Question to Mxmanic

I don't know if he "cannot" or will not or just wants to get under
everyone's skin. What you say in this post is correct. But why do people
keep responding and arguing ad nauseum with someone who can't or won't
get it? What's the dynamic? I doubt that there has ever been a pilot who
has not flown into his own wake in a constant altitude 360. So this is
not a topic that one pilot needs to prove to another pilot with a
different opinion.

Rip wrote:


Unfortunately, Anthony cannot make the simple leap from assuming his
vaunted "research" is correct, even though it provides the wrong answer,
to asking himself, "Let me assume that the empirical experiments
conducted by hundreds of thousands of real world pilots provide
hypothetical proof that an aircraft, completing a 360 degree turn at a
constant altitude, can indeed run through its own wake. What new
assumptions must I make to make this so, and how can I verify those
assumptions?"

RomeoMike wrote:

I don't know if he "cannot" or will not or just wants to get under
everyone's skin. What you say in this post is correct. But why do people
keep responding and arguing ad nauseum with someone who can't or won't
get it? What's the dynamic? I doubt that there has ever been a pilot who
has not flown into his own wake in a constant altitude 360. So this is
not a topic that one pilot needs to prove to another pilot with a
different opinion.

The only dynamic is between the pilots on the group, certainly not with
MX. But, as I mentioned, the thread forced me to ask myself just what it
was I am "running over" when I hit my own wake turbulence. Does it
matter? Probably not, but this enquiring mind wants to know. I still
don't have the answer. Rising wingtip vortices in warm air? Prop wash?
"Burbles" from the passage of non-lifting surfaces like the fuselage?

We all know it happens. I'm just one of those weirdos that wants to know
WHY it happens. As a result of this thread, it appears that nobody
knows. It's an unstudied regime of flight. I find THAT interesting!
Perhaps it could lead to some super-terrific drag reduction technique,
like surfing on your own wake? After all, that's why geese fly in "V"
formation.

Rip

"Rip" wrote ...

Oh well. The entire thread has forced me to ask myself just what the wake
behind an aircraft looks like. Like every other pilot, I know you can
intercept your own wake during a constant altitude turn, but it would be
neat to be able to SEE all of the air masses at work.

Thanks for your smoke insights ;-)
There are some great photos depicting the tip vortices he
http://www.airliners.net/open.file/1091105/M/
http://www.airliners.net/open.file/1008033/M/

Here are some real masterpieces :

http://www.airtoair.net/gallery/gallery-vortices.htm


I guess Mxmanic uses the FAA AIM as his main source in his "research".
Section 7.3.1 is about wake turbulence. A couple of interesting quotes from
that section, that Mx has not seen fit to share with us:

a) "Flight tests have shown that the vortices from larger (transport
category) aircraft sink at a rate of several hundred feet per minute,
slowing their descent and diminishing in strength with time and distance
behind the generating aircraft."

Note the explicit reference to large aircraft. In fact, it seems all actual
wake turbulence safety studies have involved large aircraft, i.e. B707 and
larger. This is in fact quite natural, as there was no real safety issue
before the large jetliners appeared.
b) "Test data have shown that vortices can rise with the air mass in which
they are embedded."

There you are, official proof to the statements of several of our
contributors.

c) "The greatest vortex strength occurs when the generating aircraft is
HEAVY, CLEAN, and SLOW."

In contrast, a light aircraft doing a 360 is usually LIGHT, CLEAN and
(relatively speaking) FAST. Very different conditions, especially regarding
two major sources of wake: the AoA of the wing (which affects the tip
vortices) and the power setting (which affects the propwash strength).

The interesting study question here, for the light airplane case, would be
the relation between the tip vortices (which presumably sink, as for large
aircraft) and the propwash (which is basically horizontal). I think glider
pilots can testify that the propwash is the dominant one, at least close
behind the tug airplane - any soarers out there who can comment?

But realistically, as the wake behind a light aircraft is no real safety
hazard, there is no compelling reason to study this case. So unless someone
can produce a reference, let's rely on the observational data from countless
pilots.

Beautiful, Snowbird. I've seen the effect in reality, but those are some
magnificent photos!

Rip

Snowbird writes:

I guess Mxmanic uses the FAA AIM as his main source in his "research".

That is only one of many sources. They all say the same thing.

a) "Flight tests have shown that the vortices from larger (transport
category) aircraft sink at a rate of several hundred feet per minute,
slowing their descent and diminishing in strength with time and distance
behind the generating aircraft."

Note the explicit reference to large aircraft. In fact, it seems all actual
wake turbulence safety studies have involved large aircraft, i.e. B707 and
larger. This is in fact quite natural, as there was no real safety issue
before the large jetliners appeared.

