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Post by Richard OConnell on Jul 27, 2021 0:10:06 GMT -5
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Post by Richard OConnell on Jul 26, 2021 1:19:01 GMT -5
Further inspecting the NGV gave us some insight into why the turbine was rubbing. It was warped, either as a manufacturing defect or something it developed over time. checking it with a multimeter revealed about .002 of warp. Chris made up a mandrel in the lathe out of stuff lying around the garage and took it down by about .004, which was still well within the clearance specifications for this motor. I'll take a breather and follow up with another progress dump tomorrow.
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Post by Richard OConnell on Jul 26, 2021 0:54:51 GMT -5
(still catching up from last weekend) Next was getting the compressor off so we can free the rotating assembly and get into the combustor. This was a lot more difficult than it should have been and I unfortunately did not take more pictures of the process. So we started like any reasonable people by removing the compressor nut and attempting to tap the wheel out. It quickly became evident that this wasnt going to do it. we tried applying a bit of heat to the compressor while shielding the center shaft as best we could to allow it to slightly expand, hopefully freeing it, but still no dice. After a brief bout of defeat and with no real options left, we did a bit of research on the compressor and came up with an 'absolute max temperature' we would allow ourselves to reach heating the compressor wheel with a heat gun. During the process, the wheel was monitored with a FLIR camera and we took constant heat samples from all over the compressor. Since we were going through such length to free the shaft, we were also taking off the gloves. More force would need to be applied to the shaft to free the compressor. We settled on using a drill press to apply force to the shaft and push it through the heated compressor wheel. Thankfully, the wheel finally freed itself before we reached our 'safety temperature' and we could proceed with disassembly. With the shaft out, we got our chance to look inside the combustor. There was a good bit of carbon buildup at the base of the combustor can and one of the vaporizer tubes was about a quarter inch shorter than it should have been. With the turbine free, we were also able to take a look there. As suspected, there was evidence along the inner wall of the NGV and the outside of the turbine blades of rubbing.
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Post by Richard OConnell on Jul 26, 2021 0:33:06 GMT -5
After moving the turbine to a more accommodating climate, we began disassembly of the MW54. Based on some issues we were seeing with the engine with temperature and performance, we had suspicions that we would find a few things: -Evidence of the turbine rubbing -Drag caused by worn bearings -Possible heat damage A few additional things we wanted to look into: -Condition of the combustor and injectors -Condition of the compressor -Any evidence of heat forward of the combustor -State of the turbine, NGV, and free turbine section -Wear on the gears aft of the free turbine. Disassembly began with separation of the free turbine housing from the gas producer. In 4 bolts the two sections could be separated. From there, the starter and FOD guard assembly was removed and the air jacket was slid off the engine. The compressor was pristine and there was no evidence of abnormalities around the diffuser. Screws and accessories were carefully bagged and labeled to ensure everything goes back where it came from. The combustor had a single crack along one wall. Reorienting the motor revealed this crack ran along the very bottom. Possible evidence that fuel may have pooled and burned at some time? A brief visual inspection of the turbine didnt reveal anything unusual. Tooling marks indicate the turbine has either been balanced many times or someone in the past may have struggled to get the balance correct. Either way, we wouldnt find out more until we got the compressor off.
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Post by Richard OConnell on Jul 25, 2021 23:33:28 GMT -5
About a week behind on posting the teardown and rebuild, but I'll try to capture as much as possible and keep it in chronological order. So the teardown started with harvesting the Wren MW54 from the pocket bike. Work started with the disconnecting of fuel lines, EGT, Tach, and starter. A few bolts later and the gas producer and power turbine were ready to be removed from the bike. With extraction complete, the motor was moved to our makeshift indoor workspace away from the summer heat
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Post by Richard OConnell on Dec 22, 2020 9:35:48 GMT -5
Also, in terms of an EGT, the "G" doesnt become "E" until after the turbine. Haha, in all seriousness, John's answer was really good. Sampling temps post-turbine means theres one less part that could break free and destroy the turbine.
