Humber,
Actually, I have a text called "The symmetry of sailing" by Ross Garrett that does refer to DDWFTTW sailing and does a pretty good job of discussing it. At the time it was written, I don't believe any boats had achieved this.
I have seen that book, and many, including me, see it as being a bit mystical.
Even still, the author does not refer to tacking props, and the boat that was built did not work.
There has been a lot of discussion about math to explain this and the primary objection seems to be a violation of conservation of energy which no one that built the cart claims. All the energy comes from the differential of the air over ground. The real "math" issue boiled down is:
There are countless over-unity cranks who claim the same. Violation of established laws, and claims of PM are unacceptable, so deny that you do.
When the cart is at 0 relative WS, is the propeller producing more thrust than the resistance of the wheels and frictional losses?
If so, the cart will accelerate past 0 WS (relative to the cart not the prop blades). So the only relevant math is: When the cart is at WS (0 relative wind), is the props thrust > or < the wheel/drivetrain resistance + frictional losses. (The cart is at 0 WS in this condition so there are no aero losses to add.) Everything else is an aside and irrelevant.
That is over-simplified and naive arithmetic, Windgrins. If physics were like that, we could all be Professors.
There is quite a lot wrong with that analysis, but where does the power come from? The entire point is that there is no power at WS. In fact, the Carteers agree, when they say balloons can travel to WS, but no further. Lower the drag, and it will go past WS?
The point about I Ratant's friend is that it is easy to confuse the idea of the props relative WS with the carts. The idea is that the prop (with a source of torque) will produce thrust at 0 WS. (otherwise a Cessna couldn't start taxiing).
A Cessna has that source of power. The engine.
This "static thrust" is exactly what BB is using when it obtains WS to accelerate.
Two falsehoods. Static thrust does no work on the prop. Check it out.
Any useful text will tell you that. The definition is a bit vague, because a pure thrust generator is not feasible, so there are work components but they are losses. If the thrust were static, the cart could not accelerate.
Again it is worth noting that there are no regimes from the props point of view once it leaves its initial "stalled condition" on start up. It produces more and more thrust until finally at well above wind speed, the carts aerodynamic and rolling drag equal the props thrust. From there it will no longer accelerate at that WS. (steady state well above WS)
Do you know how much power that prop produces at 15rpm? 3W.
That can be calculated from the "First spin up" video. There is another higher speed "Momentum Test", but I have not yet looked at that.
One can always generate more force. A garden hose can be used to increase the force or speed of the water, by adjustment of the nozzle, but the power remains the same as the input,( it will generally fall, but in simple principle it will not change)
Again, let's see that cool cart of yours on video working as described.
The trial data comes first. I know TAD's tricks, and they will excuse the TM in some way, and still insist that the trial is valid. Both barrels at once, that is why.
