September 2010 Archives

Prepped for Big Cut

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I finished yesterday with a couple of minor gaps around the front of the canopy.  I got started tonight by laying out a curve along the front edge from the gap peak to gap peak.  A few minutes with the cutoff wheel removed the scraps.



The canopy fits much better now.  There's still about a 1/16" gap in the center, but this is good enough to do the "big cut."



I taped the canopy down to prevent it from shifting.



You can sort of see here that there's less than 1/2" of space between the canopy and cabin frame.  From what I understand, this is better than most builders achieve.



I then laid a few pieces of wide masking tape along both sides of the cut line.  The theory is that this will help guide the cutoff wheel, but I'm dubious of this since the cutoff wheel basically cuts anything the moment it touches it.



Finally, I transferred the canopy to the bench and screwed down some blocks to stabilize the two halves prior to cutting it in two.  It's too late to do this tonight, but I'll try to knock it out first thing in the morning.



Made the Big Cut

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I came out to the garage this morning and made the big cut.  A lot of builders seem to get all worked up about this, but it's a total non-event.  Just go for it.  The canopy in this section is significantly thinner than around the edges (just over 1/8" thick), so it cuts fast.  The whole cut took only 2-3 minutes.



I smoothed out the edge and fit the canopy temporarily on the fuselage.  Blurry, but this looks sweet!  There's still pretty of trimming left to go though.



I also edge finished the aft window.  This will be put aside for the time being while I work on the forward canopy.



With the top center of the aft edge of the canopy flush with the line, the sides are forward of the line by nearly 1/4".  This was expected though since there was a gap at the top before the big cut.  The canopy pivoted down around the front edge.  I still have to lower the canopy more in the front though, so this will be reduced somewhat.  After the front is at the proper height, I'll remark the line and trim the aft edge to follow the line perfectly.



I'm planning on using sikaflex adhesive around the canopy channel and cabin frame, so I taped some 1/8" thick pieces of rubber to both pieces.  This will raise the canopy enough for the adhesive to fit.



After clamping the canopy in place, I marked a further trim line around the front that will finally remove the last of the flare where the front flange used to be.  I also marked a cut line along the side that will bring them up to within 1/2" of their final position.  These cuts need to be done to get the canopy to transition more smoothly to the sides.  I'll try to do these before work tomorrow.



Trimmed Forward Canopy

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I cut the canopy along the line I taped up yesterday.  As I mentioned, this completely removed the flare along the front edge.



I was a little worried that a full cut along the front edge would make the fit worse, but surprisingly it actually got better.  The fit along the sides is still great and the fit in the middle got noticeably better.



Even more surprisingly, that lowered the front enough that the back edge nearly perfectly follows the marked line.  It's within 1/32" along the whole line.



Modified Canopy Frame

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The notch in the forward canopy skin needs to be lengthened to allow the canopy to slip from the outside of the skin forward of the notch to inside of the skin behind the notch.  I'll probably have to lengthen the slot further, but I don't want to overdo it.  Most builders cut some or all of the ear away anyway.



I also marked the apex of the joggle which will define the bottom edge of the side of the canopy.



I then drilled and riveted together the forward end of the side channels and forward weldment.  Afterward, I tapered the channel a bit to provide a smoother curve onto the forward weldment.



Here's a shot from the top showing how the side flange begins to curve inward where it joins the forward weldment.



Finally, I marked and taped up a new cut line that provides a more gradual curve into the notch in the forward skin.  I also marked new side cut lines that are within 1/8" of the final position.



Further Fitting of Canopy

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I elongated the forward edge of the slot further and made a few small cuts to get the canopy up to the bottom of the slot.  Sorry about the blurry picture.  This camera I'm using has been doing this a lot lately; it lives a hard life in the garage.



I did a bunch of research on what to do with the "ears", and I ended up deciding to simply cut them off.  This whole area will be fiberglassed over anyway, so you'll never see this.  You can also see here that I elongate the forward edge of the slot even further and added a curve to it to better follow the inside of the canopy.



Finally, I trimmed the sides to basically their final positions.  There's still a little bit of interference that I have to deal with.  For example, here on the left, the bump out in the forward canopy frame weldment is preventing the canopy from dropping down all the way.  I'll need to do a little more trimming to get this to fit properly.



Before work, I sanded back the canopy so that it didn't hit the joggle.  The canopy can now be pulled down tight against the frame.  Now that the canopy is sitting down all the way, the sides will need a minor trim, but I'm going to hold off on that for the moment.



Before doing the final trimming on the canopy and drilling it to the frame, I want to finish up the canopy frame so that everything will be in precisely it's final position.  First up is to prep the canopy frame reinforcement.  These pieces further tie the forward canopy frame channel to the top skin and make the frame far more rigid.  I spent about an hour deburring these.  There are a ton of nooks and crannies.



