Question to Mxmanic

Just spoke to a friend with 26,000 hours. He confirmed that DC-8 and 707
heavies certainly do get a bump as they fly through their own wake
during a 360 degree constant altitude turn. He also said that some
Category D simulators include the effect in their motion repertoire.

Rip


Kev wrote:
On Apr 16, 10:22 am, Jose wrote:
My wake _should_ descend about 150' during that time (300
fpm). I can't imagine a C172 wake being tall enough to stay in my
way...
I can. 150 feet is not tall at all for a wake. Remember, the air
around the wake is also being dragged by the wake vortex.

Hmm. We're going to have to define a wake, methinks. I can't find
anything about body wakes, for example. Do they give much of a
bump? Glider pilots, are you listening?

On the other hand, wingtip vortices are a well-researched topic, and
if a Boeing 727's is only 9' in radius, it would be hard to imagine a
vortex being more than 5 feet in radius for a C172, if that much.
Even if larger, and sinking very slowly, it should still be 50-150'
below the aircraft if the other parameters (altitude, wind) are
static.

Regards, Kev

In rec.aviation.piloting Kev wrote:
On Apr 16, 9:41 am, Jose wrote:
I seem to recall recent magazine (web?) articles where the idea that
you can hit your own wake while actually holding altitude, should be
downplayed nowadays. You _have_ to descend a little bit to do so,

How tall is the wake?

Good point. Still, using the calculator at:

http://www.csgnetwork.com/aircraftturninfocalc.html

It's going to take about 30 seconds to fly a 360 steep turn at
100kts. My wake _should_ descend about 150' during that time (300
fpm). I can't imagine a C172 wake being tall enough to stay in my
way unless something else is ocurring (me descending, or the wake
staying up).

Would love to hear a decent explanation. Kev

Upon what do you base the assumption your wake should decend 150'?

I have never heard of any study of the wake properties of GA aircraft
and the wake of a C172 is very different than the wake of a 747 so
to extrapolate from studies of transport catagory wakes is pointless.

--
Jim Pennino

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writes:

Upon what do you base the assumption your wake should decend 150'?

All wakes descend; they have to, otherwise the aircraft could not stay aloft.
They move at a few knots, which still amounts to some 500 fpm.

I have never heard of any study of the wake properties of GA aircraft
and the wake of a C172 is very different than the wake of a 747 ...

Since you haven't heard of any study of the wake properties of GA aircraft,
you cannot possibly know whether the wake of a C172 is "very different" from
that of a 747 or not. Oops!

In fact, the general principle is the same for all aircraft wakes. They
always move downward gently. You cannot catch them in a turn unless you move
downward, too. If you are in rising air, the wake might remain stationary
relative to the ground, but then your aircraft would be rising, so you'd still
have to descend relative to the surrounding air in order to catch your wake.
And smoothly rising air isn't that common, although it's not that rare.

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"Mxsmanic" wrote in message
...
writes:

Upon what do you base the assumption your wake should decend 150'?

All wakes descend; they have to, otherwise the aircraft could not stay
aloft.
They move at a few knots, which still amounts to some 500 fpm.

I have never heard of any study of the wake properties of GA aircraft
and the wake of a C172 is very different than the wake of a 747 ...

Since you haven't heard of any study of the wake properties of GA
aircraft,
you cannot possibly know whether the wake of a C172 is "very different"
from
that of a 747 or not. Oops!

In fact, the general principle is the same for all aircraft wakes. They
always move downward gently. You cannot catch them in a turn unless you
move
downward, too. If you are in rising air, the wake might remain stationary
relative to the ground, but then your aircraft would be rising, so you'd
still
have to descend relative to the surrounding air in order to catch your
wake.
And smoothly rising air isn't that common, although it's not that rare.


You butt head. You clearly don't even understand the simplist properties of
an aircraft vortex.

In rec.aviation.piloting Mxsmanic wrote:
writes:

Upon what do you base the assumption your wake should decend 150'?

All wakes descend; they have to, otherwise the aircraft could not stay aloft.
They move at a few knots, which still amounts to some 500 fpm.

No, they don't, and no it doesn't.

You have nothing to back up what you say.

