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Saturday, April 23, 2011

Yak vs. Yak - Round 2

Scores from Round 1 will be posted shortly. Next up is the Great Planes Yak-55M Sport/Scale Aerobatic EP ARF 50". Another mouthful. Another Yak.  Notably absent from the official Great Planes supercalifragilistic naming convention, is "3D."  However, looking at the barn door control surface with 45 degrees of throw available, and the awesome T:W ratio of nearly 700W, half-weight twin engine, I'm cautiously optimistic.

The "Great Planes Supercalifragilistic Yak-55M" would be a much sweeter name for this starship (next time they'll probably ask me first).  It is, by any non-RC-indoctrinated standard, huge (super), drop-dead gorgeous (cali), and like all airplanes somewhat delicate (fragilistic).  That said, GP's interlocking, laser-cut balsa and ply construction covered in Monokote is one of the strongest builds around--more often than not flying away miraculously unscathed from some of the most shocking, high speed dirt pancakes.
The larger version of the red star on the tail is actually part of the
decal page so you can center it as shown in the upper photo set
This GPY55M is perhaps my most unbelievable deal yet. ARF quality is unreal. Price was even unreal-er. Towerhobby's promotional price of $139 stacked nicely on the usual $20 off coupon on top of free fast shipping. Total cost? An eye watering $109.  It's a crime that the flimsy little UMX Beast, with rather limited real aerobatic capability, cost me 60% more than this stunning 50" GP ARF:
The extremely expensive UMX Beast (shown with aftermarket 3mm prop adapter)
looks diminutive next to the GPY55M's huge, airfoil x-section tailplane
On the Ground:

This ePerformance series Yak goes together faster than the GP 41" class Yak-54.  Build time is advertised as "just a few hours" and for this kit it is true.  The GP Yak-55M has a higher degree of assembly than the smaller GP ARFs, and the wing attach system is quick and perfect. The sum total of wing assembly is sliding in the carbon fiber tube, gluing four small carbon fiber guide pegs (shown below poking through the fuse sidewall at the leading and trialing edge), and then a simple aluminum thumb screw does all the work:
Thumbscrews attach the wings in seconds.  Battery access is
through the top magnetic canopy hood, which clicks positively in
place with side fences to prevent a side-slip canopy departure in the air
The ARF model is perfectly jig built and beautifully finished in Monokote.  The hardest part (and it's not hard) of the "Almost" in "Ready to Fly" is inserting the metal U-bar that connects the two elevator-halves, then sliding-in the horizontal tailplane and aligning it perfectly while tacking with a bit of reasonable working-time glue. 

Aligning the horizontal stab gives a good idea of jig quality at the GP assembly house.  I like to compare multiple measurements to ensure a straight tailplane, since a true tail is so important to square aerobatics.  Whether you measure from wing tips to tail tips, wing roots to tail tips, or from various fuselage center points to tail tips, all the measurements align within a fraction of a 1/16th of an inch.  Horizontal level is on the money too, without adjustment, and the vertical tail is already installed dead perfect.  Spectacular job GP!

