Want a fast kite? paint it black..
Dan Mitchell
talking about soap box derby races, we have the following:
--cuthere--
PHYSICAL CHARACTERISTICS OF COLOR
The color that provides the least skin friction drag is black. Black also
helps prevent separation of the laminar boundary layer.
The aerodynamic book "Theory of Wing Sections", page 109, written by Ira
H. Abbott and Albert E. Von Doenhoff, explains that skin friction for an
object (soap box racer) that absorbs no heat from the free stream is, lets
say 1.330. The skin friction for a soap box that is 1/4 the absolute
temperature of the free stream is 1.420 at 50 miles per hour. This means
that the laminar skin friction increases with heat transfer from the fluid
(surrounding air) to the surface of the racer. This increase is small even
for the extremely low racer temperatures. This means that the surface
temperature of the racer should be as hot as possible. The color of the
racer should be one that absorbs as much heat as possible from the sun.
This color is black!
--cuthere--
Anyone tried this? It seems somehow unlikely that it'll make enough
difference to be worthwhile, but you never know..
-- dan
Allen Pinkley
if you think about it, that's why grass, tree leafs, and all other plants
are green and not black because it's the most efficient sun absorber...
Allen Pinkley
Perry Farmer
-> if you think about it, that's why grass, tree leafs, and all other pl
-> are green and not black because it's the most efficient sun absorber...
-> Allen Pinkley
So we should all go out and get dark green paint for our radiators?
Please name the study.
Perry
Vortex
apart from green (does that make sense?) Interesting theory though -
bin-liner pocket sled experiment anyone?
Crash Johnson
>Quoting from http://207.242.75.40/derbtech/COLORME.HTM which is, I admit,
>talking about soap box derby races, we have the following:
>
>--cuthere--
>PHYSICAL CHARACTERISTICS OF COLOR
>
>The color that provides the least skin friction drag is black. Black also
>helps prevent separation of the laminar boundary layer.
When you're hot you're hot. And fast. Why then is Queen Amydahlas
interstellar ship CHROME!?
ObFact: When racing airplanes we found the heaviest paint was yellow.
Anybody have different colors of the same cloth to check the weight?
Crash 'waiting with bated breath' Johnson
Robert Horton
closest even angstrom just how fast the air is moving. Boy am I glad I don't
live in a world with black trees. But I do like black kites. I cover them with
dimples for better lift. Keep your laminar flowing.
rjh
--
_________________________________________________
Seven raffish engines pulling in a train-
sinewed arms and shoulders muddled little brain.
_________________________________________________
Robert J. Horton Sr. Equipment Designer, CAD - retired.
b_ho...@interworldnet.net
Allen Pinkley
a small experiment for you. When it snows, get some construction paper of
all the colors and lay them spaced out on top of the snow. Monitor how much
the snow melts every hour. And Surprisingly! the snow under the green paper
will have melted the most. Why do we use black then? Cheap and almost as
efficient, so it wouldn't be cost effective to use green. However, I find
that combinations of green in a kite would be much more attractive than a
black kite...
Allen Pinkley
Who cares...
Perry Farmer wrote in message <9332...@thefarm.wa.com>...
Jerry Houk
I heard this line of reasoning back in 1959 when I built my soap box derby
racer and competed in Akron, Ohio. That year the white racers kicked butt.
Barny Townsen won the 21st All American Soap Box Derby in a white racer and
the driver from Mission City, Canada won the international guests event. He
might have won the whole competition if the racer from Rochester, New York
hadn't locked wheels with him and ripped out his rear wheels and axle spinning
them both off the track in the first heat of the race. He was able to replace
the wheels and axle and still finish a respectable fourth place with a white
racer. In theory black may be the best, but it doesn't always win. By the
way, the winner of the 1958 Derby was from Muncie, Indiana.
Jerry Houk
1959 Minneapolis Soap Box Derby Champion
(my racer was also black)
Dan Mitchell wrote:
> Quoting from http://207.242.75.40/derbtech/COLORME.HTM which is, I admit,
> talking about soap box derby races, we have the following:
>
> --cuthere--
> PHYSICAL CHARACTERISTICS OF COLOR
>
> The color that provides the least skin friction drag is black. Black also
> helps prevent separation of the laminar boundary layer.