I have never heard of any study of the wake properties of GA aircraft
and the wake of a C172 is very different than the wake of a 747 ...

Since you haven't heard of any study of the wake properties of GA aircraft,
you cannot possibly know whether the wake of a C172 is "very different" from
that of a 747 or not. Oops!

If I fly through the wake of a 747 I risk things like suddenly finding
myself inverted or structural failure.

If I fly through the wake of a C172 I feel a slight bump.

Oops!

In fact, the general principle is the same for all aircraft wakes. They
always move downward gently. You cannot catch them in a turn unless you move
downward, too. If you are in rising air, the wake might remain stationary
relative to the ground, but then your aircraft would be rising, so you'd still
have to descend relative to the surrounding air in order to catch your wake.
And smoothly rising air isn't that common, although it's not that rare.

Is this knowledge based upon your many years of playing the Flight
Simulator game?

Just because playing a Microsoft game gives you no basis for understanding
something that many thousands of people have experienced does not mean
that it doesn't exist.

--
Jim Pennino

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writes:

You have nothing to back up what you say.

I have NASA, the FAA, a couple of engineering schools at universities, and
other sources that back up what I say. I'm simply standing on the shoulders
of giants.

Is this knowledge based upon your many years of playing the Flight
Simulator game?

No, it is based upon years of studying aviation.

Flight Simulator allows me to put theory into practice, mainly.

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"Kev" wrote in message
ups.com...
On Apr 16, 9:41 am, Jose wrote:
I seem to recall recent magazine (web?) articles where the idea that
you can hit your own wake while actually holding altitude, should be
downplayed nowadays. You _have_ to descend a little bit to do so,

How tall is the wake?

Good point. Still, using the calculator at:

http://www.csgnetwork.com/aircraftturninfocalc.html

It's going to take about 30 seconds to fly a 360 steep turn at
100kts. My wake _should_ descend about 150' during that time (300
fpm). I can't imagine a C172 wake being tall enough to stay in my
way unless something else is ocurring (me descending, or the wake
staying up).

Would love to hear a decent explanation. Kev


I am certainly no expert on the subject, but I think most of the data on
wake turbulence comes from studies held at or very near the ground.
Certainly not all, because I recall an old FAA film on landing in wake
turbulence using a 182 to fly into the wake at altitude. But IIRC it was
part of an awareness film on wake turbulence on approach, just demonstrated
at altitude for safe demonstration of its actual effects.

Based on the numbers I recall, they did indeed teach that the wake from a
landing heavy would NORMALLY travel both down and away from the aircraft a 5
kts or so. But they were also quick to mention that a simple 5 kt or so
crosswind componet could leave the vortex in the middle of the runway for
quite some time.

The problem with trying to use this information at altitude is that you
don't have the ground to help stablize the vertical movement of the vortex.
And every pilot knows the air at altitude is very seldom static, especailly
in warm weather. As someone else mentioned, the vortex that started as a
very small column at the wing tip, can grow very large by the time you
complete a 360 turn at even 60 degrees of bank.

The point is, you are dealing with far to many variables to expect absolute
answers your question or even your own in flight results. Wake turbulence is
really only a problem at altitude if you don't avoid the flight path of
heaver aircraft, and understanding it's presence on take off and landing,
because it is much easier to intercept their flight path around runways.

Maxwell writes:

As someone else mentioned, the vortex that started as a
very small column at the wing tip, can grow very large by the time you
complete a 360 turn at even 60 degrees of bank.

And it will be so weak that you won't feel it even if you run into it, which
you won't do unless you descend.

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"Mxsmanic" wrote in message
...
Maxwell writes:

As someone else mentioned, the vortex that started as a
very small column at the wing tip, can grow very large by the time you
complete a 360 turn at even 60 degrees of bank.

And it will be so weak that you won't feel it even if you run into it,
which
you won't do unless you descend.


Thank you.

I just love it when you prove your ignorance and inexperience in a single
statement.

The really is thoughtful. Save the band width.

Wrong.

mike

"Mxsmanic" wrote in message
...

And it will be so weak that you won't feel it even if you run into it,
which
you won't do unless you descend.

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