Originally Posted by
Wheelnut69
You'll have to forgive my ignorance, but I always thought that one of the reasons aircraft were pressurised to 7-8000 feet was weight.
Air at sea level is 14.7psi, what is it a 8000ft, around 11psi? Does that not make a big difference to the weight of the aircraft and therefore fuel use?
The weight of the airmass inside the fuselage in flight is inconsequential, and has no impact on the flight planning for fuel consumption. Were that the case, long range aircraft might focus on oxygen use for the limited number of crew members and depressurize the aircraft.
Pressurization serves multiple functions aside from comfort and life support. It's part of the rigidity of the aircraft structure
The difference in eleven vs. 14 psi in terms of weight of the airmass inside the fuselage is negligible and not a part of structural planning for fuel consumption, strategic planning, or inflight performance or other calculations. The only time pressurization comes to bear on performance is when considering the effects of pack and bleed usage on engine efficiency, particularly during the takeoff and initial climb.