The only thing consistently lacking in these otherwise awsome GP ARFs is the wheel pants, which are typically very thin plastic.  The 55M's pants (Yak-style trailing fairings) are a little better, with basswood interior hubs for nice solid attach points.  But the hollow, molded plastic wheel fairings would only serve as two mini parachutes, so I opted for thin 2.5" wheels instead of the the included 2" wide tires, for aerodynamics sake:
Shown with 12 x 3.8 propeller
2.5" white-hub thin wheels
(the kit includes 2" wheels along with fitted 2" wheel spats)
Weight thus far is very encouraging, with a 56-58 oz GP total weight estimate.  The model as shown above, including twin tandem Super Tigre .10 engines swinging a 12x3.8 and spinner, is a dainty 36.8 oz.  My 55M still needs four x 0.7 oz metal gear micro servos to move in, plus a receiver, and motor batteries.  I'm hopeful to keep fly weight under 15 oz/sqft. CG is spot on, already, which sounds about right after two MG servos go into the tail and the batteries reside just forward of the main spar.
As shipped from the factory except for the piano wire
landing gear connection. Even the cowl's interior  firewall comes
factory assembled, magnets and all.  Tons of interior space.
Initial test runs look awsome, with fully redundant ST .10 x 2 motors running on fully independent power systems shoveling-out mega-power with little effort and feather weight (4.8 oz total motor weight, uninstalled).  Initial prop testing is finished:
  • APC 11 x 5.5 = 273W per motor, 23.8A per motor @ 10,880 RPM 
  • Sum = 546W,  47.6A
My installed thrust scale can't read high enough, but a rough uninstalled calculation is about 79 oz, or 1.6:1 at around 57 mph flat out.  Installation error from the flower pot size, scale radial cowl might lower that to a more realistic 1.4:1.  The nice thing is the low power draw, which should be good for about 13 minutes of mixed-throttle flying time with two 4.3 oz 1300mAH 3-cells and should squeak in under 50 oz RTF weight.  With double independent delivery, you get 40C for free from cheap 20C batteries, or one could up performance even more with two 40Cs for an 80C power system.
Flight tests show this configuration is as strong or stronger than a
Power 32 motor on 3S, but 3S is not enough for 3D performance.
Second prop test is now complete:
  • APC 11 x 3.8 SF = 327W and 28.7A per motor @ 10,340 RPM 
  • Sum = 654W,  57.4A
Thrust feels substantially stronger, desperately trying to rip the plane out of my tight white knuckles.  During the this trial I flew the throttle to exactly a 1:1 thrust to weight ratio, using two 6.7 oz 2200mAh 40C Lectra LiPos, or 80C in total, with an RTF weight of 52.1 oz.  That it occurred at almost exactly at the 50% throttle mark at just a smidge under 11A per motor as measured by my Wattsup. 

With the second power system option (11x3.8, 4400mAh @ 80C), one could hover for about 12 minutes, uninterrupted.  Wing loading is respectable for a 50" class model at just 15.7 oz/sq ft, up from 13.4 oz/sq ft using the 2600mAh solution.  For only a ~30% flight time reduction (a lesser hit than the straight mathematical 40% since the weight reduction also lowers thrust required over the entire flight envelop), the 2600mAh 40C battery system seems like a better way to 3D this horse.

A Z83D prop would be over-the-top efficient for the competition-minded.  the rough figures indicate my ST .10-twin with a Z83D prop would roughly double the thrust to weight ratio of any other commercially available complete power system and with higher efficiency.
What is perhaps most advantageous about the super light .10-twin is how under-worked the motors are, especially at cruise power, making it amazingly efficient compared to a single, heavier brushless outrunner.  The low operating temp makes either motor much less likely to fail than one over-worked engine, and completely redundant if one motor does fail.  In sum total, it is perhaps 16 times more reliable:
  • 4x as reliable for any twin engine design over any identical single design (factor = .5 x .5 before losing all power)
  • Double (probably more like 4x) the motor life per motor from half the Amp draw (factor = 2 x 2)
  • = about 16x less likely to lose all power in the air from motor failure
Receiver power is also redundant and independent too, eliminating the primary cause of cheap radio-induced crashes from brownout, which very common with Spektrum radios.

Interestingly, it seems that the practical kV limit kicked in, above, well before the motors were tapped out.  1250 kV * 0.80 (typical real world constant) * 10.9V (under load) = maximum of ~10,900 RPM.  I can fit a third motor to the shaft, but it is clear that this .10-twin delivers more than enough power for 3D.

In the Air:


Initial flight testing is complete, with some very interesting results.  First things first, this Yak is an excellent flier.  Even with only 9" additional span, it is exactly twice the size of the GP Yak-54 at around 55 oz current flying weight.  Wing loading is a respectable 15 oz for its scale, but its certainly not the AT Yak-54 Forrest Gump feather, not by  long shot.  Still, the overall experience is intense fun, hell, I can hardly stand it.

