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Hi all,

It's been hot here in pa in my CHT's have been hotter than I would like. Did some research and I'm thinking my inlet/exit openings are off.

117 square inches inlet versus 108 square inches exit.

4 inch cylinder holes, 9x3 oil cooler, 5x13 radiator hole, 1 exit hole at the bottom roughly 108 square inches.

Does anyone know the ratio from inlet to exit air?

I've read 120%,150%, and 1 to 3...

Where can someone measure their inlet versus exit openings on their plane for me?

 

Any help will be greatly appreciated.

Thx!

  • Re: Cowl inlet vs exit openinings

    by » 3 months ago


    Some pics if the inlet and exit

     

    https://photos.app.goo.gl/6jGojmCWXKFk7DLZ6


  • Re: Cowl inlet vs exit openinings

    by » 3 months ago


    What are the CHT and oil temps? What is the wide open throttle rpm in level flight?

     


    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


  • Re: Cowl inlet vs exit openinings

    by » 3 months ago


    On a hot day, cht will be in the 240 range on cylinder one and oil is around 220.

    I made the little air scoop in the pic for the radiator which helped. The radiator is angled backed and not perpendicular to the wind like the oil cooler.

    I also have k&n filters on the carbs. How much would hot combustion air contribute to a hotter engine?

    Wot in cruise is 5700.

     

    I've read lycomings have a specific in of water that should be measured with a manometer at the exit opening of the cowl to make sure there is enough air passing through the cowl for good cooling.

    Is there anything like that for the rotax?

    Thx!


  • Re: Cowl inlet vs exit openinings

    by » 3 months ago


    If 240F CHT and oil is only 220F is only on climb then that's fairly normal for hot summer climate. What rpm are you cruising at and are these cruise temps or climb temps? 

    Some have opened the front of their cowling opening more. Some people have added a small dam down at the bottom exit on their cowl to help bring more air flow through their cowl. It went all the way across the exit opening and protruded back and down about 2.5 inches. I don't have any pictures, but I have seen a number of them on forums and maybe even here quite a while ago,


    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


    Thank you said by: RotaxOwner Admin

  • Re: Cowl inlet vs exit openinings

    by » 3 months ago


    You say WOT in cruise is 5700... but you are not actually cruising at those rpms, are you?

    What engine are you running?


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