reedy
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Post by reedy on Jan 19, 2017 20:29:01 GMT -5
Hi Jeff
I did fit a RPM gauge on mine early on with the wooden wheel the GTBA did a electronic circuit ,i painted the top cover of the wheel half black half white then fitted a sensor in the spun ally front cover that sent out infrared and received back the reflection,think it's shown on one of my youtube videos the gauge is just a volt meter,i well try to find the info. You can buy a tacho for r/c aircraft, set it on 2 blades paint spinner half black half white and just double the reading ,think Kurt just put a blob of paint on the inner rim of the wheel,.
Turnigy Multi-Blade Micro Tachometer £11 in the Uk goes up to 99999rpm you can paint two marks even better, did not think they went up that high.use a battery touch to light the marks up don't have any fluorescent tubes on or it will pick mains cycle up.
Been looking back at your old build some nice carbon work there ,but noticed you holding the carbon base disc with the slots in, does not look right? I will have to get back to you on that.
Noticed your Dubro balancer ,make a magnetic balancer, you will be impressed how much better it is ,you may need to double up the magnets with the extra weight ,mine are 10x5 mm magnets
My pressure and rpm's won't correlate to your engine being bigger ,there is a chart in the book,if you have to buy a pressure gauge try to get one that just goes up to 15 psi for testing and as big as you can , got mine off ebay 4 inch dia , think it was something to do with a forklift trucks. has a red mark at 7 psi
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reedy
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Post by reedy on Jan 19, 2017 9:32:21 GMT -5
It's worth making a spot welder out of an old microwave transformer, just google how to mod the tranformer. The main arms are 5/8 dia or bigger copper bar the smaller electrodes are 1/4 copper these can be changed to any shape. the white block can be nylon or ptfe mill a groove to form a hinge, the bottom of the white block is bolted on. The top of the white block has an ally bar drilled off centre to work as a cam move the lever to clamp. The arms are just pinned in the white block with a 1/8 rods, works a a treat to weld the combustor. You need a timer that can be set to 0 to 3 sec's red button starts the spot weld.
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reedy
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Post by reedy on Jan 19, 2017 9:01:50 GMT -5
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reedy
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Post by reedy on Jan 19, 2017 8:24:03 GMT -5
Just all glued together can be made out of plywood brass or stainless screws, distance between magnets about 2 inch swing about 2 inch ,make it as big as you need,I use blu tack as weight this is only for static balance. tapping it helps as I said or some people use something like a vibrating pen but i found that was too much.
haven't figured out how to load pictures with words yet ,and cannot scan them drawings, got a new laptop with windows ten and will not talk to my old printer scanner !
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reedy
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Posts: 111
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Post by reedy on Jan 19, 2017 8:13:08 GMT -5
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reedy
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Post by reedy on Jan 19, 2017 8:11:17 GMT -5
video is www.youtube.com/watch?v=lR77mY0AYPU as referred to in previous post. You do need to static balance first, then dynamic balance by spinning though you can get very close with static balance,I found the shaft with bearings fitted in a slack fitting tube worked very good, just rock it back and forth on a table with the palm of your hand, move it about inch or two, the rocking gets rid of the sticktion of the bearings. Magnet method can be helped by lightly tapping the support with a pen or tap the table, put thin brass pads on the neodymium magnets to protect the point on the shaft and reduce friction . The ground point on each end(needs to be accurately ground point),needs to be stepped to pass through the compressor wheel of the FD3 . when using the magnet method back off one magnet minimum gap then only one point is in contact. posted a picture not sure if it wiil show
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reedy
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Post by reedy on Jan 19, 2017 4:48:03 GMT -5
HI Jeff
looked at your reply to you video,thing can tend to rotate around there own point of balance,hold the wheel as you are doing may not be rotating around the centre point as when on the shaft.
had another idea when i saw somebody using magnets to balance a full kj66 rotor he calls his video Manual balancing turbine shaft KJ66
don,t think it's working good enough but you could try it ,it may be improved by putting a very small ball bearing (ceramic ball even better)from a ball race into the centre drilled ends,it won,t work with the turbine on with the fd3/64 you can't get at the centre drilled hole . if you do it that way at least you know your rotating around dead centre. it may even work without magnets using screws centre drilled with one adjustable then a ceramic ball between the screw and shaft and adjust for minimum friction.
