ceilings
hello agus,
keep it simple : any powered aircraft has amongst other things : wings(2) & engine(s), so you have a max. altitude for the wings(aerodynamic ceiling) & a max. altitude for the engine(s)[propulsive ceiling]. which one you reach first depends on the choices(compromises) of the aircraft manufacturer. in general & of course i oversimplify, american planes are "overpowered", so you will reach the aerodynamic ceiling first, whilst european built aeroplanes are sometimes "underpowered" & reach the propulsive ceiling first.
now lets elaborate a little further : "altitude" in this context, means "density" altitude or "pressure" altitude(1013hPa), corrected for temperature.
aerodynamic max.altitude(max.ceiling) is that altitude where low speed stall & high speed stall(due to shockwaves), are the same. it is the so called "coffin corner".
the propulsive max.altitude, is that altitude, where max thrust from the engine(s) equals the drag. there is only one speed to fly for this : Vmin drag=finesse max =Cl/Cdmax.
absolute ceiling, is ceiling where rate of climb=0.
service ceiling(lower than absolute), is ceiling where you still have a small rate of climb available. lets finish with an example.
for the 738 max altitude/fl is the lowest of :
1) 41000ft, is a certified structural limit(max delta pressure).
2) max. cruise altitude(fms).
depends on the thrust/drag relationship
needs a min rate of climb of 150ft/min
is temperature dependent
3) buffet limits : not lower than 1.3g in smooth air.
greetings,
bm.