Paul Bradshaw’s - “E” Power Set-ups That Work

Myth #5- Real men don’t fly electrics because they sound funny.  Hmmmm, don’t know who started that one.  I think the sound of a 30” wood prop spinning at 9,000 + sounds pretty cool.  Have you heard an electric pylon plane at 200 MPH+?  It’s all relative.

Some of the confusing stuff, electric jargon  -  For many years when you saw “20C” it meant that your plane had 20 cells of ni-cad or nickel metal battery on board, it still can mean that, but if you’re talking the newer generation of E-flite it means something else.  Currently or at least most of the time when we say “C” we mean the claimed discharge or safe charge rate of a Li-po battery.  A good example would be a 3200 mh battery with a 10C rating should be able to withstand a constant load or discharge of 32 amps, a 20C battery should discharge at about 64 amps.  This all gets pretty tricky as a lot of battery manufacturers tend to distort their “C” rating.  Basically a 20C battery should be fine for most sport flying but look for 30C or higher if you intend to do a lot of 3D, helicopters, or electric ducted fans (EDF), all of the last three are pretty hard on batteries.

“S” is now usually the term used to describe how many Li-po cells you’re using in series, a 3S pack is very common and the 3S implies that it’s made up of 3 Li-po cells in series, it has about, but not quite, the same voltage as an older 10 cell ni-cad.  A fully charged single Li-po cell is about 4.2 volts as opposed to a ni-cad at about 1.5 volts.

“KV” is used to describe the RPM of a motor at one volt.  K represents 1000 and V equals one volt, so if the KV rating is 1,000 and you give the motor only one volt then it will turn 1,000 RPM, all of this is assuming that there is no load of any kind on the motor.  Why would we care about a  KV rating?  Because it directly effects the type and size of prop and amp load of our application.  Here’s an example, E-Flite makes a 25 size out-runner motor in two different KV’s, one has a KV of about 850 the other 1250.  The 850 KV motor is intended for sport and 3D flying where we may want a lot of thrust to perform aerobatics and maybe even hover.  The lower KV motor lets us run a bigger diameter prop for the extra thrust we want to hover, let’s say it might be a 14 X 6.  The higher KV motor using the same prop would probably be over loaded, pull too many amps and over heat, but if we used the higher KV motor with a smaller prop say maybe a 10 X 8 we would have a lot more speed at about the same load.  It really depends on what application you have in mind as to what KV you might be looking for.  Remember, when you’re not sure don’t reinvent the wheel, just copy what someone else may be doing with your type of application.

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