On Fri, 09 Oct 2009 20:31:39 -0500, cavelamb
wrote:

RogerN wrote:
"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



That's right.
The blades have a small tab sticking out the ends which get marked up heavily
with two different colored grease pencils.
Those tabs had a hole to hook your tiedown strap. Tail rotor was a
bit different. A grease pencil taped to a broom handle.