Better yet, couple the wind turbine (input) to a propeller at the rear (output). Free energy!
Malacandra, not only is the company a prime example of a scam artist, they are idiots, too. Ask them what college they teach physics at.
Nitpick here.
You actually CAN build a wheeled vehicle powered by the wind. Big windmill geared to the tires. And IIRC it can go upwind faster than the wind is going downwind (or some such). I certainly recall seeing a video of it not long ago (and probably from here for that matter).
Those must be some big molecules, or a very small drop (something like 10^21 molecules in an ordinary drop).
Yes, we had a thread on that some time back. But it gained extra speed, not extra energy. It did not provide perpetual motion and did not provide a net gain of energy.
My suggestion, coupling a generator to a motor, will result in a net loss of energy every time unless there is any additional input from some source.
Can we work a treadmill into this scenario?
I’ve seen the videos online. The car is a very low profile, low drag, lightweight vehicle. Apparently the windmill can convert enough energy from the wind to overcome the total drag. Seems impossible at first, but then consider that sailboats can do something similar.
Directly downwind faster than the wind. It’s not a windmill, it’s a propeller. Figure that a cart with the wheels driving a propeller, with no losses, would be in a steady state in still air - the resistance imposed by making the wheels turn the propeller is exactly balanced by the thrust from the propeller. Give it a tailwind, and the prop is still trying to advance just as far relative to the wind every time it turns, so now giving you more of a shove even if your vehicle is moving faster (over the ground) than the wind. Hence you will accelerate to infinite speed. 
But since there are various excellent reasons why you can’t do all this without friction losses, there is necessarily a limiting speed where drag equals thrust. It’s just that this can perfectly well be faster than the wind.
There was a big thread about it a while back. I started out sceptical, my penny dropped at post #24.
I have to go back and look at this, but I thought that was the downwind travel mode, i.e. traveling in the direction of the wind. I think the windmill mode works moving into the wind. Of course in that case you’re exceeding wind speed because it’s negative. You’d be exceeding wind speed even moving backwards. But they claim to be able to make forward progress.
I see no reason why a windmill-powered craft can’t go directly to windward. The DDWFTTW cart is geared, AIUI, so that the prop doesn’t have the mechanical advantage to turn the wheels; the wheels turn the prop. With a little redesign ISTM that you could have the prop turn the wheels, in which case you would be heading into wind. The faster the cart went, the stronger the apparent wind would be; of course, you won’t get infinite speed that way as the air resistance of the whole vehicle will increase the faster you head into wind.
Someone may be able to shoot this down, but I don’t think the force being exerted to rotate the windmill is accompanied by an equal force trying to push the windmill downwind (which would spell doom for this plan). Presumably blade angle of incidence affects this?
I recall something about the blades needing to be able to ‘feather’ to the angle of least resistance.
…while still having enough angle of incidence to actually windmill. 
Aeroplane props have long been able to feather to save a damaged engine further punishment after it’s been shut down, and obviously reduce drag.
Since they’re foils they’ll always windmill. If the angle of incidence reaches a stall state the drag increases.
There’s surely a particular no-stall angle of incidence at which there is no windmilling, given that at some angle the airstream would be turning the prop in its normal sense and at another it would be turning it in reverse. I agree however that the no-windmill angle need not necessarily be the minimum-drag angle so I’m probably arguing needlessly here (like it would be the first time).
That makes sense. And there’s no needless argument, just needless agreement… wait, that can’t be right :eek:
In fact, the same cart (with little redesign) that went 2.8 windspeed directly downwind in 2010, also went 2.1 windspeed directly upwind this year.
DDWFTTW:
DUWFTTW:
From: http://www.nalsa.org/
[QUOTE=NALSA]
They are at it again! A new record has been set, this time sailing dead upwind…that’s right, directly into the wind (not tacking). The NALSA Board of Directors has ratified the following two records achieved by Rick Cavallaro on New Jerusalem Airport near Tracy California on June 16, 2012, with the wind turbine driven sailing craft, Blackbird. Mr. Cavallaro achieved a maximum boat speed to wind speed ratio of 2.1:1 while sailing directly into the wind and a maximum speed in a wind turbine driven sailing craft of 22.9 mph on a different run.
On July 2, 2010 on El Mirage Dry Lake, Blackbird sailed directly down wind at a speed of 27.7 mph in a 10 mph wind to set a first record for the ratio of Boat Speed to true wind speed of 2.8. BlackBird was designed and built by the Thin Air Designs team (Rick Cavallaro and John Borton)
[/QUOTE]
Malacandra or Cardinal, how’s that hydrogen generator for your car coming along?
:rolleyes:
This sounds a lot like a current thread in General Questions; again, you can’t get more energy back no matter what you do, generating hydrogen by electrolysis might be 10% efficient if you’re lucky (engine + alternator + electrolysis, not counting whatever the efficiency of a ICE is on hydrogen/gasoline mix, which would drop it to the low single digits if it is similar to straight gasoline).
As for the windmill, same thing, maybe a bit more efficient especially if it were an electric car so you can directly use the electricity* (that said, boats can sail faster than the wind, even into the wind, but no laws of physics are broken).
*Why go through the bother of generating hydrogen if you can just tap off the alternator; of course, an electric car wouldn’t have one and there wouldn’t be any point in adding one (see efficiency losses).