Color curve chart

[Richard Riley[_1_]]

There's a chart listing ambient temperature, surface temperature and
color that composite builders take as gospel. I'm trying to get more
information about it

http://hallert.net/cozy/images/ColorCurveChart.gif

It originally comes from the Long EZ plans, Chapter 25, page 1 in the
plans and there's a handwritten note on the chart that says "Soaring
Sept 1975."

I have a call in to SSA, and they haven't been able to find a copy of
that issue. Does anyone have a copy?

In the testing that I'm doing, these temperatures seem high. White
surfaces don't seem to be more than about 10 degrees F higher than
ambient, the chart shows a white surface on a 30 degree day at 85
degrees. Yesterday it was hot in So Ca, 90 degrees ambient - but
black surfaces were coming out at 185, not 210.

If anyone knows what methods were used to gether these numbers, I'd be
thankful.

[Morgans[_2_]]

"Richard Riley" < wrote
....
> There's a chart listing ambient temperature, surface temperature and
> color that composite builders take as gospel. I'm trying to get more
> information about it
>
> http://hallert.net/cozy/images/ColorCurveChart.gif
>
>> In the testing that I'm doing, these temperatures seem high. White
> surfaces don't seem to be more than about 10 degrees F higher than
> ambient, the chart shows a white surface on a 30 degree day at 85
> degrees. Yesterday it was hot in So Ca, 90 degrees ambient - but
> black surfaces were coming out at 185, not 210.

I would attribute the lower temperatures to the fact that the sun is much
lower in the sky, than at June 21, or around then.

I'll bet it was done as a worse case scenario, with the sun's rays the most
direct, and highest in the sky.
--
Jim in NC

[Wayne Paul]

"Morgans" > wrote in message
...
>
> "Richard Riley" < wrote
> ...
>> There's a chart listing ambient temperature, surface temperature and
>> color that composite builders take as gospel. I'm trying to get more
>> information about it
>>
>> http://hallert.net/cozy/images/ColorCurveChart.gif
>>
>>> In the testing that I'm doing, these temperatures seem high. White
>> surfaces don't seem to be more than about 10 degrees F higher than
>> ambient, the chart shows a white surface on a 30 degree day at 85
>> degrees. Yesterday it was hot in So Ca, 90 degrees ambient - but
>> black surfaces were coming out at 185, not 210.
>
> I would attribute the lower temperatures to the fact that the sun is much
> lower in the sky, than at June 21, or around then.
>
> I'll bet it was done as a worse case scenario, with the sun's rays the
> most direct, and highest in the sky.
> --
> Jim in NC

Jim,

I have a metal sailplane which I keep tied down in the sun during the
soaring season. It is painted white and from my observations the white
numbers are correct.

For two weeks during the August several of us take our sailplanes to Mackay,
Idaho for a two week regatta.
(http://www.soaridaho.com/photogallery/Mackay_2006/) During that time all
the gliders are tied out in the sun. Several of the gliders have painted
wingtips. The chart appears to be correct. We all have tested it using the
"touch test" which consists of placing your hand on the white portion of a
composite wing follow by touching the painted wingtips. Blue is much hotter
then white and red is much hotter then blue.

I don't know if the low humidity and/or high mountain elevations are factors
or not. However, they do get hot tied down in the sun at 6,000 MSL with the
humidity less then 20%.

Wayne
HP-14 "6F"
http://www.soaridaho.com/Schreder/HP-14/N990/N990_Test_Brian.jpg

[[email protected]]

On Mar 13, 9:48 am, "Richard Riley" > wrote:
> There's a chart listing ambient temperature, surface temperature and
> color that composite builders take as gospel.

In my experience this wouldn't be a good idea. It is a good as a
general guide but.......

I did some testing of my own a few years ago and found there are a lot
more parameters than simple "color" that determint heat gain due to
solar radiation.

> If anyone knows what methods were used to gether these numbers, I'd be
> thankful.

I can't spaek for the original but what I ended up with was painting a
similar surface to the one I was goint to actualy finish, setting it
in the sun out of any breeeze and then using an IR pyrometer to
measure the temperature - from the back side. Metalic content, clear
coat formulation and even the varying amounts of heavy metal dyes can
change things significantly from what one would expect based only on
the mentioned chart. Which can probably be found in Rutans's composit
basics instruction guide and the plans for Quickies as well.

What caused me to do this testing was picking up some tools one day
that I had left on the ground in the sun. The chrome Snap-on ratchet
burned my hands, but the black oxide impacts were FAR cooler.
=========
Just my experience and opinions
Leon McAtee

[Bob Whelan]

Richard Riley wrote:
> There's a chart listing ambient temperature, surface temperature and
> color that composite builders take as gospel. I'm trying to get more
> information about it
>
> http://hallert.net/cozy/images/ColorCurveChart.gif
>
> It originally comes from the Long EZ plans, Chapter 25, page 1 in the
> plans and there's a handwritten note on the chart that says "Soaring
> Sept 1975."
>
> I have a call in to SSA, and they haven't been able to find a copy of
> that issue. Does anyone have a copy?
>
> In the testing that I'm doing, these temperatures seem high. White
> surfaces don't seem to be more than about 10 degrees F higher than
> ambient, the chart shows a white surface on a 30 degree day at 85
> degrees. Yesterday it was hot in So Ca, 90 degrees ambient - but
> black surfaces were coming out at 185, not 210.
>
> If anyone knows what methods were used to gether these numbers, I'd be
> thankful.
>
Richard,

On pages 22 & 23 of the Sep, 1975 issue of "Soaring" is an article by
(the late, I believe) John P. [Jack] Greene then living in New Jersey.
Article title is "Why is Whtie so Sacred?". Subtitle, "Energy
absorption & color in fierglass".

