The way I understand things the engines were so powerful and installed ahead of the center of gravity(CG) that they could make the aircraft pitch 90 deg straight up around the y-axis!
Posted on 03/20/2019 6:17:38 AM PDT by central_va
I have about 200+ hours in single engine and some instrument time though I never got that ticket. VFR for ever.
Ok, let me ask you pro's: Even if the elevator trim is jammed nose down (FOR WHATEVER REASON!) in a commercial jet and cannot be neutralized ( FOR WHATEVER REASON) can human strength overcome that and pull the nose up anyway?
Can someone please answer that question?
My hunch is that the wing is too small (designed for fuel efficiency) and that the engineers were afraid the planes would be prone to stalling
I agree partially...The wing redesign and the larger engines (which necessitated placement change on the wings) resulted in an aircraft that has stall issues with flaps up. When the design engineers identified the problems is still TBD. If the issue had been raised in the design phase, then MCAS could (and should) have been designed into the flight control software and not as an add-on system.
...a distinct dichotomy between what we know of the planes here in the US (no reports that I’m aware of filed with the FAA regarding MCAS problems) vs. the experience of these foreign pilots in the same aircraft.
I believe this is directly attributable to aircraft maintenance and pilot proficiency (training). I would be shocked if a US airline would allow an aircraft to fly with a known AOA system malfunction. US airlines have excellent training systems and own their own FAA level D simulators.
A technical article I read early on stipulated that there was a single AOA sensor feeding data to the MCAS system and it is that engineering that I cited as a failure.
Kudos to you for this observation...
Here's what I believe happened: The flaps up stall issue was discovered late in flight test program, most likely with a lot of finger pointing. The design engineers would have proposed a fully integrated MCAS system. This would have necessitated a re-write of the flight control software and a re-start of the flight test program...very expensive and would cause late deliveries (also expensive).
So management dictated an add-on MCAS which would be tested separately. If I were the chief engineer on the 737 MAX,I would have put my badge on the program manager's desk and walked out the door and hired a good lawyer.
I have a lot more to say about the designed MCAS system, but will save that for a later post.
The way I understand things the engines were so powerful and installed ahead of the center of gravity(CG) that they could make the aircraft pitch 90 deg straight up around the y-axis!
My training on SEL was full throttle on take off. Balls to the walls. That is the whole point of powered flight. Why hold back on TO?
Full power is always used during take off. The sooner you get altitude the safer you are if something goes wrong.
Engine power would be critical as it relates to how fast the plane accelerates. If the plane is trimmed for level flight at 200 KIAS and the throttles are advanced and the airplane accelerates to 350 KIAS in 5 seconds, then the pitch up will be more dramatic than if the airplane accelerates to 350 KIAS in 15 seconds.
Very good analysis. Looking forward to reading more.
Thanks for the response.
Since that is true and many aircraft have their original 'engines' replaced by newer and higher powered ones, then having higher powered engines had nothing to do with the crash.
If that were true, then every 737MAX would pitch 90 deg. straight up on full throttle. As others have said on this thread, ALL aircraft use FULL THROTTLE on TAKEOFF.
Of course. That's why the claim that the engines were too powerful makes no sense.
Why hold back on TO?
My statement that one should just hold back on the throttle was to get people such as yourself to state that all aircraft go to full throttle on takeoff. Which shows that the claim the higher powered engines caused the crash are nonsense.
So... if the AOA sensor was working correctly, would this crash have happened ?
In part because of its advances in technology and a top speed greater than existing Navy aircraft, numerous technical problems had to be solved before the Corsair entered service. Carrier suitability was a major development issue, prompting changes to the main landing gear, tail wheel and tailhook. Early F4U-1s had difficulty recovering from developed spins, since the inverted gull wing's shape interfered with elevator authority. It was also found that the Corsair's right wing could stall and drop rapidly and without warning during slow carrier landings.[28] In addition, if the throttle were suddenly advanced (for example, during an aborted landing) the left wing could stall and drop so quickly that the fighter could flip over with the rapid increase in power.[29] These potentially lethal characteristics were later solved through the addition of a small, 6 in (150 mm)-long stall strip to the leading edge of the outer right wing, just outboard of the gun ports. This allowed the right wing to stall at the same time as the left.
I have not read or seen any information that indicate that the pilots "stalled" the aircraft.
Also, there is no information indicating a software issue in the MCAS or any malfunction of auto pitch trim.
