Double-wall Canopy mod to eliminate frost

[Chris Kinnaman]

Two, possibly three years ago, I read an article in one of the gliding mags
detailing the attachment of a plexi or lexan sheet to the inside of a
canopy, creating an air space which would be warmed by solar radiation thus
preventing frost during cold-weather high-altitude flights. Trouble is, I
can't remember the magazine in which this article appeared, nor the
particular type glider. Does anyone remember this story? If anyone has a
copy of it, could it possibly be scanned and passed along to me?
Thanks in advance,
Chris

[[email protected]]

HI Chris,
I have not seen the article, but have made clear vision panels. When I was young and foolish I did quite a bit of winter wave soaring in central Oregon, and canopy and instrument frost was a frequent problem. I used high density double stick foam tape and mylar sheet. I made about six rectangles of aproximately six by eight inches and stuck them on the inside of the canopy at sensible locations. Larger sections will not conform to the compound curves of the canopy. The tape is widely available at places like Home Depot. A credit card works pretty well on the instrument faces. Not much room for error when flying in those conditions as oxygen systems can ice up as well. I carried a bail out bottle and used a old A14 regulator and military pressure mask. I also destroyed the finish on a KA6 fuselage during one of those flights. No regrets though.
Dale Bush

[bumper[_4_]]

I have made several clear vision panels.

The last one in two parts for an Arcus. No double sticky tape is used. The edges are sealed with silicone foam weatherstrip (cheaper weatherstrip can be used, but silicone weathers exceptionally well and has a broad temperature range). Panels are of polycarbonate (Lexan) and are held in place by their own tension.

Paper templates are fitted, taped in place first, then removed and using to cut the Lexan slightly oversize. Temporary pieces of cheap weatherstrip are stuck on for spacing and the panel is fitted, trimmed, fitted, repeat ad nauseum. Best to tape the canopy frame to protect if from scraping from all the fitting.

The clear vision panel will be under considerable tension to provide some compression to the silicone foam, thus the sides cannot rest on anything other than the canopy frame (i.e. it can't rest on the sliding window rail. Small leaks are okay, but generally the fit should be snug.

Depending on the glider, some have only a small amount of forward vision space above the glare shield, no forward panel may be needed. But if a vertical panel above the glare shield is desired, it should be acrylic rather than Lexan. Acrylic is better for this application as it is more optically clear and scratches can be polished out (not so with Lexan). Tabs can be added at the bottom, then heat bent to fasten to the underside of the glare shield lip. A small clearance space is desirable at the top of this panel so it does not contact the canopy and to allow the forward vent to flow at least some air around it.

As Dale mentioned, depending on the amount of compound curve of the canopy, head room will be lost with larger clear vision panels, so that's a consideration in the design. Using several strips, still spanning from one canopy rail to the other, so as to fit under tension, would be easier than one or two larger sections.

Nice thing about Lexan is it can be worked with woodworking tools. Can be cold or hot bent, is much more mechanically strong than acrylic, so cracking isn't a problem when cutting, drilling , sanding with belt or Dremel.

But - - even more than some projects, takes at least twice the labor as any reasonable estimate.

bumper

[xcnick]

Good to see you Bumper at the Perlan hanger today. This is a question we should have asked. I found keeping the canopy clear was the only challenge to wave flying (flame suit on). My solution was not elegant but 100% effective. I attached a hose to the mask so all my exhale was diverted behind me into the turtle deck. 5 min. and 5 bucks at home depot.

[Chris Kinnaman]

Thanks for the replies, everyone. The lexan & plexi sheets with edges
sealed with silicone foam is pretty much the method described in the
article.
Chris

[[email protected]]

If you aren't successful making the home made version, commercial versions called "Frost Shields" are available for truckers in Canada, Alaska, etc. I still have a few in a box from Wave flying years ago, the box shows their address: "C.T. Enterprises Ltd, 1635 13th St, Brandon, Manitoba R7A 4S7 These have a sharp ~1mm step in the plastic 1/2" from the edge. The label lists several sizes, mine are 7" x 13". They worked very well at 23,500'.
~Barny

[[email protected]]

On Wednesday, December 9, 2015 at 9:45:07 PM UTC-5, Chris Kinnaman wrote:
> Two, possibly three years ago, I read an article in one of the gliding mags
> detailing the attachment of a plexi or lexan sheet to the inside of a
> canopy, creating an air space which would be warmed by solar radiation thus
> preventing frost during cold-weather high-altitude flights. Trouble is, I
> can't remember the magazine in which this article appeared, nor the
> particular type glider. Does anyone remember this story? If anyone has a
> copy of it, could it possibly be scanned and passed along to me?
> Thanks in advance,
> Chris

Try the December 2013 issue of Soaring magazine page 32. This should answer all your questions.

[Eric Greenwell[_4_]]

bumper wrote on 12/9/2015 9:00 PM:
> The clear vision panel will be under considerable tension to provide
> some compression to the silicone foam, thus the sides cannot rest on
> anything other than the canopy frame (i.e. it can't rest on the
> sliding window rail. Small leaks are okay, but generally the fit
> should be snug


I've made clear vision panels for an ASW 20C and and ASH 26 E that do
rest on the sliding window rail. After 25+ years of total use, I've had
no problems.

Here is a pdf article describing how I do it, with pictures. With the
above exception, the method is the same as the one bumper uses.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-Launching Sailplane Operation"

https://sites.google.com/site/motorgliders/publications/download-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/Guide-to-transponders-in-sailplanes-2014A.pdf

[Eric Greenwell[_4_]]

Eric Greenwell wrote on 12/11/2015 7:51 PM:
> bumper wrote on 12/9/2015 9:00 PM:
>> The clear vision panel will be under considerable tension to provide
>> some compression to the silicone foam, thus the sides cannot rest on
>> anything other than the canopy frame (i.e. it can't rest on the
>> sliding window rail. Small leaks are okay, but generally the fit
>> should be snug
>
>
> I've made clear vision panels for an ASW 20C and and ASH 26 E that do
> rest on the sliding window rail. After 25+ years of total use, I've had
> no problems.
>
> Here is a pdf article describing how I do it, with pictures. With the
> above exception, the method is the same as the one bumper uses.
>

OK, HERE is the link to the article :^)

https://sites.google.com/site/motorgliders/clear-vision-panels

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-Launching Sailplane Operation"

https://sites.google.com/site/motorgliders/publications/download-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/Guide-to-transponders-in-sailplanes-2014A.pdf