asynchronous sidestick
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asynchronous sidestick
Hellos,
We have gone over this on the AF447 threads... I am trying to find out, is airbus the only manufacturer to have asynchronous sidesticks?
I understand that airbus is the only successful commercial jetplane maker to use side sticks.
What about other airplanes, i.e., fighters that use side sticks? Are they asynchronous as well?
We have gone over this on the AF447 threads... I am trying to find out, is airbus the only manufacturer to have asynchronous sidesticks?
I understand that airbus is the only successful commercial jetplane maker to use side sticks.
What about other airplanes, i.e., fighters that use side sticks? Are they asynchronous as well?
As the resident FBW pioneer, here goes:
The F-16 stick inputs and manual trim inputs are summed. As the sticks are not mechanically connected, there is no feedback to the troop in the other seat ( family model). Besides, the sticks only move about an eigth of an inch to help with fine corrections flying formation. From the 447 thread, my understanding is the sticks move quite a bit, as they are not pure "force transducers" as in the Viper. But they, too, sum the two inputs.
No family models for the F-22 or F-35, so N/A.
Have to ask an F-18 troop how theirs work, as they have the basic control stick between the legs. They are also not 100% BFW as the USAF birds.
Same question for Concorde crews.
The F-16 stick inputs and manual trim inputs are summed. As the sticks are not mechanically connected, there is no feedback to the troop in the other seat ( family model). Besides, the sticks only move about an eigth of an inch to help with fine corrections flying formation. From the 447 thread, my understanding is the sticks move quite a bit, as they are not pure "force transducers" as in the Viper. But they, too, sum the two inputs.
No family models for the F-22 or F-35, so N/A.
Have to ask an F-18 troop how theirs work, as they have the basic control stick between the legs. They are also not 100% BFW as the USAF birds.
Same question for Concorde crews.
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As far as i know the Embraer Legacy 500/450 uses an asynchronous sidestick concept, however with haptic feedback in case of dual input. Which is quite different from the conventional controls on the E-Jet family.
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what's the whole point of them being asynchronous on the bus anyways?
They are as noted electronically linked, albeit various modes to isolate one stick as required.
Some good questions here.
A lot of the functionality of the control input devices are part of the overall design philosophy for the FBW sytems.
Once the decision is made is to go pure FBW, then the human inputs implemented are a composite of the participating pilots in the design and the "dreams" of the engineers that think they can have a system that improves safety, reduces pilot/crew workload, accomplish the mission, etc. Sorry if I appear to have any criticism of the "engineers", but this opinion comes from a pilot that flew the first operational FBW system in USAF. Maybe Concrode prototypes were already flying, dunno. I only know that the jet should fly about as can be compared to what we were used to and what the average light plane pilot would expect. Basic flight laws that Wilbur and Orville figured out over a hundred years ago.
Several reasons not to have mechanical connections between the controls in the family models.
Imagine a failure that only allows one control stick to have the input to HAL.
Imagine a mechanical failure that locks both sticks!!!!
Imagine a situation where the troop who has a good awareness of what the jet is doing and the other troop is clueless. Think AF447.
Imagine a mechanical failure between the two controls that does not reflect what the other troop is doing.
And the beat goes on.
All I know for sure is that we never had a problem with the Viper implementation since 1973.
A lot of the functionality of the control input devices are part of the overall design philosophy for the FBW sytems.
Once the decision is made is to go pure FBW, then the human inputs implemented are a composite of the participating pilots in the design and the "dreams" of the engineers that think they can have a system that improves safety, reduces pilot/crew workload, accomplish the mission, etc. Sorry if I appear to have any criticism of the "engineers", but this opinion comes from a pilot that flew the first operational FBW system in USAF. Maybe Concrode prototypes were already flying, dunno. I only know that the jet should fly about as can be compared to what we were used to and what the average light plane pilot would expect. Basic flight laws that Wilbur and Orville figured out over a hundred years ago.
Several reasons not to have mechanical connections between the controls in the family models.
Imagine a failure that only allows one control stick to have the input to HAL.
Imagine a mechanical failure that locks both sticks!!!!
Imagine a situation where the troop who has a good awareness of what the jet is doing and the other troop is clueless. Think AF447.
Imagine a mechanical failure between the two controls that does not reflect what the other troop is doing.
And the beat goes on.
