Sailing downwind faster than the wind

[MeteorWayne]

I can give you 10 reasons to deny any test with any instrumentation.

OK, let's hear them!

 

[MeteorWayne]

Nothing's holding us back. You can see it on the "Daily Planet" on Discovery next month, and soon you'll see the NALSA ratified direct downwind record. Papers? What's that? Peer reviewed journal? Maybe - but why?

OK, be sure to let us know when that will be on.

Peer reviewed journal. Why? Because that is how real science is done.

 

[spork]

I can give you 10 reasons to deny any test with any instrumentation.

OK, let's hear them!

Describe a test, and I'll give you all the problems with it. But keep in mind, the issues I raise will be as cranky as the issues people have with our current tests.

 

[MeteorWayne]

Oh, you don't have the reasons in advance?

 

[spork]

Peer reviewed journal. Why? Because that is how real science is done.

We know how real science is done. And when you can demonstrate the real thing in real life, in such a way that others can examine and repeat it, and get the same results, it's not necessary to have your peers say "this should work".

Did the Wright brothers do "real science" in your view?

The real problem with "real science" is that so few people actually understand what that means.

 

[spork]

Oh, you don't have the reasons in advance?

You think I should have a list of problems for a test that's not been defined? I smell a troll.

 

[centsworth_II]

....in both cases: treadmill and outside in natural wind. In the reference frame of the cart the moving surface provides the power input to drive the propeller, in both cases.

Outside, it would be legitimate to herald useful energy derived from the moving surface. I'm concerned that energy is being derived from shifting wind acting at an angle.

On the treadmill, I'm not concerned with friction at the wheel/tread contact, but friction between the wheel and vehicle frame. This will cause the wheel to turn more slowly. Some of the missing speed may show up as waste heat, but some may show up as forward motion powered by the tread, not the vehicle.

Imagine two cases:

1. The wheels are locked. The vehicle will be pulled forward due solely to energy provided by the powered tread.
2. The wheels have perfectly frictionless spin. No forward pull is due to energy transferred from the powered tread.

The reality lies between the two cases. The question is, how much of the forward motion on the tread is due to the spinning wheels and how much due to the tread pulling the model forward because the wheels do not have perfectly frictionless spin.

Placing a model on a flat surface facing [away from] a fan would remove any question of wind angle and friction with powered surfaces. It seems an easy experiment to do. I'd like to see that Youtube video.

 

[centsworth_II]

...."facing into a fan" has a far more basic issue - this thing isn't designed to go upwind.

My mistake. I meant to say facing away from a fan.

 

[spork]

....in both cases: treadmill and outside in natural wind. In the reference frame of the cart the moving surface provides the power input to drive the propeller, in both cases.

Outside, it would be legitimate to herald useful energy derived from the moving surface. I'm concerned that energy is being derived from shifting wind acting at an angle.

On the treadmill, I'm not concerned with friction at the wheel/tread contact, but friction between the wheel and vehicle frame. This will cause the wheel to turn more slowly. Some of the missing speed may show up as waste heat, but some may show up as forward motion powered by the tread, not the vehicle.

Imagine two cases:

1. The wheels are locked. The vehicle will be pulled forward due solely to energy provided by the powered tread.
2. The wheels have perfectly frictionless spin. No forward pull is due to energy transferred from the powered tread.

The reality lies between the two cases. The question is, how much of the forward motion on the tread is due to the spinning wheels and how much due to the tread pulling the model forward because the wheels do not have perfectly frictionless spin.

Einstein, Newton, and Galileo tell us that it doesn't matter whether you have moving air over a stationary surface or a moving surface beneath still air. We consider their opinions good enough. Although to be more accurate, they all make it quite clear that there's no such thing as absolute motion or lack thereof.

Placing a model on a flat surface facing [away from] a fan would remove any question of wind angle and friction with powered surfaces. It seems an easy experiment to do. I'd like to see that Youtube video.

I have such a video - and it's already posted on youtube. What would you expect it to show?

