Naked Science Forum

Non Life Sciences => Technology => Topic started by: evan_au on 18/03/2019 19:59:08

Title: Why is the Max8 unusual to fly?
Post by: evan_au on 18/03/2019 19:59:08
Reports in the media identify the Max8 as a longer version of a long-standing airplane (more passengers), with more efficient engines. So far, so good - a very popular choice.

Can someone who knows about planes please explain the relationship of the following comments seen in the media:
- When talking about the stability of the plane in flight...
- The center of gravity is different from its predecessor
- In a stall, a pilot's instinctive reaction (based on the previous model) would be wrong
- The automated system forces the nose down to prevent a stall
- A single sensor failure could trigger the automated system

Thanks...
Title: Re: Why is the Max8 unusual to fly?
Post by: Kryptid on 18/03/2019 20:24:27
Perhaps the center of gravity is now closer to the center of lift. That would improve overall stability by reducing the pitching moment. I'm guessing the instinctive reaction of the pilot is to pull the nose up, which would be last thing you want to do in a stall. You'd want to reduce the angle of attack of the wing when it stalls, not increase it. Otherwise the problem becomes worse.
Title: Re: Why is the Max8 unusual to fly?
Post by: alancalverd on 18/03/2019 23:55:03
The CG of any aircraft moves in flight and with loading. If you stretch the fuselage and/or alter the fuel or baggage distribution, you will change its handling characteristics on takeoff and landing.

As I understand it, the Max8 has an additional or different antistall system from its predecessors. They seem to have progressed from whistles via "stickshakers" to auto-correct computers. Most autopilots can be overridden or cut out automatically if the pilot just grabs the control column and flies the plane manually, hence the disaster of Flight 409 where the pilot accidentally disengaged height hold without noticing, so the aircraft flew beautiful automatic racetracks, descending into the Everglades in pitch darkness. The Air France crash in the South Atlantic was due to pilots not noticing a stall in turbulence: some autopilots in height hold will respond to strong vertical gusts by pulling the plane up into a stall instead of just riding it out. So it seems that Boeing have gone for an antistall system that has to be intentionally disengaged before you can restore pilot control, and rumor has it that (a) this isn't fully explained in the handling notes or practiced in the conversion training, (b) the more you pull the stick back, the harder the system fights to get the nose down, and (c) it isn't overridden by the autopilot or ground proximity radar.

Unstalling procedure is normally full power, lower the nose smoothly to restore airflow, then climb back to height. The combination of full power and fighting the pilot to hold the stick forward, doesn't give you much time to recover from a dive towards the ground.
Title: Re: Why is the Max8 unusual to fly?
Post by: evan_au on 19/03/2019 09:11:34
Trying to interpret some other comments I heard...
- To increase fuel efficiency, the engines are physically larger
- They had to mount these larger engines forward from the wing

The description sounded like: if you increase power to get out of the stall, this turns the plane nose-up
- Turning the nose up is not good in a stall
- So in a stall on Max8, you need to avoid increased power
- Hence the recovery action to push the nose down

Does this make any sense?
Title: Re: Why is the Max8 unusual to fly?
Post by: Petrochemicals on 19/03/2019 18:58:32
Reports in the media identify the Max8 as a longer version of a long-standing airplane (more passengers), with more efficient engines. So far, so good - a very popular choice.

Can someone who knows about planes please explain the relationship of the following comments seen in the media:
- When talking about the stability of the plane in flight.
stability in aeronautics is considered to be whether the aircraft will right itself if you push the controls one direction. The media probably heard this and have nooo idea what they are regurgitating
- The center of gravity is different from its predecessor
centre of gravity as you know it, if the plane is different it will have a different centre of gravity

- In a stall, a pilot's instinctive reaction (based on the previous model) would be wrong
a stall is when the aircraft is not generating lift, because it is too slow or its lift quotent is not satisfactory too the gravity factor of earth ie falling. In a stall pilots (i cannot imagine who they are ) can try and make the aircraft regain lift by aiming up, which can exaserbate  the stall

