You guys have always been very good in answering my stupid questions so please help!!! For the first time I am using my old RAM 750F with a pipe. The manual (written before most of you were born) says turbine to pipe distance is 1 inch from the turbine can. In my searches on RCU Tam criticized someone for using that distance as it put the cone quite a bit into the pipe, but did not provide any other advice. What say you guru's???</p>

it depends on what exhaust cone you have, some 750F's have a normal RAM exhaust "pipe" while others had a JetCat P70 type exhaust "pipe" which extends only about 1/2" from the turbine can (I'm not using the word "cone" since all 750's I remember had a long concentric cone in the exhaust)... if you have the long "pipe" I would recommend 1" to 1 1/4 from the end of the cone

Here are a couple of pics of the 750 cone(s). That is why I am confused! Modern advice says usually 1/2" to 1" from end of exhaust cone to pipe but the manual drawing with this 750 cone shows 1" from base of the can, not the cone...

As stated I would not recommend running the cone inside the pipe, the exhaust will not generate the venturi effect required to pull cool air into the pipe and keep temperatures reasonable, I would use at least one inch from end of cone to start of pipe (not including the intake ring radius).

Still, you may want to wait and get some responses from other members. or you can get some ideas from here: http://www.rcuniverse.com/forum/m_8341245/tm.htm

I ran my RAM 750 inside the exhaust tube bellmouth for years. Mine RAM 750 also had the long cone on the end of the turbine. Never had a problem. Heat was not an issue either. See pic.

Terry Jacobs

I second Ruiz.

What you are looking for is the venturi effect ( what he said ) looking for cool air to be drown into the bell mouth in that way the hot air in that part of the installation will be sucked into the pipe preventing any heat problems.

1 to 1/2 inch space from the turbine cone and the bell mouth.

It is really good that Terry never had any problems with his installation. I always have and will use that distance between turbine cone and pipe/bellmouth.

Hope this helps

Ps: Tam is correct ( guest were I learned from )

Thanks guys for the input. Seems that anywhere from the manual distance to the 1/2" to 1" measurements work. The airframe/pipe combo I'm using won't allow me to have the cone outside the pipe... SOOOOO, I decided to add a pipe support to my turbine test stand and see what I get. I ran the turbine with the max distance away from the pipe I can get (which also helps with the CG) all the way down to the 1" from the can that the manual describes. From a temperature standpoint there was no difference in pipe temp among the various distances. Warm at the tip of the pipe (not hot enough to burn my fingers) and cool at the bellmouth end. I have no way to measure thrust so don't know how the measurements affect that! The pic shows the farthest out of the pipe the airframe bulkheads allow me to position the turbine so I will go with that and see what happens...

It looks ok from here, looks like you should have enough clearence to get the hot air moving into the pipe.

1/2 - 3/4 inch. I, or others I fly with, have used that on that 750, and various other thrust class engines.