737 max nacelle lift generation
There are regulations and procedures for systems that fail after dispatch (I'm assuming here that MCAS inop isn't dispatchable). Basically, you look at - given one system fails - what is the probability of the next failure that could result in a hazardous or catastrophic situation. Given the limited exposure to the next failure (the remainder of the flight), a 'relaxed' probability is used compared to what would be the case for something like an MEL dispatch. Those regulations and procedures then determine what goes into the AFM as to what to crew should do - e.g. continue on or land at the nearest suitable airport.
Something that gets tricky is accounting for inappropriate crew actions, such as continuing to pull back after getting the stick shaker (somewhat complicated in this case as the (detected) failure of an AOA sensor could also disable the stick shaker stall warning).
That's an area I didn't really get into.
Something that gets tricky is accounting for inappropriate crew actions, such as continuing to pull back after getting the stick shaker (somewhat complicated in this case as the (detected) failure of an AOA sensor could also disable the stick shaker stall warning).
That's an area I didn't really get into.
Faeries
Howdy. I once saw Snoopy's dog house fly. (Not crazy, twas an airshow).
Given sufficient velocity and AoA, a brick can fly.
(See: McD F4 Phantom). A pipe will "fly". Given enough gas path velocity, any engine can produce Lift besides thrust... imo. Navel gazing.
There are ways to stiffen the stick/yoke without using the most powerful "trim" on the plane.
How about at shaker (training) "Caution at shaker, PUSH" There is more here than CoA compliance.
We got bodies here ffs.
If you need positive controls Response supra pilots, Train train train... If the Nose gets light, push.
"Easy fix, supposedly: turn off trim!" BS, by the time a serious anomaly is apparent, it's too late...fly home in manual. Is the Max ETOPS? Thought I'd ask...
Shaker Pusher, Push the yoke briskly. The FAA demanded a failsafe. They got it, at what cost...
The aircraft flies AOA so should crew.
If the aircraft can't meet the CoA sprecs. Apply for a new certificate. Sistering the MAX onto the guppies' CoA is dishonest
Appears like the THS/MCAS pair is butting into the shaker/Pusher/crew
Given sufficient velocity and AoA, a brick can fly.
(See: McD F4 Phantom). A pipe will "fly". Given enough gas path velocity, any engine can produce Lift besides thrust... imo. Navel gazing.
There are ways to stiffen the stick/yoke without using the most powerful "trim" on the plane.
How about at shaker (training) "Caution at shaker, PUSH" There is more here than CoA compliance.
We got bodies here ffs.
If you need positive controls Response supra pilots, Train train train... If the Nose gets light, push.
"Easy fix, supposedly: turn off trim!" BS, by the time a serious anomaly is apparent, it's too late...fly home in manual. Is the Max ETOPS? Thought I'd ask...
Shaker Pusher, Push the yoke briskly. The FAA demanded a failsafe. They got it, at what cost...
The aircraft flies AOA so should crew.
If the aircraft can't meet the CoA sprecs. Apply for a new certificate. Sistering the MAX onto the guppies' CoA is dishonest
Appears like the THS/MCAS pair is butting into the shaker/Pusher/crew
Last edited by BugBear; 22nd Jun 2024 at 17:38. Reason: Puzzle
How can MCAS be inoperative alone? It's software running in a computer. There should be a large number of things that don't work if that computer fails.
"MCAS only really activates during stall," MCAS has no stall detection capacity. It activates to linearize the high AoA control column response force. The FAR that regulates that was probably in place to discourage aircraft designs that would transition from high AoA to divergent AoA where stall might be one result.
"MCAS only really activates during stall," MCAS has no stall detection capacity. It activates to linearize the high AoA control column response force. The FAR that regulates that was probably in place to discourage aircraft designs that would transition from high AoA to divergent AoA where stall might be one result.
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There is one thing will not allow the software to operate. Turning electric trim off. A trim problem did happen to a Southwest flight where they went to manual trim. They no longer had MCAS. Did the non normal procedure tell them that and to avoid clean high AOA maneuvers, one of which might be an escape from windshear. Highly unlikely the swiss cheese will line up for that to happen but is it noted in the procedure or in training?
The operative word is "alone." Turning off all electric trim inputs shuts off the control wheel switches and speed trim systems as well.
The failure most likely to affect MCAS alone is a failure to detect full retraction of the flaps.
I haven't heard of a manually trimmed Southwest flight. When was it and why did they do so?
The failure most likely to affect MCAS alone is a failure to detect full retraction of the flaps.
I haven't heard of a manually trimmed Southwest flight. When was it and why did they do so?
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The operative word is "alone." Turning off all electric trim inputs shuts off the control wheel switches and speed trim systems as well.
The failure most likely to affect MCAS alone is a failure to detect full retraction of the flaps.
I haven't heard of a manually trimmed Southwest flight. When was it and why did they do so?
The failure most likely to affect MCAS alone is a failure to detect full retraction of the flaps.
I haven't heard of a manually trimmed Southwest flight. When was it and why did they do so?
Autopilot and trim systems not working; anyone check the trim disable switches? Is there a step in pre-flight to see that the trim responds to the control wheel trim switches?
