Making WWI Rotary Engine Cylinders

Discussion in 'Tips, Tutorials & Tools' started by Gil, Apr 2, 2007.

  1. Gil

    Gil Active Member

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    A Short Tutorial on Making Finned Rotary Engine Cylinders

    The following is a way of making the finned cylinder structure of early WWI rotary engines. It is fairly easy.

    1.) Start by finding a suitable screw approximately the same diameter as the model cylinders with as fine a thread pitch as possible (10-32 shown).

    2.) Cut a length of card stock that just meets in a butt joint when wrapped around the bolt.

    3.) Dip the card stock into water to thoroughly soak. Remove any surface drops and wrap the card around the threaded section of the screw.

    4.) Wrap the card down over the screw with a strip of plastic wrap. Chase the paper down onto the threads with the edge of a steel rule or similar edge. Let assembly dry completely (I have a space heater that I put it on top of).

    5.) Remove the plastic wrap from the embossed paper cylinder. Gently remove the paper cylinder from the screw thread.

    6.) Place the embossed paper cylinder onto a brass tube approximately the same diameter (or just slightly larger). Wrap it with a layer or two of plastic wrap being careful to take the helix out of the screw thread embossed on it by moving the thread by one at the butt joint.

    7.) Use a telescoping brass rod and press on the ends of the plastic wrapped embossed paper cylinder. The embossed paper cylinder will collapse at the embossing folds. Press each end till the folds are tight.

    8.) Remove plastic wrap and give the cylinder a coat of thinned lacquer.

    9.) Use as a replacement for the cooling fin area of the models rotary cylinders.

    This should make modelers of WWI aircraft fairly happy. It also makes for a good looking hose drum for model ships and can be adapted to model flexible hosing...,

    -Gil

    [​IMG]
  2. rmks2000

    rmks2000 Member

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    Great technique! I'll have to give it a try, but it sounds a little tricky getting the helix out of the paper.
  3. Gil

    Gil Active Member

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    Actually it's not to difficult. You need to hold the alignment while starting the plastic wrap. Also the ends need to be square. A little mushrooming at the ends may occur so a little additional length is needed to account for it. Just trim the ends off before removing the plastic wrap. I was quite impressed with how easy this actually is.

    -Gil
  4. Gil

    Gil Active Member

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    Second Thoughts...,

    After some careful, self directed messing about I've decided that this method looks like a flex straw made out of paper and isn't as effective in time and looks as is the wrapped layer technique...., Oh well, back to disc punching I guess...,

    -Gil
  5. EricGoedkoop

    EricGoedkoop Member

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    I generally just stick with printed cooling fins, but there's another technique I've used in the past with cylinders built like Richard's. I superglued several lengths of 1/64th music wire side-by-side on a scrap of lumber, enough to cover an area somewhat wider and longer than the unrolled cylinder. Being careful to keep the flat cylinder square to the wires, it can easily be embossed with a ball-point pen or similar. Rolled into shape, it looks pretty good and benefits from a gentle dry-brushing with a metallic grey paint.

    It's been a while since I did this last and may have used bond paper instead of cardstock.
  6. Gil

    Gil Active Member

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    Wire & Wire Embossing...,

    Carl, I've tried the wire wrapped cylinder and it looks pretty good but still looks like wire wound on a bobbin.

    Eric, I've also tried doing the same thing with wire. It's pretty much the same as embossing with screw shaft.

    I tried embossing aluminum tape followed by wrapping it around a cylinder. It looked good but the really bright aluminum doesn't look right without applied paint whereupon the effect totally vanishes.

    The vertical fin count of rotaries varies but for the following calcualtion assume it to be about 20. This yields a scale thickness of around 0.0125. per layer. Modeling this means that 40 discs punched from index cardstock (~0.0075) would be required to stack up a full scale rendition. Times 9 cylinders yields a grand total of 360. I don't think I have the kind of patience necessary to model even half this amount indicating that an alternate (read easier) method needs to be developed.

    Another nuance is the shape of the cylinder. Straight walled cylinders lead directly to the belief that it's a model. The idea is to suspend disbelief and getting the cylinder shape somewhat near to the original is important.

    Till Next...,

    -Gil
  7. Gil

    Gil Active Member

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    A Little Progress..,

    Hi All,

    Another obsession begins..., I've made some progress toward making a more beliveable cylinder. The next iteration should be an improvement on that shown below. The fin count was decreased to one-quarter of the full scale version. The visual cortex is really lousy at finite count comparisons so this will work as long as the real version isn't anywhere near the modeled one for comparison.

    -Gil

    [​IMG]
  8. rlwhitt

    rlwhitt Active Member

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    Dang, that looks REAL! And yeah, I want a wheel tread tutorial - I'm gonna need one soon. :)

    Thanks for your obsessions, Gil!
  9. Gil

    Gil Active Member

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    Agenda Items...,

    Wheel treads will have to wait. The European modelers do magnificent work on them so there's no use reinventing their wheel..., You can make a nice tread using stretched tulle netting on the outside of the tire. It will give you a very nice diamond pattern when applied right. Small pitch aluminum mesh will also work.

    The next obsession will be how to make Spandau machine gun covers. Not much of an obsession as it's already done. The last one planned will be on aluminum-paper work for compound curved cowls. After that maybe I'll go back to paper casting...., who knows...,

    -Gil

    P.S. Part III of the Spoked Tire is still a work in progress than I need to finish...,
  10. Gil

    Gil Active Member

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    As an addendum to my last...,

    Hello All and Happy Easter!

    I may have spoken a little too soon in an earlier post regarding this technique. Directed messing about failed to test 24# copy paper with the earlier method. That attempt was performed using index card stock (67#). By using the lighter paper the number of fins per millimetre falls right into place.