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reedy
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Post by reedy on Jan 18, 2017 6:54:27 GMT -5
HI Jeff
Another thing when you m/c the slots do you use coolent ? it may contaminate the carbon slot for gluing,if you do it dry use a vacuum cleaner with a bag to take the dust away as you m/c .
west system should be fine you will need to really rough the surface up to key 80 grit maybe don,t get finger prints on it and clean off with Isopropyl alcohol.
The jigsaw blades for cutting ceramic tiles do cut carbon OK they also do hacksaw blades and round ones to fit a hacksaw you could rough out the holes then true up turn a ring for the top inlet ring. 1mm milling can't be cheap are they carbide ,just googled them about £5 in the UK say,s they are OK for dry cutting.
Sorry Jeff I do worry and try to think of the problems.
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reedy
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Post by reedy on Jan 18, 2017 6:12:03 GMT -5
Hi Jeff
your preformed blades at 40 thou thick may be Ok as long as you vacuumed bagged them?(or clamped). it will help with the 14 blades 7 full 7 half car compressor wheels are like this it frees up restriction at the inlet as will as reducing swirl back into the wheel at the tip.put a extra ring on the top plate something like the wooden wheel shape.
before you glue the top on make sure you sharpen the leading edge of the blades ,it makes a big difference to the temps.leave the outer tip square same as a car wheel.
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reedy
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Post by reedy on Jan 18, 2017 4:37:42 GMT -5
Hi Jeff
Busy today just some quick ideas to mull over .
Think you need to make the base disc a lot thicker to stop the blades bending over ,you may have enough carbon sheet to cut multiple disc's of smaller diameter,think the base at the tip needs to be 3mm min at the tip just a gut feeling not done any stress analysis (don't know how!)
Kurt said in his book that he tried just rebating the blades half way into the base and it failed that's why he went with the banding with the tows but maybe a carbon disc build up it may help to have a full uncut disc 1.5mm with 3mm cut disc ?
in the centre with more laminations built up to 6mm with the full 1.5mm the blades could step down ?
how you do the top ! maybe mold it then cut slots, fit it on then lay another layer over the top to cover and strengthen the slots remember all the stress with be centred around the hole which is the same as the base disc.
one person who made the alloy disc had it fail and break into 3 pieces a classic stress failure ,he had done a counterbore in the centre to fit and locate the spinner,this was a very high revs 85k and on a very cold day but shows you must be careful.
look into industrial glues for carbon, normal epoxy from home depots can vary from rubbery to brittle.look into hysol ? don't know which one
again like i said worth trying more blades how many did you use?
these are only ideas open to discussion ,debate,armchair design
I still love my fd3/64 it is a bit like building a better mousetrap 101 ways but can be built for cost of materials and two bearings,like building a interocitor great achievement if you get it to work but will ultimately blow up! ( this island earth 1955 sci fi film) Chris signing off
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reedy
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Post by reedy on Jan 17, 2017 18:14:31 GMT -5
i'm too slow writing you've moved on to balancing ! try the rocking method fit some cheap 608 ceramic balled races they use for skating, take the shields off wash out the grease, lube with very thin oil or paraffin then fit them on the shaft with compressor or turbine wheel, fit into a tube about 1 inch i/d does not need to be a fit on the bearings then rock the tube back and forth on a flat table heavy point will rock to the bottom. periodically clean the bearings out by spinning them up on compressed air. best to balance compressor first the mark it's position ,do turbine last and leave it on
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reedy
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Post by reedy on Jan 17, 2017 17:57:45 GMT -5
Sorry Jeff missed your question about the compressor blade 70 angle,are you meaning the way a car compressor wheel changes angle at the inducer and becomes a axial compressor,Kurt in his book (home built model turbines with the tk50 & kj66 plans) he talks about the car compressor wheel being a combined radial and axial wheel ,no point trying to make one just use a car turbo compressor wheel.like i said in the other post it may be worth trying more blades 14 total 7 full 7 half length as per some car compressor wheels,how thick was your base and how thick were the blades ? you could try gluing two or three disc together to give you the steps needed to wrap carbon tows around the circumference,you will have to rough them up on the shiny sides,not sure what glue would be best, epoxy?it never sticks a good as when you laminate it and if you go to the trouble of making a covered wheel you need that curve shape on the base plate centre. The wheel is not the same as a car wheel, it's unique in the jet world. only other thing I can think of that Kurt modded was the way the inlet nozzle fitted, bore the inlet in the wheel straight though at 35.0mm without the step then the nozzle fits further in with minimum parallel section, won't make it work better but will not be as fussy in for and aft position of wheel The compressor diffuser could be improved by curving the blades ,there is a picture in kurts book showing very short extra blades at the outer edge between the other blades, that would help on your x1.4 engine,it would help flow straighten round the corner. Your straight blade diffuser could have extra short striaght blades fitted between .i will try and find the picture. I will scan the drawing showing the curved bladed diffuser and two combuster designs for the fd3/64 one with curves fuel tubes at the front face and one with straight tubes from the back like the kj66.
