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Post by Johansson on Nov 2, 2013 4:58:58 GMT -5
It´ll look unique for sure. Space will be a major issue since we want to keep a streamlined profile for a future set of fairings, Olov is also insisting on using the four stroke oil pump instead of a 12V pump so that will also add to the volume of the engine package. Should look interesting when it is finished. *LOL*
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Post by Johansson on Nov 27, 2013 14:46:50 GMT -5
We spent an evening this week making the engine cradle and some of the turbocharger mounts, not an easy job since the two turbo flanges are nowhere near in line... =) Another evening and the turbochargers will be handing firmly in the suspended cradle above the subframe, Olov digged out two bass ports from the shed that fits like a pair of gloves. It looks absolutely insane IRL. *LOL* Cheers! /Anders
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Post by racket on Nov 27, 2013 15:17:40 GMT -5
Hi Anders
Nice touch :-)
Do those inlets come in various sizes ...............I could do with a 170 mm throated one for the SKULD
Cheers John
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Post by Johansson on Nov 27, 2013 15:53:36 GMT -5
Hi John,
Indeed, I think we can live with the added drag just because it looks faster. =)
I´ll ask Olov where he bought them, they weren´t cheap so why not turn one ourself from aluminum sheet with your lathe? Takes some practice but it should be doable and much fancier.
Cheers! /Anders
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wolfdragon
Senior Member
Joined: April 2011
Posts: 287
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Post by wolfdragon on Nov 27, 2013 16:56:10 GMT -5
ebay is lousy them, they call them "velocity stacks" for some strange reason, I guess bellmouth intake fairing was too technical of a term.
I'm with Anders, roll pressing sheet would be nice... How it's Made has a few shows making trumpets and cymbals, should be a good reference on the how to part
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Post by racket on Nov 27, 2013 18:01:13 GMT -5
LOL......yeh, lotsa velocity stacks around, but a tad small :-(
The times I have tried metal spinning it hasn't worked out all that well , but it was using stainless .
Might be easier to make a wooden pattern and get it cast with the mounting flange already attached .
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gidge348
Senior Member
Joined: September 2010
Posts: 426
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Post by gidge348 on Nov 27, 2013 20:25:51 GMT -5
Pity we don't have the same ice & snow in Australia, this looks like fun........Scary but fun.... LOL......yeh, lotsa velocity stacks around, but a tad small :-( The times I have tried metal spinning it hasn't worked out all that well , but it was using stainless . Might be easier to make a wooden pattern and get it cast with the mounting flange already attached . Yep, I found metal spinning on a lathe a pain in the lower portion of the back, until someone told me I was stretching the material instead of shrinking it. Got an "OK"... result when I used larger sheet of flat disc and shrunk it into a cone. One other thing you may want to try is making the wooden buck and making out of fibreglass? Ian...
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Post by racket on Nov 27, 2013 20:35:06 GMT -5
Hi Ian
Yep , fibreglass might be the way to go , it'll need to be strong enough to mount the starter off it though, maybe some metal "ribs" .
Cheers John
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Post by Johansson on Dec 3, 2013 16:29:21 GMT -5
I´ve run some calcs on the new twin turbo engine with the same running parameters as the old single turbo engine and got some encouraging results. With 3.6PR, 0.92kg/s mass flow and a 900°C TIT I found that a single S500 turbine should be capable of 64.3kg thrust with afterburning, times two makes it a staggering 128.6kg of thrust! The single afterburner should have a 13.5cm diameter jet nozzle, but I haven´t figured out how to calculate a suitable AB duct diameter yet. I know that you John ran me through it some years ago but I can´t find the emails anywhere. I need to get the 516.7m/s down to a speed capable of sustaining the flame so when I know that speed it should be pretty straightforward to figure out. I have access to a variety of large diameter 2mm stainless tubing so I will pick one closest to (if not spot on then larger than of course) the theoretical diameter to save us the trouble of rolling a 2mm stainless sheet into a long tube. Cheers! /Anders
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metiz
Senior Member
Joined: April 2011
Posts: 297
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Post by metiz on Dec 3, 2013 19:16:23 GMT -5
Anders, I don't want to pretend I know anything about these engines, but isn't a TIT of 900 degrees ridiculously high?
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Post by racket on Dec 3, 2013 20:16:41 GMT -5
Hi Metiz
LOL.....900 C for a TIT is "conservative" if the turbine wheel is Inco 713 , the reason why the DIY turbine community has an upper limit of ~788 C -1450 F is because the lower grade GMR235 wheels often used in diesel turbos has a roughly 200 degree C lower limit , most modern turbos now use the Inco 713 for every type of turbo, and unless you know the turbine wheel material, its safer to run at the lower limit .
