Mailing List lml@lancaironline.net Message #66564
From: Frederick Moreno <frederickmoreno@bigpond.com>
Subject: Fw: Wing closing epoxy
Date: Thu, 15 Aug 2013 09:10:09 +0800
To: Lancair Mail (lml@lancaironline.net) <lml@lancaironline.net>
Hi Mike:
 
The bond areas on the wing skins is so huge that the safety factors for strength are massive. We calculated that the bond area for the wing spare to skin alone is enough to lift a 747 using the quoted values for the earlier Hysol.  The key is resistance to avgas which all of them have.   I would use the stuff in your fridge and be confident.
 
One hint for bonding skins.  Drill lots of witness holes (1/8 in diameter works fine) over the spars. If you put a smaller drill drill or stiff wire down the holes when you bond the wing, you will know how thick the layer of epoxy is under the skin and on top of the spar.  I found that it was MUCH thicker than expected (I planned for 0.020 inch when calculating quantity), and so had to pile a lot of weight on the wing to get the squeeze out and proper wing shape.  A source of vibration would help. 
 
As it was, I had lots of lead bags and 5 gallon buckets filled with rocks for both wings, and  used them all on one wing to get the stuff to squeeze out and get the proper wing shape.  Saddles were pulled down tight, but bent.  ALL the rocks in buckets were piled on top of the lead bags in between the wing saddles of the first wing to get everything to settle into place.  The second wing skin had to wait for another day. 
 
As I recall, we used a crew of four or five  to mix epoxy, apply, put down the skin, and then lock it in place and them pile up buckets.  I would have more were I to do it again, with a good briefing at the start.
 
My guess was that we had over 500 pounds of weight to squeeze out the epoxy/flox mix.  Temperature makes a huge difference in viscosity and squeeze out.  You want cool to prevent the stuff cooking off too soon, but warm to make it thin.   Speed is important  and having lots of spreading tools and hands is mandatory.
 
Post inspection looking through the holes Into tanks and with mirrors into the fuel fill port, we found a nice squeeze out, but no drips of excess, so the estimate of 0.020 inch thickness for the bond line worked out OK.
 
Fred Moreno
 
 
 
 
-------Original Message-------
 
Date: 14/08/2013 7:51:51 PM
Subject: Wing closing epoxy
 
I am preparing to close a set of wings and have some questions about Hysol epoxy.  I've reviewed previous posts and there hasn't been much said for awhile, perhaps because wings are coming from factory closed now.

I went to Aircraft Spruce and said "I need six quarts of Hysol."  They sold me six quarts of Hysol.  I used it to epoxy in a fuel drain and probe and was asked by Matthew Colliers why it wasn't blue.  So, I looked closer at my manuals and saw that it calls for epoxy and flox if temperatures are below 70 degrees and Hysol 9339 if temperatures are above 70 degrees.  I then went to the Lancair website and found they don't even carry Hysol 9339, but have changed to Hysol 9360.  The product Aircraft Spruce sells is Hysol 9430.  Lancair tech support says they don't know why 9360 is specified.  "That was selected by the guy before me."

Aircraft Spruce says - 

"This new and improved Hysol glue replaces the old EA-9410-2 glue. EA-9430 has the same characteristics as the EA-9410, but has a 50 minute pot life instead of the 30 minute pot life of the EA-9410 at 77°F. Used extensively in the Strojnik S2A sailplane and many other homebuilts."

Locktite tech support and the data sheets show the pot life, tensile and shear strenght to be almost identical.  The one difference I can find is that the 9360 specifies shear at different temperatures while 9430 specifies the shear strenght only at 77 degrees.  The guy from Locktite couldn't explain the differences, and said "they appear to be very similar products".  Can anyone tell me what makes the 9360 product better suited for Lancair wings?  Is there a reason not to use the six quarts of 9430 in my fridge?

Mike Baudhuin
 
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