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Thursday, April 19, 2012

E-Flight UMX Gee Bee R2 BNF with AS3X - Flight Review

Standing tall (for an ankle biter).

Update 9:  See  100 mph Z8RC Piggy Bee

Update 8: Sadly the 5 x 2.75 prop has been causing frequent out of control flight conditions lately. I don't know if AS3X is dealing with more vibes as the plane ages or what, but it seems to be getting rapidly worse.  I had to switch back to the stiffer stock prop which fixed the problem.

The Gee Bee flies fine on the 5 x 2.75 without AS3X, but with AS3X the thinner material of the alternate prop resonates enough to throw AS3X for a loop.  The prop is perfectly balanced but the thin material allows a standing wave to form and AS3X goes nuts, quickly inputting full deflection aileron, elevator and rudder control gyrations. The plane suddenly spirals violently at certain power settings and air speeds. A quick-thinking change of the throttle setting brings the plane around but a 50 foot altitude loss is common.  If the throttle isn't moved promptly to a friendly setting the plane will hit the ground full force.

AS3X is turning out to be a big minus on this plane, especially considering there is little noticeable difference flying the Gee Bee with or without it.  Arguably it flies better without AS3X for intermediate skills and higher.

Update 7:  See  Z8RC UMX Gee Bee Scorches Past 50 mph (introducing the "Piggy Bee")

Update 6:  See  Flying the E-flight UMX Gee Bee withOUT AS3X

Update 5:  Added a rudder blanking video to the discussion below.

Update 4: See also: Head2Head E-Flite UMX Gee Bee R-2 vs. Great Planes Gee Bee R-1 

Update 3:  The Beast 3D 5 x 2.75 prop flies slightly better than the stock prop.  There is no difference in top speed due an offsetting increase in RPM.  But the lower prop gearing results in a top-to-bottom increase in RPM range which is useful for more controlled blowing of the vertical stabilizer at slow speeds and high AOAs.  This yields better center rudder yaw stability during landings at 10-20% throttle.    

The only issue I have with the 5 x 2.75 is a very strong AS3X-induced low frequency wing wobble from standing-wave resonance at 40% throttle.  Prop balance is perfect wide open.  It is not a factor, as the throttle setting isn't particularly useful for sustained flight and it's probably specific to my sample.  But if the resonance is universal, it might explain why E-Flite switched to a new, stiffer prop, to suppress faulty and/or overly-sensitive AS3X logic.  

You'll need to place two #6 washers behind the prop to take up extra shaft.  The wider cowl-to-prop spacing adds to the prop's increased thrust efficiency and reduced amp load. 

Flight times are improved by about a minute.

All in context, the 5 x 2.75 is definitely the preferred prop for the UMX Gee Bee. 

Update 2: See Z8RC 100% OCP Fix

Update: It seems my production-lot replacement airplane's built-in ESC is also bad.  From this failure I have to conclude the entire Gee Bee fleet is known to be marginal if not defective.  Incapable of handling the larger kV/prop combo at zero airspeed, the production sample motor is cutting out on run up too. In fairness, when unloaded in the air, the motor seems to run fine.  But also in fairness, one has to wonder if this degradation in the ESC current handling curve will continue to slump lower.

I tried a few things to fix the core problem including trimming away foam that cover the built-in ESC, and adding a heat sink to the power chips.  Unfortunately, the micro electronics forming the ESC scanned at 92.7 F degrees  maximum (68 F degrees ambient) when cut-out occurs.  Heat is not the issue.  The fact is this power system wasn't designed to handle the amp draw of the new prop.   The new prop was tested, so this  defect was known before release.  All shipping Gee Bee main boards are the same lot, so if you don't have this problem it is only because your battery is performing under spec.

Check your plane.  If your Gee Bee tests bad, send back only the airplane.  If the plane tests good, send back both the airplane and the battery.

One obvious remedy is to use 90% throttle on takeoff, or reduce throttle travel slightly with a computer radio or trim.  Another possible fix is to change the prop to one the power system can handle.

