vibrations

Sean Griffin wrote:

Rami sadeh wrote:

When cruising, this is the recommended RPM according to the manufacturer's instructions

Just a thought;

The manufacturer of the engine is Rotax - if you want the best life & performance from your engine, it behoves you to go by the Rotax recommendations.

Sean,

I’m assuming you are concerned about him flying at 4,400 RPM?  If so, what Rotax recommendation are you referencing? 

Sean,

Difficult to interpret what you posted. Please cite a Rotax technical data source and page(s).  Page 2-2 of the current ( 1 Jan 23) Rotax 912 series Operators manual lists only a minimum RPM of 1,400 for idle, a maximum RPM of 5,800, and a five minute operational time limit for operation between the maximum continuous RPM 5,500 and maximum RPM.  I’m aware of a Rotax SB citing a minimum ground RPM of 5,200 at WOT static to prevent lugging the engine and detonation in flight. Other than that I got nothing.  What Rotax technical document cites a continuous cruise or loiter RPM recommendation or restriction as you posted please?

Sorry Jim,

My reply above seems to have been extensively corrupted.

It is my contention that Rotax series 9 engines are designed to operate efficiently & continuously between 5100-5500 rpm. IE are not doing the engine any favours by conducting TO/Cruise flight significantly below/above this rev range.

Operator Manual,Page 5/5, "Performance Graph" clearly shows that the above rpm range is where the engine should be during cruise.

Also - Listen to the experts;https://www.rotax-owner.com/en/general-tech-discussion/5812-rotax-912uls-cruising-rpm

Thanks Sean. I read the opinions of both experts and amateurs in the link you provided. Unfortunately there is no data, or reference to any data from the engine manufacturer, in that discussion demonstrating the potential engine hazards of cruising at any given RPM range.  The Rotax OM performance graph informs one what power and fuel consumption to expect from the engine at given RPM and atmospheric conditions, including at 4500 and 4000 RPM. How one would interpret that as a message to avoid or adopt a certain power at cruise to prevent long term harm to the engine interests me, can you clarify with specifics?  I would think the OM would contain a note, caution, or warning about this if it were a fact.  Are you thinking the 75% cruise power setting used by most GA aircraft manufacturers in their OM cruise performance charts could be detrimental to engine life if not adhered to? Just trying to separate opinions from fact. Rami sadeh should continue to fly his aircraft per the OM for that aircraft.  Page INTRO-1 in the Rotax OM states “The aircraft manufacturers Operators Manual is therefore definitive in terms of the operation of the engine, as it contains all of the aircraft-specific instructions.”