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Thread: Ag Model PA-18 window in place of hopper hatch. Is that an STC ?

  1. #1
    Alex Clark's Avatar
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    Ag Model PA-18 window in place of hopper hatch. Is that an STC ?

    I have seen a couple A model 18s with lexan windows above the cargo bay area.
    Is that an STC or something more like an old field approval?
    Float and Tailwheel CFI,
    Dragonfly Aero
    Homer, Alaska
    dragonfly@alaska.net

    http://www.floatplanealaska.com

    or http://www.dragonflyaero.net

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    cubpilot2's Avatar
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    Alex
    If you see one with only glass on the top it is most likely a field approval from long ago. Good luck getting one now.

    There is only one STC to remove the hatch, install tubing and lexan on top and sides similer to L21.
    Flanagan STC SA887CE owned by Cub Crafters.
    Last edited by cubpilot2; 11-27-2020 at 01:48 AM.
    Ed
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    I used to fly one that had the hopper cover installed, but the fill lid was replaced with lexan. Based on the TCDS, the hopper cover is a required item. That one I mentioned, at the last fuselage rebuild, a regular PA-18 superstructure was installed, so no more flat back or hopper cover.


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    I think it’s the Flanagan STC and Cubcrafters owns it.

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    Alex Clark's Avatar
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    While 18 shopping lately I have seen two A models with hopper area windows. Like this one.
    One had X bracing inside, I am not sure about the other.
    I am looking at another 18A that does not have it, and the idea keeps floating around in my head..
    Attached Images Attached Images   
    Float and Tailwheel CFI,
    Dragonfly Aero
    Homer, Alaska
    dragonfly@alaska.net

    http://www.floatplanealaska.com

    or http://www.dragonflyaero.net
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  6. #6
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by Alex Clark View Post
    While 18 shopping lately I have seen two A models with hopper area windows. Like this one.
    One had X bracing inside, I am not sure about the other.
    I am looking at another 18A that does not have it, and the idea keeps floating around in my head..
    common...

  7. #7
    Alex Clark's Avatar
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    So Mike I take-it this is not the Flanigan STC. Just replacing the lid material with Lexan?
    Float and Tailwheel CFI,
    Dragonfly Aero
    Homer, Alaska
    dragonfly@alaska.net

    http://www.floatplanealaska.com

    or http://www.dragonflyaero.net

  8. #8
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by Alex Clark View Post
    So Mike I take-it this is not the Flanigan STC. Just replacing the lid material with Lexan?
    i didn't say that.... just a common mod

  9. #9
    cubpilot2's Avatar
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    Cub with Flanagan stc
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    Ed
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  10. #10
    skywagon8a's Avatar
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    Quote Originally Posted by Alex Clark View Post
    While 18 shopping lately I have seen two A models with hopper area windows. Like this one.
    One had X bracing inside, I am not sure about the other.
    I am looking at another 18A that does not have it, and the idea keeps floating around in my head..
    Looking at this I'm asking myself "What must be done to make this work?" The Ag model has a structural panel with a trap door. In order to remove the hopper, the panel comes off the fuselage top and the attachment where the seat back usually goes is disconnected. This is replaced with the removable seat back cross bar. Then I look at the fuselage drawing and notice a V shaped collection of tubing which is welded to the rest of the primary structure in the two place version over the space where the hopper goes. "Why is this there?" It appears it is to tie the wing center section to the aft portion of the fuselage. Aha! 2+2=4! That V tubing structure is doing the same job as the plate which covers the hopper. Conclusion, to remove the hopper plate some form of tubing or other structural member has to go in to replace it. The only question Which I can't answer is "Does the hopper cover plate utilize enough fasteners to be included as part of the structural support for it's frame?" If "yes" then what ever is done with the cover plate must also be done with the frame. If "no" then the frame could be left on and the cover could be replaced with Lexan as a minor alteration.
    So Alex, In those pictures is that the hopper frame surrounding the Lexan? Or is that just something holding the Lexan in place?



    Fuselage drawing:
    http://www.supercubproject.com/drawi...s/A3250005.pdf A3250005.pdf
    A3250005.pdf

    My suspicions are that the cover plate is part of the frame structure which is maintaining the proper strength and load path between the wing center section and the aft fuselage. And that the V shaped tubing structure or a suitable alternative is required. Perhaps a bolt in V?
    N1PA

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    now im curious as to what is under mine....it has been fabric'd over

  12. #12
    daedgerton's Avatar
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    I just purchased the Flanagan STC for my 18A. Tucked away in my files for rebuild time... Good 18A's are getting tough to find! PA-22/20-160 should chime in here at some point... He know's the "A" very well...

