[Sutripta]

^^^
Speed takes time to change.

Lets simplify. Other things being equal (ie MCAS off) for same inputs does the nose of the Max pitch up more than that of the regular 737?

Regards
Sutripta

[Jeroen]

Originally Posted by Sutripta

Lets simplify. Other things being equal (ie MCAS off) for same inputs does the nose of the Max pitch up more than that of the regular 737?

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

[Sutripta]

Originally Posted by Jeroen

No idea.

Then there is nothing to discuss, speculate, or otherwise rack our brains over.

Regards
Sutripta

[Jeroen]

Originally Posted by Sutripta

Then there is nothing to discuss, speculate, or otherwise rack our brains over.

Pitch up, or the lack thereof, is rarely, if ever, just a function of thrust. What was it you were after in the first place?

Regards,
Jeroen

[Sutripta]

Originally Posted by Jeroen

What was it you were after in the first place?

Me? Not just me! You too I would guess.

Differences in flying characteristics between regular 737s and Max (without MCAS)

Regards
Sutripta

[Jeroen]

Originally Posted by Sutripta

Me? Not just me! You too I would guess.
Differences in flying characteristics between regular 737s and Max (without MCAS)

Well, we know the answer to that one: They are near identical, or identical enough so pilots would need no SIM training, just a bit of study on an iPad. (Which was more related to systems than to actual flying characteristics).

Or at least that is how it all started out, of course. And lets face it; hundreds of pilots made thousands of hours without any major re-training and certainly no SIM time!

The MCAS only plays a role at the extremes of the flight envelope anyway. So I would say the only differences between the regular 737 and the Max is to be found at those conditions where MCAS would cut in. Everything else is identical or near enough not for pilots to worry about.

The confusion is that many people and sources talk about this tendency of the Max to pitch up, and usually add that it has to do with the engines being mounted more forward. As we discussed, that is less than half the story.

The difference is that the regular 737 had better longitudinal stability. Which only becomes noticeable at high angles of attack. Which meant that pilots would feel the required (regulation) forces on the yoke at high angles of attack. etc. etc.

Would a regular 737 pitch up more or less compared to a Max in say level flight for a given thrust increase? I don’t know, but based on the fact that originally they came under the same type approval and thus pilot proficiency, my guess is that any difference are simply not material. (from a piloting and or certification perspective).

The main differences between the Max and earlier 737 models are more about the type of engine, some systems (e.g. fly by wire spoilers) , dimensions/weight, various mechanical strengthening. But not flying characteristics!

If there had been a material flying characteristics difference, Boeing would have had to design a pilot training / SIM program. They did not, and lets face it, the plane was sold with this very item (identical flying characteristics) as one of it’s main selling feature!

But of course, all of the above is just my interpretations and there could be other factors to be considered.

Jeroen

[MegaWhat]

Originally Posted by Sutripta

Nacelle as canard/ lifting body should be easy enough to design round - make it symmetric about the horizontal axis. Will add a slight amount of drag. I would think there is more to it than that.
Surprised that no one in universities have put various models of the 737 in wind tunnels and let us know the results.

The probability of a university getting a detailed 737 model to test is close to impossible, unless Boeing has a tie up with it. In which case the data is extremely closely protected. Even universities in India that are relatively lax in IP protection end up taking things seriously when it comes to companies like Boeing. And scanning a 737, producing a replica and testing it in a wind tunnel is a sure shot way of getting sued.

As to a symmetric nacelle, yes it won't produce an unbalanced lift but only as long as its axis is aligned with the oncoming air. The moment there is a relative angle between the axis of the engine and the oncoming air, there will be an unbalanced force perpendicular to the direction of the flow. In flight, especially during climb, there is an aerodynamically significant relative angle between the air and the engine axis. So a lifting force will surely exist. And it's going to interact with the lift produced by the wings.

Originally Posted by Sutripta

First question should be validating the accepted belief that 'increasing thrust on the Max causes the nose to pitch up'. If so, then one can get into the whys. If not, question doesn't arise.

Originally Posted by Sutripta

Differences in flying characteristics between regular 737s and Max (without MCAS)

As Jeroen rightly put it, any engine mounted below the CG of an aircraft is going to generate a pitch up moment. But at this point I think we need to separate a few things. Almost every element on an aircraft will generate some pitch moment - up or down. The final output of the nose going up or down is basically just a net result of all these pitch moments. If the moments are not balanced among each other, the aircraft nose will pitch. If they are balanced by each other, the nose stays where it is.

The nose up pitching moment generated by increasing the thrust of the engine is usually gradual and predictable. It is also well controlled by the nose down pitching moment generated by the tail. However, if there's a jump in the pitch up moment generated by the engine, independent of the thrust - say due to the unbalanced aerodynamic forces of the nacelle exterior at high angles of attack - then you need to further engineer and control the downward tail moment to counter it. I think that's where MCAS comes in. And I think that's probably a difference in the flight pitch stability equation of the 737 NG vs. the MAX.

Apart from the pitch moment itself, the rate of change of the moment is extremely important. Imagine you're driving straight on a vast plain at a constant speed of 80 kmph. In one scenario you gradually turn your steering from 12o clock position to 6o clock position in around 10 seconds. That's smooth, predictable. In the second scenario you turn the steering from 12o clock to 3o clock position in 5 seconds (gradual again) but then go from 3o clock to 6o clock within 1 second. That's going to be sharp with a few dynamic forces and moments, that ideally need to be accounted for. A car designed for those forces will be able to handle them better than one which isn't.

