In article , Richard J Kinch wrote:
Doug Miller writes:

Reminds me of a friend who thought we would fly on bicycles some day,
it was just a matter of improving the mechanical efficiency. That he
couldn't run up a few flights of stairs without being exhausted
didn't seem to be a problem.

There *have* been a few flights of such aircraft already, you know.

Lean athletes in an agony of exertion pedaled around a track in a fragile
contraption. I suppose you too believe this will be perfected into a
flying bicycle for grandma someday?

Not likely, I admit -- but such machines *do* exist, and it's perhaps a bit
presumptive to suppose that we've already explored and exploited the limits of
such technology. It's still less than a century since heavier-than-air flight
was "known" to be impossible. :-)