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  • Boeing's opinion on the Airbus side stick...

    Ok, let me say that I am not trying to start a Boeing vs. Airbus thread, I have great respect for both companies.

    But, while on Boeing's website, I found this statement about the side stick used on most Airbus aircraft:

    "Existing commercial side sticks offer no visual or tactile cues to the pilot and must have restrictive performance limits." (from: http://www.boeing.com/commercial/737...echnology.html)

    Is this true? And if the limits are so restrictive, then why was Captain Sullenberger able to land an A320 that lost power in both engines, in the Hudson, with no resulting fatalities?

  • #2
    Originally posted by UALdave View Post
    "Existing commercial side sticks offer no visual or tactile cues to the pilot and must have restrictive performance limits."

    Is this true?
    Perhaps, don't know as I do not fly the A320. (or any plane for that matter) But for years already joysticks on a PC games like flight simulator have had force feedback possibility. I see no reason why this would not be an option on an airbus.
    Please visit my website! http://www.schipholspotter.com/

    Don't make me use uppercase...

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    • #3
      Originally posted by Petertenthije View Post
      Perhaps, don't know as I do not fly the A320. (or any plane for that matter) But for years already joysticks on a PC games like flight simulator have had force feedback possibility. I see no reason why this would not be an option on an airbus.
      True, although I don't know if the side stick in an Airbus gives the same amount of feedback as one used for flight simulator-ie, the Airbus one might feel tighter, in terms of movement.

      Comment


      • #4
        Please no no no stick side for Boeing. Fly by wire is kind of a little bit dangerous than yoke. The yoke stick is much safer. I would say.


        Stuart

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        • #5
          Originally posted by Big777jet View Post
          Please no no no stick side for Boeing. Fly by wire is kind of a little bit dangerous than yoke. The yoke stick is much safer. I would say.


          Stuart
          Ahhh the 777 is fly by wire...
          -Not an Airbus or Boeing guy here.
          -20 year veteran on the USN Lockheed P-3 Orion.

          Comment


          • #6
            The "restrictive limits" prevent overstressing of airframe parts. The following is a large simplification.

            For example, on a Boeing 767, the feedback into the control column means it is very difficult to overstress a part of the airframe, because the pilot can feel the resistance. For example, in the cruise, it would be almost impossible to immediately pull or push to full yoke deflection.

            On an Airbus, there is no restriction on the pysical movement of the sidestick, so it is easy for the pilot to pull the stick full back or push forward with no resistance against that movement.

            So that the flight control response is appropriate, the control computers manage the input vs the control deflection. The added "benefit" of this is that they can define an envelope of acceptable flight regimes, and the side stick input is only allowed upto the limits of that envelope.

            Of interest (as P3 says) is the fact that the 777 is Fly By Wire... but it uses a yoke and a feedback system.

            Does the Airbus sidestick need feedback? Not really. Why? Simply because the performance of the aircraft matches the input. You put in the movement, and the aircraft rolls, and it does so in a safe and defined way.

            Does the Boeing FBW yoke need feedback? Yes. Why? Because the aircraft does not fly within an envelope, and will give you whatever response you what. It would be very very difficult to fly without the feedback.

            Which is better? Horses for courses.

            Comment


            • #7
              Great response MCM...

              Originally posted by MCM View Post

              Which is better? Horses for courses.
              That is the question... It would and could only be answered by someone qualified to fly both and have a good amount of time in both. And I'm betting there aren't too many of those guys/gals around...
              -Not an Airbus or Boeing guy here.
              -20 year veteran on the USN Lockheed P-3 Orion.

              Comment


              • #8
                "Fly by wire: Can eliminate mechanical systems to lighten airplane weight, but can also increase maintenance costs and reduce dispatch reliability, depending on design."

                Rofl... I am sure the guy who created that table was giggling while writing it. Pure BS.
                He should be hired by Yemenia Air!

                Toilets with no door - Air France: no, Yemenia Air: YES!

                Toilet doors may improve privacy in some isolated cases, but they prevent fresh air from coming into the toilet.

