Premature wear of the gear box, which can generate vibrations, up to breaking point ? To to ensure the longevity of your gear box, carefully check the weigths and the moment of inertia of your propellers.
A too heavy propeller with a too high moment of inertia is really dangereous for the Rotax series 9 gear box . Some variable pitch propellers weight up to 17 kg; in this case, the gear box of the Rotax serie 9 have a lifetime lower than 400 hours. But even a 6 kg propeller might cause problems to the reducer.
The maximum moment of inertia of the Rotax serie 9 is 6.000 kg.cm². It is very important to comply with this moment of inertia. Some information on the MOI : www.e-props.fr/16/geneHEP_A.php
The E-PROPS propellers for ROTAX serie 9 are the world’s lightest, and have their MOI between 1.800 and 4.000 kg.cm², depending on the models.
To go further, an article from Jérémie Buiatti on the propellers inertia (in French) : www.e-props.fr/16/DOCS/Colloques2016BuiattiHELICE.pdf