With fully charged batteries, here is the Stock Gee Bee prop (5.25x3.5) versus the standard UMX prop (5 x 2.75).  The 5x2.75 doesn't cut-out at all, I pulled the power back each time even though the first pull was a little quick, as evidenced by the prop not stopping.  Reversing the batteries produces identical results.  Note the static thrust difference:

Replacing the Gee Bee's larger prop with the UMX Beast 3D's 5x2.75 prop solves the problem and produces 1.4 ounces more static thrust at 3.8 oz vs 2.4 oz (putting the cowling-on adds another 0.2 oz)   

While this does not appear to be an inflight-problem, Horizon releasing known defective products to the general public raises questions of willful negligence and they need to immediately  refund anyone who wants their money back.  Horizon Hobby continues to disappoint the RC community with their upper management's chronic unethical behavior.

Original review follows:

The E-Flite UMX Gee Bee R2 is one of the few attempts by large RC houses to reproduce this classic racer. It has always surprised me how difficult it is to find a decent R2 model. The few models that do exist sport basic numbers and construction methods that just don't work well, and some look way off. Until recently, the Gee Bee mostly remained a mystery to RC community, and especially to park fliers.

Thankfully the drought has ended.

Wingspan: 20.1 in (510mm)
Overall Length: 13.9 in (352mm)
Wing Area: 72.5 sq. in. (4.7 sq. dm.)
Flying Weight: 3.60 oz (102 g)
Motor Size: 180-size 3000Kv brushless outrunner

The wrap was that Granvilles were too difficult to fly if not pilot killers. I've never bought that. Jimmy Doolittle loved the R1 flight characteristics and flew it to victory himself. He made his opinion pretty clear, "She is the sweetest ship I've ever flown. She is perfect in every respect and the motor is just as good as it was a week ago. It never missed a beat and has lots of stuff in it yet. I think this proves that the Granville brothers up in Springfield build the very best speed ships in America today."

But several Gee Bees crashed, giving the plane a lethal reputation. Never mind that freak accidents caused most of the fatalities. The first crash was caused when an errant gas cap whacked the pilot. Another was CFIT, no, not today's definition of CFIT: Controlled Flight into Terrain; the 1930's version: Controlled Flight into a Tree. Cecil Allen became famous for dying in his modified R1-R2, after the Granville Brothers advised him against impairing the CG with a larger, more aft fuel tank. Then there was that old rag in the carburetor problem, causing record-setter Francisco Sarabia to pancake in the Potomac River.

More recently, Delmar Benjamin and Steve Wolf built an exact replica of an R2 and flew it in airshows for more than a decade, proving that the R2 was a fundamentally excellent and highly aerobatic airplane.

And now we have E-Flite's gorgeous little Ultra Micro. I doubt E-Flight knew Hobbico was going to release their Gee Bee R1 parkflyer when they priced their 20" UMX bird a stunning $35 higher ($10 higher before typical email coupons) than a new parkflyer that is 9 times more massive.

Look for a review of Hobbico's Gee Bee R1 soon in a Z8RC exclusive Head2Head value showdown with the E-Flight UMX.

Great Planes 38.5" Gee Bee R1 is selling for $159 minus the usual $25 or so in email coupons with free shipping.  A quick look at the parts specs derives a practical (80% of theoretical) pitch speed over 97 mph on 3-cells.  Could be gravy.
As an added bonus, both of these Gee Bees arrive at your door for free.

I know what you are thinking, this is where I rip up E-Flite's just plain stupid $170 price tag. Wrong. Well, ok, I thought about it. But given there is nothing else like this mini R2 on the market and the level of detail, I'm almost ok with the price. True, the Hobbico's 2 lb-class RxR Gee Bee R2 blows this micro midget away on price per pound, at around $135 after member coupons and free shipping. But with AS3X possibly serving a purpose in this plane and an integral Rx, customer value isn't as deep into the sewer as the typical E-Flite UMX-pensive bird.