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Post by Richard OConnell on Dec 7, 2020 14:40:00 GMT -5
Unless you're pushing an insane amount of fuel into the tailpipe, I couldnt see a fast failure happening. Watch your RPMs and EGTs. If you have too much restriction at the nozzle with afterburner lit, you can either reduce fuel entering the afterburner or open up the diameter of the nozzle a little.
You'll lose out on some thrust when afterburner is not running if you open up the nozzle, but it will also allow for you to burn more fuel and affect the upstream engine less. Fighter jets use variable nozzles to get around this problem, but they're difficult to make for stuff in the scale we work on:
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Post by Richard OConnell on Dec 7, 2020 12:13:48 GMT -5
wannabebuilderuk is absolutely right. Dont modify the amount of fuel you are dumping into the injectors in the flametube. Thats, in a sense, your engine throttle and you'd be throttling it higher than it was designed to run. It would likely cause much more flame than your combustor was designed to contain and it would melt your turbine. Only add fuel (diesel, kerosene, or Jet A) after turbine and inside the tailpipe with spray bars. The airflow from the engine will provide you all the oxygen you need to be able to light your afterburner. Once your afterburner is lit, watch for RPM drops or rising temperatures. burning fuel before a nozzle will add some resistance to the exhaust air thats trying to exit your engine and can also be catastrophic if left unchecked.
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Post by Richard OConnell on Dec 4, 2020 1:21:24 GMT -5
Welcome aboard Tony! A lot of commercial diagrams of afterburners are quite complex to replicate for the things we do. Often times, we just put a few spray bars in the tailpipe, sometimes with what is called a 'flame holder' in between to create an area of low velocity airflow to make it easier to keep the afterburner lit. Lighting the afterburner can also be a bit tricky. A lot of DIYer's do a 'hot streak', or basically squirting a VERY brief puff of fuel just before the turbine. That fuel ignites and is carried into the tailpipe where it mixes with the atomized fuel from the spray bars, igniting the afterburner. If you consider this method, be very careful. Hot streaking isnt particularly great for a turbine and if a solenoid hangs open and you keep spraying fuel, you can almost guarantee your turbine is going to vaporize. You'll want a timing mechanism that keeps the hot streak solenoid open for like a quarter second and shuts it until you activate it again. If you're looking for some reading material, check this out: authors.library.caltech.edu/21303/1/251_Zukoski_EE_1978.pdfGood luck!
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Post by Richard OConnell on Nov 25, 2020 11:51:26 GMT -5
Now says "deleted" for anything he says, I'll message him on his fb page Not seeing anything in the admin logs where an administrator deleted the account, so he must have done it himself. This is honestly the first time I've seen someone delete their own account in the 10 years this board has been up.
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Post by Richard OConnell on Nov 25, 2020 11:40:27 GMT -5
I dont think that would be unreasonable. The 201 and 301 Vipers arent impossible to find either. A bit of advice if this is your first purchase: go check out the engine in person and bring along someone who can look it over if you arent comfortable doing it yourself. Vipers are good engines, but there are a lot of them out there with burnt out hot sections.
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Post by Richard OConnell on Nov 13, 2020 1:12:44 GMT -5
Oh man, I heard about this. What's going on over at Garrett?
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Post by Richard OConnell on Nov 13, 2020 1:05:05 GMT -5
A lot is going to depend the condition, whether or not you have all parts included (starter, bang box, oil accessories) but I think they start at around $3000 USD if I recall. If its in great condition and has papers and such, you could probably fetch more.
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Post by Richard OConnell on Nov 13, 2020 1:01:46 GMT -5
Looks really clean. what printer are you using?
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Post by Richard OConnell on Nov 2, 2020 14:50:01 GMT -5
Welcome cutaway!
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