Chapter 18 – Canopy (Part 1) – 175 Hrs

I’ve been hassled to get an update out on the Cozy build. I am currently working on the Canopy chapter, and I have several modifications here, so it is taking me more time to complete than I had hoped! I also got engaged a few months ago, which in addition to some other side projects has slowed things down a bit. I’m at a good point for an update, so here it is…

Turtleback BulkheadI have the Featherlite turtleback that I got as part of the project I purchased, which I decided to modify to meet my needs for more head room. We started by cutting out the front turtleback bulkhead and Kim glassed it with 3 plies BID and 1UND on the horizontal portion. After cure, we repeated the process on the back side.


Turtleback-Adding Width and HeightSince I am making my turtleback 2″taller and 2″ wider, I started by finding the center of the turtleback and cutting it along it length and micro’d a 2″ Clark foam wedge to make it 2″ wider in front, and the same size in the rear. Glassed with 2 UND on the outside. Marked a line on the sides about 1″ above the flange and cut the flanges off with the Rockwell saw. After cleaning up the edges, I micro’d a 2″ Clark foam wedge to raise the canopy 2″ in front. Glassed with 2 UND on the outside and peel ply’d.

Attaching Firewall to TurtlebackThe turtleback was too long from Featherlite, and needed trimmed.  Since I added height and width to it, it was no longer perfectly perpendicular in the front and back. The front should not be an issue, but the rear needs to be flush with the firewall. I decided to mark the 46″ length on the flanges first, since that will be the most accurate place to measure. Then I secured the firewall against the rear of the turtleback. (Note the turtleback needs to be on a level surface) I made sure the Securing Firewallfirewall was plumb in relation to the table, and measured the distance from the firewall to my marks. They were 1.9″ from the firewall on both sides. (Perfect) Then I measured 1.9″ from the firewall in several locations around the outside of the turtleback that I could connect the dots. After drawing the cut line, I cut it to length for a perfect fit to the firewall. Much easier than some of the other methods I’ve seen, so I’m happy that worked! Sanded and cleaned up some of the foam pieces that were micro’d in last night in preparation for glassing.

Turtleback BulkheadChecked the TB bulkhead for fit, and marked the inside of the TB for reference. Marked the cut line on the inside per plans, and drilled the holes for reference. Then I decided to glass the inside over the three foam wedges I added (2 UND). The clark foam is a bit thinner in thickness than the honeycomb that Featherlite uses, so I have a bit of a gap to fill. Applied micro and covered with 2 ply UND in opposing orientation per plans. I had to wet the first ply on plastic and transfer it, so I didn’t have to worry about it soaking up any micro in to the glass. Finished with peel ply. With my leftover time, I created the 1.5″ strip that is used for the drip rail and 5 min epoxied it into one long piece. Glassed in the drip rail with 2 BID and 1 UND per plans.

Windows Cut into TurtlebackTurned the turtleback over and marked the outside cut line and started marking out the windows. I did this per the FAQ instructions, but I found out that the lines did not look right. Came to the conclusion that as long as the windows follow the lines of the exterior, that is what you are looking to achieve. My process is:

  1. Draw the horizontal lines per the FAQ.  (I made mine slightly higher to get above the 2″ wedge I added for height)
  2. Measure 2 1/8″ from the cut line to determine the inside vertical edge of the windows, so they are parallel with the cut line.
  3. Measure 5 1/4″ in from the front of the TB to give a parallel line to the front of the TB
  4. There was no dimension given from the firewall to the window in the plans, but the FAQ says 38 7/16 from the FRONT of the TB at the bottom, so I used that mark.  I then measured that mark to the firewall, and made a similar mark for the top of the window to get a parallel line.  Note that I already made the aft end of my TB plumb.  The front is no longer completely plumb, since I raised it.

