REFLECTOR:Vortex Generators on XL
Alex Balic
reflector@tvbf.org
Sat, 06 Dec 2003 18:45:08 -0600
This is a multi-part message in MIME format.
--Boundary_(ID_HYtk9MF6OnZoWbO0h6FdEw)
Content-type: text/plain; charset=iso-8859-1
Content-transfer-encoding: 7BIT
Keith,
You are correct about the way that VG's work for the most part, and I was
hoping not to start a really big discussion about this, but I suppose that
is the intent of this news group. The reason that laminar flow is lost, is
because skin friction slows the airflow within about .01 or so the surface
the surface of the wing. This flow, lacking kinetic energy (relative to the
surface of the wing) is drawn into the negative pressure area above the
wing, separates from the surface, and becomes turbulent. Vortex generators
are designed to mix the air that still contains energy (which fortunately is
close to the wing surface) with the low energy air at the wing surface, and
thereby maintaining laminar flow further back into the negative pressure
area than would be possible without this mixing. If you look at a wind
tunnel test you will see the vortices moving wildly back across the wing,
but upon close inspection, there is an energized layer of laminar flow
against the skin. This extended laminar flow is what the vortices make
possible, and what keeps the wing flying at a higher angle of attack.
-----Original Message-----
From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On Behalf
Of KeithHallsten
Sent: Saturday, December 06, 2003 4:05 PM
To: reflector@tvbf.org
Subject: Re: REFLECTOR:Vortex Generators on XL
Alex,
While your explanation of the effect of VGs is correct in the broad
outlines, they work by forcing the flow to be turbulent, not by maintaining
laminar flow. That is, they GENERATE VORTICIES! As it turns out, a
turbulent flow will adhere to the low-pressure side of a wing much better,
and the flow separation (stall) will be much less abrupt than when a laminar
flow jumps to turbulent flow in a less-controlled manner.
I remember some photographs in my old fluid mechanics textbook showing two
bowling balls impacting water after a significant fall. One of them was a
smooth ball, and generated a huge impact crater in the water. The other
ball had sand glued to the front, and generated a wake only slightly larger
than the diameter of the ball. The rough sand had tripped the flow to
turbulent on the surface of the ball. This illustrated the difference in
flow separation from laminar flow vs. turbulent flow.
Keith
----- Original Message -----
From: Alex Balic
To: reflector@tvbf.org
Sent: Saturday, December 06, 2003 10:15 AM
Subject: RE: REFLECTOR:Vortex Generators on XL
Jim,
I used the more simple term of "sticking" instead of "delayed separation
of laminar flow" because I don't want to write a thesis on laminar flow
properties on the reflector, and a lot of the readers here may no be
familiar with some of the the technical terms of fluid dynamics. I agree,
the decision to install or not to install VGs should be thoroughly simulated
and tested before installation. It appears that you have done that. Just
FYI, vortex generators are installed to promote laminar flow, and thereby DO
generally allow a given airfoil section to operate at a higher angle of
attack. This is precisely the effect that allows for a lowered stall speed,
because the wing can fly at a higher angle of attack. I personally do not
know how much laminar flow the canard is designed to "tolerate", (although I
would assume that it is published under the airfoil number) and that is why
I personally would not alter the flow there withought a through simulation
of the modification. During my undergraduate studies of this subject, we
tested several laminar flow promoting techniques, most notably vortex
generating devises, both passive and active. Sometimes the flow
modifications that resulted from these modifications were unexpected,
including some premature separation of flow in some airfoils at various
angles of attack. There are so many variables involved in the design of
VG's that make their effects extremely difficult to quantify in terms of
generalities except to say that generally they promote laminar flow. For all
I know, the Swings just started adding and moving VGs around until the
aircraft flew the way they wanted, I can not answer that question, like you,
I am not informed on their testing procedures. I am not saying that you did
anything wrong by installing VG's to your canard, as you probably know, the
Starship uses them, but I am certain that the airfoil design on that
aircraft was computer simulated before any actual flight testing, and that
you should not assume that they will have an identical effect on both the
main wing and the canard without such testing. Maybe your particular
arrangement will greatly enhance the low speed handling and lower the stall
speed of the Velocity, I hope it does, please keep us informed.
Alex
-----Original Message-----
From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
Behalf Of Jim Sower
Sent: Saturday, December 06, 2003 10:51 AM
To: reflector@tvbf.org
Subject: Re: REFLECTOR:Vortex Generators on XL
Alex Balic wrote:
Was said"
You shouldn't assume that, because the airfoils are different.
The fact that there are nearly twice as many VGs on the main wing
would tend to ensure "balance" (whatever that is).
What you want
to avoid is sticking the flow to the top of the canard more than it
was
designed to since the canard is supposed to stall before the main
wing.
