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  1. #1

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    Flywheel fins - what is the limit?

    When we convert the engines, we see that on the back of the flywheel it says 'do not alter - risk of burst damage'. We have been cutting the fins flush with the magnets. The workshops like BB, Paragon, Carr also do so. Even the US engiens are sold like that. So far it seems to be fine. Now I hear someone cutting the fins right upto the root to decrease the weight and minimize air resistance. I also want to do that but is it safe to do so? Does anyone has any knowledge of flywheel breaking away?

  2. #2

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    Flywheel fins - what is the limit?

    I've seen them cut back to where the magnet is showing and the only thing left is the magnet and the counter balance..the rest of the flywheel cut out....

    Looked verrrrrrry dangerous to me...I wouldn't run one like cut up like that..
    I never met a Chaos I didn\'t like

  3. #3

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    Flywheel fins - what is the limit?

    I ran mine like that up to 8500 RPM during bench testing. I'll admit the first 3 times I started it I was afraid it might blow up, but after tach'ing it at 8500 (from behind of course) I felt better. When I put it into a plane, I increased the load and brought the RPM's down just under 7500.

    If you plan to do this, I STRONGLY urge you to do everything you can to ensure it is balanced when you're finished.

    Here's a pic of mine after fin removal, before final polishing and balancing.
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    I try to learn from other people\'s mistakes...
    I won\'t live long enough to make them all myself.

    Dennis aka Strato911
    MAAC 43408

  4. #4
    Volfy's Avatar
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    Flywheel fins - what is the limit?

    The fins don't add much structural stength to the flywheel. It is safe to cut them completely off. The webbing between the two magnet blocks (or magnet and counterweight blocks) are a different story though. They are strudtural. Depending on the design, it may be safe to eliminate them, but I wouldn't do it if you have any doubt. If you must save weight, drill lightening hole on the webbing and even the two magnet blocks (not into the ferrite magnets themselves, of course). It's safe to do so for balance purposes anyway.

    Whatever you do though, make sure you finish grind the surfaces smooth so that there are no stress risers, which may induce crack formation.
    Si vis pacem, para bellum.

  5. #5

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    Flywheel fins - what is the limit?

    strato911:
    Man that sure is a rough looking flywheel. How pretty did the finished product look? Go ahead and show us the results of your labors.
    did you just static balance?
    trying to tax into prosperity is like a man standing in a bucket and trying to lift himself up by the handle W. Churchill

  6. #6

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    Flywheel fins - what is the limit?

    Sorry Mike, I don't have any good "AFTER" photos. From that photo onward, I used continually finer grinding disks, then polishing wheels (the ones used for making dental crowns). There are still bumps remaining where the fins used to be, but they are very smooth, and brightly polished.


    As for balancing, I made a temporary adapter so I could use a prop balancer. Once I obtained static balance, I spun it as fast as I could by hand and removed any wobble. I then re-polished the areas I had to grind for balancing, and re-confirmed the balance.
    I try to learn from other people\'s mistakes...
    I won\'t live long enough to make them all myself.

    Dennis aka Strato911
    MAAC 43408

  7. #7

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    Flywheel fins - what is the limit?

    That was the first finned one I have seen where fins were removed behind/aft of the magnet area.
    did you notice enough difference (turbulence) to remove all of the fins on other flywheels? What was the approx weight savings?
    trying to tax into prosperity is like a man standing in a bucket and trying to lift himself up by the handle W. Churchill

  8. #8

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    Flywheel fins - what is the limit?

    That is the only engine I have converted so far, and I was trying to keep the weight to a minimum (3.0Lbs w/o muffler or prop). However, I did feel it was useless to leave the fins, since they are only there for cooling the cylinder head.

    Unfortunately, due to design problems the plane crashed on it's maiden flight, and the mount for the coil broke off the engine. I don't currently have the time or money to convert to electronic ignition, so it will have to wait.
    I try to learn from other people\'s mistakes...
    I won\'t live long enough to make them all myself.

    Dennis aka Strato911
    MAAC 43408


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