I know that turbine manufacturers usually have a specific pipe gap that they recommend. I have heard that a turbine can be tuned for maximum thrust by moving the turbine to its "optimum" distance from the pipe. What are the maximum distances you guys have seen to get maximum thrust? At what point does the turbine start losing thrust and why when too close or too far?

Andy

The way I understand it is the gap helps to draw cooling air through the pipe. Too close and that doesn't happen and will have problems with heat and reduced thrust. Too far and exhaust escapes into the fuse (not pretty). Optimum distance will depend somewhat on the install.

I'm pretty appraised of these things. What causes loss of thrust by putting it too close?

Andy

Basically trying to push air through the pipe faster than it can be replaced. The turbine is acting like a cork when its too close.

Andy,

The Jet Central Rhino likes 1.5" between the turbine tailcone and the bellmouth entrance to the pipe. Cooler pipe temps and increased takeoff acceleration were noticed when I moved the Rhino from .5" to 1.5" on my F-4.

This is what I am getting at. I've heard of guys moving their turbines forward or backward depending on max thrust per specific installs instead of just relying on the same distance every time. I don't think many of us here do that, I think if we did our jets would be maximized for performance. Of course CG matters to. The compensation for added weight may blank out any gains in performance.