Going directly downwind faster than the wind?

Here is a picture of the vehicle.



Would this wind powered vehicle be possible?


I found it interesting. I was willing to believe it was possible until the people claiming they built it couldn't find the words to give an explanation in one post on the land yacht forum. Bit by bit some of their posts reveal a little bit of information.

Check here:
www.seabreeze.com.au/forums/Land-Yacht-Sailing/General/Downwind-Faster-than-the-Wind/?page=1

If you can go directly downwind faster than the wind, then however much faster than the wind you're going, you can do with no wind at all. In other words you're running on your own apparent wind, some how I don't think this is possible.

In the other thread you asked for a mathematical solution to the problem, it was provided. I can only assume you don't understand it and are just trolling for the sake of it.

If something's going downwind, faster than the wind, the apparent wind is from in front, not behind, in that case the props are going to turn in the opposite direction, powering the vehicle backwards.
I still don't believe it.

Decrepit. You have to think of this thing as a powered propellor driven craft. An aeroplane has an apparent wind from dead ahead yet the propellor still rotates (driven) moving the vehicle forward. This craft relies on the true wind over the the ground and extracts energy from this wind as do all sail craft. This thing can extract energy from the moving air while moving in the same direction but moving faster than the air.

I think that the whole wind thing gets a bit confusing, so here's an attempt to explain it in different terms:

Imagine you have a long straight road, and a 4 wheeled cart.
Push the cart down the road, and note that the wheels are doing the same speed as the road.

Now add a fifth wheel in the middle of the cart, set up so that it's not quite touching the ground, geared down so that it spins at half the speed of the main wheels.

Push the cart down the road at 10 km/h, and note that the bottom of the wheel is only doing 5 km/h in the same direction as the cart.

Now put a conveyor belt in the middle of the road, set up so that it does touch that fifth wheel, and set the speed of the conveyor belt at 5 km/h.

Note that your cart is still doing 10 km/h, without you pushing it, and is going faster than the device that is pushing it (the conveyor belt).

If you increase the speed of the conveyor to 10 km/h, then the cart will speed up to 20 km/h.

By replacing the conveyor belt with the wind, and the fifth wheel with a propellor, you can see how this device works.

You are going to have to scan a sketch cause I for one can't see your explanation. The way I see it the conveyor will drive the cart backwards.

You shouldn't have got Nebs off the hook like that, as they say a picture is worth a thousand words. Still want to see Nebs sketch though.

Bingles, this is a serious forum. Your cat reference is laughable. You want to see the wonders of physics in action?? Check out this hair. I'm sorry, but your argument is not valid.

I don't think it needs a ratchet at all...

An even simpler analogy is to have just a simple wheel, with a rod attached halfway between the centre and the radius.

Sit the wheel on the ground so that it's upright, and the attachment point is at its lowest point, with the rod horizontal.


Push on the rod.


The wheel will move faster than the rod (but only for a short distance... enough to demonstrate the principle anyway).

Ye canna change the laws of fyzacs!!





Mmmm.. use your mind young sailor or the path to the Chuck side awaits





And just for Doggie

(reckon about 80% of Treckies would pop their phasers when the saw this - the other 20% go more for Kirk)

WOW trekie BOOBS (.)(.) thanks funky I love it WOOF!

It would go faster though if it was red

I drew up some sketches of how the thing works but can't seem to upload them so a verbal description is going to have to suffice.
1/ Take a threaded rod with a screw pitch of 1.
2/Build a cart so that the wheels rotate a nut instead of a propellor. Pitch of nut =1 and cart speed of 2 will rotate nut at omega=1.
3/ Push the cart from a fixed position on the cart with the rod at rod speed =1. The cart will move along at speed =1 and the nut will rotate at omega=0.5.
4/ Now engage the rod into the nut and push the rod at speed =1. The cart will move along at speed =2 by virtue of being pushed along by the rod at speed=1 and by virtue of the nut screwing along the rod at speed=1. ie the cart speed of 2 will rotate the nut at omega=1 and this will move the nut along the rod at speed =1.
In this case the rod is analogus to the wind and the cart the propellor driven craft. Change the gearing ratio of the nut and it will change the multiple of cart speed to rod/windspeed. Obviously there are practical friction and efficiency limitations to how many multiples of windspeed can be achieved in real life.

However. you still need a "ratchet" or some means of preventing the initial push of the rod in the nut, wind blowing the propellor backwards as a turbine, or just friction/inertia when starting the conveyor from rotating the nut, propellor or fifth wheel backwards and hence the craft going backwards at startup.


In the wheel/rod case you cite the actual physical arrangement acts as a "ratchet" ie if the resistance to the axle moving forward was greater than the resistance of the tyre on the road then the rod would rotate the wheel backwards and it would roll down the road backwards. Still not worth getting hung up on this bit cause after starting all will be good. so it is really a mute point.

If we assume it rolls without slipping it should come down to prop-pitch and gear ratio. I'm pretty sure inertia is not a factor.