reedy
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Post by reedy on Jan 31, 2017 9:40:25 GMT -5
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reedy
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Posts: 111
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Post by reedy on Jan 31, 2017 4:10:55 GMT -5
Hi Jeff
Did not realize you are an aeromodeller till reading the back post, It's going be a big plane ! I will have to post a picture of my Heinkel He162.
Diffuser looks good don't forget to radius the leading edge,use a strip of fine emery cloth about a 1ft long bent round the blade and just pull it back and forth,helps if you put a small 45 degree chamfer on both edges first,smallest rad OK, don't shorten blades.
Think you misunderstood my last post,The unbladed area is big enough as in the book,don't forget with your carbon compressor wheel you have an extra unbladed area on the compressor wheel.
Are you holding the front of the engine together with the bolts in the diffuser blades ? or are you using the front black cover to the out case ?
Work out the pounds per square inch on the front face,it may worry you.
it's normal practice to use bolts through the diffuser blades and front cover,then bolt the front cover to the outer case,like i said in a previous post with the KJ66 somebody had the 4 mounting lugs rip off the diffuser.
On the original Fd3/64 I used insulation tape(wide rubber band from motorbike inner tube works) and a wire lock pushed up against the spun front step ,only good for 4 psi testing. i would say if you are going to push an engine for flight forget the spun front just turn it as it ends up very soft ally to be able to spin it. When you are finally happy with it silicone works oK as per the book.
If it's a kamps style front a groove with an o ring in works,never tried the rubber band in a groove as per the kamps book should work, he say's it swells and seals with fuel on.
The delrin black front may be a problem,if the engine seizes up you will have flames coming out of both ends,that's why wren don't recommend nylon cover for the compressor wheel but if you are careful and have the air ready you can get away with it.
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reedy
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Post by reedy on Jan 30, 2017 9:21:36 GMT -5
Hi Jeff Finish looks good on the mold . been reading about the GR180 you asked about, found a build thread on it . www.modelbouwforum.nl/threads/kj66-conversies.18237/page-44what i found intriguing what one builder ask Gerald and his reply which i did not fully understand as I do not have the drawings, can,t find them on the net,conversation below. (it may only be applicable to wedge diffuser ? ) 1: on the GR180 there is a small gap, a difference in tipheigt of the compressor and the heigt of the diffusor channels. I know this is by design, in an effort to reduce velocity somewhat. I am no expert but as I understand, all sudden changes is bad in theese velocities, it might induce a turbulence that makes the effective throat area in the beginning of the diffusor channels smaller. I have made my diffusor according to plans and you engine seem to work brillianly anyway so I might just be talking bull here Gerald replyed Yes I know, the step is in fact designed to induce some turbulence and the idea behind it is to reduce tip loss energy from the compressor, difficult to explain. Our diffusers are something else, way different compared to full-size engines. There's soo little space to do the work that extra tricks need to be done to improve pressure energy as much as possible. I did not invent this gap, just brought up by someone else to try and after some tests it worked better than a smooth transit. Some manufacturers used the same trick, Wren also did.... Still our diffusers are in developing state, latest diffuser technology is a difficult path, calculated by cfd software. My diffuser is just a compromise to make building more easy. More on this later for my GR220 design...... Can anybody comment on it.
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reedy
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Post by reedy on Jan 30, 2017 5:31:54 GMT -5
HI Jeff Have you tried hot water,or is there still wood on it.
I am going to buy some of the woods metal to have a play around with,beauty of it is you can reuse it time and again,will have to be careful with it as it has cadmium in but as long as I melt it in water it won't get too hot and fume.
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reedy
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Post by reedy on Jan 30, 2017 4:40:26 GMT -5
Hi Jeff
Don't know how your molded tool worked out but |I suspect it may be a bit soft for clamping down on,if so try slate power next time,works out at £5.50 for 5kg.
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reedy
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Post by reedy on Jan 28, 2017 16:23:49 GMT -5
Hi Jeff In my job years ago we used to make economy dies they where used for stamping thin sheet alloy out ,basically a plate the male shape of the component and a female outline ,the female shape was filled with rubber ,devcon rubber two part mix that you poured in and cured at room temp,it came in different hardness's.we used the hardest shore 94. You could try that low melting point metal,there are more common ones called Cerrobend / Wood's Metal 1KG+ (Bismuth Alloy) £24 for 1kg on ebay. www.devcon.com/userfiles/file/urethanes_user_guide.pdf not sure if this is the one, ours came in two cans one large that you poured the small one into then mixed. Checked on price too expensive for the rubber.
