Try some out of the box thinking:
Posted on 04/09/2019 12:49:46 PM PDT by CondoleezzaProtege
This Boeing 737 Max 8 problem, again, just to reset this, traces back to 2011. I’ll tell you what this is about. It’s about the bloodletting that is competition in capitalism...I think the competition in capitalism is one of the great things in the design of our country, but it can lead to some things as well. But it’s far better than anything else.
What happened was in 2011, Airbus (which really doesn’t fairly compete because they’re a government entity. The Airbus plane is the result of a coalition of governments in Europe.)
But the Airbus A320 was able to be upgraded and outfitted with new engines, more powerful and more efficient engines without redesigning or rebuilding the airplane. The competition that Boeing has for the A320 was the Boeing 737-500, -600, -700 series. The Boeing 737 design would not accommodate simply upgrading engines.
If they had just put new engines — larger but more efficient engines on those wings, because it’s so low to the ground, it would totally upset the center of gravity. It would change the angle of attack. So they had to modify certain aspects of the Boeing 737, rather than go to the expense of redesigning it, retooling the manufacturing equipment and process. And they created software to handle how the airplane would behave differently during takeoff and at flight. And that’s what the MCAS system is.
...The nose gear was actually eight inches longer to accommodate the bigger engines. So it changes the elevation of the nose of the airplane as it’s flying through the air, creating the aerodynamics that are called “lift.” So because it tended to elevate the nose, these new engines and new angle of attack, they needed software on the rear horizontal stabilizer to keep the nose down.
(Excerpt) Read more at rushlimbaugh.com ...
Rush should stay away from the technical stuff.
The latest version of the 737 is probably the ultimate limit stretch of the 737, but it is an outstanding aircraft .
The only real problem with the upgraded 737 is the augmented stability system used to allow the upgraded 737 to mimic the same flight characteristics as the older models to the 737 to allow pilot trained on older models to fly the newer version with minimal retraining
This explanation says to me stick with politics Rush.
"The nose gear was actually eight inches longer to accommodate the bigger engines. So it changes the elevation of the nose of the airplane as it’s flying through the air..."Boeing DID lengthen the landing gear, but obviously the gear are retracted in flight and do not affect the flight dynamics.
When Boeing adopted the higher-bypass LEAP engines to get improved fuel economy, they now had a ground clearance problem -- the engines were simply too big to fit under the wing. So they did two things: lengthened the landing gear AND moved the larger diameter engines forward to get the nacelles in front of the wing. In normal attitude flight, the nacelles do not generate lift, but at high angle of attack flight, they DO generate lift. Because they are further forward, this lift generates an upward pitch moment. The problem is that the upward pitch in high angle of attack flight is not what you want because it exacerbates the situation. Higher angle of attack attitude --> more upward pitch moment --> higher angle of attack --> more upward pitch, etc. (think of this as a positive feedback loop). This can happen very quickly, too, and is NOT the handling characteristic of the more neutral prior 373 types.
MCAS was added to arrest this upward pitch tendency in high AoA attitude flight. If they hadn't done this, the 737 MAX would probably have required complete re-certification as a new airframe (no longer the 737 type) at untold millions and years of delay. It was a bad FINANCIAL decision at the expense of safety.
I’m sorry, but Boeing used software as a cheap way to try to compensate for an inherent design flaw.
The aircraft is simply not airworthy. It’s natively tail heavy and the aircraft is in many ways significantly different from the preceding versions of the 737 that it should not be called a 737. I say that because a pilot who is used to a 737 is not going to be able to just sit down and drive a 737 Max without a lot of required training and without a lot of training on how to drive the thing without the MCAS.
What makes these aircraft so dangerous is that if they lose power the aircraft can’t be controlled by the crew in the same manner that a normal 737 can be controlled by a crew in a similar situation.
It’s not a safe aircraft and I will not get on one nor will anyone in my family ever set foot on one.
“Rush should stay away from the technical stuff.”
Why? Is he wrong in his presentation? Is it confusing and hard to understand if you’re not a technically-oriented person?
The A320 Family design had its share of problems: the freezing pitot tubes caused a couple of crashes due to interfering with the fly-by-wire control system. That's why Airbus had to redesign the pitot tube heaters. And it's only now that Airbus finally got reasonably reliable Pratt & Whitney PW1100G engines.
Rush should stay away from the technical stuff.
Agreed.
