05-12-2025, 08:48 PM
(05-12-2025, 12:05 AM)President Bush Wrote: Two different things.
Sailboats maximum speed downwind would be the speed of the wind. Sailboats achieve greater than wind speed by tacking off the wind, their maximum speed would be the speed at which their sail exactly misses incoming air, like lift on an airplane wing but in the horizontal direction.
Sort of the opposite of catching the incoming air ie being downwind.
Think I described that correctly.
I remember that endless debate, mostly between spork and Humber, iirc.
The Blackbird propeller cart is a different beast than a sail boat. It exploits reference frames in a way that normal sailing can't. In the argument, the nay-sayers were sailors, biased by knowledge of sailing. Those rules weren't violated; they simply didn't apply to the land cart, which had the wind acting on a turbine, which was connected to the wheels of the cart.
Sailing purists called foul, as I recall, claiming that the angled prop blades constituted a violation, equivalent to tacking a sailboat, and enabling the higher speed. Quarky was a sympathetic (with spork) oddball whom added a useful metaphor to bridge the 2 bickering camps:
Imagine a catamaran, with its two pontoons separated by a km. Yes, that's a very wide boat and needs room to play.
Suppose the wide boat is going directly downwind in a straight line. The sail, however, is mounted on a beam connecting the floats and can travel back and forth, within the wide boat, essentially tacking with the wind.
As it turns out, that doesn't explain the cart's speed either; more of a way to 'cheat' the definition of a sailboat...though, the angled blades of the rotating propeller/turbine hint at tacking. At any rate, Blackbird's victory wasn't a 'just barely' event.
The cart more than doubled wind speed, directly down wind.
If memory serves, the matter was still being debated when JREF folded, though mostly as a semantics issue.
I believe someone may have built a sailboat that uses a prop to engage the wind, which spins another one in the usual motor boat position.
Shamefully, I forget if it worked as predicted, and now must search.