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reedy
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Post by reedy on Jan 28, 2017 15:57:42 GMT -5
Hi Jeff You've probably seen it,But I found the build for the x2 schreckling interesting read the run you see on youtube is 14k at 590c. hottest spot. it did not run straight off he had to remake the turbine,his comments below- During my first test run, which i have not shown, the turbine wheel glowed bright yellow and would only self sustain for a minute or so before the wheel turned white and I had to turn the motor off. To my surprise that problem was completely cured with the second wheel, slightly longer blades3.5mm, and a 9-10mm shorter centre hub. According to Schreckling the distance between the NGV and the turbine is non critical so i let the accidentally rather long distance of 12-15mm be. Now the turbine blades are only a few mm. away from the NGV. The 3.5mm extra blade length is obviously taken from the turbine centre, so the outer diameter is still the same. The decision to make the blades longer was due to the fact that I could see that the inner part of the turbine blade, that correspond to the inner part of the NGV, could not do any use full work since the blade angel at that point was zero or close to zero. www.pulse-jets.com/phpbb3/viewtopic.php?f=6&t=5578&start=45The turbine wheel angle in the book is shown as 20 degrees at 1mm above the root ,worth checking the twist is sharp enough it may be a effect of your tougher stainless. Might be worth trying 1mm thick turbine disc on your Kamps with longer blades,very little shaping needed keeping the rev,s low just for testing . I remember some one else advocating for longer blades on a home made KJ66 using the smaller cheaper compressor wheel,I think he went down to 40mm i/d ,I will try and find the article and check up on it,Also seem to remember John wright did it on his small own design engine with heat problems but he made the whole NGV and turbine bigger. As always there is a but, which is too long a blade can flutter and break off at very high speed,it may be a scaling issue as more blades are narrower, easier to twist,may be worth trying a bit of both,at least you are only remaking the turbine wheel and it,s the same set up as Thomas had with the bigger i/d of NVG 46 and 44 i/d turbine wheel. Lots of suggestions to confuse.
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reedy
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Post by reedy on Jan 27, 2017 10:28:21 GMT -5
HI Jeff
found this on Amazon
Upgrade Billet Compressor Wheel 94-03 Powerstroke F-Series GTP38 Turbo Charger Bigger D66 wheel, Mods are needed! by Supercell Turbos Be the first to review this item Available from these sellers. Do not fit on stock TP38 GTP38 Turbo. Modifications on stock compressor housing and backing plate are needed! Inducer:66mm Exducer:88mm(stock size is 60mm/80mm) Rotation : Reverse Bore Type : Threaded-1/4-28G-RHT Bore: 6.35 mm Blade : 10+0 Tip Height: 5.99 mm Super Back Height: 4.94 mm $150
Do these sound like the right size for your x 1.4 Kamps.
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reedy
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Post by reedy on Jan 27, 2017 6:24:48 GMT -5
Hi Jeff Been looking back through your builds . I agree with you about the U shaped walking sticks being clockwise when looking at the combustor from the hot end forward,mainly because the tube ends are putting swirl in that direction.
I think the book say's 2.5 mm open for the 10x10 flaps (about the same as a 6 mm hole),one person did fine tune it (about 2 mm ) but you would need to experiment on your engine. Kurt said he did the flaps to swirl the gases but it,s in that much of a rush to get out it doesn't. but again it can be used for fine tuning the combustion, it may be opposite to what you think more closed can help the hole pattern to trap the flame at the front.
Not sure about the NGV its the kamps style, I did the flat blade with the large rad ending in line with gas flow, easy to tell the 37 degree is right and if you need to adjust it you can .(mine is set a lower angle of 36 )
Compressor wheel 75 degree tilt of blades, Don't agree with you on that one ,it may be more surface friction with the wider blades but you never know now it's made it's worth trying ,That's part of the fun. I would have tried a bigger rad on the blade inlet as per marks wheel and 7 full blades to leave more strength in the wheel centre and free up restriction at the inlet and 7 half blades in between to reduce swirl back into the wheel, Also you will lose some efficiency if the base disc is not built up in the middle as per section view, the air passage should slowly narrow in section view as the air travels to the tip as per book.
Looking forward to seeing it going. if you try it on liquid run it outside for safety's sake ,but better to get it right on gas with no flames visible at idle. Can you give us a view with another mirror looking at the hot end next video.
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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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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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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 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 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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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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