That was the first flight after delivery and after acceptance by SW; it was then given whatever post-acceptance treatment SW has and dispatched the next day; 14 hours after delivery by Boeing if the account is read correctly. It is unlikely that the Boeing delivery pilots hopped out of a plane where autopilot and electric trim didn't work. Someone messed with something after it landed.
As I have mentioned before, humans are extremely non-linear, so if there is a pilot of a 737 that has managed to completely avoid all discussions of MCAS, it doesn't matter. Amp them up with some adrenaline and they won't notice how hard they are pulling. A more sensible regulation would be a function that puts the rate at a large multiple of the trim center response when nearing stall, if it is supposed to be a deterrent.
That was the first flight after delivery and after acceptance by SW; it was then given whatever post-acceptance treatment SW has and dispatched the next day; 14 hours after delivery by Boeing if the account is read correctly. It is unlikely that the Boeing delivery pilots hopped out of a plane where autopilot and electric trim didn't work. Someone messed with something after it landed.
As I have mentioned before, humans are extremely non-linear, so if there is a pilot of a 737 that has managed to completely avoid all discussions of MCAS, it doesn't matter. Amp them up with some adrenaline and they won't notice how hard they are pulling. A more sensible regulation would be a function that puts the rate at a large multiple of the trim center response when nearing stall, if it is supposed to be a deterrent.
MechEgr
"...The failure most likely to affect MCAS alone is a failure to detect full retraction of the flaps..."
Seemingly not with Lionair... MCAS was waiting to pounce until the Flaps stowed on climbout...
I don't expect the FAA to have caught it. But isolating two different AoA channels was fatal.
Seems to me the doofus who speced it should still be....
"...MCAS has no stall detection capacity. It activates to linearize the high AoA control column..."
Perhaps no Stall value on its own, but certainly "in the loop" with AoA vane...no?
Suppose a/c Stalls, MCAS has full authority on THS.
How quickly can THS be stripped of ND? Seems it could get interesting, pulling out. What happens when pilot pushes at Stall? A surprise at the negative G? Unable to pull out, elevators unavailable,? Pull as they might...?
Seemingly not with Lionair... MCAS was waiting to pounce until the Flaps stowed on climbout...
I don't expect the FAA to have caught it. But isolating two different AoA channels was fatal.
Seems to me the doofus who speced it should still be....
"...MCAS has no stall detection capacity. It activates to linearize the high AoA control column..."
Perhaps no Stall value on its own, but certainly "in the loop" with AoA vane...no?
Suppose a/c Stalls, MCAS has full authority on THS.
How quickly can THS be stripped of ND? Seems it could get interesting, pulling out. What happens when pilot pushes at Stall? A surprise at the negative G? Unable to pull out, elevators unavailable,? Pull as they might...?
Last edited by BugBear; 23rd Jun 2024 at 16:05.
There are separate arguments and situations here. Lion Air had a problem with MCAS because the SMYD lied to MCAS about the AoA. See my evaluation above for why and how leaving the AoA sensors independent wasn't the core problem. If the SMYD is not dysfunctional as it was for Lion Air, then the MCAS protection won't be available when the flaps come up if the flap retraction isn't detected.
All the rest is the same question as Speed Trim System, which also drives the horizontal stab. As to stall condition, that stabilizer management is exactly what Airbus does.
All the rest is the same question as Speed Trim System, which also drives the horizontal stab. As to stall condition, that stabilizer management is exactly what Airbus does.
my 5 cents to the open post question, but just guessing:
it's not the more powerful engines. They are rated even a bit lower I remember to have read.
The issue is, larger nacelles. more surface to generate lift in some situations. engines further forward - their lift as well more forward, at a longer leverage.
Now if you design an aircraft from scratch, you have better chances to fully account for this and balance everything. On the 737 they possibly achieved to somehow manage it aerodynamically, but with some few issues left. So that's why they addressed the remaining issues with MCAS, and maybe also with other existing helpers.
I welcome critical check of my opinion.
it's not the more powerful engines. They are rated even a bit lower I remember to have read.
The issue is, larger nacelles. more surface to generate lift in some situations. engines further forward - their lift as well more forward, at a longer leverage.
Now if you design an aircraft from scratch, you have better chances to fully account for this and balance everything. On the 737 they possibly achieved to somehow manage it aerodynamically, but with some few issues left. So that's why they addressed the remaining issues with MCAS, and maybe also with other existing helpers.
I welcome critical check of my opinion.
Hmm
"....it's not the more powerful engines. They are rated even a bit lower I remember to have read..."
Please not to regard this as critique...
In test, at high alpha, was the nose reluctant to drop due all the Nacelle "lift"...Doubts. Why not a Lift fence to counteract all this unwanted lift? It helps Boeing sell the new configuration to the FAA....
Did Boeing reject a stick stiffener even though FAA approved it as the only device necessary? The engine provides more thrust, not less, As I recall. Did Boeing derate this monster to comply...?
The all new architecture was too much to lend sisterhood to the MAX. A new type with its prohibitively large cost made the bean counters faint. Costs won, as they do with Boeings plans.
