Constant Speed Propeller

"......can you show me where they state that in writing please?"

".....intrigued by this 5200 limitation...."

Sorry - can't find the Rotax reference, that comes from aged/defective memory. May have come from pervious aircraft POH.

I still believe that 5200 rpm is the Rotax recommended minimum engine speed for climb. Climb = increased load/stress on engine.

In my experince, engines that may be subject to load increases, should be run at an engine speed above max torque.

The 912ULS torque curve is a bit flat (poorly defined) however I would suggest  that, in Auto Cruise,  running the engine at 5200 rpm is at or slightly above, max torque. Running the engine at this speed, will accomodate any unintended /intended gentle climb, without stress on the engine. A higher speed, 5300 - 5500 rpm, would be better but this must be balanced against fuel consumption, etc.

Please remember this is about, me trying to come to an informed decision about the setting for Auto Cruise.

I can go to Manual, at any time, to adjust the pitch, should conditions demand, 

Note: I am not against running the engine at or even below 5000 rpm, should the situaton/conditions allow (pilot judgment).

The underlying reason for avoiding Wide Open Throttle (WOT) below 5200 RPM is to prevent the engine from experiencing "high torque" at low RPM, which can lead to detonation, overheating, or undue stress on engine components.

This information was found in the original version of SL-912-016 & SL-912-014, titled Essential Information Regarding Engine Behavior, Performance, and Manifold Pressure Data for Rotax Engine Type 912 and 914 (Series), issued on July 28th, 2009. (See attachment) 

(Out of date / Do not reference): https://legacy.rotaxowner.com/si_tb_info/serviceletter/sl-912-016.pdf

However!!

Revision 2 of SL-912-016 was released on December 4th, 2020, and supersedes the previous version. It includes much more information related to manifold pressure and operating performance, but no longer mentions the warning about WOT below 5200 RPM.

Search for SL-912-016 here: https://www.rotax-owner.com/en/support-topmenu/engine-manuals#current-engines

The reason the WOT limitation below 5200 RPM has been so frequently quoted is because it was hammered into iRMT instructors, iRMT mechanics, operators, and OEMs as something to avoid to prevent engine damage.

With that said!....This also shows the importance of receiving updated iRMT training and always referring to the most current information in the latest revisions of Rotax manuals and documents.

(Lost the lot AGAIN!)

Hi RO,

Thanks for all that.

Just as I thought I was narrowing down the optimum Auto Cruise setting to 5200 rpm, it seems Rotax is no longer using the engined torque performance as a guide to best operating speed(s).

Questions:

Why does Rotax not refer to the engines torque performance/curve when advising engine speed for load (climb) ?

What would you recomend as the optimum (combination of fuel consumption/minimal engine stress/ prop efficiency) engine speed?

Does the removal of the 5200 rpm advice, give the green light to loading the engine below 5200 rpm?

Sean

The MAP reading is the indication of loading.  You have to read the manifold pressure.  as shown for constant speed setting.

Cheers

(Lost my first attempt)

Thanks  RW,

Dont think you have addressed my questions

"Why does Rotax not refer to the engines torque performance/curve when advising engine speed for load (climb) ?

What would you recomend as the optimum (combination of fuel consumption/minimal engine stress/ prop efficiency) engine speed?

Does the removal of the 5200 rpm advice, give the green light to loading the engine below 5200 rpm?"