I'm interested in producing human powered vehicles. I copied below a
proposed method for generating 1800 watts of human generated power for
a period of say 1 minute. Some references suggest you might only be
able to get up to say 1,000 watts for over a minute. They say
cyclists might be able to get up to 2,000 watts but only for short
bursts. But I need this over a minute or so for my purposes.
Have their been weightlifting instances where the lifter uses both
the upper and lower body and is able to get high reps at a total
lifted weight of over 3 times their body weight?
Also, I might need the power generation to be continuous in both the
positive and negative directions. Then could a lifter pull back with
as much force when reversing a leg press as when he extended his legs?
And could he pull back with his arms when reversing a bench press with
as much force as when he extended his arms?
Bob Clark
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Newsgroups: sci.astro, sci.physics, sci.space.policy, sci.engr.mech
From: Robert Clark <rgregorycl...@yahoo.com>
Date: Tue, 13 Nov 2007 13:42:05 -0800
Local: Tues, Nov 13 2007 4:42 pm
Subject: Re: Proposal for hovering flight.
On Nov 11, 2:36 pm, "CWatters" <colin.watt...@turnersoak.plus.com>
wrote:
> news:1194789882.042070.83670@o3g2000hsb.googlegrou ps.com...
> It's interesting to take a look at how man powered flight has been
> achieved - bear in mind that racing cyclists can only put out about a third
> of a horsepower continuously...
> http://en.wikipedia.org/wiki/Man-powered_flight
> I believe the prize for a man powered helicopter is still unclaimed although
> some have managed to get off the ground on less than one horsepower!>http://www.humanpoweredhelicopters.org
....
Thanks for those links on human powered flight. I found this link
that suggested top cyclists could generate 500 watts continuously and
900 watts peak (though perhaps with some chemical augmentation ;-) )
Olympic Human Powered Flight
Human Powered Flight Undergoes Renaissance With Olympic Competition.
"//humans can produce about 100 watts continuously, with peaks of 400
watts or more// That may be so on average, but for a trained cyclist
those stats are quite low. I'm at 300 watts continuous / over 900
peak
with moderate training. Lance Armstrong somehow manages 500
continuous. It's probably safe to say Olympic cyclists can maintain
at
least 400 watts."
http://www.halfbakery.com/idea/Olymp...wered_20Flight
The prize discussed on the human powered helicopters site only
requires that the craft hover at 3 meters under human power only for
one minute.
A fit male probably could do leg presses of twice his body weight
for
several reps and bench presses of his weight for several reps. These
would only have to be done for 60 seconds.
To see these are reasonable capabilities note that in climbing
stairs
we're actually supporting our weight most of the time on one leg.
We're using both legs only for the short time when we're switching
from one leg to the other. So just climbing stairs we're doing the
equivalent of supporting twice our body weight. A normal fit person
climbing stairs certainly could go up one stair in one second, with
the stairs being about 8 inches, 20 centimeters high. Then a good
athlete could do the equivalent of 100 centimeters, one meter, per
second up the stairs if only for one minute.
For the bench press, a normal fit male could do several reps of
push-
ups, which is supporting your weight with your arm and chest muscles,
once each second. The distance would be about 2 feet. Then a good
athlete should be able to raise his weight in a bench press 1 meter
once per second for several reps for a minute.
Note for both of these I'm assuming that both the positive and
negative directions count as a single repetition, not a full cycle,
as
in normal exercising. This corresponds to how this would be useful
for our scenario since both the positive and negative directions
could
be used for driving the craft.
However, there is a question of whether both the upper and lower
body
could be used at this intensity at the same time. I think for the top
athletes this could be possible at least for one minute. Then we may
suppose a top athlete raising and lowering 3 times his weight 1 meter
once per second, that is, a full up-down cycle taking 2 seconds, for
60 seconds.
For a small 60 kg athlete, this would be 180 kg raised 1 meter per
second or 1800 N over 1 m per second, or 1800 watts. For the weight
of the person of 60 kg, this is a weight to power ratio of 33 to 1. I
will assume that the canopies and the shell holding the craft can be
made quite light, and will take simply the total weight to be 60 kg.
Remember now that the weight to power ratio is 100/v. So v is 3 m/s,
for the speed at which the canopies are brought down. Then plug this
into the equation for the drag produced to see how large the canopy
has to be raised 60 kg. We need to produce 600 N of force. This
requires a canopy diameter of about 6.6 meters.
Bob Clark
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Maximum power output for a human for short periods? 
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