Step 11.9, Cutting the canopy

First there was a big bubble of acrylic plastic.  The canopy, we'll call it.  It's a single piece of blown plastic as it comes from Van's factory.  It must be cut in two -- one to fit the tilt up portion of the canopy and the other, the back window.  So the trick, as any sculptor will atest, is to trim off the bits that don't look like the artwork.  An initial trim is required so that the big bubble will set over the fuselage in something close to its final position.  Once this is accomplished, more accurate measurements can be taken to effect the big cut.

So I eye-balled the initial trim and got pretty close.  Here is the canopy is back on the aircraft where I can mark the location of the big cut.  A mistake here could be very costly, somewhere north of $1500, so I am uncharacteristically careful to double check my trim lines.  

Back off of the aircraft, the line to cut is clearly visible.  All I need now is the nerve to plow into it.  

I tape across the cut as I go to try and keep the stress on the plastic at a minimum.  There have been a number of builders crack their canopies at this stage.  The actual cut is with a die grinder sporting a thin cut-off blade.  I don't have any pics of that as I was alone -- principally, out of concern for the safety of others should I make a mistake :)

And finally the back window is separate from the canopy.

A very relieved selfie

Now the edges are sanded smooth.  #120 to #200 and then down to #400 grit.

It's a bit of work, but the edges are smooth and straight.  Now back on the aircraft for additional measuring.

And some fine tuning of the forward edge and sides.

At this point the plastic work is done on the canopy.

Step 11.8, Canopy strut mounts and map box

To lift the tip up canopy, gas struts are employed.  These gas struts are of the same variety as are used in automobiles although they are not nearly as strong as what might be found lifting the hatchback on a PT Cruiser.  The difference, of course, is the difference in the mass of the light weight airplane component and the much more sturdily built automobile hatch back.  Fortunately, airplanes don't have to survive a 5 MPH impact in any direction except through the landing gear.

It occurs to me that another reason for having the gas struts is that they provide a lifting force that is balanced on either side.  Since the canopy is a bit wobbly even with the aluminum frame, it probably really helps to lift from both sides.  Enough with the theory, on to the construction.  Here are the raw materials: The struts and some aluminum bar stock.  I've already laid out the cut line and drill locations.

First thing is to drill the holes while the pieces are large enough to clamp in the drill press.

I cut the bar stock and start tapping the holes for the 3/8" strut bolts.

That wasn't so bad.  After a little time on the Scotch-brite wheel and some counter sinking, here are all of the pieces ready for assembly on the canopy rail.

The next project is the map box.  First, a hole is cut in the bulkhead behind the panel because the map box is longer than the area behind the panel.

Then stiffeners are added to reinforce the bulkhead around the hole.

Now we rivet the map box itself together.  Unfortunately, I failed to take any pictures of the assembly of the map box, but here it is ready to go, sans door.

And from the rear:

Van's wants the box to be attached to the panel, but I don't think so.  There would be no way to remove the panel if at the same time, the map box door is also attached to the fuselage.  Clearly it's an untenable situation, so I used screws on the door instead of rivets.  

And finally, the map box and canopy struts in action :)

Next time we glue the canopy to the frame.