UV Protection

[flyguy]

Prompted by the UV discussion here:

I have often wondered if a black paint of some kind would work as a UV coating. I am fairly sure that some black coatings would stop UV, but how well it could be used on fabric is another thing.

For example, how would black Stits color coating behave over Polybrush. Or, could you make black Polybrush? Or some other black sandable coating over the Polybrush?

I believe I read that black is used on composite surfaces for UV proofing.

For years I've though about making some test frames for function and then exposure, but never got around to doing it.

Oh, by the way, I have devised a way to correct cracks in painted Stits process fabric that works very well. It is labor intensive, but less so than everything else I have tried. The end results are much better.

DC

[Hank Jarrett]

Re: UV Protection

I guess you need to think in a little different way. We see in the visible color spectrum. UV is not visible to humans. What looks white to you could actually be black in UV and what looks black could be completely transparent. Some of the guys in the WW-I group have used a black paint that instruments showed filtered out the UV but it had to be the right brand of paint and it was NOT a certified paint. The paints with high metal solids seem to be what works best (which is why we use aluminum filled clear for UV protection. It isn't the COLOR of the paint, it's the actual metal in it that stops the UV).
A time test is not a very good way to check. You really need to actually measure how much UV is going through. This is NOT intuitive. Even if you find a good paint, the FAA has to approve it.
Hank

[N96337]

Re: UV Protection

Yep, Hank's correct. It's got nothing to do with the color, necessarily... it's the pigment. IF the black was made with lets say, flumed carbon, then it would be fine... but most blacks aren't made with that, so I'd doubt they'd do much. There was mention of "daytona creme which has good reflective quality"..... and if ya believe that one, I've got some property for sale!
It amazes me how people try to figure out ways to "improve" these fabric systems all the time... The people who developed the system in the first place put lots of time and effort and research into it, and believe me, if there was a cheap way around something, they'd use it, as it would create more profit for them! None of the systems available today were born overnight.....believe me! I've been in on ground floor testing and development of one of them... and it was alot of work! If there was an easier way that was a viable solution, it would be used.
John

[flyguy]

Re: UV Protection

Hank, I think I get what you're saying.

The wavelength of UV is less than 400nanometers and therefore shorter and outside the visible range of about 400 to 780 nanometers for the human eye. And of course it's destructive ability is greater than visible light due to its energy per quanta being E=hf, where h is Planck's constant and f is the frequency of the light. UV being of a higher frequency each photon is therefore more energetic and more damaging to light sensitive materials.

Did I get that about right?

Darryl

[Hank Jarrett]

Re: UV Protection

I usually try to stear clear of the physics since I thought not that many would care about it. I guess I was wrong!
For those so inclined, Darryl got it right. UV light is between 10 and 400 nm. Basically it accelerates chemical reactions in all kinds of materials and for fabrics that usually means it weakens the molecular bonds in the strands making the fabric weaker. The energy in UV runs from around 3 to well over 100 Electron Volts. Visible light is between 380 and 530 nm and has about 1.8 ev for red light up to about 3 ev for blue. Kind of lets you see why UV is so bad! The highest in visible light is under 4 or 5 ev and UV is from 10 to 400!
Hank

You guys really care about this stuff? I usually stick to applications when I'm not talking to NASA nerds. I have been known to OD people on the nerdy stuff when I'm not restrained. ;-)

[Larry Lyons]

Re: UV Protection

OH REALLY!


PS: OK I do enjoy techy stuff but could not pass this one up. Drag and lift coefficients will put to sleep in about 60 seconds though.

[guns68]

Re: UV Protection

I'm more of a practical application kind of guy. Although I can appriciate the science, I must admit that Darryl lost me right after the word energy.

[flyguy]

Re: UV Protection

Hank, Actually I was just poking a little fun at you in reference to your first two or 3 lecture sentences on light. It was late a night and I had entirely too much caffeine in my system. I love your dead-pan straight response. Chuckle.

I generally tend to ask simple questions that likely may mislead folks about my background knowledge of the subject.

I probably should just avoid asking such generically routine ding-a-ling questions and stick to practical things like I mention in the my last line on repairing cracks in painted fabric.

Darryl

[Hank Jarrett]

Re: UV Protection

I actually thought I had run into another professional nerd in the tribe.

There are a few of us on here but most just fly under the RADAR. I thought you might be a Physicist.

Hank

[Bob Waldron]

Re: UV Protection

Fly Guy,

What is your method of repairing Polytone cracks?

[flyguy]

Re: UV Protection

Bob,
what I was working with was "paint," of some kind unknown to me, over Stits silver. I have found that paint type topcoats are usually on the brittle side and difficult to sand down in a controlled way. It is very easy to damage fabric components trying to get through the top coat by sanding.

Paint remover is OUT as it contaminates everything.

A ninety year old AI/corporate pilot (retired, LOL) here suggest this and so I tried it. The old guy knows all kinds of tricks.

I start with the "slowest" lacquer thinner I have and apply some to the painted area around the break. I have been using a brush, but it IS hard to control without dripping except on horizontal surfaces, so I am thinking now of using cotton swabs or something similar. (I haven't tried this yet--fuzz?)

The paint will usually curl up or at least soften a lot. If not, I go to the next hotter thinner that I have. Other "hot" solvents/thinners will work.

I then scrape the paint off leaving the "cracked" silver exposed. My tool of preference is a carbon steel paring knife. Sharp is good. I use more of a slicing motion than a vertical scrape. You should only loose a minimum of silver this way, if any.

Then using a small, severely trimmed, stiff, bristle paint brush I apply a bit more of the solvent to the silver and scrub it around until the silver coat flows together and closes the crack. Go lightly as possible with the thinner here, you just want it very thick gooey.

After it dries a while I brush (yeah I know) on more silver, usually several coats done gently with a very soft brush. Using an airbrush would be a great improvement here. I try to keep it off the surrounding paint as much as possible.

Sand between coats or as you like and touch up paint.

As my plane is all go and very little show (not too bad from 10 feet away) this process has worked very well for me so far.

DC

[flyguy]

Re: UV Protection

Hank,
Nah, just a supertech/test engineer, whatever on Apollo, the Lander, Stanford linear Accelerator Operations, some radar optical communications stuff for the Navy, Nike X program in the Pacific, Fiber optic amplifiers, that kind of stuff.

But--since I have retired I find myself actually studying quantum physics, cosmology with math, especially light and other electromagnetic processes. Fascinates me. Been experimenting with the oddities of double and single-slit experiments lately. (I can see funny remarks coming on that line---) I actually have a lab of sorts in one of my spare rooms.

I didn't do it much when I was working because I had to deal with the practical side all day long and enough was enough at the end of the day, but now I have some time. Nice.

Darryl

[NY86]

Re: UV Protection

"Dumb" question:

How come Dacron sails don't disintegrate?

[Hank Jarrett]

Re: UV Protection

They do! You haven't soiled your pants like you will when a Spinnaker blows out!
Hank

[Hal]

Re: UV Protection

Hi All,
The Stewart Systems uses a black uv blocker, however I don't have a clue what the pigment is made of. At these short wavelenghts a lot of normal pigments can become very transparent.
Hal
(A recovering physicist trying not to over engineer this simple aircraft project)