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  #1  
Old 10-23-2006, 10:01 AM
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Default surface cracking

Quote:
Originally Posted by Carolynne View Post
I have never seen the sort of cracking that you describe in my aircraft or others that i have had the chance to look at. but if this really worries you, you might try adding a little flox to the micro mix. This should effectively 'cross link' the filler and provide more stability. I used this on some areas which needed a bit of a build up such as fillets between fuz and wing, wing and winglet etc.

carolyn
When I walk down the flight line and look at the canards, I see cracking. In the middle of wings, along edges. Nothing structural, just cosmetic stuff, but there all the same.

as far as checking with nobodies on the 2 oz fine weave cloth as a liner for the tanks, guess Nat Puffer is one of em cause that is who i talked to on using it.

As far as sheer strength goes, well, none of the glass has much, that is the weak point, i have pulled off the peel ply and mistakenly had glass in my hand also and ZIP, off it came with the peel ply.

I like building, hate repairing. Don't particularly like the idea of the flox added to the micro in soo many places as it would make the plane a PIA to sand.

Maybe I'll do a test layup, yeah, a test layup, thats the ticket.

Youall can tell me that this or that plane has no cracks, but, that is not what my eyes tell me, see em all over, don't want em
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  #2  
Old 10-23-2006, 12:03 PM
Lynn Erickson Lynn Erickson is offline
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Quote:
Originally Posted by Dust View Post
When I walk down the flight line and look at the canards, I see cracking. In the middle of wings, along edges. Nothing structural, just cosmetic stuff, but there all the same.

as far as checking with nobodies on the 2 oz fine weave cloth as a liner for the tanks, guess Nat Puffer is one of em cause that is who i talked to on using it.

As far as sheer strength goes, well, none of the glass has much, that is the weak point, i have pulled off the peel ply and mistakenly had glass in my hand also and ZIP, off it came with the peel ply.

I like building, hate repairing. Don't particularly like the idea of the flox added to the micro in soo many places as it would make the plane a PIA to sand.

Maybe I'll do a test layup, yeah, a test layup, thats the ticket.

Youall can tell me that this or that plane has no cracks, but, that is not what my eyes tell me, see em all over, don't want em
most of those cracks you are seeing are most likely in the paint. a lot of the canard aircraft are painted with auto paint and over time the flexing of the structure causes it to crack. we have checked many of these over the years and have never found it to be more then the paint. we see the same thing on the fiber glass car parts. also shows up on glass and carbon covered props if you add to much paint or primer.
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  #3  
Old 10-23-2006, 12:13 PM
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mmmmmmmmmmmm, its just the paint, mmmmmmmmmmmm

Well, I LIKE that answer cause it is easier, but i hate the answer cause of that, hard to trust the liking of an answer that you like. Not hard to trust you.

are the urethanes we been advised to use part of the automotive paint systems that you have seen cracking?

one plane of note is Richter's jet, not to bash him at all, just one that pops out in my memory of cracks, lots of em

Also my tech advisor has em (just a couple that bug him), I'll check on what paint system he used
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  #4  
Old 10-23-2006, 12:51 PM
SteveWrightNZ SteveWrightNZ is offline
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as long as the layers or bog and paint are thin, you should be fine - not much cracking. This means, of course, that your workmanship has to be perfect - no covering a multitude of sins with micro and twelve coats of paint. As is the usual, it takes about the same to make a thing, whether you do a tidy job underneath and little to fill, or a careless job underneath and much filling and sanding, but one will get you cracking and one will not.

S
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  #5  
Old 10-23-2006, 01:08 PM
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little fill sounds great, but the reality of my plane is not.

for example, you make beautiful wing and then attach it with 18 layers of cloth each stepped in an inch. the list goes on and on and on.

plenty of micro is goin on, that is just the way that it is.

I am confident in my ability to fill and sand so that nothing to speak of will be primer filled and the paint will be thick enough. those skills i already have in making a gloss finish on woodworking projects.

fill the grain, wet sand, 3 coats of sanding sealer, wet sand, 3 coats of gloss, wet sand, 3 more light coats of gloss or mat, wet sand and polish

All blems must be removed before i leave 36 grit and micro.
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Old 10-24-2006, 02:46 PM
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Just got off the phone with my tech advisor

1 cracks are below paint level
2 he has used the cloth i am using and in the areas he used it - no cracking

Not an answer i liked hearing
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dust

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  #7  
Old 10-24-2006, 07:59 PM
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Quote:
Just got off the phone with my tech advisor
I guess it wouldn't help you to suggest that he might be wrong, would it?
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  #8  
Old 10-25-2006, 09:46 AM
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Quote:
Originally Posted by John Slade View Post
I guess it wouldn't help you to suggest that he might be wrong, would it?
Sure, suggest it all you want, but he has been around a long long (flying long for 20 or so years) time and has seen this problem and HAS the problem. He also used the same solution I am planning on and we came up with the solution independently.

