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loop
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by loop » 28/11/08, 12:47

Hello

I tried to lay the foundations of the problem with a simplified sketch of the operation of this propeller carriage.
Forget all proportion, weight, friction and concrete values ​​to focus only on the forces at play.
Imagine that the wheel and the propeller with 1 blade form only one piece.
The treadmill applies a force Fx to the spinning wheel, and the blade therefore produces a force Fz induced by the rotation.
If we consider that this principle remains valid by orienting the axis of the propeller, and therefore Fz, in the same direction as Fx, this thanks to an angle reference, we must now ask the right question:
Can Fz be greater than Fx.
Against all expectations and after a little personal questioning, my answer is YES.

I will make an analogy with an airplane wing, capable of carrying this one, while the traction of the engine is much less than its weight.
In the example of video n ° 2, the treadmill is the driving element, the propeller is like the wing and its lift.

Image

What do you think ?

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by Christophe » 28/11/08, 12:51

Ben Fx is actually a couple in your case and Fx and Fz should be colelines according to your text.

But according to your drawing they are not, but your logic is ... logic it suits me :) :)

Otherwise pkoi not try to model it with Phun ?

We had already talked about here: https://www.econologie.com/forums/un-jeu-de- ... t5627.html

Has KK1 tested since? Watch the videos, it shows what we can do.

Only question: are there any propeller models on fun?
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Surfeurseb
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by Surfeurseb » 28/11/08, 13:02

jonule wrote:
I quote:
"the wind is in fact a field of energy": it is an explanation can spread, hat.

PS: easy to say all this, so I take part in my turn: for the example of the propeller on the car which arrives at wind speed, well yes it is still possible: it just depends on the weight of the car, its dynamism, and especially the size of the propeller and the size of the car! everything is therefore a question of sizing, looking at the size of the propeller .............


Welcome aboard Jonule!

I should perhaps say: the wind is like an energy field.


Otherwise, I fully agree with the following: everything is a matter of sizing, so that each element is in its optimum efficiency range.

christophe wrote:With this system everything can be explained with classical physics and mechanics, stop dreaming, there is nothing MAGIC !!


This is the purpose of my post. Show that you can get an unexpected result, without flouting the physical and mechanical laws!
Now, it's sure that it's very difficult to explain.

FYI, it seems that it was a thesis subject at Mc DONNEL DOUGLAS in the 80s (no evidence, sorry), with of course a positive result.


For the video where the carpet is tilted:
starting from the observation that the carriage succeeds in advancing faster than the horizontal conveyor, the experimenters therefore tilted the conveyor to the point of equilibrium of the carriage.
They show with this that the efficiency of the system makes it possible to counter an additional contrary effort (they could also have put brakes on the wheels, but that would not have had such a strong visual impact).
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by Christophe » 28/11/08, 13:07

Surfeurseb wrote:Now, it's sure that it's very difficult to explain.


This is not my opinion and we will see if PHUN thinks the same :)

Come on I install it !!
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loop
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by loop » 28/11/08, 13:14

The craft in question cleverly demonstrates that the aerodynamic result of a wing profile (or propeller but it is the same thing) is greater than the effort required to move this profile in the air.
Hats off to the experimenters, it's not easy to make an intuitive representation of it.

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Obelix
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by Obelix » 28/11/08, 13:31

Hello,

It seems to me that you could approach the theory of the Autogyres.
This is only a 90 ° rotated version.


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by jam » 28/11/08, 13:35

Hello,

I see it comes alive here.

Okay, I ask my question again:
In a large gymnasium with no wind:
An initial thrust, as on the video, the propeller starts to rotate, the machine advances, spins the propeller etc.
How far is the machine moving?

And I strongly suggest watching this video carefully:

http://fr.youtube.com/watch?v=xHsXcHoJu ... re=related

We do the history of the gadget.
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by Capt_Maloche » 28/11/08, 20:58

AH yes, this video is much more explicit

especially the passage with the inclined treadmill and the model going up the slope

it deserves a model

who sticks to it?

