DDWFTTW - Demonstration of Flawed Design

In this video we demonstrate a design proposed by one of the participants of the many on-line discussions of DDWFTTW. While there are aspects of the design that we have used ourselves to illustrate the theoretical possibility of DDWFTTW, this design lacks dynamically feathering vanes, and therefore cannot achieve DDWFTTW

Category:

Science & Technology

Tags:

• DWFTTW
• DDWFTTW
• Downwind
• FAIL

[macrumpton]

The big problem I see is this rotor does not have any particular direction that it blows air when it is spun. It blows the same amount towards the front and the back and the top and the bottom, so of course there will be no thrust. Also, Savonius type rotors use drag to create rotation from wind which is far less efficient than using an airfoil rotor. It would be interesting to see if a lenz turbine would do better, although that would not work on a treadmill, it would need to have actual wind.

[spork33]

@macrumpton - Any design that works with actual wind will work on a treadmill. There's no way to distinguish between air moving over a surface vs. the surface moving beneath the air.

[spork33]

@macrumpton

Everything you say about this design is correct. It is flawed in its very conception. That's what we set out to prove to the guy that proposed it. However, you did get one part not quite right...

>> although that would not work on a treadmill, it would need to have actual wind.

There's no such thing. The treadmill and "actual wind" are the same thing.

[mylexusis]

no wind powered craft will ever travel at a constant speed greater than the wind directly down wind , any one trying to develop such a craft is wasting there time

[spork33]

@mylexusis

Your theory has the one problem that it can't explain the fact that we did build such a vehicle. We expect to establish the first world record in that category in the next few days.

[pallidinyou]

That whole test scenario is in reverse!

The applied force is NOT supposed to be on the wheels as in this demo, rather on the vanes!

With a 2:1 ratio, air blowing 10 mph against the vanes will rotate the outer surface of the wheels at 20mph.

[spork33]

The test only looks like it's reversed. Whether the device sits on a moving surface in still air, or on a stationary surface with moving air (wind) makes absolutely no difference. In neither case will it do as you predicted.

[planetofthescums]

What happens if you blow air against the direction of the treadmill, as you would have in the real world before reaching wind speed?

[planetofthescums]

@macrumpton This principle is easily adapted... really? You can throw a rock off a building, tie a rope around a pulley and have it lift a person off into the sky. Can this be easily "adapted" to shooting people up into the with gravity?

[nickrupert]

if you had a cover on the bottom front that blocked the scoops from the headwind it would work woudln't it

[itsandbits1]

the thing all these other suggestions do is get away from the fact that the propeller is a propeller, not a turbine which is what these other sav and lenz ideas are. Of course they won't work. you need something annalagous to the wheel to propeller drive for it to work; perhaps a large helix inside a tube driven by the wheels but why not just accept the simple beauty of the unit as it is???

[UTJhn]

@macrumpton

A "lenz turbine" and all other VAWT that don't require anything to turn them into the wind have the same problem. None of them can create a directed wind. So, they can all replace a windmill (but not always as efficiently), but none can replace a propeller. And, none can be used to go DWFTTW.

But your lenz turbine might do better at going upwind than a comperable anemometer.

[UTJhn]

This tries to use the principal of an anemometer which turns directional wind into rotation. But its rotation cannot create directed wind. So it can replace a windmill but not a propeller. So it cannot go DWFTTW.

A windmill is needed for upwind, but this has the wrong ratio.

However, an anemometer attached to much smaller coaxial wheels riding on elevated rails could go upwind.

[macrumpton]

@spork33 Now that I think about it more I see you are correct.

Perhaps a gyromill type VAWT that has blades that change angle according to the wind direction would work, but then you get right back to the mechanical complexity of your design, although it would have the advantage of being able to accept wind from any direction.

[macrumpton]

@mylexusis Imagine an iceboat (which easily exceed 4x wind speed going across the wind) attached to a string going through a pulley fixed to the ground. It is easy to see that the the string will be pulled through the pulley at the speed of the iceboat in any direction you lay out the string. It is not self contained, but the principle is easily adapted.