Second things second, the twin ST .10, while providing amazing 3S thrust, was simply too high a kV at 1250 to ride this horse to glory once the cowling rode shotgun.  The after installation losses, the big ass Yak could barely hover at battery mid-life.  CG was controllable with the 3S 2600 mAh shoved into the motor mount bay; the 55M's internals are very well designed, basically a huge, flexible empty space.  Maneuverability was simply awesome.  Power delivery was less than ideal for a 3D beast, the 11" prop had too little acceleration bite, especially with the APC prop's high efficiency driving thrust output into a higher RPM regime. 

Thrust comes from mass flow, you can move a little air a lot or a lot of air a little.  This Russian thug has a flower pot for a radial cowl, almost 7" round.  A high kV, 3S solution, even my twin, simply could not turn a wide enough prop to get the thrust column out and around the cowling.  That physical constraint essentially drives the approach of pushing a lot of air a little.  Best thrust comes from spinning an 11 incher at almost 11K RPM, a little air a lot--but right into the cowling.   At 1250 RPM per volt, the twin .10 is perpetually stuck in "5th gear."  Gear reduction driving a larger prop diameter could work marvelously (essentially lowering the kV), but the solution was too involved for this test.  I entertained using a more effective slow fly prop, as lift generation is pushed outward from the hub, making it less efficient, but more effective for a big cowl.  But even so, 11" seemed a bit too fundamentally small to run through this 3D bird's veins.

The cowling diameter vs kV issue is a real shame, as the ST .10 twin generates the exact same, great motor thrust to weight ratio as the .10 single, about 16x, and it does so with a relatively light weight total power system (4.8 oz motor + 8 oz battery + 2 oz for two 30A ESCs = 14.8oz).  Doesn't matter, cause you can't use an 11" prop effectively on this big Yak.  Installation error is a cruel witch.
 
The recommended motor is a low kV Rimfire 32 and 2200mAh 4S (8 oz motor + 9 oz battery,  + 2 oz 60A ESC = 18.8 oz power system).  Since this is a Yak v Yak showdown, I decided a conventional second try was the best way to go.  Unfortunately, my LHS didn't stock the Rimfire motor, so I went a similar spec, 700W to 1000,  770 kV, e-flight Power 32. With a good stock of 3S and 4S batteries and  2-6S 60A pro ESC, this should be a lot of fun.

The 11" twin motor drove a 95 sq inch air column, of that 95", abut 40 sq inches was consumed by cowling, leaving about 52% of the thrust column to do solid work .  The recommended prop is a 12".  While only 9" wider, it shoves a 113 sq in air column, leaving 64% of its higher thrust output unscathed.  A 13" prop drives 70% of its even higher thrust around the cowl boundary.

Is this a trick question? e-flight allows 11x7 to 14x10, so 13x6 seemed about right, with the ability to swap between 3S and 4S without over-stressing the motor with some kind of 14" 4S hatchet.  And so, off we go to our knife fight, armed with a Howitzer.
The big GPY55M has it's work cut out for it, the ATY54 and GPY54
are incredibly fun and much more economical to outfit and fly.
The motor is a monster at 8 oz, even with a lower motor T:W of around 13, pure thrust is over the top for this airplane at around 110 oz, a cool 2:1 aircraft T:W.  After I saw what this plane can do at 2:1 T:W on 4S, I immediately added a few 0.25" square carbon fiber beams in support of the thin plywood motor mount box.  Holy smokes, this huge radial cowl drives some amazing overkill.

I decided to control myself and accomplished the first 32 motor flight on 3S.   On 3S, aircraft T:W seemed a little lacking, even for sport flight.  Over the tops were strained; no sustained hover, the 55m slipped lower at full bore.  Hmmm.  Time for 4S.

Boom.  Like a cannon shot, this thing rocketed off the runway and tore upward to Heaven.  What a difference a cell makes!  This airplane had finally come alive, and oh man, how alive.  With one minor problem - impending death.  The 32 motor on 13x6 swallowed 4S batteries like Shaq downing a mini box of Pringles.  5:00 minutes on 3500 mAh, if I strrrrrrrrrretched battery life.   Yikes.  What next?

