Sunday, August 15, 2010

Here We Go...The Seatback Bulkhead

Well, at long last, it's time to start building real aircraft parts.  The long journey ahead starts with the fairly straight forward building of the front seat back.  It's made out of 3/4" medium density foam, glassed on both sides, and becomes one of several structural bulkheads running from one end to another in the fuselage.  At this point I went ahead and purchased a small 10" table saw from Lowes.  It was perfect for cutting the 45 degree beveled edges at the top and bottom of the seat.  I'm sure it will come in handy more.  The beveled edges are necessary because the seat reclines 45 degrees when installed in the aircraft making for a relaxed seating position while flying.
Glassing the front went very well.  I am peel plying everything.  Peel ply is a process of applying a dacron fabric over the completed wet glass until it cures.  When you pull it off, it leaves a surface that doesn't need any sanding or other prep to be able to bond another piece to it.  Otherwise, fiberglass parts that must be bonded to other parts must be sanded with very course sandpaper to eliminate any smooth areas that won't adhere well.  The sanding process will cut fibers in the glass--not the best situation.  With the peel ply process, I don't have to worry about where I might have to bond something in the future, it will already be prepared.  The peel ply also works really well to hide transition areas between two layers of glass.

Seatback, glassed on both sides now and
 positioned approx like it will sit in the Cozy

The back side of the seat back didn't go as well.  I ended up with several lean (dry) spots under the surface as well as a few bubble type voids.  At first I was pretty dissapointed. I can only guess that I got in a hurry and didn't do an adequate job of wetting the glass cloth and moving the air out of it.  After a close inspection and a review of the inspection criteria in the plans, I decided that none if it, even taken as a whole, was severe enough to force rejection or repair.  I couldn't just leave it though, everytime I saw it I would be reminded that I could have done much better.  Besides, this would be a good opportunity to practice some of the repair techniques. In order to fill the voids, I puchased a couple of the largest syringes CVS pharmacy had in stock and carefully injected expoxy into the voids.  This worked great !  Then I thought...this might work on the lean areas?  Sure enough it did.  The trick was to poke an air relief hole on one side of the dry patch, then inject from the other side.  A little heat from a heat gun made this process a breeze.  I was able to cure most of the larger lean areas and make I then felt much better about the part.  Next time I won't let myself get rushed.


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