OldAeroGuy
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 2:20 pm

ArgentoSystems wrote:
You don't understand what "control lightening means". Normally if you are pitching up and you let go of elevator control, the airplane will return to level flight. Control lightening means aircraft loses this tendency to return to level at higher angles of attack. It will just stay at this high AoA if you let of of the controls. This new position becomes it's local stable point. Is it stable at that point? Yes. Is that a good stability? I'll let you figure out the answer.


The condition you are describing is an airplane that is neutrally stable.

For a stall handling demonstration, the airplane is trimmed by adjusting the horizontal stabilizer at 1.3 times the stall speed. Speed is then decreased by pulling on the yoke. The airplane must exhibit a steadily increasing pull on the stick as speed is reduced. Let's say the pull is 3 lbs for a 5 kt speed. reduction. If the stick is released at any point, a stable airplane will pitch down and will recover near the original 1.3 times stall speed point.

In the example above, if the stick force decreased from 3 lbs for 5 kts to 2 lbs for 5 kts at some point during the stall approach, that is "stick lightening". If the stick is released at the point the stick force gradient changes, the airplane will pitch down and recover near its original trim speed, 1.3 times the stall speed. The airplane is still stable but the stick force gradient break means it all not pass FAR 25.203.

If the stick force goes negative (the pilot has to push) for a 5 kt speed decrease during the stall approach, the airplane is unstable.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
OldAeroGuy
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 2:27 pm

kalvado wrote:
Correct me if I am wrong, but MAX wing is an NG wing, and there should be less surprises, not at the outboard portion of the wing...


For a swept wing, the outboard portion of the wing is influenced by the inboard portion. The new nacelle and its position affects the inboard wing and thus impacts the outboard wing.
Last edited by OldAeroGuy on Sat Apr 27, 2019 2:39 pm, edited 1 time in total.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
OldAeroGuy
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 2:39 pm

[quote="ArgentoSystems"
Either way, judging from the amount of intervention that MCAS was designed to do, this behavior was not as innocent as you and OAG are trying to portray.[/quote]

I am relying on the pilot comments after stalling the MAX with MCAS off in the simulator and the lack of redundancy in the whole MCAS system, either MCAS.v1 or MCAS.v2. If the MAX was "inherently unstable" as some have said, the whole MCAS system would be much more complex.

https://aviationweek.com/commercial-avi ... lator-demo

"A full aerodynamic stall with the MCAS inoperative is another exercise pilots experience in the MAX engineering cab simulator. “We reduced thrust at 5,000 ft. and slowed the aircraft at about 1 kt. per sec. We were at a midrange cg [center of gravity] with gear, slats and flats up. We trimmed until we reached 30% above stall speed and then just continued to ease back on the control wheel,” one of the pilots says.

“Pitch feel was natural, progressively increasing as airspeed decayed. Somewhere between the audible low airspeed warning and stickshaker, I felt the slightest lightening on control pressure in my fingertips. Quite candidly, if I had not been watching for it, I don’t think I would have noticed any difference between the MAX and the Next Gen [NG] models. I kept pulling back through stickshaker, then buffet, then elevator feel shift [a function that doubles the artificial control feel forces near stall] and finally until the yoke was buried in my lap. The nose just flopped down gently at the stall, and I initiated recovery as I would in most other airplanes I’ve flown,” he adds."
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
IADFCO
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 2:57 pm

morrisond wrote:
WPIAeroGuy wrote:
Absynth wrote:

It's pretty clear by now morrisond and OldAeroGuy are either engaged in astroturfing or self identify with Boeing to the point there is no point to argue with them. Claiming certification requirements for flight control and aerodynamic behaviour are not relevant to the question whether a plane is safe or stable is simply absurd.

Especially OldAeroGuy's taking issue with "unstable" in a literal sense and not the legal sense as defined by regulations is painful to watch, and clearly nobody in this forum ever suggested that. It's a red herring that I find frustrating to see propagated for about 20 pages if not longer by now with no moderation to keep this thread factual and on topic. I'm a newbie here with nothing to loose (I'll just continue lurking) and yes I read the moderation post by qf789, about calling out people but there has to be a point where facts are distorted to the point where we arent talking about disagreement of opinion anymore.

Dennis Muilenburg's statement that there was "no technical slip or gap" will be interesting to see play out in the courtroom. A fix to MCAS already proves in itself his statement is a lie on the record. This guy needs to go to jail with the key thrown away. 346 People died under his watch and he's still denying any responsibility for that. Truely sickening behaviour.


It’s because morrisond and OldAeroGuy are correct and are using the aerodynamic definition of stability. Stability has NOTHING to do with control feel. The reason those two are being so ‘stubborn’ is because there’s a huge physical difference between a stable and an unstable plane. The F-117A was unstable. It could not be flown without computer augmentation. Most modern fighters are similar.

Look at it this way. An aircraft stability analysis, based on the classical industry accepted definition of stability, is done without even knowing what the control system looks like. It is based solely off the lift, drag and moment curves of the external surfaces, fuselage, any external components, and thrust effects. For longitudinal stability, this would be looked at with the elevator fixed, and with the elevator floating.

Now, once the aircraft stability is determined, THEN you would look at the control system to make sure the control feel is correct. At this point the MAX was stable: this is not an argument, there is a very precise mathematical definition based on the analysis above. However, the control system needed to be designed to meet the stick feel inputs. I liked Zeke’s explanation several pages back about the cone and the string - the physics linkages could have been designed to increase loading at high AoA, or in a pure FBW plane this could have been baked into the software.

Basically to summarize - the stability of an airplane is an aerodynamic property and is determined independently from the design of the control system. The control system is designed to give the pilot the necessary feedback. The control system does not change the inherent aerodynamic stability of the airplane. To use a converse example: the F-117 is not aerodynamically stable because the control system makes it flyable. It is still unstable, but the control system is constantly applying control surface forces to maintain trajectory. It is controllable, but not stable.


Thank you for saying it a lot better than I could.


I agree -- I also think that two extra items need to be accounted for.

1 - Nonlinearities - The stability concept mentioned by @OldAeroGuy is a *linear* stability definition. If, when the MAX stalls, or perhaps gets close to stall, the flow over the wing is so severely disrupted by the high nacelle that the system becomes nonlinear, the concept is no longer valid, and the aircraft may very well be unstable -- but nonlinear stability is a whole lot harder to assess than linear stability, for example, it may depend on how one got into stall, slowly, quickly, with a large input, a small input, etc. In any case, nobody knows how the wings behave, so this is all at best informed speculation.

2 - Pilot coupling - That stability concept is a "fixed stick" concept, i.e., the pilot does not touch the controls. If the pilot is flying the aircraft, then the proper analysis is a *coupled* pilot-vehicle analysis. The aircraft may be stable on its own, the pilot is behaving "normally", everything is fine until the two meet, and then there might be a *coupled* instability. The change in stick force to achieve a given angle of attack is another way of saying that "pilot compensation is required", and that already costs you two points on the Cooper-Harper Rating handling qualities scale. Is the compensation required "moderate"? another two points. "extensive"? another two, and we are at a CHR=6, which is not good (worst is 10). From what we know, MCAS reduces the level of compensation required, but nobody really knows if that is true, and by how much.

