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Post by jetjeff on Jan 23, 2017 1:12:29 GMT -5
Hi John,
I'll have to check that out, thanks.
Regards
Jeff
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reedy
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Post by reedy on Jan 23, 2017 10:08:12 GMT -5
Hi Jeff video of Mark Drakes hobbyjets 631 compressor wheel notice curve of blade to centre looks more pronounced than 10mm rad of fd3/64, 7 full blades and 7 short, not equal distance between the full blades. wheel is all alloy cnc m/c with integral spinner and covered top is salt bath brazed using 6082 foil between the two parts that are then put in a molten salt bath. Engine is home built, just fitted with Marks 631 wheel. looks like it has been dropped, damage to spun case and diffuser vanes. www.youtube.com/watch?v=Pf7iYmGi9yU
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reedy
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Post by reedy on Jan 23, 2017 10:23:33 GMT -5
Hi All just a picture of my test stand with the weighing scale I use, the scales work both ways pull and push which shows a minus,still right ,i believe you can reversed it internally by swapping wires around but I just ignore the - symbol. MFA fuel pump which has brass gears ,a must. the green valve is a aquarium valve been on 20 years never let me down does not leak. The meter is just your normal pressure gauge 100 mm dia only goes to 1 bar = 15 psi bigger the better. it came with the red line marked at 7 1/2 psi just happens to be my limit for the FD3/64
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Post by jetjeff on Jan 23, 2017 15:47:07 GMT -5
Hi Chris,
What type bearings did you use in your FD3 builds? I doubt the Schreckling design warrants GRW bearing, but I may be wrong.
Off to my basement machine shop.
Regards
Jeff
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Post by jetjeff on Jan 23, 2017 17:03:07 GMT -5
Hi All, I'm not so sure this forward sweep of the blades on a Schreckling wheel is a good Idea. I made a dummy blade from an old credit card to try to visualize this. Sweeping the blades forward would increase the surface area of the blade, possibly increasing airflow, not sure about pressure ratio. Hmmmm. Regards Jeff
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reedy
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Post by reedy on Jan 23, 2017 17:15:25 GMT -5
Hi Jeff I use cheapest steel bearings to build then bin them, skate board bearings work will with ceramic balls steel race off ebay for test runs you can get 608 and 688 hybrid bearings off ebay for £5 each
get it running right and happy with the lube and turbine temp before you try anything else,if it's running hot it can cook the rear bearing.The bearing race should not go blue or purple.
When was using steel balls and race on the smaller 688 bearing if the balance was not good enough the balls can peel like an onion,on taking the engine apart it had glitter in the bearing tube !
When balanced I tended to change them every 25 flights, did not want them to fail.
I do have a dynamic balancer design from GTBA it has a bimorph sensor embedded in a thin glass fibre board it relies on resonance of the setup to increase the sensitivity.
if buying the small 688 bearing get the deep grove ones.
don't try angular contact bearings until your totally happy the balance needs to be perfect for them and the preload set right.
Like to know some details about the Kamps ,it doe not seem to be trying at all ,odd .
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reedy
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Post by reedy on Jan 23, 2017 17:44:28 GMT -5
Hi Jeff another quick point ,been looking at your pictures ,have to do it on mobil phone,when I sent you Rob's compressor wheel design the spinner needs to be concave not a cone can't see to well on your pictures also you need to sharpen the blades with a warding file as per my very rough drawing !
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Post by jetjeff on Jan 24, 2017 5:11:38 GMT -5
Hi Chris,
Thanks. My Kamps engine is a 40% enlargement of the plans. Rotation is counter clockwise. There is a mismatch of the compressor (3.15") vs the turbine (3.5"), but I thought it would still run.
Regards
Jeff
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reedy
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Post by reedy on Jan 24, 2017 6:03:45 GMT -5
Hi Jeff
Can't remember where I read it,check the kamps book when selecting a compressor -
Keep wheel to same o/d as turbine wheel
retro curved blades
Tip height of blade not to high
Inducer not to big
what's not to high and not to big is I don,t know,you will need to go through the 88mm dia wheels and see wants available,
This only applys to home built, if you are in the RC turbine business stick the biggest one you can fit in and design a really good diffuser !
