mitch
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Joined: August 2014
Posts: 285
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Post by mitch on Dec 1, 2014 18:20:24 GMT -5
First off, sorry if there is already a thread with this topic, I did a bit of searching and didn't find much on the topic specifically. While building my turbojet bike, I have recently been thinking about the possible advantages of turning my turbojet into a turboshaft. Before I decide to change my build and design the bike around a turboshaft instead of turbojet, I would like to learn more on the subject. For example, how large should the free power turbine be in comparison to the turbojet's turbine? (if it needs to be larger, this could be a problem, as my turbine is 88 mm, so finding a larger one will not be easy) What kind of reduction gearing is common for something like this? According to JetSpecs, I have a max RPM of around 96,000. I am not going for any speed records or anything fancy, just trying to create a semi reliable turbine powered bike, out of a three wheeled bicycle (it would be nice to be able to reach speeds above 45 mph or so though!) Also, what kind of bearing modifications are required when using a turbocharger turbine as the free power turbine? I would assume that some sort of ball bearing would be needed on the output shaft, to handle the increased radial ( I believe it would be radial, right?) thrust? I apologize for making such a long and wordy post, I just have many questions that I am curious to find answers to.
Any help or insight to this would be greatly appreciated, as I have little experience with gas turbine engines!
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Post by racket on Dec 1, 2014 21:44:59 GMT -5
Hi Mitch Checkout these builds for ideas jetandturbineowners.proboards.com/thread/509/turboshaft-minibike-mrt-01 jetandturbineowners.proboards.com/thread/40/2-shaft-turbine-kart-build and jetandturbineowners.proboards.com/thread/53/landspeed-bike-diy-gas-turbine If you go with a direct drive from the freepower shaft using karting chain and sprockets then you'll be limited to a freepower rpm under 20,000 , at these rpm ordinary sealed ball bearing should work fine .................my 2 shaft kart developed ~30hp with its limited rpm and 8 : 1 redux karting sprockets/chain. Generally , we need a freepower turbine with ~twice the flow area as the gas producer turbine wheel, your 88mm turb wheel is only a mid sized one so there will be bigger wheels available , find a large turbo repair shop and ask for their biggest "timed out" turb wheel , you'll be needing something like our "common" TV94 turb wheels which have a 129mm inducer , because you'll be limiting its rpm to below its normal idling rpm if using karting chain and direct drive , the fact that the wheel is a "throw out" item won't be a problem , they should just give it to you . If you need more help with designing the freepower , please ask away , shaft horsepower is the only way to go , it leaves thrust for dead :-) Cheers John
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mitch
Senior Member
Joined: August 2014
Posts: 285
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Post by mitch on Dec 2, 2014 11:15:20 GMT -5
Thanks so much for the help. I contacted a few larger turbo repair shops in the midwest, hopefully they will have something I can buy off them that will work. Why does the freepower turbine need to be so much larger than the gas producer turbine wheel? I also plan on using a gas bypass valve instead of using a clutch connected to the output shaft.
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Post by racket on Dec 2, 2014 15:00:57 GMT -5
Hi Mitch The freepower wheel needs to be physically larger as it has to process gases at a much lower density and velocity than does the gas producer turb wheel . You don't need a bypass valve or a clutch if the freepower wheel is of an adequate size and the gas producer is capable of idling at a low enough power setting that the freepower doesn't produce sufficient torque to get the vehicle moving................thats the nice thing about freepower turbines they multiply torque at stall thereby reducing the need for multi ratio gearboxes and as there isn't any physical connection between the gas producer and freepower other than a "gas connection" theres no need for a clutch to be engaged or disengaged . My first turbine bike www.youtube.com/watch?v=q_MRUxWEOZ0 has neither a clutch or bypass valve yet has reasonable road manners www.youtube.com/watch?v=P-5PgWqgIJoThe bypass "dump" on my two shaft kart was necessary because I used the "oversized" TV84 gas producer turbo from the bike , but only used a small freepower wheel that was compatible with the power limit of the karting chain . Theres no need to over complicate the freepower setup , thats why I constructed the 2 shaft kart to demonstrate how "easy??" it could be done , no need for a gearbox or high freepower rpm .........the freepower wheel in the kart was just a "scrap bin" item . Cheers John
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mitch
Senior Member
Joined: August 2014
Posts: 285
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Post by mitch on Dec 2, 2014 20:06:36 GMT -5
thanks for the input on the clutch bit, that makes sense when you explain it. The next bit I am thinking about is the freepower turbine housing. I am hoping to find a large turbine wheel with a turbine housing and even possibly a bearing core. I do not have access to a cnc machine, lathe, or mill, so if I cannot find a large turbine wheel with housing, I will have to fabricate my own with hand tools, which should be interesting! The only downside I can see to changing my turbojet bike to a turboshaft bike, is that there will no longer be an afterburner, haha.
