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airboeingbus
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Modern Aircraft Total Hydraulic Failure?

Sun Apr 03, 2016 8:32 pm

I was reading about the A380 and it's EHA back up systems which allow the aircraft to be flown without hydraulic power. I was wondering what other modern Aircraft have in terms of back up systems and redundancy systems for hydraulic loss? Which aircraft can be controlled completely with loss of all hydraulic systems?
 
roseflyer
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RE: Modern Aircraft Total Hydraulic Failure?

Sun Apr 03, 2016 9:15 pm

A 737 can be flown without hydraulic power. It has old fashion manual reversion with a cable driven elevator and aileron controls. The rudder has a standby backup hydraulic source.
If you have never designed an airplane part before, let the real designers do the work!
 
airboeingbus
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RE: Modern Aircraft Total Hydraulic Failure?

Sun Apr 03, 2016 10:30 pm

Quoting roseflyer (Reply 1):

Regarding the 737, what kind of forces would be required on the yoke in order to control an aircraft like the 737 at high speed, surely you must be pretty strong to operate one manually.
 
skyhawkmatthew
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RE: Modern Aircraft Total Hydraulic Failure?

Sun Apr 03, 2016 11:13 pm

It's a certification requirement that airliners be able to be operated with the loss of all hydraulic systems. In the 737 and other aircraft with traditional flight controls, as you surmised they will just get quite heavy (how heavy I'm not sure). Fly-by-wire aircraft get more interesting:

In an Airbus (apart from those with the EHA), you are down to using the manual stabiliser pitch trim and rudder.

In the 777, you are down to manual stab pitch trim and a single pair of cable-operated spoilers.

Differential thrust can also be used to assist directional control in this situation if really necessary.
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roseflyer
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RE: Modern Aircraft Total Hydraulic Failure?

Sun Apr 03, 2016 11:20 pm

Quoting airboeingbus (Reply 2):

Quoting roseflyer (Reply 1):

Regarding the 737, what kind of forces would be required on the yoke in order to control an aircraft like the 737 at high speed, surely you must be pretty strong to operate one manually.

The 737 wing has balance panels, tabs and balance weights. It is an amazing feat of engineering that air loads are used to assist in flight control deflection. It requires surprising little force to fly with manual reversion. It is certainly more than when fully hydraulic powered but it can be done.

[Edited 2016-04-03 16:23:21]
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zeke
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RE: Modern Aircraft Total Hydraulic Failure?

Mon Apr 04, 2016 12:13 am

Quoting skyhawkmatthew (Reply 3):
In an Airbus (apart from those with the EHA), you are down to using the manual stabiliser pitch trim and rudder.

In the 777, you are down to manual stab pitch trim and a single pair of cable-operated spoilers.

You might want to check that. FBW aircraft are normally controlled by hydraulically powered, electrically signaled actuators on the control surfaces. When a control surface is controlled mechanically rather than electrically, it is still controlling a hydraulically powered actuator.

Quoting airboeingbus (Reply 2):
Regarding the 737, what kind of forces would be required on the yoke in order to control an aircraft like the 737 at high speed, surely you must be pretty strong to operate one manually.

There are servo tabs on the control surfaces so as the airspeed is higher the aerodynamic loads on the servo tab are higher making them more effective, the role of the servo tabs in normal flight with hydraulics power available is to trim the control surface loads. With the loss of hydraulics the aircraft is controlled with these servo tabs, and if you have ever tried to flying a little single engine trainer with just the trim wheel it is not as easy as it sounds.
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RetiredWeasel
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RE: Modern Aircraft Total Hydraulic Failure?

Mon Apr 04, 2016 1:07 am

Quoting skyhawkmatthew (Reply 3):
It's a certification requirement that airliners be able to be operated with the loss of all hydraulic systems.

Pretty sure that requirement would only apply to aircraft with limited hydraulic systems. 747-2 and 747-4 have 4 completely independent hydraulic systems. If on the ridiculous premise that all 4 quick working, you're SOL. There is no manual reversion or electric backup on any of the primary controls in the 74.
 
maxpower1954
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RE: Modern Aircraft Total Hydraulic Failure?

Mon Apr 04, 2016 3:49 am

Quoting airboeingbus (Reply 2):
Regarding the 737, what kind of forces would be required on the yoke in order to control an aircraft like the 737 at high speed, surely you must be pretty strong to operate one manually.

First generation jets:

Boeing 707/720 - manually controlled ailerons and elevator, hydraulic boost on rudder beyond a certain travel.

