I cannot obtain a rotational speed from the rotor blades of my heli using the 9ZHP WC2 TX without getting dangerously close to the blades. Most of the times I am unable to get a reading at all. I've tried obtaining readings in full sun and in the shade. I've also tried to capture the sun's reflection from the top of the blades when the sun is low. Sometimes one or two numbers will appear momentarily on the RPM display, but quickly dissappear. A steady reading is usually unobtainable without dangerously standing over the heli and pointing the TAC sensor over the top of the blades while the rotational speed of the blades are turning much slower than I care to obtain a reading. Can a rotational speed be obtained at a safe distance while the heli is in a hover? Is the Tachometer a useless feature for helis on the 9ZHP WC2, or am I doing something wrong?

You're not doing anything wrong. The Tachometer function was intended to be used on propellers on airplanes. You need the sensor to be within 12" or so of the prop, and inside the diameter...that means holding the sensor in front of or behind the model to get a reading. It wasn't originally intended for heli use.

Almost any optical tach would have to be fairly close to the rotating object to get a meaninful reading.

PhysicsRider

Miniature Aircraft makes a tachometer specifically for rotor blades... You can check their speed on the ground or in the air while flying... Only thing is you need another person to check the head speed while you fly, or vice versa... Here is a blurb from their site regarding the tach:

0524 - X-Cell Optical Heli Tachometer


Designed by and for R/C Heli enthusiasts to provide the ultimate in safety and accuracy while measuring main rotor speed of any heli at any time, from lift-off to landing, regardless of altitude, air speed or attitude.

Package Contents: 1 each

You can get it for $125 from Ricks RC: www.ronlund.com for more info from the manufacture, visit: http://www.x-cellrchelicopters.com/Store/index.asp

Thanks for the prompt reply. The reason I was trying to use the tachometer on my heli is because the 9ZHP Instruction and Operation Manual states on page 27 that Since the tachometer is a useless feature for heli rotor blades and was designed only for airplanes, the suggestion that it can be used for rotor blades should be removed from the Instruction manual. Nevertheless, I think the 9ZHP is a very versatile TX.