                Comment


                • #9
                  In modern fly-by-wire, it is theoretically possible to fly an airplane with a completely immovable control stick, for example, the F-16. The original F-16s control sticks were completely immovable and responded to the amount of pressure the pilots put on the stick. Trouble was, they couldn't get the calibration right and pilots didn't know how much pressure they were putting on the stick, so they added springs and made the stick able to move within about an inch envelope.

                  but yes, it is possible to have a stick that doesn't move.


                  Comment


                  • #10
                    Originally posted by Cas View Post
                    "Fly by wire: Can eliminate mechanical systems to lighten airplane weight, but can also increase maintenance costs and reduce dispatch reliability, depending on design."

                    Rofl... I am sure the guy who created that table was giggling while writing it. Pure BS.
                    He should be hired by Yemenia Air!

                    Toilets with no door - Air France: no, Yemenia Air: YES!

                    Toilet doors may improve privacy in some isolated cases, but they prevent fresh air from coming into the toilet.
                    Yeah, it's also hypocritical for Boeing to rail against fly by wire when one of their aircraft families, the 777, uses it.

                    Comment


                    • #11
                      There are times when you need minor control inputs and times when you need large ones.

                      The side-stick has in inherently short range of motion....one little wrist twitch and a side stick airplane is potentially rolling like there's no tomorrow.

                      If you need a tiny adjustment- you have to move your wrist the tiniest amount.

                      As a contrast, let's look at a school bus steering wheel.....a little arm jerk is essentially nothing. A moderate correction- you make a real input....a hard turn- you need a hard input.

                      A genuine on-the-floor stick and or a traditional control wheel/yoke gives you several inches of movement to provide control inputs...as opposed to just a couple of inches on the sidestick.

                      I dare say this could be PART of that Germany wing scrape.....whipping a little stick back and forth- trying to get control, inducing PIO...

                      Conversely, a nice big Boeing wheel or a glider center stick, would be involve biceps, forearms, shoulders. It does not require surgical precision from the pilots fingertips and wrist...

                      ...heck even a Cessna 150 has more range of motion in its controls than an Airbus!!!!!!!!!!!!!!!!!!!!!!!!!
                      Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                      Comment


                      • #12
                        Although some pilots i know says that Airbus' sidestick is more comfortable, you only use it for a little time then autopilot takes over.

                        For me, Boeing's traditional yoke system is better. (OK im a bit biased.)

                        Comment


                        • #13
                          But you've all forgotten the single most important aspect of sidesticks.......












                          ........Boeing pilots can't eat their dinner on a tray in front of them !
                          If it 'ain't broken........ Don't try to mend it !

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                          • #14
                            I'm sorry I missed this thread back then, but I'll offer my version now.

                            First, a little bit about control forces and displacement. As an example I'll use the elevator but a similar reasoning may be made for the rest.

                            The force needed to move the elevator is proportional to the displacement from it's natural equilibrium position and to the airspeed squared. PERIOD.

                            No matter what type of control system the airplane has, someone or something will have to make that force, be it that you grab the elevator directly with your bare hands or that it is an hydraulic piston acting according to the orders of a flight computer.

                            Now, the forces that the pilot has to do differ depending on the type of control system.

                            So, in the beginning, and still in use, the control system is mechanical, with the stick or yoke linked to the elevator by pull cables or push rods, in a way that the movement of the elevator is proportional to the movement of the stick or yoke.

                            In this way, the force needed to be applied on the stick or yoke to displace the elevator is proportional to the force applied by the system on the elevator, that is proportional to displacement and speed squared. And as said just before, the displacement of the elevator is proportional to the displacement of the stick or yoke.

                            Now, this has a number of good characteristics:

                            A given displacement of the elevator (and hence of the stick/yoke) always makes the same change in angle of attack, regardless of the speed and the force needed to make such a displacement. In that way, the distance that the pilot displaces the stick/yoke is a direct feedback for angle of attack.

                            Because the force on the elevator (and hence on the stick) is proportional to the the speed squared and the lift is also proportional to the speed squared, the force applied to the elevator (and hence to the stick/yoke) is proportional to the increase in Gs, regardless of the speed and the displacement needed to do such a force. There is a key handling characteristic that is called pound per Gs. It is very important because the pilot has to apply a given force BEFORE the airplane sustain a given G, and in that way the force applied is a direct feedback for Gs. A lot of force means a lot of Gs and a risk to break the plane.