If you are happy with the wheel make another NGV and Turbine wheel (lot of work)
Sorry Jeff not much help you probably know all above,its hard to go back to an engine and rebuild.
hope somebody can chime in with compressor wheel suggestions,might be worth ringing turbo rebuild shops ,All my compressor wheels are salvage.
if you find a bigger one with a 90+ dia you could try it, if it proves too big trim the blades back at the tip but leave the disc,it's the opposite of the extended tips on m/c wheels
when testing experimental engines don' get to fussy and leave options open,if you find a wheel with a lower tip height than you have now leave the diffuser as is , make a replaceable inlet piece over the compressor wheel, Rob Wardale built a KJ66 which has a 6mm tip height, he only had a 5mm tip height wheel in it ,ran great i asked him if he had reduced the diffuser wedge height he said no, He left an out of wind 1mm step on the inlet cone which was a good fit to the wheel.
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reedy
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Post by reedy on Jan 24, 2017 7:52:33 GMT -5
Hi Jeff check out this site he goes through the design process in a more practical way. jetbeetle.com/JB_body_X150.htmgo to the articles at the bottom of the page.
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reedy
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Post by reedy on Jan 24, 2017 9:07:05 GMT -5
Hi Jeff Few more drawings showing the PT35 (FD3 Type),note the spinner shape with this flatter design of uncovered wheel. The wheel is 68 mm dia (scaled the drawing no sizes given) the spinner base and start of blades is 29 mm dia
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Post by jetjeff on Jan 24, 2017 15:50:12 GMT -5
Hi Chris, Yes I've emailed Jet Beetle (Horace T.L. Ho is the director) several times with inquires. Horace has always replied back right away,,,nice guy. His H-90 Tarantula engine is only 1/4" bigger (outer case) than my Kamps build and it kicks out 90lbs (I think was recently re-rated at 100lbs) of thrust. Has anyone from the GTBA built the UT-160 engine? Their website just has a teaser of the design. I had to make mockups of the two compressors, I just couldn't visualize it with one or two blades. I used 1/32" birch plywood. The forward slanted version seems promising with all the blades installed. The blades on the forward slanted version could remain at a 90 degree angle at the intake. I'll work on the mold for the cover plate this weekend. Regards Jeff
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Post by racket on Jan 24, 2017 17:18:22 GMT -5
Hi Jeff
Yep , Horace is a nice guy :-)
As for compressor wheels and which to use, there really is a multitude of options , also with regards setting up the turbine stage , a turb wheel the same diameter as the comp makes powering the comp "easier" , but once getting into the higher PRs from the comp that "big" turb wheel starts to suffer from excessive tip speeds so we need to reduce diameter and "restore" power by having it work harder by more gas deflection, temp , gas velocity etc etc , also the division of pressure drop across the stage can be "manipulated' , it can get complicated :-(
If you need help deciding , shoot me some questions .
Cheers John
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Post by jetjeff on Jan 24, 2017 18:43:36 GMT -5
Hi John,
Thanks. I'll probably build both carbon compressors. After what happened to me with my 1st carbon compressor, you can't have too many spares,,,lol.
Regarding my Kamps build, the turbocharger wheel is 10% smaller than the turbine. Schreckling got one of his engines to run on a 15% smaller compressor in diameter than the turbine wheel.
Regards
Jeff
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reedy
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Post by reedy on Jan 25, 2017 16:28:40 GMT -5
Hi Jeff I'm with you on the compressor size ,hard to hear it with your blower going,but does not sound like it's trying.
could you give sizes of
compressor inducer ,exducer,and working tip height ,is it retro curved(can't be sure i googled right one)
NGV inner dia ,is it 46 x1.4 ?
Turbine wheel is it twisted to 35 or m/c from solid.is the root dis 44 x1.4 ?
combuster which design is it 3rd addition with slightly bent sticks from rear. ?
Seems to run on too free when you switch off gas and air,obviously no preload but still a long run down.
sometimes easier to light with a bit of preload ,it helps to slow it down and gas pop back into can.
check compressor clearance, set it tight with 4-6 thou clearance, preload will increase clearance as the bearings seat and wear (cheap ones).
clearance can be greater at the inlet 8 thou.
when preloaded The compressor wheel will touch the front cover if you pushed turbine wheel forward, with engine bolted down and a DTI on spinner push turbine wheel with scales to check preload amount and how much clearance you have to front cover with the DTI . Put blue on compressor blades and push forward to check fit (may be hard with black delrin.) if the clearance is uneven, (one sided) it can effect the combustor.
Don,t know how to tell if a small compressor is causing the problem but you could try making a new turbine wheel pass area smaller by making the turbine wheel centre bigger to match with the NVG centre dia at 46 x1.4 . The difference in dia was done by Thomas as he figured the gas passing through the NGV needed to expand into the turbine area but Kurt dismissed this as not necessary at one of the GTBA seminars.
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