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    Click image for larger version. 

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ID:	52593Here’s the structure that replaces the hopper lid on the Flanagan stc

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    cubpilot2's Avatar
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    Quote Originally Posted by skywagon8a View Post
    Looking at this I'm asking myself "What must be done to make this work?" The Ag model has a structural panel with a trap door. In order to remove the hopper, the panel comes off the fuselage top and the attachment where the seat back usually goes is disconnected. This is replaced with the removable seat back cross bar. Then I look at the fuselage drawing and notice a V shaped collection of tubing which is welded to the rest of the primary structure in the two place version over the space where the hopper goes. "Why is this there?" It appears it is to tie the wing center section to the aft portion of the fuselage. Aha! 2+2=4! That V tubing structure is doing the same job as the plate which covers the hopper. Conclusion, to remove the hopper plate some form of tubing or other structural member has to go in to replace it. The only question Which I can't answer is "Does the hopper cover plate utilize enough fasteners to be included as part of the structural support for it's frame?" If "yes" then what ever is done with the cover plate must also be done with the frame. If "no" then the frame could be left on and the cover could be replaced with Lexan as a minor alteration.
    So Alex, In those pictures is that the hopper frame surrounding the Lexan? Or is that just something holding the Lexan in place?



    Fuselage drawing:
    http://www.supercubproject.com/drawi...s/A3250005.pdf A3250005.pdf
    A3250005.pdf

    My suspicions are that the cover plate is part of the frame structure which is maintaining the proper strength and load path between the wing center section and the aft fuselage. And that the V shaped tubing structure or a suitable alternative is required. Perhaps a bolt in V?

    When the hopper is removed the structure is supported with an aluminum framework that bolts into the upper tubing just as the hopper did. This framework is similar to a picture frame around the hatch lid, which is attached to the cover. The cover itself also has several stiffners built into it and is held to the tubing structure with lots of screws into rivnuts in the tubing. Also several screws where it surrounds the door hatch.
    The hopper is a structural component when installed as it bolts into the tubing where the picture frame was removed and supports the structure The rear seat cross bar is removed and a long all thread rod went through the tank clamping it to the frame. Additional cross members are added to carry the weight.

    The picture frame and cover are structural. I can see swapping the hopper lid with plexiglass as a minor but nothing more.

    There is an STC that Steve Bryant owns that installs a V type tubing structure of the same design as the standard frame within the hopper bay, allowing the cover to be removed. The rectangular tubing frame remains in place and is covered over with fabric. The usable baggage area is reduced to the same volume as a standard 18.

    Most common approach has been to weld in an X brace or a diagonal tube with lateral supports. Atlee had used that approach on several. I have one of his drawings for it. Back then field approvals in Alaska were easy.
    Ed
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    If you read TC AR-7, note 3 states the PA-18A can be converted to standard when done per the manufacturers instructions dated (different dates based on model). As I recall, those instructions state that the hopper cover is required when the hopper is removed. It’s been a while since I worked on a PA-18A, so I may be wrong, but that’s what I recall.


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    skywagon8a's Avatar
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    Quote Originally Posted by dgapilot View Post
    If you read TC AR-7, note 3 states the PA-18A can be converted to standard when done per the manufacturers instructions dated (different dates based on model). As I recall, those instructions state that the hopper cover is required when the hopper is removed. It’s been a while since I worked on a PA-18A, so I may be wrong, but that’s what I recall.
    Which means that it is a minor alteration log book entry, with only an A&P signature.
    N1PA

  17. #17
    cubpilot2's Avatar
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    [QUOTE=dgapilot;790199]If you read TC AR-7, note 3 states the PA-18A can be converted to standard when done per the manufacturers instructions dated (different dates based on model). As I recall, those instructions state that the hopper cover is required when the hopper is removed. It’s been a while since I worked on a PA-18A, so I may be wrong, but that’s what I recall.


    Yes
    As long as the aircraft is in “dual category”; a Standard and Restricted Airworthiness certificate. Some did not, depending on how they left the factory.

    I own two that were never sprayers as they both came directly to Alaska.
    Ed

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    BC12D-4-85's Avatar
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    FWIW....The pic Alex shows is of the standard hopper cover that's still bolted per factory specs to the upper tubing. A&P person or persons unknown removed the center portion of the metal hopper hatch and replaced it with Lexan and window tint. It's been like that for thousands of hours and is apparently still holding hands.

    Gary

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    Sure looks like someone took the hoper lid frame out and welded an X-brace in its place then put the plexiglass over it. Hard to tell for sure but I’ve seen several done that way right or wrong.
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    BC12D-4-85's Avatar
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    Gary
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