There are models that will spin with just rudder and elevator. The easiest way to get one is to take any acrobatic model that spins well with the ailerons and add a few pounds of lead on the CG. It's amazing how much better they spin with the higher wingloading. One guy at my club had a trainer that would do some of the best looking flatspins you've ever seen. After he bolted 4lbs of lead to the bottom of the fuse. With out the weight it wouldn't spin, with it, he could do a flatspin landing that wouldn't even break the prop. It was quite impressive.

You'll also discover that higher wingloadings also result in a much longer delay in getting out of the spin. I've seen models do an entire rotation after the sticks were centered before recovering. I've also seen models that would not recover with out opposite rudder, down elevator and/or other full-scale type control imputs.

My old overweight (6.5lbs) Cap 21 .40 size would do a very pretty spin with elevator only, no rudder, no aileron. Just slow it down and hold the nose level with more more elevator. Eventually the nose would drop and one wing or the other would drop and you'd spin. That plane took about 3/4 rotation to get out of a spin, and an extended vertical dive after the spin to get enough airspeed back to make a safe pull out. It also snaprolled in a blur, almost impossible to get a clean single snaproll, but double snaprolls were really easy. To get a slower snap, I'd just snap it with low-rate elevator and just a touch of rudder only. If I went at all on the ailerons, or much rudder, it would really speed up the snap.

To further confuse things, I also fly combat planes that don't have rudders. I can spin them with just elevator and aileron. And yes, it's a true spin, not a spiral dive. The nose is 45* down at most, and I can even flatten the spin by taking out some aileron after the spin starts. Of course, these planes have LOTS of elevator LOTS of aileron, and rather far back CG's.