DDWFTTW - Tests.

[John Freestone]

Mender, I'm glad you picked that up about the cart developing more thrust if it's prevented from moving. I think we've all be putting the same point to ynot in different ways. The bicycle example is good, as is the top speed of a car. I think this is just one of those things: ynot's imagination comes to different conclusions about the different scenarios. It is therefore quite valuable (to the cause) that his mistake, as I am confident it is, is rectified by empirical evidence. I don't believe Michael's cart goes faster than the ruler until he moves the damn thing, and the wheel 'definitely' doesn't rotate the way it 'should'.

I also have to say that I don't know enough about mechanics to be absolutely sure. I could imagine someone demonstrating a new type of kid's toy that, when pushed up to a certain speed and you let go, accelerates from there without any gear changes taking place. I would be dumbfounded, and before it's shown to me, I don't believe it, but there's Michael's cart again...

There is also a tiny bit of a suspicion about whether a prop suddenly accelerated to a certain speed gives the same thrust as one maintained at that speed, or more perhaps due to a sudden build-up of higher pressure air behind it, before that has time to dissipate and a steady flow develop. Again, even if there is something about that in the theory of propellers, I can't imagine that it lasts more than a fraction of a second, and would probably require an immense acceleration from standstill. (It would be a bit like the question of whether a rocket develops more thrust with a solid buffer behind it. They have them on Thunderbirds!)

Anyway, I suggest you don't neglect your building time too much to answer these posts, ynot!

 

[ThinAirDesigns]

Yes, the turntable was spun up by hand and was gradually slowing in the video. I was always fully aware of the consequences of this but I didn't mention it as I wanted to see if anyone would "spot the flaw"

Oh sure -- the old "I'll do the test in an invalid manner, present it as valid and then when busted claim that what I was *really* testing was the audience." Really great credibility you're working on Ynot.

The video and "test" was put together very quickly and probably shouldn't have been called a test.

But it *was* a test and you have clearly said what the test was -- a test of the audiences ability to spot your inability to do a test to any degree of honesty.

What I was wanting to show was that a thing can be made to move in the opposite direction of a moving surface using stored kinetic energy alone, and that it can retain this energy for much longer than most may think.

What you showed, even with your secret cheating, was a device that was always going slower than the moving surface. Ours goes faster.

JB

 

[spork]

Do you think in the test I've outline in my last post that the cart will constantly progress against the turntable?

I know for a fact that it will. It's been shown in so many different ways. And if you manage to fail to show that result - I will perform the experiment correctly.

At the moment there is no compelling reason to perform the experiment since we all know the result. If you fail, then I will feel compelled to set the record straight, and will be happy to do so.

Incidentally, Bauer did exactly the experiment you describe. Why would you expect to get different results from his (aside from being less competent)?

 

[ThinAirDesigns]

I will start by testing with the cart gradually progressing against the turntable but will test at several speeds including whether the cart can sustain a hover.

Contrary to humber's position, this device isn't "balanced". You will never find a speed where sits perfectly still on the treadmill for any length of time. Too many variables in friction, level, voltage, etc.

JB

 

[ThinAirDesigns]

Having a balanced double sided cart helps ensure that the cart is not adversely affected by any lack of perfect leveling of the turntable.

No need to worry about adversely effecting the cart in that manner -- as we've demonstrated, you could tilt the turntable by several degrees and the cart will still happily chug around.

It also allows a test to be conducted where the cart and turntable are started together from scratch with no restriction on the cart and without having the whole thing turning in to a violent bucking bronco.

Why in the world go to all the trouble of a second cart -- ever hear of a counterweight?

JB

 

[ThinAirDesigns]

... will test at several speeds including whether the cart can sustain a hover.

What's this fascination with "hover"?

We have a device that will accelerate from below wind speed to above wind speed repeatedly. We have a device that will maintain a speed greater than the wind indefintely. Any decent turntable testing will show this.

Given the above, how could the device NOT be able to merely match the speed of the wind?

I just don't get your analytical skills.

JB

 

[ThinAirDesigns]

It is not so impressive that a cart with a propeller can hover on a treadmill when a ball can be seen doing almost the same on a turntable (or treadmill).

This one is one of my favorites -- you really should join up with the perpetual motion crowd ... they "almost" can make a magnet motor spin forever.

It would have been fun being around Ynot in the early days of heavier than air flight testing ... "it's not so impressive that a object can actually fly when you consider all the flawed designs that have almost done it."

LOL

JB

 

[Michael C]

ynot, you plan to "Build a balanced, double sided two prop cart". Do you know if this will be more efficient or less efficient than a single prop cart? The working DDWFTTW carts that I have seen so far (Bauer, Goodman, Spork) only had one propeller. Are there complcations with using two propellers? Could an aerodynmics expert give an opinion here?

 

[ThinAirDesigns]

ynot, you plan to "Build a balanced, double sided two prop cart". Do you know if this will be more efficient or less efficient than a single prop cart? The working DDWFTTW carts that I have seen so far (Bauer, Goodman, Spork) only had one propeller. Are there complcations with using two propellers? Could an aerodynmics expert give an opinion here?

As far as I can tell, he's planning on two complete carts on opposite sides of the turntable.

