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[Closed] science of (tail) wind speed please

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[#528246]

Help!Was riding my dark side today with a strong tail wind, but struggled to go faster than 26mph on stretch of raod I usually sail along,(all aspects were in my favour ie flat road, fresh/fit legs etc). As it felt like I was riding into a wind I later wondered if I was riding faster than the wind speed and therefore catching it up, thus paradoxicly riding into it? Confused yet? To paraphrase this.... Is it possible to 'ride into a tail wind' and then meet its resistance?


 
Posted : 05/05/2009 10:11 pm
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Wind doesn't always blow in one direction, majority may have been behind you but you're acting against a force (Wind or not).

Where was the wind? all around you at different energy levels.

Even if you were far away or close by, the wind will exist in larger or smaller forces.

Do a physics degree???

Now I know why I chose Biochem....


 
Posted : 05/05/2009 10:15 pm
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I understood that land yachts could actually travel faster than the wind speed for some reason, I may be wrong though 😯


 
Posted : 05/05/2009 10:27 pm
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[takes a deep breath]

you can ride downwind faster than the windspeed, and it will feel like a headwind. you are moving through the body of air, and will feel resistance.

to put some numbers on it... say wind speed of 5mph, cycling speed of 15mph. if you cycle in the opposite direction to the wind it will like a 20mph headwind. if you cycle the other way it will feel like a 10 mph headwind, even though you are cycling downwind. you're overtaking the mass of air by 10 mph, so get some drag from moving through it.

also as far as i'm aware, drag from wind resistance depends on the square of the wind speed, so at 20 you get four times the drag you do at 10. you lose more into a headwind than you gain in the tailwind!

with the land yacht thing, they can go faster than the windspeed, but only across the wind (at least some crosswind component), not directly downwind. when you're going crosswind the windspeed and the groundspeed of the yacht add up (vector additon) to give more airspeed over the sail, hence zooooming crosswind...


 
Posted : 05/05/2009 11:08 pm
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the land yaht thing has another component to it.

as you go faster the apparent wind shitfs towards the front. So say I was riding at 90deg tot he true wind direction, wind speed was 20mph, my speed is 20mph. So the aparent wid angle would be 45deg. But the apparent wind speed is now 28mph, s i can go even faster. Obviously there comes a point where the extra speed shifts the wind farther foreward and it becomes counte productive, so an equilibrium is reached.

Which is why windsurfers/land yahts/cat's nearly always have the sail pulled right the way in, or at least significanlty more so than traditional dingies.

And if you want to see something fast, take a peek at ice yahting, ts positively mental!


 
Posted : 05/05/2009 11:21 pm