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Nepal Plane Crash

Old 4th Feb 2023, 19:14
  #441 (permalink)  
 
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Originally Posted by hans brinker
I mean, if the tail goes from a lot of negative lift, to just a little negative lift, so less negative lift from the tail, does that not mean "more" lift (hopefully what he meant....)? Obviously, you are correct in your reply about what aerodynamically happens, maybe just a language difference.
Just taught many moons ago to be precise especially when instructing…now that Bernoulli has been discredited and triplex systems are unnecessary glad I don’t work anymore.
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Old 4th Feb 2023, 19:36
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Originally Posted by blind pew
Just taught many moons ago to be precise especially when instructing…now that Bernoulli has been discredited and triplex systems are unnecessary glad I don’t work anymore.
Bernoulli has not been discredited at all.
When you apply his equations to problems in the right context they work perfectly.

Bernoulli equations calculate the pressure drop when some part of a fluid flows faster, this is true the pressure does drop, but trying to apply this to explain why an aerofoil produces lift is flawed because the theory of why an aerofoil produces life was flawed in the first place as the principal of equal transit times has been shown to be false.

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Old 4th Feb 2023, 21:16
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Originally Posted by michaelbinary
Bernoulli has not been discredited at all.
When you apply his equations to problems in the right context they work perfectly.

Bernoulli equations calculate the pressure drop when some part of a fluid flows faster, this is true the pressure does drop, but trying to apply this to explain why an aerofoil produces lift is flawed because the theory of why an aerofoil produces life was flawed in the first place as the principal of equal transit times has been shown to be false.
FYI, don't think you are talking about the school master or your mortgage, so : "principle" (not trying to be an @$$, but to me words matter)
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Old 4th Feb 2023, 21:19
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Originally Posted by blind pew
Just taught many moons ago to be precise especially when instructing…now that Bernoulli has been discredited and triplex systems are unnecessary glad I don’t work anymore.
See above, and I don't disagree.
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Old 5th Feb 2023, 07:33
  #445 (permalink)  
 
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In the real world, the air molecules are not moving over or under a wing. They are simply sitting still, or wandering around gently, having a great day - until suddenly some metallic object whips past them: "WTF was that?", they say. The ones above got squished up together, the ones underneath not so much.

So the air molecules are not 'trying to equalise their speed over the wing' they are sitting still while the wing is doing the moving past them and pushing them up or down.

Most wind tunnels, of course, move the air molecules while keeping the wing static, and I wonder if this is where the confusion arose?
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Old 5th Feb 2023, 08:44
  #446 (permalink)  
 
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What about when parked on the ramp...

Originally Posted by Uplinker
In the real world, the air molecules are not moving over or under a wing. They are simply sitting still, or wandering around gently, having a great day - until suddenly some metallic object whips past them: "WTF was that?", they say. The ones above got squished up together, the ones underneath not so much.

So the air molecules are not 'trying to equalise their speed over the wing' they are sitting still while the wing is doing the moving past them and pushing them up or down.

Most wind tunnels, of course, move the air molecules while keeping the wing static, and I wonder if this is where the confusion arose?
In a 50 kt wind on a remote strip in Alaska? Do the air molecules do different things there than in a wind tunnel?
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Old 5th Feb 2023, 08:47
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As with most thing, it's all relative ...
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Old 6th Feb 2023, 14:06
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"According to first analysis of the flight data recorders both propellers of the aircraft went into the feather position."

AvHerald 02/06/2023
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Old 6th Feb 2023, 15:57
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Originally Posted by Uplinker
In the real world, the air molecules are not moving over or under a wing. They are simply sitting still, or wandering around gently, having a great day - until suddenly some metallic object whips past them: "WTF was that?", they say. The ones above got squished up together, the ones underneath not so much.

So the air molecules are not 'trying to equalise their speed over the wing' they are sitting still while the wing is doing the moving past them and pushing them up or down.

