Problems in a commercial flight

Ron Natalie writes:

Sometimes, and yes.

What makes them asymmetrical?

Spiral is not an oscillation. Spiral is a departure from positive
stability when you push things too far.

Spiral instability.

Absolutely and totally incorrect.

It depends on the aircraft, but my generalization is mostly valid.

You should go read a introductory
pilots book section on flight aerodynamics.

That's the problem with pilots' books: they never go past the introduction to
these complex topics.

Now your an aerodynamics expert?

I've never claimed to be an expert. But I do know something about it.
Asserting or sharing knowledge is not a claim of expertise.

--
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Ron Natalie writes:

And you profess to know everything even though you fly nothing.

I have never claimed to know everything. I don't need to fly to know things.

Of course you'll have a terrible time convincing people of that.

Not if they understand the theory, which many pilots do not.

All coordinated flight involves is that the tail of the aircraft follow
the front in the flight path (this is confusing to most people primarily
because of the FAA's stupid pseudo-physics definition of it).

Coordinated turns maintain an acceleration vector parallel to the yaw axis.
It is impossible to do this in a 90-degree bank. There is always a vertical
component produced by gravity, and this means the acceleration vector can
never be completely horizontal, and yet it would have to be in a 90-degree
bank for a coordinated turn. The horizontal component would have to be of
infinite magnitude, which is not possible.

There
is nothing that prevents coordinated 90 degree banks. In most aircraft
however, you're not going to be able to sustain that.

You cannot achieve it in any aircraft, much less sustain it.

--
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In small aircraft, the engines are so unreliable that engine failures must be
practiced. Ironically, there's no really good way to practice them, since
full-motion simulators for small aircraft are rare, and it's too dangerous to
practice true engine failures in a real aircraft (setting an engine to idle
doesn't count).

Loon mallet please....

Mxsmanic wrote:
Sometimes it is simulated just because pilots expect it.

So you admit that in expecting it, the pilots must necessarily feel it
(or rather, expect to feel it; want to feel it; know that they should
feel it; know that it should exist).

I don't know why it's true.

Then how can you say that it is not false?

But at the same time, they
are extremely rare in large commercial airliners, so practicing them in excess
(to the detriment of practice in other, more likely emergency scnearios) is
probably not a good idea.

In small aircraft, the engines are so unreliable that engine failures must be
practiced.

Surface analysis of the NTSB database would seem to mete this out; last
year there were just 2 incidents in jets, while general aviation racked
up 25. However, without a more detailed report of accidents per flight
or per mile (or per capita), I would be hesitant to make such claims
with authority.

Ironically, more of the GA accidents with fatalities occurred in large
turbine/heavy twin aircraft, while small "tin-cans" were generally
non-fatal if not merely incidental.


(setting an engine to idle
doesn't count).

Why not, if the purpose of the practice is to experience a loss of
meaningful power and to execute the proper diagnostics to the engine as
well as the correct emergency procedures? Idling the engine would seem
to be a perfect solution.

Some Airbus aircraft are designed to be unstable, under the assumption that
computers will keep them flying straight and level.

Which?

... why design systems that fail catastrophically?

Systems fail catastrophically when they are _not_ designed. Catastrophic
failure modes are characteristic of unanticipated exceptions in digital
systems.

Surely an engineer would anticipate the failure of a computer system.
Heck, that's why we have triple-redundancy hydraulic systems (with
backup electrics, no less).

That same engineer would also surely see that using an active control
system (with a failure potential) is inferior to using plain old physics
(which has already been demonstrated on many other designs; why try to
fix what isn't broken)?

That cannot be done with digital systems. They only fail safe in modes that
are anticipated in the design; in other modes, catastrophic failure is more
likely.

But the system in question here is not digital, nor is it controlled as
such by the fly-by-wire systems. Dihedral in a wing uses physics (and a
helping hand from Mr. Daniel Bernoulli) to roll an aircraft level (or
more towards level), sans control inputs. Why would an engineer ignore
this time-tested approach to wing design in favor of an active (and
potentially failure-prone) system?

That would not be verification.

But it would start the process.

Yes, and it is vastly overrated in consequence. Many incorrectly assume that
the mere presence of references somehow validates whatever uses them.

I think many assume that the presence of references provides a trail of
fact-checking and verification which is important when trying to assert
the validity of analysis and claims made in such academia.

Your use of the term puzzled me,

I'm not sure why; I used it to indicate two separate concepts, which you
promptly corrected me by saying that they were.... independent.

It would have seemed to the outside viewer that perhaps you had not
understood the usage.

They need to do their own research.

