Painting aluminum glider trailer

If you are looking fo a cheap job (cheap is emphasised,
no flames please) you can paint aluminium with an ordinary
roller and household gloss, eg Dulux enamels, I hope
Dulux is recognisable in the USA.

Yes, I do know that if you're going to paint Alu properly
then you use epoxy etch primer and a decent topcoat,
but the raw materials alone are still going to be about
400ish dollars, trailers have a big surface area.

Compare this with 10 litres of household gloss, no
flames please, this is a cheap suggestion, it works
and has lasted for 5 years so far.

I have lived in Texas most of my life and can tell you from experience
that my trailers will ALWAYS be white. On bare aluminum, use a solution
of 10/1 water/white vinegar to etch the surface. Rinse thoroughly and
use alodine per lable directions. A good quality, latex gloss
housepaint can be rolled on with a low-stipple mohair roller and the
results look sprayed. This paint, applied properly, will last 15 years.
If you're in a dry climate and have some shade for it... it'll last
much longer than that. No primer, no spray equipment, and a decent
paint job for less than $200.00. Who could ask for anything more?

Jack Womack

Thanks, Fernando. Just two illustrating examples which everybody knows:

In winter, a metal table feels colder than a wooden table of the same
temperature, because metal conducts heat much better then wood.

In summer, you burn your feet by walking through hot sand a the beach,
but not by walking over wood of the same temperature. Same reason.


BTW, this is also the reason why it's no big deal to walk over red-hot
coal, especially if you walked through wet grass before. If you try it
with Charcoal, that is. But please don't try it with mineral coal!

Stefan

I'm going to change my thinking on this a bit and explain as well.

If you go to a thermal engineering book and lookup emissivity and
absorption then I think you will find the mirror/polished has the lowest
values which drove my original thinking.

On the sunny side with a mirror finnish you have a low absorption. The
problem with the rest of the equation is that you have low emissivity as
well, so what heat is absorbed is very poorly radiated. This low
radient level (low emissivity) causes the surface temperature of the
aluminum to be quite high. Where this looses ultimately against a white
painted surface is that you then have a high temperature surface that is
conducting with either your hand (if you touch it) as well as the air
inside the trailer so the trailer may ultimately be hotter with the
polished finish.

Go with a cheap white paint.



Bill Daniels wrote:
"Udo Rumpf" wrote in message
.. .

I agree that the most highly polished Alu
has nothing against a pure white paint when it comes the reflectivity and
absorption rates of sun light. I just do not know where this myth comes
from.
Udo


Clear reflective metal absorbs less heat than any paint, even white.

A club member painted his bare aluminum tube type trailer white and noted
that the decrease in heat buildup was very noticeable. Apparently, YMMV.

Tony V "6N"


I have to agree with Udo.

Anyone who has lived in the desert knows that polished aluminum will get hot
enough to inflict burns if left out in the sun. Painted white surfaces
won't.

The best evidence I know of for this is the telescopes at the National Solar
Observatory at Sunspot, NM. They are painted "Telescope White" to prevent
solar heating from distorting the supporting structure. If polished
aluminum worked better, that's what they would use.

The only rational reason for polishing a trailer instead of painting it
weight. Polishing is lighter than paint and that may save a little fuel.

Painting aluminum is a tiny bit involved but not difficult. Prepping the
surface with an etching wash and then using a good primer is the key -
consult with your paint supplier. Using a roller to paint a trailer is
perfectly reasonable.

Bill Daniels

Try this: http://www.umich.edu/~lowbrows/refle...1/tryan.5.html

Bill Daniels

"Gary Emerson" wrote in message
om...
I'm going to change my thinking on this a bit and explain as well.

If you go to a thermal engineering book and lookup emissivity and
absorption then I think you will find the mirror/polished has the lowest
values which drove my original thinking.

On the sunny side with a mirror finnish you have a low absorption. The
problem with the rest of the equation is that you have low emissivity as
well, so what heat is absorbed is very poorly radiated. This low radient
level (low emissivity) causes the surface temperature of the aluminum to
be quite high. Where this looses ultimately against a white painted
surface is that you then have a high temperature surface that is
conducting with either your hand (if you touch it) as well as the air
inside the trailer so the trailer may ultimately be hotter with the
polished finish.

