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Thread: Cooling air inlet duct opening.

  1. #1
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    Default Cooling air inlet duct opening.

    I am cutting the lower cowl for the radiator scoop. I would like to see the finished work (painted or not) of how people contoured the inlet, if anyone is willing to share. Did you use super fil on the edges? I was going to round the inlet. Do most make the transition a sharp corner, or a rounded edge? Does it affect airflow either way?

    I did see tropicals work. If you did it same way as he did, no need to reply.

    steve
    Last edited by Flyboy66; 05-11-2019 at 07:02 AM. Reason: More questions

  2. #2
    Senior Member Dave S's Avatar
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    Default Re: Cooling air inlet duct opening.

    Here's some.....

    Decided to reinforce the lower lip with a piece of aluminum

    Also found later that the cowl behind the radiator/below the firewall was prone to flapping from engine vibration. Fixed that with a perpendicular aluminum bar riveted to the inside of the cowl behind the radiator/below the firewall.
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    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  3. #3
    Senior Member aviator79's Avatar
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    Default Re: Cooling air inlet duct opening.

    I don't have any good pictures on hand, but I used Super Fil and made smooth transitions. The newer versions of the lower cowl have a stiffener glassed in the location Dave mentions behind the radiator, and the instructions will have you bond in a scrap piece of fiberglass to reinforce the lower lip.
    --Brian
    Flying - S7SS

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    Senior Member jiott's Avatar
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    Default Re: Cooling air inlet duct opening.

    I used fairly sharp edges, using SuperFill. I like the look of crisp edges for NACA ducts better than rounded. Personal preference. Be sure you have the duct glued in solidly with Hysol before starting the SuperFill; a friend has his crack loose after several hundred hours.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  5. #5
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    Default Re: Cooling air inlet duct opening.

    My cowling has a ridge glassed in (from factory) that is about 1/2” tall and is below, or maybe below and behind where the radiator will be located, and goes across the bottom where it is flat. I suspect it is to address that issue. Does your cowl have that?

    I glassed in the duct, and will be laying strips over the edges of the duct extending onto the cowl.
    Last edited by Flyboy66; 05-11-2019 at 11:38 AM. Reason: Mor stuff

  6. #6
    Senior Member efwd's Avatar
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    Default Re: Cooling air inlet duct opening.

    I installed mine as Dave did. At the time, I had read about NACA duct design and testing. If I recall, they are designed for maximum efficiency by having the leading edge perpendicular to the relative wind as Dave has his shaped. Also, some people have cut the aft edge round as well. That gives a tear drop shape and you are able to look right into the hose. Google NACA Vent and see if you find the same article I read on the subject. Sorry, I can't recall the source.
    Eddie Forward
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    SS7, 912iS, Garmin G3X

  7. #7
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    Default Re: Cooling air inlet duct opening.

    Quote Originally Posted by efwd View Post
    I installed mine as Dave did. At the time, I had read about NACA duct design and testing. If I recall, they are designed for maximum efficiency by having the leading edge perpendicular to the relative wind as Dave has his shaped. Also, some people have cut the aft edge round as well. That gives a tear drop shape and you are able to look right into the hose. Google NACA Vent and see if you find the same article I read on the subject. Sorry, I can't recall the source.
    No need. After looking at my work, I think I like the crisp edge appearance rather than the extra work required for rounded edges. I don’t call it lazy anymore. I am becoming an expert at minimum effort.
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    Last edited by Flyboy66; 05-11-2019 at 11:52 AM.

  8. #8
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    Default Re: Cooling air inlet duct opening.

    Alright. I have radiator attached to oil cooler. Waiting for some SS from Kitfox to make the brackets for hanging it on the airframe (aluminum temporary straps for now). It says to set it on some 3/16” shims on the floor if the cowl, but there is a ridge across the bottom (can be seen in comment before this one), and if I put shims under it, the radiator will extend even further above the duct. Modifying the duct is no problem, as I am a fiberglass guy, but I am wondering if this is the way everyone else is doing it. Picture is without shims under radiator.

    I am inclined to cut the top of the duct and extend it up further to fully draft the oil cooler, and while I am at it, I think I would extend the sides if the duct back to force the air through the radiator rather than giving it an escape route around the sides.
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    Last edited by Flyboy66; 05-11-2019 at 01:33 PM.

  9. #9
    Senior Member efwd's Avatar
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    Default Re: Cooling air inlet duct opening.

    That is interesting. My cowl didn't come with that stiffener. The manual directed me to cut the hole and then reinforcing the long edge of the hole by attaching additional fiberglass across that edge. I just used hysol to glue down remnant cowl piece. My oil cooler is mounted a good half inch lower than yours which allowed the NACA vent to slide right over the engine oil cooler after I cut notches in it to receive the hose fittings.
    BTW, I recommend using something like cowl baffle rubber. I aim to add some of that and cut away some of the fiberglass as it makes it a bit of a challenge when you try to install the lower cowl. Two ridged structures meeting up make it challenging to install the cowl without screwing up some of the fins on the oil cooler.
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    Last edited by efwd; 05-11-2019 at 01:55 PM.
    Eddie Forward
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    SS7, 912iS, Garmin G3X

  10. #10
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    Default Re: Cooling air inlet duct opening.

    Ok, that makes more sense. I thought the oil cooler was supposed to be 1/8” behind the duct, but I did not try to wiggle the oil cooler in and locate the radiator up against the duct. Headed out now.

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