slittlewing
Senior Member
Joined: November 2017
Posts: 458
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Post by slittlewing on Jun 24, 2022 7:14:47 GMT -5
Wow congratulations John!! The side camera shows the whole thing trying to shift the trailer 😅😈😈😈
How were the TOTs? Little hard to make out with the vibration. Looks like a nice stable 330-340 lbs, and maybe the 350lbs during the rather impressive machine gunning flame mode haha. Do you think it needs a tiny bit more fuel at top end to improve the stability?
Cheers
Scott
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Post by madpatty on Jun 24, 2022 14:30:14 GMT -5
Hi Racket. Congratulations on an impressive test run. Time to let go off the brakes and adding wings to the trailer.
Did the engine surge at 3:27 and 4:02 mark in "gauges" video or was it due to afterburner?
Cheers.
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Post by racket on Jun 24, 2022 17:44:06 GMT -5
Hi Guys
Yep , still a bit of surge :-( but not as bad as before :-)
The TOTs are OK , so I'm seriously considering taking a bit more off the exducer , maybe open up the throat by 10% , I can trade flow for pressure if the TOTs get a bit high at 4:1 PR , currently the P4t is "too high" making for a choked A/B nozzle , I really only want ~0.9 Bar max .
The afterburner fuel flow wasn't changed during the times it was running , I thought I'd try and see if I could get it to light off at idle , once it did, there was a sudden and "massive" increase in thrust with more P4t but little change in TOTs .
I'll probably fit the PWM I have onto the A/B pumps so that I can increase fuel at full throttle as well as reduce it to "experiment" .
Maybe go back to 12V on the flametube fuel pump now that the large fuel injectors have lowered max fuel pressure requirements , this will make the throttle a tad more "civilized" .
Lotsa things to think about , but for a first test with the A/B , I'm happy with the results , with a few tweeks I should be able to have a reliable 350 lbs of thrust .
She is one noisy beast even at idle with the afterburner on :-)
Cheers John
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Post by racket on Jun 24, 2022 19:50:49 GMT -5
Hi Patty Yes , the momentary surge at 3.27 and 4.02 on gauges vid , (3.37 and 4.12 on exterior camera and 4.31 and 5.06 on thrust camera ) was probably caused by the A/B putting too much backpressure on the engine , theres was ~1 Bar P4t at that instant, slightly larger nozzle area required, at 132 mm cold , it probably needs to be ~137mm . At least I can be confident of the thrust readings , the Loadcell is being loaned to me by Andy M , it came with a Calibration Cert. from Loadcell UK www.loadcellshop.co.uk/I'll start disassembly today to check things out Cheers John
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Post by racket on Jun 25, 2022 0:25:38 GMT -5
Hi Guys
She's pulled apart and so far everything looks nice and "cool" inside , no burnt look anywhere unlike previous disassemblies .
Theres a faint comp rub at the inducer , probably during the surge incidents .
Might need to add/replace some flow straightening at the diffuser outlets , I removed the ones I had when I fitted the "ears" to the thimbles , theres some witness marks indicating considerable swirl around the flametube .
When I reassemble the engine I can leave out the propane preheat manifold as well as the hotstreak , probably also the starter tach as I'm finding I rely more on seeing the P2 gauge needle rise than watching the tach numbers
Tomorrow I'll have a serious look at the turb exducer .
Cheers John
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Post by racket on Jun 25, 2022 20:52:14 GMT -5
Hi Guys Well , I got adventurous and ground another 3mm axially at the exducer tip ,wheel now 41mm thick at the exducer tip , original wheel was 48 mm with the tight exducer , this opened up the exducer tip throat from ~22mm to ~24.2mm , so hopefully around another 10% flow that will get me well away from the surge line and give me a safety buffer when dumping more fuel into the A/B . Exducer tip angle has been "increased" from ~40 degrees to ~47 degrees , the reduction in deflection and consequent power production should/will require higher temps to compensate , I'm hopeful that the opening up of the exducer will mean those temp increases will be mainly "lower" in the RPM range ,................the next testrun will tell me if I made the right decision. Cheers John
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Post by pitciblackscotland on Jun 25, 2022 22:59:41 GMT -5
Hi John, you think you will need to get the rotating assembly re balance again Cheers, Mark.
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Post by racket on Jun 26, 2022 0:08:23 GMT -5
Hi Mark LOL.....it might be a while Those bloody chinese compressor wheels have struck again ,........... after cleaning the turb and comp I was ready to assemble them ready for the balancing guy . BUT , I noticed a bit of Locktite, used to hold the nut to comp and stop it spinning , still in the bore of the comp and decided to use my ground 1/2" bore checker to clear it out , I tried to slip it into the inducer end but it wouldn't fit , bugger I thought , try the back side , it slipped in EASY , TOO EASY , it rattled , so out with the internal gauges which checked out at 13.1 mm instead of the 12.71 mm -1/2" it should be . A quick vernier on the comp OD came in at 176.4 instead of the 176 mm it should be ...............the bastards have used some sort of crappy alloy to machine it out of, the comp nut has crushed the front end whilst the centrifugal forces have stretched the main disc . Have sent them a query through Alibaba , will wait to hear what they have to say before taking the next step . Cheers John
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Post by racket on Jun 26, 2022 0:09:42 GMT -5
Hi Patty One for you Cheers John
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Post by pitciblackscotland on Jun 26, 2022 3:41:47 GMT -5
HI John, Yeah i don't think they would of use 6061 alloy or what other type of alloy is best to use, and if you can resleeve the bore to the right size the comp wheel may keep stretching Pain in the ass this is Cheers, Mark.
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Post by racket on Jun 26, 2022 4:04:48 GMT -5
Hi Mark Yep , the wheel is scrap :-( I've been in contact with them about the matter and their Production Manager will be following up on the complaint . They're suppose to be using 2018 www.azom.com/article.aspx?ArticleID=8719 which shouldn't have allowed this deformation . Worse case scenario I get the wheel material tested by a certified lab. It leaves me in a bit of a predicament as it took a long time to find the wheel, hopefully it can get sorted . In the meantime I'll carry on with the other little jobs that need doing. I could always use the wheel I sent to Andrew and keep the RPM down Cheers John
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Post by racket on Jun 27, 2022 0:43:37 GMT -5
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Post by pitciblackscotland on Jun 27, 2022 5:58:32 GMT -5
Hi John, WOW luckily you didn't get a nasty rub the comp housing. You think this may also cause surge I think Andrew will not be happy about this when you show him Cheers, Mark.
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Post by finiteparts on Jun 27, 2022 23:18:24 GMT -5
John,
You might want to check on how it was heat treated. Without heat treat, 6061-T0 is like 1/4 the capability in yield stress as compared to the T6 heat treated state.
Also, a usual tell tale sign of yield on machined Al is that the smooth machined surfaces will have an orange peel surface texture show up...due to the large amount of slip along the grain boundaries. I thought I saw a little of that in the video, but it is a bit unclear.
Bummer though. What was the max rpm you got to?
- Chris
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Post by racket on Jun 27, 2022 23:58:12 GMT -5
Hi Chris
No more than 60,000 rpm, which equates to ~1800 ft/sec tip speed, but only held at that for a few seconds , not long enough for the wheel temperature to get high enough to degrade the tensile strength , billet wheels should handle that with ease .
I think the main indicator of poor material is the distorting of the snout reducing the bore diameter at that point , with such a large nut and surface area , 60 -70 ft lbs of torque shouldn't cause problems .
My mate Andrew has the spare wheel and will get it checked for material quality , we'll get it sorted , just another minor holdup .
Cheers John
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