Static stability becoming relaxed/unstable has nothing to do with the empennage - so increasing the size of the elevators is not an avenue of escape. Probably nor is any other active alternative to MCAS - as certifiers may deem it susceptible to new issues in a similar vein to MCAS - indeed I think it is a direct contravention of FAR25 - which stipulates all commercial aircraft must be longitudinally statically stable.
Reprofiling the nacelle? Not even sure how much that would stop the wing acting like a slotted flap to the nacelle. The nacelle is just too high and too far forward.
Upper surface of nacelle is higher than leading edge of wing.
Could they reprofile the wing so the region aft of the nacelle is much more lift neutral? Don't think it would help at higher AoA anyway even if it were a symmetrical aerofoil profile. Deploying spoilers in the local region aft of the nacelle is no use as that would only make the problem worse - more drag, moving aero chord forward...
It's actually a right clusterf___ of a problem the more I think of it.
It is dawning on me that there is a slim but non-zero possibility that the 737max may never be cleared to operate again - unless Boeing are allowed to do something no other aircraft has been under FAR25. The FAA might buy off on it, but really dunno how that will go down across the rest of the world.
Agree with you 100%. Adding more washout to the wing would only increase the drag penalty and negate an fuel savings achieved over the range the MAX operates. Also, most stabilizers given their symmetrical profile are angled at a negative incidence angle to produce a positive moment at zero alpha w.r.t to the zero lift line. Reducing this angle would increase the pitch down moment at higher alpha but it would still remain statically unbalanced especially at rotation. I'm not sure, but I think most commercial airliners have variable incidence tailplanes but they cannot be adjusted in flight and are determined upon take/off based on weight/balance issues. I don't know the location of the c.g. w.r.t to the z-axis but my guess is spoiler deployment would produce a stabilizing pitch down moment. However, in general, at the low speeds pilots would find themselves in typical high alpha regime flight, the last thing I would want is further reduction in airspeed.
All in all, regardless of all the flaming and back and forth, this whole debacle gives me a very uneasy and sad feeling.
I am starting to lean more and more to this being the reason why MCAS was required and implemented in first place:
§ 25.203 Stall characteristics.
(a) It must be possible to produce and to correct roll and yaw by unreversed use of the aileron and rudder controls, up to the time the airplane is stalled. No abnormal nose-up pitching may occur. The longitudinal control force must be positive up to and throughout the stall.
In addition, it must be possible to promptly prevent stalling and to recover from a stall by normal use of the controls.
(b) For level wing stalls, the roll occurring between the stall and the completion of the recovery may not exceed approximately 20 degrees.
(c) For turning flight stalls, the action of the airplane after the stall may not be so violent or extreme as to make it difficult, with normal piloting skill, to effect a prompt recovery and to regain control of the airplane. The maximum bank angle that occurs during the recovery may not exceed -
(1) Approximately 60 degrees in the original direction of the turn, or 30 degrees in the opposite direction, for deceleration rates up to 1 knot per second; and
(2) Approximately 90 degrees in the original direction of the turn, or 60 degrees in the opposite direction, for deceleration rates in excess of 1 knot per second.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-84, 60 FR 30750, June 9, 1995]
I am with you wrt fear that there is a chance that MAX "as is" is possibly doomed....
I was wondering whether FAR 25.203 compliance was contingent upon Unaugmented Stability & Control characteristics when I happened upon 26.672b and 26.671
25.672 Stability augmentation and automatic and power-operated systems.
If the functioning of stability augmentation or other automatic or power-operated systems is necessary to show compliance with the flight characteristics requirements of this part, such systems must comply with §25.671 and the following:
(b) The design of the stability augmentation system or of any other automatic or power-operated system must permit initial counteraction of failures of the type specified in §25.671(c) without requiring exceptional pilot skill or strength, [b] by either the deactivation of the system
, or a failed portion thereof, or by overriding the failure by movement of the flight controls in the normal sense.
(c) The airplane must be shown by analysis, tests, or both, to be capable of continued safe flight and landing after any of the following failures or jamming in the flight control system and surfaces (including trim, lift, drag, and feel systems), within the normal flight envelope, without requiring exceptional piloting skill or strength. Probable malfunctions must have only minor effects on control system operation and must be capable of being readily counteracted by the pilot.
(1) Any single failure, excluding jamming (for example, disconnection or failure of mechanical elements, or structural failure of hydraulic components, such as actuators, control spool housing, and valves).
(2) Any combination of failures not shown to be extremely improbable, excluding jamming (for example, dual electrical or hydraulic system failures, or any single failure in combination with any probable hydraulic or electrical failure).
I'm assuming unreliable AOA and pitot-static data contributing to unreliable velocimetry leading to persistent activation of SAS in the presence of erroneous data counts as a probably malfunction. So, it expressly prohibits deactivation of MCAS in the event of a failure to recover. Doesn't disengaging the cut out switches count even though this is a sensor failure contributing to SAS activation rather than SAS failure. Of course, this may just be semantic argument and I'm missing something