One way to reconcile many opinions in this thread could be: (i) the aircraft is fixed-stick stable, (ii) without MCAS a pilot might inadvertently get into a stall or near-stall regime that, because of the size and placement of the engines, is significantly different than in the NG and handles differently, because of the different pattern of flow separation on the wing. This is all speculation in the absence of hard data, of course.

As an engineer, I'm learning a lot in this thread, especially from the comments of the pilots.
 
morrisond
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 3:03 pm

ArgentoSystems wrote:
morrisond wrote:
ArgentoSystems wrote:
You don't understand what "control lightening means". Normally if you are pitching up and you let go of elevator control, the airplane will return to level flight. Control lightening means aircraft loses this tendency to return to level at higher angles of attack. It will just stay at this high AoA if you let of of the controls. This new position becomes it's local stable point. Is it stable at that point? Yes. Is that a good stability? I'll let you figure out the answer.


If the control force goes to zero then it won't return to the previous in trim position.

But it does not go to zero - control force is still a positive number. It will return to the previous position presumably just not as fast.

well we don't know exactly how much lighter it gets close to stall, or in fact if the force remains positive. Yes theoretically if it remains positive it might eventually come back, but for all practical purposes that 'eventually' might be way too slow. It should also be noted that in this case (the control force is still positive) the tendency of the aircraft to return to level is so weak, that a bit of turbulence might catastrophically upset it.

Either way, judging from the amount of intervention that MCAS was designed to do, this behavior was not as innocent as you and OAG are trying to portray.



I'm not going to dig for it - but I remember someone pages back referring to the certification documents where it remained positive at all times.

What exactly would happen to the plane if it was caught in this control region without MCAS? The controls would get a little light - the plane does become unstable. It's a good idea for the controls not to get light as that takes away a cue that you are getting closer to a critical AOA - but I don't think any pilot would miss the stick shaker, audio warnings and frame buffeting that came after as you got closer to an actual stall.
 
ArgentoSystems
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 3:13 pm

morrisond wrote:
but I don't think any pilot would miss the stick shaker, audio warnings and frame buffeting that came after as you got closer to an actual stall.

And that is the difference between unstable and stable aircraft. One requires pilot's input to return to normal, and the other one does not.
 
ArgentoSystems
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 3:16 pm

OldAeroGuy wrote:
ArgentoSystems wrote:
Either way, judging from the amount of intervention that MCAS was designed to do, this behavior was not as innocent as you and OAG are trying to portray.


I am relying on the pilot comments after stalling the MAX with MCAS off in the simulator and the lack of redundancy in the whole MCAS system, either MCAS.v1 or MCAS.v2. If the MAX was "inherently unstable" as some have said, the whole MCAS system would be much more complex.


Well ok, on one hand is a testimony of a single unnamed pilot. On another hand, 2.5 deg nose down trim. If like he said "I felt the slightest lightening on control pressure in my fingertips. Quite candidly, if I had not been watching for it, I don’t think I would have noticed any difference between the MAX and the Next Gen [NG] models." 2.5 deg nose down trim would not be required. Again, 2.5 deg is a fact. This statement from unknown pilot, maybe not.
 
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par13del
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 3:33 pm

frmrCapCadet wrote:
Or another correct way of saying this: Without MCAS neither of the two crashes would have happened. And it is extremely unlikely that any other crash would have happened. In an in-exact sort of way MCAS as designed made the MAX dangerous. That is why a redesign of MCAS was fairly quick and easy. Or as some have suggested just get rid of it, and warn pilots that at high angles of attack the stick will lighten, and it is possible to stall the plane. (and if an amateur such as myself were improbably in the cockpit as the plane pitched up I suspect I would not be needed for the pilot to know this)

Except that cannot be done because a FAR was put in place years ago for the a/c from which the MAX is a derivative, now if you can get the Non-FAA body that was responsible for the initial requirement to agree to get rid of it for the MAX.......
 
DenverTed
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 3:33 pm

Free the MAX!
 
DenverTed
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 3:36 pm

Would MCAS be required for the NG if it was certified today? How does it handle in that part of the flight envelope? Especially the -600 with the shorter moment arm to the horizontal stab.
 
morrisond
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 4:01 pm

ArgentoSystems wrote:
morrisond wrote:
but I don't think any pilot would miss the stick shaker, audio warnings and frame buffeting that came after as you got closer to an actual stall.

And that is the difference between unstable and stable aircraft. One requires pilot's input to return to normal, and the other one does not.


No - if you relaxed the control column it should naturally get itself out of the stall but it's usually a good idea to push forward to help it along - you don't want to spend that much time that close to stall. It's only unstable once it gets into the stall - just like all other aircraft.
Last edited by morrisond on Sat Apr 27, 2019 4:05 pm, edited 1 time in total.
 
lowbank
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 4:03 pm

The major problem for the MAX is public confidence.

I have spoken to a lot of frequent flyers who will avoid the MAX at all costs as they have lost confidence in the FAA and its relationship with Boeing.

So they may certify it to fly again but some of the flying public remain to be convinced.
Every days a school day.
 
morrisond
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 4:06 pm

DenverTed wrote:
Would MCAS be required for the NG if it was certified today? How does it handle in that part of the flight envelope? Especially the -600 with the shorter moment arm to the horizontal stab.


Unknown - but if you can find the original certification with the stick force gradients that should tell a lot.
 
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SheikhDjibouti
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 4:08 pm

OldAeroGuy wrote:
https://aviationweek.com/commercial-avi ... lator-demo

"A full aerodynamic stall with the MCAS inoperative is another exercise pilots experience in the MAX engineering cab simulator. “We reduced thrust at 5,000 ft. and slowed the aircraft at about 1 kt. per sec. We were at a midrange cg [center of gravity] with gear, slats and flats up. We trimmed until we reached 30% above stall speed and then just continued to ease back on the control wheel,” one of the pilots says.

“Pitch feel was natural, progressively increasing as airspeed decayed....

This report has been quoted here by you (& others) at least seven times now, and in my head I made the same observation each time.

"We were at midrange cg..." - and the 737MAX stalled perfectly naturally even with MCAS disabled.

Well, three cheers for that. :bigthumbsup:

Is that it? Is that good enough?
From the point of view of making things tidy and simple, it's perfect. And best of all, it's all done in the simulator, not a real aircraft. :scratchchin:

What might be the effect of moving the cg to either extreme limit (forward or backwards)?
For a start, it would presumably affect the stab trim start position, and that in itself might affect elevator authority and hence the whole stall scenario.
Is the demonstration at MTOW or something less than that?
How about throwing in a gentle turn as well?