Alright, its time to see if I can find some middle ground.  Props, Watts, and Amps follow, on 4S:
Prop
Full Throttle Amps
Full Throttle Watts
Min Hover Throttle
Min Hover
Amps
Min Hover Watts
13 x 6 MAS K series
54
838
50%
25
385
12 x 6 APC Thin E
39
614



12 x 6 x 3-blade MAS
45
632



12 x 4 MAS K series
34
535
80%
28
430
12 x 3.8 APC Slo Fly
61
985
55%
26
395
What a range. 12 x 4 K tomorrow.
 ...
On 4S, the 12x4 K was too lethargic in both airspeed speed and thrust.  Amazingly, it didn't seem much better on battery life, at around 6 mins T.O. to land.   The higher throttle requirement throughout the flight envelope seems to negate most or all of the full throttle Amp draw advantage.  12x6 APC and MAS K on deck.

The 12x6 APC had plenty of top speed but was uninspiring on the low end of the airspeed range.  APC designs continue to disappoint.  Efficient blade design, yes, but that just makes the prop need to spin faster before it generates the lift you expect.  Perfect example of engineers obsessed with optimizing the most intuitive, but wrong set of metrics.

12x6x3-blade looks like it could deliver a great blend of performance and battery life.  It should generate 50% more thrust at the same RPM and give a good unloaded top speed with a 6 pitch.  It is on deck now waiting for the mini hurricane to end....

Hitec Aurora 9 vs. Spektrum DX8

The Aurora 9 has two index finger rollers on sides (not visible
in photo).  The DX8 in photo shows larger aftermarket stick grips.
As I explore alternatives to replace my Spektrum radios, the first contender is a less expensive, but more technologically advanced Hitec Aurora 9.  This is not intended to be a complete Aurora 9 or DX8 review.  My Aurora 9 flight review will come later.  This article focuses on differences.

Aurora 9 flight page: Model number and name, Flight Condition, built-in motor battery voltage telemetry, Tx battery in % remaining or volts, signal type and strength, double clicking the model type icon acts as throttle suspend, custom functions folder shortcut, settings shortcut, trim percent offset and graphic position, digital trim adjustments to programmed mixes, Tx on/off air, two timers
DX8 flight page: Mode, model number and name, transmitter volts, timer, graphic trim positions (note: there is no way to display optional telemetry on the flight page)

Basic load-outs look something like this:

Hitec Aurora 9 (paid $392)
  • 9ch Transmitter
  • 6 cell NiMH power
  • Optima 9 - 9ch Rx w/triple-redundant power & built-in telemetry.  (Free coupon) Optima 7 - 7ch Rx w/triple-redundant power & built-in telemetry.  (Half price coupon) Optima 6 Lite, 6, 7, and 9 Rxs
  • 2048 Resolution with all receivers
  • Real time response with all receivers
  • 5.1" Backlit LCD 
  • Touchscreen control
  • Acro, Heli, Glider modes
  • 9 Wing types
  • 5 Tail types
  • 8 Programmable, separate and/or cumulative, Flight Conditions 
  • 8 Programmable mixes, 5 linear and 3 with seven point curves
  • 7 Point pitch, throttle, and mix curves
  • 30 model internal memory with wireless data xfer between radios
  • 24 rate capable via 3 point switches and 8 layered flight conditions
  • Custom user menus
  • Removable/switchable sticks without opening case
  • Servo overdrive protection
  • Password protection
  • Two programmable timers
  • Adjustable motor voltage warning by model via built-in telemetry
  • Dedicated 4.8V or 6V Rx battery power module
  • NiMH charger for Tx battery and Rx switched battery power module
  • Updatable 2.4GHz module by USB connection (requires $23 HP-22 module)
  • Updatable transmitter software with above module
  • Updatable receivers with above module
  • Direct to laptop telemetry capable
  • Voice telemetry capable
  • 2.4GHz spread spectrum with adaptive frequency hopping 
  • 72 MHz digitally selectable, universally compatible  
Spectrum DX8 (paid $425)
  • 8ch Transmitter
  • 4 cell NiMH power
  • AR8000 - 8ch Rx 
  • 2048 resolution with AR8000; 1024 resolution with basic Rxs
  • Real time response with AR8000; slow response with basic Rxs
  • TM1000 with 4 function Rx telemetry including voltage sensor
  • 2.9" Backlit LCD 
  • Single axis roller control
  • Acro, Heli modes
  • 3 Wing Types
  • 5 point pitch and throttle curves 
  • 6 programmable linear mixes
  • 30 Model internal memory with SD card xfer
  • 3 rate capable via 3 point switches
  • Servo overdrive protection
  • Programmable Timer
  • NiMH charger for Tx
  • Updatable transmitter software by SD card
  • 2.4 GHz spread spectrum
Transmitters:

