Vortex Generator Technicalities, By Peter Garrison

wrote:
The Point of the Article is to understand their use.

Peter makes these statements.
"Vortex generators seem like a discordant
element in aerodynamic design" and "violating the rule that smoothness
is
desirable above all things"

Think, very hard about his statements. I have agreed with the first one
for many years.
Vortex Generators are a correction, of a poor airfoil use, at a given
angle and air pressure


ISTR hearing about someone with a Cherokee who used them to
reduce drag on his fuselage.

--

FF

cavelamb wrote:
some mindless drivel again...



http://www.home.earthlink.net/~tp-1/a4412-a.jpg
http://www.home.earthlink.net/~tp-1/a4412-b.jpg

Should be working well now.

(-a) shows section drag and moment plotted against section C Lift.

Note that teh moment curve is pretty flat, and has a negative value.
(pitches nose down?)

At the bottom of the page is the Legend.
Curves for 3, 6 and 9 mill Reynolds Number, and with split flaps.

(-b) is a handier form.
Section CL and Pitch moment are shown plotted agains Angle of Attack.

Note that the Flaps Down curve is Narrower and shihted to the left.
Interpret that aa a narrower AoA range, and at a lower AoA values,
but with higher CL/ (delta)Angle ?

(-c) if I had it handy, would be similar to -b, but details the section
Coefficient of Drag.

wrote:

wrote:

The Point of the Article is to understand their use.

Peter makes these statements.
"Vortex generators seem like a discordant
element in aerodynamic design" and "violating the rule that smoothness
is
desirable above all things"

Think, very hard about his statements. I have agreed with the first one
for many years.
Vortex Generators are a correction, of a poor airfoil use, at a given
angle and air pressure



ISTR hearing about someone with a Cherokee who used them to
reduce drag on his fuselage.


Three kinds of air flow.
Laminar, Turbulent and Separated.

Induced drag, that from generating lift, is hard to reduce significantly.

But dragging a bunch of small wakes is all parasitic drag.

Reattaching a separated wake should, in general, reduce patasitic drag,
and make the old sled that much faster...

cavelamb wrote:
cavelamb wrote:
some mindless drivel again...



http://www.home.earthlink.net/~tp-1/a4412-a.jpg
http://www.home.earthlink.net/~tp-1/a4412-b.jpg

Should be working well now.

It would work a damn sight better if the images had been created
as gifs or tifs. Then it might be possible to read the labels and
scales.

Jpeg is the worst possible common image format for line drawings
or text. Well, maybe second worst after mpeg...

Don't mean to single you out for this particular rant. Illegible
graphical information is legion on the web. It would seem that
most people posting such haven' t taken into consideration
that people seeing it may actually need to be able to read
the text.

--

FF

cavelamb wrote:

...

Note that the Flaps Down curve is Narrower and shihted to the left.
...

Remind me to stand to the RIGHT of that plane when flaps
are down ...

--

FF

"cavelamb" wrote in message
nk.net...
Morgans wrote:
"TJ400" wrote in message
oups.com...

AOA, L/D, Clmax and LE slats are what exactly?.... Been out of the
whole sport aviation for some time and just trying to grasp it all over
snip


I've also noticed that many common airfoils actually have a
_lower_ stall AoA with flaps down!


Like in a 172, notice the way the nose comes down with flaps?


When you lower the flaps, you change the angle of incidence. With a fuselage
that remained level during the change, you would have increased the AoA.

Al

wrote:
cavelamb wrote:

cavelamb wrote:
some mindless drivel again...



http://www.home.earthlink.net/~tp-1/a4412-a.jpg
http://www.home.earthlink.net/~tp-1/a4412-b.jpg

Should be working well now.


It would work a damn sight better if the images had been created
as gifs or tifs. Then it might be possible to read the labels and
scales.

Jpeg is the worst possible common image format for line drawings
or text. Well, maybe second worst after mpeg...

Don't mean to single you out for this particular rant. Illegible
graphical information is legion on the web. It would seem that
most people posting such haven' t taken into consideration
that people seeing it may actually need to be able to read
the text.


Point taken, of course.
Totally agree, Fred.
But that's all I got right now...

And I wasn't really trying to pull numbers off of them,
just the shapes of the curves - and how they shift.

Another thing about working with jpg...
Jpg LOSES picture information EACH TIME you SAVE it.

In house, I usually use PCX format.

but these were all I could find...


Rx

wrote:

cavelamb wrote:

...

Note that the Flaps Down curve is Narrower and shihted to the left.
...


Remind me to stand to the RIGHT of that plane when flaps
are down ...


The meds can sometimes be fun...

Al wrote:

"cavelamb" wrote in message
nk.net...

Morgans wrote:

"TJ400" wrote in message
egroups.com...


AOA, L/D, Clmax and LE slats are what exactly?.... Been out of the
whole sport aviation for some time and just trying to grasp it all over

snip


I've also noticed that many common airfoils actually have a
_lower_ stall AoA with flaps down!


Like in a 172, notice the way the nose comes down with flaps?



When you lower the flaps, you change the angle of incidence. With a fuselage
that remained level during the change, you would have increased the AoA.

Al



True, but we are more concerned with maintaining a given airspeed rather than
a level floor...

cavelamb wrote:
Al wrote:

"cavelamb" wrote in message
nk.net...

Morgans wrote:

"TJ400" wrote in message
egroups.com...


AOA, L/D, Clmax and LE slats are what exactly?.... Been out of the
whole sport aviation for some time and just trying to grasp it all over

snip


I've also noticed that many common airfoils actually have a
_lower_ stall AoA with flaps down!


Like in a 172, notice the way the nose comes down with flaps?



When you lower the flaps, you change the angle of incidence. With a fuselage
that remained level during the change, you would have increased the AoA.

Al



True, but we are more concerned with maintaining a given airspeed rather than
a level floor...

Some pilots are also concerned about having a good view
of the runway.

--

FF