WHAT DO THE KV RATINGS ON MOTORS MEAN?

Manufacturers use different wire winds to produce different KV results. KV stands for thousands ( K ) of rpms per volt. So, a 1000KV motor will turn 1000 rpms when 1 volt is applied. It will turn 7000 rpms if 7 volts are applied.

Lower KV motors typically produce more torque so they are typically used with large propellers that will be turned slower. These are very popular on gliders, for example, where climb angle and climb rate is much more important than top speed.

Higher KV motors are typically used with smaller props for higher top speeds. Or they can be used with gear boxes to handle those big props, providing a similar result to low KV motors. Sometimes a gear box works better in the installation.

You would also take KV into consideration based on what battery you plan to use.

If you look here you will see that a given motor is offered in several KV ratings. They make suggestions as to which motor is best matched with which prop and which battery packs. If you click on a given motor you can see what kinds of power is drawn based on which pack and which prop. If you click on each of the motors within a model you can see the very different power curves produced by the different battery/prop combos. Here you see the same motor with a different wind producing a different KV result, each optimized for a different purpose.
http://www.maxxprod.com/mpi/mpi-262.html

So, how does this add to other information about motors?

I first set a watts/pound target for my plane depending on the performance I want. I typically target between 70 and 100 watts per pound for sport planes and e-gliders.

Then I consider whether I am looking for high speed or high climb rate. A glider or a 3D plane would be optimized more toward the climb rate side of this dicussion. A pylon racer would be optimized more for speed. A pattern plane might be somewhere in the middle.

Now I get down to prop and battery. Wider prop for better climb, narrower deeper prop for higher speed. Now look at the motor character based on either battery target or prop target and choose the motor/battery/prop combo that meets your objectives.

That is kind of high level but I hope you get the thinking that goes into a motor/battery/prop choice.

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