    The picture below shows the result on a rectangle of untreated copy paper. It is remarkably flexible and for those of you into oxygen masks and radiator hoses this is the real thing (just have to find a way to tidy up the seem or just hide it). Treating the paper with lacquer should result in a crisper fold collapse. The tube that it's mounted on is about 4 mm in diameter (5/32")...,

    Till Next,

    -Gil

    [​IMG]
  11. Gil

    Gil Active Member

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    More on the above...,

    To get an idea of what the flex paper tubing would look like on a cylinder I cut a piece from above the length of an existing Oberursel Ur.I cylinder and proceeded to wrap the cylinder with glued on with PVA. Paint was applied and it was then mounted on a cylinder form for comparison to other print effect cylinders. I'm beginning to think that this actually might work...,

    Till Next...,

    -Gil

    [​IMG]
  12. Amazyah

    Amazyah Senior Member

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    Your method appears to be a big improvement over the older "wrap the 2d print" method, by a long shot!
    It is certainly more realistic looking and visually appealing.
    I bet a fully built engine of each method, standing in a side by side comparison, would really speak volumes!
    Thanks for sharing your new trick with us, Gil! It is a vast improvement!

    Russell
  13. Gil

    Gil Active Member

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    It's On Order Now...,

    Hi Russell,

    I agree it is a big improvement over the first example. The cylinder "bobbin" needs to be redesigned to account for the wall thickness of the corrugated paper cylinder. The corrugations are a little cockeyed due to the paper not being properly prepared prior to being corrugated. I'll redesign the cylinder roll-up and prep the paper properly on the next attempt along this line.

    I've also ordered a "Disc Cutter" from Harbor Freight. This version has a clear plexiglass cover which makes it easier to align the material prior to punching it. I have Pepe disc cutter and it cuts very precise, square edged discs but has a solid steel top making alignment difficult but not impossible. The Harbor Freight version should alleviate the alignment problem allowing accurate "washers" to be turned out in volume.

    The disc method should actually yield the best results and I plan to explore it fully. Making discs all the same size and circular around the center is an issue. Sanding the discs to get them circular is one method. The discs have to be packed together on a mandrel to sand them round. The end discs need to have any "mushroom" effect knocked off or they'll cause problems when used in a stack. This method requires a large amount of effort for minimal production making the disc cutter method a more attractive option...,


    -Gil
  14. Amazyah

    Amazyah Senior Member

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    I think you will find that the disc method will give a much more accurate design as you can theoretically model each individual fin. (mho)
    The cutting of and assembly of, all the discs required to produce the whole engine would also require true modelers devotion.
    I mean anyone else attempting this build, not you, Gil. I believe you have that department taken care of.

    Either way this experiment goes, it is certain to be an enjoyable journey to watch.
    Thanks again for letting us tag along.

    Russell
  15. Gil

    Gil Active Member

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    Corrugated Cylinder Method

    Hi All,

    Spent some time drawing up the corrugated cylinder core (Oberursel UR.II). Decided to use vellum for its strength (0.07 mm thickness). The plan is to wrap the corrugated cylinders around the core. We'll see how it develops...,

    Till Next...,

    -Gil

    [​IMG]
  16. Gil

    Gil Active Member

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    Revision One...,

    Hi All,

    A macro view of the terrible Revision One iteration..., the unknown horrors that lurk in photoshop revealed! Or how the worst was wrested from the horrors of the macroview..., By the way I've invented a new kind of screw..., it starts normally and cross threads itself half way through..., Should be great for the screw industry...,

    Made a corrugated tube out of untreated vellum (tracing paper) and applied it to the cylinder core. As can be seen there is room for improvement but doing is so much better a teacher than idle talk. The inset is an attempt to get a corrugated effect on the top. It doesn't show well in the photo but it shows some promise. It was punched out of the corrugated vellum and applied to 0.31 mm thick punched end plug. Making it out of 24# bond will work somewhat better...,

    Till Next...,

    -Gil

    [​IMG]
  17. Lepercan

    Lepercan Member

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    Rotary vs radial

    I'm confused (as usual). Are we talking rotary or radial engines here? Not that it makes that much difference, as they look similar on the outside.
    Lep
  18. Bengt F

    Bengt F Active Member

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    Rotary Engines (Rotating)

    Lepercan,

    I think we´re talking about rotary engines. Examples: Oberursel, Le Rhône, Goebel, Clergét, Gnôme, Thulin, etc . . .
    Those spinning engines used in the WW I machines, such as the Fokkers or Nieuports.

    Bengt :D
  19. Bengt F

    Bengt F Active Member

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    Rotary Engines (Rotating)

    Lepercan,

    I think we´re talking about rotary engines. Examples: Oberursel, Le Rhône, Goebel, Clergét, Gnôme, Thulin, etc . . .
    Those spinning engines used in the WW I machines, such as the Fokkers or Nieuports.

    Bengt :D
  20. Gil

    Gil Active Member

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    Thanks Bengt!

    Lepercan, it's on WWI rotary engines. People new to rotaries have difficulty in understanding their theory of operation which is distinctly different from radial engines. I won't go into the differences in this thread leaving that for the individual to research.

    I took another look at the post and cringed somewhat wondering what possessed me to post it in the first place (oh well). It would be ok if it were for a cartoon engine but not for a strait faced attempt at suspending someone's disbelief (which it doesn't). I have a few ideas that need to be tried which hopefully will fix some of the disparities of the last attempt. That's probably what possessed me to post it, to force me to show progress on fixing the awful thing....,

    -Gil