- The automated system forces the nose down to prevent a stall
if the aircraft gains speed the stall should end, aiming down makes the plane go faster

- A single sensor failure could trigger the automated system

Thanks...
The sensor in one way or another is making the aircraft aim at the floor due to one s3nsor. This automatic system should be able to be overridden. Turn off this system, all MaXs are safe to fly.
Title: Re: Why is the Max8 unusual to fly?
Post by: alancalverd on 20/03/2019 08:35:58
I now read that at least one such incident has been averted by switching off the attitude trim power. Interestingly, my local flying school did the same with our Piper Archers a few months ago, following a brief encounter with some vegetation, and one of the few occasions when I felt less than happy in a Cessna 172 was during an autopilot climbout demonstration by an airline captain: we set "climb ahead to height" and the bird entered a chandelle instead - very uncomfortable at 200 ft, so after the second attempt, we switched it off and flew the departure manually.

There is also a suggestion that the Boeing angle of attack sensors are less than perfect, and also that they are situated around the nose of the aircraft, thus making them potentially sensitive to gusts.  AOA indication may be helpful to an interceptor or to optimise airliner cruise attitude, but probably not the most useful control input near the ground.

Title: Re: Why is the Max8 unusual to fly?
Post by: Petrochemicals on 30/03/2019 20:04:59
Amazingly i now read that this anti stall system has been installed without being in anyway notified to the pilots, sort of like someones put a rock in your rucksack and not told you. There is an obscure reference in some part of the manuals to say this is part of the auto pilot but other than that, nothing to say turn the auto pilot off.

https://www.bbc.co.uk/news/business-47759966



Title: Re: Why is the Max8 unusual to fly?
Post by: evan_au on 30/03/2019 22:26:49
Boeing has been working on a software upgrade to make the operation clearer to the pilots.

After recent demonstrations of the old and new software versions in a flight simulator, media reports suggested that on the old software, after a sensor failure, the pilots had 40 seconds to act before the system strongly forced the nose down.

Planes have multiple sensors, so if one fails, the plane should be completely flyable. Sensor Fusion is the process of combining inputs from multiple sensors. It is a difficult problem - if different sensors provide different inputs, which one do you believe?
Title: Re: Why is the Max8 unusual to fly?
Post by: alancalverd on 31/03/2019 00:58:58
There are different approaches to this problem. Concorde in particular used three sensors for critical parameters, and a voting system that ignored one if it disagreed with the other two. Boeing has used two sensors with a "disagree" indicator that should prompt manual override, but there is a suggestion that this is an optional extra on the 8 Max.

Many years ago I was briefly involved in a discussion that resulted in a clear distinction between command and advice, and cockpit voice synthesisers are supposed now to offer advice ("ground proximity!") as distinct from commands ("pull up!"). Only real humans (pilots and traffic controllers) are permitted to issue commands. However there has been a residual problem, pointed out to me on my first flying lesson. The instructor said "This is the stall warning indicator. In all the best accidents, you will find that it has been switched off."

Following the Air France disaster, when pilots apparently did exactly the wrong thing after a stall, it looks as though Boeing's reaction has been to prevent, or at least make very obscure, any attempt to ignore or contradict the stall prevention system. Six of one, half a dozen of the other? On present showing it seems that  the statistics remain marginally in favor of warnings, not commands, and encouragement, not intervention. "Encouragement" is exemplified by autopilots which are friction-coupled rather than hard-linked to the primary controls: if you disagree with George, you can still move the controls and fly the plane against its wishes, and the stall warner just shakes the control yoke about 10 knots before an actual stall would shake the whole plane. In other words, the pilot remains in ultimate command until another human utters the magic words "I have control" or "Speedbird XX Scottish Control, immediate turn right for Dusseldorf" (subtle topical reference).

