Quote:
Originally Posted by bongodriver
I'd hate to dissapoint so here goes.
No it is a function of density altitude, a supercharger produces an excess of pressure which it can only maintain until it reaches a certain level of air density due to volumetric efficiency,atmospheric density is very much affected by temperature and atmospheric pressure is not, if conditions were ISA exactly then density altitude would equal pressure altitude, inevitably temparature varies and whenever things are on the hot side performance is reduced and vice versa, so it stands to reason performance is dependent on density, you only have to look at aircraft performance charts to see this is true, jet engines have the same problem, after all a supercharger is just a centrifugal compressor just like you find on some jets.
|
I'm glad to be corrected on this, preferably in layman's terms without underlined scans
My thinking is that supercharger keeps constant pressure up to the FTH and the mass flow through the engine and power is at maximum at FTH. Below FTH intake air is warmer and hence density at the intake manifolds is lower at given pressure and mass flow and power lower than at FTH, above FTH supercharger can't keep the pressure which reduce mass flow and power.
Let's assume that pressure altitude is keeped constant but temperature is higher. Then the mass flow through engine is reduced due to lower density and less mass flow is needed through supercharger to keep constant pressure due to same reason. The power is, of course, lower at this situtation, however, pressure ratio between manifolds and outside is still unchanged and hence the FTH unchanged as well.