wings and sails have a lot in common: what we learn from one type of foil can be
useful in understanding the others
in animals, structures concerned with flight make considerable use of resilience
and elasticity to improve efficiency of energy use
the wings of insects (especially the larger ones) and the sails we make have a
lot in common: the aerodynamics of both are influenced by passive adaptations of the
structural framework to external energy sources
the wings of bats and birds have a wider range of effective geometry due to
active (muscle-powered) adaptations within the wings - this approach is to some extent
implemented in aircraft with mechanisms such as ailerons, elevators, rudders, flaps, and
spoilers
although we do not yet fully understand flapping flight, there are certain key
things that can be said about cruising powered flight:
the downstroke must be powered
the upstroke can be achieved by lifting forces alone, and can even be a source of
energy that can be stored for use on the downstroke
there is a parallel between the stability-providing geometry of the hang-glider
and the geometry of some birds' wings: both can be envisaged as conforming to conical
surfaces
the more adaptive foils can be, whilst remaining under control, the greater the
range of activity and efficiency they have
Examples are given of adaptive sailing rigs - the Transition rig
- and adaptive sails for a proposed windmill.
"Now, if I just change this..."
Between the idea
And the reality
Between the motion
And the act
Falls the shadow.
