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Thursday, December 30, 2010

Update: Beaver Goes BL

Cost: 40" GWS Beaver ($30) + Super Tiger T 370 ($15) = $45
(reflects 20% Tower Hobbies member email discount)



Luv that Beaver. I plan to run this as a child's plane with a 10x4.7 SloFlyer and 1000 mAh 11.1V LiPo on a buddy box.  Switching to the ST 370 saves 0.9 ounces (10% of the no-battery aircraft weight), doubles max prop RPM, and allows the use of a same weight but triple capacity and 50% higher voltage 3S Lipo.   Hopefully, the BL motor doesn't tear the wings off.   Toning the throttle curve down should give 45-60 minute flight times with about 1:1 thrust to weight ratio.  I sandwiched all leading edges, the CG line, all all tail surfaces with clear mailing tape for a little more strength. 

More here when the BL Beav shoots skyward:


Houston we have a problem.  33 ounces of thrust from the ST 370 w/10x4.7.  12 ounce plane.  Time for 2s.


First test flights:

The first flights reveal what a beautiful little floater this air plane is.  It is so light that it is very sensitive to small changes in weight distribution and flight characteristics change accordingly.  Balance is gong to be a bit of a trick.  Even with a 7.2V 2S battery instead of an 11.1V 3S, the plane wants to pitch up to vertical under full power.  Elevator effectiveness is changed dramatically by thrust output (rudder effectiveness is unchanged).  At the same time, the plane is so airy, it is easy to trim out a broad range CG points.  So there needs to be a delicate balance between the trimmed elevator position, the best CG location, and the amount of power applied from glide to mil.  I am searching for the best battery position and may need to alter the recommended thrust line given the tremendous output of the feather light BL S/T 370 motor.  When I get it sorted to perfection I'll post the info/photos here.

Overall, it is easy to see that the plane will putt along like a dream at 20-30% throttle. The unique power to weight ratio of the ST 370 is presenting some solvable challenges to otherwise carefree handling.  Shouldn't be long to find the right CG placement and thrust line, if required.

Update:
Winds are not friendly to a 12 oz model, so we have a little longer development cycle than desired.  This morning I was able to float airborne in moderate swirl and identify the need to lower the thrust angle.  In order to balance the Beaver with the S/T 370 in the nose, I have pushed a 1000mAh battery all the way forward to the lip of the cowl cowl.  It is actually a very convenient spot since the wing can stay in place while changing batteries.   I was thinking 2S but for now at least, I'm going with 3S due to (1) I don't have a heavy enough 2S battery to balance the light engine and (2) the plane can barely hover with 2S.  The Beaver is perfectly balanced with the 1000mAh.


Update - Full Flight Review

Final verdict up front:  A

This little Beaver is a amazingly slow super fun flier, but because it can go so slow, it can be quite unforgiving if you fully stall it out.   If you have a small field and need short take offs and landings, it is exceptionally capable if not a bit tricky, a lot like the real thing.  It can glide incredibly far and is often advertised as a slope soarer.  In fact it can be difficult to spot land because it catches air so well and only has rudder and elevator--no slips. 

I wound up using a 3-cell brushless Super Tigre 400 ($19) that weighs less than the chunky stock brushed 2-cell, the larger coils are a better match to a smaller, low pitch prop than the 370 was at half throttle, which is where the Beaver thrives.  An 8x4 is the perfect prop size to keep both thrust and speed under control while still climbing out 80 degrees nose high in a steep torquey spiral, or straight ahead with half right rudder. The increased low rpm low prop load efficiency of this motor is impressive, average flight duration with a 1000 mAh 3-cell is about 20 minutes with mixed performance.  Practical throttle range spans from around 40% (DX8) for an easy max endurance cruise, to 60% for spirited over the tops.  A larger low pitch prop might increase cruise flight times even more at lower RPM, but full throttle thrust would probably need to be ESC travel limited to keep the plane under control at all times.


GWS Beaver  --  Super Tigre 400  --  GWS 8x4 Prop  --  1000 mAh 20C 3-cell
Flight Regime
Power Setting
Amp Draw
Flight Time
Extended glide
30%
0.3
---
Max Endurance Cruise
40%
1.2
50 minutes
Fast Cruise
50%
2.2
28 minutes
Over the Top Aerobatics
60%
3.6
16 minutes
Max
100%
6.2
10 minutes
Based on installed static thrust  - Airborne Amp draw will be lower

The plane could easily haul a 30% larger battery with the high T:W ST 400 up front, but with the above flight times, there is no need, and being an Induced Drag machine it might not fly significantly longer.  A smaller battery would likely require some lead up font to counter any weight reduction, so it may not make sense either.  I'm very happy with the overall power system/flight regime match.

The wing design of the Beaver is actually an under-cambered pocket, which provides good strength for the very light construction and an incredible amount of lift, as it is 2/3rds airplane wing and 1/3rd para-sail. The end result is an ultra light foamie with classic ($25) Beaver looks that easily flies backwards in a steady headwind. Winds are not kind to any 12 oz floater, and the GWS Beaver is no exception.