>
SportKite1
daForce
<7nqv5d$8tp$1...@news3.microserve.net>:
>Dan Mitchell wrote in message <37a09...@news.cadvision.com>...
>>Quoting from http://207.242.75.40/derbtech/COLORME.HTM which is, I admit,
>>talking about soap box derby races, we have the following:
>>
>>--cuthere--
>>PHYSICAL CHARACTERISTICS OF COLOR
>>
>>The color that provides the least skin friction drag is black. Black also
>>helps prevent separation of the laminar boundary layer.
><trim hydrothermal babble>
>
>When you're hot you're hot. And fast. Why then is Queen Amydahlas
>interstellar ship CHROME!?
cos if it was black you wou;dn't be able to see it after the raytracing
>ObFact: When racing airplanes we found the heaviest paint was yellow.
>Anybody have different colors of the same cloth to check the weight?
good idea..... bht I have no suitabel cloth
I do have the digital scale though....
>Crash 'waiting with bated breath' Johnson
what flavour bait?
daForce
<37A136BD...@ix.netcom.com>:
>Dan,
>I heard this line of reasoning back in 1959 when I built my soap
>box derby racer and competed in Akron, Ohio. That year the white
>racers kicked butt. Barny Townsen won the 21st All American Soap
>Box Derby in a white racer and the driver from Mission City,
>Canada won the international guests event. He might have won the
>whole competition if the racer from Rochester, New York hadn't
>locked wheels with him and ripped out his rear wheels and axle
>spinning them both off the track in the first heat of the race.
>He was able to replace the wheels and axle and still finish a
>respectable fourth place with a white racer. In theory black may
>be the best, but it doesn't always win. By the way, the winner of
>the 1958 Derby was from Muncie, Indiana.
anybody tried riding an ordinary buggy downhill (esp on tarmac)
I did
went buggying in the shopping center parking lot near the house
it's all downhill from there to the house
nearly shat myself, had to do serious weaving to keep the speed down
Ralph Joh
>
> While I research what the actual study was called and who proved it, here is
> a small experiment for you. When it snows, get some construction paper of
> all the colors and lay them spaced out on top of the snow. Monitor how much
> the snow melts every hour. And Surprisingly! the snow under the green paper
> will have melted the most. Why do we use black then? Cheap and almost as
> efficient, so it wouldn't be cost effective to use green. However, I find
> that combinations of green in a kite would be much more attractive than a
> black kite...
>
maximum wave length of the painted material. Maybe paper, consisting of
cellulose (plant product!), absorps very good in a different wave length
area than green, wich is obviously refected. Since black aborps all wave
length, something must be wrong with your experiment..., or Mr.
Boltzmann and Mr. Stefan a.o. must be canceled out of thermodynamic text
books.
May one should consider the surface of a golf ball in order to konstruct
a fast kite ;-)
Ralph
Carl D. Crowell
wrote:
While it may be true ( I don't know ) that a material with a high
absorption rate will assist in boundary layer control and allow for
reduced drag, I would suspect that the greater influence on the speed
of kites is weight.
The effects of weight will be different in an aeronautical vehicle
than in a land based gravity driven vehicle. Black soap-box racers
may be a good idea. Five pounds of sand in a soap-box racer may also
be a good idea. Black kites may not be so great. Five pounds of sand
is a bad idea for most kites not made by Peter Lynn.
That being said, in fabric at least, the darker the color generally
the more pigment used to obtain that color. I know several years ago
(8 or more ?) when all we lowly kite builders had was the basic
Challenge / Bainbridge fabric, white was by far the lightest and
fastest of the fabrics. Of course back then we tended to use a lot of
glass rod in our kites and had steam powered sewing machines.
-carl
dean jordan
Mitchell) writes:
>Anyone tried this? It seems somehow unlikely that it'll make enough
>difference to be worthwhile, but you never know..
I tried it when i was 13 years old on my soap box derby racer, #A 13 Lakeland
Fl.
Came in 8th. My brake broke and was dragging me down. )-: Oh well, it was a
good experience.
total AoxomoxoA brought to you by. . .
. . . dean jordan
please buy * jordan air kites * every chance you get!
13
Dan Mitchell
>In theory black may be the best, but it doesn't always win.
