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Thread: Attaching Aluminum Skin to Steel Tube

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    Registered User GESchwarz's Avatar
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    Attaching Aluminum Skin to Steel Tube

    For crash-worthiness reasons my basically all-aluminum plane will have a welded 4130 steel tube cockpit cage, much like the Mooney. What are the best methods for attaching aluminum skins to steel tube, both permanently and removable for inspection and maintenance?
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    Registered User Careca's Avatar
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    Re: Attaching Aluminum Skin to Steel Tube

    You can do something like the guys in aerobatic aircraft and use rivnuts together with bolts to hold the detachable panels. See attached link:

    http://www.pitts-special-team.de/Laser/2_10_covers.html

    For fixed panels you can simply rivet them to the structure.

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    Re: Attaching Aluminum Skin to Steel Tube

    Are you concerned about galvanic corrosion?
    Last edited by Starman; January 20th, 2010 at 10:44 PM.

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    Registered User GESchwarz's Avatar
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    Re: Attaching Aluminum Skin to Steel Tube

    Careca,

    Thanks for the link. That's a great series of photos. I'm not sure, but were all of the screw and rivet holes made into steel tabs that were welded to the structural tube, or were some holes drilled directly into the structural tube?
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    Registered User Careca's Avatar
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    Re: Attaching Aluminum Skin to Steel Tube

    Gary,

    No holes should be drilled directly to the structural elements of the truss. You should weld tabs for the rivnuts or to rivet the panels, this way you will not compromise structural integrity and make it possible to use regular rivets instead of more expensive Cherry Rivets.
    Starman is also right and I would advise to prime the truss and panels to prevent galvanic corrosion.

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    Registered User GESchwarz's Avatar
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    Re: Attaching Aluminum Skin to Steel Tube

    Okay, Thanks.
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    Registered User Tom Nalevanko's Avatar
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    Re: Attaching Aluminum Skin to Steel Tube

    I agree that no holes should normally be drilled in the structural elements of a truss. However, a rectangular cross-section tube is often used in aircraft structures. The narrow part takes the tension and compression loads while the wide part is equivalent to a shear web. Very often, holes are drilled through the wide part to fix a bolt for a pulley or other purposes. There is nothing wrong with this but you should subtract out holes from any shear strength calculations. Alternatively you could weld a bushing into the hole with a re-inforcing flange.

    For example, in the picture, note that tabs are used to affix the composite shell and there is a tab without anything for a pulley. But there is a hole drilled in the wide side of the tube with attached pulley. The camera angle and nut makes the bolt look like it touches the narrow section of the tube. It is actually a diameter or more away.
    Attached Thumbnails Attached Thumbnails Attaching Aluminum Skin to Steel Tube-image-2-4-3-98.jpg  

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