The build is more like a foam kit plane than ARF. The fuse and wings ship in halves and need to be glued up, it takes a full day or two to complete. The fuselage is tough. The wing is not very thick, but well supported with functional struts--I reinforced mine with clear mailing tape from tip to tip. The supplied push rods don't work without a secure sleeve around them (I used carbon fiber tubing pinned with foam safe CA), they bend way too easily making the plane difficult to control.  The landing gear is thin wire that flexes a lot during medium bounces, so much so, that you can strike the prop.  I solved that problem with small collars on the piano wire gear struts, close to each wheel, then I stretched a long thin rubber band over the two to act as a support and shock absorber.  The steerable cheap plastic tail wheel functions well, but the plastic has no grip--replace with a conventional rubber or foam tire for functional steering.  The plastic pinwheel mains work great, and are darn near weightless, but are the low hanging fruit to be replaced for scale looks.

Even though this plane is an exceptional slow/fun flier and excellent glider, it's not always the easiest plane to fly near the edges of its extreme performance envelope, and that will delight intermediate to advanced fliers.  The elevator can be overly sensitive to high throw due to the short distance from the CG. The wing design is pocket under-camber, which catches the air beautifully and floats just like an air-hockey puck (same principle). It has plenty of dihedral and is largely self correcting in flight, but if you push the rudder to far or too hard too fast, the wing can display some pretty unstable and asymmetrical, falling leaf stall characteristics. Loops, Hammerheads, Barrel Rolls, and 3 foot radius cornering turns are possible. It can make a really wonderful slow flying trainer after an intermediate flier trims it out and most importantly, limits the throws before handing it over.

As long as one realizes that the Beaver's amazingly short take-off rolls (5-10 feet), steep climb outs, near motionless slow flight, and glider-like engine-out performance comes at the cost of being quite tricky on the edge of those same generous limits, it will be a sure fave that can do uncanny looking stuff with the simplest maneuvers.  Commonly available for $30 or less, it's a lot more fun than ordering pizza.

Tuesday, December 21, 2010

UMX Beast Review

Addendum: As a result of my review, Horizon lowered the price of the UMX Beast to $99, earning it a B+ Z8RC overall rating.  Horizon deserves kudos for taking criticism and correcting their flaws.

Standing tall (5.5 inches)
In keeping with the theme of this blog, and unlike the unsophisticated sales pitches you'll find disguised as reviews on the popular scam sites, I am genuinely putting the new, E-Flight UMX Beast though its paces.  As always, I am not contractually bound to give a positive review that is tied to sponsorship money.   The review that follows has not been bought and paid for by the model's manufacturer.

That said, I enjoy a great product as much as the next guy.  While my reviews are a lot tougher than others because I actually know what I am doing, and have my own money at stake instead of requesting payment, perks and gifts, they are also much more fair to products that actually make sense.  
Horizon did a great job creating a tiny Pitts Model 12S II
Bryan Jensen's airshow animal, born March 27, 2009 
(Update: Died Aug 20, 2011.  RIP Bryan)

First impressions:

The 180 motor is smaller than the spinner
The little Beast is a great looking little model.  As usual, Horizon clearly paid attention to detail in an effort to deliver a high quality product, deserving of their premium pricing.  The paint job is very attractive and almost flawlessly executed.  Construction method is unusual for a micro, with a higher level of craftsmanship evident to assemble the wing struts and wires, a clear bubble canopy, and a more complex battery compartment and engine bay under a magnetic hatch.  Speaking of batteries, this is the first 2-3S ready HH micro.

Also typical for Horizon micros, is the use of fragile base material.  The flimsy foam board is well reinforced by carbon fiber wiring that mimics the 1:1 scale Pitts, but it is the same old poor quality and low durability flat sheeting.  Even the fuselage is weak compared to the better micros, if you aren't careful you could crush the integrity of the side walls with carefree handling of this product.  The clear bubble canopy is a nice touch, but it is so thin you can permanently dent it just by looking at it funny.  The wings and tail feathers need special care not to crease or snap their structural integrity during routine handling.  Reasonably strong micros, like the Hobbyzone Champ, have nothing to worry about here, Horizon/E-flight continue to churn out feeble builds that will hardly last the day if you aren't unreasonably careful.   The use of flimsy foam presumably keeps the weight down, but unfortunately for that rationalization, we've seen solid micros that weigh less.

Just to reiterate, the Beast's frail build doesn't stem from a lack of care, the problem is the selection of low grade foam as the base material.  It's a real shame, because the Beast, like many ultra flimsy Horizon micros, is a pretty cool plane.  One obvious way Horizon could reconcile their neat ideas with their inability to cobble together a durable product, is price.   With only a few happenstance crashes away from crooked obsolescence, it seems $70 would be a  more reasonable retail price point than $170.  For the amount of use even the best RC flyer will squeeze out of their low grade materials, the Horizon micro fleet is horribly overpriced and the Beast is the worst offender yet.