Hard to do without a platform to stand on from which to begin, eh? It
would hardly be fair if you wanted to verify my claims of why the sky
was blue, but you had to discover the atom first (and then molecules,
dipole bonding forces, light refraction, fusion, astronomy, and various
other sundry basal sciences), right?

Public services usually aim to provide helpful and useful information,
as well as a stepping stone for learning more about the topic, not
commands from on-high from an individual who holds himself in higher
standing than his peers.

TheSmokingGnu

Until Airbus came along.

No... wrong again.

Airbii are statically stable for efficiencies sake, their control
mechanism is irrelevant.

TheSmokingGnu writes:

So you admit that in expecting it, the pilots must necessarily feel it
(or rather, expect to feel it; want to feel it; know that they should
feel it; know that it should exist).

They want to feel it. They don't need it. It makes pilots comfortable,
especially those who dislike change. It makes them feel as if they are still
in control, even when they are not.

Then how can you say that it is not false?

I don't have to know why something is true just to know that it's true. I
know that some flowers are blue and others are red--it's definitely true--but
I don't know why.

Surface analysis of the NTSB database would seem to mete this out; last
year there were just 2 incidents in jets, while general aviation racked
up 25. However, without a more detailed report of accidents per flight
or per mile (or per capita), I would be hesitant to make such claims
with authority.

The NTSB database is pretty reliable.

Why not, if the purpose of the practice is to experience a loss of
meaningful power and to execute the proper diagnostics to the engine as
well as the correct emergency procedures?

Because an idle engine is not a stopped engine, as anyone who has experienced
an actual failure can attest.

Idling the engine would seem to be a perfect solution.

No, it just creates a false sense of security.

Which?

I've forgotten which models; presumably the more recent ones.

Surely an engineer would anticipate the failure of a computer system.

There are too many possible failure scenarios. Nobody, not even an engineer,
can anticpate them all. The ones that are not anticipated in the design will
generally produce catastrophic failures (in digital systems).

Heck, that's why we have triple-redundancy hydraulic systems (with
backup electrics, no less).

Mechanical systems are not digital. The catastrophic failures come from
software.

That same engineer would also surely see that using an active control
system (with a failure potential) is inferior to using plain old physics
(which has already been demonstrated on many other designs; why try to
fix what isn't broken)?

Sometimes engineers are seduced by the promise of better performance, to the
detriment of safety.

But the system in question here is not digital, nor is it controlled as
such by the fly-by-wire systems.

All modern fly-by-wire systems are digitally controlled, because they depend
on digital computers and software.

Dihedral in a wing uses physics (and a
helping hand from Mr. Daniel Bernoulli) to roll an aircraft level (or
more towards level), sans control inputs. Why would an engineer ignore
this time-tested approach to wing design in favor of an active (and
potentially failure-prone) system?

To improve performance. The usual reasoning is that prudent design for
default behavior is unnecessary because the computers can fix it all. This is
a very common error in engineering these days, and not just in aviation.

It's a bit like people who never learn to brake properly in wet conditions
because they expect the ABS to do it for them. The day the ABS fails comes as
a big surprise.

I think many assume that the presence of references provides a trail of
fact-checking and verification which is important when trying to assert
the validity of analysis and claims made in such academia.

That trail is useless if nobody follows it, and most people just assume that
the presence of references makes them valid, without checking. In reality,
there is no improvement in reliability just because there are references.

I'm not sure why; I used it to indicate two separate concepts ...

That's not what dichotomy means.

It would have seemed to the outside viewer that perhaps you had not
understood the usage.

That depends on the education of the outside viewer.

Hard to do without a platform to stand on from which to begin, eh?

Not at all. All research begins that way. That's why people do research.

It would hardly be fair if you wanted to verify my claims of why the sky
was blue, but you had to discover the atom first (and then molecules,
dipole bonding forces, light refraction, fusion, astronomy, and various
other sundry basal sciences), right?

Why does it have to be "fair"?

Public services usually aim to provide helpful and useful information,
as well as a stepping stone for learning more about the topic, not
commands from on-high from an individual who holds himself in higher
standing than his peers.

My public service is in forcing people to think, an activity that will benefit
them over the long term.

--
Transpose mxsmanic and gmail to reach me by e-mail.

Mxsmanic wrote:
TheSmokingGnu writes:

So you admit that in expecting it, the pilots must necessarily feel it
(or rather, expect to feel it; want to feel it; know that they should
feel it; know that it should exist).

They want to feel it. They don't need it. It makes pilots comfortable,
especially those who dislike change. It makes them feel as if they are still
in control, even when they are not.

