TV94 TurboFan Build

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Ash Powers
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Re: TV94 TurboFan Build

Post by Ash Powers » Tue Dec 02, 2008 4:52 am

After more painstaking work - several hours to radius the diffuser minor radius by hand and then turned the major diameter radius on the lathe.....

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The bearing tube and NGV baseplate is shown in the second pic. There are no bearings in the assembly at the moment - just a bore to fit the shaft into place at the moment.

I took some time last night and cut out a template vane for the axial diffuser from some wood and will be using that to cast all of the vanes. The axial diffuser will be rolled from 1/8" sheet aluminum and have a flange on the front end to bolt to the back of the diffuser. For each of the vanes I will drill two holes per vane into the sheet aluminum about 3/16" diameter and have my welder attach the vanes by welding to fill in the holes through the inside wall of the sheet - creating a weld bond to each of the vanes to fix them to the sheet. This will make the vanes permanent fixtures to the sheetmetal so I dont have to mess with a bunch of drilling/tapping or deal with all those bolts.

The axial diffuser vanes are tapered to 13 degrees to match the duct divergence angle of the radial diffuser. This will effectively provide about 6.5 inches of diffuser length all in a 9" diameter casing. :) Shoud be good for efficient diffusion not to mention this layout will be able to completely eliminate swirl in the gases before they enter the combustion chamber at the rear.

An additional idea I will implement into this design is to fabricate some parallelogram-shaped "diamonds" which will attach to the outer diameter of the NGV's baseplate to provide additional support for the core of the engine. This section you see above is quite hefty and in the current drawing, without these supports, it is going to place a lot of weight loading on the jetpipe-NGV interface which I dont think is going to be so good. These supports wont be bolted to the casing - they will be machined to fit into the main casing and just rest on the inner wall.

That's all for now - I Will have to cast all of the wedges and roll the sheetmetal before I can make the next step. Fortunately the shape of the wedges will make for easy casting - I can literally just pack up some molding sand and "poke" my template into the sand and pour away. :) I'll post back once I have the axial diffuser finished.

Ainis
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Re: TV94 TurboFan Build

Post by Ainis » Thu Dec 04, 2008 5:29 pm

Just perfect :wink:

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Re: TV94 TurboFan Build

Post by nsmikle » Tue Mar 24, 2009 4:38 am

Hello, Ash Powers..Good work again..

What influenced your choice of aluminum for the bearing housing? Why not steel/Cast iron?

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Re: TV94 TurboFan Build

Post by Ash Powers » Tue May 26, 2009 9:33 pm

Been a while since the last update on this thread but I haven't had much time to spend on the engine. Over the holiday weekend I did manage to knock out a few parts for her. :)

I rolled a 1/8" sheet of aluminum for the axial diffuser vane baseplate and made up a "poke-stick" pattern for the axial vanes. It was just a piece of wood shaped like the vane that I stuck into my molding sand and poured the aluminum into the holes. After they were all trimmed up I went to my welder yesterday to have him attach the vanes to the baseplate. Unfortunately the process didn't go quite as well as I would have liked it to.

To affix the vanes to the baseplate I drilled two 1/4" holes into the baseplate per vane and welded through the hole. There was a lot of burn-through on the vanes and baseplate but I managed to grind that out. There is still gaps between the vanes and baseplate and overall it looks pretty ugly. Here's some pics:

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I did some searching on aluminum brazing alloys and came across a really nice product by Muggy Weld. It is their Super Alloy 5 which brazes at 600F. Here's their bullets:

Flows like silver solder on thin aluminum
Bonds at half the melting point of aluminum
Matching flux not only cleans the work area, but also serves as an absolute temperature guide
Filler rod bonds right through paint, oil, dirt, grease, etc.
Can be machined, drilled, tapped, threaded, plated, anodized or even bent without causing pinholes or porosity
Creates a malleable bond that is stronger than the parent metal
Works with any heat source: propane, natural gas, oxy-acetylene, Mapp gas.
Makes an excellent tig rod!

