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Old Sep 28, 2008, 08:10 PM
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All Electric's Avatar
United States, CA, Berkeley
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Goldberg Clipped Wing Cub conversion

Since I posted the story below I have added at least some 30 more flights with the Cub and way over a hundred take-offs and landings. This is a great combination! Take-off doesn't require more than 1/4 to 1/3 throttle. Powerful aerobatics are possible, with long vertical lines and large loops. On average, I do not feel that the power diminishes until some 12 - 15 minutes into the flight. After a flight, the 5S5000 lipo is just hand warm and when I hook it up to the charger, it's still at above 19 volts (!) So, a 5000 mAh pack is not really necessary, but on days like today, with a fierce gusting cross wind hammering the runway, it's nice to know you can go 'round and 'round without the fear of the motor cutting out early. And with the 5000 mAh pack the CG was exactly where it should be. Another reason not to exchange it for a lighter pack. I actually made the battery tunnel so it can hold a 6S pack as I didn't know how this combination would perform. Needless to say that this would be a pretty useless 'upgrade', unless you'd like to hover the Cub!
The only things that remain challenging are cross wind landings. The Cub keeps floating forever and quite often ends a cross wind landing with a 'ground loop', scraping one of its wing or stabilizer tips on the concrete runway. I added a small gyro that I just happened to have to the rudder channel. That helps quite a lot in keeping the Cub on track after landing. For the rest, it's just great - and very dependable - fun!
-----------------
I just finished the first couple of flights with my new Goldberg Clipped Wing Cub, modified for AXI 4120/18. It flies at least as great as a similar Goldberg Clipped Wing Cub I used to own years ago that had an OS FS-61 Four Stroke on it. I started out with the Aniversary Edition kit and modified quite a bit of the fuselage to accept the AXI motor and 5S5000 Lipo. The prop is a 13x8E APC. The all up weight ended up being 3250 grams (7.2 Lbs). At that weight the model flies great, performing large round loops and powerful vertical climbs. At 1/4 throttle it's great for some slow and lazy flying around. The only thing I'd like to have is more drag as the Cub is a real floater when coming in for a landing. I may add the scale bungie landing gear for that purpose. As the electric motor sounds more like a turbine than a flat four boxer engine, I modified the Cub's nose to look like it houses a small turbine.
I have found that starting a brushless motor from zero to whatever RPM is always a little 'jerky' and somewhat delayed. For that reason I added a throttle mixing function that basically gives me a motor 'idle' of just a few hundred RPM. This results in a very smooth throttle curve and great handling.
Needless to say, I love to fly this new Cub!
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Last edited by All Electric; Oct 12, 2008 at 04:19 PM. Reason: New data
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Old Sep 28, 2008, 09:41 PM
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hoysome's Avatar
Alberta, Canada
Joined Jun 2008
817 Posts
How do you mix your throttle to get the jerking out?
I use a futaba 10C, plane is an e-converted Ultrastick 60. 6s lipo, axi 4130/16 outrunner, jeti 77optio.
I just set my end points tonight because i was hitting full motor throttle at 3/4 stick, and zero rpm was at 1/4 stick. its fine flying like that, but I wanted more sencitive control

Anyway, since I have a much larger movement now, I get the jerking when the motor starts up..
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Old Sep 28, 2008, 10:14 PM
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United States, CA, Berkeley
Joined Aug 2007
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Electric 'Idle'

I use a simple switch on my 6EX 2.4 GHz transmitter. It basically adds 15% to the throttle channel, so when the switch is flipped, the motor keeps running slowly, when the stick is at its low end point. You would get the same effect using the throttle trim, but using the switch is far more predictable. And should the airplane topple over, thus blocking the prop, a flick of the switch will put the motor back to 0%.
I have heard of other pilots having a speed control that only works between say 25 and 75% of the stick motion like you decribed. But that's not the issue with my (JETI) speed controller. Some of them use a helicopter throttle curve to overcome this problem. I hope this helps.
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Old Sep 28, 2008, 10:16 PM
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Alberta, Canada
Joined Jun 2008
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yeah, that will help alot
its more simple than I expected it to be.
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Old Sep 29, 2008, 02:38 PM
Visitor from Reality
United States, VA, Arlington
Joined Dec 1996
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Neat clipwing you've built yourself. Not often you see the Goldberg, very few Sig kits and mostly yellow BARFs. Love your colour scheme - the only Cub I've had from four or so that came out yellow was a 16" profile rubber model, and that because I had some handy yellow tissue.

For some atmosphere, here's a couple of shots of my somewhat non-yellow Sig 1/6th clipwing - my 1/5th was too much of a pain to carry around!