All I know for sure is that we never had a problem with the Viper implementation since 1973.
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gums
If I have understood the system neither stick moved, so on the Viper also the PNF never knew what commands the PF was making, i.e. the Viper sticks are asynchronous in practice?
Concorde b.t.w. was electrically signalled but it was an analogue system with mechanical backup and conventional stick arrangements
All I know for sure is that we never had a problem with the Viper implementation since 1973.
Concorde b.t.w. was electrically signalled but it was an analogue system with mechanical backup and conventional stick arrangements
I know you're on "our" side, Gums, but those scenarios are easily covered off:
Same as happens with conventional joined controls: you work out which one's working and use that.
Breakout, like current designs.
Good! You don't have to tell him to do something "stuff the nose down you moron!" you just do it; he gets feedback thru his stick and might even snap him out of his clueless state, esp if it jams his finger against the panel! 
Asynchronous sticks are merely an engineer's preference. Uh oh, here comes Dozy...
Originally Posted by Gums
Imagine a failure that only allows one control stick to have the input to HAL.
Imagine a mechanical failure between the two controls that does not reflect what the other troop is doing.
Imagine a mechanical failure between the two controls that does not reflect what the other troop is doing.
Imagine a mechanical failure that locks both sticks!!!!
Imagine a situation where the troop who has a good awareness of what the jet is doing and the other troop is clueless. Think AF447.
Asynchronous sticks are merely an engineer's preference. Uh oh, here comes Dozy...
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@Capn Bloggs
Having said that it is an engineers preference... They have not just left the side sticks control to being just asynchronous.
They have taken the pain of having the 'Dual Input' call outs and the take over push button as well, wonder what is the school of thought that has gone in.
Also, I'm trying to find out if the other FBW airplanes with side stick have a similar take on it.
There's always a reason to madness as there's madness to every reasoning. Wonder why chose one over the other...
Having said that it is an engineers preference... They have not just left the side sticks control to being just asynchronous.
They have taken the pain of having the 'Dual Input' call outs and the take over push button as well, wonder what is the school of thought that has gone in.
Also, I'm trying to find out if the other FBW airplanes with side stick have a similar take on it.
There's always a reason to madness as there's madness to every reasoning. Wonder why chose one over the other...
Capn Bloggs has cracked the code, heh heh. I was just offering the standard responses to those that wanted mechanically-linked controls.
And I 'spect Doze, et al, will chime in.
I discussed the stick implementation on the 447 thread because some folks thot that having 1) sticks mechanically linked and 2) being able to see what the other troop was doing could have helped the crew.
As I explained, we a) could not see what the other guy was doing, and b) it would not have made any difference because the sticks did not move! So we saw what the jet was doing and made appropriate inputs. As with the 'bus, we had a "take control" switch below the stick grip.
I always liked the force transducer implementation over a "position" design. Less to go wrong mechanically, 4 solid state transducers, and no doubt what the human command was if you relaxed pressure on the stick.
And I 'spect Doze, et al, will chime in.
I discussed the stick implementation on the 447 thread because some folks thot that having 1) sticks mechanically linked and 2) being able to see what the other troop was doing could have helped the crew.
As I explained, we a) could not see what the other guy was doing, and b) it would not have made any difference because the sticks did not move! So we saw what the jet was doing and made appropriate inputs. As with the 'bus, we had a "take control" switch below the stick grip.
I always liked the force transducer implementation over a "position" design. Less to go wrong mechanically, 4 solid state transducers, and no doubt what the human command was if you relaxed pressure on the stick.
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Originally Posted by nitpicker330
I think the side sticks ( actually not side but between the legs joy sticks? ) on the C17 Globemaster 3 have feedback between the sticks??
Originally Posted by gums
So we saw what the jet was doing and made appropriate inputs.
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Quote: Originally Posted by gums
So we saw what the jet was doing and made
appropriate inputs.
So we saw what the jet was doing and made
appropriate inputs.
For AF447 the nose came to its lowest when the the PF maintained full back stick, but none of the other guys could see the inputs ...
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Originally Posted by A33Zab
Only after being high for about 90 sec, depleting airspeed (in view!) and 60 sec of 'STALLSTALL' without any appropriate input.
Let me tell you that a fully visible control column fully aft deflected would have been the most shocking sight for that returning Captain.
