The humble beginnings of something BIG; JU-03!

[Johansson]

Richard: A burst ring is a very good idea, perhaps the best way is to have a burst blanket made that is used around tractorpulling clutches. Lightweight and easy to remove.

Chris: Then we can forget all about the 10krpm revs for this engine, since that would require a total rebuild of both the comp and turbine hubs. If you run the calcs for lets say 6000rpm, is that doable with the setup I have now with 3mm turbine blades?

The hub is welded to one side of the disc.

[richardm]

Yeap Something like this maybe www.jegs.com/p/Allstar-Performance/Allstar-Transmission-Blankets/1639912/10002/-1

[Johansson]

Jan 28, 2024 16:25:48 GMT -5 richardm said:

Yeap Something like this maybe www.jegs.com/p/Allstar-Performance/Allstar-Transmission-Blankets/1639912/10002/-1

Exactly what I was thinking about!

[Johansson]

I wrote this in an email to John last night and it sums my thoughts up about this problem:

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What I mean is, my first goal is to prove that it is possible to make a simple sheet metal engine that produces a useful amount of thrust.

When that is proven (which I think is done with a 100+kg reading on the scale) I can move on to phase 2 and start pushing the rev limit by improving the engine bit by bit.

But right now I will be thrilled if I can get it to idle with nice cool temps.

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So the idea is to keep the 10k RPM design for the stationary parts of the engine and build this rotor as good as it is possible with its now obvious limitations, run it to get some idle and mid-rpm data and use that when designing better rotor parts further down the road.

Swithing the rotors out for top grade stuff is "easy", with all the geometrics of turbine blade angles and comp measurements figured out I can have a high tensile alloy disc made for the compressor and a proper steel one made for the turbine with better blade fastening and lighter blades.

So, no tears shed over this. Thank you very much Chris and Richard for pointing this out and helping me figure out when to let go of the throttle and run for the woods.

/Anders

[Johansson]

Tonight I milled the rest of the stator vanes.



Then I pressed them into a radius to better catch the air.



The result.



I then welded them in place, only a small weld so they can be adjusted later.



With the compressor wheel in place.



Next up is to make the outer wall that directs the air flow from radially to axially, my old job has a nice pipe bending machine that I will borrow and roll a 60mm thick walled aluminum tube to the right diameter.

Then I can cut a segment from it and use, hopefully....

Cheers!
/Anders

[andym]

Looking good 

[Johansson]

Thanks!

I made the outer rim for the straightening vanes tonight, more work for the hacksaw and rollers.



An hour and a half later and the rim was tacked in place.



For the final section of outer wall closest to the compressor exducer I have reconsidered and scrapped my original idea of rolling a 60mm tube, and will make a 45 degree angled wall instead. It will do the job and I can do it with the tools I have at home.



Later I will make some kind of air deflector here that directs a part of the air inwards so the flame tube inner wall gets enough air.



Cheers!
/Anders

[wannabebuilderuk]

Damn she's starting look the part, can't wait to see the startup... Can probably be done by hand like the old rover 1s60 engines haha

[Johansson]

Hand crank start would be awesome, but I fear that I would suffer a stroke halfway to idle...

I am so looking forward to hear what Chris has to say about the turbine wheel, what its highest safe RPM is and perhaps some brainstorming about how a more suited rotor assembly should be constructed.

[wannabebuilderuk]

Something that's sounds as good as this lok youtu.be/YN_PWX7uDSw

[finiteparts]

Feb 1, 2024 11:27:26 GMT -5 Johansson said:

Hand crank start would be awesome, but I fear that I would suffer a stroke halfway to idle...

I am so looking forward to hear what Chris has to say about the turbine wheel, what its highest safe RPM is and perhaps some brainstorming about how a more suited rotor assembly should be constructed.

Trying to get some time after work to get the model running.   Also thinking about using two disks to carry the blade load.   Would you consider using a more capable material as an option?   Inco625 maybe?   I know it is expensive, but it may be one of the more doable options due to the really high pull loads.

- Chris

[Johansson]

Hi Chris!

For the mk2 version of the engine an Inconel disc is certainly an option, when the overall engine design is proven to work I am prepared to spend a reasonable amount of money to get some serious thrust out of it.

For starters I just need to get this baby running, so I would appreciate some help with the present rotor assembly first of all. Is there some easy mod that will make it a bit sturdier, and how fast can I spin it? I can weigh the parts and take more close measurements if you need it.

With an engine that idles and can be throttled a bit it will be much easier to open the wallet and have a proper rotor assembly made, as things stand now it feels like 50/50 whether it will end up as a running jet engine or a rusty piece of garden decoration.

/Anders

[richardm]

I know this might add to uncertainty and even to some frustration but should you also consider the centripetal loads on the compressor wheel component ? Since it will turn at the same speed than the turbine and it may end up to be more restrictive than the turbine itself .

[Johansson]

Indeed, and the comp wheel is much more difficult to calculate with its welded blades. But if I get a number on the turbine wheel at least I have something to consider the absolute max.

There won´t be any reason to push the limits with this rotor anyway, I just want the satisfaction of having made a running engine and then get to work with better rotor parts while doing some low rpm tests and adjustments to the engine. Mosty to scare the neighbours.

[finiteparts]

I didn't have much time to work on this model over the weekend...I had to fix my Honda Civic that had a charging system issue.  The electronic load detector failed and the ECU would not command the alternator to start charging.   Of course, no one had the part, so I had to hit up the junkyards to find one and get the car going.  

I was able to run some rotor speed checks on the main disk and unfortunately because of the limited capability of the steel, the rotational speed that it can support is also limited.   S355 has a yield stress of 355 MPa (51 ksi), which is rather low in the rotating disk world (713LC yield is around 116 ksi).  I had to bring the rotational speed down to 4500 rpm to just get the 80 mm bore close to yield.   But I am not sure that the weld will carry the stress very well, so if I assume the 110 mm bore of the outer disk, then the bore will start to yield at 4200 rpm.  The problem with the weld is, I am not sure if you have a full penetration weld between the inner and outer disk.   If it is just welded on one side, then the weld can't carry the full load.

The plot of the stresses on the outer disk is shown below:



You can see at the bore radius ( ~ 2.165 in) the hoop stress exceeds the 51ksi yield stress, and thus the bore will yield out somewhat.   This is just the load due solely to the weight of the disk itself, and does not include the stresses that would be imposed due to the pull of the blades and the bolts.   I will try to get some more time to work the numbers with the blades and bolts loads.   But it will be bad.   

The bolt holes in the disk will cause local stress concentrations (stress concentration factor (Kt) ~ 2 to 2.5).   This is due to the fact that we have removed material, to make the hole, that would have otherwise been carrying some of the hoop load.   So , even if it was out at a radius of 5.5 inches where the hoop stress is lower, with a Kt the local stress may be 40 - 50 ksi, right back up to the materials yield stress.  If there are any imperfections in the bore or the bolt holes, there will be additional stress concentrations...this is why the bore of a turbine disk is so critical and sensitive to machining finishes, nicks, etc.

Again sorry to be the bearer of bad news...I had hoped to get it up in the 5000-6000 rpm range, but that is not likely.  I will look to see if there are any other cheap materials that may be more capable.   The other thing I saw was that the material capability falls rapidly around 500C and so you would need to keep it cool also.

Chris