Thanks guys. I think my brain is getting around this. Are the following statements all correct???:
1) Using the 777, GE90 as an example, the (vague memory), the 112000 lbs of thrust it claims would be produced, at ISA condition, and ISA only. By the time you reach the cruise, the thrust ACTUALLy being produced had decreased GREATLY.
2) Just because you have a high EPR and N1 setting at FL350, it doesn't mean you are producing the same thrust at great height as you are at FL110 with the same EPR and N1 setting. You will in fact be producing LESS thrust with same setting.
3) Due to the lower ambient air pressure at height, there is less resistance to the engine exhaust which allows greater exhaust velocity and therefore energy and efficiency. (Action and reaction - Greater action?)
4) A turbine will automatically, at height,:confused confused turn at higher RPM at a given fuel input level and attain the same compression pressure.
5)Are there any turbine engines where you MANUALLY decrease the mixture at height? If so, what are you monitoring to get the correct mixture?
6) Does the lower air temperature result in greater expansion from the compressor through to the turbines, and onward, allowing for greater energy to be converted into efflux AND fan rotation via the spool?