He is also very involved in the community, when i chatted with him he is helping rebuild a long whose landing gear bulkheads failed on anothers plane. Offered him the use of my fein and he will probably use it for a day for demolition.

No need for all of us to own all tools, even though i have a rather complete set, don't mind borrowing when I do not have what is needed.

2 + 2= 4, even though I would rather take the advice given here, it is easier and simplier, I will take the other advice.
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dust

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  #9  
Old 10-26-2006, 11:35 AM
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Don't obscess about it Mike, you need some glass in some places on your plane.

Quote:
fill the grain, wet sand, 3 coats of sanding sealer, wet sand, 3 coats of gloss, wet sand, 3 more light coats of gloss or mat, wet sand and polish
Although similar process, this is not wood you're working with.
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  #10  
Old 10-26-2006, 11:50 AM
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I'm still trying to figure out how a layer of 2 oz. cloth over micro is going to stop the supposed cracking of the structural layup underneath the micro????: hysterica
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Old 10-26-2006, 12:43 PM
Wayne Hicks Wayne Hicks is offline
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Thick micro applied for cosmetic reasons can and will crack in some areas no matter how strong the structural layups are underneath. The canopy hinge areas are the prime examples. Our fantastically strong airframes are strong because they do flex. So the goal is for your workmanship to be good enough to avoid having to cover it up with --excess -- micro.

Some of us can't avoid thick micro even thoug we've done acceptable work. I missed on the shape of the fuselage at the canopy hinges. So I've got the micro on thick there. That's one of the reasons I applied a strip of UNI bonded with my structural epoxy.

Again, I had tried the 2 ounce glass and it peeled right off the micro. The UNI stayed fast.
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  #12  
Old 10-26-2006, 01:12 PM
argoldman argoldman is offline
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Quote:
Originally Posted by Wayne Hicks View Post

Again, I had tried the 2 ounce glass and it peeled right off the micro. The UNI stayed fast.

Strange, Wayne, that the adhesion to a substrate would depend on the weight (for want of a better word) of the fabric. Fiberglass does not, itself want to bond to epoxy. It is treated with a chemical so that the bond can take place. If the glass has been exposed to moisture, this can be compromised. Is it possible that you got a batch of glass that either wasn't treated, was compromised before you got it, or became compromised in your shop?? Who was your suupplier?, what was your under glass preparation??

The Osprey aircraft uses 1.45 oz glass. Have these aircraft been experiencing delams??


Hopefully I will be sealing my Aerocanard strakes/tanks this weekend.
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  #13  
Old 10-26-2006, 02:01 PM
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Quote:
Originally Posted by David Clifford View Post
I'm still trying to figure out how a layer of 2 oz. cloth over micro is going to stop the supposed cracking of the structural layup underneath the micro????: hysterica
No cracking of the structural layup has been talked about or suggested, just the micro covering and the paint over it.
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dust

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  #14  
Old 10-26-2006, 04:03 PM
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Quote:
Originally Posted by David Clifford View Post
I'm still trying to figure out how a layer of 2 oz. cloth over micro is going to stop the supposed cracking of the structural layup underneath the micro????: hysterica
Review:

Micro Ballons (AKA Micro) are hollow. That means they are filled with air.
Temperature has a direct effect on the expansion/contraction of the balloon.
If expansion is present, so is pressure on the inside walls of the balloon/balloons. Repeated expansion/contraction breaks down the bond from one balloon to the next depending on how "wet: the bond was

I think that what the're are driving at is that a thin layer of glass over , not under, the filled areas of micro will contain the possibity of cracks. That is over heavily filled areas, not everything. Maybe even some skim coats of epoxy will have the same result.

Imagine a kids balloon blown up inside of a coke bottle. As the air heats up and the balloon expands, there is not enough pressure to break the bottle.

Now for a true story.

Some engineers were working on mounting a tape encoder to the azimuth ring of a midsized telescope for astronomy. The tape, 2mm thick, had to be recessed into a 2mm groove so the tape would be flush with the circumference of the ring. Unfortunately they machined the ring way too deep.

Their solution was to fill the groove with microballons and epoxy and re-machine to the 2mm depth. Operationally telescopes are subject to temperature variations from -10 to 100+F. The end result was that the matrix of micro balloons and epoxy broke apart and the positon encoder simply fell off the ring.

This little misunderstanding of materials cost over $30,000 to fix.
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  #15  
Old 10-26-2006, 04:47 PM
Phil Kriley Phil Kriley is offline
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I hate when that happens...
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