I am no expert but I used Bob Hunt's G-10 fiberglass motor mount and two of the laser cut rings from Walter Umland's E conversion kit. This was for a profile stunter.  Hunt has a detailed instructions for installing his fiberglass motor mount in a built up stunter. Look at my "Ringmaster 576 Electric" posting for pictures of my setup. However I am sure their are many good setups using an X mount. Others should have better info than I can give.

I have had no problems with rear (X) mounted motors on my 35 sized (and smaller) profile Ringmasters.

I do recall that others have reported that the front mount is best for full sized stunters. The stresses from violent maneuvers are somewhat equalized by the front mount and adding a rear bearing should further help in that regard.

Curare:
The premise is that the front mount balances the load on the motor bearings.  Especially in the case of the larger motors with large props,  when rear mounted the motors can actually flex enough to allow the magnets to touch or scuff against the core.  However with smaller motors and props that is less of a possibility, my personal rule of thumb is not to worry about it when I am using 11” or smaller props.

I routinely use X-mounts, they provide a nice spread of the load (bigger footprint than with an IC engine), of course the cautions about wood crushing come into play.  I also like using either the 1/4" thick blind nuts (6/32 size) or the threaded brass inserts because they prevent wood crushing.


Can you elaborate on your experiences with front-mounted motors on 3D models?

Dennis, I've been flying a Sebart Wind S 110 F3a/3d model for about 5 years now. It was initially designed for a front mounted hacker, swinging an 18-19" prop. Supplied in the kit was a rear bearing and ply backplate to stabilize the motor.

Some had commented online that the rear support was not necessary, my own findings showed that I actually had the spinner touch the cowling the movement was that great, which is impressive as it's nearly a 2mm gap. This is especially prevalent in snaps.

After that I decided to go a little better than a few wood screws and some ply and made a carbon backplate held in by 4-40 bolts and servo grommets to reduce vibration transmission into the fuselage. It's been fine for about 1000 flights now.

What I believe to be the issue, is that when an engine is front mounted without a rear bearing support, there's simply not enough lever (moment) and pad area to stabilize the motor itself, I don't believe in this instance that it was the can that was moving around, I think it was the entire front end of the aircraft!

I'm not saying that you may end up with assymetry in the can, but for me I think it was to much flex in the mounting arrangement. Pays to keep em stiff!

Yeah, that makes sense, the longer the motor, the less tolerance you're going to have for eccentricity and runout, either by construction or a big swirly thing on the front of it getting yanked around by gyroscopic forces.

Thinking about in that fashion, the front mount works by removing the assymetric forces on the can, but you pay for in having less ability to hold the motor in place while running. The only way around is to support the shaft front and back, more effort but is smarter engineering practice.

In a weird way, we're back to the bearing layout of an inrunner, but with outrunner magnets!