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06-16-2008, 05:20 PM
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Join Date: Jan 2006
Location: Orange County CA
Posts: 646
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Cracked Canopy, What Now?
I've done it, bummer. The canopy is now officially cracked. I was using the countersink bit on the top spine when I noticed a problem. I now have three or four holes that look like the one below. Very small hairline cracks, moving about 1/16 to 1/8" out from the hole.
I called Vans. They said to use Weld-On to wick into the cracks and glue them shut. I also called Jeff from Airplane Plastics, since Vans gave me his number, and he said it would be better to drill out the holes large enough to remove the crack. There should be plenty of holes left to secure the canopy, and that would remove the risk of further cracking from the Weld-On joint.
So now I have conflicting advice. What do you think? Glue with Weld-On, or drill them out bigger???
__________________
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Peter McCoy
RV9A N35PM S/N:91335
First Flight: April 2013
Hobbs: 400 hours after Oshkosh 2017
www.myrv9.com
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06-16-2008, 08:50 PM
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Join Date: Jan 2005
Posts: 3,646
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Peter-
Sorry to see that. It's hard to know if those cracks will ever propogate, but I guess it's better to do something about them now, rather than wait.
I don't know anything about Van's suggested fix. Might work. Drilling the hole out will, from the looks of the picture--I think, require a much bigger hole than you'll have a good rivet for, although you could use some vinyl or surgical tubing in the oversized hole as some have done trying to forestall canopy cracks. See archives for this canopy construction method.
My thought would be to drill that hole as large as necessary to eliminate the cracks. If you haven't already drilled the aluminum strip, I'd then abandon that hole and drill a couple extra holes forward and aft of that location. Then, before putting the aluminum strip on, fill your problem canopy hole with some type of sealant (proseal or lexel would work great) and then lay the aluminum strip over it. Aside from the irregular rivet pattern on top of the canopy (which no one would see once painted), I think you'd be good to go.
If you have already drilled the aluminum strip, just order a new strip and match drill all the holes (except for your problem hole) from the old strip to the new one.
Just my initial thought. Good luck with whatever you do. I was pretty stressed with all that drilling and cutting too. I'm just glad (knock on wood) that it's over!
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Steve M.
Ellensburg WA
RV-9 Flying, 0-320, Catto
Donation reminder: Jan. 2021
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06-17-2008, 07:28 AM
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Join Date: Jan 2005
Location: St. Paul, MN.
Posts: 4,792
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I can't really tell from the picture. Is that a crack? Or a scratch? Is it all the way through?
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06-17-2008, 08:17 AM
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Join Date: Aug 2007
Location: Houston, Tx
Posts: 163
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Drill it!
I'd go with the drill oversize. Cracks gone for good.
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Bill S.
A+P, RV Dreamer + Schemer
RV-9 preplans in hand
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06-17-2008, 08:19 AM
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Join Date: Jan 2006
Location: Orange County CA
Posts: 646
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Crack
Quote:
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I can't really tell from the picture. Is that a crack? Or a scratch? Is it all the way through?
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Yes, it is cracked. At the top of the hole, two small cracks extend out from 11 & 1 on the clock. Very small, but still significant. I looked at all the remaining holes with a magnifying glass, and found a total of seven holes that have these small cracks. All of them are on the top spine of a slider. If I drill them out to a larger size, the cover strip (c-653) will hide the holes.
__________________
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Peter McCoy
RV9A N35PM S/N:91335
First Flight: April 2013
Hobbs: 400 hours after Oshkosh 2017
www.myrv9.com
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06-17-2008, 04:05 PM
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Join Date: Jan 2007
Location: TN
Posts: 183
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What'd you use to countersink?
What did you use to make those countersinks? Do you think that is what caused the cracks?
I'm going to try those special bits from Avery, since I've already paid for a new canopy, but that's another story...
Thanks,
Greg
__________________
Greg Marlow
RV-9A Flying - sold
4 pl Bearhawk - flying ("sold" to the insurance company)
RV-14A - finishing up
Dues gladly paid
East Tennessee/SW Virginia
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06-17-2008, 04:26 PM
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Senior Curmudgeon
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Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 15,420
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A thought
May I suggest that if you do drill out enough to clear the cracks, you do so extremely cautiously.
I can just see the drill catching/chattering in the current crack-----wont take much of a snag----and causing an even worse crack.
I would think about stabilizing the existing small cracks with glue, then drilling.
If you have any scrap, might try a practice run or two.
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Mike Starkey
VAF 909
Rv-10, N210LM.
Flying as of 12/4/2010
Phase 1 done, 2/4/2011 
Sold after 240+ wonderful hours of flight.
"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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06-17-2008, 05:13 PM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Pete, I'm guessing you used a standard countersink bit, the kind with three or four straight cutting edges. They chatter on plexiglass. Take a close look with a 10x magnifier. Instead of a conical cut, I think you'll see "flats" with a gouge between each, and the cracks radiating from the gouges.
Switch to a single-hole countersink (aka "zero-flute") and just barely tweak the edge of the hole. Better yet, whenever possible deburr by grinding with a small conical stone.
I like Mike's idea about wicking some Weld-On into those cracks before doing anything else.
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Dan Horton
RV-8 SS
Barrett IO-390
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06-17-2008, 05:41 PM
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Join Date: Nov 2005
Location: AUSTRALIA
Posts: 749
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How about stop drilling each crack with a small bit, say about 1/16". Another suggestion, carefully grind out each crack individually with a small grinding bit ( I am thinking no bigger than about 1/16") in a high speed Dremel. With either method the original drill hole would be left as is so you would not risk more cracking by using a bigger drill. You may consider filling in where the cracks were ground out/stop drilled with a filler/glue that sticks to plastic.
Fin
9A
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06-17-2008, 06:11 PM
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Join Date: Jan 2005
Posts: 804
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Quote:
So now I have conflicting advice. What do you think? Glue with Weld-On, or drill them out bigger???
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FWIW I would drill them out.
A Unibit (step drill) will make very clean holes in acrylic without chattering, and will easily enlarge your existing holes. Go slowly and use very little pressure.
You want all the holes to be significantly larger than the fasteners, to allow the canopy to expand and contract without being trapped between two rigid points.
You don't need to countersink the plexi holes at all. you can make them a little bigger than the outside of a dimple, dimple the "targa" strip, and avoid any contact between the canopy and the fastener
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James Freeman
RV-8 flying
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