Thanks, Simon. Displacement rather than force.. I see now.

49 minutes ago, Bobsk8 said:

They only made 70 Comets after it was fixed. 

Not very many, there was also the Caravelle, which I never flew on, that had the look of the comet.  It was a beautiful jet to look at and the 787 and A350, A220, Embraer 17x/19x all have that streamlined nose shape that reminds of the comet.  I always wonder, with legacy aircraft like the 737, 747, 777, and their European cousins, how does the fuse design factor in to the efficiency of the aircraft in the air?  They say the Piaggio Avanti propjet is one example where the entire structure generates lift.....

1 hour ago, John_Cillis said:

Not very many, there was also the Caravelle, which I never flew on, that had the look of the comet.

The Caravelle nose design was actually based directly on that of the De Havilland Comet. One of the predecessor companies that eventually went on to become Sud Aviation had previously cooperated with De Havilland on some earlier jet airliner designs. Subsequently Sud Aviation used the Comet nose design under licence from De Havilland in the production their Caravelle.

Bill

Once the operators start canning flights  left right and centre when summer starts because they got no spares floating around to replace their grounded max's  and it starts costing them big bucks, the airlines lawyers and going to start getting twitchy and lawsuits will start you just watch. 

At the moment as its winter most airlines can swap stuff about in minimal disruption but in the summer it's a whole different ball game Mark my words. 

Another issue is Pilots are going to start losing takeoff/ landing  recency in 3 months as well as losing annual line checks. Only way around that is the sim which is at a premium. 

There's always more to it than you think. 

Edited March 18, 20197 yr by tooting

2 hours ago, tooting said:

Once the operators start canning flights  left right and centre when summer starts because they got no spares floating around to replace their grounded max's  and it starts costing them big bucks, the airlines lawyers and going to start getting twitchy and lawsuits will start you just watch. 

At the moment as its winter most airlines can swap stuff about in minimal disruption but in the summer it's a whole different ball game Mark my words. 

Another issue is Pilots are going to start losing takeoff/ landing  recency in 3 months as well as losing annual line checks. Only way around that is the sim which is at a premium. 

There's always more to it than you think. 

Before that happens my guess is some orders of the Max will be switched to Airbus products. 

Switching to Airbus won’t really help - it will just put that carrier at the end of a 6 year queue 

On 3/17/2019 at 5:35 PM, skelsey said:

Stick force may be a confusing way of putting it - perhaps stick displacement is a better description (which implies a stronger pull -- increased backpressure is how I would patter it!).

So conventionally you would expect (and certification standards require) increasing aft stick displacement as you reduce speed in the approach to stall.

In the Max, the larger, higher and more forward-located engine nacelles create lift (like any other part of the airframe). At low angles of attack this is negligible (and designed to be so - the lift to drag ratio of an engine nacelle is pretty rubbish). But at higher angles of attack the lift from the nacelles is significant and it is this which results in the unstable pitch characteristics of the Max in the approach to stall. This is why it is different to the NG and older 737 models.

Just wondering where you’re picking up the nacelle lift issue? It sounds interesting, but Aviation Week, the videos posted above, and me talking with a ex boeing engineer/test pilot, all cite thrust coupling as the main problem. It’s been an issue with 737s, got kind of bad with ng’s and finally over the top with the max with their even more thrust.

6 hours ago, KevinAu said:

Just wondering where you’re picking up the nacelle lift issue? It sounds interesting, but Aviation Week, the videos posted above, and me talking with a ex boeing engineer/test pilot, all cite thrust coupling as the main problem. It’s been an issue with 737s, got kind of bad with ng’s and finally over the top with the max with their even more thrust.

Watch the two videos I posted on this thread. It is clearly explained. 

58 minutes ago, Bobsk8 said:

Watch the two videos I posted on this thread. It is clearly explained. 