DC-8 - manual elevator, boosted ailerons and rudder.

Convair 880 - manual ailerons, elevator and rudder, later models had powered rudder.

At high speed you need very little travel to do anything and you are actually moving a small servo tab which flies the control surface into position.

I had two total main system hydraulic failures in my DC-8 years with manual reversion on the ailerons and yes, the forces were heavy. (The rudder had it's own independent system).
 
thepinkmachine
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RE: Modern Aircraft Total Hydraulic Failure?

Mon Apr 04, 2016 4:40 am

AFAIK, 787 and A350 have an electrical (or electro-hydraulic) backup for some of the surfaces, that can be used in total HYD loss.

As others stated above, there no requirement for manual reversion, as long as there's enough redundancy. That's why most airliners have 3 independent hydraulic systems. Only one is sufficient to provide adequate (albeit slightly reduced) control authority. However, if you lose all 3, you lose control of the a/c. This is very unlikely, unless you get shot at (like the DHL A300 in Baghdad a couple of years ago)

The 380 and 350, because of the additional electro-hydraulic backup, have only two main HYD systems.
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WIederling
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RE: Modern Aircraft Total Hydraulic Failure?

Mon Apr 04, 2016 6:21 am

Quoting roseflyer (Reply 4):
It is an amazing feat of engineering that air loads are used to assist in flight control deflection.

Servo tabs are nearly as old as airplanes. Patented by Anton Flettner in 1918 and intensely used onwards.
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mmo
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RE: Modern Aircraft Total Hydraulic Failure?

Mon Apr 04, 2016 9:24 am

Quoting skyhawkmatthew (Reply 3):

It's a certification requirement that airliners be able to be operated with the loss of all hydraulic systems.

Really!!!??? You had better tell that to both Airbus and Boeing!! In the event of total hydraulic failure there is no backup. Statistically the that event will not happen. There is no training for that compound emergency either.
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roseflyer
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RE: Modern Aircraft Total Hydraulic Failure?

Mon Apr 04, 2016 10:31 am

Quoting WIederling (Reply 9):

Quoting roseflyer (Reply 4):
It is an amazing feat of engineering that air loads are used to assist in flight control deflection.

Servo tabs are nearly as old as airplanes. Patented by Anton Flettner in 1918 and intensely used onwards.

That is what truly impresses me. It is not just a servo tab, but balance panels using differential pressure as well. The 1940s bombers and early jets came up with some incredibly sophisticated designs without the benefits of computer models we now use. . Getting the balancing and tab functions right to keep the pilot forces reasonable is quite impressive in airplanes without fully powered hydraulics. It is a bit unfortunate but there aren't mechanical engineers at the forefront of design in aviation any more. Now it is the software, control laws and aerodynamics people doing the innovation.
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Starlionblue
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RE: Modern Aircraft Total Hydraulic Failure?

Mon Apr 04, 2016 2:20 pm

Quoting skyhawkmatthew (Reply 3):

It's a certification requirement that airliners be able to be operated with the loss of all hydraulic systems.

As mmo and thepinkmachine mention this isn't the case.

You can fly the 330 with dual hydraulic failure but it isn't pretty. If you lose the last system you're toast.

Quoting thepinkmachine (Reply 8):
That's why most airliners have 3 independent hydraulic systems. Only one is sufficient to provide adequate (albeit slightly reduced) control authority.

I'd say pretty severely reduced control authority. 
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yeelep
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RE: Modern Aircraft Total Hydraulic Failure?

Mon Apr 04, 2016 9:12 pm

Quoting zeke (Reply 5):
Quoting airboeingbus (Reply 2):
Regarding the 737, what kind of forces would be required on the yoke in order to control an aircraft like the 737 at high speed, surely you must be pretty strong to operate one manually.

There are servo tabs on the control surfaces so as the airspeed is higher the aerodynamic loads on the servo tab are higher making them more effective, the role of the servo tabs in normal flight with hydraulics power available is to trim the control surface loads. With the loss of hydraulics the aircraft is controlled with these servo tabs, and if you have ever tried to flying a little single engine trainer with just the trim wheel it is not as easy as it sounds.

There is no control input to the elevator and aileron balance tabs on 737's.
 
PGNCS
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RE: Modern Aircraft Total Hydraulic Failure?

Mon Apr 04, 2016 10:39 pm

Quoting skyhawkmatthew (Reply 3):
It's a certification requirement that airliners be able to be operated with the loss of all hydraulic systems.

False.

