Downwind Faster than the Wind (DWFTTW) Myth Challenge

This is our submission for the Mythbusters video challenge

Category:

Science & Technology

Tags:

• DWFTTW
• DDWFTTW

[WestLABoy]

Would this principle be useful for a wind-aided bicycle? Or would the propeller required be too big/heavy to be practical.

[spork33]

@WestLABoy

You could use the principle on a bicycle, but it would be impractical for a lot of reasons (not the least of which is the safety issue). Also, the torque of the prop would be trying to push you over all the time. And without pivoting the whole prop mount, it would only work directly upwind or downwind.

[paulgibeault]

Poor choice on audio mixing. It's very annoying to those of us who hear with only one ear.

[spork33]

@paulgibeault

I agree. That was not intentional. It was more a result of the free program we used - and our lack of video editing skills.  Sorry.

[spork33]

@superifico

There's really no need for them to do it now - since we've done it with a 23' tall, 450 lb, manned vehicle that will be setting a new world record in the next few weeks.

[spork33]

@grhd76

The air in the room is still. This is demonstrated in some of our other videos. Only the belt is moving. If the vehicle maintains its position on the treadmill it is going downwind at exactly wind speed. Just as you would feel no wind if you rode your bike downwind at wind speed, the cart experiences no wind at this point. If it advances on the treadmill, it begins to experience a relative headwind, as you would if you rode your bike DDWFTTW.

[michaelqshaw]

It would be opposing wind pushing against wind, which would allow it to go faster than the pushing wind. In other words there is excessive trust in relation to, ratio to, the devices total weight/drag and it accelerates because of that excess.

[michaelqshaw]

If this is based on honest people sharing what they built, the answer is mechanical advantage. If, a gear attached to the rotor is made in a ratio to rotate 3 times to the 1 time rotation of the driving gear attached to the wheels that is only mechanical advantage. Explaining why it would start on a tail wind, if the device was light enough, even against the tail wind, once the propeller began to produce thrust, it would be opposing wind pushing against wind.

[BC3012]

That is brilliant, thank you

[technolope]

@jake5680

The top speed (either upwind or down) should only be limited by the efficiency of the power transmission between the propeller and the wheels.

[technolope]

@jake5680

The top speed (either upwind or down) should only be limited by the efficiency of the power transmission between the propeller and the wheels.

[pwpike]

@tezropunkel As I said, you can build your own cart and prove this wrong if you wish. The physics seems fine to me; the evidence seems clear enough; it's been validated by an independent 3rd party; you have the ability to debunk the theory. Seems like pretty sound science to me.

[tezropunkel]

@pwpike Am i getting it right that you say that you can clearly see how fast the wind goes and compare it to the speed of the cart? I mean, I can't. Neither can anybody by the way unless he has an anemometers built inside a head or something. You know it sounds like "Look there are invisible fish in the aquarium" and believe that...

[pwpike]

@tezropunkel Depends on what you're trying to prove. I don't need to know exact numbers to see if the cart's moving 3x faster than windspeed, just like I don't need instruments to tell a car is moving faster than a bike when it's moving 3x faster. I only need those numbers if I'm trying to make a physics formula or something. I think it's pretty clear that these guys (as well as others) have demonstrated DWFTTW, and you don't need to know exactly how fast the wind or the cart was to see that.