I then proceeded to cut out the window openings starting with a hole saw and an oscillating tool making sure to leave the material proud, so I can sand to the perfect dimension.  Completed that and started removing all the nomex honeycomb.  To create a cavity for the plexiglass to fit into.  Removed the 1″ strip as shown in the plans, and began fitting windows.  Continued fitting windows into the TB.  Both copilot side windows cut for fit, and taped up on the outer surface with 1/8″ gap between tape and TB.

Prepped the rest of the windows, drilled the holes for the cleco’s, and floxed the windows in place.  After cure, I am finding out that epoxy from the wet flox seeped into the edges of the tape where they overlap another piece of tape.  Another contributing factor is the bulb was burned out in the epoxy box, so I was starting with colder epoxy than normal.  The curing of my wet flox may have warmed up the mixture enough to make the epoxy run out of the flox easier.  Bummer!

I was able to get the excess epoxy off the windows by VERY CAREFULLY using a razor blade to get under it.  Dennis tells me to be very careful with the razor, as any scratches can cause the plexi to crack later!  Finished up with lining up the turtleback and firewall to be floxed together.  Bondo’d the upper firewall to the lower firewall with angle aluminum, making sure everything was square and plumb.  Floxed the turtleback to the firewall using 1/4″ spacers under the turtleback.  At this point, I realized I needed to round off the back edge of the upper firewall so I can wrap glass around it.  Will wait until the flox cures now.  After cure, I drilled 1/4″ holes through the flange of the turtleback and into the longerons in the back half of the turtleback for locating pins.  Then cleaned up the edges where the flox squeezed out.  Rounded over the back edge and taped inside and out to connect the turtleback to the upper firewall permanently.

Placed the canopy on the fuselage and approximated it’s position.  Added layers of electrical tape to the rear edge to protect the outside while I figure where my cut line will be.  Used pallet wrap to create streams that I taped to the inside of the canopy using electrical tape, but that eventually all came falling out because it was too thick and flexing the canopy taking it off and on caused it to detach and fall inside the fuselage.  Ended up  placing multiple layers on the inside of the canopy as was on the outside when I received it, and it seems to be staying much better.  Cut out the BL0 template, but it seems everyone says it doesn’t match up.  I placed the canopy on the turtleback so the nose of the canopy was at the correct position fore and aft, and the template matched up almost perfect.  Since I raised the canopy 2″, and widened it 2″, and went with the texas canopy, perhaps that is the difference?  I will need to trim at the instrument panel 1/4″, since it is currently resting on it.  I will know for sure after I trim at the rear for length and can get a good trial fit against the turtleback.

Window StripFloxed in the fiberglass strips I cut out around the windows back on the larger windows and covered with 1 BID and peel ply.  Only did the one and left the turtleback upside down so the flox couldn’t run out.  Used the left over fiberglass to glass the brake conduit back in place on the main landing gear.  Repeated the process for the smaller windows, and turned the turtleback right side up for cure.  Then floxed in the hard points, since I confirmed with Ed Richards that his latch system keeps the same positioning per the plans.  2 BID over the top of the hard points and peel ply.