Street Price per Pound
Great Planes Electrifly Gee Bee R-1
E-Flite UMX Gee Bee R-2
After a minor delay getting a model with a fully functional main board, the Gee Bee arrives in box notably deeper than most UMs to shroud the bullet fuselage. This UMX Gee Bee will delight the buyer with the best details seen to date on any UM(X) airplane, surpassing the previous title holder, the infamous Jiggy.

Barring the pebbled beer cooler style Styrofoam, this model would be just as much at home under glass as flying down the street. But that would be pretty damn stupid.

E-Flite's cute Gee Bee R-2 has great details for a micro, although it is missing the thin black cheater lines dividing the red and white paint (except on the decals).

I spent a little extra time on the photography out of appreciation for E-Flite's obvious effort on the details. Hopefully it'll be worth dragging and dropping selected photos into the URL Address bar, then clicking them up to full size. Unfortunately, Blogger forced a 90% megapixel reduction from the 12.3MP full frame Canon L glass DSLR originals, so most of the photo detail is gone. But these pix should give you a better view than Horizon's dreadful quality web page photos.

The micro Gee Bee looks fabulous, for it's scale. This is one of the few planes that might even be cooler smaller than bigger. I think the Pony Keg look of the UMX-pensive adds to onlooker disbelief that this thing could actually be airworthy.

Unlike the UMX Beast 3D "BNFU" intentional rip off config, the UMX Gee Bee is a legitimate BNF with a 200 mAh 2S Lipo battery and a field charger to get bindable customers in the air. Still, there is no wall plug, so people who live in a house are out of luck.

The included E-Flight battery has their infamous 2S connector, meaning the plane is unflyable with other 2S mini LiPos. One of these days I'm going to finish my aircraft-side adapter to convert my UMX 2S planes to a standard 2S connector and use my stash of $2 2S Zippys. Until then, there are the outstanding $4 Turnigy Nano-Tech batteries which are sold as an E-Flite knock offs, complete with custom connector. They have more power and longer life than E-Flite originals, even at one size smaller.
The battery sits on a shelf inside a giant microscopic hatch. It is a little weird that the battery comes with velcro on the edge so that it stands on its side in the plane as configured. Like a retarded sheep, I flew mine that way, thinking it might hold some secret to a proper longitudinal CG or something.
Aside from the interior square footage, the guts will look familiar enough to UMX fliers. The E-Flite brushless 180 motor always looks small in micros, but inside this plane it's looks borderline ridiculousness. This 180 is 3000 kV, 500 up from the UMX Beast 3D. The prop is also faster at 5.25x3.5 instead of the previous 5x2.75 180 motor paddles. Pitch is usually rated around 75% radius, and with the R2's monster cowl I wonder how much of that faster air will get by.

Although my photo doesn't show it like I envisioned, there is strong aerodynamic washout very evident near the wingtips, maybe 2 degrees of forward twist. Horizon obviously read my Jiggy review. Nice.

This Gee Bee has to have the fattest, yet most insignificant rudder on the planet. It's simply perfect for the cartoon character of the airplane. It even works, sometimes.

I couldn't resist unpacking my extreme wide angle 12 mm, full frame 35mm DSLR lens for the R2 photo shoot. Shockingly, the result almost looked normal!

On the ground, this pumped-up little midget on body building steroids rocks. I love the true-to-scale wires, detailed molded foam stringers and ribs, the scale stickers, and even the pilot cranium looks ok.

Additionally, the plane has a subtle plastic chin protector and a plastic landing skid on top of the rudder--hmmm, I wonder what that's for? Great job all around!

The only drawback I see is the obvious integration of the body, wings, and tail section. Looks like it might be hard to put Humpty Dumpty back together again.

In the Air:

If you are expecting a long and twisted analysis of a devilishly tricky airplane to hurl through space, I'm sorry to disappoint you. The UMX Gee Bee is an easy airplane to fly. In fact, it flies great, but with one substantial vice.