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mitch
Senior Member
Joined: August 2014
Posts: 285
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Post by mitch on Dec 3, 2014 14:16:49 GMT -5
Also, just an update, I came across a guy selling two large CAT turbos near me. 96mm turbine inducer, It's not quite as big as recommended, but it is a bit larger than the turbine on my gas producer.
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Post by racket on Dec 3, 2014 16:14:47 GMT -5
Hi Mitch
96mm inducer won't be big enough , you'll be needing something bigger otherwise you'll have to "bypass" some of your gas producers output.
The very common Cummins ST-VT 50 turbos would have the right sized setup for you .
Cheers John
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mitch
Senior Member
Joined: August 2014
Posts: 285
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Post by mitch on Dec 3, 2014 17:37:35 GMT -5
Okay, I guess I'll have to keep looking around. I have found another guy selling a 97mm turbine with shaft, for $50. I'll just save my money and buy something that will be large enough to work without a bypass. I am considering trying to fabricate my own turbine wheel
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Post by racket on Dec 3, 2014 20:25:10 GMT -5
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mitch
Senior Member
Joined: August 2014
Posts: 285
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Post by mitch on Dec 4, 2014 11:27:09 GMT -5
Being a college student without a job, I am a bit short on cash now, especially with the holidays coming up! I think I am going to just look around until I can find a good deal on a large turbo such as the mentioned ST50 (for under $100). Until then, I am going to possibly try to fabricate my own turbine wheel, just for kicks. I looked up some specs on a turbine wheel that I believe toyota made (not entirely sure), and found some ratios between the different parts of the turbine wheel so I can scale it up to the size required for my free power turbine.
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Post by racket on Dec 4, 2014 15:44:24 GMT -5
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mitch
Senior Member
Joined: August 2014
Posts: 285
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Post by mitch on Dec 5, 2014 1:01:35 GMT -5
Hey racket, I need to be a member of the group to view that!
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mitch
Senior Member
Joined: August 2014
Posts: 285
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Post by mitch on Dec 5, 2014 1:16:51 GMT -5
I have a few different turbine blade designs, I will upload pics tomorrow. I am thinking about creating something similar to Copenhagen Suborbital's TM65 turbine pump turbine wheel, which was all hand made.
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Post by Johansson on Dec 5, 2014 12:58:56 GMT -5
You shouldn´t do any welding on a gas turbine wheel, the Copenhagen guys got away with it since they ran a "cold" H2O2 rocket into it at an unknown but supposedly low RPM compared to a gas turbine. Buy the Thomas Kamps book to find out the proper way to construct an axial turbine wheel, great reading for little money. www.amazon.com/Model-Jet-Engines-Modellers-World/dp/0951058991Cheers! /Anders
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mitch
Senior Member
Joined: August 2014
Posts: 285
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Post by mitch on Dec 5, 2014 18:12:54 GMT -5
Johansson,thanks for the input. I assume I shouldn't do any welding on the turbine, because of the fact that it would be hard to keep it balanced due to inconsistent bead sizes?
And I'll have to take a look at that book you recommended, I have so many questions regarding this subject haha.
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