Quote:
Originally Posted by some_other_dave
But we're not talking about sailing with the wind. And the propeller blades are not turning with the wind--when they turn, they are meeting it at an angle!
-soD
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1) according to Newtonian physics, the wind from behind is supplying an 'impulse' of the force (F), over a period of time. (F delta-t)
2) F delta-t = ( delta- momentum ) [ delta-p ]
3) Momentum (p) = mass-times-velocity, or p= mv
4) impulse of the force (F) = delta-p/ delta-t
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* the vehicle, with wind from behind, is a crude square-rigger.
* it's aerodynamic drag creates enough force to accelerate the vehicle, from rest V=zero, to some terminal velocity V2.
* while the vehicle is accelerating, it is building momentum as it's mass is being accelerated.
* under the force of the wind, the vehicle's wheel is transmitting power from the road/tire interface, through the wheel bearings, to the differential, to the lower sprocket, to the chain, to the upper sprocket, through the pillow block bearings, to the shaft, to the propeller, to the air, creating a counter-impulse.
* there's a specific, fixed amount of kinetic energy contained in the wind.
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* If we presumed that the vehicle was a 'perfect' sail, and could extract all the available energy from the wind, we would still be losing energy at the tire/ ground interface/ within the tires themselves/ within the wheel bearings, within the differential gears/ at the lower sprocket-to-chain interface/ within every link pivot within the chain/ within the upper chain-to-sprocket interface/ within the two pillow-block bearings-to-jackshaft interface/ and finally at the propeller-to-air interface.
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* Whatever amount of energy is delivered to the vehicle, that amount, less all the powertrain losses, is what is available at the propeller-to-atmosphere coupling.
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a) when the vehicle reaches the air speed, there is no delta-v
b) acceleration is now zero, v= constant, momentum = constant
c) whatever net-momentum exists in the vehicle, it must have a lower amount of net energy than that the surrounding airstream due to aerodynamic slippage, and rolling resistance on dirt ( very high! )
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d) in order for the propeller to push the vehicle beyond the local air velocity, would require zero aerodynamic slippage, zero rolling resistance, zero powertrain losses, and a propeller wing section exhibiting a lift-to-drag ratio at over-unity, since it's being supplied less energy than is available from it's surroundings.
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* All wing sections have a zero-lift angle of attack
* As soon as a wing begins to produce lift, it's also producing drag ( another drain on available energy )
* At maximum lift, all airfoils are producing maximum drag
* All thrusting airfoil sections are 'angled', so, an
'angled' propeller blade cannot be some new, unique quality of Rick Cavallero's system, not seen in other aerodynamic systems.
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Somehow, the phenomenon of the backward's oriented tattle-tale, has convinced observers of a reality which cannot exist in our universe.