Yes, I’ve watched your videos. No, he doesnt really get in depth into how the max is different than the others to the point of requiring mcas except for mentioning some stronger thrust coupling. I didnt see him mention anything about nacelle lift causing interesting problems before the stall recovery.

Edited March 19, 20197 yr by KevinAu

On 3/17/2019 at 9:35 PM, skelsey said:

Stick force may be a confusing way of putting it - perhaps stick displacement is a better description (which implies a stronger pull -- increased backpressure is how I would patter it!).

So conventionally you would expect (and certification standards require) increasing aft stick displacement as you reduce speed in the approach to stall.

In the Max, the larger, higher and more forward-located engine nacelles create lift (like any other part of the airframe). At low angles of attack this is negligible (and designed to be so - the lift to drag ratio of an engine nacelle is pretty rubbish). But at higher angles of attack the lift from the nacelles is significant and it is this which results in the unstable pitch characteristics of the Max in the approach to stall. This is why it is different to the NG and older 737 models.

So I keep asking myself, why would these two 737 Max crews even approach a stall condition? Four commercially rated pilots who apparently lost control of the aircraft?

I am still inclined to think some software glitch at take off/climb thrust induced a software brain fart that commanded some sort of nose down and was subsequently unrecoverable? 

Hope they release the findings quickly!

On 3/17/2019 at 12:06 PM, Bobsk8 said:

Just as I thought, a cover up by Boeing, and the FAA/White House on how  serious this issue was, because the powers to be realized that this would be a heavy hit in the US economy if this plane was grounded. Once Boeing and the White House/FAA  realized that the entire world was not buying this garbage, they had to buckle and finally ground the Max. I have been a Boeing fan for decades, in fact the NGX is my favorite sim aircraft to fly, but frankly I am disappointed in Boeing's behavior on this issue and it looks like the almighty dollar versus possible loss of life, the dollar wins with Boeing. Numerous calls between Boeing's President and the White House during this issue is another indication that something was not right. My guess is the Max will be grounded for quite awhile until they fix this design flaw. 

I know we all love a good conspiracy theory. However, the real world is more mundane. The FAA, Boeing, and most technically advanced organizations tend to eschew big jumps to conclusion on hunches and emotions and instead tend to delay taking any action until all the attainable data is obtained and analysed. What they failed to realize is that perception and assumptions are reality today. So if the initial media and public thought before seeing any actual data is that it was the second crash due to mcas, they needed to act as though it really was to not get behind the pr curve of zero tolerance for mishaps. That is why Boeing and the FAA were the last to act.

As for how this problem could have gotten past the engineers, the reason is that the engineers weren’t checked by non engineers. After the 787 and 747-8 were finished developing, Boeing cut back on their staff. One group that got cut down was their human factors group. The group in engineering that would have played the part of pilots and humans in order to quality check the engineers’ work. To ask obvious questions about how this or that would play out in real life. If they had sufficent human factors resources, at some point with regards to mcas, somebody would have surely questioned the sanity of a system that would have manifested a failure of its primary sensor as an announced unreliable airspeed situation and an unannounced runaway trim situation at the same time.

 

 

1 hour ago, charlie130 said:

So I keep asking myself, why would these two 737 Max crews even approach a stall condition? Four commercially rated pilots who apparently lost control of the aircraft?

I am still inclined to think some software glitch at take off/climb thrust induced a software brain fart that commanded some sort of nose down and was subsequently unrecoverable? 

Hope they release the findings quickly!

No, they were nowhere near stall. The aoa sensor malfunctioned and gave the stall indication.

8 hours ago, KevinAu said:

Just wondering where you’re picking up the nacelle lift issue? It sounds interesting, but Aviation Week, the videos posted above, and me talking with a ex boeing engineer/test pilot, all cite thrust coupling as the main problem. It’s been an issue with 737s, got kind of bad with ng’s and finally over the top with the max with their even more thrust.

To explain further:

This all comes about because of a certification issue: specifically FAR 25.173 which deals with static longitudinal stability.