Per the article (I don't have a scanner or I'd shoot you a copy; instead
I'll roughly paraphrase):

He gathered his data first-hand over the time span 1972 to 1974,
collecting thousands of data points, with dozens of colored samples.
Samples were prepared from polystyrene boxes measuring 7"x7"x5"
(outside dimensions), with 1' thick sides/bottom. The top face of the
box was removed and replaced with a colored fiberglass panel. A mercury
thermometer was inserted through the side of each box w. the sensing
bulb attached/encapsulated to the underside of the fiberglass panel with
epoxy resin.

Test samples were mounted in a simple frame w. the colored surfaces
aimed squarely at the sun. The frame was continuously tilted & turned
to follow the sun. Ambient air/surface-temps-of-all-samples were
continuously recorded until a peak was reached for existing conditions.
Said procedure was repeated as often as possible to assure a
statistically valid set of recorded values. "Ambient air" refers to dry
bulb temps (deg F) measured in the shade. Test requirements called for
a very clear sky w/o the slightest cloud formation or haze. The
minutest development of high haze, hardly discernible to the eye, would
immediately cause sample temps to drop and bring testing to a
conclusion. Also the slightest breeze introduced an appreciable cooling
factor and tests were conducted only in very calm air. The ultimate
goal was to determine the highest skin surface temp a colored sailplane
might experience when parked under a blazing sun with no cloud cover, no
shade, not the slightest breeze, and a very high ambient.

"After 2 years of testing, significant data was sorted out & plotted on
the curve sheet to develop temp rise curves for each color and for black
and white. Referring to these curves, note that the baseline represents
ambient air and the vertical scale represents maximum sample
temperature. As might be expected, the curves are bounded on the top by
black and on the bottom by white. These finished curves are simply a
graphical presentation of the higest temps recorded for each color sheet
on a broad ambient temp range from 30 degrees to 110 degrees."

"Now what does all this mean?...The curves clearly indicate a black
sailplane could achieve a surface temp of 115 to 120 degrees above
ambient. for example, on a day with temps of 90-95 in the shade, it's
conceivable the skin surface of a black sailpllane could reach the temp
of boiling water..."

"The curve sheet also indicates an all-white sailplane could attain a
peak temp of 45 to 50 degrees above ambient, about 70 degrees lower than
the corresponding figure for black."

Brown isn't too different from black.

Colors like red & green should be avoided if moderately high surface
temps are objectionable.

Orange and tan are near the middle, and orange has the property of being
very visible.

The coolest colors are pink, yellow and light blue, along with all the
pastel shades. Note the position of the aluminum sample.

To get an approximation of peak temp possibly expected for a specific
color on a glass sailplane: select the color & determine the max ambient
expected (for that area). On the curve baseline, find the ambient and
move upward vertically to the appropriate color line, then move
horizontally to read peak (surface) temp on the vertical scale.

End of paraphrasing/excerpting...

As I recall from decades-old gleanings from "Soaring" mag, Jack Greene:
a) was an engineer in real life (don't remember what field); b) was a
homebuilder (HP-18 and others???); and c) had an engineer's grasp of
structures and V-n diagrams, etc. My opinion is the data plotted on the
Color Curve Sheet was sensibly and meticulously gathered, and is usable
engineering data. FWIW, my own observations of the man are through the
eyes of a non-practicing aerospace engineer (1972), and glider
pilot/nut. YMMV.

Regards,
Bob Whelan

[Wayne Paul]

Richard,

In case you are not aware of the HP-18 sailplane mentioned in Bob's
comments, it was designed by Richard Schreder and has aluminum wing skins
bonded to foam ribs. As all epoxy glues, the glue used to bond the skins
weakens when heated. As a result time parked on the ramp on a hot day and
color are very important issues for the HP-18. My guess is that the bonding
concerns is what lead Jack to run the tests and resulting article for the
Soaring Society of America.

Here are links to a HP-18 picture and a couple articles.
http://tinyurl.com/2uv7rn
http://tinyurl.com/2vgfl3
http://tinyurl.com/2pw3l5

Wayne
HP-14 "6F"
http://www.soaridaho.com/Schreder

"Richard Riley" > wrote in message
...
> On Fri, 16 Mar 2007 20:52:15 -0700, Bob Whelan
> > wrote:
>
>>To get an approximation of peak temp possibly expected for a specific
>>color on a glass sailplane: select the color & determine the max ambient
>>expected (for that area). On the curve baseline, find the ambient and
>>move upward vertically to the appropriate color line, then move
>>horizontally to read peak (surface) temp on the vertical scale.
>>
>>End of paraphrasing/excerpting...
>>
>>As I recall from decades-old gleanings from "Soaring" mag, Jack Greene:
>>a) was an engineer in real life (don't remember what field); b) was a
>>homebuilder (HP-18 and others???); and c) had an engineer's grasp of
>>structures and V-n diagrams, etc. My opinion is the data plotted on the
>>Color Curve Sheet was sensibly and meticulously gathered, and is usable
>>engineering data. FWIW, my own observations of the man are through the
>>eyes of a non-practicing aerospace engineer (1972), and glider
>>pilot/nut. YMMV.
>
> Thanks, Bob. Though that's not good news for this particular project,
> it saves me a lot of work.