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Broken Canopy

Danny King

Danny King

Well Known Member
Saturday I flew over to Hicks field (T-67) to work on the RV-1 and see if my larger than Cinderella hulk would fit into the RV-1's glass slipper size cockpit. It was windy and very cold that morning. I parked the Doll out side of Jay Pratt's RV Central hanger, and went inside to get out of the wind and drink my mug of coffee. Ten minutes later, I returned to the Doll to place my empty coffee mug in the cockpit, and I discovered two cracks in the canopy, that were not there minutes earlier. The theory that Sikaflex fillets, bonding the glass to the canopy frame to relieve the stress on the rivets, proved to be ineffective. Therefore!

Do you have a finish kit, Aero Plastics, light gray tint canopy, that you do not plan to use, because you are planning to use a Todd's canopy? If so I would like to purchase it. It would be extra nice if you live near Dallas/Fort Worth.

Thanks
 
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Too sad, Danny. I just went and took a look at the Doll's picture at the root level of this site, just to pay my respects. She's a beautiful airplane!

I'm a long way from canopy work, but after a long flirtation with SikaFlex, I'd already decided to return to the tried and true when I get to that point. Your experience confirms that decision for me.

How old is the Sika bond? Are the two cracks near each other? Is there any evidence of other crazing or deformations near where the cracks started?

--
Stephen
 
That's a bummer Danny!

How was your canopy Sika'd? You mention fillets to relieve the stress on the rivets. Was the canopy drilled and installed using Van's traditional method, with Sika added afterwards?

I went 100% Sika for the canopy, skirt, windscreen, and windscreen fairing. There haven't been any issues so far, but mine's still a baby at ~100hrs.
 
Tough break on the canopy. I like others have used the sika/rivet combination. Hope I'll have better luck.

I have the issue vans canopy still in the plastic in the back of my hanger. I'll give it to you. However, I am heads down starting the 40 hour fly off and just haven't got the time to crate it etc. I live in Merritt Island, FL (Cocoa Beach).

Don Stiver
321.693.5399
 
fatherson said:
Too sad, Danny. I just went and took a look at the Doll's picture at the root level of this site, just to pay my respects. She's a beautiful airplane!

I'm a long way from canopy work, but after a long flirtation with SikaFlex, I'd already decided to return to the tried and true when I get to that point. Your experience confirms that decision for me.

How old is the Sika bond? Are the two cracks near each other? Is there any evidence of other crazing or deformations near where the cracks started?

--
Stephen
Click to expand...

Stephen,
That canopy was installed four years ago. It was attached according to assembly manual with the soft pull rivets. After that, Sikaflex was inserted to form filets between the canopy glass and the canopy frame above and below the frame.

The extreme cold wind blowing at 27 degrees F super chilled the canopy glass, and the disparity between the shrinking Lexon canopy, and the steel canopy frame, exceeded the oversize rivets holes margin, and the cold brittle canopy broke. The Sikafex did nothing to prevent the cracking. The new canopy will be attached with only Sikaflex without using the rivets at all.

Both cracks were on the left side. One was about a foot forward of the rear seat, and the other was aft of the rear seat bulkhead.
 
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Cracked Canopy

Danny,
I replaced mine last summer. Got a blemmished one from Jeff and Becky Rogers at Airplane Plastics (937-669-2677). The blem was in the forward wind screen part. $ was about half. They make them for Van's.
Jim Moore
RV8 Den
 
Jim Moore said:
Danny,
I replaced mine last summer. Got a blemmished one from Jeff and Becky Rogers at Airplane Plastics (937-669-2677). The blem was in the forward wind screen part. $ was about half. They make them for Van's.
Jim Moore
RV8 Den
Click to expand...

Jim,
Thanks for the info.
Tailwinds,
 
Looks like you've got a couple of good leads already Danny!

"Sky" and I were commiserating over this most of the day Saturday - he discovered the cracks just as we showed up at Jay's. I am still flying the Val with the crack that formed on New Year's Day...last year. new canopy sitting in the garage just waiting to be installed, but we've been sorta busy with the -3. I'm hoping that when it warms up, we'll get to install it, and we're thinking of using WAY over-sized holes with slices of surgical tubing as "grommets' for the rivets. In order to do Sika right, we'd end up changing the fit of the skirt, which would change the fit of the windshield, which is WAY too much work for me on a finished airplane.....

We've had lots more anecdotal reports of finished canopies cracking on-8's than any other model if I recall correctly . My theory is that the length of the canopy just leads to a greater expansion ( and therefore more stress at the holes) than on the shorter airplanes.
 
