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