Overall, like stated before, it feels like Boeing tried to solve a hardware problem by throwing software at it. And then not telling their stakeholders about the details of this software, thereby hiding the inherent hardware issues. And then prioritising cost and time to market by avoiding training pilots with regards to this software.

In any case, I think what we know will change as more details come out.

[MegaWhat]

Originally Posted by Jeroen

The MCAS only plays a role at the extremes of the flight envelope anyway. So I would say the only differences between the regular 737 and the Max is to be found at those conditions where MCAS would cut in. Everything else is identical or near enough not for pilots to worry about.

Indeed. The differences in handing exist only at the extremes. And the complications come to the fore only when other things - like the angle of attack sensor - go wrong at the exact same time. As you mentioned, that's why so many other MAX flights have been safe.

Originally Posted by Jeroen

The main differences between the Max and earlier 737 models are more about the type of engine, some systems (e.g. fly by wire spoilers) , dimensions/weight, various mechanical strengthening. But not flying characteristics!

At least they did not plan for the flight characteristics to be different!

[Jeroen]

Originally Posted by MegaWhat

it feels like Boeing tried to solve a hardware problem by throwing software at it. .

Yes, that appears to be the consensus. It is believed Boeing did try to solve the problem through aerodynamic solutions. Whether that was technically not feasible or too expensive is not really known. Enter MCAS.

Originally Posted by MegaWhat

At least they did not plan for the flight characteristics to be different!

It was in fact one of its BIG unique selling features. As pilots required virtually no training, no SIM time, it was very easy and economic to introduce the Max into an existing Boeing 737 fleet. Boeing’s contract with Southwest apparently has a penalty clause: if the pilots would require SIM training that would cost Boeing a million dollar per plane!

When this Max entered service, there were hardly any Max Simulators about. It was not deemed necessary!

Jeroen

[Sutripta]

Originally Posted by Jeroen

As we discussed, that is less than half the story.

So waiting for the full story.

The main differences between the Max and earlier 737 models are more about the type of engine, some systems (e.g. fly by wire spoilers) , dimensions/weight, various mechanical strengthening. But not flying characteristics!

If there had been a material flying characteristics difference, Boeing would have had to design a pilot training / SIM program. They did not, and lets face it, the plane was sold with this very item (identical flying characteristics) as one of it’s main selling feature!

And we come full circle.

But of course, all of the above is just my interpretations

Of course. Anyone saying anything else?

[Sutripta]

Originally Posted by MegaWhat

Overall, like stated before, it feels like Boeing tried to solve a hardware problem by throwing software at it. And then not telling their stakeholders about the details of this software, thereby hiding the inherent hardware issues. And then prioritising cost and time to market by avoiding training pilots with regards to this software.

Without repeating the same things over and over again, this ^^^ is the crux of the matter.

What was immediately being discussed is trying to figure out why (not what). And once again not the 'why' of why something was done (commercial reasons) but what effect each change means technically.

This thread is 33 pages long. And there is another thread too.

Regards
Sutripta

[Jeroen]

Originally Posted by Sutripta

So waiting for the full story.

And we come full circle.

The full story is always in the eye of the beholder. Just because new information will come to light, doesn’t necessary it is the full story. Even formal final accident reports tend to get discussed and debated for ever as to what really happened.

So I think there are likely to be multiple “full stories” out there for a very long time. Just as there are today.

It will be interesting to see what the various re-certifications will call for in terms of pilot training. So far I have seen emphasis only on the updated MCAS behaviour and its associated non normal routines when it comes to flight characteristics. But then the news updates on the re-certification are a bit thin these days. Especially getting detailled views.

Jeroen

[Sutripta]

In this

Originally Posted by Sutripta

So waiting for the full story.

The main differences between the Max and earlier 737 models are more about the type of engine, some systems (e.g. fly by wire spoilers) , dimensions/weight, various mechanical strengthening. But not flying characteristics!


And we come full circle.


Of course. Anyone saying anything else?

The part in bold is actually from your post, which got left behind as I was copy/ pasting. Not relevant to my post.

Regards
Sutripta

[pganapathy]

This brings up a question. Let us assume Boeing can get the Max re-certified with all regulators and flying again. Will they be able to get away with limited training on an iPad, like they did earlier, or will they be required to get all pilots simulator training. This will be expensive but will ensure much greater faith in the plane. I wonder which option Boeing is looking at.

[MegaWhat]

Originally Posted by Jeroen

So I think there are likely to be multiple “full stories” out there for a very long time. Just as there are today.

Indeed. Whatever has been discussed on the internet and on this forum is simply based on the information available in public domain today. This information & subsequent hypotheses will surely evolve.

Originally Posted by Sutripta

And once again not the 'why' of why something was done (commercial reasons) but what effect each change means technically.

I'm just summarizing my earlier comments here:

Based on my understanding and interpretation of available facts, the most significant change in the MAX vs. the NG was the new engine and it's mounting further ahead of the aircraft CG. This placement magnifies the moment created by the external aerodynamic lifting forces on the engine nacelle resulting in a pitch-up tendency at high Angles of attack which would not happen in the previous versions of the 737.

All other pieces of the puzzle (malfunctioning AoA sensor, MCAS etc.) fit in with this above pitch up tendency and make matters worse.

Again, this is only my interpretation. Things are bound to evolve. Only an aerodynamicist or a loads and control guy in Boeing would have the full picture.