RPM limiter for ROTAX 914

Duplicate post...Discussion on topic can be found here - https://www.rotax-owner.com/en/general-tech-discussion/10566-rpm-limiter-for-rotax-914_1

Ignitech.cz do ignition modules for Rotax engines with very interesting features - like rpm limiter.

Hi Peter

interesting comment.  Under any certification rules that is not allowed.  You are not allowed to have any uncommanded power change in an engine.  This is why for example we can't have a high speed idle setting for warm up as in a car, you must do it with your throttle.  All certified aircraft must fail to a run position, as in the carb springs have to pull the throttle open not closed in a linkage failure.  

RPM limiter works great in a jet boat. In an aircraft the propeller is the high speed governor. 

Cheer

Hi RW

First, not all aircraft are certified. You probably know the number, but certainly a large percentage of Rotax 914 engines are neither certified, nor installed on certified aircraft.

Second, it seems like you are avoiding the problem that arises when a turbocharged engine is used with a fixed pitich (or ground adjustable) prop and how flying at altitude might lead to over-revving the engine.

Is it your opinion that the 914 should only be used with in-flight adjustable props?

Thanks

Hi Ken.  

Fixed pitch with the 914 is always limited.  If you pitch it to hit 5800 for peak power then normally at altitude it will overspeed the engine.  Pitch it for cruise at 5500 WOT you will most likely never see 5800.  Fixed pitch is always a compromise.  There are many experimental aircraft with the 914 who pitch it for 5500, max continuous, and it works great.  Give up that small bit of peak power for a better overall operations, in my opinion. 

The issue with fixed pitch is the fact that you have engine power at altitude and the prop does not have the load from the dense air.  You have to pitch it for the average flights you do.  This would mean you might select a pitch for flying in Florida with your prop that loads it correctly for say up to 6000 ft.  If however you fly in Colorado, or many of the western states, you may well have to repitch a prop as the air density load in most  is not enough, you may need to add pitch.  

In my view it works as long as you are not asking to cover too wide a range of conditions.  Lots of Searey amphibian have the 914 with fixed pitch and it works fine.  Same for a lot of gyroplanes.  In the end it is your pick but running an underloaded prop and limiting its RPM with a rev limiter is not really a good answer as I see it. 

Cheers