As I’m working on the P&WC; PT6 engine, a somewhat advanced feature that is
missing is the propeller overspeed governor. In simple terms, it is a second,
fallback governor that kicks in if the primary governor fails and allows you
to still run the propeller. This link explains the basics about overspeed
governors: <https://www.aviationpros.com/engines-
components/article/10388997/propeller-control-for-turboprop-engines> And this
is from a propeller manufacturer, MT: <https://www.mt-
propeller.com/en/entw/pro_gov.htm> The overspeed governor comes with a “test”
pushbutton that runs the OS Governor at a specific RPM (94% in our aircraft)
to make sure everything is working well. It is done before the first flight of
the day. So to sum it up:
- OSG is a fallback system to the basic governor
- It might require its own set of PID controllers
- Assuming oil pressure remains the same, it will work based on the following basic properties
- The base governor should be able to somehow fail or turned off for the OSG to work (i.e. test mode)
- A test would need to achieve a given overspeed_governor_test_rpm value
- In normal operation, the Overspeed governor will allow you to run the engine at a higher than normal value, overspeed_governor_max_rpm
- The gearbox ratio will be the same as before, you are just allowed to go to higher Ng % with this.
- The max N1 would have to either be increased in the engines.cfg file, or a new property should be introduced for the overspeed state limit, i.e. max_n1_overspeed. That property, if blank, could default to the max N1 value that’s present anyway