Another troubling thing about the product is the battery system, some monopolistic urge convinced E-flight to stray from a standard JST 2-cell balance connector, making the included battery charger your only lifeline to air time.  That wouldn't be as bad if they included an AC power cord for their custom charger, but recharging your battery at home costs extra.  Worse, my charger was defective out of the box, failing to charge the battery after more than 90 minutes of hook-up time.  I was forced to put an adapter together to mount the included battery to a standard balance charger.

The delivery defect made me think a little more about E-flight's choice of the battery.  Shipped with 2S,  the Beast's unique power system forces you to add a small Lipo + charger inventory that really doesn't overlap anything else in the market place, effectively raising TOC substantially.  As you can see below, the stock battery won't set any endurance records either, so you'll need at least one more.  That raises the cost by $14 for another tiny 120 mAH Lipo, or $16 for the 180 mAh version, plus about $20 for an AC adapter to use the included charger at home.   If the charger itself goes poof (like mine shipped) that's another $20 (estimated since no direct replacement is available).  That makes the effective cost to both own and operate the UMX Beast around $205.

Additionally, cell's this small are hard to find on the open market, meaning there is no downward price pressure on E-flight to bring their prices in line with reality.  It strikes me that a much smarter idea would have been to supply the UMX Beast with a standard, double battery input, to internally link the required number of 1-cell's in series.  Then, users would not be forced to buy a unique charger (even with the BNF version) and could use their existing 1-cell battery pool, or at worst, have access to any number of $1 to $5 batteries (double that cost to match the stock setup).  For that matter, it would be less expensive, and provide much more flexible power and charging options to snip the connector off the included battery and toss it in the trash, then and solder up a multiple 1-cell-series connector.

It is a sad day when your customers can easily blow away your value proposition using retail price components from your own parts dept.  E-flight, either your engineers are clueless or you are offering intentionally silly product configurations for the express purposes of ripping your customers off.  Disgusting incompetence in either case.

Here is the parts list to fix E-flight's UM-intelligence:

The Beast looks the part, even as a pip squeak

The miniature Pitts 12S II tipped my scale at a portly 2.2 ounces with the included light-duty 120 mAh battery, making it very possibly the heaviest UM ever.  For comparison, the 3D Ultra Micro 4-Site mini bipe only weighs 1.3 oz with a 150 mAH, and it suffers from the same 12 hour half-life super flimsy base materials.  Fortunately, initial installed thrust tests look promising, with exactly 3.0 oz of fresh battery pull, giving the mini Beast a respectable Thrust-to-Weight Ratio of 1.36.

"Respectable," that is, while it lasts.  Beast LVC motor waver ensued after a little over 2 minutes of T:W testing at full throttle. A more realistic battery weight would impact the peppy T:W, as will a rapid degradation of available power as the flight progresses.
 
Test Area
Result
Flying Weight w/120mAh 2-cell
2.2 oz
Fresh Battery Installed Thrust
3.0 oz
Fresh Battery Max T:W Ratio
1.36
Fresh Battery 1:1 T:W
80% Throttle
Run Time – Full Throttle
2:24 to LVC
Run Time – 60% Throttle
4:53 to LVC










The UMX Beast  arrives just in time for Christmas.  
It looks so nice under the tree it is tempting to display
it instead of fly it.  Nahhh!

Flight Impressions:

Too windy for a full review, today.  

I got the little Beastie airborne for a short flight (bounced around by winds, but controllable).  I couldn't help but notice that it felt a lot like a UMX 4-Site.  I suppose that shouldn't be unexpected since the 4-Site has the same wingspan, wing area, and flat foam "airfoil."  The Beast definitely has a higher T:W, and notably heavier nose when the power is down.   In fact, I didn't put quite enough up-elevator throw in my low rate setting.   In the heart of the flight envelope, the Beast is a faster 4-Site with a little more oomph when the tail is down.  Overall though, based on the Beasts edgy advertising, I expected a more outrageous 3D experience than I got.

The Beast is built a lot better than the 4-Site, which isn't saying much.  It has a beefier fuse and more CF wires to keep the tail and wing box from going trapazoidal.  

At first blush the Beast is a really fun plane to fly, but I generally prefer the lighter wing loading and similar handling at slower speeds offered by the 4-Site.  Additionally, the 4-Site has the option of floating down-lines with its giant optional speed brakes.  At half the weight and wing loading, the 4-Site is the more capable 3D micro, with the exception of straight-up pull.  The 4-Site is more susceptible to winds, but it can also be flown in small indoor spaces.

At around $205 BNF operating cost, pre-radio, it is hard to imagine passing up a hand-covered Great Planes 41" Edge 540 ARF @ $105 for a semi-disposable die-cut foamie, or even E-flight's own 42" Pitts M12 ARF for $150.  These large, capable 3D aerobats are top performers, and they sure ain't suckin' no Chick-let battery...


