RC Airplane Motor Number Systems?

by Ron
(Riverside, CA)

Some RC airplane motors are sized by two place numbers, which seem to relate to my old nitro gas powered motors; i.e., a 25 electric motor powers. They about the same size plane as a .25 nitro motor (such as an O.S. Max .25 ).

However, many electric RC airplane motors are sized in the hundreds, i.e. 370, 400, 450, etc.

What's the difference and why two numbering systems?

How does one determine which motor to use on a plane being converted to electric?

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RC Airplane Motor Number Systems?

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Nitro sized are CC ratings
by: rcdude07

Nitro engine sizes are representative of their cubic centimeter output. So a 46 sized engine is a .46cc nitro motor.

I believe electric motors are based on kv ratings.

I'm strictly a nitro flyer, so don't quote me on the electric motor information.

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A standard naming scheme would be nice!
by: Matt

Kv rating is how many RPM's the motor runs per each volt applied to the motors. This is one of the important factors you look at when choosing a motor.

There are other factors as which can be found here. Of those, the max power and current are important ones to look at.

It is kind of confusing how different manufactures give different numbering or naming designations to their motors. Would be nice if there was a standard.

But just like nitro engine of the same size don't perform with the same amount of torque and power, the same is true with motors. There are many factors that determine how efficient the motor is. Just as with engines, the motors with more power per weight tend to cost a little more...

Electrifly has some pretty good charts that will help you convert from glow to electric. Once you find the right motor on their chart you can look for motors from other manufactures that have similar specifications.

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power ratings revisited
by: Anonymous

Thanks for your responses; but I still have questions. I realize that gas (nitro) engines are by displacement. And auto/motorcycle engines too, although they can be either by English Standard (cubic inches) or Metric (cubic centimeters, i.e. c.c.'s), but the conversion is simple. A Chevy "350" V8 small block is also known as a 5.7 Litre.

There doesn't seem to be a conversion factor for electric RC motors among themselves, let alone converting from gas engine displacement sizes.

I recently bought a Curtis Jenny like several other fliers at my field. One guy told me the kit called for a "Park" (brand name) 250 motor. But he thought that might be a little weak so he put a "30" in his for that little extra he might need.

I found a Park 250, and there are 350's, 400's, etc., but no 30's. Hobbytown did have a 10, 15, 25, and 40 sizes, but the 25 was humongous and wouldn't even fit inside the cowl of the Jenny.
They also had other brands, too, in 300+, 400, 450, and other sizes.

I found out last week that Jim put the 30 in his Jenny because he had it on hand. It looks the same size as the Park 250. It just seems stupid that this industry can't get together and agree upon a standard for sizing.

Also, the comment about kV rating; what does that have to do with RPM? kV has to do with "power", not speed. That just adds more confusion.

It kills me that many vacuum cleaner manufacturers rate their product by "amperes"; they want the unknowing consumer to think that a vacuum with a rating of 14 amps (clearly printed on the housing) is more "powerful" than one of 10 amps. Noooooo. Two motors can have the exact same amount of "power", torque or RPMs or horsepower, but the one using more amps is less efficient. It would be like taking two identical cars but different desing motors, driving side by side, equally, for a hundred miles, same speed and all, but one uses 4 gallons of gas and the other 5; which is the better car? Using more amps, or kV, to get the same job done is less efficient.

Anyway, my Jenny is almost ready to fly (ARF) this Saturday; if the bugs and heat don't deter me.

Ron

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I agree they could make it less confusing for us...
by: Matt

I started out flying glow engine planes, but I have really gotten into electric the past few years. Mainly because electric is so much more convenient.

But I will have to be honest, all these numbers are enough to make my head spin, lol. I have mainly been getting Bind N Fly planes that come with the motors and if they fail I get one about the same size.

I understand current, voltage, c rating, capacity, KV ratings and all of that good stuff. But there are a lot of variables that come into play when choosing an electric system.

The prop size and pitch which affects the size and speed you want the motor , which in turn affects what voltage and capacity of the battery you need.

You have to choose a capacity battery that is not too heavy, but is large enough for a decent duration flight...

It all has to come together. I think it's more of an art than a science. A lot of trial and error. That's why it's always good to have friends with the same plane! lol

KV rating is how fast the motor spins per volts. So you can get a good idea of how many RPM's it will run with a certain voltage battery.

Good luck with your first flight. Please stop by and let us know how it goes!

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