737 max nacelle lift generation
Violator
Violator: I think that you are confusing torque produced by the rotating assembly with the moment arm of the thrust centerline translating through the pylon forward mount on the forward spar and the main spar attachment. This "twist" is substantial....it is also "torque"....an example would be American DC 10 losing Number one when the rear pylon mount failed. It rotated forward and over the top of the wing.
Spoiler
Moderator
How, exactly, does this (Nacelle) Lift bonus help raise the nose
Were you to read the whole thread, rather than perhaps just jumping in on occasion, the phenomenon has been addressed on several occasions.
Any time fluid flow changes direction, there must be pressure gradients causing that to occur and the associated momentum change necessarily is tied up with a force.
At higher alpha, the airflow is turned downwards as it transits the forward nacelle lip region and this is associated with an upwards force, similar to what we see happening over the wing with "lift". This upwards force at the nacelle lip provides a nose up pitching moment contribution to the aeroplane's dynamics. The pilot sees this as a reduction in the stick back force needed to maintain a flight path. In the extreme, the stick force can reverse and the pilot has to push forward to stop the nose up motion of the aeroplane. That, naturally enough, is not a desirable situation. Hence, longitudinal static stability requirements require that pilot perception of stick forces remain within an acceptable range (or limits, if you prefer).
Were you to read the whole thread, rather than perhaps just jumping in on occasion, the phenomenon has been addressed on several occasions.
Any time fluid flow changes direction, there must be pressure gradients causing that to occur and the associated momentum change necessarily is tied up with a force.
At higher alpha, the airflow is turned downwards as it transits the forward nacelle lip region and this is associated with an upwards force, similar to what we see happening over the wing with "lift". This upwards force at the nacelle lip provides a nose up pitching moment contribution to the aeroplane's dynamics. The pilot sees this as a reduction in the stick back force needed to maintain a flight path. In the extreme, the stick force can reverse and the pilot has to push forward to stop the nose up motion of the aeroplane. That, naturally enough, is not a desirable situation. Hence, longitudinal static stability requirements require that pilot perception of stick forces remain within an acceptable range (or limits, if you prefer).
How, exactly, does this (Nacelle) Lift bonus help raise the nose
Were you to read the whole thread, rather than perhaps just jumping in on occasion, the phenomenon has been addressed on several occasions.
Any time fluid flow changes direction, there must be pressure gradients causing that to occur and the associated momentum change necessarily is tied up with a force.
At higher alpha, the airflow is turned downwards as it transits the forward nacelle lip region and this is associated with an upwards force, similar to what we see happening over the wing with "lift". This upwards force at the nacelle lip provides a nose up pitching moment contribution to the aeroplane's dynamics. The pilot sees this as a reduction in the stick back force needed to maintain a flight path. In the extreme, the stick force can reverse and the pilot has to push forward to stop the nose up motion of the aeroplane. That, naturally enough, is not a desirable situation. Hence, longitudinal static stability requirements require that pilot perception of stick forces remain within an acceptable range (or limits, if you prefer).
Were you to read the whole thread, rather than perhaps just jumping in on occasion, the phenomenon has been addressed on several occasions.
Any time fluid flow changes direction, there must be pressure gradients causing that to occur and the associated momentum change necessarily is tied up with a force.
At higher alpha, the airflow is turned downwards as it transits the forward nacelle lip region and this is associated with an upwards force, similar to what we see happening over the wing with "lift". This upwards force at the nacelle lip provides a nose up pitching moment contribution to the aeroplane's dynamics. The pilot sees this as a reduction in the stick back force needed to maintain a flight path. In the extreme, the stick force can reverse and the pilot has to push forward to stop the nose up motion of the aeroplane. That, naturally enough, is not a desirable situation. Hence, longitudinal static stability requirements require that pilot perception of stick forces remain within an acceptable range (or limits, if you prefer).
Aren't you describing the airflow at windmill?
(Airflow) Turned downwards, and accelerated in the inlet plenum...why we see "fog" in the inlet when engine is running above idle. The low pressure is below the nacelle lip.... Lift?
Unaccelerated airflow at TOGA...?
Originally Posted by Bugbear
This "twist" is substantial....it is also "torque"....an example would be American DC 10 losing Number one when the rear pylon mount failed. It rotated forward and over the top of the wing.
Moderator
We appear to be talking about different and varied things, here.
Aren't you describing the airflow at windmill?
