Question to Mxmanic

On Apr 13, 6:23 pm, Mxsmanic wrote:
Little Endian writes:
In the sim it makes no sense to avoid wake turbulence because you will
never know if you succeeded, its an exercise in futility.

Real life is like that, too. You only know when you fail to avoid wake
turbulence, not when you succeed.

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

OK--I consulted an aerospace engineer at the rand corporation and he
said:
"The vortex does tend to drop, but pretty slowly. Even if it does,
couldn't you be feeling the vortex off the upper (in a left bank,
the
right) wing?"

Tom L. wrote:
On Mon, 16 Apr 2007 23:33:54 +0200, Mxsmanic
wrote:

Rip writes:

I don't know, but I'm going to find out! I can envision an aircraft with
light wing loading, like a Cessna for instance, compressing the air
locally as it creates lift. After passage of the wing, the lift created
downwash would rebound upward, kind of like skipping a stone on the
water.
Virtually no compression occurs at the speeds of a Cessna. Compression is
only an issue at high speeds. At low speeds, air behaves very much like an
imcompressible fluid.

The end result is that the downwash stays at a constant altitude,
or sinks MUCH more slowly than theory would indicate.
The downwash does not stay at a constant altitude. It sinks. It has to,
otherwise the aircraft couldn't stay in the air.

It doesn't have to continue to sink forever. It can stabilize its
position at some point.

To explain the encounter with one's own wake turbulence we need some
quantification for a particular aircraft/bank/speed:
- radii of the vortices
- "sink" rate ("sink" meaning movement away from the flight path, not
necessarily downward)
- final "sink" distance

E.g. if the vertex radius is 15 feet and sink rate 20 fpm, we hit the
wake after a 30 second turn.
If the radius is 15 feet, sink rate 100 fpm, and final distance 10
feet, we still hit it.
And so on.


Hi Tom,

The key may be to understand that while the center of vortex system
moves down, air outside the vortex _has_ to move up. (By imparting
energy to the vortex (and thereby sustaining it) lift is generated). If
you like, the "top" of the vortex can stay at the same level (or even
move up) while the center of the vortex moves down as the vortex grows
with distance behind the wing. At low angles of attack the vortex center
moves slowly down and at high angles it moves down faster (and is more
intense). I'll predict that as you fly in a circle you start to create
yet _another_ vortex with a radius equal to that of the turn. This
vortex is centered on your path of flight and will become closed if you
contine the 360 degree turn. At that point, as I see it, you may
experience the angle of bank wanting to increase -have you ever felt
that? Now add in (1) parasitic drag from the airframe (2) propwash and
(3) tail vortex and you are even more likely to encounter your own
"turbulence".

Comments?

Cheers

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)

On Apr 16, 11:33 pm, Mxsmanic wrote:

Virtually no compression occurs at the speeds of a Cessna. Compression is
only an issue at high speeds. At low speeds, air behaves very much like an
imcompressible fluid.


Air does not behave very much like an imcompressible fluid at low air
speeds. Not even close.
Under some conditions, low air speeds is one of them, air can be
treated like it is an imcompressible fluid.
And that is only to simplify airflow calculations.

-Kees.

"Mxsmanic" wrote...
Tim writes:

Interestingly, MSFS will simulate this very effect in a C172 or a Baron
in a
level 360 degree turn.

Will it? It doesn't simulate wake turbulence generally, why would it
simulate
this?

Yes, it will. Try it - if you're good enough you will see it happen. If
not, you have to practice your 360s.

I wonder why the software would imitate something that cannot happen in
real
life?

So do I.

An interesting dilemma - either MSFS is bogus or Mx is wrong... has hell
frozen over?

BDS

In rec.aviation.piloting wrote:
On Apr 16, 11:33 pm, Mxsmanic wrote:

Virtually no compression occurs at the speeds of a Cessna. Compression is
only an issue at high speeds. At low speeds, air behaves very much like an
imcompressible fluid.


Air does not behave very much like an imcompressible fluid at low air
speeds. Not even close.
Under some conditions, low air speeds is one of them, air can be
treated like it is an imcompressible fluid.
And that is only to simplify airflow calculations.

-Kees.

Quite so.

Mxsmanic has once again has taken a tiny snippet of information that
is only applicable within a narrow set of constraints and arm waved
it into a truism under all conditions.

If air truely behaved like an incompressilble fluid at low air speeds,
it would be difficult, if not impossible, to breathe while jogging.

--
Jim Pennino

Remove .spam.sux to reply.

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.

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

writes:

Air does not behave very much like an imcompressible fluid at low air
speeds. Not even close.

That's not what the engineers say.

Under some conditions, low air speeds is one of them, air can be
treated like it is an imcompressible fluid.

The difference between TAS and EAS is only about 13% even at Mach 1. Since
small aircraft come nowhere near to Mach 1, for all practical purposes air is
incompressible for most calculations.

Obviously air, being a gas, can be compressed, but taking that into account at
low speeds greatly complicates the calculations, and the final result isn't
significantly different.

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

Tim writes:

An interesting dilemma - either MSFS is bogus or Mx is wrong... has hell
frozen over?

Many of the MSFS developers are pilots, for better or for worse.

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

writes:

If air truely behaved like an incompressilble fluid at low air speeds,
it would be difficult, if not impossible, to breathe while jogging.

It's possible to breathe water, which is indeed incompressible for all
practical purposes.

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