D5DBY
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Hydraulic System...if All Engines Stops

Tue Aug 30, 2005 1:19 am

if both engines would be shut of during flight...would you be able to operate the flight controls?

im talking about a AC like B737 or MD-80 which has hydraulic powered flight controls. if the engines stop working then wouldn't the hydraulic system stop working also?
 
broke
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RE: Hydraulic System...if All Engines Stops

Tue Aug 30, 2005 1:31 am

Most twin engine (and other) aircraft could power the hydraulic pumps via either a Ram Air Turbine or using the APU generator to drive electrically driven pumps. The RAT is a retractable unit with a propeller and a hydraulic pump that extends automatically into the airstream when hydraulic pressure is lost.
 
northseatiger
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RE: Hydraulic System...if All Engines Stops

Tue Aug 30, 2005 1:33 am

The super puma family have an Aux pump, an electrical hydraulic pump that provides hydraulic power to the L/H system, L/H controls, Undercarrige, A/P.
T's And P's look good....Rotate
 
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longhauler
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RE: Hydraulic System...if All Engines Stops

Tue Aug 30, 2005 1:34 am

Usually the windmilling engines power the hydraulics enough to power the flight controls. However ...

The earlier versions of the B737, (and perhaps the later as well, but I have not flown the later versions) have a "manual reversion" backup to the ailerons and the elevators. It takes a lot of control wheel force, but it is possible, and something we practised from time to time in the simulator.
Just because I stopped arguing, doesn't mean I think you are right. It just means I gave up!
 
OPNLguy
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RE: Hydraulic System...if All Engines Stops

Tue Aug 30, 2005 1:39 am

Quoting D5DBY (Thread starter):
if both engines would be shut of during flight...would you be able to operate the flight controls?

im talking about a AC like B737 or MD-80 which has hydraulic powered flight controls.

On the 737s, there are both engine-driven hydraulic pumps, and electric-driven hydraulic pumps.

On the 737-100 and 737-200, The "A" hydraulic system uses 2 engine-driven pumps, one on each engine. The "B" system uses 2 electric-driven pumps. While the engines in your scenario would preclude use of the "A" system, the "B" system could still function using electrical power from either the APU, or the aircraft battery, the latter of which wouldn't last all that long.

On the 737-300s thru 737-900s, Boeing changed things up a bit. You still have "A" and "B" systems, but now each of those systems has 1 engine-driven pump and 1 electric-driven pump associated with them. Thus, per your scenario, you'd lose the engine-driven pumps for both systems, but still retain the electric-driven pumps for both systems.

Manual reversion would also be available, but it's like trying to drive a car without power steering--you can do it, but it takes alot more effort.

The 737 doesn't have a RAT...

Don't know specifically about the DC-9s and MD-80s, but I'd suspect something similar. I haven't dispatched one in 23 years, and I've forgotten how their systems are set-up.

[Edited 2005-08-29 18:41:46]
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
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HAWK21M
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RE: Hydraulic System...if All Engines Stops

Tue Aug 30, 2005 1:42 am

On the B737.There are Two EDPs [Engine Driven Pumps],Two EMDPs [Electric Motor Driven pumps] & One Standby Pump [Also EMDP].With Three Different Hydraulic Systems.
And Manual Backup for Roll & Pitch.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
VuelingAirbus
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RE: Hydraulic System...if All Engines Stops

Tue Aug 30, 2005 1:50 am

In spite of all the back up systems LongHauler made a very valid point. If there is no mechanical damage to the engines windmilling above 20 percent N1 will power hydraulics and thats easily achieved by the drift down speed.

rgds
 
242
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RE: Hydraulic System...if All Engines Stops

Tue Aug 30, 2005 1:59 am

Quoting D5DBY (Thread starter):
MD-80 which has hydraulic powered flight controls.

Only the rudder has hydraulic assist on the MD-80. The elevator is assisted only for stall recovery, and normally operated by servo tabs. Ailerons are only operated by servo tabs as well.
 
