FIBREGLASS IS SUPPOSED TO DO WHAT?
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FIBREGLASS IS SUPPOSED TO DO WHAT?
Glassing, in my estimation is supposed to do two things
1) Strengthen the outer skin &
2) Provide an area to be painted
I have completely "covered" my first fuselage.
98% of the areas have definately strengthened the overall rigigity, however, even though the balsa has been covered with 1.5oz glass, about a 10"x 3" area along the left rear quarter is very soft. I don't know if that particular area had a less stiffness to the wood or not but my overall question is this?
Q) Even though it has a layer of glass would it be overkill to apply another layer of glas on top of it again?
marwen
1) Strengthen the outer skin &
2) Provide an area to be painted
I have completely "covered" my first fuselage.
98% of the areas have definately strengthened the overall rigigity, however, even though the balsa has been covered with 1.5oz glass, about a 10"x 3" area along the left rear quarter is very soft. I don't know if that particular area had a less stiffness to the wood or not but my overall question is this?
Q) Even though it has a layer of glass would it be overkill to apply another layer of glas on top of it again?
marwen
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RE: FIBREGLASS IS SUPPOSED TO DO WHAT?
Close, no cigar.
The glass/epoxy layer provides a surface which is ostensibly smooth and with little work, can be paint ready. The epoxy penetrates the wood structure to some extent, and while it does increase the overall strength of the model's skin, a single layer of glass and epoxy doesn't increase the stiffness of the wood or the underlying structure to any marked degree.
The wood/glass surface will be harder, i.e. more resistant to hangar rash and punctures (like from a screwdriver) but not necessarily stiffer.
Put another way, if you made a basketball from epoxy/glasss skinned balsa, it would fare better than a raw balsa basketball. The only real differrence between the two would be that after a couple minutes playing time, the glass/balsa jobbie would be more easily relocated to the dust bin because all the balsa toothpicks would still be in the epoxy/glass 'bag'.
The glass/epoxy layer provides a surface which is ostensibly smooth and with little work, can be paint ready. The epoxy penetrates the wood structure to some extent, and while it does increase the overall strength of the model's skin, a single layer of glass and epoxy doesn't increase the stiffness of the wood or the underlying structure to any marked degree.
The wood/glass surface will be harder, i.e. more resistant to hangar rash and punctures (like from a screwdriver) but not necessarily stiffer.
Put another way, if you made a basketball from epoxy/glasss skinned balsa, it would fare better than a raw balsa basketball. The only real differrence between the two would be that after a couple minutes playing time, the glass/balsa jobbie would be more easily relocated to the dust bin because all the balsa toothpicks would still be in the epoxy/glass 'bag'.
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RE: FIBREGLASS IS SUPPOSED TO DO WHAT?
I would not expect another layer of glass to help much, and it would add weight. Any chance of adding a bit of support on the inside, like a stringer or partial former?
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RE: FIBREGLASS IS SUPPOSED TO DO WHAT?
Seth has the right idea if you think it needs the help.
You see fiberglass, as a structural item and not for finishing, is strong and stiff in tension and compression provided the loads can be kept in the same plane as the cloth. To achieve good bending resistance, which is what you're asking about, you need to do one of two things. Either use lots of layers so it's a thick layup or use two outer skins with a core between. In both cases the stiffness will be determined by the spacing between the two outer layers. The stuff in the middle is only there to prevent the outer layers moving closer or further from each other. In effect you are building an I beam but in two dimensions. A common term for this cored panel method that provides good stiffness for light weight is honeycomb composites. Racing boats use balsawood endgrain blocks between to relatively thin layers of glass layups to provide excellent strength and stiffness combined with light weight. The fancy wood stripper canoes are another example of this principle at work.
All of which goes to say that a single light layer applied to only one side of the wood sheet cannot be expected to do much for adding bending resistance. In fact the 1/2 oz cloth does almost nothing for this aspect.
Now if you had put a layer on the inside of the wood before you curled it into place and then glassed the outside even the 1/2 oz cloth would have offered a high degree of added stifness. It would have done this because pushing on the outer layer would have transmitted through the wood of the sides to the inner layer and tried to stretch the inner layer rather than bend it. And since glasscloth layups are excellent at resisting stretching loads you would have found that the sides were quite stiff.
Not much you can do about it now. To achieve a decent addition of bending resistance you would need to add quite a thick layer of glass to the outside of the model. And that would be HEAVY, not to mention the much higher amount of compensatory nose weight you would require.
Just sand it down so it's nice and smooth and carry on. Remember, you don't have that much wing area on this one to carry very much extra weight.
