HN39,
Thanks for grasping the nettle and reminding me and others that the designers have to make provisions for the complications of phugoid oscillations, as confirmed by the Airbus input to the NTSB report on the Hudson River accident. That seems to be the explanation of the apparent shortfall of achieved AoA at Habsheim. My tentative suggestion that it might be a measure to allow sudden bank applications without the need to drop the nose can probably be discounted.
Hi FCSoverride,
That strikes me as a very elegant description of phugoid (some of us have been there in conventional a/c).
I think you've explained why it doesn't happen in Normal (C*) Law, and why provision has to be made for it in Alpha-Protection mode.
Quotes from gums
"I thot I saw a reference to a 'bus driver that tried to duplicate the crash. At a safe altitude, of course, and with lottsa prior planning. Reference requested."
Yes, see the BEA report, first part of Annexe X (text in French):
Habsheim F-GFKC
The flight test was performed at around 2000 ft agl, and the traces of the main parameters are superimposed on the equivalent Habsheim ones. A bit challenging to interpret.
"...the jet maintains a one gee Nz " command" corrected for attitude if the stick is in neutral ( hands off)."
In Normal Law, yes (also compensated for bank, BTW). But we are discussing Alpha-Protection mode here. The EFCS targets an AoA of alpha-prot with neutral stick, and alpha-max with the stick fully aft. Nz doesn't rule.
"So after takeoff at a 15 degree or so climb attitude, you won't have a one gee seat of the pants, but will be slightly less."
Correct, which is why, to avoid tripping over the trigonometry, I wrote "roughly 1g" in the following:
"...after the flare manoeuvre has been completed, and the new FPA has been established. Then the Nz can return to (roughly) 1g. During the flare (i.e., the period when the FPA is increasing), the increased "g" causes an increase in Valpha-max."
You can't change the trajectory of any moving object without changing the balance of forces - in this case, with a delta of lift, generating a delta of Nz.