Quote

§25.173   Static longitudinal stability.

Under the conditions specified in §25.175, the characteristics of the elevator control forces (including friction) must be as follows:

(a) A pull must be required to obtain and maintain speeds below the specified trim speed, and a push must be required to obtain and maintain speeds above the specified trim speed. This must be shown at any speed that can be obtained except speeds higher than the landing gear or wing flap operating limit speeds or VFC/MFC, whichever is appropriate, or lower than the minimum speed for steady unstalled flight.

(b) The airspeed must return to within 10 percent of the original trim speed for the climb, approach, and landing conditions specified in §25.175 (a), (c), and (d), and must return to within 7.5 percent of the original trim speed for the cruising condition specified in §25.175(b), when the control force is slowly released from any speed within the range specified in paragraph (a) of this section.

(c) The average gradient of the stable slope of the stick force versus speed curve may not be less than 1 pound for each 6 knots.

(d) Within the free return speed range specified in paragraph (b) of this section, it is permissible for the airplane, without control forces, to stabilize on speeds above or below the desired trim speeds if exceptional attention on the part of the pilot is not required to return to and maintain the desired trim speed and altitude.

(my emphasis).

As I understand it, this is where the Max encountered issues during flight test. Without MCAS, the Max does not meet the requirements.

This is flight tested at constant thrust (why would you do otherwise -- you would just be introducing an additional variable). So thrust coupling is not a factor (and in fact, given that the thrust/pitch couple is based on the amount of thrust and the lever arm -- i.e. the vertical distance from the thrust line to the CG -- I would not be surprised if with the higher mounted engines the thrust/pitch couple on the Max was actually less than on previous versions due to the shorter arm involved, but I couldn't say that for certain).

1 hour ago, charlie130 said:

So I keep asking myself, why would these two 737 Max crews even approach a stall condition?

They didn't (well, at least in the case of Lion Air - we haven't seen the data from Ethiopian). It was an erroneous AoA sensor input which resulted in MCAS activating when it shouldn't and trimming the stabiliser full nose down. The assumption is that something similar may well have occurred here.

14 hours ago, IUBrian said:

Switching to Airbus won’t really help - it will just put that carrier at the end of a 6 year queue 

6 years is probably about the length of time it will take Boeing to recover from this disastrous PR situation. IF they handle it well and with much sensitivity. 

1 hour ago, sloppysmusic said:

6 years is probably about the length of time it will take Boeing to recover from this disastrous PR situation. IF they handle it well and with much sensitivity. 

I don’t know about 6 years, but I do think more than 6 months and a software patch is required. If I were on the board of directors I’d be demanding a change in leadership, and a thorough top to bottom review not just of this particular aircraft but their QC procedures. I’d eat the loss now, but I’d come out with new management, new policies, and new procedures, and essentially remarket the Max as a new plane and Boeing as an aircraft manufacturer committed to putting the safest planes into the air. I wouldn’t say 6 years but to do it right I’d guess a minimum of 2-3. For long term sustainability I think you have to come out with the “new“ Max and the “old” Max as different as a turtle and a Peruvian Fruit Bat. You don’t come out and say “we fixed the problem. Trust us” in 6 months. I think you come out and say, “not only did we fix this problem, we wanted to know how it happened, got rid of the people responsible, and went one step further with a complete re analysis of all systems to make sure not only does this not happen again, but to try to find things we may not even have thought of to make the Max and all subsequent Boeing aircraft the safest machines in the sky.” 

Of course, I’m not accountable to shareholders. But what happened has raised awareness with the general public as to the type of plane they’re flying, whereas before most probably couldn’t tell you if they were on a Boeing or Airbus, and couldn’t care either way. What type of aircraft a carrier uses can and probably will become a marketing point. If Boeing doesn’t re-establish itself it’s not foreseeable that people may begin to choose and be willing to pay a little more to avoid flying a certain type of plane.