New video on the subject...
I think caution needs to be applied when invoking Bernoulli as an explanation of lift, primarily because this is not a closed system (in the way that fluid flow in pipe is more of a closed system).I would have left a Bernoulli comment on it, but about a million people beat me to it!
I rejected their cute illustration of two sailboats on a cylindrical world as a propellor because sailboats on a broad reach still have an apparent windspeed.
The other factor is that their propellor isn't affected by the force of the wind as a sail is. The propellor is turned by the wheels and pushes back against the wind. So, that whole analogy made no sense to me.
See post #20 for my mental evolution regarding the cart mechanics.The propeller blades of this cart also have apparent wind
Nice set of Newtonian-style vector drawings!...I rejected their cute illustration of two sailboats on a cylindrical world as a propellor because sailboats on a broad reach still have an apparent windspeed....
Yes, but the apparent wind is never zero at the propeller blades, just like it is never zero at the sail going diagonally to the wind.When the apparent wind is zero, the force is zero.
For example, a free-spinning wind turbine mounted on a truck will not spin when the truck speed is moving at the same speed as the wind.
Yup, came to peace with it in #20 after a whole lot of headbanging. The free-spinning analogy refers to the cylindrical world metaphor and why it's misleading/incorrect.But this is not a free-spinning wind turbine. It is propeller that is coupled to the wheels.
The free-spinning analogy refers to the cylindrical world metaphor and why it's misleading/incorrect.
When headed directly downwind (which is the only time you can get a zero apparent wind) the only function of the keel is drag as there are no lateral forces. In fact, sailors typically pull the daggerboard up when "running" (a downwind point of sail) to eliminate it.the role of the boat's keel which is key here. The keel drives the boat across the wind, just like the wheel drive the propeller blades across the wind.
Correct, but in their analogy the boat is not moving directly downwind, but diagonally downwind. This is equivalent to the motion of the propeller blade, which also has a velocity component perpendicular to the wind.When headed directly downwind (which is the only time you can get a zero apparent wind) the only function of the keel is drag as there are no lateral forces.
Yup, one more reason to discount it since the apparent windspeed > 0. As you can see from #20, I'm not arguing the land vehicle can't go faster than the wind downwind, or how propellors work... just that metaphor breaks down when apparent windspeed = 0. At least I don't see how it supports their case for DDWFTTW.... the boat is not moving directly downwind, but diagonally downwind...
The same is true for the propeller blades of the DDWFTTW cart, so I don't see the reason to discount it. Again, the analogy is not between the boat and the cart. It is between the sail and the propeller blade.Yup, one more reason to discount it since the apparent windspeed > 0.
It demonstrates that DDWFTTW can be achieved if you allow for moving parts, For example like this:At least I don't see how it supports their case for DDWFTTW.
I don't really question DDWFTTW since the explanation in post #20....It demonstrates that DDWFTTW can be achieved...
Look the vector diagrams in post #25. It's the same aerodynamics.what do you think the boat on the cylindrical world is demonstrating in regards to DDWFTTW?
We're still not talking the same thing, that's okay. I believe there are no aerodynamics when the apparent wind speed is 0 which I think you agree with.Look the vector diagrams in post #25. It's the same aerodynamics.
The bit with the size of the sail could be confusing as once you go faster than wind-speed, in parallel to the wind, bigger would be more drag. Also, no sail on the vehicle which might also confuse some. But it sounds like you have it, if not 100% sure see post #20.A high level conceptional overview.
Yes, but it's irrelevant. The apparent wind at the propeller blades can never be zero with this setupI believe there are no aerodynamics when the apparent wind speed is 0 which I think you agree with.
The propeller blades are the analogue to the sail.Also, no sail on the vehicle which might also confuse some.