(You will probably also find that your perforamnce notes are wrong about the getting the minimum SFC at the optimum altitude)
Yes Sir, Thats exactly what they say.. Both in the Perf. Manual and the Powerplant (jet) manual which I have been going through over the last few days with the desire to learn about Jet Performance and fill in the gaps in my overall performance knowledge.
The fact that the Optimum altitude is a compromise like you mentioned makes things much more clear to me since I was pretty sure already that It was a compromise between the engine and the airframe (ie. SFC , TAS : DRAG) and something just did not quite add up from what I was reading in the Manuals.
Thanks to the replies on this thread, I now have a better understanding of the variables involved and hence a clearer view of the big picture as a whole as well.
And if you look at a cutting-edge turbofan like the RB211 (oh well, it's only 40 years old), thrust specific fuel consumption is indeed vastly higher at higher speeds. That doesn't mean that power specific fuel consumption is constant either, it's substantially lower at higher speeds. But we're nowhere near the "ideal jet approximation" of constant TFSC.
So are you saying that TSFC increase with speed because of the increases 'Power Required' to produce the same amount of 'Thrust' ( since Power is the rate of doing word and more power would be required to overcome the same amount of drag at a higher speed ) , and/or the increase in 'Induced Momentum Drag' with speed ?
Thank You...