What is N1, which is mentioned frequently in documentations? Thnx.

For all intents purposes, it's basically to jets what RPM is to a piston engine. You'll find it as usually the upper most set of engine guages.----------------------------------------------------------------John MorganReal World: KGEG, UND Aerospace Spokane Satillite, Private ASEL 141.2 hrs, 314 landings, 46 inst. apprs.Virtual: MSFS 2004"There is a feeling about an airport that no other piece of ground can have. No matter what the name of the country on whose land it lies, an airport is a place you can see and touch that leads to a reality that can only be thought and felt." - The Bridge Across Forever: A Love Story by Richard Bach

N1 is the rotational velocity, expressed in percent of a design criteria where usually -(at least when design work commences on an engine, sometimes it changes slightly before engine enters production) - 100% is the best efficiency RPM. It really is a direct measure of how much air you have managed to put through the first stage of a jet-engine, where in a high-bypass engine the majority of the air gets ducted outside the core where combustion takes place. You can almost think of the first stage of a modern high bypass engine as a propeller working inside the nacelle. N1 is usually the primary thrust indication for a modern jet engine, and hence the gauges are placed at the "top" of the engine gauges inside the cockpit.Hope that helps. Eivind