As with driverless cars, my preference remains with a human in ultimate control. Driverless trains work OK but in a wholly controlled environment with no pedestrians or oncoming vehicles. Until someone puts tracks in the sky and stops the air moving about, I think we should persist with "instruments indicate, humans command".   
Title: Re: Why is the Max8 unusual to fly?
Post by: syhprum on 31/03/2019 12:12:48
While it may be a good idea to make fighter aircraft inherently unstable with computers to stop them crashing as the object of such machines is to kill and survive but to make a passenger aircraft inherently unstable and dependent on computers when the object is to transport passengers safely seem a crazy idea what ever the fuel saving benefits.
Title: Re: Why is the Max8 unusual to fly?
Post by: alancalverd on 31/03/2019 14:02:10
The Max8 is not inherently unstable. Properly trimmed, it will recover "hands-off" from an unusual attitude to straight and level flight, just like every other certified civil airliner. It is of course possible to stall any aircraft by choice of load distribution and power setting, which is how we land, and equally possible to destroy one by flying it into the ground at more than stall speed. 

The object of computer control in a fighter is to ensure structural integrity and hands-off recovery without compromising pitch and roll rates, which in a civil aircraft are "passively" held well below the stress limits by the fixed geometry and maximum control surface deflections.
Title: Re: Why is the Max8 unusual to fly?
Post by: Bored chemist on 31/03/2019 14:11:05
As with driverless cars, my preference remains with a human in ultimate control.
My heart agrees with you, but my head says, if we can refine the technology to the point where the machine screws up less often than the human, we should let the machine drive.
Title: Re: Why is the Max8 unusual to fly?
Post by: alancalverd on 31/03/2019 21:09:04
Lawyers love driverless cars. No point in suing a dead driver, and insurance underwriters prefer to settle rather than argue, but if there is a possibility of suing everyone from Alan Turing to the bloke who soldered the chips together, your fees are guaranteed in perpetuity.

The current issue of "Pilot" magazine (obtainable at all good news stands) has an excellent article by a 737 pilot on the shortcomings of the Max8. One interesting fact is that the bigger engines, depite moving the CG forward (which mitigates stalling) have bigger cowlings with flat bottoms, which quite suddenly generate more lift as you rotate to climbout, and thus move the center of lift forward, enhancing the rotation. Hence the need for an automatic AOA limiter. But it gets worse from there on.....in every respect, the "solution" is an accident waiting to happen.
Title: Re: Why is the Max8 unusual to fly?
Post by: Petrochemicals on 31/03/2019 21:16:39
As with driverless cars, my preference remains with a human in ultimate control.
My heart agrees with you, but my head says, if we can refine the technology to the point where the machine screws up less often than the human, we should let the machine drive.
And your pc/mobile work so well, even before the updates are installed. It is an interesting question, a human crashing into another human is accountable, a computer is not. The computer will always be questioned and always at fault as it should never crash, even though it may be less accident prone.

The current issue of "Pilot" magazine (obtainable at all good news stands) has an excellent article by a 737 pilot on the shortcomings of the Max8. One interesting fact is that the bigger engines, depite moving the CG forward (which mitigates stalling) have bigger cowlings with flat bottoms, which quite suddenly generate more lift as you rotate to climbout, and thus move the center of lift forward, enhancing the rotation. Hence the need for an automatic AOA limiter. But it gets worse from there on.....in every respect, the "solution" is an accident waiting to happen.

So thats what this limiter is for. The cowlings must generate an awful lot of lift, being only cowling too. They have been putting bigger engines powerwise on things for ever, engines have always improved. The problem with the AoA is no one told the pilots it was on the new planes.
Title: Re: Why is the Max8 unusual to fly?
Post by: alancalverd on 01/04/2019 11:08:23
You don't need much more lift forward of the nominal CoL to make a substantial difference to the trim of an aircraft at low speed, which is why the AOA sensors and antistall kit were installed in the first place. The fun is compounded by having the antistall system drive the primary stabiliser (tailplane) motor in long (apparently 10 second) bursts. After the second burst the stabiliser is at full deflection, with such a steep angle of attack that none of the controls available to the pilot can restore level flight. You can waggle the yoke all you like, but the only remaining effective control is power. Now you normally get out of a stall by, inter alia,  applying max power, but if the magical safety system has set the stabiliser at full deflection, adding power just means you hit the ground sooner. 