Am going to check out your throttle mixing set-up - I have the same tranny as you. This could be nicer than that sudden zero to 300 RPM! I still have a couple of MaxCim brushless with sensored ESCs, they would start up from zero with linear speed to stick, 'idle' being 'count the blades' slow.

Of course, 'progress' invented the sensorless motor which, with appropriate marketing, has taken over from sensored motors.

And sensorless is much cheaper to make too...

The one typical aerobatic maneuvre my Sig Cub doesn't care for is inverted - lots of push needed, around third power and she still descends a little. My inverted repertoire is a down-wind pass - that's about all I feel confident with right now, even an inverted 360 orbit feels a little flaky. Otherwise, it looks like a Cub and is great fun.

Mine might get a more-scale sprung UC this winter too!

Regards

Dereck
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Old Sep 29, 2008, 09:58 PM
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All Electric's Avatar
United States, CA, Berkeley
Joined Aug 2007
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Cub Aerobatics

That's a very nice Cub too! The Goldberg Cub by the way has no problem flying inverted whatsoever, despite the flat-bottom airfoil. The limitations are mostly caused by my flight skills .
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Old Sep 30, 2008, 03:22 PM
Visitor from Reality
United States, VA, Arlington
Joined Dec 1996
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Quote:
Originally Posted by All Electric
That's a very nice Cub too! The Goldberg Cub by the way has no problem flying inverted whatsoever, despite the flat-bottom airfoil. The limitations are mostly caused by my flight skills .
Which proves that aerodynamicals are a black art! My favourite ride is a highly hacked around Four Star 40, which has a flat bottomed wing section that designer Bruce Tharpe openly admits is a TLAR (That Looks About Right), yet the dear old thing doesn't give a hoot over which way the wheels are pointing! Both the Sig kits I've built had fairly 'scale looking' sections, mostly flat bottomed, but with a little rise towards the LE from the foremost spar - can't recall how the big one did inverted, maybe for once, I refrained from checking that out. It did loop and roll pretty Cub-ish though.

On the Cub track again - I recall reading an interesting piece on a (full size) Cub web site, the author of which was begging folk not to buy J3s in need of restoration and then clip their wings, rather to seek out already clipped examples. He stopped a little short of actually using something like 'despoiling'!

FWIW - it was a lot easier getting at the battery and RC stuff in the bigger Sig kit! It had the full blown side door and hatch, plus more internal space. I fitted a magnetic latched side door to mine, but she flies with the window stowed in her hangar

More trivia - this link's to the inspiration for mine Mine is "Monokote scale' in colour though
http://www.richard-seaman.com/Aircra...hts/index.html

Last I heard of '170, she was in a hangar somewhere in Florida, needing some repair work... Wonder why?

Regards
Dereck
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Old Nov 01, 2008, 11:01 AM
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Kenpilot's Avatar
Joined May 2006
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That is a sweet piece of work!

I am a clipped wing Goldberg Cub fan since I learned to fly on one years ago. Mine had an O.S. 70 FS. Your work has inspired me to do build an electric version.

Questions: do you have drawings of your mods at the firewall? How much noise does it make? I recently joined a club that allows electrics to fly early in the morning provided they are "quiet." This is the reason I started looking around at electric cub kits, but none seem to be like the Goldberg Cub I remember.

I also considered buying the Goldberg Cub ARF available from Tower Hobbies, but thats a full wing. That would be okay too, I just want a lazy quiet flier to enjoy those early mornings with.

Thanks for the info. Great looking Cub!

Ken.
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Old Nov 01, 2008, 08:16 PM
Visitor from Reality
United States, VA, Arlington
Joined Dec 1996
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I thought I had some others of my Sig Cub electrocution, but then I didn't really do much to the front bar add some holes to the firewall... The other big mod at the front was to be a battery hatch underneath, as in the third shot. Turned out I had good access through the scale door/window I built in - that was something of a deviation from a standard build review. Figured Sig's 1/5th has the scale access, so

My motor is a Mega 45 - sorry, can't recall the rest of the numbers, but even though its an 'inrunner', it swings a good, matching size of prop on either 3S or 4S. I don't think it could get much quieter, without leaving off the struts and never diving!

I'm kinda lucky - fly off a site that was lost to the big local club back in the 1980's thanks to a neighbour who didn't like listening to whining IC engines - how odd! - and knew where at county hall to whine himself. Some years later, the whiner had moved away and club members lead a succesful drive to recover use of the site for 'quiet flight only'. Unfortunately, the site and runways suffered from construction and other useage, but its still good to fly most electrics from.

