outflow valve

[benji123]

hi there ..does anyone know the answers to these questions..thanks a mill

A Which way would you move the outflow valve to decrease cabin altitude?
B If the cabinand aircraft are climbing at 1500ft/min what position is the outflow valve?
C Cruising at FL350 if the outflow valve is manually moced towards the closed position what will happen the diff pressure , will it increase or decrease? Any why?

[Fresca]

A. To decrease cabin altitude you are increasing the air pressure inside the cabin so you would close the outflow valve.

B. It is almost impossble to know the postition of the outflow valve during any given time. It depends on the airflow from the PACKS. But during 1500fpm climb from both the airplane and cabin, my guess is the would be somewhere in the mid-range position. One has to take into acount if the airplane is pressurized or not during the climb, and if so what is the differential pressure.

C. Druing cruise at FL350 and the outflow valve closes, the cabin would desend. That in turn would increase the differential pressure, as the difference between the outside pressure and the cabin pressure gets greater.

B. regards

Fresca

[r1flyguy35]

1) Close it - less conditioned air escaping
2) fully open - if both a/c & cabin climbing at same rate or manually opened to a point where both are equal
3) diff pressure increase - less air being evacuated from cabin, increases cabin pressure compared to external pressure therefor differential increases.

:ok:

[benji123]

thanks guys!:ok:

[bfisk]

r1flyguy35: I think there are more to question B) that that.

If the cabin and the airplane are climbing at the same rate, that only means that the _change in_ diff.pres. is zero; the diff.pres. itself may be whatever. Let's say an airplane operates at max diff press and initiates a climb at 1500fpm; the outflow valve would open, but not completely, as that would cause the airplane to depressurize altogether.

[411A]

One can also use the aircraft's outflow valves to improve cabin ventilation, if desired.
Generally speaking, selecting a lower differential pressure (higher cabin altitude) will improve the cabin airflow, all other things remaining constant.
This can be used to good advantage if the cabin becomes hot and stuffy, for whatever reason.Works on the 'ole Lockheed trimotor, anyway.