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Not_Boeing_Not_Going

NGX rudder deflection

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hello guys, i dont know if that is a stupid question or not!, but i wonder why i cant see the rudder, elevators and ailerons of ngx settle down, yoke or deflect with the direction of the wind like the queen of the sky pmdg 747 when the hyd and elec pumps are off, if someone have these movement in fsx pls send pics or it may be a property of ng737 unlike airbus or other boeing types! please send pic of 737 at gates so we can clarify this topic, thanks!

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The NG has cables connecting the yoke to the ailerons and elevators, where as the 747 is purely hydraulic. Hence when hydraulic pressure drops on the 747 the control surfaces droop; on the 737 the cables keep them in place.

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The NG has cables connecting the yoke to the ailerons and elevators, where as the 747 is purely hydraulic. Hence when hydraulic pressure drops on the 747 the control surfaces droop; on the 737 the cables keep them in place.

thank you, do you mean that hydraulics get assistance from wires unlike other aircraft, i mean which is the primary driver?

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thank you, do you mean that hydraulics get assistance from wires unlike other aircraft, i mean which is the primary driver?

 

Hydraulics provide primary control in the 737, with cables as a backup. The 747 doesn't have cables as a backup, so when pressure drops so do the control surfaces.

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Hydraulics does exactly what the power steering does on a car, it is an aid to remove forces, pilots act on steel cables, pulleys and springs, the hyd servo actuators are in the wheel well, they act after the pilot (or ap) started to move the controls.

There is no main and backup, no way to move the control if a cable of it is jammed or broken. The rudder is a different thing, it is hyd powered but cables are still present from the pedals to near the rudder where actuators are installed.

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Hydraulics does exactly what the power steering does on a car, it is an aid to remove forces, pilots act on steel cables, pulleys and springs, the hyd servo actuators are in the wheel well, they act after the pilot (or ap) started to move the controls.

There is no main and backup, no way to move the control if a cable of it is jammed or broken. The rudder is a different thing, it is hyd powered but cables are still present from the pedals to near the rudder where actuators are installed.

thank you for this hint, i want to ask what mechanism large airplanes like 777 and 747 have? i think the hyd actuators are electronically controlled when forces are applied on controls?

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thank you for this hint, i want to ask what mechanism large airplanes like 777 and 747 have? i think the hyd actuators are electronically controlled when forces are applied on controls?

 

777 is fly-by-wire, so it's just wires going to the servos. 747 is all-hydraulic.

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777 is fly-by-wire, so it's just wires going to the servos. 747 is all-hydraulic.

thank very much Ryan, I am looking forward your triple seven and will be very happy to see the actuators settle down when all pumps are idle! but i was surprised that the NG series has cables not wires! Do you think that fly by wire is more safe than cables or it is matter of large airplanes that have long distances to have cables installed?

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The main problem is not the reliability, on most of the projects it is more a balance in price, weights, certification costs and more.

There are different ways to move a surface, by cables, like on the little cessna or piper and 737, there are planes that are hydraulically powered but cables run until the actuator (like on 737 rudder and crj for all surfaces. In this case the cables have less diameter and less weight, they moves only the actuator input quadrant, this let the hyd fluid to move the surface.

Another method is the fly by wire, from the joystick or the column electric impulses are sent to computers where they are computed with some other data and "corrected" then the signal goes to the electrohyd actuators wich moves the surface.

Take in mind that in FBW planes and hyd powered planes, the primary flight controls have at least 2 hyd system powering them, if not 3.

CRJ for example uses 3 systems for rudder and elevators, only 2 for the ailerons BUT one aileron uses 1 and 3 hyd system, the other uses 2 and 3 system, this assuring that at least one of the aileron will always work.

Emb 170 is an example of hybrid flight control technology, its elevator and rudder are FBW but the aileron are like on the CRJ, hyd powered. The main reason (when I asked) is the certification costs of making a full FBW plane.

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The main problem is not the reliability, on most of the projects it is more a balance in price, weights, certification costs and more.

There are different ways to move a surface, by cables, like on the little cessna or piper and 737, there are planes that are hydraulically powered but cables run until the actuator (like on 737 rudder and crj for all surfaces. In this case the cables have less diameter and less weight, they moves only the actuator input quadrant, this let the hyd fluid to move the surface.

Another method is the fly by wire, from the joystick or the column electric impulses are sent to computers where they are computed with some other data and "corrected" then the signal goes to the electrohyd actuators wich moves the surface.

Take in mind that in FBW planes and hyd powered planes, the primary flight controls have at least 2 hyd system powering them, if not 3.

CRJ for example uses 3 systems for rudder and elevators, only 2 for the ailerons BUT one aileron uses 1 and 3 hyd system, the other uses 2 and 3 system, this assuring that at least one of the aileron will always work.

Emb 170 is an example of hybrid flight control technology, its elevator and rudder are FBW but the aileron are like on the CRJ, hyd powered. The main reason (when I asked) is the certification costs of making a full FBW plane.

another useful information, thank you very much :).

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How come when both engines die midflight and the APU is off, I lose control authority on the airfoils in the NGX? I've shut off the engines once or twice and the plane didn't respond to any control inputs. It just slides into the ocean like a missile.

