Step 12.1, Fairing the canopy

When the canopy is attached to the frame the canopy's edge is flat against the wind.  A fiberglass fairing is constructed to smooth the transition from the cowling to the canopy providing aerodynamic as well as aesthetic advantages.

The process is simple:  keep adding fiberglass layers until the transition forms a smooth arc.

The loose fabric visible on the top is not fiberglass.  It's called peel ply.  The objective of peel ply is to protect the surface of the curing fiberglass when it is planned to add additional layers.  When peel ply is used it is not necessary to prepare the surface with sanding or cleaning prior to bonding the next layer.  Just peeling the peel ply off leaves the surface clean, and the texture of the fabric gives sufficient bite to adhere the next layer of glass.

The first few layers are made black with dye because the fiberglass overlaps the canopy edge and is visible from the inside.

After five or six layers the transition is beginning to flatten out into a nice curve.

The profile of the curve is made uniform with the aid of  the reverse side of a sanding block. 

The thick black tape protects the canopy from the sandpaper.

And finally, the canopy in its finished state.  Note the tie down strap.  It's keeping the canopy from tipping over and falling off of the roll around cart while I finish off the underside.

Step 12.0, Gluing the canopy

Although I've taken the summer off from blogging, I've continued to make progress on the project. This step in the project occurred in late June.

With the canopy cut and the edges smoothed, its time to begin the process of attaching the plastic to the aluminum.  There are two main methods of attachment, glue or screws.  The Van's way is to use screws, which is the simpler of the two as it allows one to fix one point at a time.  The glue method, on the other hand, requires that the entire canopy be fixed at once.  The glue method does offer one important advantage in that no holes are drilled through the plastic.  It has been observed that canopies with cracks tend to begin cracking at a drilled hole.  And thus the genius of the glued canopy is revealed -- no holes drilled equals no place for a crack to form.

Before gluing the canopy on I thought it a good idea to paint the cowling under the canopy black to reduce reflections.  After the canopy is in place, the clearance is too limited to attempt painting in there, mostly due to the slope of the canopy.  And so I mask off the area to be glued and paint the rest black.

Next we test fit the canopy one last time and fabricate some mechanical tie downs that we can rivet in place to hold the canopy while the glue cures.

I use a wire to act as a spacer in between the canopy and the side rail. This ensures that there will be enough glue in place for a strong bond.  The danger here is that without the spacer, the canopy could contact the rail an squeeze out the glue, preventing a good bond.

The next step is to apply the primer to the plastic and the aluminum.

Then the real fun begins.  Squeezing out the glue.

During the gluing process it is necessary to get inside to scrape off the excess glue.  Getting back out is the hard part.  Here I am trying to climb back out through the baggage compartment.

With the glue on and the canopy in place there is nothing to due but wait.

I really enjoy these moments in the construction.  Applying glue brings a kind of clarity to process. There is 'before glue' and there is 'after glue' and nothing in between.  Black and white.  Once you've mixed the epoxy or squeezed out the glue there is just no going back, It's all ahead forward.   It's at these times that one really knows where they are.
  

It frequently happens that people ask me how I'm doing on the airplane.  The engineer in me struggles with this kind of question because I feel obligated to give an exact answer.  Most of the time I have a half dozen different subprojects going on simultaneously each involving many subparts and their attendant issues.  I don't really want to stop and calculate the precise level of completion that the question requires -- partly because I always realize that I'm not as far I along as I had previously thought, but also because the questioner would probably get bored and walk away while I mentally tabulate the answer.

In the end, I know that the questioner really doesn't want that kind of detail so I usually politely answer, "Oh, its going fine."

But on days like this, when I've completed a major milestone, I'm happy to add something like, "I just attached the canopy."

Curiously, I failed to photograph the canopy as it looked while the glue cured, so I add this one which gives a preview of the next step in which we fiberglass the edges of the plastic down to the aluminum cowling to form a smooth fairing.

Why does this dog keep photobombing my blog?

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.

Step 11.7, Canopy frame

At last I'm finally going to work on the canopy.  I've been alternately looking forward and dreading this task. On the one hand it will be a major milestone toward the completion of this project.  But on the other, it is rumored to be one of the most difficult aspects of the plane's construction.  The difficulty here is that the canopy assembly, when finished, must fit precisely along its entire perimeter.  This should be no problem at all if  we can assume just four things:  1, the longerons were bent symmetrically -- perfectly following the plan's curve.  2, that the roll bar was built to the correct width and height and slopes back at just the right angle.  3, that Van's has supplied a forward canopy frame assembly that just happens to match the existing fuselage dimensions.  And finally, 4, that the holes for the hinge pins can be precisely located in a difficult to reach area.   The trouble is that none of these assumptions are very likely at all. 

Before I start, I will address the airplane in an unmistakably serious tone making it very clear to the airplane that this step is going to be completed, no matter what.  All resistance is futile, and that I am very well prepared to use all manner of hammers, pliers, and clampy things that Harbor Freight can supply.

First up: a test fit of the welded aluminum canopy frame supplied by Van's.  Ok, so far, it fits the skin on the bench in the front but not along the back.  Other builders have reported the same thing.

The next step is to place it on the plane and position it for drilling the hinge pins.  Once on the aircraft, it is apparent that the frame's bow and the width of the frame at the rear of the weldment are not correct.  Bow, in this sense, is the canopy's top curvature that must match the forward bulkhead. The bow problem is addressed by brute force and some fluting.  The width of the weldment is easily changed to match the width of the fuselage at this point since the top skin has not yet been drilled.

This is a view of the hinge (top center).  The holes for the hinge pins will be drilled through these when they are properly located.

First the forward portion of the canopy frame is clamped down into position.

The splice plate and hinge supporting structure are clecoed down tight. Then a drill is run through the fuselages hinge pin holes and on into the hinge.  This makes a mark where the hinge pin hole should be drilled.

And so I did.  After taking the canopy frame back off of the fuselage, the mark can be seen.

The hole size is progressively enlarged on the drill press until its just under 3/8".  The final step is the reamer bringing the hole size up to exactly .375".

Once reamed to size the bronze bushing is pressed in using the pneumatic squeezer.

Presto! one down one to go.

So now its time to rivet the rest of the frame together.

Here it the torture device I've constructed to force the aft hoop of the canopy frame into the correct dimensions.

Riveting the top skin.

The under side of the forward canopy frame gets some re-enforcement.

And so eventually it all goes together.