Team-BHP > Commercial Vehicles


Reply
  Search this Thread
254,931 views
Old 5th May 2020, 18:44   #496
BHPian
 
Join Date: Mar 2018
Location: Bengaluru
Posts: 183
Thanked: 558 Times
Re: Boeing 737 Max crashes and grounding

Quote:
Originally Posted by Jeroen View Post
No idea. But we do know that the engines are mounted higher, so the arm is shorter to start with. So if everything else is equal, for a given thrust increase it would actually be less. But that is purely based on the fact that we know the engines are mounted a little higher. No idea about other effects, or differences.

Jeroen
The engines are higher but also more forward mounted which means that although the thrust moment arm is shorter, the moment arm of the lift generated by the engine nacelles is actually longer. Also the moment acts longitudinally ahead of of the CoG thus causing a pitch up moment in high AoA/high speed scenarios. And these scenarios were the original scope of MCAS intervention. Remember the MCAS was origianlly intended to be a longitudinally stability enhancement.
arijitkanrar is offline   (1) Thanks
Old 5th May 2020, 21:15   #497
BHPian
 
Join Date: Jan 2008
Location: Bangalore
Posts: 945
Thanked: 1,520 Times

Quote:
Originally Posted by arijitkanrar View Post
The engines are higher but also more forward mounted which means that although the thrust moment arm is shorter, the moment arm of the lift generated by the engine nacelles is actually longer. Also the moment acts longitudinally ahead of of the CoG thus causing a pitch up moment in high AoA/high speed scenarios. And these scenarios were the original scope of MCAS intervention. Remember the MCAS was origianlly intended to be a longitudinally stability enhancement.
That's exactly what I tried to explain at https://www.team-bhp.com/forum/comme...ml#post4741561 (Boeing 737 Max crashes and grounding)

Below is a pic I drew that I hope helps understand it better:

Boeing 737 Max crashes and grounding-20200505_205900.jpg

Boeing 737 Max crashes and grounding-20200505_205839.jpg

Last edited by Aditya : 6th May 2020 at 06:10. Reason: Merged to incorporate attachments
vharihar is offline   (2) Thanks
Old 6th May 2020, 00:12   #498
Distinguished - BHPian
 
Join Date: Oct 2012
Location: Delhi
Posts: 8,035
Thanked: 49,751 Times
Re: Boeing 737 Max crashes and grounding

Trying to finalise the various discussion around pitch up on the Max. Many articles in the various media will mention that the Max has a pitch up tendency, due to the fact that the engine are mounted further forward. The internet jumps on that as if that is logical. It is not.

In fact due to the fact that the Max engine are so much larger than on previous 737 the actual moment due to engine thrust (all things equal) reduces as the arm relevant for the engine thrust moment reduces. As I said before, you can mount the engine 10 meters in front of the cockpit, the arm doesn’t change.

However, under high AoA, a very different force comes into play, perpendicular to engine thrust. The engine nacelle produces additional lift.

I have made this very simple picture trying to explain the difference between the moment created due to engine thrust and aerodynamic forces on the nacelle. I have chosen an arbitrary CG, but it doesn’t really matter. What matters is that there are two very different kinds of momentum. The engine thrust related one is what most of the Internet keeps hampering on, not understanding what the relevant arm is. Engine forward mounting is of no relevant, none whatsoever. Engine height (and thus shorter arm is, but the internet is slow to pick up on that one)

Hope this helps:

Boeing 737 Max crashes and grounding-screenshot-20200505-8.30.25-pm.png

I do imagine that F2 is actually much smaller than F1, even though I have drawn about equal length. I am not sure about X length compared to Y length, but I guess they are not that different.

