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I Hate Sanding  (or, "Add a 3/4 inch extension to your canopy")

Written by Sonny Wiersema

First, I have to say thanks to Bernie Berger for his guidance in regards to this small project.  Not having built my airplane, working with fiberglass is new to me.  So when I asked Bernie for help, he gave me instructions that were detailed enough for a novice.  Thankfully, his instructions did more than just tell me how to add an extension to the aft end of my canopy - they also gave me the basic knowledge for working with fiberglass on just about any project.  With that said, I can tell you that my project turned out as I expected it would for a first timer...and because of that, it's only 95% done.  So why am I writing this article now, you ask?  Well, the remaining 5% is going to be dedicated to fixing some minor  imperfections in the work I did - but I'll get to that later.

The idea to add the extension to the canopy was brought into my head when I saw Bernie's airplane.  I noticed his right away, partly because the extension is right in your face when you enter the cockpit, but also because I was looking for a solution to prevent water from entering my airplane where the canopy meets the fuselage.  I had installed some weather stripping on the back of the canopy, but somehow water always seemed to seep in even though it "appeared" to have a tight seal.  I knew that the best prevention of water entering in that area would be to not allow water to touch the weather stripping.  My biggest concern was this was a visible part of the airplane that people would notice if it looked bad. 

I'm not an "artistic" person...I don't have patience for creating perfectly straight lines or making sure every bump or ripple is evened out.  I suppose it's the monotony of sanding, filling, sanding, filling, sanding...you get the picture.  Anyway, my girlfriend said "be patient and it'll turn out great".  Whatever...patience isn't part of my vocabulary when it comes to things like this.  I can be patient all day long during a pre-flight or when working on an engine...but not with aesthetic things.  So to begin, I had to make up my mind that I would do this right...and be patient. 

Bernie's didn't mention how much I'd be sanding - probably a good thing since I wouldn't have considered this project had I known - so once the weather cleared I got started.  The first thing I did was rough up the aft edge of the canopy bow so the epoxy had something to adhere to.  Easy enough with 60 grit sandpaper.  After that I put down vinyl tape to mark the areas that I was going to be working with.  On top of the vinyl tape on the canopy I added 2 layers of masking tape so when I was sanding I wouldn't sand through the tape and damage the Plexiglas of the canopy.  On the fuselage I had a 2.5 inch wide layer of vinyl tape covered by about 10 layers of duct tape.  I wanted to make sure that when the canopy was closed, the new extension wouldn't come in contact with the paint on the fuselage.  On top of the duct tape I added a single layer of plastic packing tape.  The epoxy wouldn't stick to the plastic tape so it would be used as a "mold release". 

Next up was cutting 4 strips of E-glass to length and mixing the epoxy.  After wetting the fiberglass strips, laying them in position was simple.  I followed Bernie's advice and stepped each new layer forward about 1/16th of an inch so there wouldn't be a noticeable hump from the Plexiglas to the canopy bow.  After the last layer of fiberglass was added, I put a layer of peel-ply on top to suck up the excess epoxy. 

After letting it bake in the sun for about 5 hours I removed the Peel-Ply.  I then let it sit overnight to completely harden before continuing with the job.  I used a Dremel tool to cut about 1/2 inch from the back of the new extension.  This would leave about 3/4 inch to overlap the fuselage...plenty to keep the water from getting in.  I made a small mixture of epoxy with Flox and added this to the inside of the canopy extension where it touched the old bow.  There was a slight gap there, and the epoxy would fill that gap, and strengthen the structure while adding a radius to the corner.  I mixed up some Aeropoxy Smooth Fill and added a few thin layers to make it more aerodynamic.  Without the Filler, the extension  had a slight "step" from where the fiberglass raised up onto the duct-tape mold I laid it over. 

After the first few layers of filler, I sanded, filled, sanded, filled, and sanded some more.  I hate sanding.  Maybe I don't hate sanding, I just hate doing things over and over.  Once I thought I had it right, I sprayed primer on the extension.  This is where the remaining "5% to complete this job" comes in.  There are 2 low spots right next to each other on the upper left corner of the bow.  If you look at it just right, you can see them - they ripple.  I don't know why I didn't fix the low spots when I noticed them - maybe because I was so close to being done and I was tired of sanding.  But I let it go hoping it wouldn't be noticeable...I was wrong.  After I sprayed the top coat on you could see the ripple.  Oh well, I figure that at this point it's doing it's job at keeping water out of the cockpit and it looks OK - not perfect, but OK.  I'm estimating that 3 hours of labor should fix it. 

I added weather stripping from Home Depot that was small and pliable, but strong.  Good timing since it started raining this morning!  I had a chance to watch the water runoff and see that it's not getting inside the airplane - at least not from the back of the canopy.  I've found that there's lots of little openings that allow water inside the airplane, but the canopy was a major one.  Overall work time for this project was 10 hours.  But due to the waiting of cure times for the epoxy and Filler, those 10 hours were spread out over a week.

I found a local paint store that carried my Pulsars' Dupont Imron paint.  They mixed some up and put it in 2 aerosol cans for a total of $30.  That was a good deal considering a pint of that stuff costs about $100.  Total for materials was over $200 because I had to buy a roll of fiberglass, Peel-ply, Aeropoxy resin & filler and miscellaneous tools.  Well worth the cost just for the learning experience alone!

If anyone has questions or comments on this article, please send an e-mail to webmaster@pulsaraviators.com.