why weld-on instead of flox?

Does anyone know why Vans decided to use Weld-On instead of epoxy/flox to bond the plexi windows to the RV10 composite cabin lid?

one reason...

Epoxy doesn't adhere very well to plexiglass...

I'm trying to get down to the fundamentals of the bond- 10,000+ RV's flying have a fiberglass fairing bonding the forward section of the plexi to the airframe. So it must adhere reasonably well. Still seems to beg the question why weld-on instead of flox. Looking for some structural tensile/peel strength insight. Perhaps Scott McDaniels could chime in?

A fair percentage also have cracks where the epoxy meets the metal, too. (Different expansion rates)

Does the Weldon stay somewhat pliable after cure, like Sikaflex? If it does, perhaps that's the reason for using it.

Pilot8 said:

I'm trying to get down to the fundamentals of the bond- 10,000+ RV's flying have a fiberglass fairing bonding the forward section of the plexi to the airframe. So it must adhere reasonably well. Still seems to beg the question why weld-on instead of flox. Looking for some structural tensile/peel strength insight. Perhaps Scott McDaniels could chime in?

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Well, the 10,000 reference is not data. So be careful with assumptions from one application to another. You are on the right track looking for peel strength numbers.

Look up West Systems flame polishing and testing. They show the peel strength is very low, and include some test data of the various preparation methods. G-Flex is better than straight epoxy.

I'll add the link, if I find it again.

Here is a GFlex reference, plexiglass is similar to the polyethylene adhesion. Use 12 inches/sec for a propane torch, the surface does not even get warm. https://www.epoxyworks.com/index.php/gluing-plastic-with-gflex-epoxy/

I asked

I also called and asked West technical. They do not recommend straight epoxy to bond plexiglass. They did say that the GFlex product would work with proper surface prep...

Pilot8 said:

I'm trying to get down to the fundamentals of the bond- 10,000+ RV's flying have a fiberglass fairing bonding the forward section of the plexi to the airframe. So it must adhere reasonably well. Still seems to beg the question why weld-on instead of flox. Looking for some structural tensile/peel strength insight. Perhaps Scott McDaniels could chime in?

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The fairing done at the base of the wind screen on all of the RV models (including the RV-10) is an important component but it is not considered structural in the context of keeping the wind screen attached to the airframe.

For this reason it has always been considered a reasonable choice for a home builder. I have never seen delamination when proper surface prep and installation procedures were done. I know of 25+ year old RV's where the canopy fiberglass still looks like it did when it was new.

Weldon was chosen for the RV-10 transparency's installation for one very simple reason.... under recommendation from one of the popular composite kit manufacturers that was consulted with at the time (Van's has decades of experience designing load baring structures with aluminum and steel.... but composites, not so much. It made sense to consult with others that had expertise in that area).

I admit the Weldon can be a pain to work with but when used properly it produces a cross linked bond to the transparency's that borders on amazing.
During RV-10 cabin top structural testing to failure, windows were broken, but any loose pieces had Weldon still adhered to them, and the cabin top surface they were adhered to. You had to chisel the Weldon off of the cabin top or window surface. The cross link bond is substantial.

I don't think I even need to mention how important the bond integrity of the wind screen and windows is. Weldon was not chosen because it was the only thing that would work, but it was chosen because we new it would. If builders choose to use something else, please do careful research and be sure the method you choose will perform equally to Weldon.

Once Again

rvbuilder2002 said:

T . . . If builders choose to use something else, please do careful research and be sure the method you choose will perform equally to Weldon.

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The Vans Team uses what they know works, 99.99% of the time. And 100% of the time if it is important.