The Aurora immediately impresses the holder with a higher apparent technology level than the relatively stark DX8.  The most obvious difference between the two transmitters is the Hitec's huge touchscreen vs the relatively small DX8 screen & roller.  Despite being more compact, the Hitec Tx weighs about 20% more, at 33oz  vs. 28 oz, including the stock 6-cell vs. 4-cell batteries.  The Aurora 9 provides 4 switches on top, two index finger rollers on the sides, 4 switches on the front face, and 7 digital trim rockers.  The DX8 has 3 switches and one knob on top, 4 switches on the front face, and 6 digital trim rockers. 

Hitec's approach labels all switches generically (Sw A, Sw B, etc), while Spektrum labels their switches for the customer (Gear, Flaps, Elev, etc.).  I don't understand the latter, since the switches do not need to, and often don't correspond to the labeled functions.  This is an interesting difference because it quickly reveals the Nanny-State mindset of the Spektrum designers, who've embedded numerous, unrelenting annoyances and deficiencies (see my DX8 review for more).  This is more than an annoyance, it is a serious defect.  For example, if you want to mix your flaps to contribute to roll control, you can't, because Spektrum's "flap channel" logically connects both sides even though you never told it to so.

Hitec's design approach is backward compatible with a free people. They simply label and treat all servos on a receiver channel as independent Channels x thru n, so there are no artificial impossibilities forced on the user. Refreshing, and a lot easier to build ; you can always sort out what got plugged into where, later.

The Aurora has 7 point pitch and throttle curves and three 7 point mix curves.  The DX8 has 5 point pitch and throttle curves. 

Additionally, the Aurora includes more detailed features and customizations within virtually every menu and sub-menu, plus allows saving to a custom menus section to add user-specific features and configurations.
Note the C at the top left of the Aurora 9's expo graph.  That means this particular sub-feature within Flight Condition 1 will be "C"ombined, with other selected Flight Conditions unless overridden by that Flight Condition.
Flight Conditions are unique to the Aurora and allow you to customize entire sets of menu features then apply them in groups assigned to a single switch movement.  There are 8 programmable Flight Conditions available to every saved model, including the base setup which serves as Flight Condition 1, named "Normal."

For example, you might create 5 different helicopter Idle-Up modes with custom Pitch and Throttle curves, as well as custom rates, servo speeds, expo, sets of mixes, and different gyro gains for each one, then assign each of those comprehensive sets of Idle-Up customizations to its own switch. 

Each feature customization within every Flight Condition can be designated as a Combined or Separate change to any other selected Flight Conditions. This multiplies the number of features available since you can layer certain Flight Conditions on top of others in a cumulative way, while keeping other Flight Condition feature changes discrete.  This makes the potential number of available mixes and feature modifications for each model, effectively unlimited.

Updates:

Both the Aurora 9 and DX8 programming software can be updated, but only the Aurora can update its frequency hopping 2.4GHz module and its 72 MHz module with new software, as well as its receivers. In contrast, Spektrum charged customers for a new radio when they updated their 2.4Ghz DSM to DSMX, plus required customers to buy all new receivers to use the new standard.  You will need to buy a new transmitter and new receivers to take advantage of a frequency hopping or otherwise improved protocol if Spektrum ever introduces one.