Since I removed 1/4″ to clear the instrument panel, I attached a 1/4″ temporary spacer for the canopy to rest on while working on it.  Cut out my templates and adjusted how far they extend inboard to account for the wider canopy.  (trial and error)  After cutting the rear of the canopy for length, I used the templates to find my tape lines.  I decided to do a sacrificial tape line below the line so my real tape line can butt up to it.  Masking tape doesn’t stretch, so it holds a straight line better, but don’t use long term, as it will be hard to get back off.  I took a tip from Tim Andres to get some 3M painters tape from the auto paint store, which I purchased 1/4″ and 1/8″.  I butted the 1/4″ next to the masking tape, and 1/8″ butted against that, then 3m electrical tape butted next to that (3 tapes wide)  Then covered the 1/4″ and 1/8″ painters tapes with electrical tape to protect it.  Then over that, I placed 3-4 layers of duct tape for the fiberglass to butt up to.  Taping is tedious Taping for Fiberglass Transitionwork, but will pay off later.  The fiberglass will end up butted up to the 1/4″ tape.  That will be removed in the finishing stage and the 1/4″ of canopy sanded for a micro filler transition from glass to canopy.  Then the 1/8″ tape is removed and 1/8″ of canopy sanded to prepare for everything being painted for a very smooth transition.  After this was done on the outside, everything is matched up on the inside.  I had a lot of trouble with the duct tape pulling off on the inside close to the front where the curve is tighter, so I recommend using short2-3″ pieces to help keep this from happening in these areas.  Then I started building my wood frame Canopy Inside Support Structurefor the foam blocks to rest on.  Since I am leaving 1/4″ for a seal between canopy and longeron, I need these raised more than a few layers of duct tape.  I added 1 layer of duct tape on the longerons and installed the boards 1/4″ above the longerons.  Then I needed to add a spacer on the longerons which I did by slicing strips of blue foam at 1/4″ and using “Great Stuff” foam to glue it onto the duct tape covering the longerons.  After drying, I sanded the tops flush, and theGlassing Turtleback to Canopy sides to the proper curvature.  (Looking back, this didn’t work out as well as I had hoped and ended up with air bubbles where the overlap transitioned from canopy to fuselage.  Something to be aware of.)  Then covered everything with a layer of duct tape.  Added a few layers underneath that layer to protect the fuselage side.  Placed the canopy on for a test fit, and floxed the canopy to the turtleback.  Added the 1 UND at the bottom of the canopy.  After cure, added the 3 BID vertical strips to secure to the turtleback.  After that cured, I started cutting blocks for the canopy frame.  Using the technique illustrated on Charles Furnwager’s site works very well to get a perfect fit the first time, but the process still takes some time.

Gluing Canopy Deck FoamAfter finishing cutting out the foam blocks, I glued them all together with Great Stuff spray foam.  I made sure to put some wax paper under all the blocks to ease with canopy frame removal in the future.

Began the process of shaping the canopy frame, using the templates as a guide.  Since I raised everything 1/4″, I had a bit of a gap to the fuselage sides for glassing.  I cut strips of 1/4″ x 1/2 foam and micro’d into the gap, holding with nails.  Once cured, I was able to sand down to a closer profile.  I will still have some gap, but much better.  Sanded in my depressions from the forward hinge canopy plans, and marked my cut line, and hopefully ready for glassing.

Glassed Canopy Deck TopI ended up cutting a pattern for pre-cutting the glass.  The plans call for 2 pieces at 45 degrees, but I confirmed with Dennis it could be in more pieces if I stagger the joints.  I chose to make it in 3 pieces, front and 2 side pieces.  I pre-cut out my 2 BID, 2 Carbon fiber, and 2 UND.  Vacuumed  and micro’d my foam and laid my first BID into the valley around the canopy.  Filled the valley with flox and laid the rest per plans.  The forward hinge canopy plans call for 2 ply carbon fiber sandwiched between the BID and UND glass, which I did.  Sounds like a lot of people say the carbon fiber isn’t needed and is over kill.  I don’t know of anyone flying the forward hings canopy without the carbon fiber, so I kept it in for piece of mind.  Completed all 6 layers with the help of my lovely assistant, and covered with peel ply to cure.

