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Thread: Lower cowl square fillter

  1. #1
    cgoldy's Avatar
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    Lower cowl square fillter

    I am finally getting around to making my new Carbon fibre lower cowl around a square filter. Any photos of square filter lowers cowls would be much appreciated.

    Thanks in advance

    Cgoldy
    Back Country O-375 wide body extended wing cub

  2. #2
    skywagon8a's Avatar
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    Does this help?


    Click image for larger version. 

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  3. #3
    cgoldy's Avatar
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    Thanks Pete,

    Am I going to regret converting to a square filter? Will my O.375 need more air?

    cgoldy
    Back Country O-375 wide body extended wing cub

  4. #4
    skywagon8a's Avatar
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    I can't answer that question Colin. My sense is that bigger is better for breathing. Was the interference with your exhaust too big an issue to work around with the round filter? Is there a longer smaller diameter filter available which would be more compatible with your installation? I can't think of any larger production airplane engine installations which use small square filters. Since you are making your own carbon fiber lower cowl, couldn't you redesign the shape to make your exhaust and round filter be compatible?

    What about something like this which seems compact with more area than a square one? This is from a Cessna 180.

    Last edited by skywagon8a; 06-01-2020 at 07:33 AM.
    N1PA

  5. #5
    CamTom12's Avatar
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    Flat filters are supposed to flow more smooth air than cone filters with the same area, since the air continues on a straight path and doesn’t have to make a turn to get to the carb.

    I don’t know how much of a real difference it makes in a practical application though. Just figure how much filter area you can get with each type filter in your space available and go with the bigger area filter type.

  6. #6
    BC12D-4-85's Avatar
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    One test for filter restriction is to install a manifold pressure gauge (temp or permanent to the induction system or cylinder). Note the MP value before startup, then any decrease in MP at full static rpm with and without a filter of choice. Lower decrease in MP or static rpm with filter installed = less filter restriction and more power. A tight seal around the carb heat flap is also important. The more the leakage of heated air the lower the power.

    Edit: This air filter comparison briefly discusses Delta-P which the above can help test: https://www.youtube.com/watch?v=HG2DA_aM1p4

    Gary
    Last edited by BC12D-4-85; 06-01-2020 at 02:09 PM.

  7. #7
    cgoldy's Avatar
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    Good info Garry. Pete, I have had cracking issues with the lower cowl and always had trouble sealing off the round filter. Thought it would be simpler, lighter and less flex with the square. Exhaust clearance problems have been fixed. The photo in your last post can’t be seen. What filter were you referring too?
    Back Country O-375 wide body extended wing cub

  8. #8
    skywagon8a's Avatar
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    Colin, There appears to be a landing strip along side the Reynolds Creek and the Seven Mile Creek in Moogerah. Would this be your airstrip?
    N1PA

  9. #9
    cgoldy's Avatar
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    You Sleuth. If you can find Mount Moon, just south of lake Moogerah. Mount Moon is on our place and Reynolds creek runs through the middle. 2300 acres. We have a 1500 ft 5* uphill strip 110/290 just to the west of Mount Moon and east of Croftby rd. We also have a 240 ft 15* strip on top of a cliff just to the south of Mount Moon. Only two planes have ever landed that one so far. Come over sometime and you can borrow my cub and explore Australia. The strip you found is an irrigation plot now I think.
    Back Country O-375 wide body extended wing cub

  10. #10
    skywagon8a's Avatar
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    I think I found it. There is a trapezoidal shaped stock pond to the north of the air strip near the house. I do not see the Cub anywhere though. Wait is that a hangar to the east of the house? I appreciate the invitation, though it is highly unlikely that I will ever travel that far afield again. Thank you, that is a generous offer. I see a couple of possibilities for the 240 foot strip near the Alford Creek.
    N1PA

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