Painting aluminum glider trailer

[John Murphy]

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.

[Bruce]

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.
>
Most of the commercial cost is in the preparation and finish. If you can get
them to agree to just spray it the price will be substantially less. This
implies you clean and prepare for painting, and they do no flatting and polishing.

As long as the surface is well prepared you can paint it with a roller, and get
reasonable looking results...
--
Bruce Greeff
Std Cirrus #57
I'm no-T at the address above.

[Stefan]

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.

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

Stefan

[Stefan]

Bruce wrote:

> As long as the surface is well prepared you can paint it with a roller,
> and get reasonable looking results...

Applying durable paint to aluminium is somewhat tricky. Cleaning the
aluminium is not enough, you need to "prime" it correctly. Of course you
can do that yourself, but you must know what you are doing.

Stefan

[Gary Emerson]

Exactly correct! The best thing to do is buff it to a mirror shine as
that will reduce the thermal absorption. Do this inside as well as
outside if you want maximum results. Doing the inside will reduce the
amount of radiated heat that goes from the inside surface directly to
the glider. Just like Techshield plywood roof decking.


Stefan wrote:
> 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.
>
>
> Clear reflective metal absorbs less heat than any paint, even white.
>
> Stefan

[Tony Verhulst]

> 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"

[Udo Rumpf]

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"

[Bill Daniels]

"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

[Francisco De Almeida]

Polished metals reflect sunlight very well - up to 90% for a highly =
polished aluminium surface. This property is easily compromised by any =
change within a depth of a few atoms near the surface. Oxidation is such =
a change and takes place quicky on most metal surfaces (except for a few =
'noble' metals whose chemical reactivity is very low). In aluminium, =
this oxidation does not look like rust and may be invisible to a casual =
observer, but causes an immediate loss of reflectivity, down to 40% or =
less. Surface contamination, dust and dirt will reduce it even further.

White paint has a reflectivity of about 20 to 30% in the visible light =
spectrum when well maintained, and is generally preferable as protection =
against solar gain.

There is a reason why a metal surface in the sun "burns the skin" while =
a painted one may not. It isn't because the metal surface is warmer - in =
fact it may be at the very same temperature. Metals, however, are =
excellent heat conductors, and will transfer heat very quickly to other =
bodies with which they come into contact. Paint, fiberglass, wood are =
essentially organic materials held together by covalent bonds and for =
this reason conduct heat less easily.

On the inside of a trailer, the property that matters most regarding =
heat transfer is the surface emissivity. Metals have a lower surface =
emissivity than other materials, even when lightly oxidised. For this =
reason, the innards of a metal trailer may well remain with their =
natural finish, except if the local climate is conducive to water =
condensation in the winter. In the later case, an internal lining with a =
vapour barrier will hinder condensation inside the trailer. Even just =
plain painting will reduce the severity of internal condensation.

Lining the inside of the trailer with any metalised, reflective foam, =
preferably leaving a small gap between this and the trailer walls, will =
do marvels in lowering internal temperatures. This is very cheap =
material and may be considered by anyone keeping a glider in a sunny =
place with large daily temperature swings. A ventilator helps too, =
mostly in avoiding condensation.

[Francisco De Almeida]

A mistake in my previous posting: white paint has a solar reflectivity =
of 70 to 80%. It is the opposite property of solar absorptivity, from a =
table of which I was quoting, that is 20-30%. I hope the argument makes =
more sense now.

[John Ferguson]

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.

[Jack]

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

[Stefan]

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

[Gary Emerson]

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
>
>

[Bill Daniels]

Try this: http://www.umich.edu/~lowbrows/reflections/2001/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

[Denis]

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 ?

[Eric Greenwell]

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"

[ContestID67]

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