p.s all your work looks first class ,welding looks really good ,wish i had your workshop.
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reedy
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Post by reedy on Jan 17, 2017 9:47:14 GMT -5
Back Again a full carbon compressor will be heavy,did you wrap carbon tows around the edge,that's a must do with the slots in the base only thing holding it together is the carbon tow banding on the edge.using full carbon for the base just increase's the weight and stress on the banding,if you use a thin carbon base then the leverage of the blades will twist them over break off and destroy the blades and top cover.if you plan out the birch plywood and carbon cloth laminate you can wrap carbon tows into the plywood,I have a Mark Drake alloy compressor wheel that use's 14 blades 7 full length and 7 half length at the edge this would increase the centre strength 4 less slots to the centre.the blades could be laminations of 0.8 ply cloth 0.8 ply (on your x1.4)preformed to shape with the outer grain parallel to the axis of the engine use carbon cloth with 2 part epoxy laminating resin,you would need to test all this with a sample to make sure epoxy bond to cloth and plywood was good. pre made carbon is too smooth to glue to ,pre preg will not have enough resin in to bond to the wood.carbon to carbon you will need to use peel ply so you can glue it later. when cutting the blade slots make the disc big enough to drill holes on the outer edge of each blade and use a jigsaw upside down and cut the blade slots from the outside to the centre try using a blade for tile cutting should cope with the carbon and may give you the right size slot. for the standard size wheel the compressor wheel gap at the edge is 7.2 mm the text say's use a 6.5 mm spacer this should be 6.2mm with 0.5 to come off edge face of the disc making 7.2mm finish this is one of the area's that Kurt say's can cause a problem too big of a gap can cause swirl back into the wheel more blades in this area will help (14 blades) especially with a bigger wheel (x1.4 ) you can also increase the diameter of the flange on the bush (T2.2). All above is untried just my ideas feel free to jump on me as in my job i did not work with carbon much,saw plenty of it and filed and drilled it but never laminated or vacuum baged it.most military jet aircraft skins are carbon now ,we called it the black death don't get splinters in your fingers if you do make sure you get them out !
Chris
p.s if the jigsaw will not do the curve grind the back of the jigsaw blade.
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reedy
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Post by reedy on Jan 17, 2017 5:14:09 GMT -5
Hi Jeff The twisted turbine wheel can be made to work well but the twist ends up being less at the root and more at the tip so work is not even as tip travels faster than root,try untwisting the tip by 2 -4 degrees ,I use shaped pliers with a curved jaw ,makes a big difference, I was a aerospace toolmaker for 40 years ,i would not make a carbon compressor wheel too much tooling! but you could try building it the way Kurt say's using laminations of plywood and carbon cloth say 1/8 plywood,the main weakness is the base centre with the slots, got to go will tell you more later Chris
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reedy
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Post by reedy on Jan 16, 2017 21:15:26 GMT -5
I built 4 fd3/64 engines with a friend about 20 years ago just starting to remember the problems and errors with the book ,i never built the original combustor it was redesigned by Mark Drake who produced the Hobbyjet 631 but John Wright of the Wren team did he managed to get it working by blocking off the path through the NGV and bearing tube (think you have already done this). and the inner cone and NGV by slitting it and opening it up (see page 14 diagram of turbo jet) all the air needs to go throught the blades of the NGV and turbine .the only cooling air you need travels down the bearing tube and the slits allow a small flow to cool the roots of the turbine blades. You picked up on this in one of your posts. Chris
will tell you about the compressor error tomorrow.
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