Spektrum updates transmitter programming with downloads to an SD card which is then inserted into a slot in the radio, and they have been very aggressive in releasing update after update to squash numerous bugs, some quite dangerous.  You will need a computer based SD card reader/writer to download and save an update, they run about $10.  

To update Hitec transmitter programing, the 2.4GHz protocol and receivers you must buy an $23 plug-in HP-22 module.Hitec has released 2 updates as of this writing, mostly to add new features.  

Ergonomics:

You can read about Spektrums major ergonomics gaffs and annoyances in my full review linked above.  Another problem, not immediately apparent, became known after the Hitec equipment arrived for a side-by-side: the DX8 stick to hand-grip distance is wrong.  Despite having reasonably large hands, I cannot keep my palm on the hand-grip while moving either stick to the full up-and-over deflection point--corresponding to [full-throttle-right-rudder] or full [down-elevator-left-aileron].  This is another inexcusable error where Spektrum engineers failed to design the radio properly, forcing people to lose firm hold of the radio while flying.  The Hitec grip distance is perfect, allowing one to properly hold the radio and fly.

The Aurora has a nicer switch layout with quite a few more controls considering it only has one additional channel.  The index finger rollers with tactile and audio centering make finding any old flaperon/spoileron setting a breeze. I much prefer the positive feel of the Aurora's trim buttons.

Binding the Aurora is a bit of a hassle, as a button on the back must be pressed at the same time as making touchscreen inputs, not the easiest trick in the world.  Perhaps worse, the Spectrum radio won't bind to high line receivers without a hardware dongle. 

Both radios feature stick tension adjustments through rubber plugs on the back face.  But only the Aurora lets you swap sticks without opening the radio box.  Both radios have rubber hand grips, the A9 box's smaller more contoured profile allows the grips to be tighter and more compact.  The A9 also has a lighter more easily manipulated stick feel.  For example, it is easy to make a circle with either A9 stick, the DX8 sticks are too firm to do so without substantial ratcheting.

Receivers:

There are several Rx differences that jump out:  Most obvious, the Optima Rx has two longer antennas which are claimed to outperform any dual receiver setup.  Another huge Optima advantage are the triple redundant power inputs:
  1. ESC
  2. Dedicated Batt pack (an AA pack with switch and NiMH charger are included) - If you want to add a dedicated battery to keep the Rx awake and also power your servos (extending motor flight time), you can plug into the Batt port with supplied AA harness/charger.  Or, connect a 6V LiFe.  No need to consume a channel port or add a Y connector to inject dedicated batt power to the Rx and servos.
  3. SPC - a direct Rx power line from any battery that is under 35Vs (voltage is regulated down but not up, so 5V+ is required).  You can use the motor LiPo, making this port function a little like a built-in switching BEC, but an added benefit of using SPC port is that it only powers the Rx electronics, not the servos, so if you use a dedicated battery, like a 2S+ LiPo, you can keep it very small and lightweight. Another benefit is SPC battery Voltage telemetry displayed on the Tx LCD even without the telemetry module--V telemetry is built-into every Rx. 
Or, you can use all three at once.  Wonderfully thought out; bulletproof.

Spectrum Rx's gain power only through the ESC port.  If either the battery or ESC so much as glitches, the plane generally crashes (100% of the time in my way too-frequent experience) while the reciever takes its sweet time rebooting, even my quick connect Rx has been too slow to avoid a dirt pancake.  You can enhance the Rx by purchasing a dedicated Rx AA (or similar) pack and charger and plugging it into any empty channel or Y harness, but that costs more and is not supported by the manufacturer.  If you do so, it is recommended that you snip the ESC power lead, so that is still not a redundant solution so it fully relies on a single battery.  It takes the ESC out of the failure loop, but it puts a battery pack in.  The same goes for buying a dedicated switching BEC, still recommended to run single source power to avoid charging/discharging/shorting issues.   Low end reliability, to say the least.