There's no doubt that pilots are aware of the AOA sensors, which are pretty standard on all jets, and are generally aware that they are not reliable, but changing their status from indication to command and making the command override exceptionally complicated, is about as safe as limiting your Jaguar to an absolute maximum of 70 mph:  you wouldn't try to overtake a 60 mph truck in a London bus, but having got halfway past it in a high performance car, it's safer to complete the manouver at 80 mph than to hang about in the face of sudden oncoming traffic. Fortunately, most car manufacturers do include kickdown override in their speed limiter, but the Boeing system needs the first officer to read the manual whilst the pilot stops flying the plane and faffs about with shrouded switches and hidden crank handles.
Title: Re: Why is the Max8 unusual to fly?
Post by: syhprum on 01/04/2019 12:13:27
Presumably you would gun your Jaguar to much more than 80 MPH to get past the truck and out of the way of the oncoming traffic, sods law dictates that there is a so called "safety" camera there for you to trigger.
Title: Re: Why is the Max8 unusual to fly?
Post by: alancalverd on 01/04/2019 14:02:21
Extraordinary device. I have never seen a photograph of safety. Does it take pictures of empty roads, or stationary vehicles?
Title: Re: Why is the Max8 unusual to fly?
Post by: syhprum on 01/04/2019 22:54:50
They call them safety cameras when their real purpose is just to collect money fair enough but they also hand out penalty  points with the disastrous effect that you can end up being disqualified for three or for accidental infringements' that have no relevance to safety in fact just the reverse people will creep past the truck at 70 MPH when it would be much safer to use the maximum acceleration of their vehicle to get past as quickly as possible 
Title: Re: Why is the Max8 unusual to fly?
Post by: alancalverd on 02/04/2019 00:47:57
As I see it, if you pass the camera at 100 mph without hitting anything, you are driving safely, but if you kill a pedestrian at 29 mph, you aren't.  People get obsessed with numbers, not facts. I have two cuttings from the same newspaper (Daily Telegraph, 16 May 2003) that I use to illustrate the point: A was jailed and banned from driving for 4 years after driving at 120 mph on an empty road without incident. B (who had never taken a driving test) was fined 200 for killing a cyclist without exceeding a speed limit.

But we are digressing. The interesting point about the original question is that in the pursuit of ultimate performance the flight envelope seems to have become so marginal that pilots are required to be systems managers rather than aviators. There are plenty of tales of derring-do and ultimate airmanship involving hand-flying warplanes to the limit of bomb load or manouevering stress, but maximising profit when carrying holidaymakers in peacetime nowadays also demands exploration of dark corners of the flight envelope. Not only does the 8Max have anti-stall gadgetry, but it is so aerodynamically clean that is also incorporates an anti-overspeed system than makes it pitch up at the critical Mach number. And since that is known to malfunction, there is an override procedure....
Title: Re: Why is the Max8 unusual to fly?
Post by: evan_au on 02/04/2019 09:42:47
Today's press suggests that the new anti-stall software will not activate if there is a big discrepancy between the two relevant sensors (indicating a sensor failure).

But the new software isn't quite ready yet...
Title: Re: Why is the Max8 unusual to fly?
Post by: alancalverd on 02/04/2019 10:03:51
It seems there is already a 3-sensor option with voting (at extra cost, complexity, maintenance, and risk of more sensor or computer failure...)  but the real problem is the refusal of the MCAS system to fully disengage when the pilot takes control.Software? Whatever became of the "off" switch?
Title: Re: Why is the Max8 unusual to fly?
Post by: syhprum on 02/04/2019 10:29:54
It seems we don't have simple things like volume control, brightness controls or on of switches anymore if I want to adjust the volume on the TV I have to  get into the built in computer ,find the appropriate page and modify the sound control routine, OK this avoids the crackles that one sometimes got with an olde worlde volume control but you have find the remote control and the right buttons.
I used to joke that we would one day have computers in our flash lights but it has already happened with people using their $1000 smart phones in loo of a $10 flashlight
 
Title: Re: Why is the Max8 unusual to fly?
Post by: alancalverd on 02/04/2019 12:45:38
New joke going the rounds last week:

"How do you milk sheep?"