Go with a cheap white paint.



Bill Daniels wrote:
"Udo Rumpf" wrote in message
.. .

I agree that the most highly polished Alu
has nothing against a pure white paint when it comes the reflectivity and
absorption rates of sun light. I just do not know where this myth comes
from.
Udo


Clear reflective metal absorbs less heat than any paint, even white.

A club member painted his bare aluminum tube type trailer white and
noted that the decrease in heat buildup was very noticeable. Apparently,
YMMV.

Tony V "6N"


I have to agree with Udo.

Anyone who has lived in the desert knows that polished aluminum will get
hot enough to inflict burns if left out in the sun. Painted white
surfaces won't.

The best evidence I know of for this is the telescopes at the National
Solar Observatory at Sunspot, NM. They are painted "Telescope White" to
prevent solar heating from distorting the supporting structure. If
polished aluminum worked better, that's what they would use.

The only rational reason for polishing a trailer instead of painting it
weight. Polishing is lighter than paint and that may save a little fuel.

Painting aluminum is a tiny bit involved but not difficult. Prepping the
surface with an etching wash and then using a good primer is the key -
consult with your paint supplier. Using a roller to paint a trailer is
perfectly reasonable.

Bill Daniels

Gary Emerson a écrit :
I'm going to change my thinking on this a bit and explain as well.

If you go to a thermal engineering book and lookup emissivity and
absorption then I think you will find the mirror/polished has the lowest
values which drove my original thinking.

On the sunny side with a mirror finnish you have a low absorption. The
problem with the rest of the equation is that you have low emissivity as
well, so what heat is absorbed is very poorly radiated. This low
radient level (low emissivity) causes the surface temperature of the
aluminum to be quite high.

Why don't you try a black paint ? It is well known that black has the
highest emissivity...

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

John Murphy wrote:
I have a 20+ year old trailer for my G102. Presently, its bare sheet
aluminum. I want to paint it white to reduce the amount of heat
absorbed by the trailer skin. A local autobody shop quoted me $1600.00
to cover with a polyurethene paint over an epoxy primer. This is far
more than I wanted to spend. Any suggestions on durable paints or
products that can be applied by a novice to sheet aluminum. I can rent
an airless sprayer if need be. Thanks.

I looked into this when I had an aluminum tube-type trailer. I compared
the air temperatures inside the trailer in several places (ceiling,
floor, inside cockpit) with those in a similar trailer painted white. As
I recall, the air temperatures in the top 6" of the trailer were 10 to
15 F hotter, but below that, the air temperatures were only a few
degrees hotter. Because the _glider_ temperatures were hardly different,
I decided the heat protection gained wasn't worth the cost and effort to
paint the trailer.

I believe the hot air convects to the top of the trailer and insulates
the rest of the air from the heat input. I notice the same effect in my
Cobra trailer, where the air near the top is very hot, but below that
the air is only a few degrees above the outside air temperature.


--
Change "netto" to "net" to email me directly

Eric Greenwell - Washington State, USA

www.motorglider.org - Download "A Guide to Self-launching Sailplane
Operation"

I painted my trailer with white two part epoxy paint. It was about
$110 for two gallons (a gallon each of part A and part B). I went
through about 3 gallons total. I mixed the first two gallons together
and when that was gone, 1/2 of each of the other two gallons. Thus I
have some left over. I put it on with a short nap roller. Looks
great.

You can't generally find this at the big box stores and have to go to a
paint only storefront that the trades use. Epoxy paint can be sprayed
but cleaning up the sprayer afterwards could be tricky.

Funny story: the counter guy at the store admonished me to not mix the
two together unless I was ready to paint. No duh. Apparently a guy
came back to the store after buying some epoxy paint holding a bucket
of now quite hard paint with a stiring stick permanently stuck in the
middle of it and wanted his money back. Uh huh, yeah, sure. Read the
label dude.

- John