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BUILDING ELECTRIC
Our thanks to Paul Click here for photo

                                                                                                                           Spring 2011

   Paul Bradshaw’s Basic Electric Flight Guidelines

Everyday I get calls or e-mails from people that say it’s too hard to understand this whole new electric thing, it’s not hard but it is different.  The whole “E” thing is really easier than figuring out a new cell phone or understanding a new video game.  Don’t try to get it all the first time through, with a little time it will become clear.  By the way it’s not new, some of us have been flying electric planes for 30 years or more.  Believe it or not Cox made an electric ARF with a 72” wingspan about 30 years ago, some will remember it as the “Sportavia” It was a semi-scale motor glider.  If you charged it just right and threw it really hard it might maintain altitude for about two minutes.  The charging system involved a six foot cord with clamps on one end for your car battery and on the other a connecter to the flight battery, you simply held the flight battery in your hand until it got warm and that was it, things have come a little ways since then.

This information is intended to be very simple, like a Reader’s Digest.  If you’re looking for the book version there are some great ones on the Internet.

The watts formula that follows is a basic calculation of how we measure the power of an electric motor, it will help you start to understand how this all works, and more importantly what will work. 

Volts X Amps= Watts   750 Watts is basically 1 horsepower.
50 watts per pound of plane = It will fly OK, very scale-like, basically gutless.
100 watts per pound = Not too bad, loops and short vertical, like a modest glow motor.
150 watts per pound = Good vertical, may even hover.
200 watts per pound = Now we’re talkin!  Unlimited vertical accelerates out of a hover.
300 watts per pound = You own the sky, 90 + MPH vertically, 130 + flat and level.
400 watts per pound = You have too much free time and money, seek professional help.

Volts are controlled by how many cells you choose to use to suit that particular plane and how you would like it to fly. Bigger planes as you might guess want or need more volts or cells.

Amps are a product of the motor and prop combination you choose, or the load you put on the battery pack, within limits.  If you find you don’t have enough power and the batteries, controller (ESC), and motor are running cool you can simply put on a bigger prop.  Putting on a bigger prop could mean diameter or pitch or both depending on what you’re trying to accomplish, when you choose a larger prop the amp load goes up, volts will stay the same because the number of cells you’re using dictates that.  One more time, because this is very important, by using different propellers you can dramatically effect the performance of any given set-up, not really so in a gas or glow set-up because they don’t have the torque that an electric motor has. Gas and glow set-up’s require several thousand RPM,s before they generate much power, not so with electric motors as they reach their maximum torque almost instantly.  If I had an electric set-up that I had been using but wanted to go a little faster I would simply reduce the diameter and put on a

 

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