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Post by jetjeff on May 27, 2016 3:51:05 GMT -5
Hi,
Yes the shaft is a hollow tube. Outer diameter is about .850", wall thickness is .050". The guy I got it from thought it to be 410 stainless, but I'm not 100% sure thats correct. It is magnetic. I went this route to reduce weight, a solid shaft of Chrome Moly would weight a lot more. Kurt Schreckling made his shafts with the center section of aluminum, my reason why was the weight savings too. Spark tests from grinding the material can be used to determine the alloy, but I'm no metallurgist for sure.
Jeff
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Adam
Veteran Member
Joined: May 2016
Posts: 101
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Post by Adam on May 28, 2016 3:56:01 GMT -5
Hi Jeff,
I've been reading a bit about stainless steel types. 410 is generally used for applications involving mild corrosion, heat resistance and high strength, it is a Martensitic (crystalline structure) stainless steel so it is magnetic, as opposed to the more common Austenitic types like 316 which are vitually non magnetic, but can become slightly magnetic from work hardening. Ferritic stainless is also magnetic.
Cheers Adam
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Post by jetjeff on May 30, 2016 6:21:38 GMT -5
Hi All, I finished 2 potato graders, A.K.A. the Schreckling inner burner can liners,,,lol. I made two to see how the cones look after having it rolled by a sheet metal shop. Kurt warns about not changing the geometry of the burner can, so I'll take his advise. Also shown is the outer liner, but I haven't cut the flaps in it yet. Side note: End-mills make a much neater hole in sheet-metal than twist drills, with much less distortion. Jeff
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Post by jetjeff on May 31, 2016 3:28:24 GMT -5
Hi All, Here is a possible fuel pump idea for smaller turbines (Schreckling, Kamps, MW54, MW44) that hit me while doing yard work over the weekend. The battery powered wand on products like weed / insect killer has a small geared pump in it. I tested it with an overnight soak of Kero, seemed ok. I took the pump apart, no neoprene pump impeller,,,hmmmmm. It's powered by 4 AA batteries. Jeff
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Adam
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Joined: May 2016
Posts: 101
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Post by Adam on May 31, 2016 4:43:53 GMT -5
Hi Jeff, the burner can liners are looking good. Did you use the circle cutter to cut the flanges for the ngv? I bought one last year but haven't used it yet, I thought I would use it to cut the flanges, but then I started wondering if it is really just for thin sheet metal.
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Post by jetjeff on Jun 1, 2016 0:25:43 GMT -5
Hi Adam,
No, I didn't use the circle cutter for the NGV flange. I've milled them out on my rotary turntable and Bridgeport and also have used my lathe to cut them out. I generally use S.S. about .050" to .060" thick. That picture that shows me cutting the NGV hole in the mini keg on the Bridgeport, the machine was not turned on, I just put a wrench on the drawbar, and applied downward pressure on the quill and did it by hand.
I did two volume/minute tests on that little pump. One test proved 420 milliliters per minute and the 2nd over 450 milliliters per minute. Thats more than a Schreckling engine needs at 160 ml/min (idle) and 200 ml/min (full throttle).
I had the inner burner can liners rolled into cones, pics coming soon
Jeff
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Adam
Veteran Member
Joined: May 2016
Posts: 101
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Post by Adam on Jun 1, 2016 2:41:16 GMT -5
Hi Jeff,
Thanks, I'll cut the flanges on my lathe. It sounds like that little pump should do the job nicely. Looking forward to seeing your pics.
Adam
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Post by jetjeff on Jun 1, 2016 3:46:33 GMT -5
Hi Adam, Here is the outer liner and inner cone pic. Not sure which inner cone I'll use. Both inner cones have the same number of holes as the Schreckling plans, but they have been enlarged 40%, the same percentage I used for the entire turbine dimensions. The smaller major diameter cone, looks (hole spacing wise) more like the inner cone from the plans. Jeff
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Adam
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Joined: May 2016
Posts: 101
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Post by Adam on Jun 1, 2016 5:11:11 GMT -5
Looking good Jeff! Do the Schreckling plans give two options for the inner cone? Are you going to make it so you can swap the inner cones to see which one works best?
Adam
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Post by jetjeff on Jun 2, 2016 15:47:20 GMT -5
Hi Adam,
Thanks. Sorry for the delayed response, no internet this morning, a squirrel must have chewed through the cable again,,,lol. No, the Schreckling plans don't show two options, that's just me being anal. I often make a part over again (and again), to make sure it's exactly correct. I'm going to use the smaller major diameter of the two cones, the hole spacing looks more closely like the Schreckling plans.
I do have two questions for the turbine experts. One, can the number of evaporator tubes be an odd number? I was thinking of using 9 at .312" outer diameter. Two, can the inner burner can liner fit outside the inner ring of the NGV? Kamps shows it fitting inside the inner ring.
Thanks All
Jeff
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Post by racket on Jun 2, 2016 21:17:51 GMT -5
Hi Jeff
The flow area thru the evap and the outer heating surface are more important than the number( odds or evens) , I've always used total cross sectional flow area of evaps at ~10-12% of comp inducer area , with the outer heating surface at 6 times inducer area
Cheers John
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Adam
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Joined: May 2016
Posts: 101
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Post by Adam on Jun 3, 2016 1:19:26 GMT -5
Hi Jeff,
I Just had a look through all of my different micro turbine drawings. Yes the Kamps micro turbine and the KJ-66 both show the combustion chamber inner on the inside of the ngv, but the drawing on the title page of the pdf "Build your own RC turbine engine" by Bob Englar shows it on the outside. In the drawing of the FD3/64 the cone ends up way inside the ngv inner ring which doesn't look good for gas flow at all! I reckon it would be better for gas flow on the outside anyway. but maybe its on the inside so so the whole combustion chamber grips onto the ngv better. Maybe you could machine a small lip on the outside of the ring so it just slips on and ends up perfectly flush.
I was just wondering today what keeps the combustion chamber from moving forward? I know there are some tags on the outside to keep it centered. Is the glow or spark plug attached to one of these or something?
Cheers Adam
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Post by jetjeff on Jun 3, 2016 2:54:11 GMT -5
Hi Adam,
The Schreckling plans show 3 small compression springs that keep it from moving forward. Kamps says the combustion chamber must not be a tight fit on the NGV assembly (page 80 in my Kamps book), but I'm not sure why, seems like you'd want it tight. I had three short pieces of wire rod welded to the burner can on my old build. They butt up against the compressor diffuser, so it can't back off the NGV assembly. My old build the burner can is a tight fit.
Thanks John for the info on flame tubes.
Jeff
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Adam
Veteran Member
Joined: May 2016
Posts: 101
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Post by Adam on Jun 3, 2016 5:17:47 GMT -5
Thanks Jeff, Its on page 76 in my book (2nd edition). In that pdf it says "The rear of the inner sleeve slides over a matching rebate on the inner NGV ring and this also provides a step free gas path". I can see one those springs on my highly pixilated fd3/64 cross section now, your way with the three wires sounds like the way to go though. Cheers Adam
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Post by jetjeff on Jun 3, 2016 23:14:03 GMT -5
Hi Adam,
I have the 3rd edition of the Kamps book,,,probably why we are 'not on the same page',,,lol.
Jeff
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