I think the last three posts make some good points. I would never say that the CG of a trainer should be at 25% of chord. There is no such thing as a universal CG point; it depends on the design.

As pointed out above, if the CG is too far forward then the throttle will have a bigger effect on pitch. You really don't want that for training, or anything else.

Also, the .46 AX is WAY more power than you need for training with that plane. So the throttle control has a big effect on power. Combine that with a forward CG and you have a recipe for big pitch changes every time you move the throttle. That will cause your plane to swoop up with full throttle. The guy who used a TT GP42 made a good choice. An OS .46 LA would be fine too. Probably the .25 suggestion would work too, but I'm not as sure about that.

Also, it is much better to use lower pitch for a trainer, and for many other planes. With less pitch you can use more diameter. I would try a 12x4 prop. It will slow down approaches and give better, easier control for landing.

Jim