Quoting roseflyer (Reply 4):
The 737 wing has balance panels, tabs and balance weights. It is an amazing feat of engineering that air loads are used to assist in flight control deflection. It requires surprising little force to fly with manual reversion. It is certainly more than when fully hydraulic powered but it can be done.

It is a feat of engineering, but I take exception to your claim "It requires surprising little force to fly with manual reversion". I'm sure you've done it in the sim, as have I, and I definitely wouldn't say it takes "surprisingly little force"; it is a workout that if the exercise goes on long enough generally requires pilots to swap PF/PM duties for a break. "Surprisingly little force" describes the DC-9 or MD-80 which are effectively always in manual reversion for pitch and roll and fly nearly as well with no hydraulics (roll authority is slightly less due to lack of differential spoiler availability.)
 
L-188
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RE: Modern Aircraft Total Hydraulic Failure?

Mon Apr 04, 2016 11:15 pm

Quoting thepinkmachine (Reply 8):
As others stated above, there no requirement for manual reversion, as long as there's enough redundancy. That's why most airliners have 3 independent hydraulic systems. Only one is sufficient to provide adequate (albeit slightly reduced) control authority. However, if you lose all 3, you lose control of the a/c. This is very unlikely, unless you get shot at (like the DHL A300 in Baghdad a couple of years ago)

Or your center engine explodes, like what happened in the famous Sioux City DC-10 crash
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thepinkmachine
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RE: Modern Aircraft Total Hydraulic Failure?

Tue Apr 05, 2016 10:21 am

Quoting Starlionblue (Reply 12):
You can fly the 330 with dual hydraulic failure but it isn't pretty. If you lose the last system you're toast.


Well, the 330 has pretty sluggish handling even with all 3 Hyd systems...   Handling with one Hyd sys remaining is indeed pretty appalling, However the powers that be decided it was good enough when certifying the a/c

The A320 OTOH handles pretty well even on one system. I don't remember any noticeable difference between 1 & 3 in the sim...
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pilotpip
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RE: Modern Aircraft Total Hydraulic Failure?

Sat Apr 09, 2016 1:20 am

If you lose all 3 hydraulic systems in an Ejet, you're boned. All you have left are the pitch trim and slats/flaps.
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113312
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RE: Modern Aircraft Total Hydraulic Failure?

Wed Apr 20, 2016 4:16 pm

You will recall that a JAL B747 crashed after all four hydraulic systems failed following the explosive loss of the rear pressure bulkhead and the partial loss of tail structure. There is no manual reversion and only limited "control" can be achieved by manipulating thrust among the four engines.

Likewise, a UAL DC-10 crashed at Sioux City following a catastrophic failure of the #2 engine that also resulted in the loss of all three hydraulic systems on that aircraft. There is no manual reversion for the flight controls and what "control" of the aircraft remained was by manipulation of thrust on the remaining two engines. While this aircraft did make it to an airport, there was insufficient control to avoid a crash landing.
 
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litz
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RE: Modern Aircraft Total Hydraulic Failure?

Wed Apr 20, 2016 7:00 pm

Add to that the A-300 in Baghdad that also lost all its hydraulics via damage due to exploding RPG.

It's the only one of the bunch that managed a landing, and they did so on differential thrust alone.
 
PhilBy
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RE: Modern Aircraft Total Hydraulic Failure?

Fri Apr 29, 2016 4:46 pm

Quoting mmo (Reply 10):
You had better tell that to both Airbus and Boeing!! In the event of total hydraulic failure there is no backup.

Theoretically the A320 can be flown and landed with all 3 hydraulic systems down. You still have rudder and elevator control plus differential thrust. I understand that this has actually been done.
 
thepinkmachine
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RE: Modern Aircraft Total Hydraulic Failure?

Fri Apr 29, 2016 9:24 pm

Quoting PhilBy (Reply 20):
Theoretically the A320 can be flown and landed with all 3 hydraulic systems down. You still have rudder and elevator control plus differential thrust. I understand that this has actually been done.

It can't. What you posted is a common misconception. The system is designed for a total electrical failure (or flight control computer loss), but not for total hydraulic loss.

Rudder and horizontal stabilizer can be MECHANICALLY CONTRLLED in case of loss of all electrics, but they are still HYDRAULICALLY ACTUATED, i.e. there is a mechanical connection between cockpit controls and servos, but actuators still need hydraulic power to move the control surfaces.

Bottom line: no hydraulics => no flight controls

[Edited 2016-04-29 14:27:15]
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