Still, I have a feeling that if you said to a slimer club that it was 'go quiet, or go', the answer could still be the same depressing one it was 20 years ago.

I think the quietest electric I ever had was an aerobatic 36" model powered by a DD Speed 400 on seven cells!

D
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Old Nov 09, 2008, 06:12 PM
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Central Lake, Michigan
Joined Dec 2002
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Been thinking about one of these. The only thing I don't like are the strip ailerons. Definately not scale, and I don't understand why Goldberg did this especially since this was a supposedly semi scale "Anniversary" kit.
My version would be to replace the "lite Ply" fuse with balsa as well as most of the formers. Modifications to the wing for barn door ailerons instead of the cheap strip. The cowl on the one I bought from my brother was of the flimsiest thinnest ABS I've ever seen. A real "testament " as to how Carl Goldberg's family felt about the business. Replace it with one from Fiberglass Specialties.
I've seen some very nice detail mods done to these "sport scale" kits, enough to make them look halfway decent.
cheers
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Old Nov 09, 2008, 10:02 PM
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Joined Dec 1996
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Roger
If you've got the carrying capacity, take a look at Sig's 1/5th scale kit - it comes with all the parts to make either the regular J3 or clipwing. I built one as a J3 a couple of years back - one of the best kits I've ever built, everything fitted and lined up superbly well. It was a very minimal electrocution, came out at a shade over 8lbs with 20 x 2000mA NiMh or 16 x 3000mA NiMh - I soon dropped the 20 pack as it was way overpowered and got airborne in around five feet every time.

It's very scale in appearance, though I didn't do any actual checking beyond eyeballing it. It has plenty of nice touches, like the heavier rear wing struts for the clipwing version, as per full size. The scale entry door/hatch makes getting to the battery very easy and the firewall is far enough forward inside the cowling that you shouldn't have to pack an electric motor very far forwards to put the prop in the right place.

Its cowling is a solid three piece and comes with enough dummy engine to look the part without involving a massive project.

One real good point - at 84.5" span, it is true 1/5th scale - unlike the rash of BARF Cubs, which are usually just above the magic 'IMAA legal' figure of 80" to cost more. The plan is CAD drawn, the parts are laser-cut, unlike many kits of older vintage, this one is right up to the minute.

In comparison, Sig's 1/6th that I recently built as a clipwing really shows its age, being a die-cut kit, though it is still pretty scale-like. It lacks the dummy engine detail though - a real omission indeed. Unfortunately, deep searching of my digital photo files has failed to unearth any shots of my 'big' Sig Cub - it was reviewed in 35mm print days, it seems.

D
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Old Nov 10, 2008, 08:47 AM
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Central Lake, Michigan
Joined Dec 2002
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Dereck I like the 1/5th Scale much better. Alas! The price increase has put me off, though I still want to get this one. Being laser cut and with Sig's quality, you can't go wrong. The quality of Goldberg kits is very unreliable.
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Old Nov 12, 2008, 11:25 PM
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eastern pa
Joined Feb 2007
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Hi guys. Just wondering, since All Electric only used 1/2 throttle to fly this Cub would it be enough to power a Nosen 108" Champ in a scale like manner? I have a partially built Champ I abandon 'cause didn't want to wet power it. Or would something else be better? I like to keep an eye on the $$$$ costs.
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Old Nov 13, 2008, 03:43 AM
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United States, TX, Sweetwater
Joined Mar 2005
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Having chugged about with an AXI 4120, I would say yes. However, I believe I'd get a 4130, wound to turn slower (big props, ya know...). Its the same money, but will handle the big Champ with more authority.


Quote:
Originally Posted by aeronca52
Hi guys. Just wondering, since All Electric only used 1/2 throttle to fly this Cub would it be enough to power a Nosen 108" Champ in a scale like manner? I have a partially built Champ I abandon 'cause didn't want to wet power it. Or would something else be better? I like to keep an eye on the $$$$ costs.
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Old Nov 13, 2008, 10:30 AM
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Central Lake, Michigan
Joined Dec 2002
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Quote:
Originally Posted by aeronca52
Hi guys. Just wondering, since All Electric only used 1/2 throttle to fly this Cub would it be enough to power a Nosen 108" Champ in a scale like manner? I have a partially built Champ I abandon 'cause didn't want to wet power it. Or would something else be better? I like to keep an eye on the $$$$ costs.
Check out some other mfgs such as:http://www.allerc.com/
http://www.innov8tivedesigns.com/
They both have very good motors at very reasonable prices.
I've seen quite a few Bud Nosen kits for sale lately both here and on E-bay. What's the quality like?
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