Sealing the Canopy

Improve performance and reduce noise

It is an art. Back in the day, before kids, I was into tuning my trusty new-to-me Discus 2AX. In the evenings and on rainy days, I sealed it. I spent roughly 100 hours sealing the glider. How much did it help? "If you make the ship one percent better, you fly five percent better!" Klaus Holighaus from George Moffat's book, Winning 2.  If you have not read Winning 2, then it should be on your winter reading list.

Rubber tubing

PIK had a pretty neat idea: a rubber tube and a bulb to inflate the tube, which rested in a channel on the canopy frame. Despite the temperature change, you could always get it to seal... in theory... Remember that as the temperature changes, the canopy's fit will change.

Temperature effects how a canopy fits

I flew a freshly refinished glider at the Pre-WGC in Uvalde, TX. The glider came from a nice, cool winter in UT. As you can imagine, Uvalde, TX, in August is not cool. We had to sand the canopy frame to remove gelcoat, which eventually wasn’t enough. I was saved by Mrs. Jaeger (Team ARC), who had ice packs from ULine, and I would put them on the canopy about 30 minutes before takeoff and put blankets over the canopy to help insulate it. It was just enough to get the canopy to shrink so I could lock it.  I remember a similar situation with the two-seat EBs at another WGC: they would pour a gallon of cold distilled water over the canopy, which allowed them to lock it, then full power as the water boy ducked under the wing.

So we have to make sure whatever we seal the canopy with is flexible enough to accommodate the change in the gap. So using silicone that has been glued to one side of the canopy probably will not work in the wide temperature spread we see.

Use of yarn as a canopy sealant

One of the simplest things I have seen is yarn. Use very small pieces of tape to attach it; you could even use an adhesive like Super 77 spray, but use very sparingly and don't glue your canopy closed. Yarn might not last the entire season; however, you could seal the canopy in about 15 minutes with about 50 cents of material… If the gap is larger, you'll want to use something like open-cell foam. Often, this will have to be cut down and shaved to fit. How do you know where it is too high? The canopy bulges out.

Use paper to test for gaps

I have used strips of paper and slide them around to see where the canopy is tight and where it is loose. I also used a shop vac on the blow, tape, and a candle to determine where the leaks were. You might only need to seal one section of the canopy. One trick is to think about how the canopy closes. How are the two surfaces going to make contact? You want the foam to be pushed straight down and not rolled out of position. This is more complicated on a side-hinging canopy; there will be a transition to a different part of the frame.

Routing out a channel

Now, if you have A LOT of patience and nerves of steel, you could even route out a small tapered channel to help the foam stay in that section. I know of 3 gliders running around with said channel. It prevents the foam from being pushed out and makes a much better seal. However, you need to route only into the filler, not the structure, or you will run into problems. If you are in doubt about your abilities, DO NOT DO THIS!!! Think Yarn...

V-Seal

We also have a great product called V-seal. Once you figure out how to use it, it is great. However, the learning curve for manipulating it around the front of the canopy is steep, and you probably will not get it on your first few tries.  You might have to make small V-cuts on the inside to get it to make the curve without wrinkling. This is best when there is a large gap between the canopy and the fuselage. It is definitely faster and cheaper than adding gelcoat to fill it in. The canopy caps will, unfortunately, shorten the V-seal's lifespan.

When I did this on my Discus, it was before smartphones with cool noise decimal apps, but with the vents closed at VNE, I thought the ASI had broken because there was no way I could possibly be going that fast; it was so quiet.

Banner photo by aeroklub krnov z.s

 Garret Willat holds a flight instructor rating with over 8000 hours in sailplanes. His parents have owned Sky Sailing Inc. since 1979. He started instructing the day after his 18th birthday. Since then, Garret has represented the US Junior team in 2003 and 2005. He graduated from Embry-Riddle with a bachelor's degree in Professional Aeronautics. Garret represented the US Open Class team in 2008 and 2010 and the Club Class team in 2014. Garret has won 3 US National Championships.