RPM and choice of propel

In the absence of the experts;

Check out the Rotax Operators Manual, (OM) for your engine:

Go to top of this Forum page;

Select; Suport/Bulletins - Engine Manuals - Current Engines - Engine Type (912ULS) - Document Type OM - (scroll down) - click on Search Database - click on Downloads.

You will find all the information, relevant to your engine operation, in this document.

In general, you should not operate your engine below 5200 rpm, under load ( ie TO & Climb). 

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Hi Mads

Good advice from Sean, get the Rotax data from the manuals.  In general you need to achieve, for fixed pitch, near to your maximum continuous RPM in straight and level flight.  As pointed out in a normal climb at WOT you should try to see peak torque, 5200, from the engine.  

The question then is, was the 4700 RPM from your data static or in climb? If it is a static, ground run, setting the aircraft would have to unload the RPM by its forward airspeed to see what you can get on climb.  The aircraft would need to be a very slippery one and have a fast speed on the climb.  

Cheers

Don't overlook calibrating the tacho. If it's the ordinary Rotax one a 200rpm error is quite feasible in my experience.