italia:
Fred, I read over the thread again and I understand what you're saying. It makes sense that if you bring it back to the same MAP, then the temperature should be the same.
I wouldn't be so quick to back-track. The question is; if you take an MAP at sea level, and then climb to 'x' grand and set the same MAP, will the air density in the manifold be the same as before? It
won’t be unless by chance the inducted air is heated by just the right amount.
The environmental lapse rate is definitely not adiabatic, whilst the process of inducting air is not strictly adiabatic either: they are different processes that exchange energy with their surroundings at a different rate per unit pressure change, are they not? ft decided “the ideal gas law seems to be valid to use for the lapse rate” by using your figures that were
already derived from the standard lapse rate! I thought you'd spotted that little error.
Merely altering the throttle to set the same manifold pressure as before is unlikely to result in the same density as before. To my mind that is a very uncontroversial concept that either someone or something has to account for if our performance data is to be valid.
If we're all on the same page, so far it seems that a reduced back pressure at altitude is the only reason for the increased power or lower MAP required? It seems then that the JAA book is wrong on that matter?
It doesn’t seem that way to me. That JAA book is certainly correct if taken in context. I’ve got the same thing in two different sets of official study material. Variation of exhaust back pressure and change of density in the manifold are both going on at the same time along with variation in throttle losses - the real variation in pumping losses.
I would certainly be hesitant to question credible texts on the basis of various ramblings in this thread.