For sure, it would make the calculations and the post-stall analysis much more difficult, but my point is that the aviationweek article is far from proof that the MAX stall behavior is acceptable in all cases. As it stands it is just a PR smokescreen, quoted and re-quoted as if it answers everything. The smart cookies here (such as yourself) probably already appreciate it's limitations, but I cannot say that for everybody here. Hell, I'm not even sure I fully understand whether these factors are significant or not. I'm just asking the question.

What I do know is that I have a Lotus that drives very nicely in a straight line on a dry road with no passengers on board.
It can do lots of other tricks too. It can handle corners faster than I dare attempt. :old:
And on a dry road, in a straight line, I can even take my hands off the wheel, hit the brakes, and everything is just peachy.
But I would want a bit more than that. I want to know that the brakes will act in a predictable manner in all situations, even if the actual stopping distance is increased.
Nothing to see here; move along please.
 
OldAeroGuy
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 4:14 pm

ArgentoSystems wrote:
OldAeroGuy wrote:
ArgentoSystems wrote:
Either way, judging from the amount of intervention that MCAS was designed to do, this behavior was not as innocent as you and OAG are trying to portray.


I am relying on the pilot comments after stalling the MAX with MCAS off in the simulator and the lack of redundancy in the whole MCAS system, either MCAS.v1 or MCAS.v2. If the MAX was "inherently unstable" as some have said, the whole MCAS system would be much more complex.


Well ok, on one hand is a testimony of a single unnamed pilot. On another hand, 2.5 deg nose down trim. If like he said "I felt the slightest lightening on control pressure in my fingertips. Quite candidly, if I had not been watching for it, I don’t think I would have noticed any difference between the MAX and the Next Gen [NG] models." 2.5 deg nose down trim would not be required. Again, 2.5 deg is a fact. This statement from unknown pilot, maybe not.


Please say why you think 2.5 deg is significant. Remember at the MCAS trim rate of .27 deg/sec, it takes about 9 secs for MCAS to travel 2.5 deg.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
WPIAeroGuy
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 4:16 pm

IADFCO wrote:
morrisond wrote:
WPIAeroGuy wrote:

It’s because morrisond and OldAeroGuy are correct and are using the aerodynamic definition of stability. Stability has NOTHING to do with control feel. The reason those two are being so ‘stubborn’ is because there’s a huge physical difference between a stable and an unstable plane. The F-117A was unstable. It could not be flown without computer augmentation. Most modern fighters are similar.

Look at it this way. An aircraft stability analysis, based on the classical industry accepted definition of stability, is done without even knowing what the control system looks like. It is based solely off the lift, drag and moment curves of the external surfaces, fuselage, any external components, and thrust effects. For longitudinal stability, this would be looked at with the elevator fixed, and with the elevator floating.

Now, once the aircraft stability is determined, THEN you would look at the control system to make sure the control feel is correct. At this point the MAX was stable: this is not an argument, there is a very precise mathematical definition based on the analysis above. However, the control system needed to be designed to meet the stick feel inputs. I liked Zeke’s explanation several pages back about the cone and the string - the physics linkages could have been designed to increase loading at high AoA, or in a pure FBW plane this could have been baked into the software.

Basically to summarize - the stability of an airplane is an aerodynamic property and is determined independently from the design of the control system. The control system is designed to give the pilot the necessary feedback. The control system does not change the inherent aerodynamic stability of the airplane. To use a converse example: the F-117 is not aerodynamically stable because the control system makes it flyable. It is still unstable, but the control system is constantly applying control surface forces to maintain trajectory. It is controllable, but not stable.


Thank you for saying it a lot better than I could.


I agree -- I also think that two extra items need to be accounted for.

1 - Nonlinearities - The stability concept mentioned by @OldAeroGuy is a *linear* stability definition. If, when the MAX stalls, or perhaps gets close to stall, the flow over the wing is so severely disrupted by the high nacelle that the system becomes nonlinear, the concept is no longer valid, and the aircraft may very well be unstable -- but nonlinear stability is a whole lot harder to assess than linear stability, for example, it may depend on how one got into stall, slowly, quickly, with a large input, a small input, etc. In any case, nobody knows how the wings behave, so this is all at best informed speculation.

2 - Pilot coupling - That stability concept is a "fixed stick" concept, i.e., the pilot does not touch the controls. If the pilot is flying the aircraft, then the proper analysis is a *coupled* pilot-vehicle analysis. The aircraft may be stable on its own, the pilot is behaving "normally", everything is fine until the two meet, and then there might be a *coupled* instability. The change in stick force to achieve a given angle of attack is another way of saying that "pilot compensation is required", and that already costs you two points on the Cooper-Harper Rating handling qualities scale. Is the compensation required "moderate"? another two points. "extensive"? another two, and we are at a CHR=6, which is not good (worst is 10). From what we know, MCAS reduces the level of compensation required, but nobody really knows if that is true, and by how much.

One way to reconcile many opinions in this thread could be: (i) the aircraft is fixed-stick stable, (ii) without MCAS a pilot might inadvertently get into a stall or near-stall regime that, because of the size and placement of the engines, is significantly different than in the NG and handles differently, because of the different pattern of flow separation on the wing. This is all speculation in the absence of hard data, of course.

As an engineer, I'm learning a lot in this thread, especially from the comments of the pilots.


Excellent addition, and I’m definitely learning a lot too.
-WPIAeroGuy
 
OldAeroGuy
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 4:20 pm

SheikhDjibouti wrote:
For sure, it would make the calculations and the post-stall analysis much more difficult, but my point is that the aviationweek article is far from proof that the MAX stall behavior is acceptable in all cases. As it stands it is just a PR smokescreen, quoted and re-quoted as if it answers everything. The smart cookies here (such as yourself) probably already appreciate it's limitations, but I cannot say that for everybody here. Hell, I'm not even sure I fully understand whether these factors are significant or not. I'm just asking the question.


Hey, I'm all for data. If any contrary data is available that proves the MAX is either neutral or unstable in pitch, I'd love to see it.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
Interested
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 4:22 pm

OldAeroGuy wrote:
ArgentoSystems wrote:
OldAeroGuy wrote:

I am relying on the pilot comments after stalling the MAX with MCAS off in the simulator and the lack of redundancy in the whole MCAS system, either MCAS.v1 or MCAS.v2. If the MAX was "inherently unstable" as some have said, the whole MCAS system would be much more complex.


Well ok, on one hand is a testimony of a single unnamed pilot. On another hand, 2.5 deg nose down trim. If like he said "I felt the slightest lightening on control pressure in my fingertips. Quite candidly, if I had not been watching for it, I don’t think I would have noticed any difference between the MAX and the Next Gen [NG] models." 2.5 deg nose down trim would not be required. Again, 2.5 deg is a fact. This statement from unknown pilot, maybe not.


Please say why you think 2.5 deg is significant. Remember at the MCAS trim rate of .27 deg/sec, it takes about 9 secs for MCAS to travel 2.5 deg.


As someone who has zero engineering knowledge isn't the fact they initially only wanted 0.6 but after flight testing increased to 2.5 very significant?

