DDWFTTW - Prop or Turbine

This video was made to address a common misconception about whether the wheels provide the torque that turns the prop or the prop (working as a turbine) provides the torque that turns the wheels. I very much look forward to the creative claims on various forums explaining how this video is a hoax.

Category:

Science & Technology

Tags:

• DDWFTTW
• DWFTTW
• Downwind

[bruceandberni]

Im sorry, my last statement was not what I wanted to say. So, here goes. Once the vehicle reaches the speed of the wind then what will be pushing it beyond the winds speed? Once at wind speed there is no other driving force, the cart has reached equlibrium with the wind. However, since the cart IS moving then the wheels and gearing are still turning the prop. So, if the prop is not underpowered then it would continue to speed up until the prop starts to cavitate. Interesting, How fast?

[spork33]

@bruceandberni

The Blackbird (our full-sized manned downwind cart) has achieved more than 3X windspeed, and currently holds the official world record at 2.8X wind speed. It can maintain this speed indefinitely. It does not go in spurts.

Props don't cavitate in air - I think you're thinking of boat props.

Additionally, the wind doesn't "push" the cart from behind. The cart is going faster than the wind and is propelling itself through the moving mass of air with its propeller.

[bruceandberni]

I understand now. If the air in the room is not moving, then the belt speed relative to the air would mean that the device should stand stil if not able to move faster than the wind. But! the wind is not driving this thing, the prop is adding to the still wind, sort of like a man walking in an airplane. is the man going faster than the plane? No, he is moving relative to the plane. So is the device moving relative to the driving force of the treadmill. Im still not sure.

[spork33]

@bruceandberni

Yes, if the man is walking forward on the airplane, he IS moving faster than the airplane relative to the air outside. And that's sort of the secret to this cart. It can travel over the road faster than the wind moves over the road. It IS powered by the wind - even though it outpaces the wind. It's a tricky devil to get your head around.

[bruceandberni]

im a bit confused. Are you claiming that the cart moves relative to the ground faster than the wind moves relative to the ground? If this is the case then you will have to show the wind speed, and the ground speed, for if you put anything in the wind that rolls via the wind, then it is simply rolling with the wind. I understand that it is gear driven by the prop in the wind. But how do i know it is moving faster than the wind?

I am not disagreeing with you. But "show me" that its faster.

[spork33]

@bruceandberni

Yes, it moves faster relative to the ground than the wind moves relative to the ground. We test it on a treadmill with no "wind" in the room in order to have perfect, steady conditions.  If it moves forward on a treadmill belt that's going backward - it's going downwind faster than the wind. It doesn't matter if the wind moves over the ground or the ground moves under the belt.

[planetofthescums]

@spork33 The wind doesn't push the cart from behind. Are you sure about that?

It seems like if you stuck a cart in the wind the wind would push on it.

[MrTweetyhack]

@Volatus now that you totally understand it, please enlighten us that don't

[myforwik]

Why do people have so many stupid questions? Go and make one its like $10 in parts.

[Volatus]

I must be one of the few people (if any) that actually totally understands that this isn't some kind of elaborate hoax. Hell, I just ordered a sticker for my laptop, "Those who say it cannot be done shouldn't interrupt the people doing it". I love doing stuff like this, and seeing this video is actually pretty damn inspirational! Seriously though, the physics just work out, in an odd sort of way. It's not defying any rules, it's just bending them in unusual ways (not many people work with air).