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.
 
Amps are a product of the motor and prop combination you choose, within limits.  If you find you don’t have enough power and the batteries 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.  More volts and less amps is slightly more efficient than the other way around.
 
Over the last few months I’ve noticed that most of my normal planes or everyday planes all end up with about one Li-po cell per pound of flying weight.  This is based on 3200 mah 20C batteries.  From my 22 pound third scale to my 10 pound Funtana 90 it seems to work, or at least in the ball field.
 
Myth #1- It sounds too complicated and it’s too hard to figure out what to use.  With a simple amp meter, tach, and digital fish scale (used to measure thrust and the weight of the plane) you can quickly see if it will fly and maybe how well.  The internet is full of helpful sites as well, too many in fact.
 
Myth #2- Lithium Polymer batteries cost too much - yes they do you’re right, but at over three bucks a gallon so does gas.  Li-po’s purchased within the last 18 months or so actually cost less than NIMH or NI-CAD’S if you measure them by the energy stored.  Newer batteries are also commonly going way beyond 400 cycles and Lithium-ions are close to 1000 cycles but a little heavy.
 
Myth #3- I’ll start with NIMH or NI-CAD and brushed motors and work my way up to save money.  Don’t do it, newer brushless motors are almost bomb proof, last forever, and are up to 50% more efficient than brushed, they truly can make the difference between success and failure
 
Myth #4- This is just a fad, it won’t last much longer, yeah and cell phones are trendy and will never catch on.  I remember when the first four stokes showed up and everybody said, no way they cost way too much!  It’s just a fad, they could never replace the good old two stroke, some people even wanted to ban them from their fields.  Electric plane sales now out number glow, not in the big ones but that may be coming.
 
Some of the confusing stuff   -  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 your 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.
 
“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 is 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.
 
So lets design a power train for an “E” plane, it really is easier than it sounds.  We’ll make it easy and say that we want a 10 pound 3 D plane.  Looking above we find that we’ll really need about 200 watts a pound to have a great performer.  That means unlimited vertical, hovering at less than half throttle, and a nice explosive pull out.  Now take the 10 pounds X 200 watts and we see that we need a motor than can sustain 2000 watts or a little less than 3 horsepower.  (1 HP = 750 watts X 3 = 2250 watts)  I like a lot of headroom in my set-ups so I’m going to look for a 2500-watt motor.
 
  E-Flite the Horizon Hobbies house brand did themselves a big favor when they started labeling their electric motors with the good old glow engine sizes, most all of us can get a good idea of the potential that way.  E-Flite also does a nice job on the actual box of  the motor showing the suggested max amp load, suggested voltage or lipo cell count (S) and even a suggested propeller.  Because of my altitude (6,000’) I find myself usually going about one inch bigger in diameter on the propellers.
 
Once we’ve looked at the E-Flite offering we find that the 110 size should do the job nicely, and it will, but who can resist all of that extra horsepower on tap with the 160, not me!  If my memory serves me right the 160 is listed at about 2500 watts and sustained loads of about 70 amps with a 10S lipo pack.  If we do the math a 10S lipo pack under load is good for about 3.7 volts per cell or 10 X 3.7 = 37 volts X 70 amps = 2590 watts.  If we divide the 2590 X 10 for the weight of the plane we have almost 260 watts per pound.  That’s almost like flying your 40 size Ugly Stik with a O.S. 120.  We should back it down a little to create that headroom we talked about.
 
I’ve decided that I’m going fly this plane with a 9S lipo pack because I have a lot of 3S packs that I can connect in series to get the 9S voltage that I need, and it creates the safety margin I like.  Additionally if I reduce the voltage a little I can run a bigger prop which is much more efficient especially at my altitudes.  The specs on the box suggested a 20 X 10 APC E prop on 10S, but for a 9S set-up and the altitude I’m going to start with a 22 X 10.  This should put us in the 65 amp territory while static on the bench. Keep in mind that when the plane is flying depending on the drag of the airframe, it could unload as much as 20% or more, dropping the full throttle amp load down to about 50-55 amps.  The only time you should see the high bench amp draw again is pulling out of a hover or other high-alpha maneuver, and that shouldn’t be for more than a few seconds.
 
The last important decision is the ESC, (electronic speed controller) based on what we think we know I want an ESC that can sustain about 75 amps with a 10S lipo pack, remember it’s that headroom thing again.  I like the Jeti Opto 77 because it’s small, light, and it’s never let me down.  Others could be the Castle HV 85, Hyperion 90, or even the Jeti 90.  Just make sure it’s a 10S controller.
 
