Rotax 912 Reduction ratios - 2.27:1 / 2.43:1

[Xavier]

I was having a chat with an instructor/owner of a Tecnam P92 with a 912UL, about RPM settings and while reading our respective 912 manuals / POH we found out that we have a different Reduction Ratio.

 

On the Savannah I have the option 2.43:1 (Same like the 912ULS) and the Tecnam has the 2.27:1 standard reduction ratio.

 

What difference this made to the engine ?

 

Does this has an impact on the propeller to select for the aircraft (type, pitch, ...) ?

 

Does this change the way the engine is tuned ?

 

Thanks for sharing your knowledge.

 

Cheers,

 

Xavier

 

 

[Downunder]

Very interesting question.....

 

Off the top of my head, I'm thinking one would be pitched slightly differently but ultimately give similar performance.

 

 

[Nobody]

In makes no difference to the engine but will change the propellor selection.

 

For the same power setting on the engine the 2.43 gearbox will have a slower propellor speed than the 2.27 gearbox but a higher torque. In general you would want a longer propellor blade on the one that turns slower.