Jeroen
Jeroen is online now  
Old 6th May 2020, 00:15   #499
Distinguished - BHPian
 
Join Date: Oct 2012
Location: Delhi
Posts: 8,035
Thanked: 49,751 Times
Re: Boeing 737 Max crashes and grounding

Quote:
Originally Posted by vharihar View Post
Below is a pic I drew that I hope helps understand it better:
I made an image in the previous post, it might be similar to what you are trying to show

Jeroen

Last edited by Aditya : 6th May 2020 at 06:11. Reason: Image issue fixed
Jeroen is online now  
Old 6th May 2020, 10:43   #500
BHPian
 
Join Date: Jan 2008
Location: Bangalore
Posts: 945
Thanked: 1,520 Times
Re: Boeing 737 Max crashes and grounding

On further thought, I admit I may be wrong, and Jeroen you may be right as regards the continued puzzlement as to why the pitch-up tendency is expected with engine moved forward.

After staring at the pics in my post longer (https://www.team-bhp.com/forum/comme...ml#post4799759 (Boeing 737 Max crashes and grounding)), I realized that r*sin(theta) is simply the *vertical* "distance" as seen in the second pic. And that remains unaffected by the engine moving forward. If at all, it may reduce bcoz I believe the engine is moved forward in the MAX-800 and also up, so the center of thrust moves up (well, it may be offset by the engine being bigger, so that may make the center of thrust move a bit down; so it will need to be seen which of the 2 opposing contributions wins and has the net effect on this "distance", or the "arm" as you call it).

So unless there are other changes in the MAX-800 that make the CG of the aircraft go up (which would contribute to a longer "arm"), my puzzlement remains.
vharihar is offline  
Old 6th May 2020, 12:56   #501
BHPian
 
MegaWhat's Avatar
 
Join Date: Apr 2020
Location: Pune/Oxford
Posts: 99
Thanked: 631 Times
Re: Boeing 737 Max crashes and grounding

Quote:
Originally Posted by Jeroen View Post
The internet jumps on that as if that is logical. It is not.
I think I would use the word "straight-forward" instead of "logical".

Quote:
Originally Posted by Jeroen View Post
However, under high AoA, a very different force comes into play, perpendicular to engine thrust. The engine nacelle produces additional lift...


...I do imagine that F2 is actually much smaller than F1, even though I have drawn about equal length. I am not sure about X length compared to Y length, but I guess they are not that different.
Thanks for the schematic!
Indeed F2 will be much smaller than F1, however Y is longer than X.
The CG of an aircraft is located approximately near 25% of the mean chord (width) of the wing. Now, because the wings of the 737 or most passenger aircraft are swept backwards and also taper outwards, the mean width gets pushed backwards as well and hence the CG is significantly behind the engine. Below is an image of the CG line for the 737 and 737 MAX. Notice the distance between the CG and the engine.


Quote:
Originally Posted by vharihar View Post
..my puzzlement remains.
Try dividing the force into two components, along the oncoming flow and perpendicular to it, and then, think of the lift (force perpendicular to the oncoming flow) created due to the engine instead of the thrust. I think that'll help understand what Jeroen and I've been talking about.
MegaWhat is offline   (4) Thanks
Old 6th May 2020, 12:58   #502
Distinguished - BHPian
 
Join Date: Oct 2012
Location: Delhi
Posts: 8,035
Thanked: 49,751 Times
Re: Boeing 737 Max crashes and grounding

Quote:
Originally Posted by vharihar View Post
so the center of thrust moves up (well, it may be offset by the engine being bigger, so that may make the center of thrust move a bit down; so it will need to be seen which of the 2 opposing contributions wins and has the net effect on this "distance", or the "arm" as you call it).
.
Thanks for your thoughts. With bigger engines, mounted a little further forward, and a little higher, with all other things remaining equal, you would expect the CG to move forward and up.

Just a few thoughts; as I mentioned earlier, the weight of the engines compared to the take of weight is about 4:82. So moving the engines around a bit is not going to have a big effect on the CG one way or the other (Although small CG changes can effect the way an aircraft handles.

The length of the arm, compared to the force (Engine thrust or Aerodynamic) is very small. In the formulae M = FxArm the arm is measured in meters and the force is Newton. These engines produce upwards of 100 kN! So a few centimeters extra or less arm is not going to change the moment by much either.

