With external engines tail slides and such are no problem. When I was doing them with my BobCat/RAM 500 I would add just a bit of throttle once the airplane quit going up. My thinking is it would keep a better flow going through the engine. But I remember on BVM's website or Inlet newsletter the advice to NOT do tailslides with an internal engine/tailpipe model. You can overheat the pipe in the model. But of course that may be old news with old technology. BV was referencing the RAM 750 in a Bandit.