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Tuesday, March 20, 2012

Great Planes Gee Bee R-1 RxR 38.5" - Flight Review

Completed model including guide wires, painted prop and 9 cylinder radial.
Update 11:  Paint and landing gear mods.  I added two 2 mm carbon fiber supports to the inner landing gear, one additional support is needed to hold the gear steady from during landing side-loads.  , I glued up the foam pant including the wing attach point all the way down through the inner pant, which greatly improved the ground handling--no more automatic somersaults on landing rollout. 

I also added oil streaks to the top fuselage for effect and 2mm carbon fiber struts to the top wing replacing the elastic.  This carbon fiber wires on the top wing noticably improve the maximum roll rate by minimizing wing twist from aileron deflection.

 

Update 10:  I tried a 1550 Kv 3-4S Radian 500 motor for grins.   The results were not usable.  Amp draw was 51A/546W with the stock prop at 300 less RPM than the Power 10.

The 3S-only Power 10 with the Trojan prop from Update 9 flew perfectly and is a genuinely fast plane, but with a but a little more power drain than I expected at 33.7A/385W static.  The Power 10/9.5x7.5 is the best motor/prop combo I've found so far.  Static pitch speed is only 69 mph at 9,680 RPM, but unloaded speed in the air is a small step up from a 10x7.   I broke my last 10x8, but I think power draw would be a little high though it should add even more speed.

The 9.5x7.5 looks 6-8 mph faster in the air than the stock motor/prop on 4S with the same Amps but fewer Watts due to 3S vs. 4S.  The P10 is a more casual performer and has no power glitches associated with quick throttle movement.  The stock motor on 4S rarely glitches with the stock prop, but it can happen on a fresh battery with a rapid idle-to-mil movement.  It glitches badly with the 9.5x7.5 prop so that is not an option.  

Whether adding a $60 motor is worth an extra 6-8 mph is a question I can't answer.  It might go 5 mph faster still with a 10x8 (testing soon). If you need to buy 4S batteries for the stock setup, that could offset some or all of the new motor cost.

Update 9: - The R-1 flew great with the Power 10 and no ballast.  I removed the front stop on the battery tray to move the battery all the way up to the motor firewall.  6-7 minutes on a 3S 2200 and it looks like a 70 mph bird.  Time to try the old Parkzone Trojan/Corsair prop.  I know form experience that prop pulls about the same current as a 10x8 but is notably faster with higher RPM and steeper pitch per turn.

Update 8:  After trying larger batteries following Update 2, I have decided that due to battery position this is not an optimal configuration.  The reason for the nose weight is the battery CG not being far enough in front of the aircraft CG.  Meaning, you need to add a huge battery to give the same aircraft CG as the 3 oz nose ballast.  The required overall weight gain results in a bad trade off.

In order to put the weight savings from Update 2 to use, that leaves moving the battery CG forward (no room) or a larger  motor.  

This is a rare case where the low motor thrust to weight ratio of the Power 10 can make some sense.  It is a powerful .10 size motor but it is heavy.  It has the same bolt pattern and motor diameter as the stock motor, but is longer.  Seems like a decent way to go.  After trimming a ring from of the middle of the faux radial, here are the numbers:

It is not as fast as I had hoped.  Only 4 mph faster than a stock GB on 4-cells, but also 5 amps more efficient: 
Prop
10x7
Battery
3S-3000mAh-35C
Amps
28.5
Watts
331
RPM
10,500
P. Speed
71

The Power 10 weighs 2 oz more than the stock motor and places that increase an inch or two farther forward than the 3 oz ballast.


