Back to the future one mo' time
Doze has iterated the basic concept of FBW.
Where application/implementation problems come into play is how much "protection" is included in the software or hard-wired analog systems we had in the early years.
- GAINS: When we had mechanical connections like push rods or cables, you could actually feel the aero pressure on the control surfaces. Then we went to "augmented" systems with hydraulics. And then we went to pure hydraulics in just about all military fighters, but not the heavies. There were still mechanical connections for another 30 years for a few control surfaces.
To keep the plane from exceeding aero/gee limits, we had "gains". The pure hydraulic systems that I flew had springs and pneumatic bellows and bob weights and such. You could "feel" what the jet was doing and adapt. One jet that I flew had "protections" - the VooDoo. AoA and gee were monitored, and unless in a pure reversion mode we had AoA "protection" to keep from the dreaded "pitch up", so I was familiar with such when checking out in the Viper 13 years later.
FBW offered the opportunity to increase the "feel", but basically it simply limited the control surface movement and rates to make the jet "feel" like the old days. Ours was a force/pressure system, but the 'bus and Boeing systems have "movement" of the stick/yoke. Big deal. Most of my ilk never yanked the stick about but used small movements or simple pressure ( the hydraulic valves got lots better, and the A-7 had some electronics that used stick pressure to "augment" actual hydraulic valve commands). So checking out in the Viper was a breeze.
- PROTECTIONS: The Viper had real "protections" for both gee and AoA. We had no "direct control laws" unless the jet went out of control and AoA was above 30 degrees. Even then, we could only control the elevator ( stabilators) directly, and rudder/aileron surfaces remained under control of the computers.
Forget the gee protection. The big one was AoA protection, hence my interest in this discussion of the 'bus 340 uncommanded climb.
We did not have a mach protection for obvious reasons, but we did lose one fellow that tried to see how fast he could go. The motor fried, not the airframe.
- AUTOPILOT/NAV connections: This disturbs me more than the modes/laws of the 'bus and the Boeings.
We did not realize that our autopilot could not command above "x" AoA for a year or more. The GD flight control folks were scared about connections with their super FBW implementaion. So we had very limited otto inputs - heading select and altitude hold. That was all. So no flight management system connects or such.
Later jets had an auto throttle system ( Hornet), and I am not sure of the implementation. Most Nasal radiators and some of us in the SLUF and Viper flew AoA on approach and cross checked the speed to make sure we had the correct configuration.
So I get very concerned when I read about all the "protection" modes and the combinations of the nav system and otto and the FBW computers.
As a full-time SLF dude nowadays, I sometimes wish I could ride the jump seat to see how good the pilots are when Hal or Otto go FUBAR.
Sorry so long a post, but had to get this off my mind.