To me it's 4 times more powerful than they had anticipated they needed?

That doesn't happen without significant reasons surely?
 
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SheikhDjibouti
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 4:28 pm

TTailedTiger wrote:
I wish there was a thread with just the facts. When will this beauty be back in the air where she belongs?

I don't know. Maybe it depends on your definition of "beauty". I'm not sure any of today's jets count as truly beautiful.

Perhaps you speaking more as a Boeing shareholder? In that respect the 737 is indeed $$$beautiful. :spin:

Meanwhile there is bound to be a hold-up whilst they sort out who is going to pay for all this palaver.

Not to mention "consequences for unfounded actions and not waiting for the results of an investigation"

TTailedTiger wrote:
If the investigations conclude that Boeing didn't build a deathtrap and they are not the primary reason for the crashes, then I believe the FAA must punish these entities somehow. The airlines and nations that grounded the 737Max and made dubious claims should have their landing and overflight rights to the US suspended for no less than one year. Any slots held at airports will be revoked and sold to the next qualified highest bidder. These entities need to understand that are consequences for unfounded actions and not waiting for the results of an investigation.

:tapedshut:
Nothing to see here; move along please.
 
kalvado
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 4:42 pm

morrisond wrote:
kalvado wrote:
morrisond wrote:

If the control force goes to zero then it won't return to the previous in trim position.

But it does not go to zero - control force is still a positive number. It will return to the previous position presumably just not as fast.

Probably not quite true. at the very least, there is hysteresis, aka flying on a step. and it is specifically mentioned in @OldAeroGuy favorite document, as far as I remember. and magnitude of that hysteresis may be another interesting thing.


So basically you are admitting you were wrong? Will or will it not return to the previous in trim state with no input? If there was a step in the control force it would go to zero at some point and not be able to get past that point.

Do you know what "hysteresis" is?
 
kalvado
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 4:48 pm

OldAeroGuy wrote:
ArgentoSystems wrote:
OldAeroGuy wrote:

I am relying on the pilot comments after stalling the MAX with MCAS off in the simulator and the lack of redundancy in the whole MCAS system, either MCAS.v1 or MCAS.v2. If the MAX was "inherently unstable" as some have said, the whole MCAS system would be much more complex.


Well ok, on one hand is a testimony of a single unnamed pilot. On another hand, 2.5 deg nose down trim. If like he said "I felt the slightest lightening on control pressure in my fingertips. Quite candidly, if I had not been watching for it, I don’t think I would have noticed any difference between the MAX and the Next Gen [NG] models." 2.5 deg nose down trim would not be required. Again, 2.5 deg is a fact. This statement from unknown pilot, maybe not.


Please say why you think 2.5 deg is significant. Remember at the MCAS trim rate of .27 deg/sec, it takes about 9 secs for MCAS to travel 2.5 deg.

What are characteristic times for airframe control? There should be some PID loops programmed in autopilot, for example I had an impression it is seconds, if not tens seconds. Otherwise a lot of cockpit procedures are meaningless, if aircraft can do several things within those 10 seconds. And if we're talking at least 10 seconds, then MCAS is pretty much an instant action
 
morrisond
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 5:09 pm

OldAeroGuy wrote:
SheikhDjibouti wrote:
For sure, it would make the calculations and the post-stall analysis much more difficult, but my point is that the aviationweek article is far from proof that the MAX stall behavior is acceptable in all cases. As it stands it is just a PR smokescreen, quoted and re-quoted as if it answers everything. The smart cookies here (such as yourself) probably already appreciate it's limitations, but I cannot say that for everybody here. Hell, I'm not even sure I fully understand whether these factors are significant or not. I'm just asking the question.


Hey, I'm all for data. If any contrary data is available that proves the MAX is either neutral or unstable in pitch, I'd love to see it.


Me as well. I'm pretty sure though the FAA did either 200 or 300 test flights on the MAX. I'm pretty sure they would have fully explored it's stall Characteristics and stability.

If not another big Black mark for the FAA
 
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hilram
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 5:11 pm

morrisond wrote:
If you want to worry about something - worry about the Engines on MAX and NEO - the failure rates on both are way higher than they should be - a loss of two of them on one flight is not inconceivable and with the demonstrated lack of airmanship in newly trained crews worldwide I would not be that confident the crews would get the aircraft safely to the ground.

If that is true, we are in big trouble. DY plans to use MAX 8 for TATL, SK plans to use A321Neo for TATL. We can safely assume that in a two engine out situation, the ETOPS 180 rating of these aircraft will provide little comfort to crew and passengers. How much worse is it then previous gen? Regardless, I suppose this will not be assessed with regards to ungrounding the MAX.
Flown on: A319, 320, 321, 332, 333, 343 | B732, 734, 735, 736, 73G, 738, 743, 744, 772, 77W | BAe-146 | DHC-6, 7, 8 | F50 | E195 | MD DC-9 41, MD-82, MD-87
 
ArgentoSystems
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 5:33 pm

OldAeroGuy wrote:
Please say why you think 2.5 deg is significant. Remember at the MCAS trim rate of .27 deg/sec, it takes about 9 secs for MCAS to travel 2.5 deg.

I remember, so? 9 sec is quite fast. 2.5 is almost half of the entire trim range. And you are saying it is insignificant?
 
WIederling
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 5:43 pm

OldAeroGuy wrote:
The nose just flopped down gently at the stall, and I initiated recovery as I would in most other airplanes I’ve flown,” he adds."


All testing done at 1g. ( what GW? )
This is about worthless, isn't it?

The relevant part of the flight envelope that needs to be touched by testing here
is in higher g regions ( like a coordinated turn ) nearer 1.5g than 1g.
Murphy is an optimist
 
ArgentoSystems
Posts: 313
Joined: Sun Mar 24, 2019 12:05 am

Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 5:57 pm

morrisond wrote:
No - if you relaxed the control column it should naturally get itself out of the stall

That's what I told. The problem is Max sans MCAS does not do that, or does it too slow.
 
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PixelFlight
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 5:59 pm

kalvado wrote:
What are characteristic times for airframe control? There should be some PID loops programmed in autopilot, for example I had an impression it is seconds, if not tens seconds. Otherwise a lot of cockpit procedures are meaningless, if aircraft can do several things within those 10 seconds. And if we're talking at least 10 seconds, then MCAS is pretty much an instant action

Don't know for the 737, but on modern aircraft with AFDX network the Bandwidth Allocation Gap values are in milliseconds: 1, 2, 4, 8, 16, 32, 64, 128, so the rate of any message to airframe control is at least 1/128e-3 = 7.8125 Hz.
https://www.edn.com/Pdf/ViewPdf?contentItemId=4134455
Page 14
 
kalvado
Posts: 2017
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 6:16 pm

PixelFlight wrote:
kalvado wrote:
What are characteristic times for airframe control? There should be some PID loops programmed in autopilot, for example I had an impression it is seconds, if not tens seconds. Otherwise a lot of cockpit procedures are meaningless, if aircraft can do several things within those 10 seconds. And if we're talking at least 10 seconds, then MCAS is pretty much an instant action

Don't know for the 737, but on modern aircraft with AFDX network the Bandwidth Allocation Gap values are in milliseconds: 1, 2, 4, 8, 16, 32, 64, 128, so the rate of any message to airframe control is at least 1/128e-3 = 7.8125 Hz.
https://www.edn.com/Pdf/ViewPdf?contentItemId=4134455
Page 14

Not sure how that is related to intrinsic timing. Those cannot be faster - but may be way slower. Oversampling is generally good for filtering, and often very affordable on electronic side of things.
 
morrisond
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 6:25 pm

ArgentoSystems wrote:
morrisond wrote:
No - if you relaxed the control column it should naturally get itself out of the stall

That's what I told. The problem is Max sans MCAS does not do that, or does it too slow.