Whether he puts two props on each cart prop shaft may or may not effect the result. We put two props on our shaft at one point (offset by 90d) and the results were not as good. I can imagine that this would depend on the props used however.

His complete lack of understanding of the basic principles involved drives him to make the testing rig unecessarily complicated -- build a very light device (I could build one for a turntable lighter than ours and that's less than 6oz) and turn it loose for a minute or an hour or a day or a week while advancing on the treadmill at a speed that's not rocking the turntable around. -- DONE!

I love the fact that his device worked so well and accelerated to the point that it went so fast against the turntable that it turned the entire thing into a "bucking bronco" and then blew itself apart. His conclusion: 'I suspect it's powered by KE" and so I'll present a intentionally dishonest "almost" faster than the wind marble test to show how "unimpressive" the other test would have been had I done it properly and showed it instead.

Freakin' hilarious.

JB

PS: Know that I love people who build and test -- just remember my comments are in the context of Ynot's constant claims that we either aren't capable of conducting proper testing, or just didn't.

 

[John Freestone]

Could an aerodynmics expert give an opinion here?

Where's that bloody goldfish when you need him?

 

[ThinAirDesigns]

where's that bloody goldfish when you need him?

don't you dare!!!!



jb

 

[Dan O.]

Ynot's contention that holding the cart in place can add momentum to the propeller that will temporarily propel the cart forward when released is correct. BUT ONLY IF holding the cart provides additional downward force that increases the traction between the wheel and the rotating disk. Restraining the cart with a horizontal tether can only impart a horizontal force so will not increase traction.

 

[ThinAirDesigns]

Ynot's contention that holding the cart in place can add momentum to the propeller that will temporarily propel the cart forward when released is correct. BUT ONLY IF holding the cart provides additional downward force that increases the traction between the wheel and the rotating disk. Restraining the cart with a horizontal tether can only impart a horizontal force so will not increase traction.

Yes, and in that case all that would demonstrate is that increasing the friction between surface and wheel (even to the point of rack and pinion) would give the steady state result that the added downward force gave.

Interestingly enough, the way I tell if the wheels we have chosen (we tested with a lot of different wheels) are gripping the surface well enough it to push down on the front of the cart while holding it still. If I can hear the prop whine increase with downward pressure I know that the wheels are slipping on the belt.

We have found that any wheel with soft rubber on the rim (or a wide rubber band application to the rim) eliminates any slipping on our treadmill.

JB

 

[spork]

I love the fact that his device worked so well and accelerated to the point that it went so fast against the turntable that it turned the entire thing into a "bucking bronco" and then blew itself apart. His conclusion: 'I suspect it's powered by KE" and so I'll present a intentionally dishonest "almost" faster than the wind marble test to show how "unimpressive" the other test would have been had I done it properly and showed it instead.

Personally, I've had my doubts from the start that he ever built a prop cart that advanced on his turntable. The more I read, the more trouble I have buying that story. It's a bit like the Roswell incident in that there's no video or stills showing any such thing. The difference being that with the Roswell incident we at least are given some exceptionally poor stills of a small portion of the "wreckage".

 

[Dan O.]

Yes, and in that case all that would demonstrate is that increasing the friction between surface and wheel (even to the point of rack and pinion) would give the steady state result that the added downward force gave.

What if when the cart is placed on the treadmill/rotating disk and forced to make contact with the track, the traction against the wheels is greater than the thrust of the propeller? In this case, when released, the cart could move forward pushing the skidding wheel down the track until the propeller looses enough momentum that it falls back to traveling slower than the wind.

Just because some cart can travel faster than the wind doesn't mean that every cart will.

 

[Dan O.]

Why in the world go to all the trouble of a second cart -- ever hear of a counterweight?

A counter weight would be counter productive because when fully balanced there would be no normal force between the wheels and the track so no traction. You could always compensate by using magnetic wheels and a steel track but everybody would then know it was the power of magnets that was then moving the cart

 

[spork]

What if when the cart is placed on the treadmill/rotating disk and forced to make contact with the track, the traction against the wheels is greater than the thrust of the propeller? In this case, when released, the cart could move forward pushing the skidding wheel down the track until the propeller looses enough momentum that it falls back to traveling slower than the wind.

Just because some cart can travel faster than the wind doesn't mean that every cart will.

True, but this is a mechanical limitation - not a theoretical one. What you describe is clearly possible. That's why we imagine a rack and pinion (un-skiddable) interface. In such a case if the cart surges forward from steady state at wind speed when released, you can be assured it will find an average speed greater than wind speed downwind.

 

[spork]

A counter weight would be counter productive because when fully balanced there would be no normal force between the wheels and the track so no traction.

The counterweight could easily be canilevered from the axis so that it provided the desired counterbalance w.r.t. centripetal force, without reducing the traction of the real cart.

 

[ynot]

"I will ignore any future insults"

 

[ynot]

ynot, you plan to "Build a balanced, double sided two prop cart". Do you know if this will be more efficient or less efficient than a single prop cart? The working DDWFTTW carts that I have seen so far (Bauer, Goodman, Spork) only had one propeller. Are there complcations with using two propellers? Could an aerodynmics expert give an opinion here?

I built and tested a cart with two props on a single shaft. It worked fine.

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