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How To Build RC Jet Turbine Exhaust Tubes

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Old 08-18-2010, 03:34 PM
  #26
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Default RE: How To Build RC Jet Turbine Exhaust Tubes


Quote:
ORIGINAL: BJ64


Quote:
ORIGINAL: grbaker

BJ

I used the same specs on the pipe I used on the Titan and it was only putting out 27# without the pipe and about 321# with. I suspect it would work well for yours..
Thanks heaps for the info, Gary

I'll use those dims to build my pipes with then.

The 96mm diameter is perfect - the only 316 0.010'' stainless I can get at a reasonable price is 305mm wide (by 1m long), so 96mm will need 301.4 of sheet. Which leaves 3-4mm overlap to spot-weld on.

I'd be more comfortable if the sheet was 310mm wide - just to give me a bit more room to move in, but I might just be able to squeeze it using the 305mm stuff.

There is one other place that I can get 316 0.010 stainless from, and it's 600mm wide - but they have a AU$60 cutting fee on top of the sheet price, which brings it closer to 200 bucks a sheet. And I'd end up with about 290mm left over that would be next to useless.

Do you have any suggestions on how to make the bellmouth on the tailpipe at the Turbine end? They look like about a 1cm flange affair...

Oh, one more question: What distance do you space the start of the tailpipe from the tip of the Turbine's exhaust cone? From a lot of pics I've seen, it looks to be around 15-20mm.

Thanks again for your help on this - much appreciated...

BJ

BJ try this site

[link=http://www.mcmaster.com/#shim-stock/=8gm41w]http://www.mcmaster.com/#shim-stock/=8gm41w[/link]


Alan
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Old 08-18-2010, 07:54 PM
  #27
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Default RE: How To Build RC Jet Turbine Exhaust Tubes

I have a question about making your own pipe, does it have to be double wall?? if so can the outter wall be Aluminum??

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Old 08-20-2010, 12:48 AM
  #28
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Default RE: How To Build RC Jet Turbine Exhaust Tubes

I'm just learning to build these things Pat.

But yes, from what I've been reading, the outer wall can be Aluminium. So long as there's about a 5mm spacing between the inner and outer walls, Ali should be fine (someone please correct me if a 5mm spacing is not enough).

I'm looking at making some tubes up using 0.010" (0.25mm) 316 grade Stainless Steel for the inner tube, and 0.010" Aluminium for the outer (to save on a bit of weight and $$$).

316 is triple the price of 304 down here, so for my 'prototypes', so I might just go with 304 for the time being.

Regards,

BJ
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Old 08-20-2010, 12:26 PM
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Default RE: How To Build RC Jet Turbine Exhaust Tubes



on 2010 jetcat katalog on page 40 there are some info about engine size=dimentions

http://www.jetcat.de/downloads/jetca...g-2010_web.pdf


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Old 08-20-2010, 05:03 PM
  #30
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Default RE: How To Build RC Jet Turbine Exhaust Tubes

Is the Aluminum spot welded to the stainless???? Can you use a Tig Torch with no filler material and just spot it, has anyone tried this? Just curious
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Old 08-20-2010, 05:07 PM
  #31
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Default RE: How To Build RC Jet Turbine Exhaust Tubes

what aluminum?

if you mean the bellmouth it can be held in place with just three screws
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Old 08-20-2010, 06:39 PM
  #32
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Default RE: How To Build RC Jet Turbine Exhaust Tubes


Quote:
ORIGINAL: jedijingle

Is the Aluminum spot welded to the stainless???? Can you use a Tig Torch with no filler material and just spot it, has anyone tried this? Just curious
The Aluminium outer tube is held a constant distance away from the inner Stainless tube by little corrugated pieces of Stainless you make up. To fix the outer Ali tube in place, the pics I've seen so far seem to show it is pop-rivetted to a couple of these 'spacers', which in turn look like they're either pop-rivetted or TIGed/Spot-welded onto the inner tube.

The bellmouth has to be Stainless, or it will melt if it is made out of Ali...

BJ
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Old 08-20-2010, 07:08 PM
  #33
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Default RE: How To Build RC Jet Turbine Exhaust Tubes

Cheers BJ64
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Old 08-21-2010, 02:18 AM
  #34
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Default RE: How To Build RC Jet Turbine Exhaust Tubes


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ORIGINAL: BJ64


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ORIGINAL: jedijingle

Is the Aluminum spot welded to the stainless???? Can you use a Tig Torch with no filler material and just spot it, has anyone tried this? Just curious
The Aluminium outer tube is held a constant distance away from the inner Stainless tube by little corrugated pieces of Stainless you make up. To fix the outer Ali tube in place, the pics I've seen so far seem to show it is pop-rivetted to a couple of these 'spacers', which in turn look like they're either pop-rivetted or TIGed/Spot-welded onto the inner tube.