Yes - that is the problem the stick forces are too light so too slow to return to original - luckily the stall or approach to stall requires the Pilot to help them along.
 
XRAYretired
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 6:51 pm

ArgentoSystems wrote:
OldAeroGuy wrote:
Please say why you think 2.5 deg is significant. Remember at the MCAS trim rate of .27 deg/sec, it takes about 9 secs for MCAS to travel 2.5 deg.

I remember, so? 9 sec is quite fast. 2.5 is almost half of the entire trim range. And you are saying it is insignificant?



I think you guys are at cross-purposes a little. In the 'no fault' scenario, MCAS would initiate on exceeding a set AOA, it will drive nose down at 0.27deg/sec for a proportion of or whole seconds until the AOA drops below the set AOA and would then be aborted until the set AOA is again exceeded. If the AOA does not drop below the set value, MCAS will operate for period of 9.26 secs (~2.5deg total nose down) and then abort for period of 5 secs, e.g. when in fault condition AOA stuck high, or otherwise interupted e.g. by thumb switch activation.

So activation of MCAS in no fault condition could result in only a small nose down in a period that could be less than 1 second.

This is why relatively simple changes to the design will actually be effective (two sensor compared, trigger on change etc.).

Ray
 
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AirlineCritic
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 6:54 pm

I don't think this thread should become a facts-only discussion. The board is for discussion. However, I do have a modest suggestion for participants and the moderators: if you find yourself making 10-15 posts per page, sometimes up to half of the content, could you perhaps slow down? You may believe you are the most expert and right person on this topic, but it is very likely that we've seen your opinion posted about thousand times (literally) already. Please slow down. Let others speak. Comment when something new happens.

And if you're reading this and go "yes, the other guy that I've been responding to is just like that", then it is very likely that the problem is (also) you. Not the other guy.

(And I should repeat that this whole exercise of trying to prove that there's no fault in my fav machine/fav crew seems pointless. For instance, machines are being modified. Training on this issue and more accurate procedures are most likely forthcoming. So there. What are you trying to accomplish by claiming that everything was fine and no one made no errors?)
 
smartplane
Posts: 1024
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 9:00 pm

SheikhDjibouti wrote:
OldAeroGuy wrote:
https://aviationweek.com/commercial-avi ... lator-demo

"A full aerodynamic stall with the MCAS inoperative is another exercise pilots experience in the MAX engineering cab simulator. “We reduced thrust at 5,000 ft. and slowed the aircraft at about 1 kt. per sec. We were at a midrange cg [center of gravity] with gear, slats and flats up. We trimmed until we reached 30% above stall speed and then just continued to ease back on the control wheel,” one of the pilots says.

“Pitch feel was natural, progressively increasing as airspeed decayed....

This report has been quoted here by you (& others) at least seven times now, and in my head I made the same observation each time.

"We were at midrange cg..." - and the 737MAX stalled perfectly naturally even with MCAS disabled.

Well, three cheers for that. :bigthumbsup:

Is that it? Is that good enough?
From the point of view of making things tidy and simple, it's perfect. And best of all, it's all done in the simulator, not a real aircraft. :scratchchin:

What might be the effect of moving the cg to either extreme limit (forward or backwards)?
For a start, it would presumably affect the stab trim start position, and that in itself might affect elevator authority and hence the whole stall scenario.
Is the demonstration at MTOW or something less than that?
How about throwing in a gentle turn as well?

For sure, it would make the calculations and the post-stall analysis much more difficult, but my point is that the aviationweek article is far from proof that the MAX stall behavior is acceptable in all cases. As it stands it is just a PR smokescreen, quoted and re-quoted as if it answers everything. The smart cookies here (such as yourself) probably already appreciate it's limitations, but I cannot say that for everybody here. Hell, I'm not even sure I fully understand whether these factors are significant or not. I'm just asking the question.

Agreed. Same questions for me.

Before Boeing branded MCAS, it was referred internally as a Pitch Stability Augmentation System. A rather less satisfactory description, especially for certification purposes, could have been a Pitch Instability Correction System.
 
kalvado
Posts: 2017
Joined: Wed Mar 01, 2006 4:29 am

Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 9:31 pm

AirlineCritic wrote:
I don't think this thread should become a facts-only discussion. The board is for discussion. However, I do have a modest suggestion for participants and the moderators: if you find yourself making 10-15 posts per page, sometimes up to half of the content, could you perhaps slow down? You may believe you are the most expert and right person on this topic, but it is very likely that we've seen your opinion posted about thousand times (literally) already. Please slow down. Let others speak. Comment when something new happens.

And if you're reading this and go "yes, the other guy that I've been responding to is just like that", then it is very likely that the problem is (also) you. Not the other guy.

(And I should repeat that this whole exercise of trying to prove that there's no fault in my fav machine/fav crew seems pointless. For instance, machines are being modified. Training on this issue and more accurate procedures are most likely forthcoming. So there. What are you trying to accomplish by claiming that everything was fine and no one made no errors?)

I, for one, was talking about a separate thread, facts-only. viewtopic.php?f=12&t=1416585
It is hard to formalize, but maybe something like "posts contain only a link to a high profile (I wanted to say reputable, but that is very difficult criteria) news site or specialized source: CNN, Seattle times, AvHerald, Leeham, NTSB, maybe few similar places, plus a 2- line summary of that link."
Will be very useful for those who want to keep track without reading tons of discussions...
 
RickNRoll
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 10:37 pm

morrisond wrote:
speedking wrote:
If the manual trim works as advertised, the 737 can be safely flown home independent what happens on the electrical / automation system. Just switch everything off.
What has to be determined for the 737 is the exact force needed to rotate the manual trim wheel in comparison with speed, altitude, trim in normal flight envelope and above.
Should wimps and/or females be forbidden from the cockpit?


There are reports from MAX and NG pilots that within normal operating speeds the manual trim wheel works fine and no unusual effort is needed.


You can see the mentour pilot YouTube video. They were in normal flight operating speeds and the effort required to manually trim was surprising.

