Chapter 21: Making the Cap Strips

I decided to follow others by glassing cap strips onto the tops of the ribs and bulkheads.  Although there are no known fallacies with the plans method (stacking flox alone), builders feel the cap strips increase the surface contact area for adhering the top strake skins to the ribs, and also reduce the chances for leaks.   

Please note that this process is NOT in the plans, and it does add several cure cycles and several days to the strake construction process. Although I have presented this process on its own web page, you must have completed the top jigs to hold the top into shape while the cap strips are installed.  Reference the next web page for that.

First Day:

• Make sure all ribs and bulkheads are trimmed to closely match the inside strake skins.

• Place the top skin on the strake.  

• Use a sharpie marker and draw a line where the ribs and bulkheads contact the upper skin.  

• Apply two pieces of 2" wide duct tape along each side of the mark on the inside skin.  Two pieces approximate the thickness of the cap strips and allow for mold release. 

• Stack some micro to the top of each rib.  (I know the plans say “flox”, but that comes later.  In this step, the micro is used like foam to merely fill in any gaps between the top strake skin and the ribs/bulkheads.) 

• Install the upper strake skin in place, weight it down, and let the micro cure.

Second Day:  

• After cure, pop the top strake skin off and remove the excess micro. (See above, right photo.)  

• Make up some 1-inch wide, 2-ply BID tapes and peel-ply one side of the BID tapes.  (Some builders prefer 2-inch wide BID tapes.  I used 1-inch.  Looks like 2-inch is too wide and too flimsy in my opinion.)  

• Remove the duct tape from the strake skin and re-apply with box tape (because box tape is thin).  

• Apply the BID tapes onto the top inside strake skin, centered on the line with the peel-plied side against/touching the box tape.   DO NOT put any peel ply between the BID tapes and where those tapes will contact the ribs and bulkheads!

• Gently scuff the tops of the micro (prep-sand),   and wet out the top of the micro with pure epoxy.

• Install the upper strake skin in place, weight it down, and let the cap strips cure.  After cure, the cap strips will permanently bond to the ribs and bulkheads in an exact fit to the strake skins.   (Cool, huh?)

Third Day

• After cure, pop the top strake skin off and REMOVE THE PEEL PLY.  Forgetting to do that will have DISASTROUS in-flight results later as your top strake skin WILL quite possibly depart the airplane.  

• Trim up the cap strips.  Remove those sections of cap strip that go over the baffle vents (semi-circles) on the interior bulkheads.  

• Prep sand the underside of all cap strips and tops of ribs and bulkheads.

• Wet out the undersides and rib/bulkhead tops with pure epoxy, and apply a small radius of flox to the underside of the cap strips (both sides of ribs/bulkheads).

• Tape the cap strips to the ribs/bulkheads by applying the 1-BID tapes to the undersides of the cap strips, lapping onto the top sides of each rib and bulkhead.

• Let cure.

Fourth Day

• After cure, pop the top strake skin off and once again, RE-CHECK that all peel-ply has been REMOVED! 

• Here's the obligatory "one-long-last-look" picture prior to floxing the top in place.

Fuselage Cap Strips

I'm not sure if I missed something in the plans, but I was very uncomfortable with simply floxing the top skin to the fuselage in the rear, inboard fuel bay.  So I created a cap strip with a 90-degree bend in it by glassing a 3-BID tape over a foam form.  I removed the form after cure.  This cap strip serves the same purpose -- to provide support for the skin, and more importantly, to create surface area to prevent leak points.  The cap strip helps to perfectly seal the join between the strake skin and fuselage by preventing the flox from running down into the fuel bay and away from the join during cure.

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