Update 7:  The perfect prop?  Although the winds preclude flying today, the Parkzone Extra 300 "Flying Brick" is actually great for something-- its prop could be perfect for this Gee Bee Sportster.  The propeller's  10.5" diameter gets air around the monster cowling, and its 9 pitch rake is very steep.  Only an option on 3S (since a 10x8 slips badly on 4S), this prop still puts up some great numbers:

Using a 3S 3000 mAh 30C, which is easily lifted due to Update 2, the strong brushless cranks out a surprising 8300 RPM and still manages a static 1:1 Thrust:Weight ratio measuring 33.3 oz of pull.  Pitch speed is the fastest so far on any cell count, 71 mph, and this prop should unload the most in the air for even higher achieved RPM.

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Update 6:  The HK401 gyro was superb in operation, both in Rate and Heading Hold modes.  In HH mode, it was near-impossible to turn the plane without using rudder.  Rate Mode also displayed impressive gyro performance, the plane Knifed Edges with no additional rudder input required after setting the nose slightly above level.  

Over-gained tail waggle occurred in Rate Mode near top speed when using the default gyro dial settings and with the airborne gain control set above roughly 50% from the controling servo channel's neutral position.  

Mapped to the Left Slider on an Aurora 9, the neutral detente/beep is no gyro, sliding up gives increasing HH Mode gain 0-to-100%, sliding down gives increasing Rate Mode gain 0-to100%.  Absolutely perfect.

All that said, the gyro is coming out.  There is no need nor any real benefit.  HH is interesting but high speed tracking is excellent without it, so why wrestle with the rudder to set the desired heading lock when you can point the plane naturally.  In Rate Mode, the gyro holds solid, but causes strong slip in turns at speed, unless it is gained way down.   Again, the nose holds just fine without it and the tail follows the nose naturally, so flight characteristics are best as the gain slider moves toward 0.   In Knife Edge, there is definite holding benefit, but by the time you set the attitude you could have established and held some rudder yourself, the plane holds a solid KE without much coupling without a gyro.  Again, not much benefit.  In fact it is overall easier to guide the natural stability of the plane than the gyro-enhanced version.

In slow flight, the rudder gyro acts just like AS3X.  With some speed (i.e. not quite slow flight), the gyro holds course steady.  But once a slow enough speed is established, still well above stall, the rudder runs out of authority and is likely blanked by the wake of the fuselage.  At that point the planes begins a gradual left yaw regardless of full right rudder, with or without a gyro.  Again, no benefit.

Slow aileron rolls are definitely more axial as the yaw axis sticks level at the 90-bank points, but again, the plane rolls nicely without the gyro, too.  This benefit is small, of little utility, and arguably not as fun to fly.

While it probably wouldn't hurt to leave this wonderfully tunable gyro in the plane, perhaps idling in a very low Rate Mode, tangible benefits are just not there.  The plane  naturally flies much more coordinated through turns and feels a lot more connected when flown aerodynamically.  

This cool experimenter has inspired me to move an non-AS3X board into the E-Flite UMX Gee Bee, to see if it results in a similar overall improvement in coordination and feel.


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Update 5: I CA'd the landing gear struts to the wing including the inner half of each wheel pant (the side with the clips).  The gear is much sturdier, hopefully making the plane less prone to ground looping.  

Z-28 Streak Trojan
To enhance  motor coil cooling on 4S, I Dremeled away the inside circle of the radial facade like my old Z-28 "Streak Trojan" shown to the right.

Taped all hinges, my left aileron was 1/3rd torn off from plain ol' speed.

Flight report on all these mods and more, soon.


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Update 4:  The question is not why, it is "why not?"   For $12, let's see how an in-flight tunable rudder gryo feels.  Yaw is the weakest axis by far at slow speed/high AOA, though rock solid toward the right side of the airspeed envelope.  With 3 oz of savings from Update 2, I could be convinced to do all three gyros for laser tracking at slow speeds, but let's see how one does, first.  Ground tests seem perfect.

Photo:  Gyro fitted between the rudder servo and inserted into Rx Ch 4.  Ch 5 remains reserved for dual ailerons to add flaperons/spoilerons, Ch 6 got the rudder gyro's yellow tunable gain lead, it is mapped to the Aurora 9's left slider (LS) enabling 0%-to-100% airborne gain adjustment. 

