fiberglass coupler anchor depth

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rbraibish

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I am installing a fiberglass coupler into a fiberglass airframe. I have long used a coupler-airframe overlap length of about 1-1.5 calibers for the separating end of the coupler - that is, how much coupler projects out from the airframe. Up until now I have just used the same overlap for the end of the coupler that is epoxied into the other section of airframe. I would like some input as to how little of an overlap would be "required" to adequately secure a coupler tube to the fixed side of the airframe/coupler joint.
If I have a 4" airframe, would 2" (.5 caliber) of epoxied overlap be sufficient assuming a full good epoxy bond between the coupler and airframe? Could I use something less, do I need something more? This particular location is at the forward end of a fincan with a zipperless design.
I understand that the length of the overlap on the un-epoxied side helps maintain airframe integrity across the joint, but for the epoxied side, just how little overlap have you had success with? I am interested in maximizing the overlap on the loose side by adjusting the depth of the bonded side.
Looking mostly for real-life experience here, I do appreciate opinions, but I would like to know what has worked (and has not worked) for folks.
Thanks.

Robert
 

COrocket

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Yeah for fiberglass 1/2 caliber should be fine when you are gluing the coupler to the tube. You want to use more on sliding joints so there is less wiggle and chance of binding.
 

markkoelsch

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I like 1-1.5 calibers. In sense it is really about the fit between coupler and air frame. If it is snug 1 caliber should be fine.
 

Bat-mite

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Yeah for fiberglass 1/2 caliber should be fine when you are gluing the coupler to the tube. You want to use more on sliding joints so there is less wiggle and chance of binding.
Yeah, just to reiterate: you never want to the free end to be shorter than the fixed end.
 

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