The wakes of smaller aircraft descend as well.

b) "Test data have shown that vortices can rise with the air mass in which
they are embedded."

There you are, official proof to the statements of several of our
contributors.

Including myself.

c) "The greatest vortex strength occurs when the generating aircraft is
HEAVY, CLEAN, and SLOW."

Yes. Although the downwash itself should be strongest when the aircraft is
dirty and slow. The reason clean and slow produces stronger _vortices_ is
that it only produces one pair, whereas flaps and other control surfaces can
produce multiple vortices of smaller size that tend to interfere with each
other and reduce overall turbulence.

In contrast, a light aircraft doing a 360 is usually LIGHT, CLEAN and
(relatively speaking) FAST. Very different conditions, especially regarding
two major sources of wake: the AoA of the wing (which affects the tip
vortices) and the power setting (which affects the propwash strength).

Which makes it all the more difficult to understand how a pilot could feel his
own wake in a level 360-degree turn.

The interesting study question here, for the light airplane case, would be
the relation between the tip vortices (which presumably sink, as for large
aircraft) and the propwash (which is basically horizontal). I think glider
pilots can testify that the propwash is the dominant one, at least close
behind the tug airplane - any soarers out there who can comment?

You're neglecting the downwash, which is present in all aircraft. Downwash
tends to pull all turbulence behind the aircraft down with it.

But realistically, as the wake behind a light aircraft is no real safety
hazard, there is no compelling reason to study this case. So unless someone
can produce a reference, let's rely on the observational data from countless
pilots.

And ignore the factual data from countless resources? What makes pilots more
reliable? Most pilots barely understand how lift works to begin with.

--
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On Apr 16, 3:47 pm, "Snowbird" wrote:
I guess Mxmanic uses the FAA AIM as his main source in his "research".
Section 7.3.1 is about wake turbulence. A couple of interesting quotes from
that section, that Mx has not seen fit to share with us:

Heh. Many of his responders seem to have done even less "research".
Instead they substitute insults for information, hoping they'll look
smarter than him. They don't seem to realize that it just makes them
look dumber.

c) "The greatest vortex strength occurs when the generating aircraft is
HEAVY, CLEAN, and SLOW."

In contrast, a light aircraft doing a 360 is usually LIGHT, CLEAN and
(relatively speaking) FAST. Very different conditions, especially regarding
two major sources of wake: the AoA of the wing (which affects the tip
vortices) and the power setting (which affects the propwash strength).

Of course, LIGHT does not mean "light aircraft". Some 152s are
vortex HEAVY in the case of big instructors and students ;-)

For vortex strength, the term HEAVY is used in a relative manner. A
small plane that is lightly loaded will create less vortex strength
than the same small plane that is heavily loaded, because the actual
AOA is larger in the latter case.

The actual AOA is the key for (HEAVY) more load, (CLEAN) less flaps
and (SLOW) less speed. It's greater in all those cases.

Auugh. Four year old calling me. Later..
Best, Kev

Rip,

As everyone else but
Anthony knows, steep turns do indeed TEND to be descending turns, unless
specific action is taken to remain at a constant altitude.


Can't follow you there. That's as useful a statement as "airplanes tend to
be stationary objects..."

--
Thomas Borchert (EDDH)

Thomas Borchert writes:

Can't follow you there. That's as useful a statement as "airplanes tend to
be stationary objects..."

In a turn, a portion of the lift produced by the wings must be used to
accelerate the aircraft laterally, and this portion of the lift is no longer
available to maintain the aircraft's altitude. Thus, without any adjustment
of pitch or power to compensate, any turn will result in a loss of altitude.

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Mxsmanic wrote:
JB writes:


You are such an idiot! Probably every GA pilot-in-training with a
C152/172 or something similar has experienced hitting their own wake
when performing their first steep turn with an instructor.


Steep turns tend to be descending turns.

Anthony, this is exactly why you antagonize so many
people in the aviation forums.

*Every* pilot (at least in the US) learns steep turns
in the context of the FAA's practical test standard.
That's a steep turn while holding your altitude +/- 100
feet. In reality, we train to hold the altitude constant
during the turn, so that involves modulated back pressure
on the stick and probably more throttle.

http://www.faa.gov/education_researc...S-8081-14A.pdf

PDF page 48.

Your original response would possibly meaningful on
a simulator forum. On a flying forum, you should
understand your lack of background and context before
posting presumptuous statements.

Jim Stewart writes:

*Every* pilot (at least in the US) learns steep turns
in the context of the FAA's practical test standard.
That's a steep turn while holding your altitude +/- 100
feet.

If you meet your wake, you're descending.

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