First things first, take off is like any tail dragger. Apply a little up-elevator to guard against a prop strike and get the power in fast enough to energize the tail for slow speed directional control. That's a complicated way of saying, power up and pull. Duh.

The Gee Bee is very nice flying airplane. It flies just like any low wing sportster, and it is very stable at speed. It's tempting to call it almost trainer-like, as long as you keep the pace clicking, it is as stable as a trainer. Unfortunately, beginners probably won't like holding a medium pace all the time, so it's probably not a great trainer.

My first flight was in 4-6 mph slightly gusty winds, and the wind didn't present that much of a problem. The plane has plenty of power to stand up for itself, but if anything it can feel a little underpowered at times. The brushless motor needs to be about 30% larger. Once you build a head of steam, speed is zippy but nothing spectacular, at it flat-lines pretty early against an aerodynamic wall. Let's just say it gives the flavor of air racer and call it good.

Flight times are lame at 2-4 minutes. I put the battery smack in the middle of the tray and the CG felt well balanced during glides, maybe a little tail happy with the motor spinning--the nose drifts into a slight climb upon speed reduction indicating a tail heavy condition. AS3X doesn't do much the keep the tail level as speed bleeds. The wing (and fuselage?) loading is low enough, so E-Flite could have included a 250-300mAh higher C rate battery with a larger motor to suit the air racer's personality.

A second possibility for the power-off climb is that E-Flite angled the thrust line a little to keep their perceived beginner-level user base out of hot water. Whatever the reason, the thrust-line-to-elevator-chord-line relationship seems a little off. For most, the easiest solution will be to nudge the battery a quarter inch forward and forgo best range glides. Another possible explanation of the manufacturer's slight miss is a heavier battery option in the works, or a larger motor version forthcoming. The plane needs both, but why not set each release up properly?

Aerobatics need pace, but are straight-forward and pure. Coupling between controls is minimal. A left bank knife edge flys almost hands off. A right 90 degree bank knife displays minor torque and elevator coupling requiring minor aileron/elevator inputs. Knife edge flight in either orientation is sustainable in the first half of battery life. Loops can be big and are generally roll-free and yaw-stable. Rolls are fairly axial and the nose stays more level than you might guess for a barrel on wings.

Power-off glides are surprisingly shallow with the slightly light nose with the default setup. Although inverted flight is cooperative, it needs about 1/3rd down-elevator, indicating the elevator and thrust line are off.

Racing flat-out evokes a shrill scream from the winged beer keg, but top speed is held firmly in check by an aerodynamic wall. Typically over-gained AS3X adds significant drama by fluttering the wings wildly while flirting with the bleeding edge of the airspeed envelope; the plane appears to be on the verge of frantic disintegration. It is by far my favorite thing about AS3X in this airplane.

Making the flying experience special, the Gee Bee's WCL measures two categories below purpose. A refreshing 10.2:

Target Wing Cube Loading
Gliders - 1 to 4
Trainers - 4 to 7
Aerobats - 8 to 11  << The UMX Gee Bee flies here
Scale - 12 to 15
Racers - 16+  << Not here

In a word, the little Gee Bee is an overachiever. Better, it carries enough aerodynamic headroom to improve the motor/power solution down the road. The stock motor is adequate for spunk, but the racer inside could use 25%+ more speed, or about double the horsepower.

I would have predicted the family-model motor was a planned obsolescence feature with a plug-in performance upgrade in the works, but given that the main board can't handle the tame stock motor at full grunt without faulting, sadly that can't be the case.

 Second UMX Gee Bee R2 Flight in 2-3 mph winds.
Video Markers:
0:32 - Aft CG, power-off climb
0:50 - Best Speed
0:52 - Uncoupled left knife
1:05 - Right weather vane, aborted right knife edge
1:10 - Aft CG, power-off climb
1:20 - Right knife edge with some cross controls
1:30 - Aft CG, power-off climb
1:40 - Inverted flight, hunting for copious down-elevator 
1:50-1:58 - Idle glide.  Already feeling the motor worble on power-up
2:17-2:20 - 10% power-on final; a very easy to land airplane with space

As I mentioned above, there is one vice with the airplane. I would call it minor, but I guess it's enough to get a beginner in trouble if they don't recognize it or have a good feel for what's going on aerodynamically.