Yes, and at takeoff thrust, and with the engine shut down. The numbers might vary but the physics is much the same. We are not so much thinking about the air that goes down the gullet but, rather, the airflow which interacts with the nacelle lip profile. Consider the section profile shape of the nacelle lip. Does it not somewhat resemble an aerofoil shape ?
why we see "fog" in the inlet when engine is running above idle
More relating to the formation of inlet vortex flows. Not really much to do with the up force. The following link has a typical picture at Fig 1.1
The inlet-vortex system of jet engines operating near the ground | Fluid Dynamics and Co-located Conferences (aiaa.org)
The same sort of thing happens with propeller airflow. For example, see Fig 2-32 in the following link https://www.aircraftspruce.com/catalog/pdf/13-09032.pdf
Aren't you describing the airflow at windmill?
Yes, and at takeoff thrust, and with the engine shut down. The numbers might vary but the physics is much the same. We are not so much thinking about the air that goes down the gullet but, rather, the airflow which interacts with the nacelle lip profile. Consider the section profile shape of the nacelle lip. Does it not somewhat resemble an aerofoil shape ?
why we see "fog" in the inlet when engine is running above idle
More relating to the formation of inlet vortex flows. Not really much to do with the up force. The following link has a typical picture at Fig 1.1
The inlet-vortex system of jet engines operating near the ground | Fluid Dynamics and Co-located Conferences (aiaa.org)
The same sort of thing happens with propeller airflow. For example, see Fig 2-32 in the following link https://www.aircraftspruce.com/catalog/pdf/13-09032.pdf
John
"Yes, and at takeoff thrust, and with the engine shut down. The numbers might vary but the physics is much the same. We are not so much thinking about the air that goes down the gullet but, rather, the airflow which interacts with the nacelle lip profile. Consider the section profile shape of the nacelle lip. Does it not somewhat resemble an aerofoil shape ?"
Air flowing into the inlet can be at velocity that
sucks away airstream inches above the bottom of the Nacelle lip. Airstream that is well below the pressure of the airstream above. This low pressure does not produce Lift...a bit like the reverse of a "blown wing"
The shape of inlet air is a cone. As more air is taken in the plenum, the cone can migrate out the lip, and remove (pull in) most all air impinging the lip, no positive pressure to push the nacelle upward. This energetic reduction of top flow (effectively) reduces the AoA of the upper nacelle. I think I'm right. But stand to be corrected. Trying to remember conversations I was fortunate to have with Robert Abernethy. We talked at length about airflow inside outside the J-58.
Yes the nacelle section looks airfoilish. Not a good design, considering the headaches that followed.
I have consistently believed that Boeing focused on "Nacelle" to redirect attention away from the newer engines, which clearly made it a new "type" aircraft.
Misdirection, imo. I won't call it fraud. Here
Air flowing into the inlet can be at velocity that
sucks away airstream inches above the bottom of the Nacelle lip. Airstream that is well below the pressure of the airstream above. This low pressure does not produce Lift...a bit like the reverse of a "blown wing"
The shape of inlet air is a cone. As more air is taken in the plenum, the cone can migrate out the lip, and remove (pull in) most all air impinging the lip, no positive pressure to push the nacelle upward. This energetic reduction of top flow (effectively) reduces the AoA of the upper nacelle. I think I'm right. But stand to be corrected. Trying to remember conversations I was fortunate to have with Robert Abernethy. We talked at length about airflow inside outside the J-58.
Yes the nacelle section looks airfoilish. Not a good design, considering the headaches that followed.
I have consistently believed that Boeing focused on "Nacelle" to redirect attention away from the newer engines, which clearly made it a new "type" aircraft.
Misdirection, imo. I won't call it fraud. Here
Last edited by BugBear; 29th Jun 2024 at 04:40.
"Boeing tried various aerodynamic doodads to reduce that aero pitch-up effect but none worked satisfactorily. That's why they ended up with MCAS."
Thanks TDR, that's the exact answer I was seeking earlier.
Thanks TDR, that's the exact answer I was seeking earlier.
Your theories are so akward, throwing in selective pieces and leaving out important factors.
You're outright dangerous if someone reads your postings without critical mind.
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AoA
And yet this anomaly with the LEAP? What of the behavior of the wing with the "Higher" angles of attack? The nacelle gets an inordinate amount of attention, what of the increase in Lift of the entire wing? The Nacelle leading edge at its peak, v. the wing?? The fan is two inches wider than the CFM.
OMG
The Nacelle lift effect was certainly there since 733 734 and maybe relatively stronger on the 735. 737 NG? yet stronger. Also on the Airbusses 318,19... any airplane with this style of engine config!
