No Black?

[marbleturtle]

Okay... I had this nice Ominous Darth Vadar "don't mess with me" image of a Black with Silver racing stripes MKIV. Then I noticed on one of the builder pages a comment about no dark colors. It mentioned about the color destroying the foam underneath and another site mentioned the composite fibers of the fiberglass. Is this a U.V. thing or a thermal retention thing? New paints can protect against U.V... or could be a form of Ice Protection. (*snicker)

 

But seriously, what is the issue and how serious is it? The CCF mascot Cozy has red on the upright rudders in full view of the sun... hmmm...

 

[John Slade]

Dark colors are a no-no. It's a heat retention / reflection thing. You won't see any dark colored composite airplanes unless they're made with (very expensive) high temp epoxy. I think there's a yellow one around somewhere, but nothing darker.

[Paul Kuntz]

You will see a number of canard aircraft with colors other than white for trim and on things like the rudders, as mentioned in the previous post.

 

However, the temperature and structural damage problems associated with non-white colors are well documented, and we all know that for much of the day even vertical surfaces are subjected to direct sunlight at high angles of incidence. I recall a post some time back on either the Cozy or canard aviators e-mail group from a canard owner who found foam damage under dark trim areas on the side of the fuselage.

 

My Cozy is going to be all-white except for the required registration numbers, and just maybe some thin trim stripes.

[marbleturtle]

So is this just for Cozy's that are parked out in the sun all day? I couldn't imagine the surface getting hot in flight.

[Wayne Hicks]

You CAN use dark colors for trim on non-critical srufaces.

 

I quote from Chapter 25 (Finishing):

 

"White is the only recommended color for these aircraft. Trim colors in non-critical areas are acceptable as desired, such as the fuselage, vertical winglet surfaces, and the underside of the wings and canard. Dark trim colors are definitely not approved on the upper surfaces of the wings and canard. Do not stripe the wing or canard with trim, except at the canard tip where structure is not critical."

 

The reason "why" is explained further by the plans:

 

"Room temperature curing epoxies soften and lose their rigidity at only moderate temperatures (160 degrees F). Foams are also heat sensitive and tend to soften and swell with moderately elevated temperature (250 degrees F)."

 

Chapter 25 provides a Color Curve Sheet that shows the peak surface temperature versus ambient air temperature for various representative colors. White surfaces absorb very little heat (approx 10%); black absorbs ALOT of heat (95% approx). Somewhere darker than light green, you start running surface temps greater than 180 degrees on a 95 degree ambient temp day.

 

Are these rules absolute? That's not for me to say. Somebody's bound to bring up the fact that AeroCad's demonstrator aircraft is decorated with orange/blue feathers on the tops of the canard and wings, and it seems to be holding up okay.

 

Just don't paint the entire paint black. :-)

 

....Wayne Hicks

[John Slade]

>So is this just for Cozy's that are parked out in the sun all day?

>I couldn't imagine the surface getting hot in flight.

 

Ever gone swimming on a windy day?

Did you get sunburned?

Any chance that you might actually PARK you're airplane for more than 20 minutes or so?

 

There was a guy at a fly-in with a dark colored composite airplane. Friendly advice from other canard drivers was VERY forthcoming.

 

When asked about the best place to put trim colors, Nat said "where the sun don't shine."

 

There has been some talk of special reflective paint, but I don't know if anyone's tried it yet. Delamination is a really bad thing.

[marbleturtle]

Is silver on the color chart? I would think reflective silver would be cooler than white.

[marbleturtle]

 

>... ever go swimming on a windy day?

 

Yes... but never at 200mph. I was COLD! But I did get Sun burned. (?)

[ekisbey]

I think what he's saying is composite aircraft can get "sunburned" too, and sunburn can happen regardless of temperature, even on an overcast windy day-- UV goes through clouds. The light color helps prevents both UV damage to the material under the skin and keeps it cooler too. I'm not sure about silver, I seem to recall a number of times where a shiny reflective surface in the sun has caused much discomfort... Think if it this way. Put two folding chairs outside in the sun on a hot august afternoon, one painted gloss white and the other a silver color, maybe even chrome. If you're wearing shorts, or less, which chair is less likely to burn you? I had a similar situation a few years ago at a BBQ and chose the shiny chair, and walked around the rest of the afternoon with a blistered backside. The white chair was considerably cooler.

 

I suppose it's possible the type of paint used could have been a big factor, it's hard to say for sure. I for one will plan for white with a small amount of brightly colored trim, for a cheerful sporty look. I'm not sure I could talk my in-laws into a menacing-looking dark colored aircraft.