I've heard a lot of complaints about Gee Bees being tricky to land, but I've yet to hear anyone finger the root problem. The single problem with the design (Gee Bee's design, not E-Flite's fault) is really as glaring and obvious as the design itself is bold, you can feel it to some small degree on just about every airborne pass in light+ wind. It's not that big a deal, but it can turn into a big deal if you let it go too far...

The bullet fuselage blanks the vertical stabilizer at moderate to high Angles of Attack (AOA).

Complicating things some, the fuse is a thick longitudinal airfoil in its own right, so it wants to weather vane by yawing into any crosswind. The whole rear fuselage is, more or less, a flying wing turned on its ear, and it forms a pretty good lifting body on knife edge.

Similarly, the tendency to weather vane into crosswind is fairly strong but the little rudder handles it fine at speed. With the plane on its side, gravity tugging on the tail creates welcome lift off the body. This is certainly by design, as it helps keep the nose up and fights sink when carving through racing pylons. The plane loses less altitude when rolled on it's side than you might expect.

Even though the small rudder is moderately effective at speed, once the plane slows down, turbulent air sliding off the obese nose reduces directional yaw control to a democracy, and rudder position only gets one vote. At slow speeds and high AOA, P-Factor and torque begin to out-vote the rudder about 2 to 1 and the nose wants to skid left regardless of rudder input. Make sure you increase rudder servo travel to 125% and don't reduce it much if any on low rates.

Interestingly, since this problem is a lack of orderly airflow over the control surface AS3X can't do much about it, and it doesn't. What AS3X does do fairly well is keep the wings level, isolating the lack of rudder control to a numb, uncooperative slow yaw rotation. This is a case where the gyro hurts a little. If the plane were reacting purely aerodynamically, a loss of rudder control might kick one wing forward into the relative wind. That wing would create more lift and the plane would start to roll, consequently, adverse yaw would tug the wing back inline. As a minimum, you'd get more aerodynamic feedback so you could counter the problem. With AS3X, the rotation is more insidious, like a flat pinwheel slowly spinning in the wind.
High AOA Rudder Blanking
This whole discussion amounts to a non-problem at medium airspeed and faster. Unless there is big hairy Weeping Willow 10 feet upwind of your flight path, the plane's weather-vaning into crosswind is easy to counter given some airspeed, but it can make finding neutral rudder trim a little tricky.

While all single engine planes do this to some extent, the difference with the Gee Bee is that the rudder surface gets almost completely blanked by turbulent air at slow speeds with an elevated AOA, so the mild yaw tends to progress regardless of rudder input. The easy answer is to to carry a few extra RPM/knots through touch down. That's a shame because the plane has plenty of lift left in it to slow down. In fact, carrying those knots makes the plane want to balloon in the flare, requiring a longer runway than other micros. A more advanced solution is to land in micro right bank to counter the anticipated left skid and help keep the rudder cutting clean air.

I'm sure there is some way to help the rudder aerodynamically, or with a mix. I'll play with it soon and post the fix here as I figure it out.

Until then, it's past time for grades:

Appearance: A
Thrilling scale lines.  With better foam, it could be a static model.

Airframe:  A
A racer, not a lover.  Slight light nose.  Glides well.  True to scale challenges.

Power System: C (Update D+, ESC is over-amped w/degradation) 
Power is just ok.  4 min flights.  Battery upgrade would help both. 

Build Quality/Durability: B

Styrofoam.  Cheap servos.  Plastic chin, toes, and rudder roll over protection. 

Value: C-
$170??  So few nice Gee Bees around.  Numbing-AS3X is a wash.

Overall Grade: A (Update B+, overloaded ESC increases risk)

Fun starts from open box.  Looks and flies great--like a Gee Bee!  
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