Hi Mike, welcome to E-Flying!
I wish I knew one site or reference to give you that explains all the different motor designations. If such a place exists, maybe some kind reader will post it here!
I believe Graupner (Hobby-lobby.com) started a "benchmark" of sorts with the Speed
designation, Speed 400, Speed 500
. etc. Later motor-makers added their own "labels" like can diameter, number of winds, can length and so on. There's been lots of suggestions for a standard table of sizes but so far, nothing. It may be too late to install one now!
I learned about 1/2 of what I know about motor sizes from the Hobby Lobby
catalog; They list comprehensive plane specs, motor, battery, prop sizes and upgrades for every plane they sell, and that's a lot of planes! So if you have a plane in mind, find a similar size and weight aircraft in the catalog and use their recommended motor.
The most common motor size is Speed 400
. This is a brushed, inexpensive ( $ 10.00) motor. Until recently, with the advent of very high output, lightweight LiPoly batteries, 400
sized planes were the vast majority of kits, ARFs, RTFs and plans available. In glow terms, a Speed 400
on direct drive (no gearbox) with 7-8 cell NiMh or 2-3 cell Lipo would swing a 5.5" x 4.5" prop around 7,000 to 9,000 RPM. About like a 1/2A, right? The planes for that power system looked
like 1/2A's, too, maybe slightly bigger and with somewhat lighter construction. Now comes the part a lot of people have problems with; Put a 4:1 gearbox (reduction gearing) on the 400
and it will really
wind up, 20,000, 30,000 or so and turn a 10" x 6" prop 1/4 of the RPM, enough thrust to easily fly a 2 meter powered glider! Not a 1/2A anymore!
So there's Direct Drive
motors, depending on the type of flying you intend to do. Little, fast planes like pylon racers would use Direct drive, small props, short duration flights.
Geared motors would be for larger, slower planes like 3D models, sailpanes and models that were intended to swing a larger prop. "Park Flyers".
Just about all of this applies to Brushless
motors, but they've added another type of motor; Outrunners
, also called "Rotating Cans" or "LRK's" in Great Britain. With this type, the outside case (can) has the magnets attached to the inside and the entire "can" rotates, also driving the prop shaft. The result is tremendous torque in a small motor, the ability to swing a much larger prop without the complexity of a gearbox. So in the Brushless
catagory there are Direct Drive, Geared
About the only site I can direct you to that might give you better idea on motor/gearbox/battery combos (besides Hobby Lobby)
would be a free "Moto-Calc" program, http://brantuas.com/ezcalc/dma1.asp
Just scroll the batteries, pick one out, pick a motor, prop. Anything will do to start; Hit "Calcuate" and watch what happens. Now change one
factor, like go from 7 cell NiCad to 8 cell Nicad, hit "Calcuate" and compare
the result. After a few of these, you'll get an idea of how these factors effect each other. It may seem like voodoo at first but hang in there. You have a BIG advantage in having flown R/C glow before. Wing loading, airspeed, power-to-weight, thrust are not any different from what you've already learned. The big difference is what turns the prop, and the "Lingo"
There is a lot of good info here at Wattflyer
, keep reading the posts, especially "Beginners" and "Power Systems".
Wish I could help more, but that's all I know! Ron