RE: Rotor RPM Problems
There are two ways you can tach a heli with a plane tach.
One is to mount the tach on the heli tailboom (rubberbands, tape etc) and have somebody else use binoculars to read the rpm.
Two is to mount the tach on a wooden stake and hover the helicopter over it. The other guy again uses binocs.
There are two popular models of heli tachs. The Model Avionics unit (see above) and the MinAir unit. Both work the same, the MinAir costs a little more. As with a plane tach, somebody else has to read the rpm while you fly.
Fritz