Hot fiber glass ?

Tom-D

Tom-D

Taxi to Parking
Joined
Feb 23, 2005
Messages
34,740
Display Name
Display name:
Tom-D
Rutan determined that fiberglass structure gets hot it looses strength, thus he advises all his designs be painted white.
The question is, how hot, before it becomes a danger? then we ask how hot will a new high vis color like the hot pink get?
 
Didn't some of the diamonds or cirrus have a temp color changing indicator or something?
 
James331 said:
Didn't some of the diamonds or cirrus have a temp color changing indicator or something?
Click to expand...
I see most of the Canard folks making their own tests. paint a square use a inferred thermometer.
 
Glass transition temp (Tg) varies with type epoxy. Room cured, I've seen transition temps anywhere from 140-200 F. With a good gel coat / white paint, it shouldn't get anywhere near that unless it's sitting on the ramp in Phoenix or something.

The little fiberglass Katana has a spar indicator to warn of Tg. Think it went off around 130 F.
 
Last edited:
Velocity173 said:
Glass transition temp (T2) varies with type epoxy. Room cured, I've seen transition temps anywhere from 140-200 F. With a good gel coat / white paint, it shouldn't get anywhere near that unless it's sitting on the ramp in Phoenix or something.

The little fiberglass Katana has a spar indicator to warn of T2. Think it went off around 130 F.
Click to expand...

Sounds about right.
Remember it's jot just the surface getting hot the whole structure woukd need to get up to temp to see a dramatic drop in strength.
Not the whole airframe but like the full thickness of the wing skins, or spar or whatever you are concerned about.

But once you get to those temps, whoa buddy. The properties of most resins fall off a cliff. Like if the flexural modulus was 100,000psi go over the 'cliff' and the bottom could be 10,000psi.

It's probably a good number to have somewhere in the back of your mind for your composite.
 
USAF T-67's had a surface temp limitation of 100F. Prefight required using an IR gun and shoot each wing for surface temp. See 100F, and crew pushed back into the shade port until cooled under that temp.
 
First off, it's not the fiberglass. Fiberglass is good to temperatures much higher than you're going to see in even a black airplane parked outside. You only tend to worry about it when you're down to engine compartments and the like. Nor is it affected particularly by UV. The issue is the RESIN that is gooping around your fiberglass to hold it in the shape of an airplane.

Epoxy has UV problems and must be painted to protect. Epoxies come with various degrees of heat tolerance. Epoxy is no good above 350F degrees at all, but it starts to soften as low as 150 or degrees. Some of the higher heat epoxies can push 200 degrees. At these ranges obviously you're getting into the range that bright sun and dark colors can cause problems.

There are other resins for fiberglass work (vinyl esters, polyester) that have better temperature and UV things but at a structural penalty (adhesion is less). The polyester resin is what is commonly used in automotive use as it can take the heat more with darker colors and the other properties aren't a problem when you're making molded parts as opposed to trying to do manual layups.
 
flyingron said:
Epoxy has UV problems and must be painted to protect. Epoxies come with various degrees of heat tolerance. Epoxy is no good above 350F degrees at all, but it starts to soften as low as 150 or degrees. Some of the higher heat epoxies can push 200 degrees. At these ranges obviously you're getting into the range that bright sun and dark colors can cause problems
Click to expand...
Thank you, do you have a reference for those temps?
 
The 350 degree number came from Wikipedia.
The 150 (really 70C) and 200 (95C) came from the Fiberglast specs on their regular and high heat epoxy mixtures, but are typical for the industry.
 
flyingron said:
Epoxy has UV problems and must be painted to protect. Epoxies come with various degrees of heat tolerance. Epoxy is no good above 350F degrees at all, but it starts to soften as low as 150 or degrees. Some of the higher heat epoxies can push 200 degrees. At these ranges obviously you're getting into the range that bright sun and dark colors can cause problems
Click to expand...
Thank you, do you have a reference for those temps?
flyingron said:
The 350 degree number came from Wikipedia.
The 150 (really 70C) and 200 (95C) came from the Fiberglast specs on their regular and high heat epoxy mixtures, but are typical for the industry.
Click to expand...
Thank you again.
 
