Chapter 18

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In this chapter, I will build the turtle back and canopy.  This is the top half of the airframe. This is a very exciting chapter.  I have been wanting to have a roof over the cockpit so it will feel more like airplane. I used plywood and lath to build the jig, just like the plans call for.

I plan to raise the front of the turtle back 2".  I decided it would be easier to modify the jig rather than add a foam wedge under the flanges later. I did not redraw the radii of the jigs, I added length to the jig where the radius meets the 3" wide flange.  I normally do not use the original drawings to cut out. I tape them to a window and trace them.  I made sure the bottom of my blank paper hung 3" below the M drawing and the page bottoms were parallel. I traced the curves right down to where the curve meets the 3/8" thick x 3" wide flange.  I did not trace the flange. I laid the tracings down on the table. and used a carpenters square to lengthen each jig bottoms.  I added 2" to the largest jig then added the flange.  I used the plans proportions to determine the last two lengths.  I added 80% of the 2" to the bottom of the second largest jig and 40% of 2" to the third largest. In order to use the standard fire wall, I left the smallest jig per the M drawing.  I added the flange to the drawings next. This worked well.

I added the foam to the jig in 6" wide strips, just like the plans called for.  I used a similar technique that I read about on the internet to cut the foam to minimize gaps.  I installed the first piece holding it in place with drywall screws.  I placed the second piece in place so it followed the curves correctly.  This left a gap.  I measured the gap and recorded the distance.  I placed a flexible straight edge on top of my second piece with the edge of the straight edge equal to the recorded gap distance from the first piece of foam.  I drew a line following the straight edge. I removed the second piece of foam and cut it on the line.  This gave me a curved edge that fit against the first piece of foam without a gap.

I did not 5 minute epoxy any of the foam pieces together. The plans tell you to epoxy a short length to each strip. I did not do that. I made sure each joint was over the lattice.  I alternated sides for the joint. I did not want two joints to line up.  When I pushed the foam in place and secured it with drywall screw, I did not have any bulging.

I added the drip rail in place per plans.  I did not install the TB-1 bulkhead.  I am not sure I want that to block the view from the back seat.  I am also considering a forward hinged canopy. I think that will be in the way of entering and exiting the plane. I keep track of items not complete in a Excel spreadsheet.  I added the bulkhead to it.  I do not want to forget to add some sort of reinforcement. I will make up my mind later.  I peel plied the entire inside lay-up.  That way I was not required to premature where the peel ply strips would be located.

 

 

 

I added the 1/4" aluminum inserts to both sides, just in case I go with the forward hinged canopy.  I used hot glue to hold the cut-out from the jigs in each end of the turtle back for support.

I did not look forward to sanding and shaping the foam. I lost sleep over nothing though. It turned out to be very easy to contour. I spent about 4 hours sanding. This included the recesses on both ends and for the drip edge.  I peel plied the outside to make finishing easier. The turtle back turned out very nice.

Alex is having fun pretending to fly. He really enjoys working with us in the basement.  I plan to install the turtleback later. I would not be able to get the plane out of my basement with it permanently installed. I floxed and bid taped the firewall to the turtleback. I used small #8 screws to hold the turtleback in place while I complete the rest of chapter 18. I also plan to install the rear windows later. I want to have the bottom of the widows as low as possible. I will not be able to install them until after the upper engine cowling is in place.

 

 

 

 

 

 

 

 

 

Mariclair climbed inside through the small hole where the center section spar should be. She was able to scrape the flox off before it could cure. This will save a bunch of effort later on. We won't have as much sanding to do at the canopy edge.

Sanding the foam blocks to fit was time consuming. I used as little micro as I felt possible and I still used to much. It is hard to guess where you will be sanding latter on. I tried to put the micro where I felt the foam would stay intact. I used a hacks saw blade and sure foam sanding planes to contour the outside of the foam. It took patience to get both sides even and looking good. I plan to have the canopy open forward, so I made the recess in the foam in different locations than the plans calls for.

Jeff just recently purchased a set of plans for the Cozy MKIV. He came over to assist my wife and I on the outside lay-up. This lay-up consisted of two ply's bid and two ply's of uni. I added a third ply of bid 6" by the width of the plane. This went just in front of the canopy bubble to stiffen it for the forward hinges. Jeff was able to get plenty of hands on instruction during the 5 hour lay-up.

 

 

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