Great Planes 41" Edge 540 is $130 as a balsa & ply ARF 
including a Super Tigre .10 motor pumping a 1.5:1 T:W ratio
(minus 15-20% with usual Towerhobbies member coupons, no affiliation)
Even the 42" span E-flight Pitts M12 is $150 in ARF form
The 33.5" Art-Tech Pitts Special is $170 as a brushless 
foam RTF with a real symmetrical airfoil and solid build 
quality, including a nice 2.4GHz Radio, 1800 mAh 3-cell Lipo,
charger (with AC adapter), sim software, and Tx cable


In the flat airfoil EP foam category, there are numerous models that outclass the micro beast for the same price or less.
32" span Great Planes Edge 540 EP 3D
costs $89 with a brushless 250 included
(minus 15-20% with usual Towerhobbies member coupons, no affiliation)
The 17" span brushless TechOne Mini Eagle is $100 Rx ready
(minus 15-20% with usual Towerhobbies member coupons, no affiliation)

TechOne's 32" span F3P is $45 in ARF form
(minus 15-20% with usual Towerhobbies member coupons, no affiliation)
Kyosho's Minimum Ultimate is $120 as an RTF, with more 
power to weight on 1S and includes an LCD radio and charger.

Having flown the Beast several times now, I feel comfortable passing judgment.  The plane is really cute and a ton of fun for the front yard, calm wind warrior.  In terms of aerobatic prowess, it isn't bad at all for the small scale, but it isn't outrageously capable, either.  Thrust-to-weight is very good, but could use a little more oomph at times, especially as the battery fades after a minute of two.  It's not easy being a micro foamie in a very big world.

As far as 3D stunts, the Beast benefits from a lack of formal definition for 3D.  It cannot hold a stable hover, even though the T:W is better than 1:1 (for the first minute or two of each flight).  It can do a respectable knife edge, though it is a bit unruly.  Spins and inverted spins are good.  Snaps are good too.  Slow flight gets a little twisted at times, but mostly controllable fun with a consistent dose of rudder.  Vertical lines are all over the place, and not always from getting bounced around by puffs of wind, from a combination of torque, an off-kilter longitudinal CG, and manners that are rough around the edges.  I think the best word to describe the UMX Beast in "3D mode" is a very solid "flailer."  It's capability is nicely matched by a lack of precision. 

I think it goes without saying that the mini-Beast has its work cut out for it at the price point E-flight selected.  As a UM foam bipe, it is basically an expensive paint job on a faster, denser build that isn't necessarily better, aerobatically, than a lightly loaded 3D bipe or monoplane, plus it forces you outdoors.  As an outdoor brushless aerobat, it gets trounced by full sized 3D models that cost less.

So for a great looking UM biplane with a premium price tag, poor predicted durability, sexed-up but familiar flat airfoil flight characteristics, and an incomplete battery/charger system, I give the E-flight Beast a D+ (Avoid).  It's simply not a smart buy for any existing class of RC fliers, and its priced to compete with a class it can't see standing on it's tippy toes (yes, it has toes).

If E-flight cut the price to the $100 range or less, I could highly recommend the micro Beast.  It could even define a new class of front yard fun.  But front yard fun isn't fun when less expensive, fully capable 3D models literally blow it away.  That said, I think the entire UM(X) category is selling about triple free market retail value, due to monopolistic bad behavior on the part of colluding manufactures majority-controlling and exploiting the influence of low-cost Chinese labor. Until we see free market distribution in this market segment, companies like Horizon will continue to push prices higher and quality lower.  Worse, they are imposing a non-competition based distribution model that forbids price competition even among retailers, ultimately spiking the retail incarnation of extremely low wholesale price tags, preventing a lot of good products from reaching the hands of kids and low income buyers.  Sad.

Like other micros in the E-flight lineup, this paper-mache UM(X) will have a half-life best measured in days to weeks given moderate use.  So far, the only Horizon micro buy that didn't make me feel painfully violated is the Hobbyzone Champ, which can be reasonably durable given great care.  If you disagree with my basic value assessment, it is definitely worth dropping $200+ on this super-cute little lawnmower and its required accessories.

To add a little more pain, the manufacturer recommends a DX6i radio or higher, due to the Beast's touchy setup on a DX5e, raising the cost of ownership by another $150 to $400 for those without a Horizon brand expo capable radio.

Oh yeah, and the prop spins the wrong way!



Friday, November 19, 2010

125 MPH for $250

I've been wanting to buy a warbird with a big engine compartment to install my single-shaft, double-brushless motor concept (post coming soon).  I figured this project would be fun and faithful to scale--a monster engine turning a 4-blade buzz saw, a strong airframe, and at least 100 mph flat out.  As it came together, I also realized this was also shaping up to be a pretty cheap model, and even faster than planned.

I decided on an F8F airframe.  Even though it's a radial, the nose is plenty big and the real Bearcat's blistering 424 MPH top speed proves this little bullet is more than up to the task.  More significantly, the Bearcat's small proportions and beefy airframe provides a strong foundation upon which to build an RC powerhouse.

