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Cabin Air vents in boot cowl

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  • Cabin Air vents in boot cowl

    I’ve started a new thread on this topic - there is a similar thread regarding wing root vents with a lot of good info.

    My plan is to install NACA intakes on the upper boot cowl, with a short scat tube feeding 2 inch panel mounted air vents on each side of the instrument panel.

    Some of you have already done this, and I see there were some reported issues where engine compartment cooling vents allowed warm air into the cold air intakes. I don’t plan to have engine compartment venting on the sides, just the standard lower outlet with a cowl flap.

    Has anyone experienced rain water running down the cowl and entering the NACA ducts while parked on the ground?

    If so, does it enter the pax compartment when speed increases, or does it trickle back out the way it entered as the tail comes up ?

    Has anyone managed to combine both warm and cold air into the same outlet vents - similar to a car ?

    Are there any other considerations I should be thinking of ?
    Nev Bailey
    Christchurch, NZ
    Builders-log
    YouTube

  • #2
    My experience is that not enough airflow happens from NACA ducts on the boot cowl. For the Texas summer heat. I prefer the Cessna style leading edge fresh air inlets. Mark

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    • #3
      A Kitplanes article in 2017 shows +/- pressure that a fuselage skin experiences in flight. Magenta is low pressure. A vent located in a magenta area may experience negative pressure and suck air out of the fuselage.

      Screen Shot 2020-10-10 at 1.04.06 PM.png

      I see Cub Crafters puts vents on the lower cowl in the same area that the above aircraft has magenta. I suppose.....its function is to suck air out of the lower cowling. Maybe air can accelerate around a fuselage like it does our wing creating low pressure.
      Screen Shot 2020-10-10 at 1.12.47 PM.png
      Brooks Cone
      Southeast Michigan
      Patrol #303, Kit build

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      • #4
        Every airplane is a little different but they work amazingly well on my Murphy. At idle they blow hard enough to help, by 120mph they blow harder than the strongest setting on my car. The eyeball vent is located perfectly to blow right up your shorts too!

        I'm hoping to set up the same system on my Bearhawk. I've never had a problem with water getting in and my plane lives outside.

        I guess placement is critical though. I'm not sure how to figure out exactly where to put them. I May wait until it's flying and tape some string to the boot cowl and see what the air flow looks like.

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        • #5
          Originally posted by TimTall View Post
          The eyeball vent is located perfectly to blow right up your shorts too!
          Great data point thanks Tim !!

          My understanding is that the NACA by design will draw air in as it creates its own low pressure area in the divergent duct. Presumably for the sum of the pressures to remain equal the airflow should increase in dynamic pressure.......my memory of Bernoulli and his ideas being somewhat distant......
          Nev Bailey
          Christchurch, NZ
          Builders-log
          YouTube

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          • svyolo
            svyolo commented
            Editing a comment
            I they don't work, at least they will still look cool. Make up something if somebody asks.

        • #6
          In the RV10, the NACA vents are just forward of and below the windscreen - work great.....

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          • #7
            I wanted NACA intakes in my boot cowl and vents in my panel but I did not have the panel space and putting them below the panel would interfere with my legs. So far the only time I need vents is in the summer while taxiing so I just open the door.

            Good chance I'm remembering wrong but I think NACA vents rely on smooth airflow over the surface. Being in a low-pressure zone should not be a significant factor as long as the airflow is smooth. Tuft testing is a good idea.
            Scratch Built 4-place Bearhawk. Continental IO-360, 88” C203 McCauley prop.

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            • Pbruce
              Pbruce commented
              Editing a comment
              The ones in my RV9 worked hardly at all. It seems comments about placement and different types are accurate. My vents were of the most basic cheapest type available, and they leaked badly when dialed closed in winter, so consider investing in quality. I’d love to know if they work out on BH Patrol.

            • Battson
              Battson commented
              Editing a comment
              The new wing root vents sold by ACS definitely don't leak.

          • #8
            I am planning to add NACA vents to my boot cowl. Mike Silvernagle used them on his Patrol and says they work extremely well. On my Citabria there are little vent "windows" on the boot cowl that work very well. I find air coming up from around my legs is more effective for cooling in summer than just Cessna style vents blasting me in the face.

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            • #9
              I wonder if the performance of all air vents is just as dependent on the outlet for the airflow as it is the inlet ? I’m planning to have an outlet at the rear underside of the fuselage near the tailwheel, basically a hole in the fabric.
              Nev Bailey
              Christchurch, NZ
              Builders-log
              YouTube

              Comment


              • #10
                The vent in the boot cowl goes to scat tubing routed under the floor to vents for the back seat. I haven't had any issues with water. That vent is mounted in an access panel that provides easier access to the back of the instrument panel and I also have a panel without the vent for cold weather. The vent in the engine cowl routes air to the muffler heat muff.
                You do not have permission to view this gallery.
                This gallery has 1 photos.
                Rollie VanDorn
                Zanesville, OH
                Patrol Quick Build

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