lag, instruments and AoA one mo' time
Salute!
- As mentioned, there can be lag in control surface position versus control stick/yoke/wheel position and rate of application ( hereafter referred to as "stick").
"lag" can be implemented to get a better handling jet or to keep you from ripping the wings off, and it can be modified by pure mechanical doofers in the actuators, feedback of surface forces in the actuator, or firmware/software.
For example, observe the Viper or Typhoon at your next airshow ( two FBW jets). Note how quickly the jet stops rolling. Lag? Yep. The roll command implements a lag filter when rolling into a bank, and a reduced lag filter when relaxing the stick. So simply relaxing pressure, or deflection of the stick, gets you back to the trimmed roll command or "protected" bank angle that the 'bus has in some laws.
- We must distinguish between "instruments", displays and sensors. Granted, the actual pneumatic sensors on the 'bus may have accurately measured AND displayed the poor data, but many folks call that "instrument failure". The AF crew even calls out " we have no indications". So what does that mean? Is it the sensor or the actual display?
With known unreliable speed at the outset of the story, when did the system ( input device, sensor, display) become reliable again? Is the pneumatic vertical velocity valid? Is an inertial vertical velocity display available to use as a crosscheck? Hmmm....
- AoA, one more time.
Why ignore the AoA sensor inputs for stall prevention/ stall indications/displays? Is the 60 knot speed doofer a poor design implementation versus a simple weight-on-wheels "switch"?
Speed ain't a good thing to use for a stall indication. You can stall at almost any speed in many planes ( high performance jets usually cannot stall when flying at the speed of stink, heh heh, as you hit structural limits before AoA limits). You stall because you exceeded some AoA.
You don't need a full time AoA indication. In the Viper, we only had an AoA "bracket" in the HUD when gear was down, and used it for best approach speed. Lots more accurate than a "speed" we got using our gross weight and configuration. Easier, too, for we single-seat types. Ask 'bird, Retired, Smilin', et al. The U.S. Navy jets had a full time AoA display called an "indexer" that told you to lower the nose or raise the nose. The A-7, F-4 and F-18 of my era when the Earth was still cooling, but aerodynamic principles were well-established, had a full time AoA indication in the HUD.
Stick and/or rudder pedal shakers are neat, as are aural warnings. But we saw the AF crew seemingly ignore the aural indication. Not much re-design effort/testing required to add a "vibrator" to the stick. But would it be valid?
"we have no indications"........
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I always wonder why the new airliners don't have a HUD.
After all, they have only been around since the late 60's.
A HUD is invaluable when landing in poor weather, and it ain't too shabby for basic climb, cruise, descent. Using inertial data for a flight path doofer ( FPM), it's an excellent thing for crosscheck with the steam gauges or cosmic flatscreen displays such as the 'bus and others utilize. Seeing the FPM caged at the bottom of the HUD is a great indication that you are descending, regardless of your pneumatic system displays. Then there's the pitch lines to show the actual angle your jet is flying and pitch attitude if you have a body reference symbol ( like your basic attitude indicator). Sheesh, that HUD will spoil your crosscheck in a hurry, and it takes lottsa discipline to include the steam gauges.
Lastly, I do not go with the yoke/wheel crowd. For some, the visual or tactile feedback might help. But mostly you see what's happening on the displays or outside the windshield and ask the other guy what he's doing if you don't understand what's happening. BTW, I am not a true dinosaur, I evolved into a bird.