You can find this product here:
http://www.muggyweld.com/super5.html

And a really good video of it being used to bond two aluminum plates:
http://www.muggyweld.com/5clip2.html

I ordered their basic startup pack which comes with several rods and the flux. I am going to give a shot at using this material to fill in all the small gaps between the vanes and the baseplate. I should be able to make this part look like it is all one solid piece and get rid of all those nasty gaps. Might even be able to get it to flow out on the vane faces to fill in the small imperfections of the castings. :)

I also machined a top cover plate for the diffuser from some 6061 billet plate:
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And I also went ahead and cut out the nozzle guide vanes. I used 316SS for these pieces which from the experience of using this alloy in the T04GT project, should produce favorable longevity. These pieces shown started out as a 12" long 1" X 1" bar of 316SS. It was bisected corner to corner and then the top corner cut off each length. I then cut the two pieces into more manageable lengths for a total of 4 sections. These will get final-cut to length once I have the baseplate for the NGV section machined. I made up a template in 1/8" aluminum plate with the vane profile which was made up from the drawings I put together for the engine. This template was used to grind the airfoil shape you see across the entire length of the pieces.

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I'm going to source some 316SS sheet this week so I can roll out the main casing for the engine - so she'll start to look like an actual engine here shortly. :) I'll post back once I get the aluminum stuff and give a shot at the axial diffuser...

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Re: TV94 TurboFan Build

Post by racketmotorman » Tue May 26, 2009 11:10 pm

Lookin' good Ash :-))

Cheers
John

Ash Powers
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Re: TV94 TurboFan Build

Post by Ash Powers » Tue Jun 02, 2009 9:53 pm

Moving right along... :) A friend of mine stopped by a few days ago and I was showing him the progress on this engine and that I had ordered some aluminum welding rod to fill in the gaps on the axial diffuser vanes. Well, he happened to have some of his own but his material has a higher melting point and greater tensile strength (720F MP and 42,000psi/in^2) so I decided to give it a whirl. It turned out pretty nicely but there are a few spots I am going to go back over to finish cleaning up the section. Regardless, I am much happier about how this part has turned out! I also rolled a piece of 16-gauge aluminized steel to form the rear section of the axial diffuser baseplate - this was welded to the NGV baseplate. I still need to roll another band of this to make a shoulder on the inner diameter of this baseplate so that it will seal up to the aluminum diffuser baseplate but I'll get to that later. I'm waiting on the stainless sheet to arrive now so I can roll the casing for the engine.

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I also received the 8" diameter 6061 billet of aluminum to machine the compressor inlet duct from and went to work on it yesterday as soon as it arrived. This piece took probably about 6 hours to machine but that 6061 cuts really nice. :)

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Here's all the material that had to be machined out of that billet, LOL!

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In the meantime I'm going to make a pattern for casting the front compressor inlet duct and get to machining on that.

I've also come up with a better idea for the rear of the engine casing instead of making "turbulent" 45-degree turns around the back of the combustion chamber. I'm going to order some stainless 2.0" diameter tube mandrel bent on a 3.5" centerline radius to make the rear end of the casing. A 2.0" diameter pipe on a 3.5" centerline radius will have an outer diameter of 9" which is the same as this engine. I'll order a u-bend which will be bisected to form the 360-degree "bowl" at the rear of the engine. I'll be doing the same with the inner diameter of the casing as well but using a 1" diameter tube bent on a 2" centerline. The combustion chamber liner will be made in the same way as well. All of this will help to maintain flow efficiency through the engine so I can get as much out of her that she's got. I've modified my drawing to reflect these changes - you can see this at the rear of the gas producer.

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Re: TV94 TurboFan Build

Post by Mike Everman » Wed Jun 03, 2009 1:28 am

Fabulous build log, as always Ash!
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Ash Powers
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Re: TV94 TurboFan Build

Post by Ash Powers » Wed Jun 03, 2009 9:18 pm

After doing some searching today for the mandrel bent tubing to form the rear of the main casing I have found that trying to locate 2.0" diameter tube bent on a 3.5" centerline radius is nearly impossible. I probably called nearly a dozen tube bending companies and while a few had the dies to make the pipe, they also wanted a couple hundred dollars to swap their tooling to make one 180-degree pipe, LOL. So, I revisited the drawings I put together for the engine and have come up with a new plan which works out really nicely actually.

