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Post by racket on Jan 28, 2022 0:46:01 GMT -5
Hi Guys I've started cutting metal Milled 18 X 0.5 inch diameter holes through the NGV wall to accept the 125 mm long vapouriser tubes , which will have my square springs inside to produce swirl and optimise evaporation of fuel . Instead of fitting "thimbles" as I did with the 12/118, at this stage I'll simply fit a cover plate over the front wall of the flametube to prevent air getting through all those holes , the air through the evaps will replace it. The setup will be fairly "conventional " RC turbine flametube , hopefully it'll work , if not, then I'll add the thimbles in a new front wall and new inner and outer flametube walls to replicate the 12/118 engines flametube . This will be a much quicker modification just a few days instead of weeks . Cheers John
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Post by racket on Jan 29, 2022 23:21:49 GMT -5
Hi Guys Evap tubes cut to length , 125mm long , 12.7mm OD , o.63mm wall thickness, 800 series alloy , thankfully my tubing came in 250 mm length , so no wasteage. Ends bellmouthed and "flattened" for TIG "spot" welding . Square springs made and fitted to ID of tubes and spring end TIG'ed to NGV to maintain position, not that I think they'll move as it needs > 10 kgs of force to pull them into the tubes . Time to think about a fuel manifold Some pics Cheers John
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Post by pitciblackscotland on Jan 30, 2022 3:01:34 GMT -5
Hi John, Hope this will fix the issue I was thinking of posting to you that HP gear pump i have to test out for fuel pressure issues. Cheers, Mark.
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Post by racket on Jan 30, 2022 5:09:02 GMT -5
H iMark
I'll be back to nice modest pressures now so no issues with flow, a single 044 pump should be enough :-)
It'll be interesting to see what differences there are whilst still using the original flametube which has some less than ideal hole positioning in relation to the evap tubes .
It was a tight fit getting the evap tubes past the NGV so they aren't too far from being centralised in the annulus , I might add a couple of holes in the outer wall opposite each evap outlet to blow the fuel more towards the centre.
Cheers John
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Post by racket on Jan 30, 2022 22:40:50 GMT -5
Hi Guys A couple of pics of the "square spring" making process For a 5 inch X 1/2" tube I start with a 400mm long piece of 0.060" - 1/16" - 1.5mm Inco wire , it doesn't need to be such a high grade I only use it because I've had it sitting around for 20 years , any decent "high tensile" wire that will have "springiness" will do . I mark off ~130-140 mm on the wire and have that point secured in a groove cut in the 1/4" key steel in the vice jaws , the 1/4" key steel has 20 mm "pitch" marks and the 4 sharp edges of the steel are ground off so as not to produce a high stress point as well as to "size" the OD of the spring so that its a tight fit in the tube bore . Wind the wire as tightly as possible around the key steel , it wants to "spring off" so it needs a firm hand , with each rotation producing the 20mm pitch , the pitch is important , too close and the air wants to tumble over the wire , too large a pitch and theres not enough rotation to centrifuge the fuel , I found the 20mm pitch was "just right" and the air engages the "rifling" , like a bullet in a barrel I obtain ~6-7 turns before running out of wire . With the key steel removed from the vice the spring is easily slid off , the 130mm section is bent axial to the spring and slid into the evap tube at the bellmouth end , with just enough protruding from the outlet end for the pliers to grab hold of so that the spring can be pulled into the tube . Excess bits of wire are cut off, and only another 17 to make .... my hands and fingers are sore and bleeding from the bending and nicks and scratches, but they're done The square spring only has 4 points of contact with the evap tube ID for each rotation , and more importantly there are 4 "culverts" per rotation that the fuel is able to use to spread out under the wire as it "randomly" travels down the length of the tube . Heh heh , thats my theory anyway :-) Cheers John
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Post by racket on Feb 8, 2022 19:05:50 GMT -5
Hi Guys Bit of an update . Almost ready to put the engine back together , just waiting on the new 18G syringe needles to arrive in the Post , hopefully this week . Fuel manifold made along with propane preheat manifold feeding several evap tubes on the ignitor side of the engine , I'll try to fire her up without the preheat , but if it doesn't ignite, I can feed in some propane . Flametube front wall has a cover plate fitted over it, hopefully it won't leak fuel too readily, its only a temporary measure , a new flametube will be made if combustion is OK and the pulsing ceases . Maybe a testrun next week where I can also measure static air pressure just forward of the comp inducer , I drilled a 1.1mm hole through the alloy housing which I can slide a 19G syringe needle into to pickup the pressure . Cheers John
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Post by racket on Feb 10, 2022 23:38:17 GMT -5
Hi Guys The 18G syringes finally arrived in the Post A pretty simply job to grind back the sharp point by about half, clean the bore with an oxy torch tip cleaner and gently tap the syringe through the slight inference 1.25 mm hole in the manifold , and with compressed air being fed into the manifold the Dremel cutoff disc took care of removing the plastic bit, a bit more emery to take off the rough edges and another clean of the bore with the tip cleaner and one injector in place. A dob of 45% silver content silver solder on each to seal and hold them and the job was done With the manifold fitted to the engine along with a propane preheat manifold it was time to fit the outer can The engine is now mounted back on the test stand Test run next week Cheers John
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Post by finiteparts on Feb 11, 2022 8:35:29 GMT -5
Looking good. Can't wait to see how it does.
What is the id of the fuel manifold?
