you have to fight the wind too sideways on (say on the curves).. it's not the equivalent of it being 'flat' (if we look at the comparison with hills).
you have to fight the wind too sideways on (say on the curves).. it's not the equivalent of it being 'flat' (if we look at the comparison with hills).
ok, easiest way to explain it.
for demonstrations sake, you are running 12 mph. there is a 10 mph wind. When that wind is coming into your face it will obviously affect you and make u run harder. When that wind is behind u, u will be out running it, you move faster than the wind so it doesn't help you at all (or at least the amount of aid it would provide would be almost non exsistent). as the speed of the wind increases this affect still applies.
zzzzzzzz wrote:
http://sheldonbrown.com/brandt/wind.html
dukerdog wrote:
Actually, I think there is a mistake in the analysis at this link. I don't think a crosswind will result in an increase in drag except to the extent that it increases turbulence.
I was wrong about this. A crosswind will, in fact, increase the resistance you feel when running. However, the resistance will not be proportional to the square of the wind velocity.
Kind of sucks doesn't it? Even with a wind at your side it's harder than running with no wind.
Nice catch. I was getting ready to write a rebuttal until I clicked onto the second page.
There's a current discussion on this on the newsgroup rec.bicycle.tech. If you are really interested in the topic, you can ask questions there. Here's the archived portion of it:
Most of the thread swings angles off into whether or not height matters in air drag, but Jobst Brandt does clear up some questions that someone had about that essay near the bottom of the thread. This is a part hasn't been archived in googlegroups yet:
Rik O'Shea (really?) writes:
>> Seat height is immaterial with respect to wind drag. It's the
>> frontal area that makes the difference. Pro racer Oscar Camenzind
>> (CH) descended bent over the bars with his head near the front tire
>> while his body was as high as ever, believing that, like and
>> ostrich (burying head in the sand), the wind could not see him if
>> he got his head low enough. Low seat hight is likewise not the
>> measure of effective cross section in the wind.
>> Recently being caught taking EPO, we don't see his style anymore.
>> Just the same, the concepts presented in the rider/wind analysis is
>> germane:
>>
http://www.sheldonbrown.com/brandt/wind.html
>> The graphs clearly show how wind direction affects effort.
> Thanks for posting this, it makes interesting reading.
> From the graphs presented it appears that a "tailwind" is not always
> beneficial (compares with no wind). A tailwind is defined by a wind
> angle between 90 and 180 degree and only has a benefit to the rider
> when the wind angle is greater than ~ 101 degrees!
Well not exactly. That also depends on wind speed relative to rider
speed. When riding slowly (where there are almost no wind drag
losses) any wind beyond 90 degrees helps since there are essentially
no other components to total drag, other than that wind.
> A second point related to your comment above is that although
> Camenzind may not have been reducing his frontal area (at least not
> significantly) he is changing his "shape coefficient". The force
> required to overcome wind drag is dependent not just on frontal area
> but the product of frontal area and shape coefficient (generally
> referred to as CdA) - a circular disk and a circular cone may have
> the same frontal area but the cone generates less wind drag due to
> the fact that it's shape facilitates the air stream to move over its
> surface more easily than the circular disk.
I think there is a bit of confusion about wind drag, it being made of
two components, shear and resulting turbulence. Shear is the air
sliding over the surface of the body while turbulence is how much
swirl one causes and leaves behind. Turbulence is the main loss and
it is primarily caused by frontal area... altered by the drag
coefficient (CdA), the multiplying factor for how much that frontal
area affects the turbulence caused by passing.
For bicyclists no manner of tucking-in changes drag coefficient as was
made clear by Milliken's wind tunnel test that showed the bicyclist is
a "bluff body" with respect to winds from any angle. That is why that
curve is shown and compared to the simple cubic equation for drag
power. Camenzind could not affect drag other than reducing his
frontal area... which he didn't. His buttock was higher than it would
have been seated with his chin on his hands on the bar stem.
Chief Broom wrote:
What is the airspeed velocity of an unladen swallow?
It depends. Is it an African or a European swallow?
meichenl wrote:
this is the correct explanation.
when something hits you, the amount it will slow you down depends on its momemtum, p.
momentum is mass * velocity
p = mv
in this case, you are being hit constantly by the wind, so to figure out how much it slows you down, you need to know not total momentum but the rate of momentum, i.e. momentum of the wind per unit time.
p/t = (mv)/t = m/t*v = wind resistance
the mass of wind per unit time that hits you is the density of wind, d, times the wind's velocity
m/t = dv
putting it all together
p/t = m/t*v=d*v*v = d*v^2 = wind resistance
that is why wind resistance goes with velocity squared
(p.s. technically, it should say d*v^2 is proportional to wind resistance, but i can't make the little jesus fish symbol with my keyboard)
... and he goes to Cal Tech, so he'd better be right!