This seemingly amazing buy from Hobby King, further discounted to $80 via a pop-up promotional code:


Too good to be true?   No way, this kit far exceeded my expectations, the build quality and strength is formidable.  The entire airframe came assembled in interlocking, laser cut plywood.  This amazing find is 90% sheeted in balsa (Fuselage: 100%; Wing 80%), then covered in high-strength film.  The 35" wing, almost fully sheeted in wood, is one of the strongest I've seen in an RC kit.  This was the perfect choice for my WWII era demon.

My current iteration is a hybrid test platform, more traditional than its final destination.  It weighs in at 34 oz with its chunky 4S battery, a hefty 16 oz/ft^2 wing loading, a 14.8V .10 size motor driving a GWS 10x8x4 prop, a 60 Amp ESC (draws 61 Amps @ static full throttle), and a thifty OrangeRX 6ch Spektrum DSM2 RX (replaced with Spektrum AR500 due to consistent link dropping).  A functional side scoop keeps ESC temp in check.

Total cost?

$78 (with the usual HK "you've been looking at this a while" discount) for the Bearcat + $25 Temp Motor + $9 4S battery pack + $84 E-flight 60A  Pro ESC + 3 $15 Hitec MG servos + $8 RX = about $250.  Thrust to Weight Ratio?  Approaching 3:1.


With its scale-look 10x8x4 prop (shown) the little F8F can pull a 3 lb barbell, straight up, along with its own weight.  With a speed prop, 125 mph is well with reach.



Airborne telemetry shows some solid numbers:

With a 4S, full speed runs with a 10 x 8 x 2-blade draws about 600W.  Max static thrust pulls 1000W.  Not bad for a 35 inch wingspan, 30 oz'er.  

Flying Impressions:

This plane is a bullet (minus the stability of a bullet).  I need to tone the throws down some more.  Particularly, the elevator is touchy, probably due to the short distance from the CG.  The plane also has a strong desire to climb straight up under full power.  Balance seems ok in flight tests, and a bit tail heavy in others, but wow this thing rockets skyward.  I adjusted the thrust angle more downward, it doesn't seem to care much about that.  Makes me wonder a little about the fundamental angles of the wing and horizontal stab.  Maybe a THR>ELEV mix is in the cards, but I hate to resort to that.  More testing soon...

Notes from Dec 26, 2010 - Before taking the runway, a routine flight control check caught a dead left aileron.  I'm not sure how or when it happened.  Removing the wing revealed one of the threaded rods had pulled through the clevis and detached.  While fixing it, I decided to take the opportunity to add a bit of washout via slight permanent spoileron.  TP stall characteristics were noticeably improved, with nice symmetrical breaks and no tendency to dip a wing or spin.  This allowed me to flare the landing a bit more without planting a wheel.  I'll do more testing to find the right amount, for now I have each aileron displaced upward by one trailing edge width (about 1/16").

I tried an experimental THR>ELEV mix, but it was too much and pulled down under heavy throttle.  Overall though, the plane still feels reasonably well balanced over a wide range of speeds.  I'm leaning towards tail heavy as the culprit for the pitch hunting.  Next time out, I'm going to add some weight to the nose to assess results.

Dec 30, 2010

Found the high power climb culprit -- unwanted (or perhaps neutral) flaperon.  Screwing in a tiny dose of  permanent spoileron has completely fixed the handling of this model, making it beautifully stable and arrow-straight at high speeds. Vertical is unlike anything else I've seen or flown, it tears skyward with no respect for gravity.  

The only issue is seeing/orienting the solid blue paint scheme, going straight up turns the F8F into a dot in record time.  It is so fun to see a plane vanish in a second or two, then reality sets in that the plane vanished in a second or two.  Thrust is so strong that you can see the bullet hit terminal velocity, clearly prop limited, like it is attached to the throttle stick. By the time the stick hits your upper stop, so does the plane's speed, though it does take some room (like a small state) to slow down.    In fact, this plane rockets to top speed and disappears so fast, I'm contemplating adding streamers to the wingtips to help with orientation. 

Still a touch tail heavy with a 1300 mAh 4-cell.  The plane doesn't want to come down as it slows down, the tail droops as throttle comes out and up it stays.  You have to push it down final.  I've got a 2200 mAh up to 50C 4-cell on the way to fix that.  

First RADAR gun speed trials are scheduled this Monday.  Will start with a 100 mph setup, I want to take it slow.  If all goes well and the weather cooperates, we'll shoot for a 125 mph RADAR pass on video when the heavier battery arrives, hopefully late next week.

Jan 6, 2011

Tenergy battery company defaulted on the my order, noting they could not honor the price listed and  ordered from their website, paid for, and shipped (complete with a Fedex tracking number showing delivery today--all a scam info.  Amazing.)  So the RADAR test is delayed until I get the fast 4S I need to blow through 125 mph from a real company.

Sunday, October 31, 2010

20" Micro Wright Flyer

Coming Soon... Blade MCX conversion to a 20" wingspan, gyro-stabilized Wright Flyer.

