PPRuNe Forums - View Single Post - AF 447 Thread No. 8
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Old 21st Jun 2012, 01:27
  #1360 (permalink)  
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Join Date: Jun 2009
Location: florida
Age: 81
Posts: 1,610
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Good curve fit, 'nuts.

A year or more ago I raised the issue of "standby gains" to use a given value for dynamic pressure should the normal sensors go off to wonderland or the system deems the values FUBAR. Unfortunately, the 'bus laws are not designed to provide the AoA/speed "feeling"most pilots are used to. Only time we had that in the Viper was gear down, and even that mechanization was a kludge.

The 'bus laws are primarily a Nz command ( just as ours were, and best I can tell) and looks to me that AoA and other inputs only come into play when approaching a stall AoA. And then the system appears to ignore AoA if the dynamic/static pressure inputs are deemed to be unreliable ( and the infamous 60 knot deal), or we are in sub-mode "c", of mode "b", and the beat goes on.

As 'doze has pointed out over and over, and on end, our FLCS was designed for a different mission, but I can tell you that we would like to have had an airspeed/dynamic pressure feedback when gear up to "feel" more like a normal jet. Our feel was strickly biased according to the commanded Nz we had set using a roller wheel or the hat switch on the stick. let go of the stick and the jet assumed the "trimmed" gee, and rather aggressively, heh heh.

@ rouli

Probably the best flight instrument ever invented for us was that flight path marker in the HUD. Ooooops, the 'bus didn't have one. We had it back as far as 1968 - 1969 in the A-7D. No air data required. The sucker used inertial data only, and showed where the jet was gonna impact the ground or climb above the ridge or.... Invaluable for an instrument approach. And with AF447, it would have shown that the aircraft velocity vector was approaching zero pitch well before they flew into the stall. My lef failure video shows the ILS "cross bars" which I used to help in the dubious WX I had to deal with. You can also see where I mistakenly had my vector slightly short of the runway, as I expectd it to move down the runway when I got close and "flared". Hell, was 30 knots above approach speed, but happy I still had roll control.

http://www.sluf.org/warbirds/lef-landing.m4v

For now, I can still see a procedure change and maybe a tweak to the 'bus flight control laws and reversion sequence.
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