Going faster than the wind is not a concern, but in the second video presented at the start of this topic, there is hardly any, barely a light breeze

this is where i don't get it
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by bpval » 28/11/08, 21:12

Bonsoir

Good Marcel ... what the hell are you doing
We're waiting for you
PAAAAsCAAL same

and the others ... it's important
FAKE or NOT

That's not a forum like the others
There are opinions that it is important to have

THANK YOU

Hello
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by Olivier22 » 29/11/08, 04:37

Hello
The 2 videos of the 1st post show exactly the same thing in fact. In the first, the carriage moves on the ground at a speed Vs greater than the wind speed Vv.
In the second, Vv is the speed of the treadmill (well yes ... it's a relative speed! Whether it's the wind going forward or the ground going backwards it's the same thing)
and Vs is the speed of the carriage relative to the ground (carpet); here again Vs is greater than Vv so the carriage advances although the belt moves back.

Now, to explain how it is possible that Vs is greater than Vv, the comparison with a sailing boat is very relevant, with an airplane even more (looping hat), but more difficult to visualize!

Good, some diagrams are clearer than any speech (except for the blind - good OK it sucks, but at the same time it is late)



Image
When stationary, the wind perceived by the blade is the real wind. It tends to make it turn in the opposite direction, but the horizontal traction which it applies to it at the same time (and a not too great reduction) means that it is driven willy-nilly by the carriage, in the "right" direction. .


-----------------------------------------
Image
The carriage rolls: the perceived horizontal wind is reduced. In addition, as the speed of the propeller increases, the vertical component increases. The result (in red) therefore tilts.


-----------------------------------------
Image
On the left, the carriage reaches wind speed: the result is equal to the vertical component. The profile always tows under this incidence, with a horizontal force greater than the vertical drag. (That's what happens on the treadmill video!)
This comes from an essential characteristic of thin profiles: they have a (very) fineness greater than 1, which means that their lift is (very) greater than their drag. (up to 60 times higher for a good glider ...)

Right: that's it we have exceeded the wind speed! It therefore has a relative wind component from the front, which further reduces the incidence of the resulting wind on the profile. In addition, the wind induced by the rotation has increased further, so the resulting wind has a high speed (the vertical component also helps to give a little impact to the resultant, which can not do any harm! Lol)
This is where the finesse of the profile comes in: the "thinner" it is (in the aerodynamic sense of the term), the more efficient it will be under low incidence.
Under too low an incidence, the lift (which causes the traction) becomes too weak to compensate for the drag.
(for info, the incidence is the angle between the resulting wind (red) and the blade).
And there is not only the efficiency of the blade itself, but also the friction of the mechanism etc ... You need a machine with a correct output to be able to go faster than the wind!

Now why does the treadmill have to go so fast to get the thing going? And why does the other cart start to work so well from a certain speed?
This is because in the left case of the 2nd image (wind perpendicular to the blade), the lift is not very good. The profile is off the hook. The lift becomes significantly better when the incidence decreases a little (knowing that for these models, this is accompanied in addition to an increase in the resulting wind! That helps)
The lift / incidence curve is commonly called the "polar", we must find examples on google images, we can clearly see which bearings are better than others.
(Little aside: If someone had fun calculating a reduction for a car of this kind, be careful not to interpret the polar of an existing profile directly, because unlike an airplane wing the lift that we want to get here (what traction) is not perpendicular to the relative wind (resulting) ... A polar gives a lift perpendicular to the relative wind. So we would have to make a projection.)


NB: it is the gear ratio that does everything. Here, it should not be too large (otherwise the propeller starts to turn in the opposite direction and the machine backs up, facing the wind). There is a competition for cars moving in this way facing the wind thanks to a greatly multiplied propeller - cars with wind turbines! In this case, the relative wind is added to the real wind so the behavior is similar: increasing resulting wind! But can we go faster than the wind FACE to the wind? Certainly, but I'm not going to try to demonstrate it now (fed up!), Fans! lol 8)

And to talk a little about the sails (still nicer than the propellers!), A basic sport sailing yacht like what they have in a club (Quebec etc), in the air it can reach 3 times the wind speed. ..
But in downwind, it is dragging (sail perpendicular to the wind: stall position, traction is very weak)
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