The bellmouth has to be Stainless, or it will melt if it is made out of Ali...

BJ

this is what i call bellmouth and it has no proomblem to be made from aluminum
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Old 08-21-2010, 04:47 AM
  #35
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Default RE: How To Build RC Jet Turbine Exhaust Tubes

From what I understand 5mm is a good air gap to be running with aluminium outer pipes, a friend who makes laser welded pipes uses ali outer pipes to save weight.

What should be remembered on twin wall pipes is you must not fix or weld the 'ripple rings' to both inner and outer pipes, one should float over the other - just pop rivet them to the outer aluminium pipe so they can slide over the inner, heat expansion will cause all sorts of issues otherwise.
If the bell mouth is fixed to the framework, and the rear outer aluminium tube is fixed at the rear end, the inner and outer can slide without fear for buckling and possible failure.

Inner pipes get hot (see pic) so don't underestimate the expansion factor.



marcs

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Old 08-21-2010, 05:52 AM
  #36
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Default RE: How To Build RC Jet Turbine Exhaust Tubes

Marc

Wow that pipe has got hot!

If I am not mistaken the outlet is smaller than the inlet which explains why it has been severely overheated. Not sure who made the pipe. If you make the pipe with a short section that expands the air after the bellmounth it will drag loads of cool air in and it lines the inside of the wall with cool air. On my own engines, provided they have not been subject to hot starts it is possible to run the pipe so it gets no hotter than straw colour. There should be no particular reason to use a second wall unless you want extra security against hot starts.

John
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Old 08-21-2010, 06:42 AM
  #37
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Default RE: How To Build RC Jet Turbine Exhaust Tubes

John,

This was a testing rig, to see the effects of different pipe designs, it was posted to indicate that things get hot - but not always this hot
Expansion should always be considered though when using two walled pipes.

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Old 08-21-2010, 11:51 PM
  #38
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Default RE: How To Build RC Jet Turbine Exhaust Tubes


Quote:
ORIGINAL: marc s

From what I understand 5mm is a good air gap to be running with aluminium outer pipes, a friend who makes laser welded pipes uses ali outer pipes to save weight.

What should be remembered on twin wall pipes is you must not fix or weld the 'ripple rings' to both inner and outer pipes, one should float over the other - just pop rivet them to the outer aluminium pipe so they can slide over the inner, heat expansion will cause all sorts of issues otherwise.
If the bell mouth is fixed to the framework, and the rear outer aluminium tube is fixed at the rear end, the inner and outer can slide without fear for buckling and possible failure.

Inner pipes get hot (see pic) so don't underestimate the expansion factor.



marcs

Great info regarding not fixing the inner and outer tubes together and a great pic of the 'hot' tube too - thanks

BJ
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Old 09-10-2010, 09:31 AM
  #39
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Default RE: How To Build RC Jet Turbine Exhaust Tubes


Quote:
ORIGINAL: DelGatoGrande


Quote:
ORIGINAL: BJ64


Quote:
ORIGINAL: jedijingle

Is the Aluminum spot welded to the stainless???? Can you use a Tig Torch with no filler material and just spot it, has anyone tried this? Just curious
The Aluminium outer tube is held a constant distance away from the inner Stainless tube by little corrugated pieces of Stainless you make up. To fix the outer Ali tube in place, the pics I've seen so far seem to show it is pop-rivetted to a couple of these 'spacers', which in turn look like they're either pop-rivetted or TIGed/Spot-welded onto the inner tube.

The bellmouth has to be Stainless, or it will melt if it is made out of Ali...

BJ

this is what i call bellmouth and it has no proomblem to be made from aluminum
So spinnig up a bellmouth made of Aluminium on a Lathe is ok?

I would have thought aht Aluminium would fail at the temps that can come out of the exhaust of the Turbine ??

Being able to use Ali for the bellmouth would sure makes things easier

Sooo...when you fix the the Ali bellmouth to the inner tube, can you use 'normal' pop-rivets, or is it wiser to use a couple of stainless steel rivets instead?

BJ
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Old 09-10-2010, 04:54 PM
  #40
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Default RE: How To Build RC Jet Turbine Exhaust Tubes

Use ss screws on the bellmouth. Rivits for ss to Alum. walls, but you can weld it if the inner and outer walls are the same material. Make your inner wall ever so slightly oversized around your alum bellmouth as the alum will expand more than the ss.