 

[Mee_n_Mac]

I think some of the force diagrams show below might help even if they're refering to "normal" sail craft.

http://www.animations.physics.unsw.edu. ... iling.html

Note how in two examples (upwind and downwind) both the boat and apparent wind are greater than the actual wind (over ground) speed.

 

[ThinAirDesigns]

Placing a model on a flat surface facing [away from] a fan would remove any question of wind angle and friction with powered surfaces. It seems an easy experiment to do. I'd like to see that Youtube video.

That is an easy test and I'm happy to do it and video it if you can explain your test a bit better and convince me of it's value.

A: If the vehicle moves towards the fan what does it tell you?

B: If it moves away from the fan what does it tell you?

C: How would you tell if it went faster than the wind the fan was blowing?

JB

 

[centsworth_II]

I have such a video - and it's already posted on youtube. What would you expect it to show?

Ideally it would show a wind velocity gauge showing the speed of the fan-created wind and a time/distance measure of the vehicle's motion from which its speed is calculated. The comparison of those two speeds would be interesting. By the way, a paper would be good, no need for a video.

Has this experiment been done? Could we see the facts and figures?

 

[ThinAirDesigns]

I have such a video - and it's already posted on youtube. What would you expect it to show?

Ideally it would show a wind velocity gauge showing the speed of the fan-created wind and a time/distance measure of the vehicle's motion from which its speed is calculated. The comparison of those two speeds would be interesting. By the way, a paper would be good, no need for a video.

Has this experiment been done? Could we see the facts and figures?

Are you really trying to tell us that you believe that the output of a fan is *less* turbulent and more measurable than the wind outside on a dry lake bed? Have you blown smoke through a fan to see what it does?

The air velocity of a fan also drops off dramatically as a function of distance. It will have drop to 10% of initial velocity in just a short distance.

The output of a fan it a huge, expanding (and thus falling velocity) turbulent cone.

JB

 

[centsworth_II]

How would you tell if it went faster than the wind the fan was blowing?

The critical thing here is the measurements: wind speed and vehicle speed. It is also critical that outside influences like shifting, variable wind and powered treads are removed.

 

[spork]

Ideally it would show a wind velocity gauge showing the speed of the fan-created wind and a time/distance measure of the vehicle's motion from which its speed is calculated. The comparison of those two speeds would be interesting.

Have you seen the detailed build videos I've posted? I'm sure you have access to a fan, the necessary instrumentation, and a video camera. I can hardly wait. I'm sure no one will have any questions or concerns with this final and decisive demonstration.

By the way, a paper would be good, no need for a video.

In other words "sure it works in real life - but can you prove it works in theory?"

Has this experiment been done? Could we see the facts and figures?

You said "put the thing in front of a fan". Yes that has been done and posted. Now you've added a great deal more to that experiment. Let me know when you feel the experiment is truly properly defined.

The critical thing here is the measurements: wind speed and vehicle speed. It is also critical that outside influences like shifting, variable wind and powered treads are removed.

Our only claim relates to RELATVE vehicle speed and wind speed. Our vehicle CLEARLY goes faster than the belt. The very reason for the treadmill test is to eliminate variables. Your fan would introduce far more variables than our treadmill. But I look forward to you performing that test and posting the video nevertheless.

 

[ThinAirDesigns]

How would you tell if it went faster than the wind the fan was blowing?

The critical thing here is the measurements: wind speed and vehicle speed.

Yes, but I ask you *HOW* you propose to measure this "critical" wind speed that is output by a turbulent fan along the length of the vehicles course.

???

JB

 

[centsworth_II]

Are you really trying to tell us that you believe that the output of a fan is *less* turbulent and more measurable than the wind outside on a dry lake bed?

Right. The best setup would be a wind tunnel with the fan pulling air through the tunnel. A relatively cheap one could be made with a plastic viewing port. The speed of the vehicule would be easy to determine from distance traveled/time. The wind in the tunnel should be pretty steady from one end to the other. Variable placement of a wind gauge could test this.