Hitec makes four compatible Optima Rxs, a 6 and 6 lite, a 7, and a 9 channel, plus a Minima line for micros and profiles, all are 2048 resolution with built in Voltage telemetry and programmable fail safe modes (= servos and throttles go to your selected pre-programmed positions if the link is lost).   Street price is about, $45, $50, $85 (minus 10-20% if you are a Towerhobbies club member--no affliation).  All of them are software updatable and updates have been released.

Horizon charges 30%-50% more for the same number of channels, with lower reliability, a less sophisticated link, slower response time, less resolution, no fail safe mode, delayed re-links, and no built-in Rx telemetry.   None of them are software updatable. Spektrum's low technology level and poor value falls off the bottom of the chart.

Hitec Rxs are sold in even more cost-effective 3-packs and multiples with this and other radios, Spektrum Rxs are not.

This video (not mine) is a nice demonstration of Aurora 9 receiver boot time and re-link performance, although the servo motor is slow:

Airborne Operation and Response:

Great news!  I'm a heckuva lot better rc flier than I thought.  I had no idea how much the vagueness of the Spectrum standard had been holding me back.  Perfectly straight horizontals, verticals, quicker snaps, double  the hover stability, supreme glide path control, dancing wheel landings...WOW, this is fun!!!

I could go on and on about the gross superiority and shear dominance of the Aurora system over Specktrum, but int he interest of charity and brevity, I will limit it to a few quick observations:

From the instant of takeoff, the difference was blatant. Throttle response is quicker and step-by-step more accurate.  No more roll, trim trim, roll trim trim--roll, stop, rock stable, roll, stop, rock stable--straight lines with no centering drift whatsoever.  Faster servo movement.  New level of precision.  Easier spot landings.  I love the left index finger roller with center-detent (and beep) to allow the immediate selection of any flap position, or for 3D aircraft, any double-servo aileron position from full flaperons to full spoilerons--a programmable elevator position follows, both up and down.

This radio will save me money daily, through less wear and tear, outstanding control, and Rx power redundancy, link speed, and link reliability.  I would have saved so much and had so much more fun if I went with with the Aurora from the beginning.  Painful.

The great news for those who may disagree is that I'll be selling off my perfectly good (as in, perfectly good shape and fully functional) collection of Spectrum Rxs and also my transmitters (DX5e, DX6i, but not the defective DX8 unless someone wants to buy it knowing that (a) it is no different than any other DX8 new or used, and (b) that it is a horrible radio).  I'll be listing the Spektrum equipment I have for sale in the comments section of this post, or in a separate post as I replace it.  Please zap me an email or leave a comment if you wish to make an offer.

Head-to-Head fly-off:
For the H2H, I flew off the razor sharp Great Planes Electrify 41" Edge 540 in full DX8/AR8000 regalia against the Great Planes Electrify 41" Yak-54 3D in Hitec garb.  The GP Edge is an amazingly preceise 3D/pattern spaceship with near infinite pull.  The GP Yak-54 is a 3D scalpel that floats like blimp and hauls ass as fast as its 10K RPM, 3.8 pitch prop can chop air.  By any estimation, this should be a heckuva shoot out.

It wasn't.

The Aurora 9 decisively beat the DX8.  The difference in feel, responsiveness, programming features, and safety features was night and day.  Thank you Hitec for an amazing product selling at lower than reasonable prices.  The switch is on.

Side note: One thing that could be more clear in the A9 manual  is how the SPC (direct Rx power) connector works.  So here is how it actually works - The SPC port pin-out is the same as any servo connector as far as where the positive wire needs to connect (middle pin of 3) and where the negative wire goes (same orientation as any servo's black wire within its female connector plug).   The third pin of the receiver's SPC port, which would normally correspond to the servo control signal wire, stays unconnected.    You can modify any old servo extension cord to connect the SPC port to the battery (the Rx comes with one that only has a black and red wire, the third pin is empty).  Run the black wire to the black battery terminal, run the red (middle) wire to the red battery terminal.  The best place to connect these two wires is on the ESC-side of your airplane ESC battery connector, then to the SPC port, that way it stays connected and ready as part of the airplane's electronics.  Once you have this connection in place, the LCD touchscreen of the A9 transmitter will read out battery voltage via telemetry.  If you do not connect the SPC port, that field will show Rx voltage, or around 5V no matter what the battery's voltage state.

