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Post by jetjeff on Mar 26, 2017 0:43:17 GMT -5
Hi All, I've been thinning the turbine blades even further. This wheel weighs .28 lbs, Heineken 1 is .30 lbs, so I know the blades are quite a bit thinner. Regards Jeff
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Post by jetjeff on Apr 1, 2017 13:15:09 GMT -5
H All, The shaft is almost complete. I'll have to accurately measure how long it needs to be. Making a modular shaft with a hollow tube has it's advantages. If I muck up the threads or one of the dimensions is not accurate enough (I actually machined 3 of the turbine end spigots,,,lol), I just remake the bearing spigot ends instead of the whole shaft. The turbine spins much truer than Heineken I does. Making the jig to hold the turbine hub central while it was welded worked pretty good. Regards Jeff
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reedy
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Post by reedy on Apr 2, 2017 10:19:32 GMT -5
Making your own form tools out of gauge plate,he shows milling it then hardening and tempering after,with a convex rad you can put top rake angle using a ball slot drill,works will used on my wooden compressor wheel for the alloy spinner rad and the top an bottom form on the plywood disc. Also used to form rad on my nylon intake on my kamps engine,as i did the shape i had the compressor wheel in the tailstock with bedding blue to check the fit. www.youtube.com/watch?v=RsSRQwDlWFs
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Post by jetjeff on Apr 12, 2017 3:48:33 GMT -5
Hi All, I made a dummy shaft just to accurately measure how long the actual shaft needs to be. Regards Jeff
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reedy
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Post by reedy on Apr 12, 2017 15:25:03 GMT -5
Hi Jeff
I can open up the picture on my laptop now,only been able to view them on my Mobil,anyway can see your turbine wheel,looks like tip angle is 45 degree,I know you twisted it right just looks a lot compared to mine,i only ground the underchambered side and lightly file the curved side to thin and taper the trailing edge .with that angle it will run hot, shape looks good and you can always adjust after test run.
Chris
P.s how long did it take to polish it! you've got more patience than me.
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Post by jetjeff on Apr 12, 2017 20:58:45 GMT -5
Hi Chris, Here is a pic of my wheel, next to Schrecklings. I tried getting the blade angle as close to 37 degrees as possible. It took a long time polishing the wheel. Regards Jeff
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reedy
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Post by reedy on Apr 13, 2017 2:35:01 GMT -5
Hi Jeff
It does look more on the centre blade? nobody got the FD3 to run cool with the stated angles,try it and see if you still have heat problems at least you have a quick fix but if your NGV is at 38 with gaps and the turbine is 37 you will have heat problems,the first one I made had an error of 2 degrees in the NGV and even backing the turbine angle down could not get it to run cool until I remade the NGV at 36 degrees.
Chris
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reedy
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Post by reedy on Apr 13, 2017 3:05:25 GMT -5
Hi Jeff
Quick Quote
Insanity: doing the same thing over and over again and expecting different results. Albert Einstein
Keep smiling it's only a hobby until you retire !
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Post by racket on Apr 13, 2017 4:22:06 GMT -5
Hi Guys
I notice you talk in "angles", when the throat areas of both NGV and wheel is what determines gas velocities and ultimate gas deflection when taken in conjunction with the angle and design mass flow.
I sorta get the feeling from this conversation that perhaps theres more to the problem than just angles , a couple of degrees one way or the other shouldn't make an engine run or not run ........LOL, the hairs on my butt are feeling uncomfortable , ..........the influence of a change in ambient conditions will have more effect than a couple of degrees of angle, an engine shouldn't be that finely balanced , otherwise it'd only work on a freezing cold day under a high pressure system and not work on a STP day .
Chris , I like your Albert quote , somehow I feel a familiarity with it ;-)
Cheers John
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reedy
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Post by reedy on Apr 13, 2017 5:05:37 GMT -5
Hi Jeff drawn a line touching blade leading edge then another line on the back face as he grinds the concave face I get 32.5 interesting, about the same as mine never done that before. Tried it again with a line more on top 4 blades 35 degree not a good thing to do unless the wheel is vertical.
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reedy
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Post by reedy on Apr 13, 2017 6:00:47 GMT -5
Hi John
Home made axial wheels are not the best thing bit of a black art ,you guy's use radial wheels professionally designed and made wheels out of the correct material, the GTBA where looking into designing a model engine to use radial wheels don't think it happened, when I made a KJ66 using a car compressor and a Cast wheel and it just worked no messing. The FD3 is very low pressure makes the combuster struggle to work as Kurt say's in his book at 40 degrees turbine blade angle it goes into melt down,he was trying to get the most out of it he could with building it very light 0.9kg and low rev,s 75k ,it's a lot easier when you can build thicker material and stronger. People try to treat the FD3 as a car turbo compressor wheel and it's not the same, interesting and challenging and unique with that compressor wheel.