Saturday, October 23, 2010

Fixing Flyzone's Select Scale Super Cub

Updated in yellow.

A flurry of Super Cub's have hit the market, it's an embarrassment of riches.  Flyzone's entry, their Select Scale Super Cub is one of the best looking Cubs on the shelf, and it comes in a PNP and RTF version.  How much more could one ask?

Well.... a lot, as it turns out.

This Cub looks so good and is so reasonably priced, I guess something had to give.  Flyzone has managed to embed all sorts of nasty vices in a simple Cub, and that's really hard to do.  They must have people who specialize in complicating the handling of simple planes.  I know, I know, every review of this plane is 100% raves.  Well, the plane isn't a great flier; it actually flies rather poorly in stock form.  Those websites only want to take your money to pump their paid sponsors; time for a dose of reality: 

Photo shows various upgrades and fixes, including:
motor/prop upgrade, LED mod w/wiring in the wing leading
edge and landing lights visable, gear and empennage bracing, 
and increased Dihedral.  I use clear mailing tape for strength
on all leading edges and to create "handles" at the wing root 
to avoid dirtying the foam over time.

The good news is that Flyzone's numerous mis-steps are, for the most part, fixable.  It is a basic Cub underneath, after all.  Here how to fix Flyzone's list of mistakes:
 
First, a list of the largest flaws:
  1. There is essentially no dihedral.  Perhaps this is true to scale, but the scale Cub is designed to be strong and cheap, first and foremost.  There is no reason to duplicate a straight wing in an RC trainer, when you can have massively improved handling by sneaking in a little wing angle--unless--your engineers don't understand basic aerodynamic trades, and Flyzone's clearly do not.  There is slight negative stability, meaning, if you set the Cub out of level, it will slowly increase, not decrease both pitch and roll until it hits the ground.  This holds true through out the entire flight envelope.  That's crazy--for a Cub.
  2. There is not enough geometric or aerodynamic washout, impairing slow flight handling.  See #8 for a related vice. 
  3. Empennage construction is too weak; the alignment of the horizontal stabilizer "floats" in flight, inducing slight, unpredictable roll with solid pitch changes.
  4. The Cub's wingspan is too wide for it's length, and/or, the size of the vertical stabilizer is ineffective.  Adverse yaw is excessive.
  5. There is erroneous reverse-differential aileron movement baked into the internal hardware mechanism, exacerbating the adverse yaw problem.
  6. The gear suspension is excellent in function, but the top spring wires are too weak to handle a medium bounce.
  7. The Cub is significantly underpowered with a full battery charge, and becomes severely underpowered at half battery life.  The plane struggles to get over-the-top with a fresh battery, falling off to one side unless the entry is down-hill.  Takeoff is tricky unless your extended runway center-line is  free of obstacles.  
  8. Traffic pattern stall tenancy is to snap into a tight, 90 degree nose-low, rapid spin.  The worst full stall handling I've ever seen.  
  9. The paint is inconsistent in color.  The cowling is a non-matching pale yellow, while the ailerons are a the warmest yellow on the plane and they don't match the wing color.  The fuselage changes color from nose to tail.
  10. The standard wing fit is loose, possibly adding to some of the Cub's squirrelly yaw behavior in the air.

    Fixes so far:
    1. Insert a nut between the metal wing strut and wing surface to increase dihedral.  The increased static stress on the strut seems reasonable, and will likely disappear in the air.  I used #4 1/2" wood screws through 1/4" nuts and washers.  Do not over-tighten.
    2. Insert both a nut and a washer between the rear struts and wings.
    3. Add carbon fiber bracing to the tail section (shown).  I penetrated the foam by about 1/8" then anchored with a tiny drop of Gorilla Glue.
    4. I recently added a clear plastic vertical stabilizer extension in front of the tail wheel, sticking down, F-16 style.  I'll provide a picture and flight report if it helps enough.
    5. Mix approx. 10% rudder in the direction of aileron movement. This will make adverse yaw worse whenever you are flying inverted, but that overall trade is probably worthwhile.
    6. Add carbon fiber bracing (shown).
    7. Change to a 9x3.8 prop for a little more pull.  Use higher C rate batteries.  Switch to a 400 or .10 size motor.  The Super Tigre 400 ($20) is a drop-in replacement using the Cub's own plastic mounting bracket.  The Super Tigre .10 ($23) also drops in with 1/4 inch tube spacers (since you can't use the included plastic mount adapter) but the bottom two mounts must be zip tied (still a stronger mount than the foam nose that holds it all together).  The ST 400 saves weight and adds about 50% more power given a large enough prop diameter to translate it's lower kV into more thrust (like a 9" to 10" diameter slo fly prop).  The ST .10 is the same weight as the stock motor and adds about 300% more power.  If you keep the cheap, low gauge ESC, make sure you don't pro-up the upgraded motors beyond 18 Amps.  The ST .10 only pulls 14 Amps max with a 9x3.8 (compare to 54 Amps with the Bf 109 3-blade) with less than 50% throttle required for spirited flight, and battery life is as good as stock (about 12 minutes from a 1350 mAh 3-cell).  With a .10 motor and the small 9x3.8 prop, Thrust-to-Weight ratio is only slightly less than 1:1.  To handle the increased thrust without excessive climb and yaw under power use 2 washers under the top right engine mount (model's pilot perspective) to angle the trust vector down, and use 3 washers on the left mount to create a (very) slight right thrust vector.  The prop shaft should still fit through the hole in the cowl, barely.  See the 1st pic below.
    8. Fix #2 helps.
    9. No fix required.
    10. With the wing removed, add two strips of very thin foam weather stripping to the top of each side of the cabin area, to seal the wing/fuse attachment lines.  I also dripped a few drops Gorilla glue down around the base of the small pole that holds the wing mount bracket in place, so its held more securely by the foam around it.  100% fix.