Here is one take I’ve read:
“It has already been well established that the new Max version of the 737 has greater tendencies for the nose to climb higher under heavy thrust conditions than previous models. There appear to be several factors that may contribute to this. When this plane first came out back in ‘69 or so, the point where the thrust from the engine met the surrounding environment (push point as I call it) was well behind the wing, and vertically very close to the wing’s rotation axis with the long skinny JT-8 engine. When the larger diameter CFM 56 engines were later installed with 61” diameter fans, this “push point” was moved near the front of the wing, but it appears this was not enough to cause serious handling problems.
Because the engines of the new Max version now have a fan diameter of 69 1/2”, and are 21” longer, (124” vs 103”) the engine and push points have been moved forward yet again. I recently overlaid 2D CAD drawings for both planes, and discovered that the exit point for the thrust from the bypass shroud has been moved forward by 22”, and the exit point for thrust generated by the LP turbine has been moved a whopping 29” ahead of the old locations. The leading edge of the nacelle is now 13 1/2” inches ahead of the old location. The axial center line of both engines is roughly the same, with the additional diameter being divided equally above and below the old location.
So from a purely mathematical perspective, as long as the plane is flying relatively flat at high speed, this horizontal shift shouldn’t have much effect, but now that both the LP and bypass thrust points are much further forward than before, and the LP/bypass ratio has changed, the effects of this could be fairly dramatic under certain conditions.An example would be if the plane is oriented at a pitch of say 45 degrees, but flying at a low enough speed that it’s trajectory is still roughly parallel to the ground plane, the downward projecting thrust from the engine would be would be at least somewhat deflected up and back and into the front of the wing as it traverses across the stationary air. This would in theory at least create additional lift at the front of the wing, inducing more pitch rotation forces.
Using the same two CAD models but this time oriented with a 45 degree pitch, some interesting things started to appear. The first is that the top edge of the bypass shroud outlet is now horizontally or slightly above the leading edge of the wing, (18” higher than the older model), and exits very close to the wing’s leading edge at this angle. How much effect this has on lift I’m not sure, but I was very intrigued by a photo of the A 320 NEO that showed where Airbus added long “ear” shaped extensions to the top (and bottom) of both the bypass shroud and LP exit point to deflect thrust away from the wing. (Boeing has a smaller one on the LP section only).
Another part of the equation that I noticed relates to the nacelles themselves in relationship to the axis of rotation. With the same models pitched at 45 degrees, the bottom of the nacelles are so much higher than the rotation axis of the wing root that they would act as lift devices for sure, and to some degree air brakes as well depending on severity of pitch. I measured the distance from the bottom front of the LEAP nacelle to the approximate centeroid of the wing root and found it to be 113” above, and 180” in front of the root center. The older version had measurements of 106” and 168” respectively, along with less surface area at the front of the nacelle where this potential leverage would be the greatest.
At first I didn’t think too much of it as the nacelles are rounded rather than flat planes, but the projected surface area of the nacelle is roughly 60% of the horizontal stabilizer, so there would be enough surface area to affect the dynamics of the plane. Regardless of whether my theories are correct or not, it is well known that this plane is not as aerodynamically stable as previous versions, as the implementation of MCAS was from what I’ve read, was apparently required for certification. Whether the plane is unstable enough that it truly requires MCAS to stay in the air, or whether it was only implemented to help the pilots deal with a few handling quirks under certain conditions, that I can’t say. If my theory on thrust deflection is correct, then a relatively easy fix for this plane’s stability issues may be to modify the bypass shroud for more lineal control of the thrust direction. If not correct, then there’s likely no fix to the stability issues other than re designing the entire wing root to accommodate longer landing gear, which is not likely to happen.” ~ Greg Miller
Try some out of the box thinking:
That is generally consistent with the explanation I provided. Thanks.
It’s interesting that the author you cited found the nacelles have a projected frontal area 60% of the horizontal stabilizer. The nacelle lift at high AoA is now farther forward of the aircraft CG, creating the upward pitching moment.
I.guess the average employed pilot know to keep his mouth shut on the 737MAX contraversy.
“Why? Is he wrong in his presentation? “
For starters:
“And they created software to handle how the airplane would behave differently during takeoff and at flight. And that’s what the MCAS system is.”
And you obtained this false info exactly where?
“And you obtained this false info exactly where?”
I’ve flown a King Air 250 and without the autopilot on you know what happens when you let go of the yoke in level flight?
It flies.
What happens when you do the same thing in a 737 Max?
You die.
It’s really that simple.
The question is the Max stable enough to be hand flown under all conditions? Or is it dangerously unstable ?
“Whether the plane is unstable enough that it truly requires MCAS to stay in the air, or whether it was only implemented to help the pilots deal with a few handling quirks under certain conditions, that I can’t say.”
Dude must live in a cave with no internet ...
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