The manual effort required to manually trim went up significantly with the change to the NG when the larger instrument panels required the trim weeks to be made smaller and a damper had to be added to stop snap back. Boeing was aware from the early days that excessive force could be required to manually trim and used to publish advice on how to make manual trim possible when the physical force required was too high.
 
morrisond
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 10:44 pm

smartplane wrote:
SheikhDjibouti wrote:
OldAeroGuy wrote:
https://aviationweek.com/commercial-avi ... lator-demo

"A full aerodynamic stall with the MCAS inoperative is another exercise pilots experience in the MAX engineering cab simulator. “We reduced thrust at 5,000 ft. and slowed the aircraft at about 1 kt. per sec. We were at a midrange cg [center of gravity] with gear, slats and flats up. We trimmed until we reached 30% above stall speed and then just continued to ease back on the control wheel,” one of the pilots says.

“Pitch feel was natural, progressively increasing as airspeed decayed....

This report has been quoted here by you (& others) at least seven times now, and in my head I made the same observation each time.

"We were at midrange cg..." - and the 737MAX stalled perfectly naturally even with MCAS disabled.

Well, three cheers for that. :bigthumbsup:

Is that it? Is that good enough?
From the point of view of making things tidy and simple, it's perfect. And best of all, it's all done in the simulator, not a real aircraft. :scratchchin:

What might be the effect of moving the cg to either extreme limit (forward or backwards)?
For a start, it would presumably affect the stab trim start position, and that in itself might affect elevator authority and hence the whole stall scenario.
Is the demonstration at MTOW or something less than that?
How about throwing in a gentle turn as well?

For sure, it would make the calculations and the post-stall analysis much more difficult, but my point is that the aviationweek article is far from proof that the MAX stall behavior is acceptable in all cases. As it stands it is just a PR smokescreen, quoted and re-quoted as if it answers everything. The smart cookies here (such as yourself) probably already appreciate it's limitations, but I cannot say that for everybody here. Hell, I'm not even sure I fully understand whether these factors are significant or not. I'm just asking the question.

Agreed. Same questions for me.

Before Boeing branded MCAS, it was referred internally as a Pitch Stability Augmentation System. A rather less satisfactory description, especially for certification purposes, could have been a Pitch Instability Correction System.



You wonder why this post keeps going back and forth is because of posts like this.

If you are going to keep making accusations that the MAX is unstable in pitch please provide some evidence or at least some credible theory.

It's like me making something up like the reason the plane crashed is the Pilots were on Coke and they crashed on purpose to get back at those evil capitalists the Americans.
 
OldAeroGuy
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 11:35 pm

XRAYretired wrote:
ArgentoSystems wrote:
OldAeroGuy wrote:
Please say why you think 2.5 deg is significant. Remember at the MCAS trim rate of .27 deg/sec, it takes about 9 secs for MCAS to travel 2.5 deg.

I remember, so? 9 sec is quite fast. 2.5 is almost half of the entire trim range. And you are saying it is insignificant?



I think you guys are at cross-purposes a little. In the 'no fault' scenario, MCAS would initiate on exceeding a set AOA, it will drive nose down at 0.27deg/sec for a proportion of or whole seconds until the AOA drops below the set AOA and would then be aborted until the set AOA is again exceeded. If the AOA does not drop below the set value, MCAS will operate for period of 9.26 secs (~2.5deg total nose down) and then abort for period of 5 secs, e.g. when in fault condition AOA stuck high, or otherwise interupted e.g. by thumb switch activation.

So activation of MCAS in no fault condition could result in only a small nose down in a period that could be less than 1 second.

This is why relatively simple changes to the design will actually be effective (two sensor compared, trigger on change etc.).

Ray


I agree with what you've said. My curiosity is that Interested, ArgentoSystems and others have been fretting about the MCAS authority change from 0.6 deg preflight to 2.5 deg after flight test.

I'm curious as to why they are so concerned.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
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7BOEING7
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 11:37 pm

RickNRoll wrote:
morrisond wrote:
speedking wrote:
If the manual trim works as advertised, the 737 can be safely flown home independent what happens on the electrical / automation system. Just switch everything off.
What has to be determined for the 737 is the exact force needed to rotate the manual trim wheel in comparison with speed, altitude, trim in normal flight envelope and above.
Should wimps and/or females be forbidden from the cockpit?


There are reports from MAX and NG pilots that within normal operating speeds the manual trim wheel works fine and no unusual effort is needed.


You can see the mentour pilot YouTube video. They were in normal flight operating speeds and the effort required to manually trim was surprising.

The manual effort required to manually trim went up significantly with the change to the NG when the larger instrument panels required the trim weeks to be made smaller and a damper had to be added to stop snap back. Boeing was aware from the early days that excessive force could be required to manually trim and used to publish advice on how to make manual trim possible when the physical force required was too high.


Don't know what "normal flight operating speeds" mentour was simulating, but based on my experience manually trimming the 737 (Jurrasic, Classic and Next Gen -- several hundred times) at altitudes from 15000ft to FL350 at "normal flight operating speeds" his simulation looked bogus.

I also didn't notice any "significant" difference between the Classic and Next Gen when using manual trim and none of the pilots I flew with be they male or female had an issue either.

As for the "published advice" that apparently was issued in the days of the -200, 40 years ago, I never heard it discussed or trained too during my career.
 
OldAeroGuy
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 11:43 pm

WIederling wrote:
OldAeroGuy wrote:
The nose just flopped down gently at the stall, and I initiated recovery as I would in most other airplanes I’ve flown,” he adds."


All testing done at 1g. ( what GW? )
This is about worthless, isn't it?

The relevant part of the flight envelope that needs to be touched by testing here
is in higher g regions ( like a coordinated turn ) nearer 1.5g than 1g.


Stick force requirements must be passed for both 1.0g flight and in turning flight.

There's information that it looks like the 1.0g is pretty benign without MACS. With MCAS, 1.0g stall stick forces are probably a sure pass.

I don't have any data yet on higher "g" (turning flight) stalls. Do you? If so, I'd love to see it.
Last edited by OldAeroGuy on Sun Apr 28, 2019 12:03 am, edited 1 time in total.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
1lovetotravel1
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 11:49 pm

Is this type of plane supposed to be grounded worldwide? How is that i was a passenger in one on March 24th of this year?

Not like i was scared or anything, but this question has puzzled me for some time. I even took a picture of the emergency instructuons so i had proof i was in one.

Or have i misunderstood and it's up to the airlines if they are to be used ir not?
 
OldAeroGuy
Posts: 3886
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Re: B737MAX Grounded Worldwide

Sat Apr 27, 2019 11:54 pm

AirlineCritic wrote:
I don't think this thread should become a facts-only discussion. The board is for discussion. However, I do have a modest suggestion for participants and the moderators: if you find yourself making 10-15 posts per page, sometimes up to half of the content, could you perhaps slow down? You may believe you are the most expert and right person on this topic, but it is very likely that we've seen your opinion posted about thousand times (literally) already. Please slow down. Let others speak. Comment when something new happens.

And if you're reading this and go "yes, the other guy that I've been responding to is just like that", then it is very likely that the problem is (also) you. Not the other guy.