While it is bit inconvenient to have to solder-in your voltage telemetry, the A9 solution is no different from Spektrum's same requirement, but it is far less expensive since Hitec does not  mandate the purchase of a dedicated telemetry module (e.g. a Spektrum TM1000) which costs as much as the receiver itself.   Hitec packages free V telem with every Rx, as well as 2048 resolution.  The result is a Hitec cost savings of approx $150 per airplane over Spektrum ($130 for a 2048 resolution Rx, $56 for a TM1000 module, minus the cost of a Hitec Rx) to obtain these two critical features.

Final weighted scoring:

Spectrum DX8:  49.4
Hitec Aurora 9:   92.0 

Sunday, April 17, 2011

Z-8 RC Wheel Brakes

As I test fly, and quickly iterate the GP Yak-55M, one need that became very apparent was a wheel brake solution to operate this big boy out of my FOB.  The 55M lands slow enough, but it was clear after the first touchdown that the relatively high mass of the airplane and slightly larger than stock wheels (2.75") can really roll out, and roll out, and roll out, with very little incentive to slow down.  Add yesterdays mild tail wind to my downhill overrun, and well, I seriously need some brakes.
As is often the case, I looked online and found nothing except a few gold-plated, probably heavy, and needlessly complex/expensive solutions.  So I played with a few ideas of my own, from servo-triggered or applied brake application to electric thrust reversing.  Necessity is the mother of invention, so here is a very simple solution that worked absolutely perfectly on the first outing:
  1. Drill out the wheel hubs to add 1/16" more diameter
  2. Wrap the airplane wheel axles in shrink tubing
    The result is a wheel brake that increases braking action as lift decreases, and decreases braking action as lift increases.  Happily, this shortens both the takeoff (slightly) and landing roll (a whole lot). 

    Landing roll decreased by 75%.  Brake drag was perfectly symmetrical.  Takeoff roll was a bit shorter, due to the lack of much roll during power run up, reduced braking action as lift generation relieves the brake, and there was no tendency at all to nose over even without additional elevator compensation.  Taxi was much safer as well.

    Simple.  Perfect.

    Thursday, April 7, 2011

    Double reliability, double performance, half price

    This $7 gem does all of the above:
    Consider:
    By hooking two half-size batteries in parallel, you get twice the discharge rate while total battery weight stays exactly proportional to total capacity.   Cost savings can be significant, as both larger and higher discharge rate batteries are more than proportionately expensive.

    Less obvious advantages are perhaps more important:
    • You now have redundant batteries, doing nothing else doubles your receiver power reliability in the event of battery failure. 
    • If you split a BEC off of your ESC battery power connector, you now have a redundantly powered BEC supplying power directly to the receiver, even Rx's that do not have redundant power inputs.  ESC failure is no longer catastrophic.  This eliminates the argument that the external BEC may be as likely to fail as an ESC's internal BEC.
    • Batteries are half as strained at the same level of performance, so they should last longer
    • Batteries may be more flexibly arranged for balance/CG/space constraints
    • You can have two flyable battery sizes instead of one (e.g. 1300mAh and 2600mAh)
    • You can also have three flyable sizes if you split asymmetrically (e.g. 1000mAh, 1600mAh, 2600mAh)

    There is no need to match battery sizes, but you do have to match the cell count.  Parallel batteries will always drain together, their voltage will remain matched as they drain.  The down side of having a large and a small battery hooked in parallel is that the larger battery will be supplying the majority of the current at any given instant, meaning that total discharge rate is increased but not fully doubled.
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