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Update 3: The Super Tigre .10 develops the exact same static RPM using the stock prop, but I don't think this is simple as equality.  The ST motor appears to be geared higher, not lower as specs suggest, since steeper props generate less static RPM, and lower gearing spins faster.   So although the static RPM is the same at 10x7 I expect the Super Tiger to fly faster on 3S once taller gearing is unloaded in the air.  Plus it is 0.4 oz lighter, X mount inclusive.  If you plan on flying 3S only, it might be worth switching, the ST will probably result in 5-10% faster top speed and/or 5-10% longer flight times. 

Personally, with 3 oz of buckshot removed I'm going to go with the stock motor running a 4S 3000mAh 20C, since I have a lot of those batteries and they seem well matched to the power system with a lightened nose.  

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Update 2:  A few great mods in progress.   Upon testing the Super Tigre .10 which is a drop-in, plug n play replacement (limited to 3S), I discovered and removed 2.97 oz of buckshot hidden in a black box directly below the motor.  Yuck!  Why didn't Great Planes recommend a 3000 mAh battery instead?  The world will never know. Dead weight thrown overboard.  Crazy.
 
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Update:  Two passes on 3S and two on 4S with stock 10x7 prop. 
Original article follows:

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Seems like yesterday there weren't any decent Gee Bee models on the market. Wait, it was only yesterday.  Suddenly we have two!  Great Planes released this gorgeous Gee Bee R-1 RxR right before Horizon brought their miniature Gee Bee micro to market.
Think fish bowl versus 20 gallon tank.
Almost as it sits in the box.  The aircraft portion of the Great planes Receiver-Ready (RxR) Gee Bee is identical to the Ready-to-Fly version, minus radio.  Assembly time to a flyable state is just a few minutes.
The E-Flite UMX Gee Bee R-2 proved to be one fun little mini. True, the manufacturer shipped it with a propensity for catastrophic motor failure on takeoff.  But within a day, Z8RC had a 10 second free and permanent fix posted;  E-Flite is still scratching their collective heads on the phone to China. I guess that's the  problem distributing and marking up few-dollar Chinese products that you just don't understand.  That said, given the simplicity and ease of the Z8RC solution, I recommended the E-Flite UMX Gee Bee R-2 (EFGBR2) anyway.  It is one of many Horizon Hobby imports that are well worth owning (please see my RECOMMENDED list). 
 
In their marketing campaign, E-Flite often reiterated that their near-scale Gee Bee would have been impossible to do before AS3X, their proprietary micro 3-axis gyro tack-on.  This claim piqued my curiosity.  I wondered how Great Planes could build an even more to-scale Gee Bee that might fly well without gyros.   Given that context, coincident timing, and the same price tag after adding one's choice of receiver, I decided to combine my GPGBR1 flight review with a Head2Head value comparo with the EFGBR2.
Note the illustrated rigging is not installed on my impatient photos.
Wingspan: 38.5 in  
Length: 27 in
Wing Area: 241 sq in
Fly Weight: 30 oz
Motor:  Brushless 1450 kV 

ESC:  Great Planes Silver Series 35-40A, 3-4S 
Recommended Battery:  3S 2200mAh 30-50C
Street Price:  $140 w/free shipping

Target Wing Cube Loading
Gliders - 1 to 4
Trainers - 4 to 7
Aerobatic - 8 to 11 
Scale - 12 to 14
<< Wing Cube Loading = 13.8 (or 12.5 after Update 2)
Racers - 15+

Just in case E-Flite is right and the GPGBR1 proves to be less than adorable in the air, and given the easy success of Z83X, I ordered 3 Futaba GY401-clones for a total of $36 from HK.  Those are waiting under plastic for the Bat Phone to ring.


