I'm missing some part of the story about current generation jet engines, that of variable thrust. Since the CFM-56 (in variations) is a common engine and powers many frames from both big producers, I'll use that as my example. CFM's own website lists a range of thrust options for each of its variants on the '56, even some ranges for specific air frames. I get the part about adequate thrust for the weight, some extra for high/hot applications, but I do not understand how this is accomplished. If the engine's thrust range is (random numbers), 27000# to 33000#, is this set in advance? If max available is set at 28000#, is that based on airframe and MTOW numbers or something else. In a crunch, perhaps an engine failure after Vr, can the pilot get a little more?
I well appreciate that running engines at something less than their maximum output can extend their lives and service intervals, but I do not understand why engine providers provide a range of thrust outputs for a given sub-model of an engine. Can someone help me understand this? Does max available power setting affect engine cost per hour, even if the operator chooses to use less than max for most take-off operations?
Put differently, how is engine time paid when airline X uses higher thrust than airline Y - in actual operations? And lastly, if a typical engine is 'set' to run at a higher maximum thrust than its identical twin, on a differenet airplane, is it expected wear faster or need more frequent service? How finely is this detail recorded and how does it affect engine time charges?
I know that is a mouthful. Those who know/understand the finer details will understand my question; others, please just read along and learn..
. And, Thank you!!
