Boeing 737 Max Software Fixes Due to Lion Air Crash Delayed
The issue here is that certification rules require that increasing pull pitch controller input must be needed to command ever increasing AOA / normal load factor. Without MCAS there are 737MAX flight conditions where AOA / normal load factor can increase with constant column pull such that the pilot would need to relax the pull force in order to avoid exceeding their target nose up pitch maneuver. This characteristic does not comply with certification requirements and thus MCAS was introduced to assure that a steady increase in AOA / normal load factor requires a steady increase in column pull force.
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Boeing favors a relatively simple solution that would primarily reduce the power and, under some circumstances, probably the repetitive nature of the flight-control system in question, called MCAS
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Am I right in my interpretation that they will still rely on a single AOA sensor?
It would seem logical at first blush that the only sane fix here for such a critical sensor is to add two more AOA sensors and use a voting system (or other way to sanity-check the data) as per the 747's triple INS setup as RatherBeFlying mentioned above?
It seems that any other solution which still relies on one AOA sensor is likely to simply end up a poor-quality patch job, assuming no other sensor input is available that can be relied upon should the sole AOA sensor go faulty.
/Alex - not qualified to talk on this matter at all, so take my post with the bucket of salt it deserves...
It would seem logical at first blush that the only sane fix here for such a critical sensor is to add two more AOA sensors and use a voting system (or other way to sanity-check the data) as per the 747's triple INS setup as RatherBeFlying mentioned above?
It seems that any other solution which still relies on one AOA sensor is likely to simply end up a poor-quality patch job, assuming no other sensor input is available that can be relied upon should the sole AOA sensor go faulty.
/Alex - not qualified to talk on this matter at all, so take my post with the bucket of salt it deserves...
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Thank you Gums! If I may be so bold: What was the design philosophy on the F-16 early on? Did it require a "chorus" of sensors to pass data on re AOA, airspeed, etc to render a decision?
As with many complex systems it appears to this observer that "post marketing experience" with the 737 Max has uncovered a design flaw....
As with many complex systems it appears to this observer that "post marketing experience" with the 737 Max has uncovered a design flaw....
Salute averow
Our AoA data for the FBW system used two conical sensors and one hemisphericl probe that used differentail air pressure for pitch, yaw and total pressure. The pressure probe data was decoded in a special box, and the mechanical AoA values were basically sent to the main FLCS computers ( four of them).
I may have to get with one of the guys over on the F-16.net forums to verify my data, but seems I recall middle value logic until down to two sensor input, then the most benign value.
Our system used only three of the computers until one went tits up, and we brought in the 4th. Looking back, we had a very graceful degradation until all was lost.
Unlike the 737, we depended entirely upon the FBW and associated computers that interpreted our control inputs and then moved the control surfaces. But the 737 was supposed to be aerodynamically a "normal" airplane and not intentionally unstable as was the Viper ( below 0.95M +/-).
It looks to me that the newer variations of the 737 are more like the VooDoo I flew a half century ago. That thing got "light" on the stick when you got close to the critical AoA, and if you kept pulling then the plane increasd AoA all by itself with no stick command or even forward stick. Wahoo!!!
The VooDoo had two AoA and gee limiters depending whether you had the autopilot engaged or not. Also had a stick pusher for rate limiting and actual AoA limits. Worked for me. And all that was back in 1965 or so. Our roll "feel" was only some springs and no change if we were at 300 knots or 700 knots. Pitch was helped by a bellows to account for CAS and a bob-weight to help for our pitch rate commands at higher gee. In short, nothing fancy like we see with the 737 feel system and STS and now the MCAS.
Thanks for the questions...
Gums sends...
Our AoA data for the FBW system used two conical sensors and one hemisphericl probe that used differentail air pressure for pitch, yaw and total pressure. The pressure probe data was decoded in a special box, and the mechanical AoA values were basically sent to the main FLCS computers ( four of them).
I may have to get with one of the guys over on the F-16.net forums to verify my data, but seems I recall middle value logic until down to two sensor input, then the most benign value.
Our system used only three of the computers until one went tits up, and we brought in the 4th. Looking back, we had a very graceful degradation until all was lost.
Unlike the 737, we depended entirely upon the FBW and associated computers that interpreted our control inputs and then moved the control surfaces. But the 737 was supposed to be aerodynamically a "normal" airplane and not intentionally unstable as was the Viper ( below 0.95M +/-).
