Originally Posted by gums
I saw your neat graphic for the phugoid, but seems the condition for the model was thrust equals drag.
I described the initial condition as level flight, constant speed, i.e. thrust equal to drag. What matters for the phugoid is the thrust set at t=0, which exceeds drag by sin 8.5 degrees times weight.
I would have preferred a graph of unrestricted FPA using the configuration and commanded gee/AoA.
Sorry, but I must be misunderstanding what you are saying here. The FPA is unrestricted and the graph is independent of configuration. The only 'aerodynamics' that goes into the calculation is the fact that at constant AoA lift is proportional to airspeed-squared. "gee" is not commanded but is proportional to airspeed-squared. AoA is 'commanded' to remain constant throughout.
As with others here, I think the phugoid considerations for the 'bus FCS had negligible effects upon the incident.
What matters is not the phugoid but the control law that reduces the commanded AoA when speed decreases and/or pitch increases.