Yet the designer were able to balance that and every other influence aerodynamically. Or with FBW.
The MAX obviously was the one where it couldn't be balanced with aerodynamics alone anymore. Edit: And even then only in a small corner of the flight envelope.
Right? Right!
The Nacelle lift effect was certainly there since 733 734 and maybe relatively stronger on the 735. 737 NG? yet stronger. Also on the Airbusses 318,19... any airplane with this style of engine config!
Yet the designer were able to balance that and every other influence aerodynamically. Or with FBW.
The MAX obviously was the one where it couldn't be balanced with aerodynamics alone anymore. Edit: And even then only in a small corner of the flight envelope.
Right? Right!
Last edited by waito; 29th Jun 2024 at 17:18.
Originally Posted by BugBear
I have consistently believed that Boeing focused on "Nacelle" to redirect attention away from the newer engines, which clearly made it a new "type" aircraft.
I have consistently believed that Boeing focused on "Nacelle" to redirect attention away from the newer engines, which clearly made it a new "type" aircraft.
CPR is rather complex, but it has a table listing what can be changed without resulting in it being a "new type" aircraft. New engines are listed in the table - require a revised type cert but not a new type cert.
In short - per CPR - when a revised type cert is called for, systems that are significantly changed must step up to the latest regs, systems that are not significantly changed can keep their original cert basis.
You're debating subjects that you simply do not have the background needed.
Waito - exactly.
waito
"...The MAX obviously was the one where it couldn't be balanced with aerodynamics alone anymore..."
But it was mitigated aerodynamically. Without fanfare, without training. MCAS. What is it about the aerodynamics that imparts Downforce on the tail...needing an auto correction...to prevent a Stall.
But it was mitigated aerodynamically. Without fanfare, without training. MCAS. What is it about the aerodynamics that imparts Downforce on the tail...needing an auto correction...to prevent a Stall.
td
"...That is all covered in the "Changed Product Rule" (CPR) - harmonized over two decades ago between the FAA and EASA...."
Thanks, I get that.. CPR. Changing Pitch Rate...
What is it about UNCOMMANDED Rapid descents that is NOT affiliated with MCAS??
LIH, ETI, OKC, LIONAIR?
Thanks, I get that.. CPR. Changing Pitch Rate...
What is it about UNCOMMANDED Rapid descents that is NOT affiliated with MCAS??
LIH, ETI, OKC, LIONAIR?
Sorry, but I have no time for arguing with people who simply want to argue.
I'm done with this thread. Again.
I'm done with this thread. Again.
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Respect, you're not arguing. You're demanding silence. If John wants me to stop posting, I will.
Just block me
Wondering why Boeing sought such a powerful authority to control Pitch. Is it because as the aircraft starts to lose pItch up authority with elevators, is it too late for elevators to Pitch the aircraft down? Has the Shaker Pusher lost its efficacy? Nose Down THS is all that's left? Is this not about Pitch necessarily but too far aft CG? Why the prohibition against MCAS with ANY Flap? If elevators are out of the solution lacking authority to quickly lower AoA, isn't the jet already LOC?
Just block me
Wondering why Boeing sought such a powerful authority to control Pitch. Is it because as the aircraft starts to lose pItch up authority with elevators, is it too late for elevators to Pitch the aircraft down? Has the Shaker Pusher lost its efficacy? Nose Down THS is all that's left? Is this not about Pitch necessarily but too far aft CG? Why the prohibition against MCAS with ANY Flap? If elevators are out of the solution lacking authority to quickly lower AoA, isn't the jet already LOC?
Last edited by BugBear; 29th Jun 2024 at 21:24.
BB, the issue primarily involved the requirements for longitudinal stability; often described as stick force vs airspeed (for a given trimmed condition); it did not involve the stall.
Because stick force - what the pilot feels, during pitch control involves the elevator and trimmed tail surfaces, these were involved with the solution, but not massively so.
The power of the tail trim only became a dominant factor after the failure of an AoA input to a poorly engineered system - ok in theory, but not so with failures, nor the belief that pilot detection and intervention (without training) was a mitigation.
Because stick force - what the pilot feels, during pitch control involves the elevator and trimmed tail surfaces, these were involved with the solution, but not massively so.
The power of the tail trim only became a dominant factor after the failure of an AoA input to a poorly engineered system - ok in theory, but not so with failures, nor the belief that pilot detection and intervention (without training) was a mitigation.
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