                            Finally, the relationship between force and displacement gives a direct feedback of speed. If you need to make a lot of force to displace the yoke a little you are going fast, if you need to make little force to displace the yoke a lot (mushy controls) you are slow.

                            That may sound complicated, but if you think a minute it's the same than a steering-wheel in a car.

                            Turning the steering wheel a certain angle will make the car turn with the same radius (assuming the car doesn't skid) regardless of the speed or of how much force is needed to move the steering-wheel that much.

                            Applying a given turning force on the steering wheel always puts the car (and the occupants) under the same centrifugal force (or lateral Gs) regardless of the speed or of how much the steering wheel is turned to get that force. Again, this is a key characteristic because that force gives a direct feedback to the driver of how close is the car from skidding.

                            Finally, when you go slow (but not too slow) you can turn the steering-wheel a lot with little force, and when you go fast you need a good force to turn it just a couple of inches. So the relationship between displacement and force is a feedback for speed.

                            Enough for mechanic controls. Then came hydraulics, or better servo-hydraulics.

                            In servo-hydraulic systems the yoke moves a servo-valve which proportionally controls the displacement in the hydraulic piston that moves the elevator. The problem here is that moving a servo-valve doesn't require any force and any force applied to the elevator doesn't transmit to the servo-valve and hence to the yoke. Bye-bye feedback.

                            This is very dangerous, because the pilot could for example displace the yoke enough to apply a lot of Gs and realize only when the plane (and the pilot itself) is already under those Gs, or when the plane breaks under those excessive Gs.

                            This problem is so serious, and the mechanical system gave such a good feedback, that the airplanes manufacturers, all of them (including Airbus in the early models), decided to design something that they called "artificial feel" and that would be the equivalent of the "force feedback" in modern PC joystics and steering-wheels. And they designed the artificial feel so that the forces on the yoke were proportional to the displacement and to the speed squared! Not by chance that's exactly the same than the mechanical controls.

                            Then came fly-by-wire.

                            Fly-by-wire means that the control that the pilot manipulates, regardless of what it looks like, sends digital signals to a computer which then send orders to a hydraulic system to move the elevator. The "dictionary" in the flight computer that translates the the pilot's input into commands to move the elevator is called "flight control law", or control law for short. And here is where manufacturers start to diverge.

                            The Boeing 777 is fly-by-wire. But the control law is simple: The computer will command the elevator to move proportionally to the displacement of the yoke, just like in the mechanical or hydraulic systems. Also like in mechanical and hydraulic systems, the force needed to displace the yoke that much will be proportional to the displacement and the speed squared, of course again with the help of an "artificial feel" system.

                            Airbus followed a different philosophy. They decided to take advantage of the power of computers and the flexibility of software programs to create some advanced features.

                            To begin with, they went for a joystick type of control instead of a yoke. In my opinion, that's the most irrelevant difference (unless there are some issues with the range of motion available).

                            Then, they got rid of the "artificial feel" system. The joystick is simply a spring-loaded self centering joystick.

                            Now, with a small control that has no mechanical linkage or hydraulic servo-valves and doesn't even has a force feedback system, the whole device got small enough to be placed virtually anywhere. So they put it at the side thus creating the side-stick. That location has several advantages: It gives the pilot an easier access too and egress from his seat, it lets the pilot hold a chart, a laptop or a tray of food on his lap, it lets the non-flying pilot to cross his legs, and it doesn't obstruct the view to any portion of the instrument panel.

                            Because the spring-loading and lack of artificial feel, now force and displacement of the joystick are always proportional one to the other. That means that force and displacement now feed back the same piece information, instead of three different pieces of information as the other cases (including the fly-by-wire B-777). Now which piece of information would that be will depend on the design of control law.

                            Airbus decided not to keep the proportionality between the joystick displacement and the elevator displacement, as had been the case up to then. Instead, they decided that the computer will move the elevator as needed to achieve a G load proportional to the joystick displacement. That means that the same joystick displacement will produce different elevator displacements in function of things such as speed, aircraft weight, and bank angle.

                            So now the Gs are proportional to the joystick displacement and to the force applied to the joystick. So now both joystick force and joystick displacement are two different feedback for Gs. The feedback for angle of attack and the feedback for speed are gone.

