h a l f b a k e r yRenovating the wheel
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There's been a flurry of attempts on the hour cycling record recently,
with the latest attempt due later today in the village of London. It's
generally considered to be a very pure measure of endurance riding
since it's an attempt against the clock on a (usually) indoor
velodrome. The only significant
variables are therefore the fitness of
the athlete and the air density. The latter is estimated to be worth
up to a kilometre and so can certainly mean the difference between
success and failure. This idea is simply to base the record on a
"corrected" distance which accounts for differences from standard
atmospheric conditions using a kind of equivalent airspeed. Further
correction may be required to account for the partial pressure of
oxygen and its affect on metabolic rate.
http://xkcd.com/852/
[pertinax, Jun 07 2015]
[link]
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^ We would vote for that. All those irritating lycra-clad nurks lying strewn around in their silly trousers like a swarm of dead flies ... marvellous. |
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Isn't the reduced drag from lower air density offset
by the reduced partial pressure of O2? |
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I did allude to that [MB] in the description, and I don't know
which effect is more powerful. My main motivation for
posting this idea was to get some opinions on this very
point. |
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Obviously the entire velodrome needs to be depressurized,
to perhaps 2.2 pounds per square inch of pure Oxygen (that
converts to about 1kg per 645 sq. mm). It is barely possible
for someone to climb Mt Everest without oxygen assistance;
the partial pressure of oxygen there is about 2 pounds per
square inch. So, add a little more oxygen, and remove all
the rest of the stuff in the air, and THEN do your contest! |
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//I did allude to that [MB]// |
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Ah, so you did - my apologies. |
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Well he got the record (quite emphatically) but fell short of
his own target, citing atmospheric pressure as the main
reason. |
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If you assume that metabolic rate and drag both vary with
air density then the effect of pressure cancels out. So
either the sports scientists are wrong or I'm missing
something important. It occurs to me that the drag
coefficient will reduce as air pressure increases (higher
Reynolds number), but this would have the opposite effect
to that required. I don't get it. |
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[Vernon], I agree with your logic but not your numbers. At
sea level the partial pressure of oxygen is about 3psi. On
the top of Everest it's around 1psi. So 3psi of pure oxygen,
or possibly a bit higher may be optimal. |
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I was going to mention differences in gravity depending on location, but [pertinax] beat me to it. I'm not sure if less gravity is better or worse...? |
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//If you assume that metabolic rate and drag both
vary with air density then the effect of pressure
cancels out.// |
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That statement makes no sense. If you assume that
the effects of metabolic rate and drag are depend
_equally_ and oppositely on air pressure, then it's
true. |
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In any case, the effect on metabolic rate should be
zero or negligible. At typical air pressures (or even
at 50% normal pressure), blood leaving the lungs is
close to 100% saturated with oxygen. Changing air
pressure by even 10% will have no detectable impact
on blood oxygen saturation. However, it would have
a significant impact on air resistance. |
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There should be a team of Sherpas from Nepal.
They would totally kick butt in endurance races. |
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