737: Reversible flight controls?
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Joined: Apr 2011
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From: Not in Honduras
737: Reversible flight controls?
Hi PPruners,
I've had this question in the back of my head for a long time:
Does the 737 qualify as having reversible flight controls (assuming normal ops with hydraulics on)?
(And let's ignore the MAX's FBW spoilers for now)
While, unlike most other jet transport category aircraft, the 737 has direct links to the ailerons/elevators so with hydraulics off, it is quite clear that the 737 has a reversible flight control system (for those two axes). The rudder is controlled by PCUs and thus there is no movement of the rudder surface without hydraulics if the pedals are moved.
But what does it look like when hydraulics are on?
The elevator clearly has an artificial feel computer to simulate aerodynamic forces. What about the ailerons?
And... assuming the hydraulics are on and someone would step on the elevator (or aileron) flight control surface, would the control column move? If it would move, then probably that would be proof that the flight control system is indeed reversible. If it would however not move, then that would probably prove that the flight controls are indeed irreversible, as (aerodynamic) forces are not transmitted to the control wheel.
Any thoughts on this?
Many thanks!
I've had this question in the back of my head for a long time:
Does the 737 qualify as having reversible flight controls (assuming normal ops with hydraulics on)?
(And let's ignore the MAX's FBW spoilers for now)
While, unlike most other jet transport category aircraft, the 737 has direct links to the ailerons/elevators so with hydraulics off, it is quite clear that the 737 has a reversible flight control system (for those two axes). The rudder is controlled by PCUs and thus there is no movement of the rudder surface without hydraulics if the pedals are moved.
But what does it look like when hydraulics are on?
The elevator clearly has an artificial feel computer to simulate aerodynamic forces. What about the ailerons?
And... assuming the hydraulics are on and someone would step on the elevator (or aileron) flight control surface, would the control column move? If it would move, then probably that would be proof that the flight control system is indeed reversible. If it would however not move, then that would probably prove that the flight controls are indeed irreversible, as (aerodynamic) forces are not transmitted to the control wheel.
Any thoughts on this?
Many thanks!
Joined: Oct 2019
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From: USA
The engineering term is "back drive" or "back driven." Reversible is when someone routes the cables around a pulley the wrong way or mis-connects a couple of wires in the side stick and push left makes the ailerons, for example, go right. I pick on ailerons as that is the only control reversal due to mis-installation that I am aware of. Aerodynamic reversal is a separate topic.
Chesty - that is a mental picture I did not want. It cost nothing to not write that.
There is probably some wise acre who used this on a pilot during training. "Lean way down and check to see if the rudder pedals move" while grabbing an aileron and giving it a swift jerk.
Chesty - that is a mental picture I did not want. It cost nothing to not write that.
There is probably some wise acre who used this on a pilot during training. "Lean way down and check to see if the rudder pedals move" while grabbing an aileron and giving it a swift jerk.
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From: USA
Joined: Sep 2003
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From: away from home
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From: UK
Here's me thinking this thread was about transonic control reversal.
I've never heard the term 'reversible controls' used in the way described by the OP.
Definitely been smacked in the chops by the yoke on a windy night though.
Does the OP mean 'reversion'? As in manual reversion with hydraulics off?
Edit, just realised Ocean crosser said the same thing.
I've never heard the term 'reversible controls' used in the way described by the OP.
Definitely been smacked in the chops by the yoke on a windy night though.
Does the OP mean 'reversion'? As in manual reversion with hydraulics off?
Edit, just realised Ocean crosser said the same thing.
Joined: Sep 2016
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From: USA
He clearly described what he meant, in asking if moving the control surface would move the yoke (the reverse of how the control linkage is normally used) like a Cessna 172.
With the hysterics powered, I would venture that yes they are technically reversible, but at some ungodly force ratio that they're effectively irreversible.
With the hysterics powered, I would venture that yes they are technically reversible, but at some ungodly force ratio that they're effectively irreversible.
Joined: Apr 2004
Posts: 2,166
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From: Planet Earth
Hi PPruners,
I've had this question in the back of my head for a long time:
Does the 737 qualify as having reversible flight controls (assuming normal ops with hydraulics on)?
(And let's ignore the MAX's FBW spoilers for now)
While, unlike most other jet transport category aircraft, the 737 has direct links to the ailerons/elevators so with hydraulics off, it is quite clear that the 737 has a reversible flight control system (for those two axes). The rudder is controlled by PCUs and thus there is no movement of the rudder surface without hydraulics if the pedals are moved.
But what does it look like when hydraulics are on?
The elevator clearly has an artificial feel computer to simulate aerodynamic forces. What about the ailerons?
And... assuming the hydraulics are on and someone would step on the elevator (or aileron) flight control surface, would the control column move? If it would move, then probably that would be proof that the flight control system is indeed reversible. If it would however not move, then that would probably prove that the flight controls are indeed irreversible, as (aerodynamic) forces are not transmitted to the control wheel.
Any thoughts on this?
Many thanks!
I've had this question in the back of my head for a long time:
Does the 737 qualify as having reversible flight controls (assuming normal ops with hydraulics on)?
