Well maybe switch to singing or something.

GAC06 said:

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TexasRebel said:

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Bernoulli.

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Thrust reversers are actuated hydraulically. Normally I'd say you're embarrassing yourself but you've been doing it long enough that this may be your normal state. What is your day job?

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hydraulic pistons/motors are still limited in the amount of force/torque they can exert.

Same reason the wings generate lift, the vector plates entering a turbine exhaust takes force.

Neat

A10s still aren't flight worthy without the GAU8 (or the equivalent in counterweight).

I had eggs for breakfast

Fried chicken embryos.

TexasRebel said:

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the vector plates entering a turbine exhaust takes force.

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1. TR's are not thrust vectors

2. so what?

3. I STILL don't know what your hang up is

Back on topic,
What you're saying is the reverse thrusters can be deployed with the throttle levers at idle, but the turbines still providing thrust.

Is this correct?

TexasRebel said:

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Back on topic,
What you're saying is the reverse thrusters can be deployed with the throttle levers at idle, but the turbines still providing thrust.

Is this correct?

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The Turbines are always producing thrust while running

coconutED said:

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1. TR's are not thrust vectors

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Yes they are.

They are plates that vector the normally rearward thrust more than 90 degrees to give the thrust positive forward vector.

The engines always produce some amount of thrust if they're on. Once reverse thrust is selected, the engines spool up to the commanded amount of reverse thrust

Again, and I feel like this is a simple question, but maybe you're dodging because you don't know… that's fine.

Do the turbines have to be spooled down to idle before reverse thrusters are deployed, or is the lever position the only thing that matters?

They were on centerline the entire way down the runway. You can see where the engines were dragging.

The thrust reversers (that's what they're called) can only be activated with weight on wheels or radalt under ten feet, which means that thrust levers will almost always be at idle.

Is that a requirement? I don't know, Boeing likes to keep secrets. If one did slam the thrust levers to idle then immediately actuate the thrust reversers, hypothetically it would provide a better response.

TexasRebel said:

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spooled down to idle

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What do you think this means?

The cam mechanism posted earlier guarantees that the throttle levers must be at idle before the thrust reversers can be deployed, but without another lockout (firmware or hardware) that mechanism alone does not take turbine RPM as input.

In both the hardware and software side of my career it's these tiny details that can make huge "undesired operation" events because an assumed state was not achieved.

How do you think any of that is relevant l?

Damaged mechanisms that can't provide full force to move vector plates into position through the force of heavy turbine exhaust. (If they even still exist)

Panicked pilots that go from throttle-up through throttle-idle directly to full reverse.

737 screaming down the runway because the turbines didn't know the thrust was going the wrong direction, but all the hardware, firmware, and software had no idea.

TexasRebel said:

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Damaged mechanisms that can't provide full force to move vector plates into position through the force of heavy turbine exhaust. (If they even still exist)

Panicked pilots that go from throttle-up through throttle-idle directly to full reverse.

737 screaming down the runway because the turbines didn't know the thrust was going the wrong direction, but all the hardware, firmware, and software had no idea.

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Which mechanisms were damaged?

Which thrust reversers were commanded to deploy? Which were commanded but failed to deploy?

Did the pilots change the throttle setting on the runway? Do you comprehend that's not how the systems work?

Here the last bit of attention you'll get from me.

People like you make me regret sharing actual knowledge to those who are curious.

There are two steams exiting the back of the CFM56 turbofan engines on a 737-800: bypass air and the turbine exhaust. I can't find an exact figure, but the bulk of the thrust is coming from the bypass air (probably well over 50% of total thrust) and this is the reason why turbofans are so much more fuel efficient than a straight gas turbine engine with low/no bypass flow.

Most (all?) turbofans including the CFM56 use cold air / bypass air reversers. That is, they only redirect the flow of the bypass air and the turbine exhaust flow is not redirected. This of course does reduce the reverser effectiveness, but this is the system design.

The turbine has to be spinning to generate the bypass air flow that will be reversed in the first place.

Also, I'm no pilot, but aren't the reversers used on rejected takeoffs? If that is true, the reverser system has to be able to handle going from TOGA power setting, straight to idle, and into thrust reverse very rapidly and at whatever condition the engine is operating at (i.e. near maximum output).

Those are things that, unfortunately, only failure analysis will determine.

GAC06 said:

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Did the pilots change the throttle setting on the runway? Do you comprehend that's not how the systems work?

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Are you now saying that the throttle setting cannot be altered on the runway? Because that's what you just said.

TexasRebel said:

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Damaged mechanisms that can't provide full force to move vector plates into position through the force of heavy turbine exhaust. (If they even still exist)

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Or maybe, Boeing thought of that and the thrust reversers have the huevos to flip down (or over or wtf) even if the engine was still running at full plaid ludicrous speed. Seems like the hydraulics which operate these contraptions have serious huevos because they can hold them in position when reverse thrust is wide open if the pilots floors it.

