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| Mess with your minds: A wind powered craft going faster than a tail wind speed. |
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| electrodacus:
--- Quote from: IanB on December 14, 2021, 11:40:07 pm --- If the vehicle speed is nearly zero the power is nearly zero because Power = Force x (very small number). --- End quote --- You are looking at this from the opposite direction. You just think the vehicle is powered from an internal on (board) energy source and there is no wind. The highest power is available from wind when vehicle speed is lowest relative to the ground. The lowest power available is when vehicle speed is almost the same as wind speed while vehicle travels directly downwind. |
| electrodacus:
--- Quote from: IanB on December 14, 2021, 11:46:06 pm --- --- Quote from: electrodacus on December 14, 2021, 11:44:09 pm ---Not sure if you are familiar with power (it is an electronics forum) but do you find that a 10m/s (22mph) wind pushing on 1m^2 (10.7sqft) sail can be slowed down to 0.001m/s by 60mW ? --- End quote --- Yes! --- End quote --- :) That is a very big Yes for a wrong answer. |
| bdunham7:
--- Quote from: electrodacus on December 14, 2021, 11:44:09 pm ---Not sure if you are familiar with power (it is an electronics forum) but do you find that a 10m/s (22mph) wind pushing on 1m^2 (10.7sqft) sail can be slowed down to 0.001m/s by 60mW ? The mistake you make is using the 0.001m/s instead of (10m/s-0.001m/s) --- End quote --- I'm not sure if you can say you are 'slowing the wind down' to the vehicle speed, but since you said it, lets use that. If I can slow the wind down from 10m/s to ZERO using by dissipating 0 power, why is it so difficult to believe that I can slow it down to 0.001m/s with dissipating 60mW? |
| electrodacus:
--- Quote from: bdunham7 on December 14, 2021, 11:51:25 pm --- --- Quote from: electrodacus on December 14, 2021, 11:44:09 pm ---Not sure if you are familiar with power (it is an electronics forum) but do you find that a 10m/s (22mph) wind pushing on 1m^2 (10.7sqft) sail can be slowed down to 0.001m/s by 60mW ? The mistake you make is using the 0.001m/s instead of (10m/s-0.001m/s) --- End quote --- I'm not sure if you can say you are 'slowing the wind down' to the vehicle speed, but since you said it, lets use that. If I can slow the wind down from 10m/s to ZERO using by dissipating 0 power, why is it so difficult to believe that I can slow it down to 0.001m/s with dissipating 60mW? --- End quote --- You need to use brakes and sufficient large contact with ground to transfer that static force to ground so then ground deals with that. Let's take this in reverse and say you have an onboard battery and electric motor and want to drive upwind at 0.001m/s in to a 10m/s wind with a 1m^2 frontal area and COD (coefficient of drag) of 1. You think you can manage that with 60mW ? (ideal vehicle no friction). |
| bdunham7:
--- Quote from: electrodacus on December 14, 2021, 11:59:27 pm ---You need to use brakes and sufficient large contact with ground to transfer that static force to ground so then ground deals with that. Let's take this in reverse and say you have an onboard battery and electric motor and want to drive upwind at 0.001m/s in to a 10m/s wind with a 1m^2 frontal area and COD (coefficient of drag) of 1. You think you can manage that with 60mW ? (ideal vehicle no friction). --- End quote --- I think perhaps you don't realize that "the ground deals with that" in all of the situations, not just the zero speed one? Yes, if the sail is producing about 60N force, then 60mW will get me upwind at 1mm/s, provided there are no losses. |
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