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Thread: reenforcing lower cowl

  1. #1
    Senior Member Dorsal's Avatar
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    Default reenforcing lower cowl

    On my list of "once I retire" things I have for my plane is to chase down some of the vibrations (small but noticeable) I feel at various flight attitudes. One that I am fairly confident of is the lower cowl which strikes me as a little flimsy along the back edge. Have others strengthened this? put a reenforcing strip across or made an attach strap to the firewall?
    Dorsal ~~^~~
    Series 7 - Tri-Gear
    912 ULS Warp Drive

  2. #2
    Senior Member Esser's Avatar
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    Default Re: reenforcing lower cowl

    My kit has a large reinforcement that doubles up as a damn for the air just below the rad. I find mine quite sturdy. Does yours not have this?
    ------------------
    Josh Esser
    Flying SS7
    Rotax 914iS
    AirMaster Prop

    Edmonton, AB, CWL3

  3. #3
    Senior Member Dave S's Avatar
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    Default Re: reenforcing lower cowl

    Dorsal,


    Similar issue up here. Back when I started testing the plane, one of my hangar neighbors observed that the lower rear part of the cowl where the air exits the cowl behind the radiator was vibrating up and down quite visibly.



    With the nose gear, some material is cut out of the rear of the cowl bottom and I originally though the cutout was in part responsible for weaking this part of the cowl and exacerbating the vibration problem - not so sure now.



    To reinforce the cowl in this area, I riveted an aluminum bar across the bottom of the cowl in this area with the bar on the inside surface of the cowl. That seems to have solved the issue. I don't have the precise dimension of the aluminum bar right off hand, but I believe it was approximately 1/8" thick.


    The other thing I did on the cowl bottom was to rivet in a fabricated aluminum "U" shaped edge for the NACA duct - this won't help the vibration at the back issue but I wanted something a bit more solid than the simple fiberglass edge. Photo attached; but, photo included to show approximately where the rear lip reinforcing bar went in later - the bar was riveted in just a bit forward from the notch in the rear of the cowl for the nose gear, on the flat part of the cowl, so it would not be near the radiator bottom.



    If I recall, the vintage of your kit and mine is about the same.
    Attached Images Attached Images
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  4. #4
    Senior Member Dorsal's Avatar
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    Default Re: reenforcing lower cowl

    Esser, No it does not, do you have a pic? I like the idea of closing the gap under the radiator, any challenges getting the cowl on and off?

    Dave, that is kind of what I was thinking, how wide is your bar (was thinking 1.5" or 2")?
    Dorsal ~~^~~
    Series 7 - Tri-Gear
    912 ULS Warp Drive

  5. #5
    Senior Member Dave S's Avatar
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    Default Re: reenforcing lower cowl

    Dorsal,


    I'll get an exact measurement tomorrow and get back to you.
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  6. #6
    Senior Member Dorsal's Avatar
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    Default Re: reenforcing lower cowl

    My solution, noticeably less vibration in climb out, seems less in cruise too.
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    Dorsal ~~^~~
    Series 7 - Tri-Gear
    912 ULS Warp Drive

  7. #7
    Senior Member Esser's Avatar
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    Default Re: reenforcing lower cowl

    Not sure how well you can see it
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    ------------------
    Josh Esser
    Flying SS7
    Rotax 914iS
    AirMaster Prop

    Edmonton, AB, CWL3

  8. #8
    Senior Member Dorsal's Avatar
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    Default Re: reenforcing lower cowl

    Thanks, seems the same idea though I don't think anything will bond to the bottom of my cowl now, has become kinda oily over the years.
    Dorsal ~~^~~
    Series 7 - Tri-Gear
    912 ULS Warp Drive

  9. #9
    Senior Member Esser's Avatar
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    Default Re: reenforcing lower cowl

    Some alcohol and a scrub brush should fix that up fairly easily
    ------------------
    Josh Esser
    Flying SS7
    Rotax 914iS
    AirMaster Prop

    Edmonton, AB, CWL3

  10. #10
    Senior Member efwd's Avatar
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    Default Re: reenforcing lower cowl

    How would one be able to tell they need to reinforce this area. The builder manual advised to reinforce the NACA opening but nothing of this much wider surface. Then again its not facing into the relative wind. What was the experience you had in flight that led you to reinforce?
    Eddie
    Eddie Forward
    Flying
    SS7, 912iS, Garmin G3X

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