DrMotor

Hello rosnik, it is very good indeed to hear from you.
You and I have discussed Motrolfly motors before -we discussed the DM 3615 750Kvmotor.
The good thing about Motrolfly motors is that they have a larger diameterand are shorter in length than other types of motors. And some people think that this makes the motor perform better because it keeps the stator closer to the magnets, because the stator has little chance to "rock around" on the shorter shaft; In comparison to a motor with a much longer shaft and smaller diameter stator, which might well "rock around" on the shaft at one end, and perhaps because of this perform less well:
e.g. http://www.rcgroups.com/forums/showp...postcount=4209
Re: 30-size motors: " ... Regardless of brand anything, over 20mm long stator seems to be potentially problematic on motors with a 5mm shaft. The long can and stator lead to magnet to stator contact and high stress in the stator tube. I now favour motors that are short and larger diameter. That's where the Motrolfly DM3615 scores, it's got a 15mm long stator and a short 6mm dia shaft. ..."

So: the Motrolfly DM 4315 motor you mention, has a 4315 stator, and may be good in this respect. It is 280g, D55 L42; 6mm shaft;
-It is in the same weight range as a: Hacker A50-14 XS V2 -which is the same motor as a Torque 4014T/570, LiPolice LP-4020 /14T-550KV and HYPERION Z4020 14T etc etc.

http://www.motrolfly.com/product.asp?lb=47 -for some reason, this particular 4315 motor is not shown on Motrolfly website

http://www.scmodels.com.au/electric-motors/index.html:
DM4315-714KV is for 4S LiPo; DM4315-480KV is for 6S LiPo

See: http://www.rcgroups.com/forums/showthread.php?t=1515376 -Motrolfly 4315-500kv; LOTS and lots of info here

http://shop.subsonicplanes.com/product.sc?productId=348
Motrolfly Brushless Motor DM 4315 $124.95
Motor Design: -Basic Version -Light Aluminum Mount (+$2.95) -Light Fiberglass Mount (+$6.95)
Select: 300Kv 380Kv 480Kv 500Kv 668Kv 714Kv 780Kv

So: Seem to be3 types of mount, and7 different Kv's for this motor ...!
-It is not a cheap motor ... but may be a good one.

Have you got a plane in mind for this motor ...? Extreme Flight MXS perhaps ?