"Charge them 1000 for a new phone."

And you are lucky to have a television with reasonable sound at all. In the bid to make them thinner, manufacturers have compromised the sound quality to the point that you have to buy an additional "sound bar" for the midfrequencies and a fat woofer box for the bass.

Not that there's any point in watching TV these days. Brexit is slower than postal chess and the "debate" is at the intellectual level of shin-kicking. You might watch one episode of a thriller, only to learn that you need 20 meg broadband to see the rest. Or you could watch people who are not very good at cooking, dancing, skating, or quizzes, (i.e. "celebrities") doing it badly.Time was when you might get a really good singer, comedian or magician to perform for you: nowadays you have to sit through weeks of auditions. Thank God for rugby and The Simpsons.
Title: Re: Why is the Max8 unusual to fly?
Post by: Petrochemicals on 04/04/2019 21:44:29
Apparently I see now in the latest updates they turned Mcas off, yet still fought the autopilot to recover from a stall, and from the altitude graph they literally fell from the sky like a brick. How on earth with the nose down action off does a modern airliner fight its own pilot to the point it falls from the sky ? It has incredibly powerful engines, too powerful according to one expert (even though i cannot understand this ) and the stability of a brick down a well. How on earth can 2 pilots not right the plane ? Level flight extra thrust should do it, especially with the engines that they have.

Also, If you dive the centre of lift goes out at an angle so you gain less lift, so am i right in thinking a dive will not be the best option, as this may result in the lift force increacing the likelyhood of stall due to the interference of aerodynamic flow parallel to the ground ?
Title: Re: Why is the Max8 unusual to fly?
Post by: syhprum on 04/04/2019 22:10:16
Could the pilots as a desperate last measure rolled the aircraft so it was upside down ?, would this have done any good ?
Title: Re: Why is the Max8 unusual to fly?
Post by: alancalverd on 05/04/2019 00:56:31
Some debate now suggests that the pilots regained control by following the book, then as per the book, re-engaged MCAS, but at each iteration they ended up with a lower nose attitude. If the nose is well below the horizon and the wing is not stalled, adding power just makes it go faster downwards.   

Rolling inverted was a good film plot and has indeed saved the life of at least one aerobatic display pilot with a cracked wing spar, but probably not feasible at low level in a 737.
Title: Re: Why is the Max8 unusual to fly?
Post by: Petrochemicals on 05/04/2019 12:35:31
Apparently it is not the power of the engines or centre of lift through any new bits that is at fault. The super heavy new engines have moved the CG backward meaning the plane nose ups. Why  cannot this be corrected with trim ?
Could the pilots as a desperate last measure rolled the aircraft so it was upside down ?, would this have done any good ?
Probably not due to wing shape being completly different between aerobatic planes and honed for efficiency airliners. I think it would make them fly even faster into the floor.
Title: Re: Why is the Max8 unusual to fly?
Post by: alancalverd on 05/04/2019 13:41:23
According to the guys that fly them, the heavier engine moves the empty CG forward, which makes sense.

You need to adopt a nose-up attitude to leave  the ground, which is why the rear of the fuselage tapers upwards, so you don't scrape the tail on the deck as you rotate. This brings you close to a stall condition if the power fails, which isn't normally a problem: elementary training tells you to push the stick forward until the plane glides, then sort out the engines. It worked OK for Sully, and it's something every pilot practices regularly.

The problem with the Max 8 seems to derive from two sources. The Air France cruise altitude stall was compounded by pilot error so there was a move to "improve" stall warnings by adding some automatic nosedown. Fair enough but the Max 8 makes it very difficult to override the auto system if it malfunctions, and having done so, it re-engages in the fault condition. Second problem is the peculiar quirk of the Max 8 that the engine cowlings generate additional lift as you pass through the normal climb attitude at low speed, so increase the angle of attack. Not a problem if you are used to the peculairities of any particular aircraft but instead of including this in the conversion training, it is left to the auto system to sort out, which is fine if the auto system is working.

