Tech Question : Split elevator ??
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Tech Question : Split elevator ??
Can someone tell me what a "split elevator" warning (B717) is, and what effect it has on aircraft performance/operation??
non-flying chapi
non-flying chapi
No one seems to have noticed your question so I'll give it whirl. Not a 717 person at all however some things tend to be common.
Most large aircraft have their controls surfaces designed so that they can be made to operate independently, but are normally linked so that they operate together. If something was to interfer with the mechanism of one surface to jam or restrict movement then its mate can still be made to work. The aircraft would have reduced handling qualities but still be controllable.
There needs to be some means of warning the crew if those mated surface are not acting in unison eg the same amount of movement, all actuators functioning etc.
Don't know about the B717 specifically since I don't know anything about its design & systems. It might be common in the B717 due to some design quirk eg on the ground before systems are powered up or a certain speed is reached by which the warning must cease, or it might ground the a/c until fixed.
Hope that helps?
Most large aircraft have their controls surfaces designed so that they can be made to operate independently, but are normally linked so that they operate together. If something was to interfer with the mechanism of one surface to jam or restrict movement then its mate can still be made to work. The aircraft would have reduced handling qualities but still be controllable.
There needs to be some means of warning the crew if those mated surface are not acting in unison eg the same amount of movement, all actuators functioning etc.
Don't know about the B717 specifically since I don't know anything about its design & systems. It might be common in the B717 due to some design quirk eg on the ground before systems are powered up or a certain speed is reached by which the warning must cease, or it might ground the a/c until fixed.
Hope that helps?
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Didn't that EgyptAir 767 out of New York get a split elevator when the dual control columns shear pins were broken?
Not sure of the 767... but figured maybe if the columns indidually controlled a different system/different surface then you could split the elevators manually with a bit of elbow grease...
Not sure of the 767... but figured maybe if the columns indidually controlled a different system/different surface then you could split the elevators manually with a bit of elbow grease...
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In my limited experience both the DH8 and BAe146 have elevators that can be split. This way, if one jams, either insitu or has a fouled control run, the remaing elevator can be disconnected to maintain a level of control.
I was told some time ago that the Fokker 50 was really a variant of the F27 as it didn't have split controls (being a 1950's design) and had it not been certified as an F27 it couldn't have been certified as a new type in its own right.
I was told some time ago that the Fokker 50 was really a variant of the F27 as it didn't have split controls (being a 1950's design) and had it not been certified as an F27 it couldn't have been certified as a new type in its own right.
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I remember years ago seeing DC9's (717 ancestor) sitting on the ground with one side of the elevator down and the other side of the elevator up.
I always did wonder about the reason.
DHC8's, and many other aircraft, have systems that can be split but they normally need some failure to occur before they will operate independantly.
Any 717 drivers or old DC9 drivers able to give it to us from the horse's mouth?
SS
I always did wonder about the reason.
DHC8's, and many other aircraft, have systems that can be split but they normally need some failure to occur before they will operate independantly.
Any 717 drivers or old DC9 drivers able to give it to us from the horse's mouth?
SS
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The split control design is, as has been said, a design feature in bigger aircraft designs.
In the roll control, usually when the split is activated, one pilot has the ailerons and the other the spoilers.
Some aircraft (De Hav Canada design comes to mind) also have a "surface jam" feature where, say the bellcrank at the aileron has an upper and lower segment connected by a spring loaded locking ball engaging the crank with the rest of the ailreon control system. Now if an aileron jammed from icing or similar, the ball would ride up out of its normal location and allow the two halves of the crank to rotate independently. That is one half remains frozen with the jammed control and the other continues to rotate and the aileron control system remains free to operate - albeit minus one controlling surface.
With regard to the 717 and its DC9 ancestors, remember they are not boosted flight controls (except rudder) and the pilots are controlling the aircraft by flying the tab and not the control surface on those beasts, so the control surfaces (particulary elevators) at rest can do some strange things!
In the roll control, usually when the split is activated, one pilot has the ailerons and the other the spoilers.
Some aircraft (De Hav Canada design comes to mind) also have a "surface jam" feature where, say the bellcrank at the aileron has an upper and lower segment connected by a spring loaded locking ball engaging the crank with the rest of the ailreon control system. Now if an aileron jammed from icing or similar, the ball would ride up out of its normal location and allow the two halves of the crank to rotate independently. That is one half remains frozen with the jammed control and the other continues to rotate and the aileron control system remains free to operate - albeit minus one controlling surface.
With regard to the 717 and its DC9 ancestors, remember they are not boosted flight controls (except rudder) and the pilots are controlling the aircraft by flying the tab and not the control surface on those beasts, so the control surfaces (particulary elevators) at rest can do some strange things!
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The DC9 and MD80s have independent elevators, thus with no airflow (like parked on ground) one can be full up and one full down. 
However the B717, has as far as I know, powered elevators, so with hydraulics available, they should not be split.
Thus the warning, which is not required on a DC9.
However the B717, has as far as I know, powered elevators, so with hydraulics available, they should not be split.
Thus the warning, which is not required on a DC9.
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I take it you mean on the B717?
I am not familiar with them, but I know that they do have powered elevators unlike the DC9.
I would "assume" that they are bussed together?
Any B717 lames out there...............
I am not familiar with them, but I know that they do have powered elevators unlike the DC9.
I would "assume" that they are bussed together?
Any B717 lames out there...............
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The only powered assistance the 717 has in the elevators is hydraulic, which is activated only by the stick pusher.
Other than that they are aerodynamically positioned via trim tabs - moving the control wheel forwards or back sends inputs to the trim tabs, which then deflects the elevator in the required direction.
Ailerons work the same. No direct link from control wheel to elevators or ailerons.
Other than that they are aerodynamically positioned via trim tabs - moving the control wheel forwards or back sends inputs to the trim tabs, which then deflects the elevator in the required direction.
Ailerons work the same. No direct link from control wheel to elevators or ailerons.
