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How To Build RC Jet Turbine Exhaust Tubes
Hi Guys'n'Gals :D
I've started this thread in the hope of pooling together ideas and experience from those who have built RC Jet Turbine exhaust tubes - both single and double-walled. Any info you have regarding the initial calculation of the tube length, front and rear diameters, offset between the tube and the Turbine's exhaust, and dimensions of the bellmouth etc. would be great. And of course, the actual build - what materials to use, how to shape/form them, how to spot-weld/other kinds of welds etc. Pics, pointers to other threads/material - all most welcome... Regards, BJ:) |
RE: How To Build RC Jet Turbine Exhaust Tubes
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 |
RE: How To Build RC Jet Turbine Exhaust Tubes
any one know numbers between:
engine size=pipe inner diameter=inner tube wall thicfkness? .. |
RE: How To Build RC Jet Turbine Exhaust Tubes
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RE: How To Build RC Jet Turbine Exhaust Tubes
Some excellent links and reading there, thanks Gary :D
BJ:) |
RE: How To Build RC Jet Turbine Exhaust Tubes
A couple of things, and a further question.
Wren (Mike Murphy?) published a couple of articles on the augmented thrust of slightly divergent pipes (larger end of the cone towards aft) in RCJI a number of years ago, along with tests of the proper distance from turbine tail cone to bell mouth opening. Their pipes for the smaller ('44 and '54 sized) turbines seem to be largely single walled .007 or .008 SS, for the cone (remains cool anyway) and the straight segment towards the rear (that gets hot). They use a 1.5-2 inch 'extractor' double-walled segment at the exit of the aircraft, with 5-8 mm corregated or waffled SS to separate the outer from the inner part, with outer part extending 5-10 mm aftwards of the inner part. Pipes for larger thrust turbines are not usually divergent, as they presumably don't need the augmented thrust from a venturi, maybe run hotter and need perhaps full length double walls. Another good question is does anyone know about the design and construction of double exit pipes-eg F4, and the A6. What thrust losses can be expected compared to single straight back pipes, what angles can be used and how heavy must the SS be to tolerate the heat just aft of the turbine? I think only Tam makes them and might have the experience to comment on them. |
RE: How To Build RC Jet Turbine Exhaust Tubes
augmented thrust of slightly divergent pipes (larger end of the cone towards aft) The thrust augmenting pipes work well for the larger turbines as well, but the pipe size at the exit end gets too large to fit into some scale planes. I have built a couple of augmenting pipes for a Jetcat Titan and a Merlin 160 with excellent results. |
RE: How To Build RC Jet Turbine Exhaust Tubes
It was me that did the testing and published in RCJI. The effects of the augmentation principles work equally well on all sizes of our engines running from the Lambert size up to P200 size. The great thing is that the augmentation sucks in a large amount of cool air together with the hot gasses. This cool air runs down the pipe against the wall and keeps it cool. If you are careful and do not have hot starts it is possible to keep a single walled pipe from going any hotter than a straw colour. I did some work on bifurcated pipes and managed to make one that had almost no loss. Most standard straight pipes have a significant measurable loss and bifurcated ones can be much worse.
John |
RE: How To Build RC Jet Turbine Exhaust Tubes
How do you guys fix the middle 'rippled' separation stips between the inner and outer tubes? Spot-weld there too?
And... if running an Aluminium outer tube, would pop-rivets take the interstitial heat between the inner tube and the outer tube? BJ:) |
RE: How To Build RC Jet Turbine Exhaust Tubes
How much are you guys overseas paying for the Stainless?
I just got a couple of quotes today for -.010" (0.254mm) 316 grade stainless - 1000mm x 305mm for around AUS$130 a sheet, or 1000mm x 600mm for $140 a sheet but with a $60 cutting fee, which makes it around $200 a sheet. I really need to work out what diameter my pipes would need to be on a 15kg (30lb) thrust Turbine before ordering, as a 100m diam pipe is going to need around 314mm of material, plus overlap - so a 305mm sheet isn't going to work... BJ"_ |
RE: How To Build RC Jet Turbine Exhaust Tubes
Are there any charts or formulas around to help you calculate what diameter the front and rear of the exhaust tube needs to be?
What size the bellmouth needs to be? What the distance between the Turbines exhaust cone and the inlet of the exhaust tube needs to be? And if you need to run a parallel or tapered tube? BJ:) |
RE: How To Build RC Jet Turbine Exhaust Tubes
Hmmm...
