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Old Aug 06, 2010, 03:00 AM
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joy4u's Avatar
Joined Feb 2006
105 Posts
How to compare brushless with the glow engine power..??

I am more into glow planes....

I want to convert some of my planes to the electric....
How do I compare a motor power with the engine I am using in that plane and match for conversion...??

Like I am using a OS .40 engine on my highwinger 40 size plane...What motor will I need to use to convert it to electric flight...???

More over I have some motors and how do I come to know what size plane can I make to power it with that motor...???
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Old Aug 06, 2010, 03:40 AM
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Letchworth, Great Britain (UK)
Joined Jul 2004
12,312 Posts
Some manufacturers -- Eflite comes to mind -- describe their motors by equivalent glow engine size, which makes life easy.

With others, all you really need to know is that 746watts = 1 horsepower. Watts = volts x amps, so you can calculate a motor's power (if it's not given in the spec) by multiplying recommended voltage by recommended maximum amps. This works fine so long as you choose motors which also have a kv rating (rpm per volt) of about 1000 or less. If they have higher kv they're going to spin very small props very fast, or they're going to need a gearbox to get the speed down so they can use a prop that's roughly the size you would expect on the equivalent glow engine.

As a rule of thumb, you need between about 75 watts and 200 watts for every pound of model weight (incl. battery, ready to fly), depending on the model type and your flying style.
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Old Aug 06, 2010, 09:25 AM
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USA, IL, Oak Lawn
Joined Apr 2007
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I go by watts per pound. I have converted a H9 p-47 and installed a power 90 on 7S getting 139 watts per pound. It flys great.
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Old Aug 06, 2010, 04:08 PM
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Ken Myers's Avatar
Commerce Township, MI
Joined Aug 2001
4,610 Posts

You might find the article "Comparing Glow Engine to Electric Power - Again"

in the August 2010 issue of the Ampeer helpful. Found here:
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Old Aug 11, 2010, 01:13 AM
Rangers Lead the Way
Joined Mar 2010
2,267 Posts
E-Flite makes it easy and others will give you comparison. I would say though that a Power 60 is probably ultimately more powerful than a 60-size slimer because the outrunner motor has more torque and can spin a bigger or multiblade prop for scale. Basically, an electric motor will extract whatever amps it needs to achieve a certain speed - like a carb that automatically jets up. As an example, for the 1/7 Sea Fury, a Power 110 has no problem swinging a 5-blade 16x8 Zinger prop, and an 18x8 is also possible at somewhat lower speeds. You would probably need a 150 4-stroke minimum to achieve this and there is no way a 110 2S can do this.

My Power 15 Super Sportster flies with noticeably more authority than my flying buddy's .25 nitro equipped Sportster despite approx the same AUW.
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