 

[spork]

The best setup would be a wind tunnel with the fan pulling air through the tunnel. A relatively cheap one could be made with a plastic viewing port. The speed of the vehicule would be easy to determine from distance traveled/time. The wind in the tunnel should be pretty steady from one end to the other. Variable placement of a wind gauge could test this.

That will be even better than your fan test. When can we expect to see it?

 

[origin]

The craft is powered by the wind

Yes, by the "true wind" : air movement relative to the ground. By using inaccurate language and ambiguous terms like "wind" you confuse yourself, and fail to see the inconsistency in your argument:

If the craft is going in the direction of the wind faster than the wind then there will be no relative wind for power

Wrong. The cart is not driven by the relative wind on the chassis.

So again just so I don't confuse myself with the wrong termonology lets look at an example:

There is a 10 mph wind blowing due north relative to the ground. Your craft is traveling due north at 45 mph. This results in the craft having a relative wind speed (the air velocity relative to the craft) of 30 mph in the opposite direction of travel. The craft maintains a constant speed because of the power from the 10 mph wind relative to the ground.

Is this correct? And if this is correct, are you serious?

 

[origin]

The best setup would be a wind tunnel with the fan pulling air through the tunnel. A relatively cheap one could be made with a plastic viewing port. The speed of the vehicule would be easy to determine from distance traveled/time. The wind in the tunnel should be pretty steady from one end to the other. Variable placement of a wind gauge could test this.

That will be even better than your fan test. When can we expect to see it?

Centsworth_II is just trying to help you guys prove your case in a scientific manner. Why so snippy, it is almost like you think that any controlled scientific study would show that your craft doesn't work as advertised.

 

[spork]

So again just so I don't confuse myself with the wrong termonology lets look at an example:

There is a 10 mph wind blowing due north relative to the ground. Your craft is traveling due north at 45 mph. This results in the craft having a relative wind speed (the air velocity relative to the craft) of 30 mph in the opposite direction of travel. The craft maintains a constant speed because of the power from the 10 mph wind relative to the ground.

Is this correct?

Yes, this is correct.

And if this is correct, are you serious?

Yes, we're serious.

Centsworth_II is just trying to help you guys prove your case in a scientific manner. Why so snippy, it is almost like you think that any controlled scientific study would show that your craft doesn't work as advertised.

We've grown a bit weary of people explaining that every test or demonstration we've done is faulty, and that if we do their one simple test, that will put the matter to rest. Invariably, their one simple test is always complicated and hopelessly flawed. We've designed and built these things, tested, documented, and even presented build videos so others could do the same. Additionally, I built 10 of the small treadmill carts for the people that were either skeptical or wanted to try it themselves. If anyone actually has a reasonable test, that can be done without enlisting NASA and all its resources, and it actually produces useful data that isn't well covered in our existing tests and demos, I'll try and do that test - and document it. But if people have really great ideas on how to do a test that I see no value in, they're invited to do that test and document it for the world as we have.

Try and keep in mind, you folks were having this debate before I arrived. I am here to share the real-world data and experience we have on the topic. It's not my obligation to spend my time and my life savings settling a debate for you. But I'm happy to tell you what we've learned.

 

[ThinAirDesigns]

Centsworth_II is just trying to help you guys prove your case in a scientific manner.

I'm sure that's what he's *trying* to do, but his presentation of his "fan" test as simple and definitive shows how little he actually understands about "scientific manner". A fan's output is so turbulent and short as to render such a test completely useless.

JB

 

[spork]

A fan's output is so turbulent and short as to render such a test completely useless.

JB

As I mentioned, we've already done the test and posted the results on youtube. That's why I asked him what results he'd expect. That's where the whole thing goes south.

 

[nimbus]

Not gonna read this thread or anything about this contraption after all, if that's the debaters' attitude. Plane on a conveyor belt, politics, religion; inflamed fundie debates, been there done that.

Good luck with everything.

 

[spork]

Not gonna read this thread or anything about this contraption after all...

Thanks for the heads up. It's too bad that you don't approve of our attitude of not being responsible to jump at anyone's request to do and document any ridiculous test.