Hi Bret

On Nov 4, 11:04 am, Bret Cahill wrote:
Have they tried dimples on radio controlled aircraft? The size and
speed could designed around the magic Reynolds number = 100,000 where
the coefficient of drag drops precipitously.

Dimpling could vastly extent the range of large and slow as well as
small and fast radio controlled aircraft.

A competitive cyclist is the right size and speed for Nre = 100,000 so
dimple suits can work. Same for golf balls.

Nre = 100,000 for widebodies going 0.5 knots so dimples won't work
except on the runway.

From fluid mechanics the Reynolds number is the ratio of inertial
forces/viscous forces.

N re = Diameter X velocity X density of fluid/viscosity of fluid.

Bret Cahill

I design/build model gliders as a hobby, (not an expert :-).
The dimples on golf balls are primarily to operate aero-
dynamically when spinning, like baseball seams,
http://en.wikipedia.org/wiki/Baseball_(ball)
As Mr Brought posted so well, they react with turbulent flow.

I think the Reynolds number is actually a quantum effect
because air is particles, so flying insect wing design is
quite different from an average birds, due to scaling.

I should mention some mysteries, such as the roughness
of shark skin and the unusual nature of feathers that are
rough at a smaller size, that have quite different Reynolds,
that seem to contribute to improved gliding performance,
thus supporting your suggestion.

Interesting subject.
Ken