Instead of trying to piece the rear of the casing together using various diameter bent tubing it occurred to me that all I need is a 3" diameter pipe bent on a 3" centerline radius. This will form a 9" o.d. and a 3.0" i.d. for the jetpipe and create the smoothest transition possible for the airflow around the back of the motor. I already have a 2.0" diameter pipe in 321 stainless (not cheap stuff BTW) bent on a 3" centerline which I will use for the rear cap of the combustion chamber liner. I went ahead and ordered two 3" diameter, 3"CLR 304SS 90-degree bends and they'll probably be here by the end of the week along with the sheet I ordered to roll the main casing from. I've updated the drawing once again showing the change to the casing and combustion chamber liner - I will work up some numbers on the combustion chamber this evening to make sure I have ample volume for combustion and make any changes to the drawing as needed.

I also ordered the 316SS sheet for the rest of the combustion chamber liner and will probably have that in the beginning of next week as well.

Here is a revised drawing of the engine:
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Viv
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Re: TV94 TurboFan Build

Post by Viv » Wed Jun 03, 2009 10:23 pm

Hi Ash

You may find this NACA paper useful if you have not seen it before while working out the bend

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Rossco
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Re: TV94 TurboFan Build

Post by Rossco » Tue Jun 09, 2009 1:45 pm

Hey Ash,
Drop me a line when your about next.
I see you went with the TV94, did i miss what made up your mind?

Rossco
Big, fast, broke, fix it, bigger, better, faster...
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Re: TV94 TurboFan Build

Post by Johansson » Wed Jun 10, 2009 5:08 am

Looking really good Ash! :D

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Re: TV94 TurboFan Build

Post by Ash Powers » Sun Jun 21, 2009 7:26 pm

Well, my petrobond molding sand pile had finally shrunk to a volume no longer able to fill my molding flask so had to order some clay resin and pickup a bag of silica sand to beef up my supply. I turned a pattern on the lathe using a high-density foam block so I could cast the compressor inlet duct - the part turned out very nicely and didn't require machining of a solid billet - the process only took a few hours. :)

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This piece will be TIG welded to the inducer flange at a later time once I have bored all of the mounting holes to fasten the inducer flange to the diffuser front plate. I'll end up making a pattern from another block of the foam to produce a nice fiberglass cowling for the front of the engine later in the project as well.

I also received the 304SS sheet to roll the main housing for the engine and took it up to my welder's shop to roll it out. It turned out pretty nicely but will be getting several additions before it is complete. I also received the 3"dia 3"CLR 304SS tubing to make the endcap of the housing and got those pieces cut out and welded together. They could have been a little more perfect but this section will be covered by a shroud when it is complete - I cleaned up the welds real nice and just let it be. For the time being the endcap is just tack welded as it still needs to be machined to have a flat joining face for mating to the casing.

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I also received the thin 316SS sheet to make the combustion chamber from - 0.023" thickness. Before I start shaping all of those pieces up I'm hoping that Rossco will be so kind once again to help with the modeling - this time I'd rather model it and make changes there rather than doing it backwards and modeling an already built part, LOL!

Rossco has once again impressed me very much by his talents with Solidworks and sent over some initial renderings of the engine. It is, well, I'll let you fill in the blanks. :)

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Re: TV94 TurboFan Build

Post by Ash Powers » Wed Jun 24, 2009 12:56 pm

Walmart SCORE. :) Stopped by the local wally world with my stanley tape measure and found a suitable shroud for the front of the motor. It is a 4-quart bowl of some sort - perhaps for whipping up cake mix or something - nice and thin and easy to carve out. A bit more of a "retro" look than what I was originally envisioning but it has a sort of elegance to it that has its appeal. This is really just an aesthetic component so the "surprise" as to how it has ended up is a sort of happy accident, if you will. The thing really looks like one huge hollowpoint bullet, LOL. :)

The piece isn't fully finished quite yet though - that small ~1/4" lip at the bottom will be cut off and a ring mounted to the diffuser plate will provide the threaded mounting points to hold the piece in place.

