Rydawg82 From United States of America, joined Sep 2001, 774 posts, RR: 8 Posted (10 years 4 months 5 days 3 hours ago) and read 3294 times:
Hello....
I am trying to find out what a few "possible vents" are, when they open/close, and what controls them (pilot or auto system etc) any solid information from mechanics, pilots or ops manuals would be great....
First, on the DC-10 you can notice the vent, its square in shape and has the cover perpendicular inside it (when open)....Its located 3-4 windows aft the 2nd boarding door and then below.
Sorry for the number of photos but what is this moving mystery? When/how does it open?
Also the MD-80 has one (its round and just below the left engine)....I have watched this open about 20 seconds before touchdown) On this aircraft Im guessing its for the APU, but can someone explain its operation....
Mr Spaceman From Canada, joined Mar 2001, 2777 posts, RR: 18 Reply 1, posted (10 years 4 months 5 days 2 hours ago) and read 3184 times:
Hi Rydawg82.
The vent you're looking at on the DC-10 is called the Cabin Pressure Control Valve Group. It's made of 3 separate components...The cabin pressure Outflow Ram Air Shield, the cabin pressure Outflow Butterfly Valve, and the cabin pressure Thrust Recovery Valve.
If you search Planespoterx's profile and click on thread starters for the Tech Forum, you'll see his post called "Missing Panel On DC-10". If you read 747Teach's reply, you'll understand how the DC-10's Cabin Pressure Control Valve Group works. It's great info.
I believe the vent you can see on the rear of the MD-80 is also a Cabin Pressure Control Valve (you can see the buterfly plate). I'm sure the reason it opens around 20 seconds before touchdown is to equalize the air pressure between the cabin and outside. This way there's no pressure forces acting on the cabin doors when they are opened.
Chdmcmanus From United States of America, joined Mar 2001, 374 posts, RR: 3 Reply 2, posted (10 years 4 months 5 days 1 hour ago) and read 3164 times:
Mr. Spaceman and 747Teach are right on the money about the -10. One additional comment on the later -10's (The AF KC-10 and MD-11), you will notice that they only have the thrust recovery valve. The system works extremely well, and in the later models, MD decided not to include the cabin pressure Outflow Ram Air Shield or the cabin pressure Outflow Butterfly Valve. Only the cabin pressure Thrust Recovery Valve (lt side) and the pressure relief valves, 3ea (rt side). I'm not exactly sure why this was done; maybe someone else could help?
Critter From United States of America, joined Jan 2000, 267 posts, RR: 3 Reply 5, posted (10 years 4 months 4 days 22 hours ago) and read 3130 times:
Yes the round buterfly valve on the MD-80/DC-9 etc. is the Ground controlled outflow valve. It is sometimes scheduled to open just before touch down to ensure an unpressurized cabin upon landing. If you look about two to three feet aft of the butterfly valve you will see the opening for the main cabin pressure control valve. This closes after the Buterfly valve is completely closed and opens before the buterfly valve. In flight the aft valve, or "sugar scoop" as we call it, is the main pressure control valve. There is a rod that physically connects the two for scheduling purposes.
critter
P.S. The B717 does not have the round buterfly valve. It only has a "sugar scoop".
FBU 4EVER! From Norway, joined Jan 2001, 998 posts, RR: 8 Reply 6, posted (10 years 4 months 2 days 12 hours ago) and read 3078 times:
As has been mentioned,the round valve on the DC-9/MD-80 and 90 has to do with the cabin pressurization system.In my manuals,it is called the Cabin Air Outflow Valve and can be operated in automatic or manual modes.
In auto mode,it will start to close as the power levers are advanced for take-off,with cabin pressure starting to increase during the T/O roll.This prevents a "pressure bump" which would normally happen at lift-off.If the power levers are retarded,or the plane is not airborne within 60 seconds,this valve will open automatically and dump the pressure.
During approach,the valve is scheduled to open just prior to touchdown,but dependent upon the accuracy with which the pilot has set the cabin pressure controller,it may open several seconds before landing and sometimes even after touchdown.
It can be manually controlled from the cockpit by a control wheel located between the power levers and the flap/slat handle.Manual control is normally used by the mechanics when preparing the plane for a night stop when they close it.
Rydawg82 From United States of America, joined Sep 2001, 774 posts, RR: 8 Reply 7, posted (10 years 4 months 1 day 20 hours ago) and read 3067 times:
FBU 4Ever....Great Info!!!! Thank you for the information, was watching an American MD-80 today in Denver, and sure enough it began to open about 5 seconds before crossing the numbers....
Can anyone supply information about the modes *if any* that the DC-10 uses to open and close....Thanks RyRy
You can take the pup out of Alaska, but you can't take the Alaska out of the pup.
FBU 4EVER! From Norway, joined Jan 2001, 998 posts, RR: 8 Reply 9, posted (10 years 4 months 1 day 16 hours ago) and read 3048 times:
Have tried to get in contact with my father who flew DC-10's,but he's out on a trip somewhere.Hopefully,he should still have his old manuals with the required info.
FBU
Chdmcmanus From United States of America, joined Mar 2001, 374 posts, RR: 3 Reply 11, posted (10 years 4 months 1 day 7 hours ago) and read 3043 times:
The DC-10 uses three modes of operation, Auto, Semi-Auto and manual. In a nutshell,
1. Auto- The valves are controlled by the Pressure Controller, and operates on a pre-set cycle, with the only operator input being the rate of change selection, between 500 and 1000 fpm, and the landing airfield barometer setting. A typical cycle is initiated when the nosewheel lifts off.
A. Maintains 0 differential until nosewheel liftoff,
B. Maintains sea level until 5000 ft msl, then begins isobaric pressurization at 500 fpm until 8.3-8.3 psid
C. Maintains this differential until descent, throttle switches at idle initiates this mode, cabin descends at 300fpm until landing field altimeter setting is reached, and maintains .5 psid until touchdown.
D. After touchdown, depressurizes at 750 fpm until 0 differential is met, normally by the end of rollout. This is a pax comfort feature, however, the emergency operation of the cabin doors in a DC-10 will allow the doors to open up to .7 psid, should the system not function properly and a ground egress is required.
2. Semi Auto- Essentially the same as auto, except acft does not attempt to maintain sea level until 5000msl, and the actual cabin altitude is set manually by a cabin alt selector. The rate of change capability is also increased to 200-2000 fpm. This mode is used when a nonstandard cabin pressure is needed (medical emergency, engine out performance, structural capabilities after ERD etc), or touch-and-goes are being performed. If there is a system malfunction BOTH the auto and semi-auto are inop, and manual must be used.
3. Manual- A lever next to the manual press wheel disengages the thrust recovery valve from the pressurization controller and allows manual operation through the use of a control wheel on the lwr lt side of the FE panel. The FE (DC/KC-10) or FO (MD-10/MD-11) then uses the cabin rate of change indicator and cabin alt gauges to determine the position of the outflow valve and pressurize the acft based on Isobaric charts in the flight manual.
In the picture, the Pneumatics Panel is in the center, immediately above the fuel panel (bottom, just above the desk), on the right side is two large gauges, they are the cabin rate of change, and cabin alt / differential gauges. Below is the isobaric chart, and finally on the bottom the auto/ semi-auto switch, the “cabin alt” window, the “landing baro set” window and “rate of change” knob. On the far left of the fuel panel, see a yellow lever and hashed wheel, that is the clutch disengage and the manual control wheel.
Just as a side note, you can tell this is a DC-10-10, no center gear light, and no center aux fuel tank.
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