Those on the Beginners Forum told me those on the Electric Flight Forum know more about this, so here goes.

OK, I read & follow all kinds of posts, different forums, several mags, helpful info on dealer sites and much more, and I still don't know what all the number mean. For example, 20, 40, 60, 90 all relate to size of Planes and Heli's. Those number do not mean a thing to me as I find no relationship to any real measurement. How or where can I learn how to relate these numbers to some real life specific measurement.

Next, is motor or engine designations. I understand (basically) about KV (RPM per volt) I think. However I see numbers like 2800/12 or /10 and on and on. Are these only a manufactuers designation of a specific product ie: size, power, etc motor or engine? How can we new to the hobby beginners learn about such information? Where do we go? How do we calculate the power needed to fly a given model and the power of any specific powerplant? Some motors are 21mm, 28mm who knows what else? I understand these are metric measurements and lengths are also in mm. I can convert and measure these any way necessary. My problem is that I can't relate these figures to what may be needed for a specific application. How does anyone compare two or more items when totally diferent number are used to describe them? Makes no sense to me.

I have for example exchanged a GWS 400 motor for a 200W motor from another maker for my new plane. I am told it is intended for my plane, but what does 200W mean in terms of power, KV, Amps and any other related term? How does it stack up to the EP400 from GWS? I am thoroughly confused at this point. I would like to find answers to these questions and learn to work all these numbers into a single related, useful and understandable system as much as possible. I know different Mfg's may have different ways of ID'ing their products but AXI, Neu, Medusa and all the rest are related and I need to somehow make sense of it all.

If there are places to go to learn more about these things I would appreciate knowing. I am sure others are in the same boat. It is all very confusing, but fun anyway.

I know it will come with time but I hate to just have a blank stare when some one reels off the numbers for their Plane, Heli or Sailplane. I'm impressed all to heck when a guy tells me I have a 30 at home, also a 90 Heli and I'm building a 50 scale using a 3700KV motor. What?

The 20, 30, 40, 60 and 90-numbers refer to an IC (internal Combustion) engine. A 60 (or more exactly .60) have 0.60 cubic-inches or 10ccm combustion chamber. A 2-litre motor is a 2000ccm motor. The numbers/class tells how big engine is required to make the plane or heli fly properly.

When it comes to electric motors the numbers vary a lot from manufactorer to manufactorer. All AXI-motors have numbers telling the diameter and length of the stator, and in addition the number of windings of copper on each stator... Thus a 2820/12 have a stator with 28mm diameter, 20mm length, and 12 windings on each stator. Compared to the 2820/10 which is equal except the numbers of windings the 2820/12 will have a lower kV because the wires are thinner to allow the stators to be filled, the /12 takes more voltage and spins larger diameter propellers, but at lower RPM. This makes the 2820/12 good for sailplanes and 3D, but the 2820/10 is better for pattern, with less diameter and higher pitch propeller. This give more speed, but less thrust...

When you choose a motoor for your plane you must first find how much power you need. Power = Watts! To fly a trainer you need 150Watt per kilo model. For 3D you need the double, 300 Watt per kilo at least. Then a suitable kV when you know the voltage your batteries chosen will have.

An example: you have built a sportplane weighing 2 kilos. You want to run it on a 4S LiPo battery, which give a voltage of appr 14 volt at load. 2 kilo model, needing 200 watt per kilo mean you need 400 watt at least. To get 400 Watt to a motor at 14 volt the amperes will be 400/14 = 29 amperes. You need a motor, battery and ESC able to deal with AT LEAST 29A. Add some margins...
If you look at AXI the 2820/12 will be a good choice on 4S LiPo. Add a 12x6 APC-E propeller, and you are at appr 33A and well within the "efficient" range for the motor.
Or buy any electric motor able to deal with 35A or more, with a kV in the 1000-area.

I appreciate the explanation and the time you took to make it. Its beginning to make a little sense now. There is an awful lot to learn. Thanks a lot. Ed

The biggest thing to keep in mind is that those numbers are for marketing, especially the motor numbers. Don't get hung up on trying to somehow translate "2841/99" into something useful, because for our purposes, they could've just named the motor "Fred."

That's why I appreciate the Eflite practice of using glow sizes in their electric motor designations for the larger motors.. The Power 25 is pretty much a direct replacement for a .25, for instance.
The smaller motors with their 370,-480 designations only mean something to someone who has used the equivalent can motors.
Standardization across the industry would make it a lot easier for everyone.
When I see a Great Planes kit I might want, but it specifies some motor in the specific to Great Planes nomenclature, I don't buy that kit, having no way of relating the spiffy name of the motor to what I'm familiar with.