Canopy Support StructureRemoved the peel ply and trimmed the front to be flush with F28.  Then I started building my canopy frame supports and bondo’d them to the canopy frame.  I also decided to add a little more strength to keep the canopy from sagging while sitting on the table.  Figured it a good time to replace the hardboard on my work table, and used the old hard board for the support.  Worked the edges loose with a hacksaw blade which released easier than expected.  Once released, I moved the entire top to the table, and continued to cut the turtleback free.  Not floxing the rear turtleback in place proved helpful here, as it was hard to cut through the turtleback flanges all the way through without boogering up the outside skin.  I was able to turn the canopy frame upside down to finish freeing it.  I was then able to clean up the edge of the rear turtleback and glass the drip rail.  With the canopy upside down, I was able to begin mapping out my hard points and contour the inside foam.  After some research on the forward hinge canopy, and thinking through the geometry, I figured out how the hinges would need to be mounted.  Three main things to watch out for:

  1.   Be sure the foam is removed all the way to the skin so that the hinge pins can be mounted as close to the outer skin as possible.  The hard points for the hinge pads will probably have to be built at an angle for this to work properly.
  2. Be sure the hinge pads are level in relation to each other, or you will risk binding.
  3. The cut line needs to be aft of the hinges, or things can pinch.  If you thing of a teeter totter on the playground, you know the only part of the board that moves up, is on one side of the hinge, and the other side actually moves in the wrong direction, and will cause pinching on your canopy.  The further rearward from the hinge, the better for this endeavor.  Hopefully it will be that easy, so time will tell!

Exothermed Canopy Hinge Hard PointI have been unfortunately been dealing with some setbacks in this portion.  After getting the main hinge hard points figured out, (which required me to build up the aft edge of the hard point by 1″, essentially creating a wedge) I glassed them with the flox/BID process spelled out in the plans.  I should have known better, but I got distracted and ended up completing these very thick hard points in one layup.  I was on the last layer, getting ready to peel ply, when the layup Canopy Hard Point Fixstarted to exotherm!  I attempted to get a fan on to cool it down and opened the garage door, which allowed me to keep it from starting a fire or melting through the upper skin, but the whole layup heaved and cured completely un-flat.  I ended up having to remove the Canopy Hard Point Fixmelted foam from around the hard points after cure, and grind most of the hard points out.  I then built up the surrounding area with new foam and got all my angles correct again.  I waited to shape the outside of the foam area until after the hardpoints were completed this time too, in case I ran into more issues.  This time I completed the hard point in multiple layups (2 large, and needed one additional for a minor touch Finished Fixed Canopy Hinge Hard Pointup)  After cure, I was able to fair the surrounding foam into the rest of the foam on the canopy frame.  Then continued to fill the rest of the hard points.  I am waiting to do the hard points for the gas springs until I have a better idea what the best positioning should be.  It will be much easier to handle the canopy not having to worry about dinging the foam or having things sag.  Since I am having the canopy top extended lower than the longerons to help prevent air leakage, I ran into some issues with air bubbles in the 3/4″ below the longerons.  With the carbon fiber, this is impossible to see, since it is completely opaque.  After grinding out the bubbles with the dremmel, I am able to fill in the areas with more carbon fiber, so the thickness will be Fix Canpoy Air Bubblesmore consistent when the inside layers are applied.  I also found that there were significant gaps between the canopy and turtleback where I added the foam wedges to add width and height, since it didn’t match the curvature as well.  Here I ground down the turtleback on the inside where it stood proud, then added a thin layer of flox and 2 BID over it to patch.

Back Arm Rest KeeperPatched up the air bubble locations and floxed and 2 BID the rear arm rest guides to the rear seat bulkhead to stiffen it up when installed.

F28 StiffenersCut out the F28 doublers and floxed onto F28.  Glassed with 3 ply BID.  Since I made the hinge pads larger on the canopy to facilitate moving the hinges more inboard, I made the doublers wider to accommodate too.

Glassing Inside Canopy DeckGlassed the inside of the canopy today (partially).  Glassed both sides with 2 BID, 2 Carbon Fiber, and 2 UND per the forward hinge canopy plans.  I left the overlap sections staggered at the front so I can come back and finish the front.  Covered with peel ply, and finished up the front section of the inside canopy after cure.



About Tarmac Grazer

I have recently purchased Cozy MK IV Plans #1627, and will be using this blog to log my build progress.
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