Gone a bit quiet in here... BJ:) |
RE: How To Build RC Jet Turbine Exhaust Tubes
This looks interesting. Might need a set of longer tongs for most pipes.
http://www.harborfreight.com/115-vol...der-45689.html PaulD |
RE: How To Build RC Jet Turbine Exhaust Tubes
BJ,
Both of the tailpipes I built used the John Wright thrust augmenting pipe design. They were used for a Jetcat Titan and a Merlin 160. They were about 86mm @ the inlet, tapering up to 96mm (at about 180mm from the inlet) and then 96mm all the way to the exit. On a test stand I measured about a 5# increase in thrust (over no tailpipe at all) with the Titan but never tried the Merlin on the stand. I'm probably going to build a new tailpie for my JMP T-33, but I won't be able to build a thrust augmenting pipe due to the scale exhaust opening being too small. It would be nice if someone published a chart with tailpipe sizes for various engine sizes. Paul, the spot welder shwn is the one I used to weld my pipes. Harbour Freight sells longer electrodes for that welder. |
RE: How To Build RC Jet Turbine Exhaust Tubes
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ORIGINAL: PaulD This looks interesting. Might need a set of longer tongs for most pipes. http://www.harborfreight.com/115-vol...der-45689.html PaulD It's supposed to do the welds from one side only. I haven't tried it out yet. What I am finding, though, how unbelievably difficult it is to find stainless shim material. So far, I've only managed to find 2 sources of 316 grade 0.010" stainless in the whole country. And boy, that stuff ain't cheap - around AU$150 for a 3ft x 1ft piece :eek: BJ:) |
RE: How To Build RC Jet Turbine Exhaust Tubes
ORIGINAL: grbaker BJ, Both of the tailpipes I built used the John Wright thrust augmenting pipe design. They were used for a Jetcat Titan and a Merlin 160. They were about 86mm @ the inlet, tapering up to 96mm (at about 180mm from the inlet) and then 96mm all the way to the exit. On a test stand I measured about a 5# increase in thrust (over no tailpipe at all) with the Titan but never tried the Merlin on the stand. I'm probably going to build a new tailpie for my JMP T-33, but I won't be able to build a thrust augmenting pipe due to the scale exhaust opening being too small. It would be nice if someone published a chart with tailpipe sizes for various engine sizes. Paul, the spot welder shwn is the one I used to weld my pipes. Harbour Freight sells longer electrodes for that welder. Would those dimensions work on a 30lb thrust Turbine? (I think the Merlin is 38lbs??) BJ:) |
RE: How To Build RC Jet Turbine Exhaust Tubes
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.. |
RE: How To Build RC Jet Turbine Exhaust Tubes
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.. 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:) |
RE: How To Build RC Jet Turbine Exhaust Tubes
I had a bellmouth from another pipe that worked for one of them and I modified the carbon fiber tailpipe inlet from a Eurosport for the other.
You will need to experiment with your pipe to turbine spacing to get the most gain. It will probably be more like 30 to 40 mm. |
RE: How To Build RC Jet Turbine Exhaust Tubes
ORIGINAL: grbaker I had a bellmouth from another pipe that worked for one of them and I modified the carbon fiber tailpipe inlet from a Eurosport for the other. You will need to experiment with your pipe to turbine spacing to get the most gain. It will probably be more like 30 to 40 mm. I'm trying to get my head around how to design/build one. I guess it's not much more than turning up a wood/aluminium blank on a lathe, then panel-beating some stainless shim material into shape using the blank, and finally spot-welding that 'trumpet' onto the front of the tailpipe. Again - thanks for your input. It is priceless and much appreciated... BJ:) |
RE: How To Build RC Jet Turbine Exhaust Tubes
Would anyone have any suggestions on how to build the bellmouth... and what rough dimensions that it should be?
Cheers :D BJ:) |
RE: How To Build RC Jet Turbine Exhaust Tubes
Call Tam, He'll make whatever you want !!!!:)
D |
RE: How To Build RC Jet Turbine Exhaust Tubes
ORIGINAL: rcjetsaok Call Tam, He'll make whatever you want !!!!:) D The idea is to learn how to build them myself - seein as I have at least 4 tubes I need for various "projects"... BJ:) |
RE: How To Build RC Jet Turbine Exhaust Tubes
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RE: How To Build RC Jet Turbine Exhaust Tubes
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I have made one tube so far, and so far I am very happy with it. It is the augmenting type, and I made it from .008" 304 from McMasterCarr.
Bellmouths: I once found a formula that said the radius should be internal dia/5. This is what I used, and the proportions seem good. Bellmouth was spun over a mdf plug in the lathe. I use full length lithoplate aluminum outer duct, 4mm spacing at the rear, and 6mm extension beyound the inner duct. I am running a JG100 engine, so the dimensions should be ok with 120 class turbines. Lars |
RE: How To Build RC Jet Turbine Exhaust Tubes
ORIGINAL: BJ64 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.. 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 |
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??
Pat |
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:) |
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 |
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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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 |
RE: How To Build RC Jet Turbine Exhaust Tubes
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 bellmouth has to be Stainless, or it will melt if it is made out of Ali... BJ:) |
RE: How To Build RC Jet Turbine Exhaust Tubes
Cheers BJ64
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RE: How To Build RC Jet Turbine Exhaust Tubes
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ORIGINAL: BJ64 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 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 |
RE: How To Build RC Jet Turbine Exhaust Tubes
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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 |
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 |
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. marcs |
RE: How To Build RC Jet Turbine Exhaust Tubes
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 BJ:) |
RE: How To Build RC Jet Turbine Exhaust Tubes
ORIGINAL: DelGatoGrande ORIGINAL: BJ64 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 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 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:) |
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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