OT: Can a wind powered land craft go faster than a tail wind speed?

Rick C snipped-for-privacy@gmail.com wrote in news:27601b00-e707- snipped-for-privacy@googlegroups.com:

Only if the operator holds his tongue a certain way.

Or do the test down at "The Racetrack" in Death Valley National Park.

The surface winds push 700 Lb stones around like heavy ice skaters.

Slip Slidin' Away...

It's just a tack to the left...

And then a tack to the riiiight!

With your hands on your hips... You bring your knees in tight...

Let's do the tail wind again!

(that didn't sound right)

long thread about it here,

It's not really complicated. The wind pushes the car up to the speed of the wind. As the car is pushed along the wheels turn the propeller which propels the car faster.

Another way to look at it is to set the wind as the zero speed reference and see what happens as you move the ground under the car. Initially the momentum of the vehicle has to be overcome. Once the propeller is turning it creates a force that is relative to the stationary wind. So even as the car approaches zero wind speed, there is still significant force on the propellers from the air. The only question is whether the force from the wheels being turned is greater than the force on the propeller. So maybe it won't work. I guess I'll have to watch the video after all.

Does conservation of energy hold OK in the proposed contraption? I don't think the energy available in a tailwind somehow becomes zero when your speed >= tailwind speed it sounds like an extraction problem, not an availability problem.

The sailing analogy is more than apt, considering that by tacking, a sailboat moves into the wind's direction.

The sail would still work, if rotating on it's average plane. Converting this rotation through a gearbox is going to add complexity to a relatively handsome physical exchange, simply to avoid the 'tack'.

RL

Tacking on a roadway might be problematic...even more so on a train track!

Oh, I can imagine doing it; just hold a balsa toy plane backward in the wind to wind its propellor up and twist that rubber band tight... then aim it downwind and let it fly.

Wind powered? check. Airspeed pius windspeed greater than windspeed? check.

That is very disingenuous. The time while you are holding the plane is simply storing energy. That energy runs out and the plane no longer flies faster than the wind.

The guy said something near the end that makes it work for me. When the car is moving at the wind speed the prop is pushing the car still but the wheels are resisting. The reason why the prop can overcome the wheels is because the ground speed is more than the air speed. So a smaller force on the wheels can create a larger force through the prop from essentially the gearing and prop pitch. The power is constant through the gearing, so the prop can create more force at a slower speed.

We all remember that acceleration is determined by the force, not the power, right?

Interesting that this can be done with boats on the water where the keel provides resistance to allow the boat to travel at an angle to the wind and so faster. This can be done in a car where the wheels contact with the ground can provide the force to make it run faster than the wind. But you can't do this in the air at all. That would be a neat trick to figure out how to do it in the air alone!

Yes.

What's more, there's no theoretical upper limit to its speed (if we ignore relativistic effects).

The trick is to have the part of the craft that's catching the wind (the wind catcher) moving relative to the rest of the craft, and cause that part to be connected to the wheels. The craft's overall equilibrium speed is then when the wind catcher is not moving relative to the wind.

The rest is just engineering to minimise friction in the linkage between the wheels and the wind catcher, the frontal area of the body of the craft, and so on.

Sylvia.

I would trust this more if the panels on the vehicle were clear. Isn't it possible to hide batteries and electric motors?

Looking at how the propeller is turning it isn't turning as if it is being pushed by the wind from the rear - it would turn in reverse then. Based on what I see, the prop is turning the wrong way for the apparent visible blade pitch and a rear source of energy (wind).

Looks like a trick to me. Was this filmed on April 1?

John

James Randi (the magician) used to say that scientists (and possibly engineers) were easy to fool because they assumed the equipment wasn't cheating...

John :-#)#

The propeller doesn't look like the wind is turning it because the wind isn't turning it. The wheels turn the prop! That's the whole point. As the wind starts pushing, the prop is more of a kite than a prop. As the car moves, the wheels turn the prop faster so it is pulling the car in the direction it is already moving. As the car speeds up the propeller spins faster and pushes the car harder. By the time the car is matching the wind speed, the prop is pushing fairly hard and the car will continue to speed up.

I think it is funny that you suspect batteries in the body.

I'm really impressed anyone would actually build this.

In this case there is also the fact that the idea actually makes sense. Some people can't see it, but it's as real as LENR! No, wait...

Ecat SKLep

Wow! That guy is still raking it in with his frauds.

I believe the force of the wind on a propeller works in much the same way as on the sail of a boat that is tacking. If that is correct, a propeller based car can go faster than the wind, precisely because it /is/ tacking - even when the car is going in a straight line.

It is also possible for a propeller powered car to run directly into the wind.

You might actually give that one a bit of thought. Look at the two cars and consider the detailed forces and how they are generated. I think you will find it's the same car and always goes downwind, just with more or less efficiency, i.e. forwards or backwards.

I haven't looked at the video - I was talking in general about propeller powered cars.

It is possible to draw an analogy with electronics. The first time you hear of a voltage regulator that can give out a higher voltage than it takes in, or voltage in the other direction (i.e., a negative voltage), it can be a surprise.

In the OP's video the vehicle was not tacking so I'd still need to see a better explanation - math would help - but for now call me unconvinced, but curious.

I may yet have to reconsider my position...ice boats can go several multiples of wind speed when tacking.

Always happy to be proven wrong (or right!) - that is the only way knowledge grows!

John :-#(#

Some guys who built one posted here for a while. The concept apparently started as a college thesus. I recall that the wheels drive the prop, and the prop spins in the direction to push the cart faster than the tailwind. Something like that.

We went over this in great detail some years ago in sci.electronics.basics:

You really can do it.

Cheers

Phil Hobbs