So you admit that the feeling does exist, that it has existed in the
past, that the pilots HAVE felt it, and that they have used it as a
kinesthetic aid to understanding their control (or lack thereof) of the
aircraft.

If they spend all their time ignoring feel, why should they need to add
it back when it's removed from the equation? Shouldn't this have made
their jobs easier?


Then how can you say that it is not false?

I don't have to know why something is true just to know that it's true. I
know that some flowers are blue and others are red--it's definitely true--but
I don't know why.

Your example is intrinsic observation, while the topic under discussion
is analytic, which requires evidence and reasoning. Thus, you cannot
intrinsically say that it is true just because you feel or think that it
should be, but must reinforce your hypothesis (as indeed, that is all
that it is, less a law).

The NTSB database is pretty reliable.

Indeed, but the argument was over taking statistics derived from such
out of context of actual accident rates (and then trying to draw
conclusions).

Because an idle engine is not a stopped engine, as anyone who has experienced
an actual failure can attest.

This does nothing, however, to prevent you from performing the correct
emergency procedures, which is the point of the exercise. Besides, an
idle engine is often worse for performance than a properly stopped one
(vis a vis, a feathered prop), so if you practice with and plan for
reduced glide capability, a real emergency should be a piece of cake.

No, it just creates a false sense of security.

Security in what?

Which?

I've forgotten which models; presumably the more recent ones.

Then how can you make this claim?

A380:
http://www.airliners.net/open.file/1174138/M/

A340-600:
http://www.airliners.net/open.file/1186466/M/

A320-211:
http://www.airliners.net/open.file/1189003/M/

Which of these relatively recent models does not use dihedral in its wing?


Surely an engineer would anticipate the failure of a computer system.

There are too many possible failure scenarios. Nobody, not even an engineer,
can anticpate them all. The ones that are not anticipated in the design will
generally produce catastrophic failures (in digital systems).

I think you'll find (or will soon find out) that engineers spend the
VAST amount of their time coming up with failure scenarios and building
programming to mitigate them. The normal operating code is dead simple.

Most computer systems have fail-safe modes (by most I mean any system
which is critical to keep plane A from falling out of sky B), which at
the very least rescind their automatic functions back to the pilots, or
in the case of fly-by-wire computers, carry triple redundancy (AND still
have a "dumb" mode where they operate the control surfaces directly from
stick input, without translation or interpretation).

So, I reiterate, why would an engineer, whom specifically works on
projects such as failure states, fail to design a system that will fail
in an acceptable manner, especially where lives are concerned?

Mechanical systems are not digital. The catastrophic failures come from
software.

Catastrophic failure comes from wherever Murphy decides, regardless of
digital or mechanical systems. A 1 may accidentally be a 0 and try to
fly the plane backwards just as surely as a 10 cent cotter pin comes
loose in a hydraulic pump and disables the ailerons. The quest is and
has always been to design systems that will tolerate that kind of
failure (if only to abdicate control to another), and to use as few
moving and/or thinking parts as possible.

Why then, is it feasible that Airbus (and curiously, Airbus alone)
designed a system perfectly counter to this philosophy?

Sometimes engineers are seduced by the promise of better performance, to the
detriment of safety.

Would you care to cite any specific examples?

All modern fly-by-wire systems are digitally controlled, because they depend
on digital computers and software.

As I said, we're discussing a specific wing design, not the fly-by-wire
system (although the topic has veered). The fly-by-wire doesn't keep the
wings level (although you seem to assert so), but the in-built dihedral
of the wings does.

To improve performance. The usual reasoning is that prudent design for
default behavior is unnecessary because the computers can fix it all. This is
a very common error in engineering these days, and not just in aviation.

Again, I would ask for a more specific example. I think you'll find that
engineers always, ALWAYS use a prudent, proven design over a new one
(that's why airliners are almost exclusively swept-wing, long straight
fuselage, twin under-wing engined, traditional tailed craft; because the
engineers know the design works and that it has favorable flight
characteristics). Computer systems are only used as an aid or
convenience to alleviate the humans operating the system of some tedium
or micromanagement, never as the crutch of normal operation, and they
are certainly not allowed to be the progenitor of catastrophic failures.

It's a bit like people who never learn to brake properly in wet conditions
because they expect the ABS to do it for them. The day the ABS fails comes as
a big surprise.

If the ABS failed prior to the stop, it would be indicated on the
dashboard, and so should be taken in for maintenance (this is not a
failure caused by the computer then, but human negligence or error).

If the ABS fails mid-stop, there isn't much you could do, anyway,
technique or no. Your brain isn't fast enough to react to the change in
brake action, recognize the situation, decide on the proper course of
action, and send signals to your foot in the split-seconds you have
before impact.

