" lets the airplane down under control, tail wheel first.  And why not?  Controlling the Yak's decent in the flare is as easy as goosing the power just before the shadow touches the rear wheel.  Landing rolls are reminiscent of catching the approach end cable with the hook.   The cheap landing gear is plenty long to protect the prop from a minor tussle with pavement, but the Yak is fully capable of nicking one prop per flight.

    At 19 oz out of the box, the plane has a lot of potential as a 3D trainer/contender, but as perhaps as expected at this price point, a few things are in serious need of improvement. Rather than beat an inexpensive plane up because it isn't perfect, I'm going to stop here and give the A-T Yak an A- for superb, low budget flying qualities with a few significant execution errors.

    As usual, I'm not going to complain without showing the fixes. I'll keep it cheap and limit the work to a few hours so we can stay fun and low risk. Good news is, it's not hard to turn a fun foam sponge, based on a killer foundation, into a 3D scalpel.  Look for another post within a day or three called, "Fixing the Art Tech Yak 54."
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