You see fiberglass, as a structural item and not for finishing, is strong and stiff in tension and compression provided the loads can be kept in the same plane as the cloth. To achieve good bending resistance, which is what you're asking about, you need to do one of two things. Either use lots of layers so it's a thick layup or use two outer skins with a core between. In both cases the stiffness will be determined by the spacing between the two outer layers. The stuff in the middle is only there to prevent the outer layers moving closer or further from each other. In effect you are building an I beam but in two dimensions. A common term for this cored panel method that provides good stiffness for light weight is honeycomb composites. Racing boats use balsawood endgrain blocks between to relatively thin layers of glass layups to provide excellent strength and stiffness combined with light weight. The fancy wood stripper canoes are another example of this principle at work.
All of which goes to say that a single light layer applied to only one side of the wood sheet cannot be expected to do much for adding bending resistance. In fact the 1/2 oz cloth does almost nothing for this aspect.
Now if you had put a layer on the inside of the wood before you curled it into place and then glassed the outside even the 1/2 oz cloth would have offered a high degree of added stifness. It would have done this because pushing on the outer layer would have transmitted through the wood of the sides to the inner layer and tried to stretch the inner layer rather than bend it. And since glasscloth layups are excellent at resisting stretching loads you would have found that the sides were quite stiff.
Not much you can do about it now. To achieve a decent addition of bending resistance you would need to add quite a thick layer of glass to the outside of the model. And that would be HEAVY, not to mention the much higher amount of compensatory nose weight you would require.
Just sand it down so it's nice and smooth and carry on. Remember, you don't have that much wing area on this one to carry very much extra weight.
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RE: FIBREGLASS IS SUPPOSED TO DO WHAT?
I spoke to SoCal yesterday, he seemed to think that I had a bad mix of z-pxy for that particular area and suggested that I take the "denaturered alcohol" and slowly remve the existing appication y wicking it back to the whitenwss of the glass - allow it to dry a day or so and reapply the poxy.
In my way f thinking, if this is the route to go - it woulad totally be easier to simply remove the area - balsa, glass & z-poxy - and replace the balsa. Start the glassing aplication in that area over again.
???
marwen
In my way f thinking, if this is the route to go - it woulad totally be easier to simply remove the area - balsa, glass & z-poxy - and replace the balsa. Start the glassing aplication in that area over again.
???
marwen
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RE: FIBREGLASS IS SUPPOSED TO DO WHAT?
Depends what you mean by soft. I thought you meant the region was cured but still flexible. Is the glass/epoxy still soft (e.g., can you scrape some up with your fingernail - does it not sand?) If the latter, yes it could be due to poor mixing. You might be able to soak some out. Reapplying more resin might help the uncured residue to cure. I'd thin the new application of epoxy 50% so it will penetrate. Putting it in a warm area will help too.
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RE: FIBREGLASS IS SUPPOSED TO DO WHAT?
Most of the time if I want to warm up my poxy - I'll take a HOT pot of water and sit the poxy A & B in it for about 30 minutes or so. If I need it in a hurry then I;'ll do the mix - put it into a 1oz plastic cup & nuke it for 10 secs
That has worked well in the past.
The finished zpoxy section is hard and cured but there seems to be a couple of areas that will indent a little. See the oval areas in the attachment
Other than that it's pretty much ready to apply its second (diluted) zpoxy to get rid of the glass threads.
marwen
That has worked well in the past.
The finished zpoxy section is hard and cured but there seems to be a couple of areas that will indent a little. See the oval areas in the attachment
Other than that it's pretty much ready to apply its second (diluted) zpoxy to get rid of the glass threads.
marwen
#8
RE: FIBREGLASS IS SUPPOSED TO DO WHAT?
Spray painting a base color of Klass-Kote will make the cloth stiffer.
I do this so as to make it more difficult to "ding" the skin of the aircraft.
It isn't a perfect solution, but since you are going to paint the plane anyhow, why not use a paint that will create a hardened surface?
Dave Platt uses it.
Try it, I think you will like it.
Ron
I do this so as to make it more difficult to "ding" the skin of the aircraft.
It isn't a perfect solution, but since you are going to paint the plane anyhow, why not use a paint that will create a hardened surface?
Dave Platt uses it.
Try it, I think you will like it.
Ron
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RE: FIBREGLASS IS SUPPOSED TO DO WHAT?
You don't by chance have a void behind those spots do you? Like maybe the cloth is not sticking to the wood in those spots? Is the cloth clear and you can see the wood grain in those areas clearly or is it whitish and cloudy?
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RE: FIBREGLASS IS SUPPOSED TO DO WHAT?
As you (hopefully) can see with the overlay attachment, I took a much earlier shot of the skeletal trussing as I progressed my building.