The holes need to have flanges to stiffen them.  Following the advice of several builders, I quickly fabricated this little tool out of some scrap angle and the rollers from the Avery hand rolling tool.



I bent the flanges in one of the pieces.  This was pretty hard on my hands, so I stopped after the first piece.  I'll finish these up tomorrow and then start trying to fit them to the frame.  It's really amazing how much these flanges stiffen these pieces.



I finished flanging the lightening holes and then fit the center reinforcement and drilled it to the forward channel.  The rear flange won't be drilled to the skin until the frame is clamped back to the fuselage.



The side reinforcements are much trickier.  The flanges placed around the holes severely distort them, and it takes quite a while to bend them even close to the final shape.



After much fiddling, I drilled the forward flanges to the channel.  I then tweaked the aft flanges so they lay flat against the skin.  I need to do a little trimming along the inner edge (along the black line that's partly visible on the left) to provide some clearance from the hinge supports.  The reinforcements needed to be shifted inward so that one hole that's shared with existing structure will have sufficient edge distance.



I finished drilling the canopy frame reinforcement pieces to the forward channel.



Six little clips need to be fabricated from some 0.032" stock.  I cut pieces out slightly oversized using snips then stacked and drilled them.  Using some clecoes to keep them aligned, I then sanded them so they were uniform and rounded the ends.



After individually touching them up on the scotchbrite wheel, they're ready for attachment to the canopy reinforcement pieces.



I clamped them in place and drilled one side of each piece.  I'll drill the other side once the canopy frame is square.



I put the canopy frame back on the fuselage so that it's locked in its final position.  I then clamped a piece of scrap wood across the top skin to keep it flat while drilling the aft flanges of the reinforcements.



Here you can see that the other side of the clamp is holding another piece of scrap wood that is keeping the center reinforcement piece tight against the skin.  Without this clamped, it's hard to know how hard to push up on the reinforcement while drilling.  Too hard, and the top skin will bow upward.



Here you can see that the entire aft flange of the reinforcement pieces have been drilled (the center lateral row of clecoes.  The only thing left is a couple of the end flanges that still only have one hole.



I'm not sure why I took this, but here's the inside.



I finished drilling the end flanges of the reinforcement pieces and then disassembled the frame.  My buddy Andre stopped by and got most of this deburred.



While he was working on that, I fabricated the forward strut mounting points from bar stock.  Somehow the center holes ended up drilling up slightly off-center, but this won't matter as the aft attach points can easily be adjusted to make the struts the right length.  These were surprisingly time consuming to make since their fabricated from raw stock.  They have to be cut to length, corners rounded, holes drilled and tapped.  There's at least an hour of work in these two pieces.



I drilled the forward strut mounts to the canopy frame using a #21 bit.  I was a little worried that the bit could damage the threads I already tapped into these holes but it was a non issue.  The shavings did clog up the threads, but running the tap back through them cleaned them up nicely and the screws still threaded in snugly.



I then clecoed the skin back on and opened the holes up to #12.



I attached the mounting blocks using some scrap bolts.  The frame will eventually get countersunk and the skin dimpled, so these will be replaced with flush head screws, but this is fine for the remainder of the fitting.



Here's the inside of the mounting block.  The ball fitting for the strut will thread into the center hole.



Using some 1/8" thick aluminum sheet, I fabricated the components for the aft strut mounts.  The strut ball ends mount through the large holes on the top.  The smaller pieces are spacers to keep the struts from hitting the canopy frame.



The aft mounts need to be mounted 6.125" aft of the canopy rail split line.  I measured and laid out a mark.



I positioned the mount and used a small vise-grip clamp to clamp it to the aft canopy rail, then drilled it to the rail.  I then tried to bolt the mounts to the canopy rails while they were in place, but this proved to be too much of a pain given the limited access behind the rail.  I ended up pulling the canopy rails off to bolt these in place.



I also screwed the forward ball ends into the forward mounts.



Finally, I popped the struts in place.  This took a huge amount of force, but this is expected given that these need to lift a fairly heavy canopy with a pretty short lever arm.  The force of this strut did slightly alter the canopy position which created a tiny gap between the forward canopy skin and the forward canopy rail.  The gap is too small to do anything about though, so I'm going to leave it.



Disassembled Canopy Frame

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I disassembled the canopy frame so that I can prep it for final assembly.  I can already tell that the struts push the canopy frame far enough forward that the front edge of the canopy skin will need a little more trimming to keep from interfering with the forward top skin.  This whole process has been much slower than I'd like because everything you do causes something to shift and parts have to go on and off so many times.  I'd rather take my time and hopefully end up with a canopy that fits nicely instead of trying to rush through this and end up with a sloppy fit.



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This page is an archive of entries from September 2010 listed from newest to oldest.

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