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Thread: Elbow engine

  1. #1
    mklotz mklotz's Avatar
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    Elbow engine

    The so-called elbow engine is a popular model among engine modelers...




    The engine consists of two, free to rotate, cylinder blocks with three equally-spaced cylinders mounted at 90 deg to each other. One block is pivoted to the base and the other, carrying the flywheel is pivoted on an upright. The pistons connect these two blocks. Each piston actually consists of two orthogonal pistons, each fitted into a cylinder in one of the blocks. Valving is passive and consists of recesses carved into the base and upright behind each block. Holes drilled through the base and upright conduct air/steam to the valves.

    Air is supplied simultaneously to each piston of a pair. This forces them out of their respective blocks and, by this action, generates a torque on the blocks and this leads to rotation of the blocks.

    At first blush it looks like it should be mechanically locked up and unable to rotate. Yet it does, as the video below proves.

    Two remarks about this engine...

    It's a hideous air hog, perhaps the least efficient engine I've ever built. There's really no way to seal it properly and it needs about 20 psi to get going. Thankfully, it's only a novelty and no one would ever build one for a practical application.

    Building these engines is no easy task. Maintaining orthogonality between the cylinders and bending the piston assemblies to exact orthogonality is absolutely essential. Don't try it as your first engine modelling attempt.


    Last edited by mklotz; 07-23-2017 at 08:04 AM.
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  2. The Following 8 Users Say Thank You to mklotz For This Useful Post:

    Captainleeward (07-27-2016), Jon (06-14-2016), kngtek (04-25-2017), KustomsbyKent (04-24-2017), lazarus (06-15-2016), Paul Jones (08-22-2016), Strostkovy (07-04-2016), Toolmaker51 (06-14-2016)

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    As if straight cylinders, properly fit pistons and rings aren't tough enough already!
    Holy Moley Marv, had to watch the video 2x, with the look of amazement each time. Cool as can be; for sure.

    Toolmaker51; on HMT
    Trying to learn something everyday keeps me purdy dang busy...

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    Looks like a lot of thought went into the design. Another engineering marvel. If you could run it off magnets, you might become rich.
    Really cool build. I like weird things like this.

    Ben

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    mklotz mklotz's Avatar
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    I neglected to mention...

    Since the engine is totally symmetric reversing it involves nothing more than moving the air supply from the "intake" to the "exhaust" port.
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    The video is really helpful to show how it works. The picture really looks like it would be mechanically locked until you really thinking about what is moving and how that works. I had it worked out in my mind from the picture, then the video confirmed that.
    Really cool that you got it fabricated and working. I bet it is pretty amusing to hear people argue about why it won't work at these engine shows!

    Do you have any drawings or schematics on the inner workings, and what you can't see because of the flywheel? Just curious to learn more.

    Thanks for sharing with us!

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    mklotz mklotz's Avatar
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    Quote Originally Posted by KustomsbyKent View Post
    Do you have any drawings or schematics on the inner workings, and what you can't see because of the flywheel? Just curious to learn more.

    Thanks for sharing with us!
    The original plans for the Elbow Engine are here...

    http://www.john-tom.com/MyPlans/Stea...lbowEngine.pdf

    My version incorporates a number of deviations from the plans to accommodate the tools and materials I had available but functionally my engine is the same as the plans.

    Because the engine is totally symmetric it can be reversed by merely interchanging the inlet and exhaust attachments.

    If you're a fan of unusual and complex mechanical drives, you may enjoy watching the Almond right angle drive in action...



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