Sika

I' sorry to hear about your loss, but I cannot believe that it was temp change that caused the cracking. I did my 7A canopy with sika and eighth inch spacers. I fly my 7 back and forth between Granby and Fort Collins and have seen as much 50 degrees or more at altitude difference,as high as 17,5 over the divide with no sign of any cracking. So far it has been four winters with nothing. any way, good luck with the new canopy.. Dave
 
mtnflyer said:
I' sorry to hear about your loss, but I cannot believe that it was temp change that caused the cracking. I did my 7A canopy with sika and eighth inch spacers. I fly my 7 back and forth between Granby and Fort Collins and have seen as much 50 degrees or more at altitude difference,as high as 17,5 over the divide with no sign of any cracking. So far it has been four winters with nothing. any way, good luck with the new canopy.. Dave
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Good point, but every canopy that cracked that I've heard of, regardless of model, happened in cold conditions. A local RV-6 canopy cracked while climbing to 17,000 feet. Ironflight's canopy cracked in-flight in cold conditions in California. Four years ago, we had three local RV-8 canopies crack while in the hanger during the same very cold night.

I believe Paul is on to the solution for a finished RV-8 with the canopy attached as per plans. The standard oversize holes specified for the soft pull rivets is not sufficient for the large RV-8 canopy.
 
Sorry to hear about the canopy, Danny. :mad:

However, before you blame the balmy North Texas temperatures, check the ramp security cameras. You'll probably see Jay out there with a ball peen hammer, tapping on your canopy. :eek:

Lemme know if you want help fitting your new canopy. I'll fly down and give you a hand. However, I won't fly until it warms up. :)
 
Danny King said:
I believe Paul is on to the solution for a finished RV-8 with the canopy attached as per plans. The standard oversize holes specified for the soft pull rivets is not sufficient for the large RV-8 canopy.
Click to expand...

Totally agree (run the numbers with coefficient of thermal expansion for steel and plexiglass), but I'd like to add one detail. Next time you drill and deburr a hole in plexiglass, examine it with a 10x magnifier. What looks ok to the naked eye is too often a collection of stress concentrations, in particular when deburred with a cutter.

I got the best results with high speed, low pressure drilling, then using a cone-shaped fine grit stone for the deburring step....a ground edge on the hole rather than a cut edge.
 
Another One

I found two cracks in my RV-8 canopy after landing in Kalispell, MT, back in September. I think it was probaly caused by turblence combined with colder temperatures at altitude. I have stop drilled both cracks for now.

Sitting in the back seat, both cracks are the on the left hand side each starting from a rivet hole.

Paul

RV-8
Calgary
~150 hours
 
My -9's canopy cracked while up in Michigan visiting Mom for Easter. The OAT the morning I found the crack it was +5*F on the ground.
 
Danny, sorry to hear about your canopy!

When I built my canopy I drilled for rivets, but used Silka totally and only used the rivet holes for the clecos to hold her down while the gue setup. No cracks so far (knock on wood 3 times) Order some of the clecos with long tangs to get to the steel frame. I also used a tinted canopy from Todd. Great fellow with a great warranty! I'd buy from him again.
bluebird013.jpg
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Pirep on attachment with grommets

Paul's idea sounds good, just a caveat that when you put something pliable like surgical tubing around a fastener, ( which is exactly what we did on our sliding canopy Jodel in 1975) we found that the weight of the canopy, flex, aerodynamic changes, all served to take the grommet to its limit, and then it pretty much stayed there; the fastener was no longer nicely centred in the holes, with room for expansion all around it.
I'm not that familiar with the -8 canopy, but it looks big, heavy, long etc. and it would be very hard to fit so precisely as to keep all those fasteners centred.

( but then again, they don't let me work on the shuttle either! :)

YMMMV $.02 etc.
 
Cracked Canopy

Danny,

Please post some pics of your cracks. I will post my cracks of my Todds. I have a better solution for the new canopy install.

I will be making a bezel to hold the canopy to the frame and form fit around the front bow. I plan to use a high quality 3m (or similar)adhesive silicone used for mounting windows in high-rises...no holes in the plastic and it will float within the bezel when expansion and contraction occurs w/temp and aerobatics!

Zman
N742PZ
 
OVERSIZE HOLES

What is the standard oversize hole 5/32?
Ironflight said:
Looks like you've got a couple of good leads already Danny!

