Xairflyer

My Feedback: (1)

I know it is normal to have a clearance from the end of a turbine tailcone to the jetpipe/tailpipe of around 15-20mm and from what I have read it is to do with help keeping the tailpipe cool?

I notice on some installations the turbine tailcone would be inside a large Bellmouth but still back from the start of the jetpipe main diameter.

What I want to know is would it be ok to have the end of the turbine tailcone just inside the jetpipe if the jetpipe was alot bigger, i.e. the tailpipe outlet is 40mm (P60) and the jetpipe mouth dia is 80mm ?

rcpete347

My Feedback: (251)

pics would be good.
Rcpete

Xairflyer

My Feedback: (1)

This is the best I have

Dave Wilshere

You can probably get away with it on that difference, but with a large pipe and small turbine you will suffer with poor static thrust till model is moving quite fast. The gasses expand into the larger tube and slow down...

Dave

Xairflyer

My Feedback: (1)

Never thought about the static thrust issue, snag is I want to refit my Wren54 once I get it rebuilt so dont want to shorten the jetpipe.

Xairflyer

My Feedback: (1)

Well it worked ok, flew it on Sunday P60 in a AMD Hawk, did'nt seem to effect the static thrust as it bombed down the runway on takeoff, sounded really good in the air and very quite.

Shaun Evans

Hi,

Sounds like you have a decent setup and lucked out with performance. That static thrust thing is real, though. I was a doubter for a while, but Gary Mueller schooled me on the matter and I retrofit a Tam pipe with a Mueller augmenter pipe (smaller diameter and a taper about halfway down) and whaaaat a difference. This was on a Yellow F-16, and the difference in takeoff performance with a P-60 was astonishing.

Rush!

Could you guys clarify the static thrust issue?  I'm not clear on the spacing rule between the nozzle and the pipe lip.  I have seen some plans that require only 5mm distance between them (i.e. Avonds F15 _120) and the more common rule of 3/4"separation... 

I also have a large diameter pipe and a smaller exhaust nozzle.  Distance between the bellmouth lip and exhaust lip is 20mm also. 

Thanks!

Rob

Xairflyer

My Feedback: (1)

Just thought I would update on this, apart from performing and sounding really well my EGT's are now a lot lower as well.

As I started my turbine life with a JetJoe , I have kept a record of the runs/temps etc of all my turbines since.

The Avg EGT's are now 50degC lower than they were when fitted in my Boomerang and this has been consistent for the past couple of hours.
Lower EGT's tend to equal lower thrust, but also longer life so a good thing.

grumania

Hi guys , the formula for the correct distance is:
D2 minus D1
D2 is the diameter of the pipe, D1 the diametre of the turbine nozzle. A correctly shaped inlet is also important.
Here you can see some examples of optimized inlet shrouds:
http://www.grumania.com/xtcommerce/i...chubrohre.html

Ilja

Couch Potato

Thanks Ilja, a formula I can easily remember.