Like most big jets, the 737 has an "all flying tail", with very small fine trim tabs. The trick is to get the whole tailplane at optimum AoA with zero tab displacement, to minimse drag. The antistall unit drives the main stabiliser in 10 second bursts, and apparently if you disconnect and reconnect, it starts from where it left off, so after the second  burst the stabiliser is at maximum deflection and the fine trim is pretty near useless.

You might adjust trim by pumping fuel around or shifting cargo, but there isn't much time to do that at 250 mph and 1000 ft off the deck. The remarkable thing is that the pilots of both Lion and Ethiopian got as far from the airfield as they did, by brute force and brilliance, but a runaway elevator is usually fatal. 
Title: Re: Why is the Max8 unusual to fly?
Post by: Bored chemist on 05/04/2019 17:42:16
Today's press suggests that the new anti-stall software will not activate if there is a big discrepancy between the two relevant sensors (indicating a sensor failure).

But the new software isn't quite ready yet...
Fly by wire : brings a new meaning to the phrase "blue screen of death".
Title: Re: Why is the Max8 unusual to fly?
Post by: Petrochemicals on 05/04/2019 18:35:19
Its not just the cowling shape, being positioned furthe forward also has an effect.

https://leehamnews.com/2018/11/14/boeings-automatic-trim-for-the-737-max-was-not-disclosed-to-the-pilots/
Title: Re: Why is the Max8 unusual to fly?
Post by: Petrochemicals on 09/04/2019 00:39:21
So if ive got this right the new engines, as they are so much larger and further forward, in angles of attack relative to forward motion create alot of lift. Is this because they themselves create lift, or is it because the airflow over the is forced to a higher speed above and lower below than would normally take place.
Title: Re: Why is the Max8 unusual to fly?
Post by: alancalverd on 09/04/2019 23:18:32
It's because the new cowlings have flattened bottoms. When the chord is parallel to the airflow, i.e. on the ground run, the cowlings may even produce a little downward thrust  as they look like inverted aerofoils in section view, but as you rotate for takeoff, they suddenly present a flat surface inclined at a positive angle of attack in addition to the intended airflow over the wing - almost as if you have just added a small auxiliary wing ahead of the main plane, and this enhances the rotation.

Not a problem if the aircraft has been designed and flown with this in mind, and plenty have. Problem is that if you take a standard design like a 737 and add this new effect, you need to review your takeoff procedure and train for it, but it seems Boeing decided instead to "automate the effect away"  instead of offering type-conversion training to cover it.
Title: Re: Why is the Max8 unusual to fly?
Post by: Petrochemicals on 10/04/2019 15:41:24
So this flat bottom then, not only acting as an auxilliary wing unlike before, is also set forward, leading to a large turning moment in relation to the CG and the wing as before. That would add up to the 14 percent increace then.
Title: Re: Why is the Max8 unusual to fly?
Post by: alancalverd on 11/04/2019 00:06:29
I didn't realise it was as much as 14%. That makes it a completely different aircraft to handle from any other 737. Easy enough to simulate, or teach "live",  but a real handful for a regular 737 pilot who has just read the Boeing instruction book, so the auto trim is pretty well essential for a smooth transition to climb.
Title: Re: Why is the Max8 unusual to fly?
Post by: Petrochemicals on 11/04/2019 18:25:01
I got it wrong its 14degrees aoa ie wings relative to the motion, vut it must be pretty big considering the pilots are considered incapable of dealing with it. 40 seconds before terminal decent apparently.

