Chapter 18 - Section 12

Carving the Inside Foam


Marking Hinge Pad Locations

I first marked the 2 - 1.6" flat surfaces along the longerons. Then I joined the dots with a flexible aluminum strip - that was straight forward. 


The next step was to mark the locations of the hinge pads along both sides of the longerons per Fig. 51. I set up my straight edge, T-ruler and cross-hair laser for the task (left). I made sure my T-ruler / straight edge was lined up along the center of the canopy / TB. With the cross-hair laser, I was able to determine the exact locations for the hinge and reinforcement pads along the canopy sides.


While I was fussing over the position of the straight edge, my T-ruler slipped over its side and BAM...dropped right on top of the canopy ~!@#$%^&*...~!@#$%^&*! Fortunately I had 3 layers of Spraylat on it prior. A double layer of packing material for added protection is warranted!!!   


After I marked the hinge pad locations, I dug out all the foam down to the glass - creating a cavity for the subsequent step.


I jumped forward to Section 13 - filling the cavity with flox/glass before I shaped the underside foam - to make sure I do not carve away the supporting foam for the flox/glass hard points.


Shaping Canopy Underside Foam

I was having difficulty in determining where to begin shaping the underside foam as I wanted to make it symmetrical on both sides - my free hand is out of the question. Some form of a guide is needed. Since the canopy is elliptical, I felt the shaping direction of the foam should be 90o to (or straight out of) the curved surface of the canopy.


To determine the foam shaping direction, I cut up a 3/4" wide strip of wood with a line drawn along the center. I made sure the base of the strip was exactly 90o to its center line. By butting the base of the strip against the inside perimeter of the canopy, I basically projected a 90o line from the tangent of the curved surface. With a cross laser, I projected this vertical line onto the foam, thus providing me a foam shaping direction. I repeated this process along the entire inner perimeter of the canopy, thus plotting out the entire shaping scheme.







Then I took several straight edges and 'dug' into the foam (along the shaping directions) with one end of the straight edge sitting on top of the canopy edge, and the other against the foam edge per Fig. 51. The straight edges show how much foam I need to remove at each location - looks like it's quite a bit...









I was a bit careful not to remove too much foam using a sanding belt. I ended up getting a convex shape foam surface. If you look closely, you can see the straight edge marks. Though it looked reasonably nice, it still had too much foam left. 










I decided to take a more aggressive approach by using a hacksaw blade to scrape most of the foam off. I then followed up with a foam block and 220 grit sand paper. A lot of foam dust - but its more like it...


I made two (2) extra deep depressions to accommodate the top edge of the instrument panel (the 2 yellow strips).