[FoRK] dQ/dt

Dave Long dave.long at bluewin.ch
Tue Mar 16 08:21:37 PDT 2010


>> (horses can move 1'800L/min of air when working at 6,5kW.  What's  
>> the equivalent for human heat exchange?)
>
> [3] doesn't have running in their metabolic table.  It would range  
> up to and past their highest sport: tennis at 8.7 "met".  A met ==  
> 58.2 W/m^2.  A human male has a surface area of about 1.8m^2 [4].
> So a human can produce at least 9*58.2*1.8 = 942.84 ~= 1KW of heat  
> and can bleed it off at 0.10 KW or handle 0.15 KW for a short time.
> [3] http://personal.cityu.edu.hk/~bsapplec/heat.htm

I believe if you line up the entries in that table that 8.7 "met" was  
for wrestling, not tennis, so it's probably fairly close to max  
generation.

Note that the 6,5 kW above is output, no doubt metabolic power is  
much higher.  (although the indication I get from most papers is that  
horses are surprisingly efficient runners, for wetware)

Looking for human output, the Gossamer Albatross apparently flew for  
3 hours at 300W minimum, and Da Vinci III is designed for optimal  
efficiency at 400W.

Cycle track sprinters apparently hit around 1'800 W, but that's only  
over 200m.  It seems over much longer distances average power output  
in the final sprint for human bikers is on the order of 1kW.
cf. http://www.wisil.recumbents.com/wisil/MartinDocs/Sprint%20cycling% 
20performance%20review.pdf

What would be ideal would be comparable events in the several minute  
range.  Or maybe power output over marathons vs. endurance horses?   
Or scale Quarter Horse races (which yield 70kph over 20 seconds  
instead of 60kph over 120), but how?  with a cubic term?

(aside)
A story I've heard is that someone originally bet one of the Tevis'  
that he couldn't ride across California in a day.  But by using a  
relay of polo ponies (much like the ancient persians) he made it from  
Tahoe to the track in San Francisco with time to spare...  Much later  
the Tevis Cup was started, on similar lines but with much different  
rules.
(end of aside)

> Most numbers published are for average people, not trained athletic  
> ones.  Few doctors care about those, since they don't give as much  
> business perhaps.

Heh.  For horses it's the opposite; most numbers published are for  
racers.  Probably for the same reasons.

-Dave



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