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Why is polycarbonate not allowed for ordinary cars? It seems like it would accomplish the same goal as automotive safety glass, namely preventing injuries from

by Zak 15y ago

Why is polycarbonate not allowed for ordinary cars? It seems like it would accomplish the same goal as automotive safety glass, namely preventing injuries from sharp shards of glass in a collision.

deleted 15y ago
[deleted]
sliverstorm 15y ago
It may be one of those plastics that grow opaque as they age. It may not be strong enough. It may have worse glare problems. It may not resist chips and scratches as well. Or it may simply not have been fully tested for the job.
rfreytag 15y ago
Polycarbonate is not used widely because is VERY expensive to fit and replace. My glider canopy is $5000 replaced: http://www.mikeash.com/my_glider.html http://www.mikeash.com/my_glider.html (ask me how I know). Note even the canopy for the ancient but popular ASK-13 is over $2000 on this site: http://www.wingsandwheels.com/glider_canopies.htm http://www.wingsandwheels.com/glider_canopies.htm Installing these babies is really tricky. Nothing ever fits quite right from the factory. Worth another $3000 easy in labor; after all it is an aircraft.
- Zak 15y ago
  I'm not asking why it isn't widely used. I'm asking why it's apparently forbidden by law or regulation, requiring an exemption for the application described in the original post.
spoondan 15y ago
It appears that there is no specific prohibition against polycarbonate windshields for cars. The exemption in this case is required because the polycarbonate windshields that Terrafugia currently uses do not pass the required abrasion tests: basically, they scratch too easily and are too prone to reduced visibility. Terrafugia requested the exemption because it is still searching for a vendor that passes the compliance tests and meets the vehicle's unique requirements. Apparently, vehicles with the current windshields will be required to undergo regular and frequent inspection and repair. See the page numbered 38273 in the PDF: http://www.terrafugia.com/pdf/2011-16222_NHTSA_EXEMPTION_GRANT.pdf http://www.terrafugia.com/pdf/2011-16222_NHTSA_EXEMPTION_GRA...
jws 15y ago
CDs are polycarbonate and shatter sharp. Maybe there is polycarbonate that doesn't. Autoglass is required to shatter into slightly dull bits. Pitting would likely also be a problem causing reduced visibility. Aircraft stay above most land blown grit.
Daniel_Newby 15y ago
"Why is polycarbonate not allowed for ordinary cars?" Go to a parking lot and look at the plastic headlight covers on high-mileage cars. Many are frosted to opaqueness because of impact with grit.

by Zak 15y ago

Why is polycarbonate not allowed for ordinary cars? It seems like it would accomplish the same goal as automotive safety glass, namely preventing injuries from sharp shards of glass in a collision.

deleted 15y ago

[deleted]

sliverstorm 15y ago

It may be one of those plastics that grow opaque as they age. It may not be strong enough. It may have worse glare problems. It may not resist chips and scratches as well. Or it may simply not have been fully tested for the job.

rfreytag 15y ago

Polycarbonate is not used widely because is VERY expensive to fit and replace. My glider canopy is $5000 replaced: http://www.mikeash.com/my_glider.html http://www.mikeash.com/my_glider.html (ask me how I know). Note even the canopy for the ancient but popular ASK-13 is over $2000 on this site: http://www.wingsandwheels.com/glider_canopies.htm http://www.wingsandwheels.com/glider_canopies.htm Installing these babies is really tricky. Nothing ever fits quite right from the factory. Worth another $3000 easy in labor; after all it is an aircraft.

Zak 15y ago
I'm not asking why it isn't widely used. I'm asking why it's apparently forbidden by law or regulation, requiring an exemption for the application described in the original post.

spoondan 15y ago

It appears that there is no specific prohibition against polycarbonate windshields for cars. The exemption in this case is required because the polycarbonate windshields that Terrafugia currently uses do not pass the required abrasion tests: basically, they scratch too easily and are too prone to reduced visibility. Terrafugia requested the exemption because it is still searching for a vendor that passes the compliance tests and meets the vehicle's unique requirements. Apparently, vehicles with the current windshields will be required to undergo regular and frequent inspection and repair. See the page numbered 38273 in the PDF: http://www.terrafugia.com/pdf/2011-16222_NHTSA_EXEMPTION_GRANT.pdf http://www.terrafugia.com/pdf/2011-16222_NHTSA_EXEMPTION_GRA...

jws 15y ago

CDs are polycarbonate and shatter sharp. Maybe there is polycarbonate that doesn't. Autoglass is required to shatter into slightly dull bits. Pitting would likely also be a problem causing reduced visibility. Aircraft stay above most land blown grit.

Daniel_Newby 15y ago

"Why is polycarbonate not allowed for ordinary cars?" Go to a parking lot and look at the plastic headlight covers on high-mileage cars. Many are frosted to opaqueness because of impact with grit.