Having owned many Hobbico (Great Planes) RxRs and ARFs, I know they are every bit as prone to critical quality failure as oft-shoddy Horizon Hobby Chinese stock. Let's face it, the recent surge in Chinese RC imports isn't due to impeccable QC. To the contrary, the only thing well controlled about these imports is a consistent lack of QC spanning all brands.

The difference between the two giants, Hobbico and Horizon Hobby, and more organic Chinese brands like J-Power, Art-Tech and the occasional FLYFLY or Angel or similar near-no-name, is mostly price followed by spare parts support.   But those two attributes generally offset when you can  buy two or more no-name brands for the same or less than one model from a larger distributor.   In general, I've found the quality of all Chinese imports to be about the same, with a small flying qualities edge going to the more generic Art Tech, J-Power, Angel class of planes. Mark-up, OTOH, fluctuates wildly.
The decaling looks great.  The black cheater stripe is delicate and needs to be sprayed with an acrylic gloss clear coat.
High quality Gee Bee models have been difficult to find, until now. The fact that one has come from Hobbico and the other from Horizon means we'll have to pay to play, but so be it, to the victor go the spoils. And isn't it great that sub-$200 for BNF/RxR models feels like high pricing in 2012?  What a blessing Red Capitalist sweat shops and comprehensive environmental disregard has been to our hobby!

So off we go with our pair of spanking-new pony keg air racers.  It's time to find out if the AS0X Great Planes Gee Bee R-1 can hold its own.
Hobbico's Aerocell foam is smooth and tough.  The paint is perfect and doesn't peel easily, even with the careful application and removal of tape. Molded panel lines and fuse stringers are true to scale. Even the aileron servo covers continue the numeric decals.
Ah ha!  No wonder this big blow fish is so bloated, it swallowed a rusty old 1 gallon paint can, whole.  I pulled it out to lighten things up:
This R-1 is a much bigger fish than your usual 38"' catch.
This Gee Bee has to be the biggest 38" wingspan model on Earth.  I love the jug fuselage, or is a planter?  No wait, I know, it is supposed to keep your beer cold on the way to the field!  This plane takes practicality to another level.
The Great Planes Gee Bee R-1 "Flying Beer Cooler"
All the servos and push rods are installed, don't forget to clip the elevator clevis after popping the horizontal stab in place.

There are incredibly strong rare Earth magnets everywhere--the battery hatch, the cowl, the horizontal tail, even magnetic wheel pants that pop over the wheels in halves.  Keep people with Pacemakers at a safe distance.  The Mayans predicted the Earth's magnetic poles would swap in 2012, causing cataclysmic damage to the planet.  The GPGBR1 could be the reason why.

I wound up removing the two front magnets from the fuselage side of the battery hatch, the magnets in the hatch itself go too deep to remove cleanly, and it still closes way too strong. 
There is almost enough room for a lead acid car battery.  Note the wing bolt installs invisibly inside the battery hatch, top-down.
Great Planes installed one of its 35-40 Amp Silver Series ESCs under the motor box.  I haven't even started the plane up and I'm already wondering about 4S growth potential.  The only specs listed for the new motor are a 35mm diameter and 1450 kV.   It uses the same form factor as a  Super Tigre .10 1200 kV so there is at least one drop-in substitute.

Motor fit is very tight behind the plastic radial facade, you can hear the faintest scraping as you manually crank the propeller.  
The new motor is 1450 kV and uses a Super Tigre .10 form factor.  The plywood motor box has been painted black to blend behind the mock radial motor.  Clean.

On the Great Planes Gee Bee website they state, "You can be assured that the pre-installed brushless motor, ESC and servos have been selected as the ideal electronics for this exciting electric sport model." That is really great news.  Let me take that to heart for a minute.

Ok, minute's over.

