Where the back of the canopy meets the turtle deck

[tmobbs]

Sonex LLC always emphasises that the Sonex is a simple, VFR aeroplane, not intended to be flown in the rain, and I am happy with that. But sometimes you can just get caught out by rain, at least here in the UK.

As I am working on my windshield and canopy right now, I am wondering if it would be possible to have the rear of the canopy extend a few mm over the turtle deck, so as to keep the rain out. The plans show a small gap between the canopy and the turtle deck which seems very likely to let in the rain.

So does the rain get in, in practice?
Has anyone extended the canopy a few mm so that it covers the gap, and if so, does it keep out the rain?

Tim Mobbs
Sonex #1555 Aerovee #0672
Bungay, Suffolk, England

[mike.smith]

Hi, Tim,
I haven't flown my own plane in the rain. When I was doing the Sonex T-flight training we did get some light drizzle near the airport (still VFR, by the way). The only place I saw water lightly dripping in was between the windscreen and the canopy.

The thing to keep in mind about the canopy is that it is not well restrained, so it expands and contracts a LOT when it's in and out of the sun. So if you try to make a close fit to anything at the rear of the canopy, it's going to change depending on the weather. I made a nice gap of less than 1/8" between the canopy and the turtle deck. That worked fine in my basement, but when I got it out in the sun it expanded and rubbed on the turtle deck. I had to do some sanding. I would not want to try to overlap the canopy with the turtle deck. I think some people have tried to put some kind of a gasket back there, attached to the front face of the turtle deck formers, but I don't have any photos of an example.

[tmobbs]

Hi Mike

Thanks for your thoughts. But I fear I may have given you the wrong idea. I am not thinking of decreasing the gap between the canopy and the first former of the turtle deck. As you point out, a 1/16th or even 1/8th inch gap is quite snug for a material that expands and contracts as much as the Sonex canopy material does, and anyway there has to be some "play" to enable the canopy to open and close smoothly.

No, what I have in mind is having the canopy extend maybe 1/4" on top of / outside the turtle deck, so there is no gap. The rear canopy bow would still be in front of the first former of the turtle deck. but it's curvature would be almost exactly the same size as the turtle deck curvature so the rear edge of the canopy would extend over/ outside the turtle deck, so there would be no gap at all.

You say you wouldn't try overlapping there, but why not?

Incidentally, I quite expect there to be some rain penetration at the interface of the canopy and the windscreen, but at least there is the windshield strap providing some continuity between the canopy and the screen. What I was aiming for was a similar effect at the back.

Tim Mobbs
Sonex #1555 Aerovee #0672
Bungay, Suffolk, England

[sonex892]

Tim
My sonex canopy is standard with the gap, but with my previous plane I used a strip of aluminium to overlap the turtledeck. I see no reason the same couldn't be done with the Sonex. Could possibly could do the same at the front where the canopy meets the windshield.

making a template


The finished canopy the aluminium strip overlapped about 6mm


Steve
Sonex 892

[DCASonex]

Have not done it with mine, but see no reason why a length of round bead type weatherstrip could not be fastened to the turtle deck former to meet with canopy in its normal position.

David A.

[N111YX]

I've been in a fair amount of rain in my Waiex but just good old American rain and not the English type. However, I did fly into some English-Style rain near Cleveland a few years back. I would classify it as "moderate" for about 15 minutes. The only seepage that I get is at the front bow. I think that a good canopy fit at the aft area of about 1/16'ths of an inch would keep that water out in back. It just seems to flow over that area without a problem.

The front bow is another matter. I use a soft-sided Velcro sticky strip around the front lip in an effort to seal it. However, after being in light rain for about five minutes I must use a towel on the glareshield to protect the panel as the drips begin. I'm not sure what I would use if I were try to remedy the front leaks but I might begin with a rubber U-channel wrapped around the leading edge of the canopy. A near-perfect canopy fit in front would go a long way with any option.

I would suggest a Prince propeller as well as mine takes the rain very well without erosion.

Regards,

[mike.smith]

Hi Mike

No, what I have in mind is having the canopy extend maybe 1/4" on top of / outside the turtle deck, so there is no gap. The rear canopy bow would still be in front of the first former of the turtle deck. but it's curvature would be almost exactly the same size as the turtle deck curvature so the rear edge of the canopy would extend over/ outside the turtle deck, so there would be no gap at all.

You say you wouldn't try overlapping there, but why not?

Incidentally, I quite expect there to be some rain penetration at the interface of the canopy and the windscreen, but at least there is the windshield strap providing some continuity between the canopy and the screen. What I was aiming for was a similar effect at the back.

Hello, again:

I knew what you meant, I just didn't do a good job of explaining myself :-) The point is the same. I think you will end up with something that fits well one hour, and through expansion or contraction not so well the next hour. Is your fuselage painted or polished? If painted, any contact by the canopy is going to wear away the paint quickly. If polished, it's going to get a rash from the canopy.

I'm not an aerodynamic engineer, but I think there is a drag effect from a blunt surface shedding air off the back side (the rear canopy edge in this case).

If you do decide to try it, I might suggest adding a gasket on the turtle deck former, extending up so it touches the canopy. Maybe that way the gasket will keep the canopy's shape and prevent it from contacting the turtle deck.

Just thinking out loud. I could be completely off base. It is "experimental" aviation after all ;)

[tmobbs]

Thanks, everyone, for their thoughts. The aircraft will be painted. I will probably stick to the plans re the rear of the canopy. What various people have said about the canopy / windshield line letting in water is probably a more serious matter anyway, given the proximity of the panel. Kip's towel may be the most practical answer!
Best wishes
Tim Mobbs
Sonex #1555 Aerovee #0672
Bungay Suffolk England

[peter anson]

Hi Tim, I think the small change I made to my Sonex can probably fix the problem. I didn't like the idea of the rear of the canopy not having any support (unlike the front) so I folded a couple of thin angles from .025" aluminium and fluted them to match the curve of the turtle deck. It is offset from the turtle deck skin by the canopy thickness. I think it works well to match the shape of the canopy to the turtle deck. The top is coated with a thin layer of PR compound in an attempt to make a seal, but it would probably be better if the angle was offset slightly more and a rubber strip was glued to the top. It does keep most of the rain out when parked.

Some sort of seal at the front would be beneficial too as I have had to do some mopping on the odd times when I have flown in rain.

Peter Anson
Sonex 894

[DCASonex]

If you have not fitted your canopy or windshield yet, consider bonding a double layer of black felt on top of forward bow strap so that it is held in place by the windshield, and provides a bit of cushion and seal for canopy. Not a perfect seal, but quick cheap and some improvement.

David A.