777wt
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RE: Hydraulic System...if All Engines Stops

Tue Aug 30, 2005 2:56 am

And for the landing, the hyd accumulator will be all left to use if the Engine Driven Pumps are InOp and the electrical pumps are InOp too.
 
kaddyuk
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RE: Hydraulic System...if All Engines Stops

Tue Aug 30, 2005 7:20 am

Quoting VuelingAirbus (Reply 6):
In spite of all the back up systems LongHauler made a very valid point. If there is no mechanical damage to the engines windmilling above 20 percent N1 will power hydraulics and thats easily achieved by the drift down speed.

Correct, boeing decided that with the B747-400, the speed of four windmilling engines would be sufficient to provide hydraulic power. I think to give enough pushing power on the PFCU's, the hydraulics need to be pressurised to a minimum of 500psi. Windmilling engines should provide around 1200psi...
Whoever said "laughter is the best medicine" never had Gonorrhea
 
B747FE
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RE: Hydraulic System...if All Engines Stops

Tue Aug 30, 2005 1:56 pm

Quoting Kaddyuk (Reply 9):
Correct, boeing decided that with the B747-400, the speed of four windmilling engines would be sufficient to provide hydraulic power.

Valid for the 747 classic also. A minimum of 160 KIAS or 1.3 stalling speed (whichever is greater), will provide adequate hydraulic power to control the aircraft in the event all engine power is lost. Normally, windmilling engines can provide full pressure for the hydraulic system.

Regards,
B747FE.
"Flying is more than a sport and more than a job; flying is pure passion and desire, which fill a lifetime"
 
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HAWK21M
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RE: Hydraulic System...if All Engines Stops

Tue Aug 30, 2005 5:23 pm

Quoting B747FE (Reply 10):
Normally, windmilling engines can provide full pressure for the hydraulic system.

What made the A320 want a RAT when the B737 did not.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
VuelingAirbus
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RE: Hydraulic System...if All Engines Stops

Tue Aug 30, 2005 9:53 pm

Quoting HAWK21M (Reply 11):
What made the A320 want a RAT when the B737 did not.

Loss of AC BUS 1 & 2 (where the RAT dropes out automatically - in case of hydraulic loss blue system you might extend it manually)
 
mrocktor
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RE: Hydraulic System...if All Engines Stops

Tue Aug 30, 2005 9:55 pm

Quoting HAWK21M (Reply 11):
What made the A320 want a RAT when the B737 did not.

The A320 does not have mechanical linkages to the ailerons and elevators, thus maintaining hydraulic power is essential to safe flight. FAR/JAR 25.671(d) requires control of the aircraft be maintained with both engines shut down, thus the RAT is necessary.

mrocktor
 
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HAWK21M
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RE: Hydraulic System...if All Engines Stops

Tue Aug 30, 2005 10:31 pm

Quoting Mrocktor (Reply 13):
The A320 does not have mechanical linkages to the ailerons and elevators, thus maintaining hydraulic power is essential to safe flight. FAR/JAR 25.671(d) requires control of the aircraft be maintained with both engines shut down, thus the RAT is necessary.

Makes Sense.
If FBW have a RAT.If Cable connected/Hydraulic backup no RAT.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
HT1000
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RE: Hydraulic System...if All Engines Stops

Fri Sep 02, 2005 12:39 pm

So what about 777/787 ?

Does it have a mechanical backup for flight controls ?

Regards.
HT1000
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DC8FriendShip
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RE: Hydraulic System...if All Engines Stops

Fri Sep 02, 2005 11:55 pm

Quoting HT1000 (Reply 15):
So what about 777/787 ?

Does it have a mechanical backup for flight controls ?

I believe it has a RAT, as does the 757 and 767.
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HAWK21M
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RE: Hydraulic System...if All Engines Stops

Sat Sep 03, 2005 8:38 pm

Quoting DC8FriendShip (Reply 16):
believe it has a RAT, as

Are you saying the B787 is also going to be RAT Equipped.
regds
MEL
I may not win often, but I damn well never lose!!! ;)

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