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I've got a few other obligations going on which will pull me away from having much time for the GT project but I'll be back to it again in short time. Time now to move on to the hot parts. :)

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Re: TV94 TurboFan Build

Post by Ash Powers » Tue Jul 21, 2009 7:25 pm

Been making some progress on the TV94 this past week. :) I ordered some angular contact bearings, 20mmX47mmX14mm and went to work on machining the turbine shaft, bearing housing, and spacer for the bearings. I'm pretty happy with the fitment of the bearings onto the shaft - just a little bit of resistance when sliding them on. :)

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This arrangement is just temporary with the dual-bearing layout - I really only ordered the bearings to get the shaft and bearing tube machined but I will still be machining a bronze sleeve for the bearing tube and using two pairs of bearings. I have also been trying to work out how to handle the axial loads placed on the rotating group by way of pressure building up behind the compressor wheel and think I have a pretty solid arrangement - after hours/days of considering it all. I have put together a new drawing showing the changes to the bearing tube:

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I'm going to incorporate a labyrinth seal just behind the compressor wheel (red) and make it from PEEK (PolyEtherEtherKetone). This material can withstand temps up to around 500F which it will never see in this application but it also has good impact resistance as well as offering very very low friction - similar to that of PTFE (teflon). The one main difference between PEEK and PTFE though is the tensile strength - PEEK is actually a very hard material and with that it can be relied on to maintain its tolerances - teflon is just far too "flimsy" to expect it to hold shape. This seal will reduce the amount of air that bleeds behind the compressor wheel but there is still the need to have a dump port to the inside of the seal since this seal is not 100%. Instead of having to use two air dump ports, one for the labyrinth seal and one for the cooling air feed to the bearings, I figured I could knock two birds out with one stone and use the air bleeding past the labyrinth seal to cool the bearings. You can see the air path in light blue - although only one "port" is shown, I will actually have four of these ports running through the diffuser plate and bearing tube - kindof hard to show all of them in a 2-d drawing. I will be installing a shaft seal just behind the compressor wheel to seal it up to the diffuser plate so that none of the lube (green) can find its way behind the compressor wheel. I have also drawn in small bleed ports through the NGV baseplate (also in blue) as well as the heat shield just behind the turbine - there will be about 15 of these ports drilled to allow cooling air to flow over the hot parts.

I have also figured out a way to check what kind of axial loading the rotating bits are under as well as integrate a shut-down feature if the loading becomes excessive. In the bearing configuration I'll be using, the front bearings are handling the axial loading and are constrained by the lip at the front of the bearing tube. I'm planning to use a thin-profile, high-K washer spring between the front bearing and the seat which will allow the rotating bits to move slightly forward as axial load increases. Using a washer spring of known tension/displacement, the axial loading can be measured by metering the position of the shaft out at the compressor inlet end. Obviously the motion will have to be constrained within just a few thousandths forward to prevent the compressor from burying itself into the inlet duct as well as prevent the turbine from grinding into the heat shield, but with a stiff enough washer spring this shouldn't be a problem. To monitor the axial loading I plan to install a small adjustable contact point into the inlet duct that sits directly in front of the end of the shaft, electrically insulated from the casing. I can set up the engine control unit to monitor this contact and if contact occurs, it will shut down the fuel pump.

The bottom line here is that I really want to know what kind of axial load the rotating group is under since this factor is largely tied into bearing failures. The approach to minimizing this axial load by way of the labyrinth seal is yet of unknown effectiveness and I would rather not destroy nearly $500 worth of rotating bits just to "test and see" with fingers crossed, LOL.

I'll hopefully be ordering the sheet of PEEK to make the seal soon - the stuff is very expensive: for a 6" X 6" X 0.25" sheet of the stuff it is $100.... .for a little plate of "plastic", LOL.

I've also been looking into alternate alloys of stainless for making up the NGV backplate and exducer flange from. I have made up the vanes already using 316SS which should work out well but for the 316SS to make these other two parts from it is in the neighborhood of $220 - a bit pricey for my blood.. Interestingly enough, I've found that 303SS is actually very heat resistant - even moreso than 316SS in terms of scale and corrosion resistance.... and it is about 1/2 the cost of 316SS. I'll be ordering up some of that soon as well along with the bronze for the bearing sleeve. :)

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Re: TV94 TurboFan Build

Post by Johansson » Tue Jul 21, 2009 8:14 pm

Interesting reading as always Ash! :D

Regarding the axial bearing stress, have you discussed the use of a PBD (pressure balance disc) to counter the axial load on the bearings? I´m not 100% clear with how it will work but since it is used on commercial engines it should be useful.

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