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Thread: Cog Belt PSRU

  1. #1
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    Cog Belt PSRU

    Hi, all you rotary people. I'm a new member, and I just started to build my BushCaddy L-164 plane. My BushCaddy will be powered with a new (89 miles on it) RENESIS engine. I plan on using the factory intake so I need to lower the engine about 8" to clear the cowl. Does anyone have any info as to where I might be able to buy a cog belt PSRU for my RENESIS engine? Also if anyone has done a rotary with a cog belt PSRU I would love to talk to them.

    I'm open to all pro's and con's on this type of PSRU on a rotary.

    Many Thanks,
    Bob F.

  2. #2
    Super Moderator orion's Avatar
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    Personally, I haven't seen any belt drive (cog, HTD, etc.) reduction systems used on rotarys for quite some time. Most of the reductions used today are gear based, although I think I remember one some time back that used the silent chain.

    There are pros and cons to the belts and I think the cons outweigh the benefits. On the pro side, the cog belts tend to be lighter than the gear or chain based units, they are easier to inspect, do not require lubrication, and if wear is detected, are easier to repair. The units also have inherent properties that allow the belts to aleviate some levels of the torsional feedback problem (without going to fancy couplings) that is problematic with the rotary application.

    On the con side, the cog belt systems require very precise allignment - even very small amounts of inaccuracy can substantially reduce the life of the belt or even that of the cog pulleys themsleves. They are sensitive to contamination. And in case of torsional feedback, can disintegrate rather rapidly.

    Torsional feedback is energy. This energy has to be absorbed by the system and so is seen by the components as heat. If not cooled or taken care of properly, the life of the unit can be as little as a few hours. In order for all this to be done correctly, the reduction drive has to be designed very carefully, addressing all these issues in a way that long life is assured. I have not seen any cog based systems that do all these things well and that is I think one of the reasons that we don't tend to see these today in any application but especially on the rotary engines.

  3. #3
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    I am not sure how much you know about the rotary engines in airplanes, but if it is not much. Then you really should read up on what it takes to make them work in airplanes.

    http://www.canardaviationforum.dmt.net Has many threads about rotary engines, with links to many helpful websites.

    http://rotaryresources.com/index.php - videos, parts

    http://www.racingbeat.com/ - aluminum housings, parts for Mazdas

    http://rotaryaviation.com/ "real world solutions" - reduction drives, renesis info, parts, videos

    http://www.yawpower.com/ - engine building, parts, tech articles

    http://www.mistral-engines.com/ reduction drives, engines parts

    You can also search this website for lots of information.

    Personally, I would rework the top part of the intake to work with the part that attaches to the block. (assuming my memory of the engine is correct)

  4. #4
    Registered User lehanover's Avatar
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    The belt drive from "Belted Air Power would work fine.

    Also Ken Welter at "Rotary Coot sells a number of ratios for his belted reduction system.

    There is another made in the northwest but I forgot the name.

    Use the Google search engine to find what you want.


    Lynn E. Hanover

  5. #5
    Super Moderator orion's Avatar
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    The belt reduction drive from our area (Northwest) is from Northwest Aero Products. It is a good, durable unit but to the best of my knowlege it has never been installed nor tested on a rotary. I'm not sure that he even has an option for that installation - most of his components are designed for mounting on a GM V-8 or V6.

    Before you select a reduction drive for a rotary, make sure the developer has actually done that installation and tested it. Rotary's have unique characteristics that require specialized attention, especially in areas of torsional feedback and pulse harmonics. If all the developer does is just puts a rigid coupling or a spring plate between the engine and redrive, look elsewhere.

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