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how can we ride 40-50 mph in only 20-25 mph of wind?

Posted: Thu Jun 08, 2006 5:36 am
by kitesurferbum
im just tryin to grasp the concept that we use the wind to travel but yet we can go faster then it at the same time, how is this possible? cool shit though....latas...add comments pleez

Posted: Thu Jun 08, 2006 5:43 am
by ImagineParadise
:thumb:

Posted: Thu Jun 08, 2006 8:34 am
by spork
Imagine squirting a watermellon seed from between your thumb and forefinger. Becuase of the narrow angle of the seed it will shoot out at a much faster speed than the speed at which your fingers come together. This is basically the same principle that allows us to travel faster than the wind that is propelling us.

If we consider a windsurfer, we have two wings. One is the sail and the other is the fin. The wind and the water passing over these wings act as the fingers that squeeze the watermellon seed.

Here's the REALLY crazy part (and yes I'm prepared for full flamage). It's actually possible to construct a wind powered vehicle that goes DIRECTLY downwind, faster than the wind, powered only by the wind. I know there are plenty of people that will claim this breaks every law of physics, but I assure you it doesn't. I have far too much respect for the laws of physics to go around breaking them like that.

Posted: Thu Jun 08, 2006 9:01 am
by Klaus (c:E
Hai,

keywords are: apparent wind, wind window and L/D ratio.
In the picture it´s shown for low wind speeds where You might ride faster than the windspeed but still gain hight. Really going fast is the same on a room course.

Translations:
Wind -> wind
Fahrt -> fair wind
Scheinbarer Wind -> apparent wind

Sea You: Klaus (c:E

Posted: Thu Jun 08, 2006 9:42 am
by bob10
as you start to get faster the apparent wind picks up
(apparent wind is wot u feel in a car ie:u are moving creates wind)
as you go along this casuse the wind to increase and gives the ipression that u start going upwind mroe cos the wind is coming in front of you.

ill shut up now. im half asleep

Posted: Thu Jun 08, 2006 10:55 am
by Puetz
G'day,

3 years ago when I was still windsurfing, I stood at the waters edge with an anemometer and measured 15 knots steady. I took off and when I was up to speed, pulled the anemometer out again and measured 27 knot peaks with the average of 23 knots. I don't know what board speed over the ground I had but it was amazing to get readings like that. Good old apparent wind.

Seeya,

Robert.

Posted: Thu Jun 08, 2006 7:19 pm
by ImagineParadise
wind going over your sail will increase its velocity but only for the second or two when it passes over your sail. the air moves faster at that point alone because its trying to catch up to the wind on the other side of the sail. Your not going 25kts or whatever. its called air pressure. As you move, your sail creates a slight vaccuum making the air around one side go faster than the other. just like a wing on an airplane. you might go a little faster than the measured wind on the shore but your not going as fast as your anemometer says the wind around you is going. :bye:

anyone want to contridict this is more than welcome.

Posted: Thu Jun 08, 2006 7:36 pm
by spork
ImagineParadise wrote:wind going over your sail will increase its velocity but only for the second or two when it passes over your sail.
True, but this isn't the apparent or relative wind people are talking about. The apparent wind is faster than the "true" wind even when it's nowhere close to you or your sail. It's simply the vector sum of the "true" wind and your velocity.
ImagineParadise wrote: the air moves faster at that point alone because its trying to catch up to the wind on the other side of the sail..
This is a very common misconception. The wind over a wing in a high lift configuration doesn't merely "catch up" to the wind under the wing. It reaches the trailing edge much sooner.

Posted: Thu Jun 08, 2006 7:38 pm
by ryansurf1
imagineparadise....i don't think i know what i am talking about, but i know you don't know what you are talking about.

kiters can travel well in excess of the actual wind speed....kiters on ice can travel at speeds multiples of the wind speed.

Posted: Thu Jun 08, 2006 7:42 pm
by Tinman
Klaus (c:E wrote:Hai,

keywords are: apparent wind, wind window and L/D ratio.
In the picture it´s shown for low wind speeds where You might ride faster than the windspeed but still gain hight. Really going fast is the same on a room course.

Translations:
Wind -> wind
Fahrt -> fair wind
Scheinbarer Wind -> apparent wind

Sea You: Klaus (c:E
Klaus I'm not sure I would call a "Fahrt" fair wind...... more like bad wind.

But I can see by your diagram that it does add to your velocity when used in the direction of travel!

:lol: