Originally Posted by
edmundronald
MechEngr,
You have very cogently made the case -by reasoning- for the need for something like MCAS; of course if a new force is introduced it would be desirable to offset it if one wishes to use an extant control model.
However you haven't really explored the issues which lead to this need, in other words what piloting a MAX without MCAS would look like.
Also it is not at all obvious -in fact extremely improbable- that a given control model can be perfectly grafted on a different airframe by means of a simple mechanical accessory. Of course one could make the case that the mechanical aid creates a similar linearised behavior around equilibrium, bu it would still be required to demonstrate that the relinearised zones share the same volumes of state space, and that these volumes are the only regimes which are of practical importance during flight. Hence it would be very difficult to demonstrate by maths alone, without extensive testing that the MAX shares a control model with the NG and thus can share its certification. There is no evidence to date of the results of such testing.
My understanding that under current regulatory règimes for civilian aircraft, acceptance of the airframe design WITH MCAS is conditioned on the behavior WITHOUT MCAS. Namely if without MCAS the airframe cannot be flown easily ie. can tend to stall or dive or do other wierd things, then the design would be classed as necessitating active control (MCAS) and couldn't be certified. Which is why Boeing so prudently talks of "linearizing" stick feel.
I continue to believe that in a rush to acquire a grandfathered certification, Boeing was overly economical with the truth in its descriptions of the 737 dynamics, which explains Boeing's reluctance to reveal the exact design goals of MCAS.
Most of the pilot readers here would appear to have no issue with MCAS certification if it were "just" a stick-pusher, but if it is a more complex entity as now seems likely, then a more careful certification process seems necessary.
Edmund
The question is about what it would feel like. I think it would feel as much like an NG at a similar load as anything because pilots spend so little time at high AoA and also little time hand flying that they have no good basis for comparison. We already have record of a flight without MCAS in the first Lion Air situation non-crash flight. The pilots made no comment on any difficulty of hand flying besides the obvious loss of electric trim.
You cannot use a stick pusher to change the balance of aerodynamic forces on the the plane, which MCAS does and a stick pusher does not. And if that stick pusher had the same authority to apply full-down elevator with as much force on the column as MCAS produced because, for the same AoA system malfunction, the controls felt the plane was in a deep stall, there would still be the same crashes.