[dust]

Fiberglass doesn't like uv but that is not the problem, paint solves that. Epoxy stays thermoplastic, in other words if you paint your plane black the wings will droop if left out in the sun to bake. The charts always quote that in MICHIGAN the skin temperature can go to 180 on a sunny summer day. What they don't say is that in phoenix the temp in the shade starts at that!

 

This is a memory estimate.

 

Room temperature curing gives stability to 160 degrees(time also plays a factor in this). Heating the plane up to 150 will then give you protection to 170, you get 20 degrees more protection than the plane is exposed to.

 

Many many many people have built this and other planes with these materials, and none has had a white plane droop, that i know of or have heard of.

 

Now the guy that lost the exhaust pipe and the exhaust exited from various areas around the cowl did get a droopey main spar and wings, but thats another story that i mentioned for those of you looking for reasons not to build!

 

Current practice by many is to post cure the plane with all parts well supported, some build big ovens and some merely drape plane with black in Michigan sun.

[John Slade]

Don't you mean drape the plane with white?

[dust]

drape with black for the heat to post cure after supporting all surfaces to stop drooping/deforming

[John Slade]

Ah! Post curing. Right. I thought you meant later when parking.

My "attempt" at post curing was to support the wings and simply leave them in the Florida sun for a few weeks.

[ekisbey]

What does "well supported" mean? In other words, are you supporting only the flying surfaces or are you making a frame or a jig for the whole aircraft tot sit in?

[John Slade]

I didn't post cure the whole aircraft assembled. I did each part seperately. I think some make a jig for the wings and canard. I just laid them flat on the ground, then wedged blue foam underneath at about 18 inch intervals. I didnt cover anything with black drape. It gets hot down here in summer and I didnt want to risk overdoing it. Note that most canards flying today were not post cured, and were built with an epoxy with a much lower tg (read melt point) than the MGS stuff I'm using. The hotter it gets, the more support you should have.

 

I often put small parts in the epoxy hot-box overnight to speed up the cure and give them a bit of a post cure.

 

It's a good idea to post cure after finishing with micro, but before final paint. This will tend force any shrinkage to happen when you can fix it easily.

[unick3]

In the future I think we will see lots more cool (temp wise) colors to paint our planes.

 

The is a LOT of research going on by the military on colors (greens, blues, browns, etc) that are highly reflective and do not get hot. Has a lot to do with thermal imaging of military vehicles by infrared cameras.... I have read about some amazing results.

[John Slade]

Room temperature curing gives stability to 160 degrees(time also plays a factor in this). Heating the plane up to 150 will then give you protection to 170, you get 20 degrees more protection than the plane is exposed to.

 

Marc Zeitlin mentioned that there was inaccurate information in this thread. I think the above paragraph may be what he was referring to. If not, Marc, please jump in.

 

The temperatures depend on the resin used. TG is the temperature at which the epoxy starts to "melt". (Chemists will have a better way to describe this). Different resin and hardener combinations have different TGs. Some have much higher TG than others. Search for TG and EPOXY in the Cozy archives and you'll find lots of good (and some bad) information on the issue. Warming the part during post cure or while parked on a ramp DOES increase the TG, but there's no strict 20 degree increment and the start and end points depend on the resin. Again, good (and bad) information on post cure methods can be found in the Cozy list archives. There's also some discussion on epoxy in my web site introduction chapter. As with many other issues in building, there is no one place where everything you read is accurate and correct (except perhaps the plans themselves). You need to get input from lots of places. Eventually you'll start to see a consensus after reading a LOT of text. I guess this is how we learn.

[marbleturtle]

The question about black was obviously "tongue-n-cheek"... but I did want to find out if anyone had experience with the reflective paints. The thermal imaging information would be interesting to see... any links?

[dust]

"This is a memory estimate." my information was correct, that is what I remembered. But the reality of it is, the manufactures of the resin/hardener (once mixed called epoxy) is the correct place to find out the exact technicle information and procedure for curing and post curing.

 

My post was just to educate on general epoxy qualities, not a technical disertation on post curing procedures, ifin it was I would have gone to "general canard construction" and started a "how to post cure when using mgs (msg) epoxy system" thread

Mike

[ekisbey]

I wouldn't hold out hope for any paints developed by the military making their way down to the civilian market any time soon. The military uses primarily CARC type paint, and it's quite toxic in its liquid form. It requires personnel trained in HAZMAT handling procedures just to store the stuff. Anything they come up with in the near future will likely fall into this same category, as the CARC we're using now already has near-infra-red properties to fool nightvision.

 

I don't know about the rest of you, but I like children with ten fingers and toes more than a plane I can paint black.

[marbleturtle]

hmmm... stealth Cozy... kids with enough digits to count to twenty... decisions decisions.

[John Slade]

No problem.

Get 'em a calculator

[marbleturtle]

... a man with his priorities straight!