Today's posts have left me with a feeling of deep unease. I don't want Boeing to be brought to its knees, though I imagine there are more than a few people sharpening their swards. The whole slew of issues is desperately saddening, but with a lifetime's passionate interest in flying, electronics and mechanical systems, I don't see how the MAX will ever be anything but a compromise - at least with existing hints of corrective plans.
I suggest, without qualification, that MCAS should not have direct control of the Horizontal Stabilizer, but by definition, it has to augment control, so my very suggestion implies it has to be scrapped altogether. How one would stop the engine cowlings from flying - without dragging back a lot of the new performance, is something I don't have an answer to.
If STS is allowed to stay, then it seems logical that MCAS could be made to input safely. At the very least I'd want this previously hidden system to leave me in
no doubt it had started to run, and if I pressed the warning, it would not run again until it was reset manually. Sim training for this is an obvious must.
An AoA vane comparator would be high on my list of demands. Having the logic to determine the failed side with a high probability seems doable. Even if it fails to do this, at least the crew would be alerted to make their own decision on the side to use. Not a terribly complex memory item but also not a quick iPad note.
The ground clearance issue might be corrected by a dash 10 type gear extension but I am certainly not suggesting the engines should be returned from whence they came! Someone replied to one of my posts that the wheels were displaced (rearward?) but the Y-Tube seems to show clearly the half scale model extending the (real scale) length/height by 10". It's a mechanism that has to be incredibly robust, the one in the model, a 3D print, left me a tad concerned about it coping with a thumper or two. The answer has to be some kind of leg mechanism since a bay redesign is beyond financial reach. As it is, the aircraft just looks wrong, and I have a gut feeling doing nothing is not an option.
Back to that stabilizer.
Dave's re-reply.
I'd be very surprised if there is/was much scope for redesigning the stab pivot and/or the jackscrew geometry in a way that would significantly reduce the aerodynamic loads on the jackscrew (and therefore on the trim wheel).
As I said, I have no idea why it was ever 'hinged' at the rear. No one in their right mind would do that just to make the mechanism easier to design . . . would they? IIRC, when we gave the Americans the original idea it lead to a stability that allowed supersonic flight. What happened next? Well, it seemed to be doing a great job - until one reads about the fact that when it comes to hand flying, it hasn't actually been put to the test as much as one would have imagined. Also, now and then, it's handed out some surprises which just seem to have been lost in the mists of time - unless you were involved, and then I'd imagine the memories would be rather vivid.
All of us on this forum are aware of the loading issues and desperate attempts at off-loading to crank in some ANU trim, but it seems to me that it would be a far smoother, less demanding system, if it were 'hinged' at least near the front of that vast surface.
Dave's quote, little scope, sums it up perfectly, I might as well suggest moving the wings forward a bit, but an aircraft with a trailing stab would address so many issues, so there has to be a reason it's never been done.
Just supposing the powers that be deem the inability to manually trim a prime design flaw - a scenario that must be in the nightmares of more than a few senior Boeing staff. If that became reality, there is just the possibility that the airframes could be saved from total loss with hydraulic power, the designs taken from other types.
The incredible irony is that the total power required to move that stab is not very great but it is just the means of conveying that power to the tail in an emergency that makes it likely to fail the crews - because of the very method retained from the old, safe, steel cable, days.
When we consider the counterintuitive design issues, there are only a few but they do sum up to being very costly if the job is to be done well. It's vital for the future of Boeing to address these problems with utterly solid remedies; a software rewrite won't come close. The whole world will be watching and I don't envy the folk under that gaze one little bit.
.
.
.