Chris
P.s the FD3 almost drove me nuts built the Kamps and KJ both worked well and then I went back to the FD3, Don't like to be beaten, the twisted wheel is hard to get right but succeeded in flying it. early on I did fly one with the wooden compressor wheel and twisted blade turbine wheel but only low 4.5lb thrust finished up at about 6.5 lb with ally wheel at 85k easier if you m/c the turbine wheel from solid gives you better root profile but that takes you into shaft problems with the weight the FD3 has a very long shaft, really a blind alley for Kurt who started again with the KJ design but he did fly a heli FD3 powered in the 90s using shaft power at the suction side, saw it at a GTBA lecture somebody said why did you not use the hot end as twice the power his reply was you do it ! following year he turned up with a turbo prop driven from the hot end.check my vids on youtube under reedy
have you ever looked at the math of the FD3 Kurt does do unusual and interesting designs, he does a twin shaft turbo prop and fan design with one shaft running though another and the Tk50 50mm wheels in a bigger 95mm can for efficiency.
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Post by jetjeff on Apr 13, 2017 15:15:46 GMT -5
Hi John / Chris,
I really feel the reason Heineken 1 ran so hot, is the angle of compressor blades were off by at least 17 degrees. Schreckling referred to the blade angle as B2, and from his many experiments on compressor wheels, determined "real problems occur if the diameter of the wheel, exit blade height and B2 are excessive".
Yep, I agree on the insanity thing,,,I've regressed way beyond talking to myself and now have imaginary friends,,,lol.
Regards
Jeff
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Post by racket on Apr 13, 2017 23:45:25 GMT -5
Hi Chris
I agree the Schreckling engine is "different" , but it still achieve a P2 of 0.5 bar , which is quite respectable , and as such should behave as any other engine , I'll have a good read through my copy of his book to see what /why he designs the way he does .
Cheers John
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reedy
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Post by reedy on Apr 14, 2017 2:36:21 GMT -5
Hi John I built 4 Fd3 engines still have the original one but it's like a old broom the back NGV was cut off fitted with another, the diffusser was unriveted angle changed to 23 degrees with curved blades this change was because I increased the o/d of the compressor wheel to 68mm and m/c it from aluminium with no top cover to the wheel replaced with a nylon cover close fitting this was following geoff Vaizy PT35 design who went through the math in the GTBA newsletter think he even did a simple program,not sure now so long ago.
Kurt set the design temp at 650c and with early combuster design you had hot spots of 750-800c which just distorted the whole back end so people increased the turbine clearance then it was a vicious circle . I tried to keep the temp at 550- 600c
The combustor was changed about 2-3 times never did the original vaporizer coil combustor it puffed like a steam train at low rev,s think the engine had problems with too much percentage air to cool the turbine wheel disc. There is a gap to the bearing tube which I did not do as it allowed the turbine to move and catch the NGV housing stopping the control of the turbine gap which i closed up as tight as possible,about 5-6 thou.
I changed the oil system to oil in fuel system feed to the front of the front bearing all cooling air for the bearing flows through the front from the diffusser area and the hole in the middle of the tube was closed off as the combustor does tend to drop carbon soot and can contaminate the bearings.
So a FD3 not really as Kurt designed but follows standard practice as with Kamps and KJ66. things moved quickly early on and I moved from the FD3 to Kamps then KJ66 gave up after this as £120 for a pair of bearings ,NGV £150 , ECU £250 ? to be able to rev to 115k a cast turbine wheel £150 got too much to risk flying and the models ended up big with the power and fuel weight.
Almost finished built a mw54 but gave up due to cost and still to big a model to lug around,lambert Kolibri turbine would be nice but silly cost, I also lost use of a old airfield with tarmac runway.
makes me smile now as gone to 90mm EDF and get more thrust than my FD3 also get the same sound with the multi bladed fans,but miss that aroma as you do a fast fly past !
Still think the FD3 is a good engine to make,you will always be able to get the bits as you make everything apart from the bearings,can be made for £100 with all start equipment,you learn a lot about how gas turbines work but not my first choice for flying a r/c aircraft.
Chris
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Post by jetjeff on Apr 14, 2017 4:11:01 GMT -5
Hi John,
Kurt kept his design simple, requiring a relatively short list of tools/machines, 6" lathe, drill press, Dremel grinder and MIG welding equipment, to allow for "relatively" easy home build ability. The design, using a covered compressor wheel, just about removes the critical compressor to front cover gap.
Kamps (and all other turbocharger based turbines) doesn't mention a mill in his book, but building one without a mill would be challenging (but not impossible) IMO.
The Schreckling engine does have a different sound while running, much quieter than a turbo based engine. Kurt stated in his book, while flying downwind, he often thought the engine flamed out, but was actually still running.
Regards
Jeff
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