Which would be about a 10-fold increase in power (and would seriously ruin the CG).
How much of a power difference (increase in thrust) is there between the original engines on the 737 and the newer engines on the 737MAX ?
In the case of the F4U...no super computers or CFD software. Flight test was the only way to validate the design.
WRT the F4U rapid throttle advance at slow speed...the issue here is the torque of the propeller. There is not enough aileron/rudder effectiveness to keep the wings level. The A-1 Skyraider had the same issue.
Does the 737MAX have only one AOA sensor ?
I believe that the MAX has 2 AOA sensors. However, as logi_cal869 stated in an earlier post, the MCAS only used the AOA input from one AOA sensor (pilot side).
Disclosure: I am not an engineer...my experience is pilot based, mostly in the F-4. I also have 19 years experience in Aerospace, mostly in program management. I do have experience with glass cockpit aircraft.
I have absolutely no knowledge of Boeing's designs or data. The information to be presented is generic and is only for discussion purposes.
A computerized aircraft would have a "central" computer system with dual or triple redundancy. In the military, this computer is called the mission computer. I am not going to discuss how redundancy is achieved as there are several ways this can be done, all acceptable. The central computer gets data from on-board and off-board sensors through a data bus architecture...the data bus also contains redundancy.
The on-board sensors can be analog or digital. If they are analog, then there is some type of adapter tied to the sensor that converts the analog signal to digital and puts the data on the data bus. The central computer then analyzes all of the data and displays some of the data on the pilot's displays. It also sends data to other on-board computers, such as the FADECs (which control the engines) and the auto-flight system. Note: auto-flight could be stand alone or integrated into the central computer.
When analyzing the sensor data, the central computer is comparing inputs from like sensors (data from the pilot's AOA sensor is compared to the data from the co-pilot's AOA sensor). If the data agrees, then there is no problem. Problems arise when the data disagrees. If there is a disagreement, the central computer can calculate what the AOA should be, based on airspeed, g-loading, bank angle, pitch angle. Based on that calculation, the central computer can determine which AOA sensor is malfunctioning.
So...based on what logi_cal869 and I have read, the MCAS only uses one AOA sensor and does not interface directly with the central computer. In fact, the MCAS has authority over the central computer and can command the pitch trim system to lower the nose (reduce AOA), even if the central computer knows that the aircraft is nowhere near stall.
To me, this design in unbelievable.
I plan to add some more comments later...feel free to comment and ask questions.
It is madness.
We have a system that will literally fly the aircraft into the ground.
This page is not being archived for whatever reason, so capture it if the need suits you.
It elaborates upon the general discussion with much detail, including Boeing looking at using input from both AOA sensors for MCAS. After reading this page, I’m satisfied that they grounded the model until the problem is worked out and that they are investigating its certification.
The prior paper I’d read was either unclear or I misunderstood the reason for the 2 AOA sensors: Clearly there is one for each station and MCAS gets data from one of these.
Here is the passage that concerns me most:
“In the event of erroneous AOA data, the pitch trim system can trim the stabilizer nose down in increments lasting up to 10 seconds.”
“Erroneous data” is not elaborated upon as yet. That’s a RED FLAG. Proper training is obviously a critical safety tool to ensure there is no flight departure at low altitudes during takeoff. Somebody effed up bigtime if the pilots of the crashed planes were never instructed. There is no time to read a damned manual at takeoff altitude for an aircraft that’s pitching down against pilot inputs. Furthermore, under “Runaway Stabilizer” it is stated that “the 737-8*-9 uses a Flight Control Computer command of pitch trim to improve longitudinal handling characteristics. In the event of erroneous Angle of Attack (AOA) input...” and you get responses from the aircraft outlined by AIRWORTHINESS DIRECTIVE 2018-23-51 https://ad.easa.europa.eu/blob/2018-23-51_FR_Correction.pdf/AD_US-2018-23-51_1:
> Continuous or intermittent stick shaker on the affected side only.
> Minimum speed bar (red and black) on the affected side only.
> Increasing nose down control forces.
> IAS DISAGREE alert.
> ALT DISAGREE alert.
> AOA DISAGREE alert (if the option is installed)
> FEEL DIFF PRESS light.
> Autopilot may disengage.
> Inability to engage autopilot.
Something is clearly wrong here...
http://www.b737.org.uk/mcas.htm
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