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Author Topic: They call the wind Myria  (Read 1202 times)

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Fiddlehead44

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They call the wind Myria
« on: February 13, 2006, 12:20:07 PM »
A little off beat. I would like to understand

why a 20 MPH wind will propell this craft at

40 to 50 MPH. I would think that would be causing

backdrag.    Fiddlehead

« Last Edit: February 13, 2006, 12:20:07 PM by (unknown) »
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nanotech

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Re: They call the wind Myria
« Reply #1 on: February 13, 2006, 06:20:34 AM »
It's the same principle as TSR.  How a 10mph wind can have the tip of a HAWT blade going 20mph (or even faster).


They don't use the sail as a drag system, they use it in a lift fashion - taking the headwind across the beam and making it go "around" the sail, which will actually propel the craft faster "out of the way" than the wind is travelling...

« Last Edit: February 13, 2006, 06:20:34 AM by nanotech »
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SparWeb

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Re: They call the wind Myria
« Reply #2 on: February 13, 2006, 12:42:04 PM »
A sail generates both LIFT and drag.  It's just not as efficient as an aircraft wing, and pointed in the wrong direction.


Compare a boat sail with a glider (take the engines out of the equation).


As a glider moves forward, it is descending gradually.  Given the L/D ratio can be about 30, then gliding at 90 MPH requires a descent at 3 MPH to profide enough energy for the wings to create the lift you need to fly.


The sail isn't much different.  With 20 MPH winds from the North, you can go 50 MPH to the East or West because the Lift/Drag ratio is about 2.  To go straight South with that wind, you cannot go faster than 20 MPH.

« Last Edit: February 13, 2006, 12:42:04 PM by SparWeb »
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Kwazai

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Re: They call the wind Myria
« Reply #3 on: February 13, 2006, 01:34:14 PM »
« Last Edit: February 13, 2006, 01:34:14 PM by Kwazai »
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whatsnext

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Re: They call the wind Myria
« Reply #4 on: February 15, 2006, 06:38:19 PM »
Ice boats with better sail design can go about five to six times the wind speed so your little Sunfished rigged boat doing two to two point five times is not too suprising. Iceboats are really incredable to ride in.

John..
« Last Edit: February 15, 2006, 06:38:19 PM by whatsnext »
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