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Old Nov 03, 2012, 10:38 AM
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sixfins's Avatar
United States, FL, Sunrise
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Resurrecting Goldberg Super Chipmunk Gas or Electric?

I have an old Goldberg Super Chipmunk that I built for nitro (had an old HB .61 PDP Blitz). I am considering whether to convert it to gas (guessing 10-15cc) or electric. I'm currently leaning towards electric, but concerned about mods that will have to be done for the batteries. Since I don't want to have to remove the wing to change the battery. The plane was built almost 20 years ago. It has a smoke system, flaps, fixed gear (no retracts) and currently no power, it's covered and painted already. It was ready to fly and I got out of the hobby, didn't sell my gear. I just got bored and quit flying, now a little older and ready to come back. Any input as to the right size/model powerplant would be of great help.
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Old Nov 03, 2012, 09:06 PM
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United States, CA, San Diego
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I have one as well with a .61 Magnum installed. That is one great aircraft. Flying nitro here in san diego has become inconvinient at best, and I may want to convert mine as well. Right now I am getting my electric feet wet with smaller systems, less money and less grief if I miscalculate while figgering out the motor/batt/prop relationships. I imagine a plane like the chipmunk would take well to electric conversion; mine was a great flier and didn't need anywhere near all the .61 had to offer. tk
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Old Nov 04, 2012, 05:44 PM
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A rimfire 1.20 with a 6cell would fly this plane with ease.
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Old Nov 04, 2012, 06:05 PM
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You don't think the 1.20 on 6s would be huge overkill. It's only supposed to weigh 6-8lbs. and mine is probably on the lighter end of that. With radio, fuel/smoke tanks installed it's between 3-3.5lbs. just missing a power supply. If I go electric, obviously I will remove the smoke pump/system making it even lighter.
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Old Nov 04, 2012, 07:22 PM
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United States, VA, Arlington
Joined Dec 1996
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I'll vote for electric power, but the smoke system better go

Mods for the battery and motor? Figure out the CG shift of using a lighter motor than the glow lump, and how to mount your motor to put the prop in the right place for the cowling. Lose whatever the fuel tank was sitting on, and eyeball the battery fore and aft to hit the CG.

You really need an access hatch that enables you to remove and replace the battery - having a LiPo in the depths of a model where the only way to get at the battery is to invert the model, unbolt and unplug the wing and then go battery digging is not good. Go read the stickies on LiPo fires up in the batteries forum for suitable depression.

Motor sizing? Either look up some of the highly technical spreadsheet style figuring methods, then match a motor to your findings, or look around here for similar sized models of similar flight envelopes and see what they use.

Without sounding more depressing, you're going to be putting a fair amount of power into this model and if you buy a cheap Chinese ripoff motor, you'll be buying a cheap piece of junk. In terms of power, you're going to want enough to perform Chipmunk style aerobatics - which, having flown in one years ago, does not involve hovering, doo-floppy-dops or other such pranks. It is, however, always best to have a little more grunt up front than the bare minimum, so don't skimp too much.

You should be able to arrive at your old glow powered flying weight by the time you're done. Take that in pounds, multiply it by around 130 - 150W for a 'Watts per Pound' rating that should see you flying nicely like she should.

The Chippie is a sweetie, good luck with getting yours flying again

Dereck
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Old Nov 04, 2012, 11:17 PM
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Canada, BC, Richmond
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Quote:
Originally Posted by sixfins View Post
You don't think the 1.20 on 6s would be huge overkill. It's only supposed to weigh 6-8lbs. and mine is probably on the lighter end of that. With radio, fuel/smoke tanks installed it's between 3-3.5lbs. just missing a power supply. If I go electric, obviously I will remove the smoke pump/system making it even lighter.
No, I dont think its over kill........Better be over then under powered.

Back in 1994, I used to fly one with a super tiger 75, was a lot of fun.
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Old Nov 05, 2012, 07:14 PM
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Well the RIMfire would do the job with ease.

I would go with this setup. It can haul 12 pounds and do it well.

Motor
http://www.hobbypartz.com/bigfooutrubr.html

Battery
http://www.hobbypartz.com/98p-25c-5500-6s1p.html

ESC
http://www.hobbypartz.com/07e06-proton-60a.html

Use an APC 16X8 E prop and it will fly like it has a 91 fs in the nose. If you want more power then bump the prop up to a 16X10 or even a 18X6. I use this setup to fly my glider tug. It has no problem with power.

Would you be able to pull the canopy without breaking it and make a battery hatch under the cockpit?


Buzz.
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