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Canopy's cracks

R

RV-4

Well Known Member
Well today I had the displeasure of finding a crack in my RV-4 's canopy....

This canopy was installed in 2010 ( # 3 ) using Sikaflex and only 4 screws to hold it in place...

When I received the canopy from VAN'S I made a remark that I found it very thin and wouldn't be surprise if it eventually cracked...well today it proofed me right...

The next one is going to be a Todd's canopy...His are .220'' thick vs .177 for the Van's ( Aero-Plastics ) ones so hopefully it 's gonna last a little longer..

Any feedbacks on Todd's Canopy you guys will like to add?

Thanks

Bruno
[email protected]
 
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Cracked Canopy

It did cracked from an aera bonded by Sikaflex.

There was a smaller crack from the beginning at one of the screw.I stop-drilled it and it hasn't expanded yet...

Looking at it closely today, I noticed that the crack ( located just aft of the rear seat on the L/H side ) was in line with the joint in the skirt. It may have caused a stress or weak point.

My canopy was also rubbing slighly when I closed it so it may also have caused some stress and with the thickness of the canopy not being the greatest at this location, it eventually let go..

I have glued the crack shut with Weldon 3 so hopefully it will hold until I get the new one ready.

I've got a new Todd's Canopy on order and will use a complete Sikaflex bonding with the new one without screws or rivets...


Bruno
 
Crack

I now have two cracks in my 8a canopy. Besides stop drilling them I got clear Gorilla tape and put a strip on both the inside and outside of canopy. It might be a little ugly but I think it will hold just fine.
 
Canopy

The most likely cause for cracks not involving a fastener is inadequate finishing of the edges. After doing as much as possible with a file, the edges should be sanded with wet or dry sandpaper starting with 320 grit and finishing with 400. Wrap the sandpaper around a small wood block and sand lengthwise along the edges. There should also be a nice smooth chamfer on all edges, polished the same way.
One of the fairly recent issues that now affects ALL acrylic sheet is the lack of quality control. Material that should measure .250 might actually be as thin as .230. When this is formed into a canopy the thickness will be much less in thin areas.
In most cases small cracks can be reinforced on the inside with bonded doublers. In most cases these will not interfere with vision and are only mildly annoying cosmetically. Any plastic supplier should have the "glue" for making repairs. You can form the doubler with a heat gun before bonding simply by heating it and then holding it in place against the canopy. One method of doing this is to use a wood block with a piece of medium hardness rubber glued to it, then a piece of cotton fabric wrapped around the block. Form the block, let it cool, then bon d it in place. The proper type of cement actually melts the acrylic slightly and then cures quickly.
I know of two midget racing airplanes that had canopies made from Aeronca 7AC windshields. The windshields were split down the middle and a strip was bonded down the middle on the inside. Lasted over thirty years. One was a very fast airplane that went at least 270 m/h.
 
Canopy

For new construction an inside reinforcement can be created in highly stressed areas by bonding a narrow strip of cloth and epoxy to the inside of the canopy. This would be especially useful if any fasteners are used. The strip would be narrow enough so not to be visible when the canopy is finished.
 
Canopy

I did the light tint canopy from Todd, and it is real nice. It is a little taller than Vans' canopy as well as thicker. Todd recommended that I use 3M 5200 Fast Cure to bond canopy on. One tube at $25 and it is done, never ever to come off.
 
Cracked Canopy

Thanks a lot to everyone who provided feedbacks on your experience with your canopy.

I've used the original canopy frame that was on the aircraft when I bought it 3 times now and will most likely go with a new frame next time around( will see how it goes eventough I think that the original frame should be just fine )

I ordered a new canopy from Todd and should be getting in about 3-4 weeks I would say..I can still fly the aircraft even with the crack..( I welded it shut with Weldon 3 so I'll see how it goes.

Doug: I don't have a picture but will try to remember to take one tomorrow if I go flying..Send me your e-mail and I'll send it to you ( I can't post it here..)

Keep on sending feedbacks and trick...much appreciated

Bruno
[email protected]
 
3 Canopys!

Is there a chance you could post some pic's of the canopy support tube- plexy glass intersection. and what size holes are you drilling for the few pop-rivets? If there is tension at the pop-rivet a crack propagate from there.
 
RV-4 Cracked Canopy

CarPart ( David)

Yes this will be # 4 on this RV-4. No luck I guess :rolleyes:

The first one was cracked all the way around by vandals during the first winter that I owned the a/c ( Aircraft was parked outside and it appears they tried to get inside and broke the canopy in the process.

The second one ended up with a stress crack starting from a rivet after 5 years.

The third broke this week after being on the a/c for 4 years. It may have flex a little when I closed the canopy( The canopy is touching a little bit in the rear left corner and it might be a possible cause, this will be fixed if I decide to use the old frame again, haven't decided yet )

Dayton : I took a picture of the crack today with my cell but don't have an account to host the picture to use as a link to this site.

The next one will be completly Sikaflex, no more screws or rivets..and will be a Todd's canopy.

Bruno
[email protected]
 
Now if the cracks are always in a similar location then that would be interesting.

Like many, I have a taxi position on my canopy for those hot days, which pretty much seems like every day under a bubble canopy. I find that when I taxi, the canopy sometimes bounces around quite a bit on the taxi lock which is at the roll bar. I have been worried that this could lead to a crack eventually. Lately I have been closing the canopy when in motion, suffering thru the heat.
 
Cracked Canopy

David

No, the previous canopies cracked at different location...:eek:

I've got a new one on the way from Todd's

Bruno
 
Canopies crack because of a bad combination. We (1) introduce weak spots, and then (2) guarantee high stress by attaching them to a relatively rigid steel frame with an inelastic fastening system (rivets and screws).

The weak spots are the holes, as well as various nicks/gouges on panel edges and the edges of the holes. The stress multiplication factor of a clean hole is 3. The stress multiplication factor of a nick varies from small to infinity, depending on the sharpness. The really bad news? If you look at one of your drilled holes with a magnifier you'll learn that a drill rarely leaves a clean hole in plexiglass. The edges are full of nicks unless you carefully grind them to smoothness. Shape a small, fine rotary rock and use it rather than a deburring tool.

Steel and plexiglass both change dimension with temperature change, but their coefficient of thermal expansion is different by a factor of 6 or more. For each degree of temperature change the plexiglass expands or contracts 6X more than the steel. The actual dimension change is huge, about 1/16" per linear foot per 100F temperature delta.
 
Bruno's Pictures

CANOPY%252520CRACK%252520%252523%2525202.JPG

CANOPY%252520CRACK.JPG
 
Bruno's Pictures

Thank you Bill for posting the pictures...really appreciated..

You will noticed that the # 2 picture shows the crack as being a little fuzzy, it is because it was taken after I used Weldon 3 to glue in back together..

Dan, my canopy was Sikaflex in place..there were only 4 screws holding it in place and they were at different location than the crack.The next one won't have any screws or rivets.

As I mentioned in previous post, my canopy wasn't closing perfectly, it was touching a little in the back and may have contribute to the canopy cracking...It will be fixed on the new one..

TurboFan : Yes the Todd's Canopies are a little taller from what I've seen and he also has a Tall Man option..

Bruno
 
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