Most wind tunnels, of course, move the air molecules while keeping the wing static, and I wonder if this is where the confusion arose?
In physics it doesn't matter which frame of reference you choose.
Youbtakenthebframe of the air, in which the wing is moving. But it is totally equivalent to see it dromen the frame of the wing, in which the air is moving.
Both will come to the same result.
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Old 6th Feb 2023, 16:13
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Originally Posted by gearlever
"According to first analysis of the flight data recorders both propellers of the aircraft went into the feather position."
wow that doesn’t help for sure. Any ATR driver willing to elaborate about how such a thing might happen !?
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Old 6th Feb 2023, 16:15
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Were they immediately identifying Dead engines ? So they would be flying very close to V (mca) after noticing either of the engine failed , Would Feathering Both engines be a safe way to keep the plane gliding until they identify failed engine .
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Old 6th Feb 2023, 16:31
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I would suggest fire-walling the engines would be a somewhat better reaction whilst you identify any failed engine. Gliding from low altitude is rather time limited.
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Old 6th Feb 2023, 16:52
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A possibility is that they may have been too high to change runway and decided to put the engines into 100% over-ride (fine pitch) using the condition levers to create drag and maybe move them back to the Auto position when they got on the new profile but mistakenly brought them to feather.
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Old 6th Feb 2023, 16:54
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Originally Posted by gearlever
"According to first analysis of the flight data recorders both propellers of the aircraft went into the feather position."

AvHerald 02/06/2023
Spurious auto-feather happened before:

Spurious auto-feather on TransAsia Airways ATR 72-600

And that is, indeed, what happened, according to the formal investigation conducted by the Aviation Safety Council of Taiwan (ASC). However, the instigating factor likely came as a surprise to most aviation safety specialists due to its rarity: The ASC found that the accident was prompted by a spurious activation of the propeller autofeather system.

Moreover, the council’s final report indicated that even before the accident occurred the morning of Feb. 4, 2015, there was evidence that the system could fail. It had happened twice (without further mishap) due to intermittent signal discontinuities related to aging of the system, and the engine manufacturer had issued service instructions to address the problem.

The ASC found that the airline, TransAsia Airways, had not adequately informed its flight crews of the problem and had not issued clear instructions that a takeoff must be rejected if there are any signs that the autofeather system is not working properly.
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Old 6th Feb 2023, 18:10
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A spurious (uncommanded) auto-feather of both engines simultaneously would be really bad luck ...
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Old 6th Feb 2023, 18:17
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Originally Posted by DaveReidUK
A spurious (uncommanded) auto-feather of both engines simultaneously would be really bad luck ...
Nicely put......
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Old 6th Feb 2023, 19:17
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Is there any recorded aviation accident when both props would auto feather at the same time without crew input (regardless of type) ?
Now how they achieved that will be an interesting read…
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Old 6th Feb 2023, 22:34
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Originally Posted by blind pew
Just taught many moons ago to be precise especially when instructing…now that Bernoulli has been discredited and triplex systems are unnecessary glad I don’t work anymore.
Originally Posted by michaelbinary
Bernoulli has not been discredited at all.
When you apply his equations to problems in the right context they work perfectly.

Bernoulli equations calculate the pressure drop when some part of a fluid flows faster, this is true the pressure does drop, but trying to apply this to explain why an aerofoil produces lift is flawed because the theory of why an aerofoil produces life was flawed in the first place as the principal of equal transit times has been shown to be false.
BP, fair comments, MB is also correct that Bernoulli's equations give correct answers, but the conceptual Bernoulli model is incorrect at a detail level. For a single element foil or single body, Bernoulli is good enuff, it gets all squirrelly with multi element foils or dealing with separated flow conditions where some magic can happen.
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Old 7th Feb 2023, 07:22
  #459 (permalink)  
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Originally Posted by atakacs
Is there any recorded aviation accident when both props would auto feather at the same time without crew input (regardless of type) ?
Might have been in the early pistons aircraft types when it was introduced, but all the events I remember were I always at or right after take off , Having that on base leg with reduced power ? and as you said, on both engines at the same time ? Weird.
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Old 7th Feb 2023, 09:56
  #460 (permalink)  
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Originally Posted by ATC Watcher
Might have been in the early pistons aircraft types when it was introduced, but all the events I remember were I always at or right after take off , Having that on base leg with reduced power ? and as you said, on both engines at the same time ? Weird.
I've heard of un commanded auto feather at reduced power setting on the Basler (Turbine DC-3) Which I'm sure have a more Mickey Mouse type of auto feather system than the ATR. The thing to know is if you have an un commanded prop going feather by itself while both engines are at low power settings, as they normally would be close to final, the highest torque of the two would be the one who feathered! Not the other way around. So if you rush things it's easy to "secure" the wrong engine thinking the good one has failed ending up with both prop feathered.

Disclaimer: I'm in no point saying that's what happened there but that is a possible scenario on another type of aircraft.
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