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The reason larger planes don't have cable backups is because the control surfaces are larger and in flight the force to move them would be too heavy for and average human to move. During manual reversion in the 737 the controls are very difficult to move. Some planes like the MD-80 have control tabs which are smaller control surfaces attached to the main control surface that when deflected cause the main control surface to deflect but I am given to believe even those wouldn't work on larger planes.

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Be nice to my little Cessnas!

Always ;)

 

How come when both engines die midflight and the APU is off, I lose control authority on the airfoils in the NGX? I've shut off the engines once or twice and the plane didn't respond to any control inputs. It just slides into the ocean like a missile.

 

PMDG tried to simulate how hard is to control the aircraft with no hyd power, however they exceeded in doing that and the aircraft is almost unflyable. Control deflection and effectivity is reduced to a 5-10% wich is insufficient for pitch control if you lost also the electrical power and you must use the stab trim manually (another thing PMDG simulated).

So, I sent a ticket to them and they told that probably they will review that feature for SP2 (maybe after 777 release) to add more control if the controls are kept out of center for some time. This will simulate "harder controls without limiting too much the usage of the plane.

 

Now, returning to the real, the 737 includes servotabs for elevator and aileron,these servotabs are installed on the trailing edge of the surface and work inconjunction with aileron/elevator movement but in the opposite direction, this means that when the elevator is up, the tab is down, this tab will help pushing up the surface removing some forces to the pilots in manual reversion. Other planes uses the same system, other will use the tab to move the surface directly.

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Hello all,

 

Great thread and information above. Just one mention though: regardless of plane, some cable/mechanical control remains even in the most advancd FBW.

 

For example, in 777 cable controls run from yoke to spoilers 4 and 11 in order to provide mechanical backup for roll control. It basically spoils (pun intended) the lift on one or the other wing to add in lowering that respective wing.

 

At Airbus, there is mechanical backup to control the horisontal stabilizer (the trim wheels) and the rudders.

 

So, I don't think that there is so much a problem of cost and certiication as it is an apprehension on the engineering side to leave an aircraft completely electric/hydraulic without any mechanical backup.

 

In 737, indeed, cables control directly the hydraulic actuators but with a computer that intermediates the direct motion of the control depending on the airspeed. In other words, as speed increases, the maximum possible deflection is reduced to protect the structure and against overcontrol. When the HYD is out, the mechanism does not assist with power, defelction computer is out and gives direct deflection control this time fully proportional with control movement, feel mechanism on the feel and center unit does not artificially create any feel because it cannot anymore (also HYD actuated) and you are dealing with the real forces now anyway :). Oh, and there is also mach trim to prevent mach ducking based on pitot like sensors on the vertical stabiliser and a computer just for that.

 

In 747, cables go to hydraulic actuators and that's it as mentioned above. That makes possible the "falling" of the controls when off as well as the locking of the ailerons after M.53 or 256 IAS. Hope the numbers are correct as there is a small hysteresis loop going up and down through speed; in that case flapperons do the jub from the root of the wing.

 

In B777, ailerons can also droop while flying to act as flaps and still do the roll job because are mechanically independent.

 

 

Ionut "John" Micu

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thank you all very much for these useful and interesting topics, i hope to see the PMDG 777 flight controls drop down because this is give you interesting feel of realism although it is not a very important thing to be simulated!.

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In 737, indeed, cables control directly the hydraulic actuators but with a computer that intermediates the direct motion of the control depending on the airspeed. In other words, as speed increases, the maximum possible deflection is reduced to protect the structure and against overcontrol. When the HYD is out, the mechanism does not assist with power, defelction computer is out and gives direct deflection control this time fully proportional with control movement, feel mechanism on the feel and center unit does not artificially create any feel because it cannot anymore (also HYD actuated) and you are dealing with the real forces now anyway :). Oh, and there is also mach trim to prevent mach ducking based on pitot like sensors on the vertical stabiliser and a computer just for that.

The 737 elevators work 99% similar to the 737-100 elevator.

There is no electrical computer acting on the feel force, there is a "computer" but it is fully hydromechanical and it only change the centering spring lenght by adding or removing forces, if hydraulic will be lost, the pressure drops and the forces will be released.

For the actuator, it is near the elevators, it works in normal conditions preventing that control column acts directl on the surface, but, when in manual reversion mechanical stops inside the PCU will move the surface like it is on a cessna (more force is required). The "freedom" is +-1° of column movement.

Other planes works different, the cables ends to the input quadrant and all is then moved by pressure, no pressure, no movement.

In the 737 without a cable cut or a jam or other strange not normal reasons, the surface will always move with the column, same (limited by the 1 or 2° of freedom) as the column, this giving no way to change the surface usage, ailerons will always work, and will be never used like flaps, something that FBW planes or fully hyd planes are able to do as there is no mechanical link. The same planes will need a RAT or ADG in case of a complete power failure and/or they will need some mechanical backups... 737 doesn't need a rat, it can still fly with battery power only.

The logic of using cables still on full FBW planes is to give a "last chance" to land the plane in case of a very bad day. the stabilizer can be used to pitch the plane, rudder and engines to roll and steer. All of them are redundant systems that engineers and laws requires for a safe aircraft.

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