-Chris
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Post by racket on Feb 11, 2022 16:08:39 GMT -5
Hi Chris
The fuel manifold is made from 5/16" steel bundy tube( brake line) , ID is 6.8 mm , supply line to the manifold Tee piece is 1/4" OD bundy tube , all entries to injectors are positioned on the downstream side of flow in the manifold to minimise flow variations
I'm keen to see how it performs with the mods, hopefully the pulsing will subside and I'll get her up to at least a 4:1 PR and some serious thrust levels :-)
Cheers John
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Post by racket on Feb 12, 2022 20:49:41 GMT -5
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Post by pitciblackscotland on Feb 12, 2022 21:44:44 GMT -5
Hi John, Nice those mods made a good improvement in thrust Cheers, Mark.
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Post by racket on Feb 13, 2022 0:25:55 GMT -5
Hi Mark
Yep , sure did , well onto a second go around the dial , LOL, I couldn't find the needle the first time I looked , I wasn't expecting that much increase in thrust :-)
I've pulled the engine apart and alls well inside , still the original soot on the front wall and not much combustion happening any earlier than before , the evap tubes have a tad of "colour" .
Good to see 55,000 on the tach , so a tip speed ~1640 ft/sec , my "design " 1700 ft/sec if we use tip speed squared for increasing P2 it should give another 7.4% ,1.074 X 3.75 = 4.02 PR ,.......just right :-)
I'll make a new flametube thats more sympathetic towards the evap tube placement , currently a number of tubes have "cold" air blowing onto them , it'll also have the "thimbles" in the front wall to get air and fuel mixing earlier , I'll have a think on the thimble desiogn to see if I can make something thats easier to manufacture .
I think I can call it a successful testrun, a few more steps forward towards her 250 lbs of dry thrust, she's rumbling nicely .
Cheers John
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jetric
Veteran Member
Joined: December 2014
Posts: 141
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Post by jetric on Feb 13, 2022 5:32:41 GMT -5
John, Was I seeing right your EGT was over 900oC!! Ouch Richard S. Hi Mark Yep , sure did , well onto a second go around the dial , LOL, I couldn't find the needle the first time I looked , I wasn't expecting that much increase in thrust :-) I've pulled the engine apart and alls well inside , still the original soot on the front wall and not much combustion happening any earlier than before , the evap tubes have a tad of "colour" . Good to see 55,000 on the tach , so a tip speed ~1640 ft/sec , my "design " 1700 ft/sec if we use tip speed squared for increasing P2 it should give another 7.4% ,1.074 X 3.75 = 4.02 PR ,.......just right :-) I'll make a new flametube thats more sympathetic towards the evap tube placement , currently a number of tubes have "cold" air blowing onto them , it'll also have the "thimbles" in the front wall to get air and fuel mixing earlier , I'll have a think on the thimble desiogn to see if I can make something thats easier to manufacture . I think I can call it a successful testrun, a few more steps forward towards her 250 lbs of dry thrust, she's rumbling nicely . Cheers John
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Post by pitciblackscotland on Feb 13, 2022 6:38:49 GMT -5
Hi Mark Yep , sure did , well onto a second go around the dial , LOL, I couldn't find the needle the first time I looked , I wasn't expecting that much increase in thrust :-) I've pulled the engine apart and alls well inside , still the original soot on the front wall and not much combustion happening any earlier than before , the evap tubes have a tad of "colour" . Good to see 55,000 on the tach , so a tip speed ~1640 ft/sec , my "design " 1700 ft/sec if we use tip speed squared for increasing P2 it should give another 7.4% ,1.074 X 3.75 = 4.02 PR ,.......just right :-) I'll make a new flametube thats more sympathetic towards the evap tube placement , currently a number of tubes have "cold" air blowing onto them , it'll also have the "thimbles" in the front wall to get air and fuel mixing earlier , I'll have a think on the thimble desiogn to see if I can make something thats easier to manufacture . I think I can call it a successful testrun, a few more steps forward towards her 250 lbs of dry thrust, she's rumbling nicely . Cheers John Good for you John Your hard work will pay off eventually looking forward to see that 250 lbs of thrust and then with AB OH MY Cheers, Mark.
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Post by andym on Feb 13, 2022 6:49:19 GMT -5
Hi Mark Yep , sure did , well onto a second go around the dial , LOL, I couldn't find the needle the first time I looked , I wasn't expecting that much increase in thrust :-) I've pulled the engine apart and alls well inside , still the original soot on the front wall and not much combustion happening any earlier than before , the evap tubes have a tad of "colour" . Good to see 55,000 on the tach , so a tip speed ~1640 ft/sec , my "design " 1700 ft/sec if we use tip speed squared for increasing P2 it should give another 7.4% ,1.074 X 3.75 = 4.02 PR ,.......just right :-) I'll make a new flametube thats more sympathetic towards the evap tube placement , currently a number of tubes have "cold" air blowing onto them , it'll also have the "thimbles" in the front wall to get air and fuel mixing earlier , I'll have a think on the thimble desiogn to see if I can make something thats easier to manufacture . I think I can call it a successful testrun, a few more steps forward towards her 250 lbs of dry thrust, she's rumbling nicely . Cheers John Nice run John..... did notice when it was started.... you could still see some bounce in the readings..... but once thing heated up ? seemed to sort its self out Nice to see the trust numbers Will call you tonight....if your home
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