"Dan" wrote in message
...
RogerN wrote:
"cavelamb" wrote in message
m...
Stu,

Have you seen this one?

http://www.wimp.com/impossiblehelicopter/

There are optical tachs used on R/C heli's that you adjust the speed of a
shutter to make the blades appear still then read the rotor RPM.

RogerN


The military used to use strobe lights on real helicopters to "stop"
rotors. Another neat gag was a large F shaped devise that had a strip of
fabric across the opening. I think it was used to find out who was crazy
enough to approach the tips of spinning main rotors with it.

Dan, U.S. Air Force, retired

I'm wondering if the F shaped device was to detect blade tracking, to see if
one blade was flying higher than the other?

RogerN