Seems like you're wrapped up in engine speed when the thrust stick goes into idle and whether the thrust reverser is gonna get bounced out and not work because the engine/turbine/motor was going to fast. Considering the dude who flies one of these ain't worried about it, I'd venture a guess Boeing figured it out a long time ago and it ain't an aha moment.

No. A good design would over-center so once in place the thrust keeps them in place instead of requiring constant force from the hydraulics to maintain thrust reversing.

I still have no idea what you're on about...

What's the "design flaw?" Why do you think it's a flaw? How do you think it ought to work?

No throttle if it can be detected thrust isn't going the intended direction.

Are you the N8Dawg that had a detached retina about 13 years ago?

If so, great to see you & how've you been?

Gator92 said:

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GAC06 said:

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These kind of threads are irresistible to know it all types.

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Pilot v Wannabe Pilot Pissing Contest...

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Engineer v. Plane Driver.

Sorry, I'm not the N8Dawg you know. My retinas are still on their original attatchment run.

Great to see ya anyway.

For those with the aerodynamic knowledge, where was the estimated point of no return on this doomed landing? I know that may be hard to answer with still too many unknowns. It seems the plane was still traveling full speed halfway down the runway. I saw on one of the videos they estimated 150 knots at impact? What speed would need to be generated to create enough lift?

Was it possible for the pilots to abort the landing over the runway when they realized they didn't touch down or was it likely already too late?

GAC06 said:

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TexasRebel said:

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Damaged mechanisms that can't provide full force to move vector plates into position through the force of heavy turbine exhaust. (If they even still exist)

Panicked pilots that go from throttle-up through throttle-idle directly to full reverse.

737 screaming down the runway because the turbines didn't know the thrust was going the wrong direction, but all the hardware, firmware, and software had no idea.

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Which mechanisms were damaged?

Which thrust reversers were commanded to deploy? Which were commanded but failed to deploy?

Did the pilots change the throttle setting on the runway? Do you comprehend that's not how the systems work?

Here the last bit of attention you'll get from me.

People like you make me regret sharing actual knowledge to those who are curious.

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Not sure what all is going on here but from the videos the
- port engine was not showing to have the reverse thruster active (the doors on the engine nacelle were visible closed)
- starboard engine looked to be using reverse thrust but some speculate that it was not actually reverse thrust but a damaged nacelle on the engine from a possible bird strike
- as far as I know it is not confirmed that reverse thrust was engaged but the engines could still be heard after touchdown and possible could have been throttle up after touchdown.

Just seems like major f-ups by the pilots and a huge design flaw at the airport that increased the lethality of the pilots mistakes

If someone, short of the investigative report, could explain why: The gear was not down, some flap deployed, and no spoiler deployment can be observed, then all the rest is noise. They had the plane on centerline (in control of the airplane), at least one engine was providing thrust, they had time to do what they had done in probably 1000 landings, and did not do it?

TexasRebel said:

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Gator92 said:

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GAC06 said:

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These kind of threads are irresistible to know it all types.

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Pilot v Wannabe Pilot Pissing Contest...

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Engineer v. Plane Driver.

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I was just thinking the same.

I'm not a pilot and really not an engineer. Even tho my diploma says I have a BS from the College of Engineering.

I've been to PWC, Chance Vought, GD, LM, Bell, NASA, Boeing, GE, Siemens among others over the years. I have been involved w/ turbine root cutters, turbine blade grinding, rivet bucking, turbine blade ultraviolet dye inspection and other specialty aeospace and gas turbine specialty tooling, cleaning and inspection.

I deal w/ real engineers often and can tell what's goin on here...

TexasRebel said:

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No throttle if it can be detected thrust isn't going the intended direction.

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OK, I THINK I've got my head wrapped around what's got your jimmies, so let's go through this from the top.

First...A thrust reverser does not have "vector plates." They are doors, and they are designed such that once they are cracked open, the aircraft airspeed and/or engine bypass will force them open the rest of the way.



As someone else pointed out, TR's are indeed used for Rejected Take-offs, so you can bet they are certificated to deploy fully at very high, if not full power. And before you ask, yes the locks can fail and cause uncommanded deployment...that's a scenario that is specifically trained for.

Next, When TR's are commanded deployed, increasing engine power is inhibited unless the doors are actually open. This is done either through a mechanical interlock or FADEC logic...possibly both. If I had to bet, I'd say the B737 uses the former. Maybe when GAC wakes up in the morning he can break out his systems manual and look it up.

That being said... This accident (not a Boeing) may be of interest to you:

Quote:

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the reversers were never deployed, and moving the controls to the Maximum Reverse position caused an increase of forward thrust in both engines

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Now, as for our current event, there is speculation that the entire TR assembly was ripped off due to the engine skidding along the ground at high speed...in that case, all bets are off, YMMV...literally.

Hope this helps

BTW...the going rate for a type rating is ~$30K. I expect payment within 30 days.