Question to Mxmanic

On Apr 16, 11:15 am, "Maxwell" wrote:
"Kev" wrote in message
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).

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.

My searches on the web show the opposite... or at least that there's
studies both at altitude and near the ground. For examples:

http://www.nasa.gov/centers/dryden/a...4-14-DFRC.html

"NASA research has shown that as large aircraft move through the air,
trailing vortices tend to remain spaced less than a wingspan apart
while sinking at a rate of several hundred feet per minute. Over time,
the sink rate will slow and their strength will taper off. Research
has shown, however, that vortices can also rise during conditions of
ambient thermal lifting."

"Aircraft Accident Reconstruction and Litigation" By M. P. Papadakis,
Barnes Warnock MacCormick, states that vortices descend 5-10 fps
(30-600 fpm).

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.

Yes, we were all taught that part.

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.

Here is information taken at altitude: Vortices are 14-36 feet in
diameter, approx the wingspan apart, and sink 160 - 1100 fpm.

http://www.airpower.maxwell.af.mil/a...ug/carten.html

I just think it's an interesting question, because we've all had it
happen, but no one here can give a definitive reason for it (beyond
"yo stupid of course it does" which is pretty lame even for the usual
Mx bashers ;-)

I think I've convinced myself that since I don't always hit my wake on
a perfect steep turn, and because it mostly seems to happen over areas
of rising air, that the explanation is simple. Unless someone can
post better research.

Thanks, Kev

"Kev" wrote in message
oups.com...

I think I've convinced myself that since I don't always hit my wake on
a perfect steep turn, and because it mostly seems to happen over areas
of rising air, that the explanation is simple. Unless someone can
post better research.


Great, now what do you intend to do with the imformation?

In rec.aviation.piloting Kev wrote:
On Apr 16, 11:15 am, "Maxwell" wrote:
"Kev" wrote in message
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).

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.

My searches on the web show the opposite... or at least that there's
studies both at altitude and near the ground. For examples:

http://www.nasa.gov/centers/dryden/a...4-14-DFRC.html




|||||
"NASA research has shown that as large aircraft move through the air,
|||||
trailing vortices tend to remain spaced less than a wingspan apart
while sinking at a rate of several hundred feet per minute. Over time,
the sink rate will slow and their strength will taper off. Research
has shown, however, that vortices can also rise during conditions of
ambient thermal lifting."

"Aircraft Accident Reconstruction and Litigation" By M. P. Papadakis,
Barnes Warnock MacCormick, states that vortices descend 5-10 fps
(30-600 fpm).

Where's the data for C172 sized aircraft?

People are assuming numbers for a specific type of aircraft are
applicable to very different aircraft.

I see no justification for this.

snip rest

--
Jim Pennino

Remove .spam.sux to reply.

writes:

Where's the data for C172 sized aircraft?

Small aircraft work the same way, since they have wings that work the same
way.

People are assuming numbers for a specific type of aircraft are
applicable to very different aircraft.

These facts are applicable to all fixed-wing aircraft.

I see no justification for this.

You're assuming a difference where no evidence for a difference exists.

--
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What is the vertical component of the vector if you have the wake traveling
outward perpindicular to the wings? It will be 150' from the original path,
but at an angle to vertical.

mike

"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

Jose writes:

How tall is the wake?

The downwash is at least equal in height to the total wingspan of the
aircraft. Downwash is a large mass of air moving slowly. Still, you should
not be hitting your own wake in a 360-degree turn unless you are descending to
catch it. Oddly enough, if you are descending, the wake moves more slowly
(because you are generating less lift).

--
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"Mxsmanic" wrote in message
...
Jose writes:

How tall is the wake?

The downwash is at least equal in height to the total wingspan of the
aircraft. Downwash is a large mass of air moving slowly. Still, you
should
not be hitting your own wake in a 360-degree turn unless you are
descending to
catch it. Oddly enough, if you are descending, the wake moves more slowly
(because you are generating less lift).


Priceless bucko!!!!!

It sounds to me like you are experiencing some serious wake tubulence in the
airspace between your ears.

Kev writes:

On a warm clear day (which is when I've hit my own
wake), I betcha that the wake is being held upward a tiny bit by the
heat from the ground.

Then you must be descending through the rising column of air.

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On Apr 16, 10:45 am, Mxsmanic wrote:
Kev writes:
On a warm clear day (which is when I've hit my own
wake), I betcha that the wake is being held upward a tiny bit by the
heat from the ground.

Then you must be descending through the rising column of air.

--
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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. I know I
did. I routinely show non-flying friends this phenomenon when I take
them flying.

But go ahead...keep arguing with experience that you don't have.

--Jeff

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.

--
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