Jeroen
Jeroen is online now   (1) Thanks
Old 11th June 2020, 01:31   #503
Distinguished - BHPian
 
Join Date: Oct 2012
Location: Delhi
Posts: 8,035
Thanked: 49,751 Times
Re: Boeing 737 Max crashes and grounding

Boeing appears to aim for recertification flight (s) by the end of the month (June).

FAA pilot will be in command, not a Boeing pilot.

They have also re-started Max production since end of May.

https://www.cnbc.com/2020/06/10/boei...d-of-june.html

Jeroen
Jeroen is online now   (3) Thanks
Old 29th June 2020, 09:13   #504
Team-BHP Support
 
Join Date: Sep 2010
Location: All over!
Posts: 7,591
Thanked: 18,197 Times
Re: Boeing 737 Max crashes and grounding

Quote:
Originally Posted by Jeroen View Post
Boeing appears to aim for recertification flight (s) by the end of the month (June).
Right on schedule.

Quote:
Boeing has received clearance to begin test flights of its troubled 737 Max jet, a spokesperson for the Federal Aviation Administration said Sunday. The test flights of could begin as early as Monday.

The move marks an important step in the process to re-certify the 737 Max, which has been grounded since March 2019, for passenger flights.
Boeing has said it expects to receive full approval for the plane to fly passengers by the middle of this year. The FAA in a letter to Congress Sunday said it does not yet have a date for when the grounding will be lifted.
https://edition.cnn.com/2020/06/28/b...ved/index.html

The problem now, would be if any airliner actually has sufficient flights to ply the 737 Max on!
libranof1987 is offline   (1) Thanks
Old 3rd July 2020, 14:11   #505
Senior - BHPian
 
AlphaKilo's Avatar
 
Join Date: Nov 2010
Location: VOMM-EDDW-EDDM
Posts: 1,162
Thanked: 1,187 Times
Re: Boeing 737 Max crashes and grounding

First step towards final certification achieved.

https://www.faa.gov/news/updates/?newsId=93206

Quote:
The FAA and Boeing today completed the certification flight tests on the Boeing 737 MAX. During three days of testing this week, FAA pilots and engineers evaluated Boeing’s proposed changes in connection with the automated flight control system on the aircraft. While completion of the flights is an important milestone, a number of key tasks remain, including evaluating the data gathered during these flights. The agency is following a deliberate process and will take the time it needs to thoroughly review Boeing’s work. We will lift the grounding order only after FAA safety experts are satisfied that the aircraft meets certification standards.
AlphaKilo is offline   (3) Thanks
Old 3rd July 2020, 14:19   #506
Distinguished - BHPian
 
Reinhard's Avatar
 
Join Date: Nov 2010
Location: Pune
Posts: 4,841
Thanked: 17,639 Times
Re: Boeing 737 Max crashes and grounding

Quote:
Originally Posted by AlphaKilo View Post
First step towards final certification achieved.
Slightly OT but just like the fighter test pilots across air forces, I have a tremendous respect for these pilots, test engineers and experts that board brand new planes & especially the planes like the MAX that have fatal accidents on record. Takes some courage to take that step into the plane regardless of how much the plane maker assures safety.

I wonder when exactly the MAX will come back into service & with Covid-19 still around - how many of those parked planes really will get pushed into service again after refits over next 3-4 years. Air travel demand is going to take a huge hit and the extra range that is the MAX's USP might not be needed with quite a lot of international travels going to be on back burner.
Reinhard is online now   (1) Thanks
Old 5th July 2020, 19:08   #507
Distinguished - BHPian
 
anjan_c2007's Avatar
 
Join Date: Jul 2008
Location: India
Posts: 8,255
Thanked: 20,263 Times
Re: Boeing 737 Max crashes and grounding

Flyers need to know about the Boeing 737 MAX due to the fact that it is most likely to get the Federal Aviation Administration (FAA) certification to become fit to fly by 2020 end, as the newsreport says. The timeline for it's fitness after the fault rectifications has though not been officially announced. The FAA needs to be convinced that the aircraft is fit to fly again and only then it will lift the grounding orders.

