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Mess with your minds: A wind powered craft going faster than a tail wind speed.
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IanB:

--- Quote from: jeffjmr on September 05, 2021, 12:28:41 am ---Not only do I not believe this vehicle’s speed can exceed the wind speed when aligned downwind, I don’t believe it can equal the wind speed due to frictional losses. Believers will have to explain to me what source of energy can accelerate this vehicle above the wind speed once the speed is equivalent, at which point every molecule of air surrounding and in contact with it has 0 relative velocity, and overcoming frictional losses at the same time!

Set this up with anemometers along the path to confirm the constant wind velocity, evidence of perfect alignment with the wind, a long enough course to eliminate the possible effects of wind gusts, and an unedited, continuous video, and you’ll have my attention. Until then, to me this myth is busted.
--- End quote ---

The key point is that the air surrounding the vehicle may have zero relative velocity, but in the vehicle's frame of reference, the ground beneath the wheels is moving very fast. By coupling the wheels to the propeller, the propeller can produce additional thrust to exceed the wind's velocity.

On a calm day this wouldn't work because frictional drag from the surrounding air would exceed the power generated from the wheels and the vehicle would slow down to a standstill. But when the air has no relative velocity to the vehicle there is no aerodynamic drag to overcome, and the entire thrust from the propeller can accelerate the vehicle.

The wind is still the source of energy, but it is indirectly coupled to the vehicle by various mechanical linkages through the wheels and propeller, rather than by direct action on a sail.

The "zero wind velocity, fast moving ground" is the rationale for the treadmill experiment, as it exactly duplicates this scenario. With the treadmill, it is only necessary for the propeller to generate a forward force large enough to overcome the backward push of the moving belt under the wheels. If it can do that, the vehicle can move forwards. With the right gearing and pitch on the propeller it is possible.
Psi:
I wonder if this might be easier to demonstrate if you replace the air for water.

Water flowing through a pipe is somewhat easier to DIY than a wind tunnel.

And you can also show the flow of water visually using a flow indicator.

The coupling of a propeller to water is also much stronger than to air, so the effect maybe more dramatic and easier to see?

Do you get laminar flow issues in a water pipe? I would imagine it's much easer to do than air?

Obviously need to set it up so the scale model can be stationary like in treadmill demo, so you don't need a huge setup with an impractically long pipe.
However if the people against the idea have issues with frames of reference then they would probably have issues with that too.

I dunno.
IanB:
I think there is not much point demonstrating things with experiments, because if people don't like what the experiment shows they will find reasons to dismiss what they see.
Psi:

--- Quote from: IanB on September 05, 2021, 04:25:30 am ---I think there is not much point demonstrating things with experiments, because if people don't like what the experiment shows they will find reasons to dismiss what they see.

--- End quote ---

Sure, some have definitely made up their mind and wont accept any evidence. but i don't think that describes everyone.
Brumby:

--- Quote from: Labrat101 on September 04, 2021, 06:25:41 pm --- I am sorry and not being rude but you have not got any idea in real world industrial physics
--- End quote ---
Passive-aggressive much?    :-DD


--- Quote ---
  If this had been your own personal project Then you would look at it differently  and in that case I would not have cared .

This a wind tunnel from a car manufacture ..   If they could do this on a Treadmill, That are relatively cheap .
  .   
 NO..  They go too all that trouble in building a wind tunnel that costs $ Millions .

   :scared:  They could have just got a Treadmill from BangUgood  for $200 .
 
        Enjoy the video .

    << Link to totally irrelevant video >>


--- End quote ---

This perfectly illustrates the fact that you have no clue about the actual processes involved.  You should be embarrassed - but I doubt you will.

The principle of the Blackbird can be demonstrated in a wind tunnel, as long as it is properly set up - which is no mean feat.  But it can also be demonstrated on a treadmill with far less effort.  If you have trouble with that, then you have no idea about frames of reference and you should give up now.  All the subtle eddies and other artifacts you throw around like confetti have no significant role in such a demonstration.

Certainly, if you wanted to do a full aerodynamic analysis with the purpose of maximising efficiency, say, then by all means the treadmill will be inappropriate and the wind tunnel is the way to go.  Motor vehicle and aerospace designers are way beyond demonstrating principles which is why they go for the high tech wind tunnel.


But that seems to be a subtlety beyond your comprehension.
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