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| Mess with your minds: A wind powered craft going faster than a tail wind speed. |
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| IanB:
--- Quote from: thm_w on December 15, 2021, 10:29:33 pm ---Not according to this: https://www.omnicalculator.com/sports/cycling-wattage Its ~10W at 1km/h vs ~300W at 36km/h --- End quote --- That's a nice calculator. A screen grab is attached below. |
| electrodacus:
--- Quote from: bdunham7 on December 15, 2021, 10:02:58 pm --- The relative wind speed produces, as you say, the same force. That force, multiplied by the speed of the bicycle, is the power required. The power required is not the same in each case. --- End quote --- Sorry to say but that is complete nonsense. Not quite sure where do you get this sort of intuition. A bicycle as far as I know without the brakes applied will roll backwards (unless you have some sort of special bicycle that will not allow that). So just sitting still not pedaling you will act like a 0.5m^2 sail (may be less depending on your position on the bike but we will use this round number). A sail of that size in 35km/h = 9.72m/s will provide an equivalent power of 0.5 * 1.2 * 0.5 * 9.72^3 = 275.5W So if you want to drive upwind at 1km/h in a 35km/h headwind you will need to provide 0.5 * 1.2 * 0.5 * 10^3 = 300W Bicycles are fairly efficient so if you ignore the rolling resistance and small frictions between pedals and wheels you need to provide 300W to maintain 1km/h with a constant 35km/h headwind. Have you ever used a bicycle or pedaled upwind ? It is the same principle as driving on an incline. Maybe it is not that windy where you live. How about ever being in a river and trying to move upstreem vs downstreem. Curious if any of you ever left the house :) |
| electrodacus:
--- Quote from: IanB on December 15, 2021, 11:12:59 pm ---That's a nice calculator. A screen grab is attached below. --- End quote --- That calculator does not even have the input data it will need to calculate the correct result as there is no wind direction and no frontal area. |
| thm_w:
--- Quote from: electrodacus on December 15, 2021, 11:28:17 pm ---That calculator does not even have the input data it will need to calculate the correct result as there is no wind direction and no frontal area. --- End quote --- Wind direction is toward the rider (head wind, it says if you hover over the box). Frontal area (Cd*A) is determined by Position of the rider, roughly. Its described on the right hand page. --- Quote ---tops 0.408, hoods 0.324, drops 0.307, aerobars 0.2914 --- End quote --- |
| BrianHG:
--- Quote from: thm_w on December 15, 2021, 10:29:33 pm --- --- Quote from: electrodacus on December 15, 2021, 09:43:52 pm ---You need 300W to cycle at 36km/h with no wind and also 300W to cycle at 1km/h with a 35km/h head wind. --- End quote --- Not according to this: https://www.omnicalculator.com/sports/cycling-wattage Its ~10W at 1km/h vs ~300W at 36km/h --- End quote --- Most of that excess power difference is due to rubber tires on asphalt which is really affected by tire pressure. I know that over-inflated 125psi high pressure narrow racing tires take half the effort compared having the same tires inflated to 80psi. Even worse compared to fat underinflated mountain-bike tires. Like a train, if your bike had metal wheels driving on a flat steel beam, then wind preasure would be more dominating. Also, the wattage in that calculator, it that the human muscle exertion's calorie burn, or torque at the pedals? Yes, the wind is still a major factor as it also pushes on every moving surface. |
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