Downwind Faster than the Wind - Successful Run by manned cart

Pierrome said:
No, you seem to be saying that it is working as a wind-turbine in the apparent wind. It's not, it's working as a propeller and accelerating the apparent wind.
What you're saying is that the propeller of a plane must be driven by the apparent wind. It's not - its the other way round. The prop is driving the wind resulting in an apparent wind to the whole plane.
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Where do you get your remarkable interpretations from?
In sentence one you say I'm suggesting the prop is acting as a wind turbine...
And in sentence two you introduce airscrews - I never mentioned airscrews! - there is no NEED to mention airscrews!
WHERE did I suggest a plane prop was driven by the wind?

And not that I want to get into it, but a plane prop creates a very REAL wind for the plane but the plane, by spinning the prop, creates an apparent wind for the prop.
 
saltwater_gypsy said:
if you draw a proper parallelogram of vectors....

Come on ...back to school Physics!!
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Parallelogram of vectors.

foil3.jpg


Where's your problem?
 
mikemonty said:
Where do you get your remarkable interpretations from?
In sentence one you say I'm suggesting the prop is acting as a wind turbine...
And in sentence two you introduce airscrews - I never mentioned airscrews! - there is no NEED to mention airscrews!
WHERE did I suggest a plane prop was driven by the wind?

And not that I want to get into it, but a plane prop creates a very REAL wind for the plane but the plane, by spinning the prop, creates an apparent wind for the prop.
Click to expand...

That sounds as if you think that a propeller and an airscrew are different things.
 
Pierrome said:
MM.
Wrong here. The prop blades are not analagous to the sails of the boat.
On the boat, the sails are the collectors of energy.
On the cart, the wheels are the collectors of energy.
You have fallen into the obvious trap that because prop blades look like sails, they must be doing the same job. They're not - its like the difference between a wind-turbine and a propeller - they look the same but they are doing opposite jobs.
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Will you stop with the energy! I think that we have dispensed with energy.

There is a fundamental difference in our opinions that is irreconcilable - it concerns the principle and role of the prop on the cart.

I have given a reasonable and hopefully understandable explanation of my theory and it hinges on a plausible chain of cause and effect and the use of a propellor form suited to aerodynamic lift.

You have given a strange (to me) theory involving large feathery props being driven like a spitfire via energy from the ground and exotic frames of reference.

Occam, as far as I'm concerned doesn't need too sharp a razor here.
 
mikemonty said:
Will you stop with the energy! I think that we have dispensed with energy.

There is a fundamental difference in our opinions that is irreconcilable - it concerns the principle and role of the prop on the cart.

I have given a reasonable and hopefully understandable explanation of my theory and it hinges on a plausible chain of cause and effect and the use of a propellor form suited to aerodynamic lift.

You have given a strange (to me) theory involving large feathery props being driven like a spitfire via energy from the ground and exotic frames of reference.

Occam, as far as I'm concerned doesn't need too sharp a razor here.
Click to expand...

However, interesting as your theory is. It is not the one shared by any others including those who have built and successfully tested the downwind cart.
So we will have to leave it there.
 
Pierrome said:
MM
Why you should think this is a mystery. The prop is obviously pitched (that means the angle of the blades relative to the airflow) so that this is not the case. Also by the time it reaches windspeed it is rotating fast, which also increases the apparent angle of attack of the blades relative to the air.

How does a plane start its takeoff run then? - please answer that.
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Why do you think that I think it is a mystery?

Yes, I know what pitch is.

Where did the plane takeoff thing come from?
In fact the angle of attack will depend on the planes windspeed as well as the props RPM.
How does a plane start its take off? Why in the name of Biggles and Algie are you asking that?

You puzzle me deeply my bizarrely-wired correspondent!
 
mikemonty said:
Why do you think that I think it is a mystery?

Yes, I know what pitch is.

Where did the plane takeoff thing come from?
In fact the angle of attack will depend on the planes windspeed as well as the props RPM.
How does a plane start its take off? Why in the name of Biggles and Algie are you asking that?

You puzzle me deeply my bizarrely-wired correspondent!
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You really shouldn't need this to be explained to you, however I will go through it piece by piece (sigh!)

The cart has a propeller.
The purpose of the propeller is to pull the cart through the air.
The plane has a propeller.
The purpose of the propeller is to pull the plane through the air.

You said that the pitch of the prop on the cart was in "neutral" when the cart was in static air. (I'm still not sure why you think this).