                            So to prevent that the pilot inadvertently stalls or overspeed the plane, they programmed restrictions in the control law. If the pilot pulls up to command a G load that, at the current speed, would make the airplane stall, it will not comply and will command a pull up just before the stall. If the pilot pushed down into a dive or advances the throttles in a way that would cause an overspeed, the computer won't comply and will pull up to reduce speed before an overspeed happens.

                            Despite being there two different feedback for Gs (joystick displacement and joystick force), perhaps because the range of displacement is small and the control forces are low they added also a restriction to the Gs. The computer won't command a pull up past the design max Gs despite of how hard the pilot pulls up trying to do so.

                            With the pilot pulling up hard to avoid a mountain, the computer will fly into the mountain rather than letting the plane break-up due to overstress or stall.

                            That restricts the pilot authority, but in many cases can be good.

                            For example, if the pilot finds himself flying into a mountain he can simply apply full power and pull up to the stops without worrying about stalling or breaking the plane. The computer will pull up as much as it can be done without that happening. If that doesn't save the day, nothing will. In any of other systems, the pilot has to "fine tune" his pull-up to achieve that optimum performance. If he just scares and pulls-up hard he can stall and crash in a situation where a max performance escape maneuver might have saved the day. It's like the ABS in your car. It won't let you brake so hard to lock the wheels.

                            Another important advantage of this philosophy is standardization of the handling characteristics: Moving the side-stick one inch back always requires 0.5 pounds of force and always produce a 1.2Gs pull-up regardless of whether the plane is going fast or slow, is heavy or light, has the center of gravity on the forward or aft limit, or it is a small A 319 or a huge A 380. (the numbers there are not real, I just made them up for the example). That simplifies training and transition between types a lot, and hence saves money to the airlines.

                            Another difference is that the side-stick is out of the field of view, specially the other pilot's sidestick, and the side-stick are not linked one to the other so when one pilot moves his joystick the other joystick just stays still. That removes the visual feedback for the non-flying pilot to know what flight control inputs the flying pilot is commanding.

                            Finally, another difference between the Boeing philosophy and the airbus philosophy is how the automation (autopilot and autothrust) controls the systems.

                            In the Boeing philosophy, the autopilot and autothrottles move the yoke and the throttles like the human pilot would, and then the yoke and throttles transmit the commands in the same way as if it was the pilot who had moved them. This gives the pilot the visual feedback of what the autopilot is doing. The human pilot actually sees the yoke move back when the autopilot pulls-up, and the throttles move forward when the autothrottle adds power.

                            In the Airbus philosophy the autopilot and autothrust actuate directly on the systems bypassing the yoke and throttle levers. The autopilot tells the flight control computer to pull up, the side-stick doesn't move. The autothrust tells the FADEC to increase power, the throttle levers don't move. So here again, a visual feedback is removed.

                            It is important to note that this difference have nothing to do with intrinsic characteristics of the side-stick or the fly-by-wire concepts.

                            The Cirrus SR-20 is a general aviation piston single that is flown using a side-stick, but it's not fly-by-wire. That side-stick is mechanically linked to the elevator, so it shares all the feed-back characteristics of the mechanical control systems.

                            The Boeing 777 is fly-by-wire and uses a yoke that emulates a mechanical control system. They could have chosen to use a side-stick and still emulate a mechanical control system.

                            Most Airbus use a sidestick with no force feedback and that doesn't move when the other pilot or the autopilot make control inputs. They could have kept those concepts and the same control laws with a yoke instead of a side-stick.

                            So whoever at Boeing wrote that, he was very careful to word the sentence as to be correct:

                            "Existing commercial side sticks offer no visual or tactile cues to the pilot and must have restrictive performance limits."

                            "Existing commercial side sticks" basically means "Airbus side-sticks".

                            And yes, Airbus sidestick, coupled with Airbus flight laws and the other design features mentioned, offer no visual an little tactile cues to the pilot and have restrictive performance limits.

                            Still, a yoke could be like that too, and a side stick doesn't need to be like that.

                            Those are not intrinsic characteristics, but design decisions.

                            And of course, that doesn't mean that "existing sidestick" are worse than "existing yokes". Neither the contrary.

                            --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                            --- Defend what you say with arguments, not by imposing your credentials ---

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                            • #15
                              Thanks Gabriel, very informative and through.

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