(And let's ignore the MAX's FBW spoilers for now)
While, unlike most other jet transport category aircraft, the 737 has direct links to the ailerons/elevators so with hydraulics off, it is quite clear that the 737 has a reversible flight control system (for those two axes). The rudder is controlled by PCUs and thus there is no movement of the rudder surface without hydraulics if the pedals are moved.
But what does it look like when hydraulics are on?
The elevator clearly has an artificial feel computer to simulate aerodynamic forces. What about the ailerons?
And... assuming the hydraulics are on and someone would step on the elevator (or aileron) flight control surface, would the control column move? If it would move, then probably that would be proof that the flight control system is indeed reversible. If it would however not move, then that would probably prove that the flight controls are indeed irreversible, as (aerodynamic) forces are not transmitted to the control wheel.
Any thoughts on this?
Many thanks!
Are you related to the person we knew as 411A ?
Joined: Sep 2003
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From: away from home
He clearly described what he meant, in asking if moving the control surface would move the yoke (the reverse of how the control linkage is normally used) like a Cessna 172.
With the hysterics powered, I would venture that yes they are technically reversible, but at some ungodly force ratio that they're effectively irreversible.
With the hysterics powered, I would venture that yes they are technically reversible, but at some ungodly force ratio that they're effectively irreversible.
Thread Starter
Joined: Apr 2011
Posts: 33
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From: Not in Honduras
The terminology 'reversible flight control systems' might be an engineering term, but is used e.g. in this paper from the USAF test pilot school: https://apps.dtic.mil/sti/tr/pdf/ADA319984.pdf
And no, my question is not related to the concept of manual reversion. That is quite clear and without hydraulics, the flight control system of the 737 is reversible (for pitch and roll) - as I also outlined above.
My question really relates only to the "normal ops" condition where hydraulics are powered.
E.g. would you be able to 'feel' ice build-up on the aileron / elevator on the yoke provided the control surface isn't jammed? So a situation similar to American Eagle flight 4184 where ice build-up led to unexpected aileron hinge moment reversal that moved the aileron (and in return also the control wheel),
The ATR72 as in that case does have a reversible flight control system but I'm wondering how this would play out on the 737 (in theory). I believe with newer designs of non-FBW aircraft such as the 747,757,767,A310 this wouldn't be the case, since the flight control surfaces are indirectly actuated by PCUs.
But as we know, the 737 is a little 'special' here.
And no, my question is not related to the concept of manual reversion. That is quite clear and without hydraulics, the flight control system of the 737 is reversible (for pitch and roll) - as I also outlined above.
My question really relates only to the "normal ops" condition where hydraulics are powered.
E.g. would you be able to 'feel' ice build-up on the aileron / elevator on the yoke provided the control surface isn't jammed? So a situation similar to American Eagle flight 4184 where ice build-up led to unexpected aileron hinge moment reversal that moved the aileron (and in return also the control wheel),
The ATR72 as in that case does have a reversible flight control system but I'm wondering how this would play out on the 737 (in theory). I believe with newer designs of non-FBW aircraft such as the 747,757,767,A310 this wouldn't be the case, since the flight control surfaces are indirectly actuated by PCUs.
But as we know, the 737 is a little 'special' here.
Joined: Feb 2023
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From: Aachen
I would say no, you wouldn't notice it. Have a look at this training manual: https://de.scribd.com/document/32673...-3-ATA-27-L3-e
When the flight controls are in normal hydraulic operation they should just behave like the ones of the planes you mentioned above.
But maybe you ask somebody in the engineers/techs sub forum, who should know the details of the mechanism...
Hope I could help a bit though
Simon
When the flight controls are in normal hydraulic operation they should just behave like the ones of the planes you mentioned above.
But maybe you ask somebody in the engineers/techs sub forum, who should know the details of the mechanism...
Hope I could help a bit though
Simon
Thread Starter
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From: Not in Honduras
Joined: Oct 2013
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From: McHales Island
4111A,
Methinks your wires are a bit crossed. TURIN and oceancrosser are on the money. On the 737 with hydraulics turned off, the term used is called "Manual Reversion" whereby the flight controls are still operating in the correct sense via pilot input but without hydraulic assistance. Hope this helps.
Rgds McHale.
Methinks your wires are a bit crossed. TURIN and oceancrosser are on the money. On the 737 with hydraulics turned off, the term used is called "Manual Reversion" whereby the flight controls are still operating in the correct sense via pilot input but without hydraulic assistance. Hope this helps.
Rgds McHale.
Joined: Sep 2016
Posts: 937
Likes: 67
From: USA
4111A,
Methinks your wires are a bit crossed. TURIN and oceancrosser are on the money. On the 737 with hydraulics turned off, the term used is called "Manual Reversion" whereby the flight controls are still operating in the correct sense via pilot input but without hydraulic assistance. Hope this helps.
Rgds McHale.
Methinks your wires are a bit crossed. TURIN and oceancrosser are on the money. On the 737 with hydraulics turned off, the term used is called "Manual Reversion" whereby the flight controls are still operating in the correct sense via pilot input but without hydraulic assistance. Hope this helps.
Rgds McHale.
And no, my question is not related to the concept of manual reversion.
And no, my question is not related to the concept of manual reversion.
And no, my question is not related to the concept of manual reversion.
And no, my question is not related to the concept of manual reversion.
