wrote in message
...
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

We competitive cyclists use dimples already on our disk wheels. And some
skinsuits incorporate them. But they don't look like the dimples on a golf
ball. They are shaped differently and they are shallow.

Check out Zipp disk wheel dimples
hehttp://www.zipp.com/wheels/detail.php?ID=33

Over a 40K ITT this rear wheel can give you a 30-40 second advantage over
smooth disk wheels.

\ A model plane about the size of a cyclist would benefit most from
\ dimples if it only went cycling speeds, 20 - 25 knots.
\
\ Smaller aircraft would need to be designed to go faster inverse with
\ size.
\
\ A golf ball sized aircraft would have to go 200 mph for dimples to
\ work.

I wonder if anybody has thought of putting the appropriate dimples on the
surface of propellers? Seems like reducing drag there would increase RPM and
reduce HP required.

A bicycle wheel spins much faster than 20-25 knots apparent to the air it
interfaces with. At 30 knots, for example, the surface of the wheel might be
moving closer to 100 knots apparent to the wind.

--
Gregory Hall