The stock prop is 10x7.  A 10x8 prop seems reasonable for the motor specs and could boost speed another 15%.  If the motor can handle 4S like the ESC, a 4-banger battery would be another effortless upgrade.  The real Gee Bee did 294.3 mph.  This sounds like fun already.
The mock radial looks nice ...ready for paint. 
Time to crash proof the foam and grab some engine run numbers.

Ok, here are the real world specs, hot off the grill:
Prop
Battery
Amps
Watts
RPM
MPH
10x7
9.5x7.5
3S-2200mAh-25C
3S-2200mAh-35C
25.5
25.6
287
297
8600
8820
57
63
10x7
4S-2200mAh-35C
33.7
467
9900
67
10x8
3S-2200mAh-35C
29.8
327
8100
62
9.25x8
4S-2200mAh-20C
38.2
555
9050
69
That's right, it's 4S ready out of the box!  The 14.4V specs are well within the ESC's limits.  We are left guessing about the motor's continuous and burst rating, but 467W could really be pushing it.  The motor's core has the same dimensions as a Rimfire .10 35-30-1250, which is max surge rated to 35A/390W.   Hmmm, maybe with 25C or careful throttle management 4S could work.  OTOH, a 3S with a higher C-rating might be just as fast after weight savings. 

The new motor's 3S numbers are similar, if not slightly better than the Super Tigre .10.  The ST .10 spiked to $30 after I started raving about it's ultra-high T:W.  This motor has a higher kV and a 4S option.  For $26 before Tower's barrage of email coupons, it looks like I might have a new favorite motor. 

I tried a 10x8 and9.25x8 (clipped 10") for the heck of it.  Both are too hot for 4S and the motor timing slips if you advance the throttle too quickly.   A 10x8 works well on 3S and is probably within limits.  It could result a touch more speed on 3S, but the increased fuel flow might not be worth the few extra mph.  I want to try the old Parkzone 9.5x7.5 Corsair prop on 3S, it might be the sweet spot.


Overall, it looks like Great Planes did a fine job of providing well matched, high quality electronics with plenty of headroom.   Wow.  That's different.  I was expecting an acrid smell and maybe a brief flash fire.  Sweet.

In the air:
Ready to rumble.
The winds have been out of control lately with days of driving rain and mild flooding.  When the Sun came out with forecast 2-3 mph winds all day long, I woke up early.  Bzzzzzt.  10-20 mph gusts with flags whipping on their poles.  I hate incompetence, and today's super-computer driven weather wind forecasting has become so inaccurate, so consistently 180-out from reality, you'd have to be mildly retarded to visit  the websites.  I guess that's a damning self assessment.  I remember reliable wind forecasting a few decades ago. Along with so many lost sciences and art forms, knowledge has been lost to modern-day, computer-distracted junk food education in a mostly sham university system, where no one with the cash to pay can ever be wrong, and the teaching staffs from Atlantic to Pacific collectively don't know $#@*.   Sheeze.  No wonder it was so windy today.  Ahhhhh, that's been bothering me for a long time, ok, now, with that off my chest...

Given the conditions, I decided to launch under 4S for a little more nose weight and power. 
This 4S setup balances exactly on the recommended CG.
The Gee Bee R-1 flew beautifully.  In spite of some fierce gusts, this pugnacious little racer established a pretty solid platform and flew with good balance, somewhat nose heavy.  The roll axis is quick and axial.  Elevator sensitivity is spot on, not touchy like I anticipated.  Yaw is like you'd expect, a little numb near the extremes but well mannered in between.  I noticed a little nose-down, wrap-up tendency while reversing heading with increasing bank angles, but today it was hard to say what was behavioral and what was gust-induced.

The plane was able to fly slower and under more control than I expected, but I'll need lighter winds to feel out the slow flight side of the envelope.

The GPGBR1 definitely has a racer personality.  It is also a more connected flyer than the UMX Gee Bee with AS3X chattering, but it is also more than twice as fast so at times it can seem mildly ferocious.  My initial impression is great, but this plane is intended for a fairly advanced crowd.

