OK, I tell you my secret:</p>

What I have learned so far about outrunners is that 2 values are the most important: kV and weight.</p>

1) From kV or rpm/volt we know how a certain motor is going to perform, hence at 37V (or 3,7V per cell) on a 10S pack under load that motor would be at 8880 rpm if it would be 100% efficient. Well there is no such thing which is 100% efficient and usually at full power you get somewhere around 85% efficiency hence in this case 7500 rpm.</p>

2) A prop of certain size needs certain amount of power to spin at certain revs, so if I use any of calc programs (in this case Scorpion Calc which can be found on Scorpion site, and is freeware) I can see that 19x12 needs 2,4kW for 7.600 rpm. So this is absolutely within power limits for this motor as at 60% throttle in level flight we usually use very little power, not more than 20% with a 19x12 prop. This can be calculated in Motocalc.</p>

3) The weight of a motor can also (usually) tell us how much power (heat) a certain motor can absorb (dissipate) but luckily Neu and Scorpion give us these values.
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This was the hard way how to determine which combo for which motor, but there is an easy way, my favorite: go to Axi site http://www.modelmotors.cz/ check what combo (prop and bat) Axi is suggesting for a certain kV and weight , stay within 5% of the Axi values and voila; for our case the most similar Axi motor to Neu 1917 2.5Y would be 5325/24 232kV with 570g spinning up to 20x13 on 10S.

What should be remembered is that Neu motors have one of the best power/weight ratio together with Scorpion (but we all know that Hacker and Axi are under rated). Probably Neu is using magnets as well as Scorpion is which are resistant up to 200 degrees Celsius, some 120 degrees more what most of the others use.</p>

And for any other setup this is what I wrote somewhere else:</p>

To determine my initial setup I always first visit AXI site http://www.modelmotors.cz/ as there is a very nice tool: FAST AXI SETUP , you can find it on the right hand side of the home page.

In that tool you can now choose type of model (in this case aerobatic) and the total weight on take off (in our case 1500g). Lets click on FIND SETUP, the tool now suggests various AXI motors, and as I always prefer to have more reserve of power than AXI suggests I would take 2820/12 which is good up to 2000g aerobatic. The suggested battery in this case is 3S, 40A ESC and 12x6 prop. I do agree with bat, but would take a larger ESC (60A) and the prop is OK. Also by selecting a slightly larger motor you do not need to push it to the max all the time, a lot of benefits for only very small gain in weight.

Now If we want to get an AXI motor we are fine, but if we don't want an AXI what have we learned from this? Any other motor of this size (equal diameter and weight) with this or a kV within 5% difference will be OK. So now we can go and choose whatever we want, Hacker, Scorpion, Turnigy, Hyperion ...

What I can add here that not all motors are built the same, and this results in higher efficiency, heat tolerance and durability. Is Neu 1917 worth more than Scorpion 4035 as much as it costs more? Well, from what Iread about Neu, my guess is yes.</p>

So this is my 4 year experience with electro, use it wisely ... </p>

Velco</p>