Those bell mouths have to be purchased somewhere else. Like many things in this hobby parts can be found in production and being used on other non hobby related things. Maybe they are some sort of plumbing fixture or hvac part. HUmmmmmmmmmmm. I would like to know where to buy them. The ones I have seen are spun alum. I dont mean on a lathe either.
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Old 09-15-2010, 10:07 AM
  #41
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Default RE: How To Build RC Jet Turbine Exhaust Tubes

...all's quiet on the Western Front...

BJ
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Old 10-10-2010, 03:43 PM
  #42
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Default RE: How To Build RC Jet Turbine Exhaust Tubes

Im looking to build a bifurcated pipe for a 22lb engine (52mm exhaust dia) with a divergent area / bell intake for my MiG 144

Assuming a divergence of ~20% increase in area, for a bifurcated pipe should this happen immediately after the split for say 100mm then remain the same size thereafter?

Im thinking of a 85mm inlet dia leading to two 60mm outlets (approx same area as inlet) which open up to 65mm (approx 120% inlet area) for the remaining length. Does this seem sensible?

Ive looked at jetcats dimensions they all seem to converge rather than diverge.

Any tips or pointers welcomed.

Thanks
Dave
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Old 10-13-2010, 05:31 AM
  #43
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Default RE: How To Build RC Jet Turbine Exhaust Tubes

You might want to give GTBA a try there Windy.

You have to pay to join, and I haven't had a lot of success there in getting direct answers that I'm looking for re building some single-tubed exhausts myself, but I do recall seeing an article related to bifurcated pipes.

Might be worth a shot?

BJ
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Old 10-13-2010, 07:02 AM
  #44
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Default RE: How To Build RC Jet Turbine Exhaust Tubes

Hi Bj

Its an home built engine and im in the GTBA so ive posted similar there too alrerady!

Cheers
Dave
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Old 10-13-2010, 08:23 AM
  #45
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Default RE: How To Build RC Jet Turbine Exhaust Tubes


Quote:
ORIGINAL: dave.windymiller

Hi Bj

Its an home built engine and im in the GTBA so ive posted similar there too alrerady!

Cheers
Dave

In that case then - just whack a second Turbine in there, and be done with it.. LoL

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Old 10-13-2010, 02:09 PM
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Default RE: How To Build RC Jet Turbine Exhaust Tubes

The first one took nearly 10 years so thats an unlikely option!!!

Cheers
Dave
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Old 10-14-2010, 09:55 PM
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Default RE: How To Build RC Jet Turbine Exhaust Tubes


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ORIGINAL: dave.windymiller

The first one took nearly 10 years so thats an unlikely option!!!

Cheers
Dave
So??

You should have the process down-pat now, and be able to turn the next one out in only 10 Months LoL

BJ
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Old 10-14-2010, 10:04 PM
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Default RE: How To Build RC Jet Turbine Exhaust Tubes

BJ,
I am currenly searching for someone locally to produce these for me.. I need to get them for the F9F Panther and F-100 I have coming out of the molds...
If you want I can let you know what I find.. in the mean time if you find someone who can do it let me know..


Rob
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Old 10-15-2010, 08:16 AM
  #49
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Default RE: How To Build RC Jet Turbine Exhaust Tubes

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ORIGINAL: rorrock

BJ,
I am currenly searching for someone locally to produce these for me.. I need to get them for the F9F Panther and F-100 I have coming out of the molds...
If you want I can let you know what I find.. in the mean time if you find someone who can do it let me know..


Rob
Hi Rob.

Do you mean single, or bifurcated Tubes?

BJ
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Old 11-30-2010, 07:51 AM
  #50
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Default RE: How To Build RC Jet Turbine Exhaust Tubes


Quote:
ORIGINAL: jetrichie

I seen some details on the GTBA site once on making a spot welder that might help, also 304 spec stainless is ok 316 would be better.

Got the guys in my workshop to make one once for a 14lb turbine, made the inner diameter the same as the NGV with the front flared out, length was just made to suit model.
You make the zig zag spacer between the walls with a strip about 10mm wide and fed through a gear mesh, or just fold with pliers..

Spot welder is important and makes the job fairly easy, check out GTBA or google on making one.

no doubt someone will correct me and give a more accurate method of calc dia etc.

Gap from tailcone to tube is important, 15-20mm seem to be the norm

This thread is a little dated but came across it and wondered if anyone here is still looking for a schematic of a spot welder.See below link:

http://www.philpem.me.uk/elec/welder/

I built this welder some time ago to spot weld nickel tabs onto batteries for flight packs and found that this unit has plenty of power to spot weld sheet stainless for exhaust pipes.
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