Oh, certainly -- the page I quoted from continues to say (summarising)
"while black may have theoretical aerodynamic advantages, you can gain
significantly more by making your vehicle sufficiently obnoxious colours
that you gain a psychological edge over the opposition". This only applies
when other people are around, though -- if it's just you and the wind,
then I can't see the wind being put off by ghastly colourschemes..
-- dan
van Westrenen
green!
but in the other way.... maybe it "relaxes" us because it's our natural
living place.
(by the way.... my desctop is all green.... :-)
bye bye, I'm gone for two weeks!
Robin van Westrenen
http://hier.is/Tribbin
Allen Pinkley heeft geschreven in bericht
<7nq6km$6pm$1...@nntp5.atl.mindspring.net>...
>Actually there was a study done and dark green absorbs the most heat. And
>if you think about it, that's why grass, tree leafs, and all other plants
>are green and not black because it's the most efficient sun absorber...
>
>Allen Pinkley
>
>
>
van Westrenen
are two of them. does black absorbs them? (I don't know)
this could be the reason!
Robin van Westrenen
(my English is not that well... maybe "infa red" (Dutch: infa rood) and
"ultra violet" (Dutch: ultra violet) does not Xist)
Ralph Joh heeft geschreven in bericht <37A16A...@planet-interkom.de>...
van Westrenen
Tel
The reason, I believe, that golf balls are as they are is to produce more drag. The effect when they are
spinning is to produce more swerve as the airflow is influenced more when there is a greater drag. Up, down or
sideways depending on the spin. If the ball is in backspin then the velocity of the airflow on the underside
is reduced more and the velocity on the top side is increased compared to a smooth ball. The result is a
higher pressure on the underside and lower on the upper side, ie lift.
It should work for the kite formed as a globe and suspended on a line.
Thanks, I needed that, I had been wondering about golf balls.
Tel.
Aiken
Perry Farmer wrote:
>
> -> Actually there was a study done and dark green absorbs the most heat.
> -> if you think about it, that's why grass, tree leafs, and all other pl
> -> are green and not black because it's the most efficient sun absorber...
>
> -> Allen Pinkley
>
> So we should all go out and get dark green paint for our radiators?
>
Only if they're turned off - heat *absorption* is the thing here ...
otherwise, white's OK :O)
Aik
PS Isn't green unlucky for kites ? (something to do with young Cody?)
Gene
Then what happens when the near static volume of air inside a black(or
green) parafoil heats up. It will in theory be warmer than the outside
air... not? Sort of a hot air ballon effect....
We used to stick 10 or so black rubbish bags/bin liners together, end to end
to form a big tube. Inflated and left in the sun(especially in wintertime)
it would eventually start to rise and make a great attraction when tied to
an anchor piont from a long piece of fishing line.
Just pondering!
Ciao,
Just fishing for angels!
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SportKite1 <sport...@aol.comfly> wrote in message
news:19990730013228...@ng-bj1.aol.com...
Bruno Benvenuti
Allen Pinkley ha scritto nel messaggio
<7nq6km$6pm$1...@nntp5.atl.mindspring.net>...
>Actually there was a study done and dark green absorbs the most heat. And
>if you think about it, that's why grass, tree leafs, and all other plants
>are green and not black because it's the most efficient sun absorber...
I think because light is only a component needed for life and many grades of
colours can exist, but black only one.
Then, image what terrible world all in black :-)))
ciao
Bruno
Robear
Bruno Benvenuti wrote:
>
> Allen Pinkley ha scritto nel messaggio
> <7nq6km$6pm$1...@nntp5.atl.mindspring.net>...
> >Actually there was a study done and dark green absorbs the most heat. And
> >if you think about it, that's why grass, tree leafs, and all other plants
> >are green and not black because it's the most efficient sun absorber...
Not really, no. Plants don't want to overheat any more than we do. They
use green because chlorphyll is green. Earlier plants, some still extant,
used red or brown chemicals to convert light (but not IR) to energy. We
just have green now because chlorophyll-based plants took over a while back.
Seaweed is often brown or red, and lichen are red or brown also.
> I think because light is only a component needed for life and many grades of
> colours can exist, but black only one.
>
> Then, image what terrible world all in black :-)))
You mean, like nighttime? :-)
--
David Pipes
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ICQ 23347222
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