is the Kv rating of a motor an indication of it's power ?
I see some 1/2A's running somewhere around 1200-2200 kv.

Kv is something like a gear ratio, and gear box does not change power, only speed (rpm) and torque.

the lower kv, the lower rpm (per volt) and higher torque (per Ampere)

Ok, well I want an outrunner. I think those are the ones that are like cd drive motors ?

yup.

I want to spin a 5-6 inch pro around 13-14k

That's down into low performance 049 territory, if you want to equate it to a gas engine.  One of the nice things about electrics is that you can jigger the numbers a bit and spin a bigger prop slower, which increases the prop efficiency*.  Unless you're building a speed demon, you maybe want to think 7 or 8 inches to equal a modern 049 with a 5-inch prop.

Check your motor/ESC combo -- because outrunners are designed to run slow, your motor/ESC may not be happy at such a high speed.  If you buy it from a hobby shop, see if they'll let you run it, and tach it for speed.  At the very least scrutinize the motor specifications carefully and try to get one that is specified to go that fast.

On the plus side, until you make it fly apart from centripetal effect, burn up the bearings or terminally confuse the ESC, an electric motor is a constant-torque device -- this is why inrunners do so well with gearboxes.  So you'll be able to get away with a smaller motor than your power input may otherwise indicate, which will save a modicum of weight.

Not sure if I'll need 2 cell or 3.

That depends -- there are plenty of small motors that'll work on two cells, and plenty that'll work on three.  If you really want to aim for 14K then you'll need a motor with a Kv of

WARNING!  MATH SHOWERS AHEAD WITH A CHANCE OF USEFUL RESULTS!  SMALL CRAFT ARE ADVISED TO SEEK SHELTER!
Kv = RPM / volts = (14000 RPM) / (7V) = 2000 RPM/Volt

for two cells, or

Kv = RPM / volts = (14000 RPM) / (11.5V) = 1333 RPM/Volt

for three.

If you're not alienated by the math, then you can use the above expressions to calculate Kv for whatever your target RPM is.

Looking at those Kv numbers you may well have to go with three cells, unless you can find a motor that's really intended to run fairly slowly on one cell, or one that's intended for little, fast planes.  Since the market seems to like 3D you'll probably be stuck with three cells -- which will make finding a pack an interesting exercise.

I've  got a concept in mind. But figure I'll find motor,batter and such. Looking to build somewhat smaller and stay light around the concept I'm thinking of. Once I find the power train then I can draw fuse and wing joint to get it togeter. Plan is to have everything enclosed kind of.

Good thought.

If you can, leave spare room in the battery compartment.  Batteries wear out, and battery technology evolves.  Every time I build a plane with a nicely ducted, tightly fitting battery compartment I end up getting a new battery that's lighter, less volume, and significantly smaller in two dimensions out of the three than the other one -- and that third dimension blows outside of my battery compartment space claim.

The more I play with electrics, the more I think that the best battery compartment is a big flat plate covered with a huge patch of Velcro!

* Which conforms to full-scale practice -- there are a lot of geared airplane engines out there for the same reason.

So a 6 oz plane needs a .6 ounce motor ? am I getting it right..
 And I'l like to keep the props in the old .049 area though I know most have gone to 7 or 8 even. It's no really the same...

my 160g indoor needed 32g motor

So a 6 oz plane needs a .6 ounce motor ? am I getting it right..
 And I'l like to keep the props in the old .049 area though I know most have gone to 7 or 8 even. It's no really the same...

Hi Jim,
No, that rule falls apart for airplane weights under about 30 ounces.
It's pretty fair above that figure, and I was simply not considering small planes like 1/2-As.

As Igor points out, for very small airplanes the motor is about twice as heavy compared to the total.
The reason any kind of rule like this works is that the airplane weight dictates the power consumption needed to fly properly.
The ability of the motor to handle the power is related to how much weight of magnet/iron/and copper wiring it has, so there is a rough proportionality ...
Motors still have to have propshafts and bearings, no matter how small, so small motors end up weighing more.

An 049 probably puts out about 75 watts so find a motor that will handle 100. The manufacturers post ratings for them.
Better yet, go look for successful 1/2-A setups in the sticky thread.

have fun,
 Dean P.

2) i looked at the brodak page and was wondering how much battery one needs to charge 1/2A batteries.
Can the charger be used in the field from a 5 amp hour SLA battery ?
Or maybe 2 of them ?
I can buy 2 or 3 batteries but being able to charge up while out flying would be nice.

If you have an efficient charger (i.e. if most of the energy going into the charger goes into the battery under charge), and a three-cell pack, then you can probably equate amp-hours into the LiPo with amp-hours out of the field battery.  So if you (fer instance) have a 500mAh pack, then you could charge it somewhere around eight or ten times.

I don't know how efficient chargers are, though -- I always connect mine to my car battery, and I never measure the input current to the thing.