Those sidesticks are not the best tool for CRM.
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School of thought
Having said that it is an engineers preference... They have not just left the side sticks control to being just asynchronous.
They have taken the pain of having the 'Dual Input' call outs and the take over push button as well, wonder what is the school of thought that has gone in.
Also, I'm trying to find out if the other FBW airplanes with side stick have a similar take on it.
There's always a reason to madness as there's madness to every reasoning. Wonder why chose one over the other...
They have taken the pain of having the 'Dual Input' call outs and the take over push button as well, wonder what is the school of thought that has gone in.
Also, I'm trying to find out if the other FBW airplanes with side stick have a similar take on it.
There's always a reason to madness as there's madness to every reasoning. Wonder why chose one over the other...
The reason I see is the choice of using the C* law, piloting Nz and not speed. Not only A and B limit Nz (they called that "protection", and A managed a hard limitation when B managed a soft limitation), but A and B pilot their effective system to Nz=1. It attenuates low turbulence, and that is a commercial choice done with the engineer fantasm to reduce "noise" and to realize more than the pilots are able to do (competition between pilots and enginers).
The feedback in the closed loop in consequence modifies the result of pilot's stick input with the help of aerodynamic force of autotrim. In result nor A nor B can disconnect the autotrim.
And you put the Nz law equation in the feedback. Nz is not the speed but its derivative. The output Nz of the feedback goes bakwards to meet the pilot's stick want, both are compared in the sommator and difference is the "input" of the closed loop.
If you want to add the pilot's want (the stick position and tendances) the system must use use the same dimension than Nz that is acceleration L.T-² and no more speed. In the direct loop the first thing you have to do then is an integration of the input signal. You can watch that integration appears as the factor 1/s in the A333Zab old schematic, where "s" is the Lagrangian operator).
That integration logic operates and appears in the small movements of the stick described by PJ2 or Bubbers44 and gums and in the slow accumulated movement of elevator autotrim and in the fact that seeing the stick position (of both pilots) cannot be interpretated like classic position of sticks and control.
The Viper needs the Nz feedback to realize hard and high limitations needed by modern air combat uses, not to try to increase the crews comfort... with nz=1! They need other values of Nz that gums could modify with the thumb on the top of the stick, piloting himself Nz and not leaving Nz control to the effective system like A or B.
Could some of you (A, B, FBW fighter pilots, engineers, designers, salers) confirm? Thanks.
Last edited by roulishollandais; 29th Jul 2013 at 10:47.
Originally Posted by vinayak
I understand that airbus is the only successful commercial jetplane maker to use side sticks.
"The only one" in this context actually represents 50% of world's successful commercial jetplane makers.
Originally Posted by LouthGirl
what's the whole point of them being asynchronous on the bus anyways?
Originally Posted by gums
I only know that the jet should fly about as can be compared to what we were used to and what the average light plane pilot would expect. Basic flight laws that Wilbur and Orville figured out over a hundred years ago.
Seriously; there are folks who know quite a lot about how the jet transport should behave and their views are regarded most solemnly; we call them certification test pilots. They have taken a hard look at Airbus FBW and pronounced it airworthy. Lo and behold! A couple of decades and a couple of million flight hours later, their judgement has been vindicated by reality.
Except virtual one, prospering on anonymous internet fora.
Originally Posted by gums
Imagine a situation where the troop who has a good awareness of what the jet is doing and the other troop is clueless. Think AF447.
Originally Posted by Capn Bloggs
Same as happens with conventional joined controls: you work out which one's working and use that.
Originally Posted by capn Bloggs
Asynchronous sticks are merely an engineer's preference.
Originally Posted by vinayak
They have taken the pain of having the 'Dual Input' call outs and the take over push button as well, wonder what is the school of thought that has gone in.
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Originally Posted by clandestino
Airbus mechanically independent sidesticks enable people with scant knowledge and understanding of: a) flying in general b) way passenger aeroplanes are flown and operated c) Airbus FBW to provide some low quality entertainment by airing their unsubstantiated and wrong opinion on uncoupled sidesticks as if it were factual.
This is a reality documented also by the ... AAIB.
Are they also 'low quality entertainment' ?
Until such a time when reference is provided that unequivocally demonstrates BEA considers the Airbus sidestick philosophy is suppressing valuable information to a PNF, it might be.