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 Post subject: Re: Does density of air affect kite power?Posted: Mon Jul 23, 2012 10:13 pm
 Rare Poster

Joined: Mon Feb 07, 2011 10:16 pm
Posts: 7

http://en.wikipedia.org/wiki/Forces_on_sails#Value_of_force
and
http://en.wikipedia.org/wiki/Density_of_air

The force on a sail is:

F = 1/2 x rho x Area x C x V^2

All other variables are equal so it is based on rho(density of air)

If the air temperature changes between 95F(35C) to 32F(0C) the change in the force on the sail(kite) would be about a 12.8% increase.

I did this kinda quick but I think the math is correct.

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 Post subject: Re: Does density of air affect kite power?Posted: Tue Jul 24, 2012 12:51 am
 Very Frequent Poster

Joined: Sun Sep 04, 2011 5:37 pm
Posts: 960
Fly your kite at sea-level, in 30deg temperature air.
Now go fly it at the same altitude near Palm-Springs in 110deg temperature.

The force of the kite felt on your harness in both places will be the same
But
The guy flying his kite in Palm-Springs will need to fly his kite "Faster" to get
that same pull, because there's not as much air occupying a given cubic measurement
of space.
And here's Why :

Take say a cubic yard of air at 30 degrees caged in a wire mesh cage.
drive out toward palm springs in july with that cage in the back of the truck.
As it heats up the air expands out the sides of the cage. You still have a cage
full of air but there's less of it in a given space now that its hotter.
the hot air inside that cubic yard cage should now weigh less because there's less of it.

In order for your glider plane or kite to fly,
the force of the air hitting it is the weight of the air times the speed the kite hit's the air at.
So Ya gotta fly Faster to achieve the same force on the wing. Drag won't increase, even though
because there's less air in a cubic measurement of aria when it's Hot.

OK -- That's just temperature's affect on air density.
Elevation , and Relative humidity and barometric pressure,(Hg) ---also have an effect on the amount of air molecules that
occupy a given amount of space.

Play with this calculator and maybe you can see the affect that each have on air density :
http://wahiduddin.net/calc/calc_da_rh.htm

Bille

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 Post subject: Re: Does density of air affect kite power?Posted: Tue Jul 24, 2012 3:05 am
 Very Frequent Poster

Joined: Fri Jul 16, 2010 6:27 am
Posts: 1326
Location: Ford Lake, Michigan
Rainey wrote:
95F(35C) to 32F(0C) the change in the force on the sail(kite) would be about a 12.8% increase.

I did this kinda quick but I think the math is correct.

that's the rite math.

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 Post subject: Re: Does density of air affect kite power?Posted: Tue Jul 24, 2012 1:04 pm
 Rare Poster

Joined: Wed Oct 05, 2011 4:09 am
Posts: 9
when on http://localkitespots.com to check wind speed, next row there is the boost factor.
practically speed +/- boost = feel speed

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