I know for a fact that the trusses went all the way back to the "H" former.
This shot was prior to that timeframe, but what I have tried to do here is line up the formers and where my current oval sketches are on the glassed fuse.
The ovals are around the "F" & "G" formers
As I recall, the farther back the fuse went, the trussing support became more elongated.
My guess here is that even though the finished glass "looks" just like the mojority of the glassing (no white areas) there is probably not as much support in that area as I would like there to be.
The 2nd attachment shows the depth of trsuues as I went along. However, the bulkhead we can see to the left of the image is only "E" former.
marwen
I know for a fact that the trusses went all the way back to the "H" former.
This shot was prior to that timeframe, but what I have tried to do here is line up the formers and where my current oval sketches are on the glassed fuse.
The ovals are around the "F" & "G" formers
As I recall, the farther back the fuse went, the trussing support became more elongated.
My guess here is that even though the finished glass "looks" just like the mojority of the glassing (no white areas) there is probably not as much support in that area as I would like there to be.
The 2nd attachment shows the depth of trsuues as I went along. However, the bulkhead we can see to the left of the image is only "E" former.
marwen
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RE: FIBREGLASS IS SUPPOSED TO DO WHAT?
PROBLEM SOLVED
I put a #2 - (500watt) photoflood light bulbinto a lamp and held the fuse up to it.
The longerons run on top of and immediately below my soft spots! Apparently, the trusswork did not come out and hit the bulhead wall..
Consequently, a "spongy" area!
Now, to try & figure out how to stiffen that few square inches of "in & out"
My guess is that if I were able to measure the depth of the depression(s) - perhaps no more than 1/16" of travel.. and again ONLY in the areas that were shown in the ovals in post a few back in this thread.
marwen
I put a #2 - (500watt) photoflood light bulbinto a lamp and held the fuse up to it.
The longerons run on top of and immediately below my soft spots! Apparently, the trusswork did not come out and hit the bulhead wall..
Consequently, a "spongy" area!
Now, to try & figure out how to stiffen that few square inches of "in & out"
My guess is that if I were able to measure the depth of the depression(s) - perhaps no more than 1/16" of travel.. and again ONLY in the areas that were shown in the ovals in post a few back in this thread.
marwen
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RE: FIBREGLASS IS SUPPOSED TO DO WHAT?
Looks like a nice build, I would not sweat the "soft spots". Like Bruce said "stay away" from touching them, while in the air. LOL
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RE: FIBREGLASS IS SUPPOSED TO DO WHAT?
iron eagle
Here is a shot of a small 36" version of this 96" AIRHOPPER.
Bruce: It looks I have most of the kinks taken out of this project.
Q) Is it possible to monokote over top of the zpoxy coat?
A while ago we were addrssing the wing that was a little warped. I took off the 1/32" balsa that was on it. It warp remained. I find that it will be much easier to redo the entire wing extension. If you recall that wing was fairly high-aspect ratio, consequently, there's not much wing there to lift the increase in weight that has built up throughout its transformation from a totally FREE FLIGHT to that of RC
Q) Would it be possible to add 2" to 3" to the Root chord? The center section is permanent at an 8" chord. The increase would fit easily enough and would certainly help increasing the lifting capabilities.
marwen
Here is a shot of a small 36" version of this 96" AIRHOPPER.
Bruce: It looks I have most of the kinks taken out of this project.
Q) Is it possible to monokote over top of the zpoxy coat?
A while ago we were addrssing the wing that was a little warped. I took off the 1/32" balsa that was on it. It warp remained. I find that it will be much easier to redo the entire wing extension. If you recall that wing was fairly high-aspect ratio, consequently, there's not much wing there to lift the increase in weight that has built up throughout its transformation from a totally FREE FLIGHT to that of RC
Q) Would it be possible to add 2" to 3" to the Root chord? The center section is permanent at an 8" chord. The increase would fit easily enough and would certainly help increasing the lifting capabilities.
marwen
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RE: FIBREGLASS IS SUPPOSED TO DO WHAT?
ORIGINAL: marwen
Q) Is it possible to monokote over top of the zpoxy coat?
Q) Is it possible to monokote over top of the zpoxy coat?
Theres a legion of problems with putting an iron on over epoxy. For starters the heat will soften and tend to melt the epoxy. Second is that the monokote will show air bubbles galore. It's hard enough to put the stuff down over regular balsa where the air can leak through. Sure it's slow but it does leak through. But with epoxy they would stay forever.
Nope... primer, wet sand and then spray bomb it or use a spray gun. You're stuck with paint now. But don't sweat it. Paint over epoxy/glass is going to give a really nice finish.