Chapter 21: Transition Blocks and Leading Edges

(New NASA X-38 Crew Return Vehicle...he, he!)

I decided to use left-over blue wing foam instead of urethane foam for the transition blocks and leading edges.   Blue wing foam affords the opportunity to make and shape bigger blocks (as compared to stacking and microing 2-inch urethane blocks).  Blue wing foam shapes nicely and fiberglass adheres better to it than urethane.  The only drawback is that blue wing foam is not fuel-compatible.  Any leak later in life could melt the foam and cause a void, thus compromising the integrity of the skins.  So you must ensure your strakes are leak-free.  

Transition Blocks

I hot-wired and microed the transition blocks as shown in the pictures below.  I made them to be flush with the leading edge bulkheads.  I figured it would be easier to do it this way rather than try to carve a leading edge into the transition block   


Leading Edges

To form the leading edges, the plans have you micro some urethane foam onto the leading edges and spline sand them into shape using the tips of the R33 and R57 strake ribs as guides.  From a few web pages ago, you know that I removed the tips from the R33 and R57 strake ribs to simplify strake construction and to reduce the potential leak points.  (BTW:  I remain absolutely convinced that I did the right thing.)  

Now, I thought it would be easier to hotwire some leading edge cores.  Well.....(grovel, grovel, grovel)...I regressed and simply followed the plans!  Using a trick from the archives, I glued a template of the wing root onto the end of the spar.   I ran some dental floss from the fuselage to the wing root template to locate the 17.4-inch water mark, then glued the R33 and R57 tips back on the strakes.  I also made a third tip and glued it on nearer to the fuselage.  I placed a straight edge at various points along the tips to locate and remove any high spots.  I fitted and microed the foam blocks into place.  After cure, I had leading edges in less than 30 minutes!  BTW, it's absolutely essential to have a good spline sander.  The one in the pictures below is a 4-foot section of C channel with sandpaper glued to the flat side.

A convenient way to glass the leading edges is to put the plane on its ass like the Space Shuttle.  (See picture above.)  Talk about turning heads!  You can blow a few peoples' minds, especially when you conveniently leave a few rocket engine articles, drawings, and specifications nearby. :-)