"Sky" and I were commiserating over this most of the day Saturday - he discovered the cracks just as we showed up at Jay's. I am still flying the Val with the crack that formed on New Year's Day...last year. new canopy sitting in the garage just waiting to be installed, but we've been sorta busy with the -3. I'm hoping that when it warms up, we'll get to install it, and we're thinking of using WAY over-sized holes with slices of surgical tubing as "grommets' for the rivets. In order to do Sika right, we'd end up changing the fit of the skirt, which would change the fit of the windshield, which is WAY too much work for me on a finished airplane.....

We've had lots more anecdotal reports of finished canopies cracking on-8's than any other model if I recall correctly . My theory is that the length of the canopy just leads to a greater expansion ( and therefore more stress at the holes) than on the shorter airplanes.
Click to expand...
 
-*A Canopy Crack

My -8A canopy doesn't have a single rivit - all Sika. Still, last Oct on one of the first cool mornings here in the desert, I discovered a 4 inch vertical crack on the left side at the rear frame crossbar attach area. That roar you heard in the air was me going through my vocabulary - several times.

Several folks have commented that perhaps I didn't properly smooth the canopy edge - that there was an undetected nick that turned into a stress riser. Can't tell - I stop drilled the thing and have pressed on without removing any of the glue.

So far the only lesson learned is to be very attentive to proper smoothing of the canopy edges. Also, I used fairly widely spaced clamps, not close-spaced clecoes, to hold the canopy against the frame for gluing. Perhaps I induced a stress during that process. But still, I thought the Sika was supposed to flex enough to eliminate such potential stress.

Hadn't thought much about it until reading this thrad. I'm still really upset.
 
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Cracked Canopy

Mine Cracked at about 1100 hours and 8 years of service. It cracked at a rivet hole on the left side behind the rear seat. It was installed per Vans instructions.

My opinion here: I think what we can learn from all of this is that the canopy is not suitable for it's planned service in an RV. It should not be so fragile that it does not survive regular (real life) service. Canopy makers take note.
 
As I understand the canopy making process, each is different and has varying thicknesses throughout the canopy. Perhaps you engineering types know whether a thicker canopy would be the solution. Assuming that holes are all adequately deburred, oversized and all edges smoothed, these really shouldn't crack from cold temps and/or turbulence.

My original canopy cracked because I had a brain fart and used the wrong kind of rivet. I stop-drilled the crack and flowed in cyanoacrylate and the crack never progressed, even though I flew it throughout the cold winter months. Apparently, the crack was a sufficient stress reliever, at least in that part of the canopy.

How about it? Should the canopies be a wee bit thicker?
 
Talk to Jeff @ Airplane Plastics in Dayton OH, I'm sure he can fix you up with a thicker canopy. They supply all of Van's plexiglass parts. He won't sell a Van's canopy direct, but they'll tell you how to custom order one thru Van's. I just picked a custom canopy from them not too long ago for my -6 rebuild.
 
RV-8 canopy cracks

This thread has pointed out that most cracks happen on the left side of the canopies. I've noticed that the canopy latch, on the left side, pulls the canopy forward as it is latched, causing the entire canopy to list to the port side. I'm wondering if that puts additional stress on the left side of the canopy glass.

In the future, I will side the canopy closed, but will not latch it on cold days. I wonder if I had either left the Doll's canopy open, or simply not latched it last Saturday in front of Jay Pratt's RV Central if we would be talking about this problem now. Any thoughts?
 
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One datum

Danny King said:
This thread has pointed out that most cracks happen on the left side of the canopies. I've noticed that the canopy latch, on the left side, pulls the canopy forward as it is latched, causing the entire canopy to list to the port side. I'm wondering if that puts additional stress on the left side of the canopy glass.

In the future, I will side the canopy closed, but will not latch it on cold days. I wonder if I had either left the Doll's canopy open, or simply not latched it last Saturday in front of Jay Pratt's RV Central if we would be talking about this problem now. Any thoughts?
Click to expand...

The Valkyrie's crack is on the right side, behind the passenger's head.
 
Danny King said:
This thread has pointed out that most cracks happen on the left side of the canopies. I've noticed that the canopy latch, on the left side, pulls the canopy forward as it is latched, causing the entire canopy to list to the port side. I'm wondering if that puts additional stress on the left side of the canopy glass.
Click to expand...

I was told ,or read , that the latch should be adjusted so it doesn't apply any forward pressure to the frame. Pulling the frame forward with the latch racks the frame out of alignment and puts stress on the whole canopy.
 
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