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Thread: Model IV Firewall - Cowl

  1. #11
    Super Moderator Av8r3400's Avatar
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    Default Re: Model IV Firewall - Cowl

    I know and understand that there will never be a perfect seal on the firewall to cowl. However, the seal that I had was less than terrible. There was a noticeable leak of fumes and (cold Wisconsin) air into the cabin. Much more than was on my previous plane.

    This is my fault. I did not spend the time I should have on the firewall and cowl. The original builder used expanding foam to seal the very poorly fit cowl. I chose not to rework the same cowl and firewall to fit properly. (...and I can't stand the idea of using great stuff to seal the gap!)

    My idea is coming together and I'll get a photo or two of the finished product.


    As I said in the original post, in a long enough time line, I will rework the entire firewall forward on this plane, just not right now.
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
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  2. #12
    Senior Member
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    Default Re: Model IV Firewall - Cowl

    In regard to Dusty's comment about extending the bottom of the firewall back, I did that on my Avid Flyer. Controls and floorboards were installed before I covered the plane, so I ran the fabric all the way to the front first of all, as well as up the sides in front of the doors part way. In addition, I put a piece of thin aluminum sheet on the bottom of the plane from the firewall back to just in front of the landing gear. (standard bungee gear) My firewall bends back at the bottom about an inch, and the aluminum goes above it and they are fastened together and through the floorboards. I glued a few 1/2" thick wood blocks to the underside of the floorboards so I could run some screws up through the aluminum and hold it in place. Bent the sides of the aluminum up 90 degrees and put a few screws into small wood blocks glued to the top side of the floorboards. That seals up the bottom quite well. Northern Mn is cold in the winter and anything stopping the wind is welcome. (we have 3" of snow now, and it was +2 F last night) Hope you were able to follow my explanation. JImChuk

  3. #13
    Senior Member Dusty's Avatar
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    Default Re: Model IV Firewall - Cowl

    Quote Originally Posted by HighWing View Post
    Dusty,
    I have been thinking about your idea for several days. I have built two Model IVs and try as I might, the firewall seals were not perfect on either one. I put 900 hours on the first one and about a hundred on the second one. I guess I am curious of what exactly you are wanting to correct or prevent by the modification you are suggesting. One of the things I really like about the earlier models is the ready access to the back side of the panel, the pedals and the brake master cylinders by simply removing a couple dozen or so Clecos. If you are concerned about the CO possibility, my suggestion would be to put a monitor on your panel for a glance or two while flying. As I mentioned 900 hours on the first one and much of that was alongside other IV owners and none of us ever felt an issue with that risk given the typical "ventilation" elsewhere around the cockpit.
    Lowell
    My main reason for trying to get a better seal is cold air.I have tried different seals but my lower cowling is now a little distorted from the pressure from these.
    Additional panels must be easily removable for inspections ,as easy access is another great Kitfox feature I wouldn't want to lose.
    The rest of the cabin is surprisingly draft free.

  4. #14
    Guy Buchanan's Avatar
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    Default Re: Model IV Firewall - Cowl

    My upper cowl is split. I have a flange on the upper firewall that contains nutplates for both he forward and aft half. The purpose was to be able to totally seal the back half from rain, preventing nasty electrical problems, while leaving the forward half relatively easy to remove. The back half is sealed using standard white bathroom sealant. (No need for fire barrier.)

    The bottom cowl is still full length and to seal that to the firewall I had a bunch of stainless angle formed that has a rolled edge. I then attached these to both sides of the firewall such that by bending them I'd end up about 1/8" away from the cowl, all along the join. I stuffed the triangle gap between the two flanges with the 3M fire barrier moldable putty. It seals pretty well to the cowl. I run a line of 2" aluminum tape on the cowl where the seal is to get a better seal and to make it easier to clean. In case of a fire, the moldable putty chars and seals the engine compartment until the cowl burns.
    Attached Images Attached Images
    Guy Buchanan
    San Diego, CA
    Deceased K-IV 1200 / 912uls / 70" Warp 3cs

    gebuchanan@cox.net

  5. #15
    Super Moderator Av8r3400's Avatar
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    Default Re: Model IV Firewall - Cowl

    I like your idea of splitting the upper cowl into two pieces for weather sealing. Sounds like something to consider on my eventual front end rebuild.
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
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