(And I should repeat that this whole exercise of trying to prove that there's no fault in my fav machine/fav crew seems pointless. For instance, machines are being modified. Training on this issue and more accurate procedures are most likely forthcoming. So there. What are you trying to accomplish by claiming that everything was fine and no one made no errors?)


I agree with your post to certain extent, but this should be a facts based discussion.

Many individuals have made claims that the 737 MAX is unstable and that's the reason MCAS is needed.

Others, myself included, believe the MAX is stable but its pitch characteristics require MCAS to pass FAA stall handling characteristics.

Shouldn't the discussion hinge on available data and new data as it is brought to the table to support either of these two positions?
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
speedking
Posts: 68
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Re: B737MAX Grounded Worldwide

Sun Apr 28, 2019 12:21 am

7BOEING7 wrote:
RickNRoll wrote:
morrisond wrote:

There are reports from MAX and NG pilots that within normal operating speeds the manual trim wheel works fine and no unusual effort is needed.


You can see the mentour pilot YouTube video. They were in normal flight operating speeds and the effort required to manually trim was surprising.

The manual effort required to manually trim went up significantly with the change to the NG when the larger instrument panels required the trim weeks to be made smaller and a damper had to be added to stop snap back. Boeing was aware from the early days that excessive force could be required to manually trim and used to publish advice on how to make manual trim possible when the physical force required was too high.


Don't know what "normal flight operating speeds" mentour was simulating, but based on my experience manually trimming the 737 (Jurrasic, Classic and Next Gen -- several hundred times) at altitudes from 15000ft to FL350 at "normal flight operating speeds" his simulation looked bogus.

I also didn't notice any "significant" difference between the Classic and Next Gen when using manual trim and none of the pilots I flew with be they male or female had an issue either.

As for the "published advice" that apparently was issued in the days of the -200, 40 years ago, I never heard it discussed or trained too during my career.


I'm somewhat concerned why this issue seem to have been hidden for 40 years. Even now it is buried in a side note attached to the runaway stabilizer checklist.
Instead of relying on personal or sisters roommates friends opinion, I believe, with the available modern design capabilities, the force can be pretty easily calculated over the whole flight envelope and above and verified by simulations and flight tests.
Of course if there is nothing to hide.
 
kalvado
Posts: 2017
Joined: Wed Mar 01, 2006 4:29 am

Re: B737MAX Grounded Worldwide

Sun Apr 28, 2019 12:43 am

OldAeroGuy wrote:
Shouldn't the discussion hinge on available data and new data as it is brought to the table to support either of these two positions?

We may disagree over the physics aspect, by we have to agree over the lack of data fuelling this discussion.
 
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7BOEING7
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Re: B737MAX Grounded Worldwide

Sun Apr 28, 2019 1:17 am

speedking wrote:
7BOEING7 wrote:

Don't know what "normal flight operating speeds" mentour was simulating, but based on my experience manually trimming the 737 (Jurrasic, Classic and Next Gen -- several hundred times) at altitudes from 15000ft to FL350 at "normal flight operating speeds" his simulation looked bogus.

I also didn't notice any "significant" difference between the Classic and Next Gen when using manual trim and none of the pilots I flew with be they male or female had an issue either.

As for the "published advice" that apparently was issued in the days of the -200, 40 years ago, I never heard it discussed or trained too during my career.


I'm somewhat concerned why this issue seem to have been hidden for 40 years. Even now it is buried in a side note attached to the runaway stabilizer checklist.
Instead of relying on personal or sisters roommates friends opinion, I believe, with the available modern design capabilities, the force can be pretty easily calculated over the whole flight envelope and above and verified by simulations and flight tests.Of course if there is nothing to hide.


I think we're talking about different subjects. I thought RicknRoll was discussing the unload/load work around that has been mentioned. What are you taking about? Which side note?
 
acechip
Posts: 35
Joined: Fri Nov 30, 2018 12:22 am

Re: B737MAX Grounded Worldwide

Sun Apr 28, 2019 1:27 am

OldAeroGuy wrote:
AirlineCritic wrote:
I don't think this thread should become a facts-only discussion. The board is for discussion. However, I do have a modest suggestion for participants and the moderators: if you find yourself making 10-15 posts per page, sometimes up to half of the content, could you perhaps slow down? You may believe you are the most expert and right person on this topic, but it is very likely that we've seen your opinion posted about thousand times (literally) already. Please slow down. Let others speak. Comment when something new happens.

And if you're reading this and go "yes, the other guy that I've been responding to is just like that", then it is very likely that the problem is (also) you. Not the other guy.

(And I should repeat that this whole exercise of trying to prove that there's no fault in my fav machine/fav crew seems pointless. For instance, machines are being modified. Training on this issue and more accurate procedures are most likely forthcoming. So there. What are you trying to accomplish by claiming that everything was fine and no one made no errors?)


I agree with your post to certain extent, but this should be a facts based discussion.

Many individuals have made claims that the 737 MAX is unstable and that's the reason MCAS is needed.

Others, myself included, believe the MAX is stable but its pitch characteristics require MCAS to pass FAA stall handling characteristics.

Shouldn't the discussion hinge on available data and new data as it is brought to the table to support either of these two positions?


Just for comparisons sake, I would like to understand, FBW laws aside, is the Airbus A320 an aerodynamically stable design i.e, in absence of control authority software, can the pilot fly the plane well enough to complete a flight safely? And in the absence of MCAS, can a B Max pilot do the same ?
 
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7BOEING7
Posts: 3039
Joined: Fri Oct 12, 2012 5:28 pm

Re: B737MAX Grounded Worldwide

Sun Apr 28, 2019 1:35 am

acechip wrote:
OldAeroGuy wrote:
AirlineCritic wrote:
I don't think this thread should become a facts-only discussion. The board is for discussion. However, I do have a modest suggestion for participants and the moderators: if you find yourself making 10-15 posts per page, sometimes up to half of the content, could you perhaps slow down? You may believe you are the most expert and right person on this topic, but it is very likely that we've seen your opinion posted about thousand times (literally) already. Please slow down. Let others speak. Comment when something new happens.

And if you're reading this and go "yes, the other guy that I've been responding to is just like that", then it is very likely that the problem is (also) you. Not the other guy.

(And I should repeat that this whole exercise of trying to prove that there's no fault in my fav machine/fav crew seems pointless. For instance, machines are being modified. Training on this issue and more accurate procedures are most likely forthcoming. So there. What are you trying to accomplish by claiming that everything was fine and no one made no errors?)


I agree with your post to certain extent, but this should be a facts based discussion.

Many individuals have made claims that the 737 MAX is unstable and that's the reason MCAS is needed.

Others, myself included, believe the MAX is stable but its pitch characteristics require MCAS to pass FAA stall handling characteristics.

Shouldn't the discussion hinge on available data and new data as it is brought to the table to support either of these two positions?


