Oberursel URII revolving cylinder engine buit in 1917, a possible next project ?

[fumopuc]

Hi Mike,
thanks for the link, that give a lot of information about the internals of the early rotary engines.
I am happy, that the Oberursel UR2 with its 2 valve solution is hopefully not so complicated.


If of any interest, here a model of the Gnome Monosoupape ca. 1916.
Shown shortly at a German show. It starts at 05:07.
<a href="https://www.youtube.com/watch?v=iZtFkFO3IZc" target="_blank">http://www.youtube.com/watch?v=iZtFkFO3IZc</a>
Some information about the making of.
The engine is built by the plans of Stephen Wessel.
https://modelengineeringwebsite.com/Wessel_drawings.html


<a href="https://www.youtube.com/watch?v=sJOPd_MhMeE" target="_blank">http://www.youtube.com/watch?v=sJOPd_MhMeE</a>


and part two with the running engine. Have fun.


<a href="https://www.youtube.com/watch?v=NcBUZYfhaN4" target="_blank">http://www.youtube.com/watch?v=NcBUZYfhaN4</a>


I have had the opportunity to see it running live at a show in the "Flugwerft Oberschleißheim" part of the "Deutsches Museum München" some years ago.
The guy who built it, Robert Weber, is living not far from me, next to one of the big lakes, "Starnberger See".

[fumopuc]

Hi everybody,
I have got the plan set beginning of this week.
Far more than 100 pages of paper.
The  description is not been seen/read completely, but all plans have been studied.
Two pages of the plans are still missing but I am in contact with them.
By request, I have got the lobes/cam data and a STL file which does represent the upper part of the inlet tube at the head.
This is in my eyes overall not an easy design.
Modern manufacture technologies are used, like 3D metal printing for the upper inlet manifold and aluminum cylinders without any liner with Nickel Silicon Carbide coating like the Nikasil from Mahle or similar.   
Due to the design of the main and articulated con rods, like in a rotary engine, there a con rods with different length and stroke in it.
To compensate this, the compression ratio is the factor what will be adjusted for each cylinder to be the same.
To archive this, the cylinders do have a thread at its lower end in the crank case, M42x1,5, to adjust the assembled length a bit.
So each cylinder has a special value for the distance from piston crown to the cylinder edge at top dead center.
Unfortunately you have to do this, before the hole pattern for the cylinder head can be drilled.
I have tried to get any information about a successfully built model here, but I failed.
Some things I am struggling a bit, is i.e. the cylinder material.
The drawing says EN AW 7075 as material for the cylinders.
I am not sure if this is the best combination for Nikasil or similar coating.
Also I know, that AW 7075 does not like temperatures above 140° C, there is a rapid loose of stability.
But, what shall´s. From buying my V12 plan set until making first swarf for it, nearly five years went down.
I will start to model a solid of the crank case in my CAD first and sent it to the 3d printer.
With this dummy part I will check different set up possibilities at my little CNC mill and others.
May be I can use my 4th axis by an adapter, to lift it a bit.
And the big hole pattern maybe can be split in two set ups by indexed rotation at the mill table.
We will see.

[crueby]

Very complex looking build, will be following along with interest!

[Vixen]

snip....... aluminum cylinders without any liner with Nickel Silicon Carbide coating like the Nikasil from Mahle or similar........

The drawing says EN AW 7075 as material for the cylinders.
I am not sure if this is the best combination for Nikasil or similar coating
Also I know, that AW 7075 does not like temperatures above 140° C, there is a rapid loose of stability.........

Achim,
The use of Nikasil coated aluminium cylinders is very unusual. It is often used in lightweight, high performance engines as a wear resistant coating. It's use in a model of a vintage rotary engine is questionable. I would have thought a conventional iron or steel cylinder would have been a far better choice.

Out of interest, how was the Nikasil material applied to the aluminium cylinders? Did you need to send th justifye completed cylinders to a specialist supplier (Mahle) or is it a process you can do in your home workshop? What does Mr Volker Jung say to justify its use on this model engine?

Mike

[fumopuc]

Hi Mike,
a Nikasil or similar coating is a common method of cylinder coating in a lot of actual motor cycle engines until today.
Car engines, or better said the automotive industries have changed its method for cast aluminium cylinder blocks to LDS in the meantime.
https://www.scheuchl.de/en/machinery-and-plant-engineering/foundry-technology/translate-to-englisch-lds-anlagen
The basic idea here in this case seems to be, to reduce the rotating mass, what seems to be very logical for me.
For the Nikasil coating a special diameter tool/jig/fixture is necessary, so I have ask directly if there is any supplier recommendation, with the idea that the cost for tooling has been paid already. The answer was no.
It seems to be there that until today no real hard ware or real parts are made from these drawings.
If a Nikasil or similar coating will be done, it should mostly be necessary to be in contact with coating company about best required thickness of the coating.
That means the prepared bore dimension should be checked with them. 
After the coating a honing to final dimension is the next step.
Also this should be planed in advance, because the lathe and a brake honing tool seems not to be the right process in this case.
I have seen some fresh coatings there in my life, which needs a bit more material to reduce.
So at the end this all is far away of the hobby workshop.
In the cylinder design I do not see any real space for a cast iron liner.
The bore is 37,3 mm and cylinder outer diameter without the fins 41 mm.
So reducing the cylinder material by another 3 mm, 1,5 mm wall thickness of the liner, we will have 0,5 mm reaming wall thickness of the aluminium.