Last but not least is the battery pack size.  For some reason I’ve ended up with a number of 3200 mah 3S packs.  Some may think these are a bit small for some purposes but I really like the weight advantage over the more common 5000 mah packs.  The 3200’s have a 20C discharge rating so pulling 64-70 amps is no sweat and when you finish this set-up with the 3200’s it saves more than an entire pound of weight on a 10 pound plane.(9.2 vs. 10.5) It make s a difference.  As far as flying time I set my timer at about 8 minutes and I’m usually down by 9.  The 5000’s are good for about 12-13, I have a short attention span so the 3200’s work for me.
 
One more little detail, receiver power.  Most of us have lots of receiver packs lying around and they often serve as a CG device, so be it, just don’t use that monster 4800 mah ni-cad out of your old gasser.  Keep it reasonable or maybe even better if you don’t need the weight to balance think about a BEC (battery eliminator circuit) or regulator that you can run of the motor pack.  Quite a few to choose from now, I like the UBEC from Hobby Lobby at about 1 ounce, It’s really more about convenience, just plug and play.
 
This is pretty much the current set-up I’m using in a Funtana 90, with batteries on board it weighs 9 pounds 4 ounces, the new Funtana 100 should be a little lighter.  Lot’s of power, instant acceleration, 65 MPH vertical, too much fun.
 
The E-Flite 160 we used in this set-up is an outrunner, in the mid-size planes like this they’re great and inexpensive but only about 80-85% efficient and a little heavier.  Inrunners with gearbox’s are in the 90-95% area, weigh less, but more money and a little noisier.  When the plane gets bigger it becomes more of an issue but that’s another story for another time.
 
                            Basic Disclaimer
          (This will help you avoid the on-going debate of  electric vs. glow and gas)
Electric is not better or worse, it’s just different.  It’s personal, relative, and subjective.  Two years ago it was definitely more expensive, today it’s getting pretty close, next year it may be cheaper.  Electric is usually smoother, quieter, and more dependable, but not always. I like glow I just don’t like the clean up and noise.  I still have one gas plane and I like it, but I don’t trust it to hover 6” off the deck, but a lot of people do.  There is no right answer just a different answer.
 
Following are a few things that have worked well for me in the last few years, remember this is free advice so proceed at your own risk;
 
Batteries- Currently all of my planes from about .25 glow size and up, including
Some 1/3 scale stuff use a combination of either 2S or 3S 3200’s put together in series or parallel.  This makes it very easy and cheap as you can fly most all planes with the same batteries.
 
Connecters- for almost 25 years I’ve used the Anderson Power Poles or some people call them Sermos.  The ones you see around the hobby are the S35 which means they really only rate them to 35 amps, but I commonly pull up to 80+ amps and have never had a failure.  The common Dean’s connecters that we see around are hands down a better connecter, but not as versatile when plugging together packs to get the desired voltage.  Any time I’m hooking up a motor to an ESC, I either solder or use the round “Bullet” connecters.
 
Chargers- I’ve been a big Astro-Flight fan for years and still am but the Great Planes Li-poly 4 charger is hard to beat.  Most people I know locally use them and love them.  They’re cheap, easy, and so far idiot proof.  I own a couple and I’ve tried to trick them with dead or overcharged batteries and they figure it out every time.  Set it, push the button, and walk away, as long as you keep an eye on them.  The new Thunder Power and Hyperion chargers seem to have a good fan base so be sure to look around.
 
Charging Safety- You can’t be too safe.  Never leave them alone or on a flammable surface while charging, and you should really always travel with them in a fireproof box.  At home I’ve made a fireproof area out of Home Depot .99-cent pavers, I’ve only had one catch fire in the last few years and that was my mistake for setting the charger incorrectly.  As far as I know they don’t really explode but rather go off like a road flare.
 
Radio Interference- I’ve always tried to keep the receiver in the back of the plane or at least mid-ship.  My belief is that with the higher voltage set-ups that some of us are using it creates a very dirty environment, always be sure to do a very good range check at full power with a friend.  It seems like the 2.4’s have helped, I ‘m currently using the XPS Extreme Link 2.4 system and it seems “Bullet Proof”.
 
If you’re having trouble with an electric project or would just like another opinion feel free to drop me an e-mail.  Following are planes I’ve actually done or have helped others do, they all fly very well and some have made hundreds of flights with these set-ups.  As far as local support goes it seems that most all of the local shops have some “E” experience now.  Pat and his crew at “Some Dudes” are “E” fliers themselves with a lot of good knowledge and an “E” inventory.
paulb at jeld-wen.com

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