PGNCS From United States of America, joined Apr 2007, 2860 posts, RR: 49
Reply 1, posted (6 years 3 weeks 5 days ago) and read 4950 times:
These vents are not equivalent. The vents on the wing undersides are fuel tank vents; the openings on the L-1011 are the inlets for the air conditioning pack cooling. The cooling air is subsequently vented overboard through the louvers you see behind the openings on the L-1011.
EMBQA From United States of America, joined Oct 2003, 9364 posts, RR: 11
Reply 7, posted (6 years 3 weeks 4 days 10 hours ago) and read 4682 times:
Quoting AC320tech (Thread starter): I was told (at least on the Airbuses) that this vent has something to do with the fuel tanks.
First. it's really an inlet...not a vent. When used with fuel tanks it allows air to enter the tanks and provide a positive pressure into the surge tank. When used with ACM intakes it provides a smooth airflow into the compressor. The V shaped inlet is still called a NACA Duct....... It's just how its used.
"It's not the size of the dog in the fight, but the size of the fight in the dog"
Tdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 8, posted (6 years 3 weeks 4 days 5 hours ago) and read 4578 times:
Quoting EMBQA (Reply 7): Quoting AC320tech (Thread starter):
I was told (at least on the Airbuses) that this vent has something to do with the fuel tanks.
First. it's really an inlet...not a vent. When used with fuel tanks it allows air to enter the tanks and provide a positive pressure into the surge tank.
It's both. During level flight, it provides a slight positive pressure to the tanks and lets air in to replace burned fuel (extremely small flow rate, it's really more of a pressure port). However, during a climb the pressure lapse rate is far higher than the fuel consumption rate, so it's actually a pretty significant vent, otherwise you'd overpressure the wing on climbout. Also, during fueling, it's a vent since the air has to leave to make room for the fuel.
During descent it reverses and that's the only time it's really behaving like an inlet, since you need to repressurize the wing during descent.
TristarSteve From Sweden, joined Nov 2005, 4092 posts, RR: 33
Reply 9, posted (6 years 3 weeks 4 days 3 hours ago) and read 4540 times:
Quoting Tdscanuck (Reply 8): Also, during fueling, it's a vent since the air has to leave to make room for the fuel.
And if you see fuel coming out you have a problem!
The vents are part of small (normally) empty tanks at the wingtips. If during refuelling the tank high level shut off does not work, then the fuel goes through the vent system, and fills up the vent/surge tank. If there is space in the wing tanks, this fuel will drain back in, but more normally it pours out of the vents. On most aircraft, when you stop the refuelling, the overflow stops, but on a B744, because the wing tips hang down when the tanks are full, the fuel continues to syphon its way out and doesn't stop very quickly. You can sometimes see it coming out of here during the taxy. The B744 sways sideways, and fuel is spilled into the tank and drains out.
But must admit it is not that common. Hasn't happened to me for a few years.