It looks to me that the newer variations of the 737 are more like the VooDoo I flew a half century ago. That thing got "light" on the stick when you got close to the critical AoA, and if you kept pulling then the plane increasd AoA all by itself with no stick command or even forward stick. Wahoo!!!
The VooDoo had two AoA and gee limiters depending whether you had the autopilot engaged or not. Also had a stick pusher for rate limiting and actual AoA limits. Worked for me. And all that was back in 1965 or so. Our roll "feel" was only some springs and no change if we were at 300 knots or 700 knots. Pitch was helped by a bellows to account for CAS and a bob-weight to help for our pitch rate commands at higher gee. In short, nothing fancy like we see with the 737 feel system and STS and now the MCAS.
Thanks for the questions...
Gums sends...
Last edited by gums; 12th Feb 2019 at 01:54. Reason: typos and readability
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how about more rubber and bigger brakes so that it doesn’t need more runway than a 767? Oh wait, the gear can’t be longer because that’s where the wheel wells are. Maybe fewer humps in the floor and a JS that isn’t 90 degrees? How about single channel go around too? The 737 is a brand new record player with a digital display.
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Gums, Betcha forgot about your downsprings on your VooDoo.
Other than the pusher, it had a lot in common with the Phantom in its design concept.
Overall, when I look at the design concept for the NG and Max, it seems that the control forces can get awfully high, and when you begin to get into cable stretch force levels, you lose control authority.
As FCEng84 pointed out elsewhere, the elevator is hinge moment limited as to how much deflection it can generate and that too limits a pilot's ability to control his aircraft
I have read that when stall AOA threshold is reached, the control system further increases control forces in order to make it harder to pull further into a stall. How do you spell more loss of control authority?
On the surface, it seems logical, but it all works to take away a pilot's ability to control his aircraft.
Does a transport really have to fly like a truck?
Other than the pusher, it had a lot in common with the Phantom in its design concept.
Overall, when I look at the design concept for the NG and Max, it seems that the control forces can get awfully high, and when you begin to get into cable stretch force levels, you lose control authority.
As FCEng84 pointed out elsewhere, the elevator is hinge moment limited as to how much deflection it can generate and that too limits a pilot's ability to control his aircraft
I have read that when stall AOA threshold is reached, the control system further increases control forces in order to make it harder to pull further into a stall. How do you spell more loss of control authority?
On the surface, it seems logical, but it all works to take away a pilot's ability to control his aircraft.
Does a transport really have to fly like a truck?
Time to stop when too many aerodynamic band-aids required
It looks like the 37 has finally been stretched [promoted] to its level of incompetence.
Two possible ways out:
Two possible ways out:
- Shorten the 87
- Use Embraer 195 as a base design.
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WeeMonkey
Pimped up 737-800 , the P8.
It will be interesting to see what they plan to do low level with it.
The power power coupling with rapid pwr changes is nasty if one is used to a P3 I suppose.
The slow trim with flap up is also an issue if yanking and banking at low level. Gets quite heavy.
I know it is supposed to do most of its work from 30 000 feet , but I suspect we will see them at 100 feet up the fjord as well?
It will be interesting to see what they plan to do low level with it.
The power power coupling with rapid pwr changes is nasty if one is used to a P3 I suppose.
The slow trim with flap up is also an issue if yanking and banking at low level. Gets quite heavy.
I know it is supposed to do most of its work from 30 000 feet , but I suspect we will see them at 100 feet up the fjord as well?
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as I vaguely recall- ONE of the requirements by the navy was low level flight in bad weather on one engine- and was demonstrated with a standard 737 prior to contract award.
and see also
https://www.seattletimes.com/busines...ng-submarines/
Boeing’s P-8 is the 737 with missiles, sonar and a specialty in hunting submarines
and see also
https://www.seattletimes.com/busines...ng-submarines/
Boeing’s P-8 is the 737 with missiles, sonar and a specialty in hunting submarines
737-P8 sub hunter article
https://www.seattletimes.com/busines...ng-submarines/
and post numbers 12 and 13 - answer = 200 feet and maybe even lower
737-P8 sub hunter article
https://www.seattletimes.com/busines...ng-submarines/
and post numbers 12 and 13 - answer = 200 feet and maybe even lower
737-P8 sub hunter article
Last edited by CONSO; 12th Feb 2019 at 23:19. Reason: provide links