As ever...
Please not to regard this as critique...
In test, at high alpha, was the nose reluctant to drop due all the Nacelle "lift"...Doubts. Why not a Lift fence to counteract all this unwanted lift? It helps Boeing sell the new configuration to the FAA....
Did Boeing reject a stick stiffener even though FAA approved it as the only device necessary? The engine provides more thrust, not less, As I recall. Did Boeing derate this monster to comply...?
The all new architecture was too much to lend sisterhood to the MAX. A new type with its prohibitively large cost made the bean counters faint. Costs won, as they do with Boeings plans.
As ever...
The thrust levels of the LEAP engines is very close to the CFM56-7 (max thrust is limited by the tail authority, so they can't really increase it for a given length - i.e. the moment arm of the tail).
Boeing tried various aero fixes, but none gave them the desired effect. MCAS did - and it wasn't the concept of MCAS that was flawed, it was the implementation.
Anything you discover during flight test is - pretty much by definition - late in the program and there is great pressure to come up with a fix quickly to avoid delaying the entire cert program.
Boeing tried various aero fixes, but none gave them the desired effect. MCAS did - and it wasn't the concept of MCAS that was flawed, it was the implementation.
Anything you discover during flight test is - pretty much by definition - late in the program and there is great pressure to come up with a fix quickly to avoid delaying the entire cert program.
MechEgr
"..All the rest is the same question as Speed Trim System, which also drives the horizontal stab. As to stall condition, that stabilizer management is exactly what Airbus does..."
So now the Boeing is Pitch stable, like Airbus?
Cannot Stall? Not a new type then? Just a better guppy?
Just like the guppy? The Max won't drop it's nose at Stall? No "descent" No Nose Down? Stalled Mush,?
Airbus has a "gentle" "Stall",
No airframe cues. Only a forestalled belly flop?
So now the Boeing is Pitch stable, like Airbus?
Cannot Stall? Not a new type then? Just a better guppy?
Just like the guppy? The Max won't drop it's nose at Stall? No "descent" No Nose Down? Stalled Mush,?
Airbus has a "gentle" "Stall",
No airframe cues. Only a forestalled belly flop?
Last edited by BugBear; 23rd Jun 2024 at 20:21.
Thank you tdracer
I learned you mostly worked on the engine side, and not on the MAX anymore (right?), but maybe you still have an informed opinion: Given a whole new aircraft design, and for some reason having to place the engines as far in front as on the MAX, do you think it could have been addressed purely by weight balance and aerodynamics - avoiding something like MCAS?
I know it's just an academic question.
I know it's just an academic question.
The more important reason was timing. The A320 NEO family catched Boeing by surprise. They didn't have time to go for a new design. Plus their important customers wanted tight commonality. How much innovations can you hope for within these restrictions?
Exactly
Changing aircraft architecture (that's the ticket) Thrust aside (derating to dampen the extended moment arm). The Max was a problem, shoehorning it into a CoA that prexisted!!
Ongoing...without the Max, Boeing does not survive...
Last edited by BugBear; 23rd Jun 2024 at 21:02.
Tdracer
(max thrust is limited by the tail authority, so they can't really increase it for a given length - i.e. the moment arm of the tail).
Isn't that just what MCAS does? Increase the (moment)arm of the tail? Enhanced authority in Pitch Down needs more power to counter with Pitch Up. Would seem critical even... Does FCM Uprate the engines with MCAS.?
NO wonder both Maxes had amazing vertical speed at impact..
Isn't that just what MCAS does? Increase the (moment)arm of the tail? Enhanced authority in Pitch Down needs more power to counter with Pitch Up. Would seem critical even... Does FCM Uprate the engines with MCAS.?
NO wonder both Maxes had amazing vertical speed at impact..
Last edited by BugBear; 23rd Jun 2024 at 21:01. Reason: T
No, you completely misunderstand MCAS. When approaching stall (as indicated by the AOA), the control forces to keep pulling up got lighter due to the lift on those big engine nacelles (undesirable and contrary to the regulations - you want the force to get heavier, not lighter, as you approach stall). MCAS, by putting in nose down stab trim - pushed the nose down - increasing the force needed to keep pulling up. Sort of like a stick pusher, but done aerodynamically instead of actually pushing on the stick.
Thank you tdracer
I learned you mostly worked on the engine side, and not on the MAX anymore (right?), but maybe you still have an informed opinion: Given a whole new aircraft design, and for some reason having to place the engines as far in front as on the MAX, do you think it could have been addressed purely by weight balance and aerodynamics - avoiding something like MCAS?
I know it's just an academic question.
I learned you mostly worked on the engine side, and not on the MAX anymore (right?), but maybe you still have an informed opinion: Given a whole new aircraft design, and for some reason having to place the engines as far in front as on the MAX, do you think it could have been addressed purely by weight balance and aerodynamics - avoiding something like MCAS?
I know it's just an academic question.
No, you completely misunderstand MCAS. When approaching stall (as indicated by the AOA), the control forces to keep pulling up got lighter due to the lift on those big engine nacelles (undesirable and contrary to the regulations - you want the force to get heavier, not lighter,.
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