I would argue that a bird that needs a running start to get launched is
not equivalent to, say, a Boeing 747 that needs a runway to get launched.
The question is not whether the flying thingie or beastie needs to gather
momentum before flight. The question is whether it needs an artificial
aid to gather that momentum, and I think that a long, paved runway is not
much different from a catapult in this sense. A swan might need a
running start but it does not need a *runway.* There are airplanes that
don't require long, paved runways, of course--but most commercial jets do.
As for the wide variety of flying thingies that now exist, and
which owe their existence to things learned after the first
airplanes, I think that how we classify them is largely arbitrary,
depending mainly on how specific we want to be. A hang glider with an
engine is a lot like an ultralight, and I can imagine an ultralight
qualifying as an airplane for the purposes of the crowds in 1906, say, but
in 1906 they probably could never have built an engine small, light, and
powerful enough to serve the purpose. They might not have had the
light-but-strong composite & synthetic materials needed for the frame and
wings, either.
Marvin Long
Austin, Texas