The facts flyers need to know about the Boeing 737 MAX include which airlines fly the MAX. Boeing had delivered 370 aircraft to 47 customers, the largest being South West Airlines with 34. Also flyers need to know routes the MAX flies, how they know they are booking a MAX flight ?

The answer to know whether they are booking a MAX :-

Quote:

For example, American Airlines previously listed the Max on its website booking page as the “7M8” aircraft, which stands for Boeing 737 MAX 8. (There are 7, 8, 9 and 10 numbered variants, depending on the seating capacity). Southwest has a webpage that lets you identify what plane you are scheduled to fly on. However, the plane that is scheduled to fly a route can change for myriad reasons, ranging from run-of-the-mill maintenance issues to poor weather causing network delays.
The fact is that MAX is 17 % more fuel efficient than the older 737 siblings and that matters a lot for the presently cash strapped airlines. The other commercial airliner that has been successfully rehabilitated is the Boeing 787 Dreamliner, which was grounded for four months during 2013 due to it's smoking lithium ion batteries. The Dreamliner 787 is now the darling of both flyers and airlines, with no fatal crashes on record.

Recognising whether an airplane being boarded is a MAX ?

Quote:

How can I tell if I’m flying on a Max?
If you’re waiting at the gate and see your plane, look for large and pointy fins extending above and below the wingtips called winglets. Winglets come in all manner of similar designs, but the Max’s stand out.
And about refunds for flights booked in MAX airplanes ?

Quote:

Will airlines allow me to rebook or get a refund if I don’t want to fly on the Max?
Rebook? Yes. Refund? No. U.S. carriers have not yet announced policies related to the return of service of the Max. However, in a statement this week to The New York Times, a United Airlines spokeswoman said that the company “will be transparent — and communicate in advance — with our customers who are booked to fly on a Max aircraft, will rebook those who do not want to fly on a Max at no charge.” Expect other airlines to follow United’s lead.
The full news story link :-

https://www.nytimes.com/2020/07/02/t...section=Travel

Last edited by anjan_c2007 : 5th July 2020 at 19:14.
anjan_c2007 is online now   (1) Thanks
Old 6th July 2020, 00:45   #508
Distinguished - BHPian
 
Join Date: Oct 2012
Location: Delhi
Posts: 8,035
Thanked: 49,751 Times

If its any consolation, the changes of catching the Corona Virus whilst traveling on any plane is considerable larger then crashing whilst traveling on the Max.

Jeroen
Jeroen is online now   (3) Thanks
Old 4th August 2020, 19:18   #509
Distinguished - BHPian
 
Join Date: Oct 2012
Location: Delhi
Posts: 8,035
Thanked: 49,751 Times
Re: Boeing 737 Max crashes and grounding

Here we go, at long last: he FAA sent a notice of proposed rulemaking (NPRM) for a Boeing 737 MAX airworthiness directive (AD) (PDF) to the Office of the Federal Register for publication.

Here it is: https://www.faa.gov/news/media/attac...-R3-8-3-20.pdf

Some of the relevant bits:

