FBW and pilot controls
One mo' time
We have returned to many discussions from the AF447 thread.
Once the decision is made to move from a control stick/wheel that provides mechanical connections to the jet's control surfaces, we must consider the implementation of the controls.
We went thru this in the 50's when hydraulic valves at the base of the stick/wheel controlled pressure to actuators out on the wings or tail. Many commercial jets maintained actual mechanical linkages to the control surfaces, and maybe a few still do. By 1960, only a few military trainers and older designs did that. All we had were valves at the base of the stick/wheel to control pressure to the control surface actuators. Control feedback was extremely artificial, as using springs!!!! No aero force feedback whatsoever. One jet used a bellows to help with backstick pressures in order not to over-gee the plane. But that went away by the 70's.
Then we came to FBW.
Do we mechanically connect dual-control jet sticks/wheels? Do we implement some kinda feedback as to how much we pilots are commanding of the control surfaces? Do we use a stick that moves or simply use stick pressure? and the beat goes on.
And then we had the "protections" and the autopilot and autothrottle connections to our flight control systems. GASP!!! To this day I am amazed at all the modes and control laws of the systems in operation today. Even a techno-geek pilot such as myself gets confused. And make no mistake, I would appreciate a simple control law that closely resembled what we had in the "old days", like late 60's. Heh heh. This would still require electronic analogs to the old hydraulic valves and feedback springs and such that we had. Hence, we have "gains" that limit control surface rates and total movement depending upon dynamic pressure the jet is experiencing. So only a so-called "direct" control law would resemble the "old days", and even then such an implementation could have problems with over controlling.
From my point of view, mechanically connected flight controls in family models seem like a good idea most of the time. But we still have to engineer the electronic connections to the jet's flight control system. Failure modes and "who has control" issues come to mind. I can tellya that I "helped" many a nugget land during severe turbulence/crosswind landings in one of the "old" systems. Then did same in a FBW system with zero control feedback from the jet or the nugget in the other seat. Know what? No difference. The AF447 situtation was different, and I believe that control position feedback might have made a difference in the PNF reactions ( although he mentioned a few times "we're climbing", etc).
As with Asiana, et al, it's up to the "pilot in command" to harp on the nugget and/or take control himself when things aren't going right. Regardless of the control implementation, it's up the aircraft commander to do as much as possible to ensure a safe recovery from an unusual situation or a sloppy approach or...... This requires knowing what the jet is doing versus what it's supposed to be doing, no matter what the "other guy" is doing. There should be a clear chain of command, and if the aircraft commander decides to take action, then it is mandatory to do so regardless of the rank or experience of the other guy. Any objections to that point of view?
Last edited by gums; 8th August 2013 at 20:29.