As vlizard said...ATF type F has a "friction enhancer" in it.
Now what exactly the friction enhancer is or what it does is
beyond me. But I have to believe it would not be good to
put in your model engine.

Stick with Dexron or Mercon ATF. Works just fine.
I personally use a 50/50 mix of Marvels Mystery Oil
and Dexron III ATF.

Mike Hammer