In any case, this example does not provide a situation where the
computer system is the crutch of the operation, nor one where the
failure is catastrophic, nor one where the failure is the fault of the
computer system. The brakes are still connected hydraulically to the
pads (and always will be, regardless of the ABS' actions), the failure
did not disable the brake system (and cannot, short of simultaneously
bursting all of the brake hard-lines; an impossibility). The computer
system did not command the stop, nor did it begin the stop, nor has it
disabled any functionality that the driver possessed, before or after
the failure.

Thus, I submit that the example is not applicable.

That trail is useless if nobody follows it, and most people just assume that
the presence of references makes them valid, without checking.

That trail is even more useless when it isn't iterated in the first
place. Even if only one person uses it, you have helped that one person
to greater understanding. Even if only one actually checks the
references, doubts what is said, and learns more by it, that number is
still much, much larger than zero, which is the number possible by NOT
providing references.

That's not what dichotomy means.

http://dictionary.reference.com/search?q=dichotomy

especially:

2. division into two mutually exclusive, opposed, or contradictory
groups: a dichotomy between thought and action.

Hard to do without a platform to stand on from which to begin, eh?

Not at all. All research begins that way. That's why people do research.

People wishing to explore the quantum state (for example) don't need to
reperform all research and analysis which led to that point from the
discovery of the electron, and yet that is what you're forcing people to
do when they have no references. They cannot even look at the specific
texts from which you draw your own conclusion, much less discover the
topic and learn more from it. They must either accept your word at its
face or be forced to strike out some lucky Google search. Hardly an
equitable solution.

Why does it have to be "fair"?

It's a figure of speech, I mean that it is incorrect to provide no basis
for your claims, to refuse to issue reference texts, and then to deride
and belittle others for not doing the research which, if not impossible,
you make very improbable in the first place. It is proper to provide
those you wish to respect you academically (if at all) with a grounding
in your understanding and analysis.

My public service is in forcing people to think, an activity that will benefit
them over the long term.

You cannot contemplate facts into being, even Aristotle recognized this
2,000 years ago in the Nicomachean Ethics. Research is done to provide
factual, objective basis from which original analysis and conclusions
can be drawn (which is admittedly what you are trying to do). Academic
peers seek this basis, from which to debate or criticize your viewpoint,
to draw their own conclusions, or to learn more about the topic at hand.
You are denying them this basic academic freedom and obscuring it under
the guise of a service.

TheSmokingGnu

MXMORON writes:

Since you haven't tried, how can you know this?

Research.

--
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Mxsmanic wrote:


Coordinated turns maintain an acceleration vector parallel to the yaw axis.

Not true. In a normal coordinated turn (lets do 45 degrees of bank),
the acceleration vector points towards the inside of the turn. The
yaw axis itself is canted at a 45 degree angle.

It is impossible to do this in a 90-degree bank. There is always a vertical
component produced by gravity, and this means the acceleration vector can
never be completely horizontal, and yet it would have to be in a 90-degree
bank for a coordinated turn. The horizontal component would have to be of
infinite magnitude, which is not possible.

Sorry, that's untrue. The acceleration is always horizontal in a level
turn regardless of bank.

There
is nothing that prevents coordinated 90 degree banks. In most aircraft
however, you're not going to be able to sustain that.

You cannot achieve it in any aircraft, much less sustain it.

That would be news to a lot of acro pilots. The fallacy (in addition
to your other mistakes of physics and aerodynamics) is that the wings
are the only aerodynamic surface in play.

Mxsmanic wrote:
Ron Natalie writes:

Sometimes, and yes.

What makes them asymmetrical?

Spiral is not an oscillation. Spiral is a departure from positive
stability when you push things too far.

Spiral instability.

Instability is not necessarily an oscillation. You said oscillation.
You are wrong


Absolutely and totally incorrect.

It depends on the aircraft, but my generalization is mostly valid.

No it isn't. If you think the control surfaces can't move without
either the pilot or the autopilot acting on them, you're daft. It's
true in EVERY SINGLE AIRPLANE IN THE WORLD. Have you ever heard of
the concept of trim? This is a little aerodynamic device that moves
the control surface dynamically to obtain given stable position.

Further some airliners don't even have a direct connection between
the yoke/autopilot and the control surface. Instead, these are
connected to a servo tab that moves the surface by aerodynamic means.

You should go read a introductory
pilots book section on flight aerodynamics.

That's the problem with pilots' books: they never go past the introduction to
these complex topics.

Yes, but they explain the simple topics you don't seem to begin to
understand.