 Fully laden aoa  has always been a factor, but what i dont get is how a aoa on a commercial plane can give you lift, it does seem a bit unstable. The aoa has always  been known,  but for an aoa lift instability of a sheet of a4 through the air if you approach14 degrees is a major problem for a cargo plane
Title: Re: Why is the Max8 unusual to fly?
Post by: evan_au on 11/04/2019 22:35:52
Quote from: Petrochemicals
14degrees aoa
aoa=Angle of attack: The angle of the wings relative to the air around the plane

See: https://en.wikipedia.org/wiki/Angle_of_attack
Title: Re: Why is the Max8 unusual to fly?
Post by: alancalverd on 12/04/2019 00:17:04
14 degrees AOA is uncomfortable near the ground as the stall angle for most transport aerofoils is about 16 degrees. You can expect the stall warning horns to bleep a bit if you rotate at too low a forward speed but a couple of degrees less for a couple of seconds should restore normality if you have set the takeoff trim correctly.
Title: Re: Why is the Max8 unusual to fly?
Post by: evan_au on 28/04/2019 03:41:52
Quote from: OP
A single sensor failure could trigger the automated system
Like many commercial jets, the Max8 has duplicated pitot tubes to measure airspeed, and duplicated angle-of-attack sensors on each side of the plane, feeding the pilot and copilot displays.

I read a semi-technical description which suggested that the Max8's duplicated flight control computer acted as an "active+standby" mode, so only one computer was in control at any one time (like a pilot and copilot).

However, a pilot and copilot can cross-check each other's instruments in case of doubt. They can also cross-check the artificial horizon (and real horizon, when visible) to detect a faulty instrument.

Apparently, in the original Max8 software, each flight control computer only considered readings from sensors on its "own" side, and did not cross-check with the sensors feeding the "standby" computer. So a single faulty sensor could trigger the stall-avoidance function.

Given the frequent and extreme swings in temperature, pressure, humidity etc involved in airflight, the occasional sensor malfunction is not unexpected.
Title: Re: Why is the Max8 unusual to fly?
Post by: evan_au on 02/05/2019 22:22:36
Quote from: OP
The automated system forces the nose down to prevent a stall
I read some more on this comment...

Apparently the US Federal Aviation Authority (FAA) has a rule that the angle of the plane should not change significantly when the power level is increased (eg on takeoff)
- Due to the position and shape of the new, bigger engines, this plane tends to raise the nose when you increase the power
- Rather than tell the pilots and FAA, they decided to to fix it in software
- If the pilots knew about this behavior, they could train for it (eg in simulators) and compensate
- If the FAA knew about this behavior, they may not be so charitable

The release date of the new flight control software may depend on how charitable the FAA is feeling at the moment (and how much pressure comes from the White House?)
Title: Re: Why is the Max8 unusual to fly?
Post by: Petrochemicals on 03/05/2019 02:20:17
14degrees
It all boils down to trying to squeeze efficiency out of regigging an old design. It should have been trimmed in someway, but this would have led to drag and bad efficiency.

  I bet they wish they hadnt now, especially considering the supremecy of the dream liner and the associated sales. If they had run a complete redesign of the fleet then they may have put airbus out of business ! Its all about sales volume versus development these days as in the case of the a380. I would not touch that 737max considering the cost of development was so small, the hodgepodge it is and the fact that the. profits so big
Title: Re: Why is the Max8 unusual to fly?
Post by: alancalverd on 03/05/2019 08:01:42
It's all market-driven. In this case, they had a very popular and competent basic design with customer demand for more passenger capacity and longer range pulling in one direction and engine manufacturer offering a substantial upgrade, pushing in the same direction. So far, so good. Even the antistall system is a good idea, but the inability of the pilot to completely disengage the system with a single button, and the lack of mandatory simulator or hot seat training on the quirky takeoff characteristic (which would make hand-flying "different but safe") seems to be spoiling the ship (literally) for a hap'orth of tar.

Plenty of aircraft do slightly idiosyncratic things close to the ground, which is "type ratings" are added to pilot licences, but the idea of getting a significant type rating by reading the small print and not actually flying a few circuits with a company-rated instructor, is pushing the envelope too far. Even converting from a Piper Archer (the 4-seat rental "spam can" that practically everyone has flown at some time in basic training) to a Cirrus (same configuration but much slipperier and more electronic) requires 5 hours with a company-certified instructor nowadays.
Title: Re: Why is the Max8 unusual to fly?
Post by: Petrochemicals on 27/06/2019 03:21:53
https://www.bbc.co.uk/news/business-48752932