Tachometer problems

You have not received a response from the experts - so I will do what I can.

I doubt my response will be a of assistance, however you should know, I have never heard of a Rotax installation using propeller speed - it's always engine speed.

I understand this may require a mental shift, for those used to direct drive engines, however as far as I know Rotax engine management recommendation are all in engine speed (rpm).

Could your problem relate to the calibration of your electronic engine management system having difficulty (out of callibration) converting engine speed to propeller speed?😈

First, this is a certified aircraft, it is made to be as near to other conventional aircraft as possible that are for the most part direct drive.  (therefore crankshaft and prop RPM are the same}  All said the numbers are fine to use.  

The Rotax 912S, like the ULS experimental version, uses a signal from a trigger mounted at the flywheel.  The ground is via the bolts to the crankcase and the signal goes to the instrument.  The normal issue with errant signals is the signal wire picks up a high tension wire (spark plug lead) interference.  My suggestion is look at the routing and make sure that that it is not too near the plug leads.  Remember that each spark that occurs causes a field around the plug wire, this can be sensed in some cases and will lead to changes in the reading.  

Actual P leads (power from charge coil to module, the red ones) are not routed near the tach wire normally.  Check your plug to tack wire locations.  See what has changed.  There should be a small plastic sleeve on the tach wire from the trigger to the connector, be sure that is intact and not making contact with your high tension cables. 

Cheers

".......it is made to be as near to other conventional aircraft as possible that are for the most part direct drive"

My completely biased opinion;

What a load of rubbish - If a pilot can not accomodate engine speed, as the appropriate parameter, for management, he/she should not be allowed in the cockpit.

The only reason for prop speed, as an engine management tool, is the predominance of direct drive ie prop/engine rpm the same.

The above statement panders to lazy inflexible thinking - not what you want in pilot, who should be able to accomodate atypical situations.

😈

Even though its unusual, how are you to know what reasons someone may have for wanting to display prop speed. Your unthinking hasty and biased opinion is a load of rubbish; my opinion of course.

Paul,

I could not find wiring examples for connecting the GEA 71 to the Rotax tach coil. I suppose it uses one of the digital inputs. The only example shown is with a three wire transducer driving the tach signal.  

Because far more of these engines are installed in SLSA or ELSA, it’s  more common to see the Garmin GEA-24 or even the GSU-73 for engine function monitoring with the Rotax engine. There are wiring examples in the G3X installation manual for both of these modules connected to the Rotax tach coil. In both cases they require a 300 ohm resistor between the coil input and ground at the module, along with a diode and zener diode in the circuit. This acts as a buffer/regulator to the circuit. I don’t know if this is required for the GEA-71 but I would bet it is. I’m wondering if Tecnam may have overlooked this. You might call Garmin and ask them for a connection diagram and compare it to what you have.