Just for comparisons sake, I would like to understand, FBW laws aside, is the Airbus A320 an aerodynamically stable design i.e, in absence of control authority software, can the pilot fly the plane well enough to complete a flight safely? And in the absence of MCAS, can a B Max pilot do the same ?


Yes and yes.
 
pugman211
Posts: 474
Joined: Thu Dec 20, 2012 1:55 pm

Re: B737MAX Grounded Worldwide

Sun Apr 28, 2019 5:30 am

7BOEING7 wrote:
speedking wrote:
7BOEING7 wrote:

Don't know what "normal flight operating speeds" mentour was simulating, but based on my experience manually trimming the 737 (Jurrasic, Classic and Next Gen -- several hundred times) at altitudes from 15000ft to FL350 at "normal flight operating speeds" his simulation looked bogus.

I also didn't notice any "significant" difference between the Classic and Next Gen when using manual trim and none of the pilots I flew with be they male or female had an issue either.

As for the "published advice" that apparently was issued in the days of the -200, 40 years ago, I never heard it discussed or trained too during my career.


I'm somewhat concerned why this issue seem to have been hidden for 40 years. Even now it is buried in a side note attached to the runaway stabilizer checklist.
Instead of relying on personal or sisters roommates friends opinion, I believe, with the available modern design capabilities, the force can be pretty easily calculated over the whole flight envelope and above and verified by simulations and flight tests.Of course if there is nothing to hide.


I think we're talking about different subjects. I thought RicknRoll was discussing the unload/load work around that has been mentioned. What are you taking about? Which side note?



In the Mentour Pilot video thrust was set to 75% iirc, which is part of a IAS Disagree checklist maybe?? But the reason why the manual trim was so hard was the fact the stabilizer was loaded intentionally for the purpose of the video, and he stated that.

Maybe manual wheel trim that people state is easy to move is down to the fact that they haven't loaded the stabilizer. I imagine that the elevators will be in a fairly neutral position when they move the trim wheels? Unless you have first hand experience and tried to move the trim wheels with high elevator deflection then the level of force required to move the trim wheels is unknown, surely.
 
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aerolimani
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Re: B737MAX Grounded Worldwide

Sun Apr 28, 2019 6:01 am

pugman211 wrote:
7BOEING7 wrote:
speedking wrote:

I'm somewhat concerned why this issue seem to have been hidden for 40 years. Even now it is buried in a side note attached to the runaway stabilizer checklist.
Instead of relying on personal or sisters roommates friends opinion, I believe, with the available modern design capabilities, the force can be pretty easily calculated over the whole flight envelope and above and verified by simulations and flight tests.Of course if there is nothing to hide.


I think we're talking about different subjects. I thought RicknRoll was discussing the unload/load work around that has been mentioned. What are you taking about? Which side note?



In the Mentour Pilot video thrust was set to 75% iirc, which is part of a IAS Disagree checklist maybe?? But the reason why the manual trim was so hard was the fact the stabilizer was loaded intentionally for the purpose of the video, and he stated that.

Maybe manual wheel trim that people state is easy to move is down to the fact that they haven't loaded the stabilizer. I imagine that the elevators will be in a fairly neutral position when they move the trim wheels? Unless you have first hand experience and tried to move the trim wheels with high elevator deflection then the level of force required to move the trim wheels is unknown, surely.

Yes. They were simulating a severe out-of trim situation where the pilot flying was counteracting the nose down trim (with the elevators) by pulling back on the yoke. They were simulating the type of out-of-trim situation that MCAS v1 could have put an aircraft in, as opposed to the operation of the manual trim wheel in a normal flight situation.
 
AirwayBill
Posts: 141
Joined: Fri Mar 29, 2019 8:37 am

Re: B737MAX Grounded Worldwide

Sun Apr 28, 2019 6:22 am

On Apr 27th 2019 it became known, that four independent whistleblowers, current and former Boeing employees, had called the FAA hotline for whistleblowers regarding aviation safety concerns on Apr 5th 2019. The concerns reported were wiring damage to the AoA related wiring as result of foreign object damage as well as concerns with the TRIM CUTOUT switches. The FAA believes these reports may open completely new investigative angles into the causes of the two crashes in Indonesia and Ethiopia.


Source: http://avherald.com/h?article=4c534c4a/0045&opt=0
 
flipdewaf
Posts: 2894
Joined: Thu Jul 20, 2006 6:28 am

Re: B737MAX Grounded Worldwide

Sun Apr 28, 2019 6:47 am

morrisond wrote:
ArgentoSystems wrote:
I'd like to break the endless back and forth that is going for the last 10 pages, and leads nowhere.

Instead, please answer the question: what would be an effect of SINGLE (one time, 2.5deg down) false MCAS activation at low altitude. Say, shortly after take-off. How quickly do you think a prepared pilot notice the uncommanded nose down? Will they be able to recover then?


If they are flying manually and climbing they should be scanning their instruments and the horizon alternatively every second or so - it should be pretty evident pretty quickly and only take a second to flick off the switches after they counter the last MCAS input if they have identified it as a MCAS failure. If they have yet to determine that it is a MCAS failure they should be counter acting it with Electric Trim and or column pressure. ET obviously noticed this (nose dropping as MCAS was activating) as they correctly used Electric Trim to counter it twice I believe before they switched Electric Trim off (but not counteracting the MCAS inputs fully). Lionair counteracted MCAS inputs correctly 22 times before the FO failed to do as the pilot did.

If they aren't scanning the horizon and instruments at low levels constantly so that they would notice this(nose dropping) - they aren't doing what they should be and shouldn't be in the cockpit flying manually.

Shoulda, Coulda, Woulda!
Other planes aren’t crashing like this. Maybe they ‘should’ have been scanning the instruments and horizon like you suggest but if they aren’t I see no reason why they also wouldn’t be doing it in other aircraft and they are not crashing.

It’s all very well to say if they had don’t it like this then they wouldn’t have crashed but aircraft manufacturers have a duty to set up their systems and controls in a way that their operators can and will operate them safely. If Boeing set up the controls for how they want them to be used rather than how a human will use them then they have failed.

Fred


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Image
 
WIederling
Posts: 8888
Joined: Sun Sep 13, 2015 2:15 pm

Re: B737MAX Grounded Worldwide

Sun Apr 28, 2019 7:12 am

OldAeroGuy wrote:
WIederling wrote:
is in higher g regions ( like a coordinated turn ) nearer 1.5g than 1g.


Stick force requirements must be passed for both 1.0g flight and in turning flight.

There's information that it looks like the 1.0g is pretty benign without MACS. With MCAS, 1.0g stall stick forces are probably a sure pass.

I don't have any data yet on higher "g" (turning flight) stalls. Do you? If so, I'd love to see it.

me neither. but you can estimate.
"working" AoA for the same speed and higher load ( via increased g ) will be higher.
Higher in proportion than the increased load would suggest. AoA vs lift is not linear but slightly degressive
lift vs drag:
Image
( until you reach the turning point in lift generation when it turns mostly draggy :-)
Murphy is an optimist

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