big rascal

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hi all i have plans to build a rv3 it has a 38 inch span it should wiegh around 2.5 to 3 lbs rtf for power i'm looking at using a 2.5:1 gear box and a brushed motor with an 8x5 or 9x6 prop the set up tached with a tach at 8010 rpm with a 9x6 wood prop on 9.6 volts my question is should this power set up fly the rv3 in this lbs range? and comments?

Matt Kirsch

My Feedback: (21)

What "9.6V battery" are you using? I ran the setup through P-calc at www.flydma.com, and got ~11400 RPM and over 43 Amps. I have a sneaky suspicion that your battery can't handle the stress, and is fading quickly under the load. That's why you're only seeing 8000 RPM.

When powering with electrics, you have to look at more than just prop size and RPM. Sure, the plane will fly on a 9x6 prop at 8000 RPM, but what's that doing to the motor behind the scenes? Can the motor take it? Can the battery pack take it? Can the ESC take it? You've got to answer those questions or you'll end up with a smouldering heap buried out in the weeds somewhere.

Prop size and RPM are generally the LAST thing we look at with an electric, because it all boils down to power. If you've got enough power, you can adjust the prop size and RPM through the use of different motors and/or gearing. The beauty of electrics is you can dictate exactly how much power your plane will have, based on some simple rules of thumb.

big rascal

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hi thanks for the inf. the motor and esc get hardly warm and i get 6 min of full throttle on it. again thanks for the response.