    The Cub is easy to retrofit with ultra-bright Radio Shack 4-pin square LEDs.  These LEDs operate on 2.3V to 5V.  They are almost too bright to view comfortably at night with one LED wired in series for each Lipo battery cell, and they run hot enough to harden the Cub's "aerocell" foam after a few minutes of stationary use, so consider running 4 in series (12.6V/4 = 3.15V; falling to about 2.5V per LED when the battery is empty).

    My Super Cub (shown) has 6 LEDs, 3 wired in series on each side of the plane (the colored Navigation Lights are double-LEDs).  The Nav Lights face inward, toward the fuselage, lighting the Cub up like a billboard at night, and reducing the blinding effect when the plane is viewed from the side.  You can see the LED on/off micro toggle (also Radio Shack) in the photo, above.

     
    Z8RC's rating for Flyzone's Select Scale Super Cub: B-.  Great looks, good price, no power (easily fixable +$20), aerodynamic design incompetence (mostly fixable).  I hope to get this plane to an A- flyer with the listed fixes--I still have to finish up some testing.

    UPDATE:  The fixes outlined above bring the FZSSSC to A level handling.  Stability is noticably enhanced, and the plane is eager to float effortlessly behind it's 1 oz  lighter nose (1 oz saved by the motor, another by removing the factory ballast between the cowl and fuselage side walls).  Increased thrust is welcome in all flight regimes, but most helpful is instant activation of the smallish rudder during the takeoff roll, following quickly by very strong climb-out capability.

    The Cub's new found dihedral and wash out is especially successful, allowing the plane to finally become docile and agreeable about where you point it.  One thing you might notice is a need to increase up-elevator a bit more aggressively as the plane slows near touchdown speed.  That is because the wing tips are now at a lower angle of attack than the wing roots, decreasing tip lift, meaning, the stall will now develop at the root first, reducing any tendancy to drop a wing hard.  A side effect is less overall lift at any given incidence angle, meaning you might need to raise the nose a bit more as the plane settles into a now more symmetrical stall condition.

    I added a clear plastic shark fin under the empennage, in front of the nose wheel to set her even straighter.  Great improvement in the willingness to glide-- the Cub takes a few dozen feet (less than before) to chin-up from a TP stall, hands and power off, but once it settles into a glide the nose stays up and the speed peels away until it appears darn near motionless - luv the improvement!  Now that's a Super Cub! 

    (could use one more washer per strut!)

    Addendum:
    I'm currently using one nut + 1 washer in the front and 2 nuts in the back.  Here is a picture of the clear plastic vertical stabilizer extension, it helps a lot but if I had to do it over again I'd make it 2about 20% larger.


    Tuesday, October 12, 2010

    Quick Take: Great Planes' $89 Fokker Dr.1 Triplane (ARF)

    I like to collect classic airplanes, so the gorgeous little Great Planes Electrifly Fokker Dr.1 Tridecker was a natural choice.
    Great Planes continues to release wonderful ARFs.  This kit is no exception.  For those used to foam airplanes forming the most popular RTF offerings, you are in for a treat.  The Great Planes ARF kits get you in the air in a reasonable amount of time and are in a much higher quality class than relatively junky RTF/ARF foam airplanes.  Thankfully the price is low enough to add quality servos and still come out ahead, at at least even with, foam RTF offerings from Parkzone and the like which are sold with junk electronics.  

    This kit is balsa and ply, roughly 5 times stronger than foam, truer flying, and covered in Monokote with a high gloss finish that doesn't deteriorate with use.  

    The plane has nice scale details, but for just $79 after Towerhobbies.com (no affiliation) usual discounts, nothing that will knock you over.  The Tridecker ships with is a thin plastic scale cowing the snaps in place using pre-installed rare earth magnets, a black radial engine bottom (I painted mine up a little), and two, pre-painted black balsa wood machine guns.  The wheels are sturdy and look great on the custom landing gear.  The "fouth wing" between the wheels is counted in Great Planes 300 square inch wing area, and 10-12 ounce wing loading calculations.  