The Garrett low cost turbojet, Model 1030, using a basic turbocharger , used a very high 1037C - 1900 F for the TIT , it was only expected to run for half an hour at those temps.
Cheers John
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Post by racket on Dec 3, 2013 20:49:14 GMT -5
Hi Anders
I'd go for an 8 inch - 200 mm diameter afterburner for the twin .
Here's the reasoning ............my GT6041 afterburner was made from a 6 inch section of SS tubing , assuming you'll be running a total of ~4 lbs/sec from the two turbos and I was running ~2.75 lbs/sec from the GT6041 , the 4 : 2.75 ratio is ~1.45:1 so lets go 1.5 times , my 6 inch tube with 1/16th wall thickness , meant a 5.875" ID for an area of 27.1 sq inches , lets multiply by our flow ratio of 1.5 which gives us 40.7 sq ins or 7.2 inches for the ID , a section of "off the shelf" 8 inch - 200mm dia SS tubing will provide a bit more area for lower gas velocities and "easier??" combustion , and be OK for your AB body .
The Garrett turbojet used a 7 inch dia AB for the Model 1030 which was flowing ~2.88 lbs/sec , they felt the 6 inch diameter was tad too small and the 8 inch a bit too big even though it would have improved combustion but at lower overall efficiency due to large losses from the larger sudden expansion ratio in the dump style afterburner.
If you are going to use flameholders rather than a dump style then we need to get gas velocity down to ~400 ft/sec at the flameholder, assuming a T I T of ~900 C then TOT will be say 750 C -1023 K at a pressure of say 10psi -1.68 PR in the AB , density will be ~27.6 cu ft/lb so ~110 cu ft/sec for your 4 lbs/sec , 110 div by 400 =0.276 sq ft or 39.76 sq inches , or roughly our 7.2 inch dia as above , ..................yep , an 8 incher will keep you happy ;-)
Cheers John
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nersut
Veteran Member
Joined: September 2012
Posts: 223
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Post by nersut on Dec 4, 2013 0:17:24 GMT -5
Hi John & Anders I found a 171 page R&D document about the AiResearch ETJ131 Model 1030, 201 lb's thrust afterburning turbojet based on the T18A turbocharger. Happy reading Link
Cheers Erik
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Post by Johansson on Dec 4, 2013 1:33:16 GMT -5
Hi Anders I'd go for an 8 inch - 200 mm diameter afterburner for the twin . Here's the reasoning ............my GT6041 afterburner was made from a 6 inch section of SS tubing , assuming you'll be running a total of ~4 lbs/sec from the two turbos and I was running ~2.75 lbs/sec from the GT6041 , the 4 : 2.75 ratio is ~1.45:1 so lets go 1.5 times , my 6 inch tube with 1/16th wall thickness , meant a 5.875" ID for an area of 27.1 sq inches , lets multiply by our flow ratio of 1.5 which gives us 40.7 sq ins or 7.2 inches for the ID , a section of "off the shelf" 8 inch - 200mm dia SS tubing will provide a bit more area for lower gas velocities and "easier??" combustion , and be OK for your AB body . The Garrett turbojet used a 7 inch dia AB for the Model 1030 which was flowing ~2.88 lbs/sec , they felt the 6 inch diameter was tad too small and the 8 inch a bit too big even though it would have improved combustion but at lower overall efficiency due to large losses from the larger sudden expansion ratio in the dump style afterburner. If you are going to use flameholders rather than a dump style then we need to get gas velocity down to ~400 ft/sec at the flameholder, assuming a T I T of ~900 C then TOT will be say 750 C -1023 K at a pressure of say 10psi -1.68 PR in the AB , density will be ~27.6 cu ft/lb so ~110 cu ft/sec for your 4 lbs/sec , 110 div by 400 =0.276 sq ft or 39.76 sq inches , or roughly our 7.2 inch dia as above , ..................yep , an 8 incher will keep you happy ;-) Cheers John Hi John, A 200mm afterburner is great since it leaves "plenty" of room for a decent heat shield between Olovs legs. I have a small supply of SS2368(253MA) and inconel sheet that I will use to make a flame holder from, in the old afterburner we used regular SS2333 for the flame holder but after a couple of runs all that was left was black stumps closest to the AB wall... -"an 8 incher will keep you happy ;-)" I´ll tell Anna you said that. *LOL* Cheers! /Anders
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Post by racket on Dec 4, 2013 3:27:49 GMT -5
Hi Eric
Yep , I was given a CD of it by a good mate , lotsa interesting reading :-)
Cheers John
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