Merged DDWFTTW in a “Real” Wind

[I Ratant]

No. That is not what I said. Spork's submission model has the thrust and generator power rising linearly with cart speed.

I said the load presented by the prop will increase as w^3, but power from the generator increases with w. The gearing ties w directly to the speed of the cart. For a constant torque that is the case.

....

.
How about a graph?
windspeed, vehicle speed, prop rpm, wheel rpm?
Don't care to math anything, just look at pichurs.

 

[A.T.]

The wheels drive the prop,

That means only: prop rotates in the direction of the torque from the wheels

so the reaction is at the prop not the wheels.

Sorry that doesn't follow from the above, and is a meaningless statement, because it doesn't say what the action is.

Reaction to the wheels torque is at the prop.
Reaction to the prop torque is at the wheels.

 

[I Ratant]

The wheels provide a reaction to the lift force of the propeller blades, even if the cart goes ddw.


There is a torque on the shaft that reflects that force. When lateral movement becomes rotation, the lateral forces become torques.

.
I got no difference in the run path yesterday with the prop offset right, left or straight.
And the course included a wind direction change which the vehicle followed each time.
No wind today.

 

[I Ratant]

Proving only that it isn't wise to drink and derive.

.
Another winnah!
The videos don't look Photoshopped.

 

[humber]

So the cart can never move. Yet it moves. What have you forgotten?

Your conclusion is false. I have explained that.

 

[humber]

.
Another winnah!
The videos don't look Photoshopped.

They are genuine videos of a sail cart.

 

[humber]

That means only: prop rotates in the direction of the torque from the wheels


Sorry that doesn't follow from the above, and is a meaningless statement, because it doesn't say what the action is.

Reaction to the wheels torque is at the prop.
Reaction to the prop torque is at the wheels.

Sure. You keep making it up as you go along.
Find the text book support.
The force that you once said was not additional but now is, would turn up in measurement, and it doesn't. It is pure fantasy.

 

[humber]

.
How about a graph?
windspeed, vehicle speed, prop rpm, wheel rpm?
Don't care to math anything, just look at pichurs.

Like a turbine, the power at the shaft of a propeller is related to w^3.
A hobbyist used calibrated stick to test engines
http://www.rcgroups.com/forums/showthread.php?t=1077012
The theory and math can be readily found to confirm that the w^3 relationship is correct.

See the Submission report. This toy formula can be derived from it

Thrust = Vcart/Vp*Drag_wheel*n

Simpler to say that the cart is moving at 20m/s (Vcart) the headwind is 5m/s (Vp).
n =overall efficiency.
When in a 15m/s wind the headwind is 5m/s, so the thrust is 20/5 = 4 times the drag ignoring losses. A win! No.

The gears relate the speed of the cart to the wheel's angular velocity,
so V can be written in terms of w.
P_prop ~ w^3
P_wheel ~ w^2

There is more power at the prop than at the wheel. If this idea were to work, then over-unity is a breeze.

 

[A.T.]

The force that you once said was not additional but now is, would turn up in measurement, and it doesn't.

Pure gibberish

 

[Jack by the hedge]

Please explain why you believe
(P_prop ~ w^3 and P_wheel ~ w^2) implies (P_prop > P_wheel)

 

[humber]

Please explain why you believe
(P_prop ~ w^3 and P_wheel ~ w^2) implies (P_prop > P_wheel)

You will need to accept fact as fact, or do your own work.

 

[Llyricist]

I think he his trying to claim that the resistance force from the wheel (beyond rolling resistance) is a function of aerodynamic drag, instead of the torque demand from the propeller.

 

[Jack by the hedge]

You will need to accept fact as fact, or do your own work.

If A is proportional to X² and B is proportional to X³ then you claim B > A in all cases. Is that right?

So A = N*X² and B = M*X³
B/A = X * M/N

B/A = (X*M) / N

and your claim is that B/A > 1 for all M, N and X. Is that right?

Can you see where this is going yet?

 

[CORed]

Doh.
Read again Delta V is the acceleration additional velocity.
That is power applied to the shaft.
Don't take ride in a rickshaw. It's a scam. As you know, they can't work because they don't have an "engine".
ETA: And Drela's man-powered plane. All a fake. Is that right?

You tell me. It was you who asserted that a prop would only work if driven by an engine. As usual, you're doing a pretty good job of refuting yourself.

 

[jadebox]

All vehicles lose KE when braked. It is pedantry to invoke acceleration to include +ve acceleration, when the word "braked" is employed.

Of course, I was being pedantic. It was a deliberate response to someone demanidning that we "show the math" in cases where simple analogies or thought experiments were sufficient to show that he was wrong.

-- Roger

 

[humber]

If A is proportional to X² and B is proportional to X³ then you claim B > A in all cases. Is that right?

So A = N*X² and B = M*X³
B/A = X * M/N

B/A = (X*M) / N

and your claim is that B/A > 1 for all M, N and X. Is that right?

Can you see where this is going yet?

A and B are not independent.
Try
(1) P_prop = T*w^3
(2) P_wheel = T*w
Unless you are claiming over-unity, and the wheel drives the prop, and you insist it does, then P_prop < Pwheel
Allow 100% and equate (1) and (2)

It's a sail cart. That is all it is, and ever was.
Just because that surprises you, does not mean it's wrong. After all, it may be "counter-intuitive.". Not a good way to learn.
Logic and math much better.

 

[Llyricist]

A and B are not independent.
Try
(1) P_prop = T*w^3
(2) P_wheel = T*w
Unless you are claiming over-unity, and the wheel drives the prop, and you insist it does, then P_prop < Pwheel
Allow 100% and equate (1) and (2)

It's a sail cart. That is all it is, and ever was.
Just because that surprises you, does not mean it's wrong. After all, it may be "counter-intuitive.". Not a good way to learn.
Logic and math much better.

Try
P_prop shaft = n * (T*3)*(w/3)³P_wheel = T*w

 

[Jack by the hedge]

Unless you are claiming over-unity, and the wheel drives the prop, and you insist it does, then P_prop < Pwheel

It's a sail cart. That is all it is, and ever was.
<condescention snipped>.

I think you might be getting it, humber. It's a sail cart, which is pushed DDW by the wind, faster than the wind.

 

[zooterkin]

Can you see where this is going yet?

Are you taking bets?

 

[humber]

I think you might be getting it, humber. It's a sail cart, which is pushed DDW by the wind, faster than the wind.

It was. It was pushed to 11mph in a nominal 10mph wind. Check the chart.
And the formula stands.