WDB
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Banned...
Mar 13, 2019 10:58:14 GMT
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Post by WDB on Mar 13, 2019 10:58:14 GMT
...from UK airspace. Well, not me but the 737 Max 8 that was supposed to fly me home from Warsaw yesterday. The LOT people had brought it up to the gate and everything... ...but there it just sat for nearly an hour, while they eventually found us a bus and chugged us across the airfield to an Embraer that had been enjoying its afternoon off. The usual coda to a change-of-plane story is lost luggage, but mine turned up as promptly as T2 ever manages. Once they’d got us on the plane, there were no more adventures. But I’ve done three Max 8 flights now. Do I get a special Survivor’s hat?
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Deleted
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Mar 13, 2019 21:24:06 GMT
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Post by Deleted on Mar 13, 2019 21:24:06 GMT
Without doubt.
I've been following the Max 8 story on various aero sites and the similarity with the Lion Air crash was identified very quickly.
It seems that Boeing have over developed the 737 and the possible cause of both crashes is the software designed to stop a consequence of the update. A bit like installing traction control on a Triumph Herald fitted with a Ferrari engine. It would been better to design a new car in which to use the engine instead.
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Post by bromptonaut on Mar 13, 2019 21:42:06 GMT
Without doubt. I've been following the Max 8 story on various aero sites and the similarity with the Lion Air crash was identified very quickly. It seems that Boeing have over developed the 737 and the possible cause of both crashes is the software designed to stop a consequence of the update. A bit like installing traction control on a Triumph Herald fitted with a Ferrari engine. It would been better to design a new car in which to use the engine instead. I like that analogy a lot.
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Rob
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Post by Rob on Mar 13, 2019 23:40:45 GMT
When I saw images of a 737 MAX 8 and saw the engines further forward and higher I immediately thought.... that's not going to fly or handle the same. And it's ultimately an old aircraft with it's origins in the late 60s.
Could be very costly to fix. They will no doubt: (1) have to compensate airlines, (2) spend a lot of money finding a software fix that works, (3) spend a lot of money proving it really really is a fix and (4) loss of orders in the meantime with airlines perhaps turning to Airbus (if their fleet allows it).
Wasn't the 737 MAX a response to the A320neo? The 320neo had larger engines (bigger fans than even the 737 MAX engines) to increase efficiency. Boeing were looking at a new aircraft but went for a 737 overhaul to get to market quicker. That's my interpretation.
I like Espada's analogy too :-)
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Deleted
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Post by Deleted on Mar 13, 2019 23:49:20 GMT
Thank you.
Of course I should have added that the hypothetical Herald had cross ply tyres and the traction control stopped you accelerating away from a situation, where getting away was the best thing to do. Hence the danger...
The A320 is a 1980s design but a lot better as a passenger aircraft than the B737 whose origins are the 707 and 727, so really 1950s. The A320neo works because the basic design permits larger engines without affecting the rest of the plane or its flyability.
Compared to the Golf, it's about time Boeing replaced their Mk1 model with a Mk7 and missed out all the iterations in between.
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Rob
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Post by Rob on Mar 14, 2019 0:34:07 GMT
>> Compared to the Golf, it's about time Boeing replaced their Mk1 model with a Mk7 and missed out all the iterations in between.
Again I like the analogy.
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Rob
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Post by Rob on Mar 14, 2019 0:51:18 GMT
Looking at 737 images for interim models the engines had already moved forward more than I had realised. I'm sure it's fixable. Just like Brexit. Just need a few more years.
But the engines are a lot bigger. So Espada's analogy is spot on. Without the right software this will not handle like pilots expect. So much for standard aircraft classes etc
I must have assumed when on recent 737 that the engine still extended under the wing.
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WDB
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Mar 14, 2019 8:18:32 GMT
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Post by WDB on Mar 14, 2019 8:18:32 GMT
Careful with the analogies because it’s not that simple. The Max is the fourth significant iteration of 737, so much closer to the Golf than Esp’s Herald-Ferrari. About the only parts of the 1969 737 that remain are the basic fuselage structure and bits of wing and tail. Even those use modern materials that 1960s engineers wouldn’t recognize. But the short-legged landing gear endures, which has puzzled me for 30 years.
The 737 got a huge rework in the 1980s — that’s when the funny, flat-bottomed engine casings first appeared, to keep high-bypass turbofans from rubbing on the ground. And the NG 700-800-900 moved things on again, in terms of avionics and fuel efficiency. So the Max really isn’t a sudden lurch from 1950s 707 to the 2010s.
I confess I’d not noticed the new engines and their position. (I’m strictly an aisle-seat flyer and they don’t look that different seen front-on from the gate.) They do have the serrated ends that are a signature of new Boeings, but the big change is that they’re larger in diameter and need to be mounted in free air to achieve fuel efficiency. The short legs leave no extra room below the wing, hence the new pylons that move them forwards. Whether any of this had a bearing on flight performance, we will have to wait and see.
I do prefer the A320 family, but because the cabin is a touch wider allowing marginally more shoulder room. And, although it looks a little ungainly on the ground, it was designed from the start with high-bypass engines in mind.
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Deleted
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Post by Deleted on Mar 14, 2019 15:07:42 GMT
It was only the 737 -100 and -200 that had the cigar style engines running under the wing front front to back and using clamshell thrust reversers.
So, I was being a little tongue in cheek about Mk1 - Mk7 Golf, but the comment in the aviation world is that Boeing should have done a brand new plane and took the cheapskate route instead...
