I have a trainer that I fly on a regular basis. It will do a "flat spin" quite nicely. The fuse is nearly level, and the wing is stalled.

Entry is engine at idle, full up elevator.

Just as the nose drops, full left rudder and a quick blip of full throttle then back to idle. This creates a ton of yaw, and stalls one wing much more than the other.

After a about a half rotation, the ailerons are moved slowly to full right aileron, which keeps the nose up and the angle of bank level.

Throttle is bumped up to a couple of clicks above idle to sustain the spin.

If I just release the controls, I get anywhere from 3-4 rotations before the plane recovers on it's own. Opposite rudder and down elevator and full power will pull it out quickly.

The trainer has a fair amount of downthrust, so much engine power seems to pull the nose down and break the spin. I also never use aileron with rudder to spin, the ailerons seem to overpower the stalll, and the result is a rolling dive, regardless of rudder or elevator.

This trainer has the CG moved way way WAY back, a ton of elevator and rudder travel, and now has a bigger rudder than stock, though it actually was better with the smaller rudder. I should cut down the vertical stab, and keep the larger rudder, that would probibly help.

I've surprised many "experts" at my field with this trick. Most of them have said things like "trainers can't spin" or "it won't be a true spin". The first time I actually got the spin to flatten out, I almost lost the plane, I wasn't ready for the 3-4 rotations after releasing the controls, so I didn't get right on the opposite rudder and elevator.

The same plane will spin inverted, but won't raise the nose, and the rate of rotation is much faster inverted than upright.

All in all, it's a heck of a lot of fun.