Painting composites today

[Chairboy]

I notice that Lancair/Columbia is offering aircraft outside of the normal range of whites that other composites are limited to.

 

For example: http://www.lancairusa.com/warranty.html

 

In the warranty, they mention that something about their technique allows surface temperatures of up to 175F, which allows lots of color options.

 

Does anyone know what they do? Is it the difference between the old stuff and using MGS?

 

Finally, even if the Columbia technique isn't used, any thoughts on whether a paint scheme like this would be safe?

 

http://hallert.net/cozy/paintideas.htm

 

Thanks!

[Wayne Hicks]

Lancair uses mostly carbon honeycomb (no faom) that is cured at elevated temperatures in an autoclave. Thus, the resulting structure has a higher Tg (pronounced T sub G). Tg is the temperature at which an epoxy matrix will begin yielding, becoming elastic, and begin losing its strength properties.

 

On Rutan-type canard aircraft, the limiting factors are the room-temperature curing epoxy and the foam. I quote from the Cozy plans, Chapter 25:

 

"Epoxies and foams are all sensitive to high temperatures. 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).

 

Since the Lancair's Tg is high (I don't know how high) and they don't use foams in strucutral areas, they can get away with using paint colors other than white. You can raise the Tg on Rutan-type canards by post-curing, but the max Tg is dependent on the epoxy's characteristics. It's my guess that Lancair uses an epoxy that can attain a higher Tg than we can with home-builder friendly epoxies.

 

On Rutan-type aircraft, it is permissible to use darker colors given these limitations, and I quote again:

 

"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 surface of the wings and canard. Do not stripe the wing or canard with trim, except at the canard tip where structure is not critical."

 

One obvious no-no on your paint scheme are the faux reinforced carbon-carbon (RCC) on the leading edges. You might be okay with everything else.

[Chairboy]

One obvious no-no on your paint scheme are the faux reinforced carbon-carbon (RCC) on the leading edges. You might be okay with everything else.

Thanks for the post, very informative! Well, I've got a few years to hash something out in the meantime. Maybe the faux carbon-carbon will be more of an alabaster or something for the final product. Also, who knows, maybe the horse will learn to talk (and there'll be some third option that's not immediately apparent).

 

I guess one of my next assignments will be to learn more about epoxies, eg, what are the differences between MGS and what Rutan originally used, and stuff like that.

 

I love this project, I'm learning more every day. I can't wait until I can start on chapter 1. It's gonna be soon, I can feel it. A week or two maybe, we'll see.

[Jon Matcho]

I guess one of my next assignments will be to learn more about epoxies, eg, what are the differences between MGS and what Rutan originally used, and stuff like that.

The epoxy systems RAF initially approved had strong odor and some carcinogenics. MGS is now what's most used, doesn't stink when mixed (the hardener does), and doesn't contain MDA. You still can't drink it, and it is not to get in contact with your skin, but its properties are good for our purposes. As Wayne said, "homebuilder-friendly" is the key word here. You can use "space shuttle epoxy" if you have enough money and the equipment to post-process it. Our epoxy systems are designed for hand layups and room temperature cures, and also support higher temp post-cures as an option.

 

Consider getting a 'practice kit' from Aircraft Spruce or Wicks for about $50 or so. They give you a small amount of epoxy (EZ-Poxy I think) to build some practice pieces with.

 

Nice Web site BTW.