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Old Dec 02, 2014, 03:51 PM
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Joined Dec 2014
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99 in butterfly setup ?

I'm building the "Butterfly" which calls for a 15 glow engine but I would rather make it electric. It has a 99 inch wingspan and flying weight around 50 ounces - wing loading around 7 and a half oz. What I want to know is what do I need in the way of a brushless setup?? motor size/esc/battery??
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Old Dec 02, 2014, 05:35 PM
If it flies - I want one!
Petem's Avatar
Werribee, Victoria, Australia
Joined Jul 2008
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Butterfly elec conversion

The Butterfly is basically a powered glider, so a good starting point might be between 150 and 200 watts per kilo of all-up weight.
Weight should increase very little with the conversion, so work on 1.5kg total, that gives somewhere between 225 and 300 watts - or 20 to 30 amps from a 3S LiPo delivering approx 10V under load.
A battery to deliver that sort of power for, say, six minutes will need to be around 2200mAh.
For the motor, have a look at the HK SK3 Gliderdrive series with the hard case and connectors on the back - the 3.5 960kv might work well here, with a 10x6 folding prop. Easy to install and will handle the power you need.
For a speed control, allow some 'headroom' and go for a 40A ESC - I use the Turnigy Plush series with zero problems.
Be aware, though, that there are as many answers to your question as there are modellers - you can certainly spend a fair bit more on a quality setup if you prefer that route (and I do, with my larger or more expensive models), but the setup above should work well and provide good performance at very moderate cost.
Cheers, and have fun,
PeteM
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Old Dec 02, 2014, 08:41 PM
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ScottSails's Avatar
Upstate NY
Joined May 2005
1,275 Posts
I think you have good advice above from Pete! That motor is very easy to mount compared to other brush-less motors (no wires to rub).

I would add that you want an ESC with a switching BEC (as opposed to linear), they cost a "little" more but worth the "buffer" for servos.

If you are going to fly this like a glider, a smaller battery (3Cell 40C 1800mAH) will be better and possibly a 11x6 prop. If you want it to fly like a powered plane, go with the bigger battery for longer run time.

From a safety perspective, get a spinner that allows you to use Aeronaut or Graupner (Esprit hobby is a great source) folding props (assuming you want a folder). There are various brands but these have published specs' on speed and are a known quantity. I am not a fan of some the Hobby King plastic ones...

Scott
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Old Dec 02, 2014, 10:17 PM
If it flies - I want one!
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Werribee, Victoria, Australia
Joined Jul 2008
1,080 Posts
Agree all, Scott: I buy lots of stuff from HK, but have found their props to be something of a lottery in balance, fit and strength/longevity. Trouble is, a decent folder setup can cost more than the rest of the equipment fit!
And you are right, if model is to be flown as a powered aircraft most of the time, a folder is not needed.
Pete
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Old Dec 02, 2014, 10:18 PM
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United States, IN, Indianapolis
Joined May 2002
4,379 Posts
Hi,
Nice info shared.
I would also check out this thread as Kimber ended up extending the nose some to aid in balance.

http://www.rcgroups.com/forums/showt...y#post24523609

Jared
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Old Yesterday, 01:05 PM
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Joined Dec 2014
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Since the butterfly has a tendency to be tail heavy and since my wing is 5/8 inches wider than the plan shows, should I move the wing forward or back 5/8th of an inch to compensate ? I'm still in the build stage and a little confused on this question.
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Old Yesterday, 01:23 PM
Dragons, WindMills, all Same
jcstalls's Avatar
United States, IN, Indianapolis
Joined May 2002
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Hi,
Well, if you read through the whole thread, you should be fine if you are extending the nose.
5/8th either way is not that much for the main wing.
Split the difference and move on.

Where are the snappies,

Jared
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