Hi,
The Rotax tacho really cannot be trusted. Many years ago, one of my customers
told
me that when he fitted a CSC-1/P constant speed controller, it showed 600
RPM more than the Rotax tacho! So when the customer thought he was using around
5700 RPM on takeoff he had actually been using 6300 every time. Somewhat ironic
that installing the CS controller actually reduced his takeoff performance
by about 10% (but hopefully prolonged the life of his 912S).
The Rotax tacho has a little pot in it you can twiddle to adjust the displayed
RPM but it's impossible to get at when the thing is in situ. Also, if memory
serves
me right, Rotax decreed that it should be calibrated something like every
50 hours!
Cheers,
Mark
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