   

[Vixen]

Hello Achim,

Thank you for the detailed explanation of the Nikasil coating process. As you point out it is a complex industrial process and far removed from the hobby workshop.

That was exactly the point I was making when I said "It's use in a model of a vintage rotary engine is questionable. I would have thought a conventional iron or steel cylinder would have been a far better choice.".



The original cylinders had very thin walls and integral cylinder heads and were turned from a steel forging. They were one piece and did not have a liner. I would have thought a similar construction would be more suitable for a model engine replica than Nikasil. Many models of the Oberursel, Le Rhone and Gnome rotary engines have been successfully made and run using one piece steel or cast iron cylinders. It should be no surprise to find that no model cylinders have yet been made from the Jung drawings using the Nikasil process.

Mike

[Jasonb]

Cutting from steel would seem the better option though the blind bore is not going to be the easiest when it comes to honing.

Any chance that the bore could be reduced and a separate iron liner added? That would also make honing a lot easier as you would in effect just be working with a tube. If you took the Aluminium fins out to 38mm then a bore of 35mm would be possible. You would need to check that conrods don't hit the bottom of the bore.

I'm inclined to say put this one on a back burner until the design has been proven, preferably by Jungs making one that runs.

Jung also seems to makea engines that have the potential to be used in an RC aircraft, if you only intend your engine to run as a disply piece then  the performance and weight become less of an issue and the design adjusted accordingly.

[fumopuc]

I'm inclined to say put this one on a back burner until the design has been proven, preferably by Jungs making one that runs.

Hi Jason, 100% agreed, that is exactly what it is in my mind.

[fumopuc]

Hi everybody,concerning the general model engine design I have made a visual comparison to all the very useful information at this sit.
https://thevintageaviator.co.nz/projects/oberursel-engine
I assume that these guys there have got basic information from Company Motorenwerke Oberursel for the redesign and build of their replica engines.
There are drawings and CAD pictures, as shown by Mike already.
There are detailed assembly pictures and also from part making with some small video sequences.
Off course additional information about the history, also.
Everybody with real interest can find lots of details there about this special engine from 1917.
I would like to accept the copyright of the CAD Jung design, so no direct copies of their drawings here to see.
But I can say, that the model engine design is really very very close to all shown details from this replica engine.
In shape and functionality two things are conspicuous only.
First the original concept with the con rods and the guidance by the sliders
and
second the from Mike already shown concept of the cylinder/head one part concept.
The model engine is designed with
normal radial engine design of main and articulated con rod
and
normal concept of cylinder and cylinder head, with a gasket and removable cylinder head.

[Roger B]

That looks to be quite a challenging project if you follow the Jung design  As you say maybe some parts can be made in a more conventional 'model' way 

[fumopuc]

Hi Roger, it is really a bit challenging.
Today I have made my CAD model from the CAD Jung drawings of the crankcase.
First to make a 3D print and also for better understanding of the part and of course for later possible CAM preparation.
I have sent 4 mails to Mr Jung, asked overall for 7 dimensions, which I could not find at any of the drawings.
For some I have got some clearance by looking at the matching parts.
Some others I made by best guess for the moment.
The printed drawings I have got are at some places a black surfaces only, due to the multiple lines crossing at one place and the bad resolution of the printer.
This is a special case with the crankcase, because the scale is lower than 1.
To be honest, I am not amused.

[fumopuc]

This morning I have made a short video.
Making of the crankcase CAD model.
It is made in the same way I would like to machine it.
Started by some round bar stock d=160 x 77 (plus) mm on the lathe as a raw part for the CNC mill.
The 3D printer is busy now to make a dummy crankcase for further research about possible set ups.
<a href="https://www.youtube.com/watch?v=uFgOGAbD1U0" target="_blank">http://www.youtube.com/watch?v=uFgOGAbD1U0</a>

[fumopuc]

The printer has made the job.
Not a nice print, but a very quick one, with minor support, less than 6 hours.
But it looks good concerning the set up on the CNC mill.
Also the 4th axis seems to be a usable part of it.

[fumopuc]

Achim

I recommend buying the  Bentley BR2 book by Lou Blackmore ISBN 0949135 04 6. Although not the engine you wish to build it is full of useful info and methods of construction.
I build mine some 35 years ago

Mike

Hi Mike, I have got the used copy today from a book shop in the UK.
Very interesting to see how the model was made with conventional machines only.
The model seems to be a bit smaller than my research object, Oberursel ORII.
The bore is 33 mm and cast iron liner are used.
My bore should be 37 mm.

[fumopuc]

Some progress with the CAD model.
And the virtual first motion available.
<a href="https://www.youtube.com/watch?v=WloRlkUlcto" target="_blank">http://www.youtube.com/watch?v=WloRlkUlcto</a>