Anyway, hopefully this second unfortunate incident in which over 150 lost their lives will be a catalyst for some serious soul searching at Boeing.
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Deleted
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Post by Deleted on Mar 14, 2019 15:20:43 GMT
The following is a posting from an aviation forum which explains the problem very clearly...
"For those who want to understand how we came to this amateur job:
It’s unique to the MAX because the 737 MAX no longer has the docile pitch characteristics of the 737NG at high Angles Of Attack (AOA). This is caused by the larger engine nacelles covering the higher bypass LEAP-1B engines. The nacelles for the MAX are larger and placed higher and further forward of the wing,
By placing the nacelle further forward of the wing, it could be placed higher. Combined with a higher nose landing gear, which raises the nacelle further, the same ground clearance could be achieved for the nacelle as for the 737NG.
The drawback of a larger nacelle, placed further forward, is it destabilizes the aircraft in pitch. All objects on an aircraft placed ahead of the Center of Gravity will contribute to destabilize the aircraft in pitch.
The 737 is a classical flight control aircraft. It relies on a naturally stable base aircraft for its flight control design, augmented in selected areas. Once such area is the artificial yaw damping, present on virtually all larger aircraft (to stop passengers getting sick from the aircraft’s natural tendency to Dutch Roll = Wagging its tail).
Until the MAX, there was no need for artificial aids in pitch. Once the aircraft entered a stall, there were several actions described l which assisted the pilot to exit the stall.
The larger nacelles, called for by the higher bypass LEAP-1B engines, changed this. When flying at normal angles of attack (3° at cruise and say 5° in a turn) the destabilizing effect of the larger engines are not felt.
The nacelles are designed to not generate lift in normal flight. It would generate unnecessary drag as the aspect ratio of an engine nacelle is lousy. The aircraft designer focuses the lift to the high aspect ratio wings.
But if the pilot for whatever reason manoeuvres the aircraft hard, generating an angle of attack close to the stall angle of around 14°, the previously neutral engine nacelle generates lift. A lift which is felt by the aircraft as a pitch up moment (as its ahead of the CG line), now stronger than on the 737NG. This destabilizes the MAX in pitch at higher Angles Of Attack (AOA). The most difficult situation is when the manoeuvre has a high pitch ratio. The aircraft’s inertia can then provoke an over-swing into stall AOA.
To counter the MAX’s lower stability margins at high AOA, Boeing introduced MCAS. Dependent on AOA value and rate, altitude (air density) and Mach (changed flow conditions) the MCAS, which is a software loop in the Flight Control computer, initiates a nose down trim above a threshold AOA.
It can be stopped by the Pilot counter-trimming on the Yoke or by him hitting the CUTOUT switches on the center pedestal. It’s not stopped by the Pilot pulling the Yoke, which for normal trim from the autopilot or runaway manual trim triggers trim hold sensors. This would negate why MCAS was implemented, the Pilot pulling so hard on the Yoke that the aircraft is flying close to stall.
It’s probably this counterintuitive characteristic, which goes against what has been trained many times in the simulator for unwanted autopilot trim or manual trim runaway, which has confused the pilots of JT610. They learned that holding against the trim stopped the nose down, and then they could take action, like counter-trimming or outright CUTOUT the trim servo. But it didn’t. After a 10 second trim to a 2.5° nose down stabilizer position, the trimming started again despite the Pilots pulling against it. The faulty high AOA signal was still present.
How should they know that pulling on the Yoke didn’t stop the trim? It was described nowhere; neither in the aircraft’s manual, the AFM, nor in the Pilot’s manual, the FCOM. This has created strong reactions from airlines with the 737 MAX on the flight line and their Pilots. They have learned the NG and the MAX flies the same. They fly them interchangeably during the week.
They do fly the same as long as no fault appears. Then there are differences, and the Pilots should have been informed about the differences.
Unfortunately the lion and Ethiopian's pilots have not had this chance"
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Post by bromptonaut on Mar 17, 2019 16:38:41 GMT
But the short-legged landing gear endures, which has puzzled me for 30 years. IIRC the short landing gear was a design feature. Keeping the fuselage close to the ground meant the 737's baggage holds could be loaded without use of conveyors etc allowing it to serve airfields with limited facilities. An integral forward air stair was offered for same reason. Think ease of loading was one reason Ryanair chose the 737 over the Airbus when they moved on from secondhand 200 series machines to the 800 variant which, bar one 700 series, is only type in their fleet.
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WDB
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Post by WDB on Mar 17, 2019 18:27:09 GMT
That may have been sound reasoning in 1967. It's hard to imagine it still being valid today, when the A320 is the de facto industry standard and airports that mean business equip themselves to suit. I've flown to some out of the way places and not yet seen one that 737s could serve but A320s couldn't.
I wonder if the wing being where it is (in the fore-and-aft sense) means the plane would be unstable on taller landing gear. Or perhaps it would require extra pilot training and hurt the economic case for single-typing. (Although the same pilots can fly the 757 and 767, which you'd think would have much greater differences.
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Post by bromptonaut on Mar 18, 2019 11:01:16 GMT
I'm sure that if Boeing started with a clean sheet of paper they'd allow more ground clearance. As WDB says there few if any places now where the original rationale of limited ground service at out of way destinations applies. Fitting a longer undercarriage to the existing airframe would be difficult without a major redesign, a redesign so major that the 'grandfathering' approvals derived from original 100/200 series could be lost. Quora article here goes some way to explain: www.quora.com/Why-doesnt-the-Boeing-737-aircraft-have-their-landing-wheels-covered-when-retracted
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