Problem with Variezes isn't glass transition but coorosion on the spar cap. 2.5 G limit. :(
 
Velocity173 said:
Problem with Variezes isn't glass transition but coorosion on the spar cap. 2.5 G limit. :(
Click to expand...
very very few have the problem. they have been identified and cured. it is easy to remove the filler and inspect for the problem.
 
Tom-D said:
very very few have the problem. they have been identified and cured. it is easy to remove the filler and inspect for the problem.
Click to expand...

Are you saying that Burt lifted the +2.5 G and -1.5 G restriction? Even if no corrosion is found, Burt said to placard at 2.5 & 1.5.

This was from 2014 and Marc Z said it was still in effect then. Even without the spar cap limitation, Marc agreed with the 2.5 G limit based on his structural testing of the fiberglass alone.

https://groups.google.com/forum/m/#!topic/cozy_builders/POwl1duvBOE
 
Last edited:
Velocity173 said:
Are you saying that Burt lifted the +2.5 G and -1.5 G restriction? Even if no coorosion is found, Burt said to placard at 2.5 & 1.5.

This was from 2014 and Marc Z said it was still in effect then. Even without the spar cap limitation, Marc agreed with the 2.5 G limit based on his structural testing of the fiberglass alone.

https://groups.google.com/forum/m/#!topic/cozy_builders/POwl1duvBOE
Click to expand...

I'm not saying any thing like that. I said there are very few that have the problem, they have been identified and cured or removed from service.
 
I don't know what the attitude is all about. Rutan uses Epolite 2427 as his "Rutan Brand" epoxy. It's good to 140 degree Fahrenheit. Some of his practice kits include EZ Poxy good to 148.

Here's the temperatures of the various popular resins:

Fiberglast 2000 180-194 depending on which hardener is used
SAF-T-Poxy 2410 182-184
Epolite 2427 (Rutan) 140
EZPoxy EZ10 148
RAE 2426 145
West 125R 146

Are you going to tell me that Rutan's recommendation that you not use a color other than white due to the temperature problem is unjustified.

The only thing in this entire thread that is incorrect was TomD's statement on UV vs. Heat. Both are a concern and UV isn't the only contributor to heat load (if it were, you'd not worry about paint color). As I stated in my original answer: EPOXY is UV degraded. It needs some sort of top coat. Most of the resins used for hand layups in kit planes are NOT stable much above 140-150 degrees. You need a color that is not going to absorb a lot of heat.

This is the fundamental property of the materials. It doesn't matter whether it is Rutan or Seadoo building the thing.
 
Burt has been pretty vocal about white only. He didn't even like the fact his brother's Long Eze was light blue...amoung other mods he didn't approve of.

Having said that, I've seen light blue, yellow and silver on canards and haven't heard of one yet with a Tg problem.
 
I'm not one to stray far from the design.
 

Attachments

  • 20160705_194040(0).jpg
    20160705_194040(0).jpg
    108.7 KB · Views: 19
  • 20160706_135129.jpg
    20160706_135129.jpg
    177.9 KB · Views: 18
Velocity173 said:
Burt has been pretty vocal about white only. He didn't even like the fact his brother's Long Eze was light blue...amoung other mods he didn't approve of.

Having said that, I've seen light blue, yellow and silver on canards and haven't heard of one yet with a Tg problem.
Click to expand...
I'm guessing that no one knows how hot the new high vis paints will get.
 
From an Advanced Composite Textbook I have:

Ultraviolet light will slowly attack cured epoxy and cause the resin matrix to become brittle and prone to cracking over time.

Epoxy service temperature range - 150° - 375°F
 
Epoxy service temperature range - 150° - 375°F
Click to expand...
As I stated, the ones commonly used for hand building are definitely in the lower range. There are high temperature epoxies but they come with other tradeoffs.
 
It goes on to say: Aramid fibers (Kevlar) are also subject to weakening with prolonged UV exposure. One can easily protect composites from UV by using an opaque paint with a UV barrier.

Infrared light heat radiationis a particular problem while aircraft are parked on black asphalt ramp on hot summer days. Temperatures of 225°F have been measured in such conditions, while air temperatures were 120°F. Protection from this condition by painting surfaces white, which will reflect away most of the infrared radiation.
 
You must log in or register to reply here.
Back
Top