The plane (before it takes off) is also in staticl air.
But it still manages to pull away from rest.

Could it not be possible, that the cart could also pull itself along in the same way?
 
Pierrome said:
You really shouldn't need this to be explained to you, however I will go through it piece by piece (sigh!)

The cart has a propeller.
The purpose of the propeller is to pull the cart through the air.
The plane has a propeller.
The purpose of the propeller is to pull the plane through the air.

You said that the pitch of the prop on the cart was in "neutral" when the cart was in static air. (I'm still not sure why you think this).

The plane (before it takes off) is also in staticl air.
But it still manages to pull away from rest.

Could it not be possible, that the cart could also pull itself along in the same way?
Click to expand...

Yes I KNOW it's difficult for you, but eventually you'll get there.

The purpose of the carts propellor is to drive the wheel (aerodynamic force to torque at the prop spindle to the wheel)

The purpose of the planes propellor is to DRIVE the plane through the air (mainly reaction force)

"You said that the pitch of the prop on the cart was in "neutral" when the cart was in static air. (I'm still not sure why you think this)."
I searched my posts for this statement and can't find it, and I can't see why you think there's a point in there even if i'd said it.

"Could it not be possible, that the cart could also pull itself along in the same way?"
It could NOT be possible because the airplane has a bluddy great internal combustion engine, the cart... does not.
 
We're getting badly bogged down about whether the prop is driving the wheels or the wheels driving the prop.

Think back to the cart under the ruler film. Is the top wheel driving the bottom ot the other way round? The answer is that both are reacting with the surface they are in contact with and the combination is producing the forward motion.

It's a difficult one to get your head round but the prop produces the forward motion which turns the wheels and the turning of the wheels turns the prop. So why isn't it perpetual motion? - because the two media, the road and the air, are moving at different speeds, just like the ruler and the bench.

For those who haven't seen the flim clip, this was the setup

ruler.jpg
 
I know I keep saying no more posts, but......
My little model, as noted, has the centre of the prop blade, by way of the 1:2 propshaft gearing, moving at a spiral angle of 45 degrees to the forward cart motion. Look at the model from sideways on a table top as you push it a short distance; this can be instantly verified visually. Yet my prop blade at this point has a pitch of 32 degrees; I checked with a protractor. So the prop isn't producing any propellor thrust by being driven by the wheels- it's at 13 degrees negative to it's direction of motion, and will be producing reverse thrust if the cart travels in still air! So much for the perpetual motion.
Now, consider what is happening with a yacht/ ice yacht on a broad reach. The vector diagrams will show you that, travelling at 45 degrees to the wind, downwind, at a boat speed of 0.707 of the wind speed, the apparent wind is at 90 degrees to the boat; at a speed of 1.414 times the wind speed, it will be from 45 degrees ahead, with an apparent velocity equal to the wind speed. If you don't get that, how did you pass any RYA exams, and why are you sailing?

So my model, travelling at above wind speed, will have the propellor blade travelling at an angle of 45 degrees to the wind, with the tailwind component giving the blade a healthy apparent headwind, from the front, at 45 degrees to the blade, and at right angles to the cart; the blade, with its pitch angle of 32 degrees, is now at a positive pitch of 13 degrees to the 45 degree apparent headwind, and, presto! we have a forward thrust component. As the blade is at 32 degrees pitch, assuming the lift is at 90 degrees to the blade angle, the lift component is going to be about 58 degrees from the direction of the cart's travel, which is in fact better than the ice yacht's much smaller component. The prop is only fully efficient at one speed; a VP prop would be far better, and the equivalent of sheeting in as your speed builds.
All energy is from the TAILWIND, via the triangle of velocities posted many times above.
Gentlemen, my case rests!

Edited at 22.36, to point out the clanger no-one has yet noticed. If the prop pitch is 32 degrees, this is taken from the plane of rotation. If the lift is at right angles to the blade, the lift component is going to be 32 degees, not 58, from the direction of the cart's motion. Even better!
 
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Pierrome said:
The prop blades are not analogous to the sails of the boat.
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Sails can be used in different ways. When a sail vehicle tacks downwind with a VMG greater than wind-speed, it's sail is behaving exactly like the propeller blades on the DDWFTTW-vehicle. See the last two animations in this post:
http://www.ybw.com/forums/showthread.php?p=2470824&postcount=277

Similarly the sail of a sail vehicle tacking upwind behaves like the turbine blades of a turbine(windmill) cart/boat, which can go directly upwind.
 
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