Gearbox ratio 912UL

Thanks to Rob Seaton, whose reply to someone else's question answered mine.

This link provided the answer to my question. Don't know why it took me two days to find that conversation, so I will leave this in case it might help someone else.

https://www.flyrotax.com/engine-configuration-search.html

Thank you again, Rob and others who share what they have learned.

If by any chance you want to get anal about it...
The exact ratio is 50:22 = 2.272727...

The 912ULS ratio is 51:21 = 2.428571...

The EIS (Engine Information System) should display the Engine RPM, not the Propeller RPM.
The gear ratio does not play into the RPM Display.

MAX rpm will be 5800 rpm: Not 5800/2.2727 = 2552 rpm

The way I was trying to verify the tachometer reading was by getting the propeller rpm with a strobe type digital tachometer.  That would require converting the prop rpm to the engine rpm. I think that would mean multiplying the propeller rpm by the reduction ration.

I have yet to get the cheap digital tach to give what I think is a reasonable reading.

I have a 3 blade prop, so I have tried pointing the tach through the prop but that returned a very low reading. I put reflective tape on one prop blade, but that returned a very low reading.

Worked on another issue, but next step is to put reflective tape on all three blades, get reading, divide by 3, multiply by reduction ratio.

I am open to suggestions as to how else to verify the rpm reading on my MGL Stratomaster Velocity EMS.

Hi Bert,

With the risk of telling you what you already know:

When I used a "cheap" optical/laser tacho and got good repeatable readings, I;

First, determined exactly where the tacho had to be placed (on the cowling) to both get a good reading, and read the display.

Taped an exact outline of lasers position, so that I (the fall guy) could be sure of placing it correctly each time.

My Son (who always seems to get the easy job) sat in the cockpit, controlling & recording (we agreed on three target settings)  the engine rpm.

We then did the maths & compared the Dynon rpm display with laser tacho & adjusted accordingly.