Crap, my newsreader does nothing with that link. It adds a couple forward slashes after the colon, and a forward slash at the very end. But no action when I click.
Blowhards Sailing Downwind
Aug 01, 2010
73 Replies
I was dumbstruck. I think it reached 400 MPH when the belt broke.
It's over on alt.binaries.schematics.electronic, subject: "DWFTTW
concept cart."
If you can't get abse, email me your email addy and I'll send you a
copy.
Nice! "3 ROTATION" points the wrong direction though.
From a stop, the car backs up into the wind.
If the car's already moving downwind when the system is engaged, the windmilling propeller will brake the wheel's rotation.
If some sort of lock is holding the prop stationary until the system is engaged, that doesn't work either. The wheel has to counter wind-applied torque at the prop shaft the instant it's unlocked.
Adding a gravity blocker on the side of the ascending propeller blade might do the trick. Or maybe use hollow blades partially filled with water that's pumped back and forth so the descending side is always heavier.
Thanks! :-)
More properly, to overcome the torque generated by the wind flowing
across the prop.
...
This is the same as the BeanieMoBile that goes upwind, but here you "think" you have it headed downwind because the left side is pointier in your drawing.
OK, have it your way...
And if a lock is needed (if only to clarify the situation), the wheels can drive the propeller via a worm gear. This ensures that the propeller cannot act as a turbine.
Problem with that is that the cart can never go faster than the wind.
How so?
When the cart is heading into the wind, the propeller becomes a
turbine.
er
Assuming you are talking about heading into a relative headwind here ..
The prop NEVER becomes a turbine, it ALWAYS works as a prop. (think about it, it would mean the energy was going the wrong way, from prop to wheels)
As the machine starts going a greater ratio of wind speed, it also goes a greater speed over the ground, so the prop turns faster. However, as the ratio increases, at some ratio the increase in speed of the prop can't keep up with the increase in apparent headwind, which determines what the max ratio of windspeed that the machine can get to. This ratio is determined by the gearing, and the pitch of the prop. You might think to use a different gearing/pitch, set for a higher ratio, but the problem would be that this would require more power extracted from the wheels. For a given cart, there will be an optimum gearing/pitch, beyond which you cannot go. Further, the optimum will have poor acceleration compared to a cart which is geared for a lower ratio of windspeed (which is why I believe they eventually went to a variable pitch prop on the actual cart)
Assume that there is no wind, and of course the cart will sit
motionless.
Now assume the cart experiences a headwind.
Where will the power to turn the wheels come from?
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