    My model finished up at 24.2 ounces including adding 2 ounces of lead in the nose for balance.  (since removed, no need)

    I installed a Super Tigre .10 motor with a 10 x 6 hand-balanced Top Flight wooden prop. An 11 x 6 prop is shown, but is a bit power hungry for a 1300 mAh; flight times are only 6.5 minutes and thrust-to-weight is over-the-top.  Max thrust on a 1300 mAh 25C with a 10 x 6 is in the 29 ounce range, for about a 1.1 to 1 Thrust to Weight ratio at the Triplane's flying weight.  The $20 Super Tigre .10 is the perfect motor for this menacing presence in the sky, if not a bit too strong (is there such a thing?).  The motor is both too strong and too light for the plane, a thrilling combination.  Thrust is spectacular, as is top speed and agility.  Torque roll is an issue when slow, as the Triplane packs it's high aspect ratio 90" wingspan into just 30" on the top wing.

    Construction is straight forward, but the plane is not, so it takes some thought to put this baby together.  The nose is so stubby you have to be absolutely obsessive about saving weight in the tail section.  Each ounce of heft here will mandate about 5 ounces of nose ballast.  That's a lot for a 24 ounce model.  Be careful.  Cram every component you install as far forward as possible, if not under the cowling.  I sliced out the plywood battery brace, to shove the battery about half an inch farther into the nose.

    Balance is critical in a Tridecker, more so than most airplanes because there is so little nose moment arm. Make certain you balance the model using some sort of jig with a bubble level fixed to the horizontal stabilizer (but don't weigh down the tail).  I found the book CG of 2" back from the leading edge, a bit too nose heavy, so I removed about an ounce of the 2 ounces I originally installed for balance.  Yay--I really hate weighing down an airplane.

    This kit has a reputation for a weak firewall, so I added medium balsa cross bracing behind mine, as well as 0.25" balsa studs butting up along the left and right sides.   The end result is strong enough for an even larger motor, and the ST .10 is so light you'll still probably need to add a little ballast up front.  

    Visual control surface alignment is difficult, as the ailerons extend beyond the wings, and with 3.5 wings, one has to wonder how much twist and alignment error you can comprehend without simply giving it a try.  One wing shipped badly twisted--the one between the wheels.  A heat gun and some coercing untied about half the warp.  With that and a little aileron eyeballing, this WWI villain was ready to take to air.

    Take off was easy.  The gear is solid, and I installed an ultra-light tail-wheel for control.  Once airborne, the initial setup was a handful.  The plane wanted to roll hard left, no doubt due to unanticipated non-offsetting errors from all the wings.   I pointed the nose toward a 3/4 Moon and ran the trim right. Ahhh, much better. 

    Once trimmed up, this airplane flies great and looks even better.  What fun to see the abnormally tall three wing stack circling in sun-lit crimson.  As odd as the Tridecker is, it flies very well and is extremely agile in the air.  It has no apparent vices, but the excellent responsiveness and maneuverability need to be tamed with a healthy dose of expo. 

    My first loop was only slightly ajar upon exit, due to a little cross control from my immature rudder and aileron trim settings.  After trimming out the glide, loops became axial.  Nose track around turns is tremendous, making the Dr.1 an ultimate single-circle fighter.  I was afraid speed would bleed quickly, given the nose rate, but the agile flying wing box never dropped a wing exiting from some uncanny turns.

    One can feel the appeal of this age-old classic, you'll get a first hand appreciation for the men who loved piloting this vicious killer.  

    The 3.5 wing arrangement is almost square when viewed nose or tail-on, which could also be described as a circle (circumscribing the square).  This makes for exceptional longitudinal in-stability.  This is a great attribute for a fighter, but it is not the most relaxing configuration for sport flying.  With a good computer radio (mine bound to a DX8) unwanted roll can be all but exterminated.  That is, until, you run out of airspeed.  Point the nose skyward, pull the power back to essentially hover, and away she goes, rotating absolutely uncontrollably, opposite prop torque.  The Dr.1 is a very interesting combination of supreme roll-ability inherent to the design, while at the same time suffering from a relatively ineffective, top-wing-only aileron design.  The rare combination adds up to some of the most outrageous torque roll's you'll see this side of Oshkosh.  Luv it!!

    Landing? Who needs it.  Good thing cause this plane is a little bit of a handful.  My first landing was definitely hot, resulting is a well controlled, arcing bounce that quickly morphed into a miniature bouncing PIO.  Not too bad, no wing scrape and I rolled away.  The roll sensitivity is challenging, but also incredibly fun.    Nose authority remains high all the way through the round-out; greasing it on is definitely an option. 

    Overall, this plane was a great buy, a very strong and equally unique flier.  It is certainly not a first or second plane due to the interesting scale handling and the ability to out-maneuver yourself.  But for classic scale lovers who want a better appreciation for the great designs of history: I give it a B (Recommended), plus bonus points for some really fun quirks.  


    Well done, Great Planes, can we have a 40" version?



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