I wanted to get a maiden video up today given the long weather delay.   But I am going to wait for better winds and another flight or three before issuing my grades.   I hope to have a thorough flight examination up soon.
Crazy winds and a very topsy turvy landing.  What fun!

The winds fell to 6-8mph late this evening, so I raced the racer back outside approaching sunset.  Great Planes seems to have done an excellent job optimizing the power system, and since I only had light for one or two flights, I decided to fly the plane stock on its 10x7 with a 3S-2200-35C.  To my surprise, the plane went quite fast, only slightly slower than 4S/10x7.  Handling wasn't noticeably different with the lighter battery, but it seemed to slow down a little better.

Takeoffs are fairly short and the plane has a tendency to leap into the air once the efficient wing catches wind.  The right rudder requirement is magnified from a typical airplane.  Make sure you have plenty of rudder deflection available if you like to take off on low rates.

The GPGBR1 is a surprisingly amiable airplane.  The big bullet fuselage really is not that noticeable in the air, though the yaw axis is clearly the least stable particularly at slow speeds. Loop and roll aerobatics and hammerheads are not only within this plane's vocabulary, but performed from a very solid platform with little coupling; the airplane makes a downright proficient barnstormer.  Amazing!

That said, the plane can get tricky because rudder requirements are magnified.  One reason is the small size of the rudder relative to the airplane's mass.  Another reason is the large fuselage blanking the rudder, starving it of airflow, when AOA increases.  And a third reason is a powerful motor and large prop requiring a very large rudder correction between idle and military power.   Although the Gee Bee is very easy to fly at cruise speed and faster, it is not so easy to get into the cruise phase and then back on the ground again.  The plane is best suited for advanced fliers.

Landings are difficult for a few reasons:  
  • The plane seems nose heavy, but given the design's muted rudder effectiveness at times, I can see why a nose heavy condition might be warranted.   Finding the proper elevator and rudder trim position for landing is challenging. 
  • Nose heavy tail draggers like to somersault as they stop.
  • The gear is close together making it harder to land without scrapping a wingtip which can induce side loads onto the main gear.
  • The rudder loses effectiveness as you slow down and lift the nose, inducing yaw, making it harder to touch down without any crab.  Landing in a crab puts side loads on the main gear.
  • In order to land somewhat nose heavy, the main wheels are pushed pretty far forward.  Tail draggers with the main gear far forward like to ground loop when the gear, which are in front of the CG or center of rotation, get tapped with side loads--easily induced by two previous bullets. 
If you like a challenge you'll love landing the Gee Bee.  Give yourself plenty of runway.  Landing between curbs is not advised. 

65+ mph passes in stock config (battery choice doesn't count as a mod in my book) exceeded my expectations, but I really wasn't expecting that much for sub-$200.  The motor is an excellent and economical choice.  It performs better than most will probably expect, with copious vertical, flat speed to satisfy, and respectable flight times.

All that said, the racing bug is contagious.  Although Great Planes did a super job extracting most of the available performance out of their motor, the airframe seems to have a lot of capability left on the table.  I need to think about that some more...

No need for gyros here.

Time for grades:


Appearance: A+ 
Awesome presence. Beautiful execution.  Smooth EPO.  Perfect paint.

Airframe: A

Fully controlled at ramming speed.  Min coupling.  Rudder fades when slow.


Power System: A+
Rousing performance on 3S or weak 4S.  High quality.  Well optimized.

Build Quality/Durability: A
EPO
takes abuse.  Snap together/snap apart.  Standout craftsmanship.
 
Value: A+

Hard to imagine packing more into this deal. Discounts are common.
 
Overall Grade: A+

Just gorgeous. A true head turner. Quality components & EPO. Good price.




Head2Head with the E-Flite UMX Gee Bee R-2

Please see:  http://z8rc.blogspot.com/2012/02/head2head-e-flite-umx-gee-bee-r-1-with.html

....up soon.
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