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Good question – Can a wind-powered vehicle travel faster than the wind?
December 3, 2008
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It seems to be intuitively obvious that a wind-powered device cannot travel faster than the wind that is powering it. But is it true? “If you were to race a floating balloon downwind in a wind-powered vehicle”, could you ever beat the balloon? Here’s one look at the answer:
Many people are working on this question:
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4 Responses to “Good question – Can a wind-powered vehicle travel faster than the wind?”
Thanks for writing. When you think about it in your head, Do you have a favorite explanation for what is happening with the cart?
Marshall, here is my best ’short version’:
It’s been long established that craft with traditional sailing rigs (sail boats, ice-boats, land-yachts) exceed the downwind component of the wind on a regular basis. This is especialy prevelant among ice-boats and land-yachts but also is accomplished by the best racing sailboats of this era.
Now the above sailcraft must be running at an angle to the wind to accomplish this feat — but even with the longer angled path, their VMG(velocity made good) is faster than the wind.
This means that if a land-yacht races a neutral bouyancy balloon down a course from a start point to a downwind finish point, the yacht will take a zig and then a zag and the balloon will follow a straight downwind path. In spite of the longer path of the yacht, it still beats the balloon by a very large margin to the finish line. High performance rigs can ~3x VMG the speed of the balloon/wind.
The two sails (otherwise called a prop) in the video cart are geared to the wheels in such a way to provide the same angle constraint that the keel/skate/wheel provides on sailboats, ice-boats and land-yachts respectively.
By changing the gearing on the cart, you can decide if you want the sails to take a 45d path downwind (or any other angle)– all with the chassis of the cart continuing straight downwind. Once you settle on the angle of the path you wish the sail to follow, changing the pitch of the prop is the equivalent of adjusting the sail to the apparent wind seen along said path.
The adjustments truly are exactly the same adjustments one could make with a traditional sailing rig, just implemented in a different form.
The result is the same in one respect, a VMG of greater than that of the wind, but different in that the frame of the cart doesn’t have to zig and zag to do it — only the sails do that.
Hope this helps.
JB
This forum thread shows you the depth of the discussion:
http://forums.randi.org/showthread.php?t=128483
I am the guy in the first video and the builder of several of the carts in that video.
Traveling faster than the wind in a wind powered device is done often — sailboats, ice-boats and land-yachts do this regularly. The more unusual trick is to go faster than the wind in the same direction the wind is blowing (sailboats etc, do in on an angle).
It IS possible to do it directly downwind and this has been shown by several independent parties.
If you’ve got questions, fire away.
JB