Quote:
To ensure that an erroneous signal from a failed single AOA sensor does not prevent continued safe flight and landing, and specifically that it does not generate erroneous MCAS activation, the FAA proposes to require installation of updated FCC software with revised flight control laws 10 associated with MCAS. These revised flight control laws would use inputs from both AOA sensors to activate MCAS. This is in contrast to the original MCAS design, which relied on data from only one sensor at a time, and allowed repeated MCAS activation as a result of input from a single AOA sensor.
The updated FCC software would also compare the inputs from the two sensors to detect a failed AOA sensor. If the difference between the AOA sensor inputs is above a calculated threshold, 11 the FCC would disable the speed trim system (STS), including its MCAS function, for the remainder of that flight, and provide a corresponding indication of such deactivation on the flight deck.
To ensure that MCAS will not command repeated movements of the horizontal stabilizer, the revised flight control laws would permit only one activation of MCAS per sensed high AOA event. A subsequent activation of MCAS would be possible only after the airplane returns to a low AOA state, below the threshold that would cause MCAS activation.
The updated FCC software would also limit12 the magnitude of any MCAS command to move the horizontal stabilizer, such that the final horizontal stabilizer position (after the MCAS command) would preserve the flightcrew’s ability to control the airplane pitch by using only the control column. The original design allowed MCAS commands to be made without consideration of the horizontal stabilizer position – before or after the MCAS command.
An undesired MCAS activation could prompt the flightcrew to perform a nonnormal procedure. To ensure that after any foreseeable failure of the stabilizer system, safe flight is not dependent on the timeliness of the flightcrew performing a non-normal procedure, the FAA proposes multiple changes.
First, as previously discussed, the flight control laws would be changed to instead use inputs from two AOA sensors for MCAS activation, so that there would not be an undesired MCAS activation due to a single AOA sensor failure that could lead a flightcrew to perform a non-normal procedure.
Second, in the event that MCAS is activated as intended (i.e., during a high AOA event), the updated flight control laws software would limit the number of MCAS activations to one per high AOA event, and limit the magnitude of any single activation so that the flightcrew could maintain pitch control without needing to perform a nonnormal procedure.
The FAA also proposes requiring an additional software update that would alert the flightcrew to a disagreement between the two AOA sensors. This disagreement indicates certain AOA sensor failures or a significant calibration issue. The updated MDS software would implement an AOA DISAGREE alert on all 737 MAX airplanes. Some 737 MAX airplanes were delivered without this alert feature, by error. While the lack of an AOA DISAGREE alert is not an unsafe condition itself, the FAA is proposing to mandate this software update to restore compliance with 14 CFR 25.1301 and because the flightcrew procedures mandated by this AD now rely on this alert to guide flightcrew action. As a result of the changes proposed in this AD, differences between the two AOA sensors greater than a certain threshold13 would cause an AOA DISAGREE alert on the primary flight displays (PFDs).
...
...
As part of the FAA’s review of these design changes, the agency reviewed the entirety of the 737 MAX horizontal stabilizer control system. This review revealed that the physical separation of the horizontal stabilizer trim arm wiring and the horizontal stabilizer trim control wiring does not meet the criteria specified in 14 CFR 25.1707. This design standard was promulgated in 2007 and therefore is part of the certification basis of the 737 MAX but not of previous Boeing Model 737 airplanes. Certain wiring installations must have enough physical separation so that a wiring failure cannot create a hazard. Since design changes must comply with FAA regulations, the FAA proposes to require changes to the wiring installation to meet the required physical separation between the horizontal stabilizer trim arm wiring and the horizontal stabilizer trim control wiring. The FAA proposes this action to bring the airplanes into regulatory compliance.
What is interesting to note is that the FAA proposes the Max can be flown with both AOA sensors out of action! It does make you wonder why Boeing put MCAS in there in the first place. According to some comments on PRUnE:

Quote:
Many failures of safety and envelope protection systems result in them being locked out for the rest of the flight following a sensor or computer malfunction, you normally can't dispatch without them but if they fail in flight you continue with appropriate mitigations.
So it is down to the statistical change of something happening and the trade off to economic damage (land asap!)

Jeroen
Jeroen is online now   (1) Thanks
Old 5th August 2020, 10:00   #510
Senior - BHPian
 
Join Date: Jul 2009
Location: Calcutta
Posts: 4,668
Thanked: 6,213 Times
Re: Boeing 737 Max crashes and grounding

For us laymen
https://www.reuters.com/video/watch/idPVy1?now=true

Sutripta
Sutripta is offline   (2) Thanks
Reply

Most Viewed
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Copyright ©2000 - 2024, Team-BHP.com
Proudly powered by E2E Networks