Van's Air Force
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What is up with my windscreen?
- Thread starter N64GH
- Start date
jjconstant
Well Known Member
If you can't feel it on either side I doubt that you can polish it out. I have seen that sort of crazing when the plexi was exposed to chemicals that it shouldn't have been exposed to. When I first saw this sort of crazing I was surprised that you couldn't feel anything other than a normal smooth texture of the surfaces of the plexi. In one case there was a lot of speculation that included a chemist and the consensus was it was avgas spillage or fumes from filling the header tank on a plane that had the header tank just below the base of the windscreen. The solution there was to replace the windscreen.
In your case I don't know if there was overspray of something that did this or stress cracks/crazing developed over time from thermal cycles or the plexi being installed with stresses in it. I've also seen much smaller crazing around holes in the plexi from people using Loctite on screws, as was mentioned in another recent thread. I think the most common cause is chemical...
I hope someone here has a more hopeful analysis...
In your case I don't know if there was overspray of something that did this or stress cracks/crazing developed over time from thermal cycles or the plexi being installed with stresses in it. I've also seen much smaller crazing around holes in the plexi from people using Loctite on screws, as was mentioned in another recent thread. I think the most common cause is chemical...I hope someone here has a more hopeful analysis...
Solvents
Almost certainly caused by exposure to some sort of solvent, usually combined with sun exposure over time. Could have happened weeks, months or even years ago.
Avoid using the aromatic solvents for cleaning (MEK, thinners, acetone etc), and certainly avoid ammonia based products found in many of the various glass cleaners that are available. In the absence of dedicated acrylic cleaners, turps or kerosene can be safely used to remove various residues like sticky tape glue etc. Be sure to wash the residue off with soapy water afterwards.
LP Aero Plastics have a pretty good info page on their website about this very subject.
In your case there is not much that can be done other than replace or put up with it.
Clive Whittfield
Auckland
New Zealand
Almost certainly caused by exposure to some sort of solvent, usually combined with sun exposure over time. Could have happened weeks, months or even years ago.
Avoid using the aromatic solvents for cleaning (MEK, thinners, acetone etc), and certainly avoid ammonia based products found in many of the various glass cleaners that are available. In the absence of dedicated acrylic cleaners, turps or kerosene can be safely used to remove various residues like sticky tape glue etc. Be sure to wash the residue off with soapy water afterwards.
LP Aero Plastics have a pretty good info page on their website about this very subject.
In your case there is not much that can be done other than replace or put up with it.
Clive Whittfield
Auckland
New Zealand
flyboy1963
Well Known Member
some theories, but no 'fixes'
Mike, I can't quite tell the age of your -6, was it built in 2000, or 2007?
in any case....
....this internal 'crazing' I have experienced to varying degrees; much more with polycarbonate than acrylic.
some theories;
If your bird is 10+ years old, is stored outside or in hi temps, then a good part of the condition is likely just 'age'. The resins harden, UV changes the properties etc.
If the canopy was pulled into position with any force, then that can show up as stress risers later...you'll rarely see this on a flat, non-stressed area.
The edge of the acrylic is much more prone to attack than the faces, so if some type of sealant was used at the base of the windscreen, it can start stresses or even full-on mechanical cracking at the edge, that slowly migrates upward.
I hate to say it, but you might be looking at a new windshield, ( I find this kind of thing nearly intolerable when the sun is at just the 'wrong' angle.)
again, seek out other professional help as suggested by others.
good luck!
Mike, I can't quite tell the age of your -6, was it built in 2000, or 2007?
in any case....
....this internal 'crazing' I have experienced to varying degrees; much more with polycarbonate than acrylic.
some theories;
If your bird is 10+ years old, is stored outside or in hi temps, then a good part of the condition is likely just 'age'. The resins harden, UV changes the properties etc.
If the canopy was pulled into position with any force, then that can show up as stress risers later...you'll rarely see this on a flat, non-stressed area.
The edge of the acrylic is much more prone to attack than the faces, so if some type of sealant was used at the base of the windscreen, it can start stresses or even full-on mechanical cracking at the edge, that slowly migrates upward.
I hate to say it, but you might be looking at a new windshield, ( I find this kind of thing nearly intolerable when the sun is at just the 'wrong' angle.)
again, seek out other professional help as suggested by others.
good luck!
Crazed Plexi
I had this same thing happen to the windscreen on my Titan Tornado several years ago. The paint shop did it by not keeping the masking paper and tape on while it was stored in a paint shop where other planes were being painted. Yes, just fumes from solvents will cause this and I've been told that things like regular glass cleaners can do it too but I have never experienced this because I had been forewarned about it. If it doesn't bother you too much I would just live with it but I would carefully check it before each flight to make sure it isn't getting any worse.
I had this same thing happen to the windscreen on my Titan Tornado several years ago. The paint shop did it by not keeping the masking paper and tape on while it was stored in a paint shop where other planes were being painted. Yes, just fumes from solvents will cause this and I've been told that things like regular glass cleaners can do it too but I have never experienced this because I had been forewarned about it. If it doesn't bother you too much I would just live with it but I would carefully check it before each flight to make sure it isn't getting any worse.