.... sticking ... more than it was designed to ...
What exactly does "sticking" mean and how much "sticking", precisely,
was the canard designed to tolerate? Is there a report somewhere in the
Velocity archives that you can quote or I can read?
The canard airfoil does have more chamber than the main wing,
precisely to make it stall at a lower AoA than the main wing. I don't
believe VGs alter that.
If the canard becomes more stall resistant (better flow adhesion due
to well
placed VG's), you will have a big problem unless the wing has the
same or
better improvement,
Which is why I used the same placement of VGs on the canard and wing -
neither is more "well placed" than the other.
since there is some leeway built into the design, you
hopefully won't have a problem, but really, you should get the
situation
analyzed professionally before venturing out,
That is what I thought I was doing when I consulted with Dr. Price
otherwise, stick to VG's on
the mains only......... The VG's will not change the center of lift
appreciably,
I disagree. It may not move the CL of the wing, but by increasing the
lift of the wing, will move the CL of the airplane aft, having the effect of
a forward CG and defeating the purpose of installing the VGs
just move the point of flow separation further back, and allow
the airfoil to fly at a higher angle of attack.
If you move the point of separation further back, doesn't that cause
the CP to move back?
What I would appreciate hearing is less unsupported generalities and
vague terms like "sticking" and "balance" and all and more specific
engineering and hard science.
A lot of folks have been alluding (rather vaguely) to "factory
approved" placement of VGs. I would really appreciate someone comparing the
way I did mine and how, precisely it differs from how "the factory" did
theirs. We could then have a rational discussion as to what effect my
departures from the "gospel according to Duane" might have on the flight
characteristics of my airplane. I am at quite a disadvantage here in that I
have no specifics at all on how the factory does this, but you folks have
all the details on my approach. I can't make specific comparisons, and
until now, for some reason you folks won't. I feel that further discussion,
if it is to be rational and useful, must involve specifics. Absent details
and some engineering principles applied to them, it's all bullshit and black
magic.
I can't learn much from unsupported generalities. That's why I went
to Jim Price .... Jim S.
-----Original Message-----
From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
Behalf Of John Dibble
Sent: Friday, December 05, 2003 3:50 PM
To: reflector@tvbf.org
Subject: Re: REFLECTOR:Vortex Generators on XL
Jim Sower wrote:
>
>If one were to install VGs on the wing or canard and not the other,
it
might "mess up"
>the "lift ratio". I used the same VGs in the same pattern and
location on
both
>surfaces. No reason to believe that would "mess up" anything.
>
My SRG is aft cg when I fly solo. Could I install vgs on the main
wing
only to reduce the aft cg situation?
John
_______________________________________________
To change your email address, visit
http://www.tvbf.org/mailman/listinfo/reflector
Visit the gallery! www.tvbf.org/gallery
user:pw = tvbf:jamaicangoose
Check new archives: www.tvbf.org/pipermail
Check old archives:
http://www.tvbf.org/archives/velocity/maillist.html
_______________________________________________
To change your email address, visit
http://www.tvbf.org/mailman/listinfo/reflector
Visit the gallery! www.tvbf.org/gallery
user:pw = tvbf:jamaicangoose
Check new archives: www.tvbf.org/pipermail
Check old archives:
http://www.tvbf.org/archives/velocity/maillist.html
--
Jim Sower
Crossville, TN; Chapter 5
Long-EZ N83RT, Velocity N4095T
--Boundary_(ID_HYtk9MF6OnZoWbO0h6FdEw)
Content-type: text/html; charset=iso-8859-1
Content-transfer-encoding: 7BIT
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=Content-Type content="text/html; charset=iso-8859-1">
<META content="MSHTML 6.00.2800.1264" name=GENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=#ffffff>
<DIV><SPAN class=243531900-07122003><FONT face=Arial color=#0000ff size=2>Keith,
</FONT></SPAN></DIV>
<DIV><SPAN class=243531900-07122003><FONT face=Arial color=#0000ff size=2>You
are correct about the way that VG's work for the most part, and I was hoping not
to start a really big discussion about this, but I suppose that is the intent of
this news group. The reason that laminar flow is lost, is because skin
friction slows the airflow within about .01 or so the
surface the surface of the wing. This flow, lacking kinetic energy
(relative to the surface of the wing) is drawn into the negative pressure area
above the wing, separates from the surface, and becomes
turbulent. Vortex generators are designed to mix the air that still
contains energy (which fortunately is close to the wing
surface)</FONT></SPAN><SPAN class=243531900-07122003><FONT face=Arial
color=#0000ff size=2> with the low energy air at the wing surface, and thereby
maintaining laminar flow further back into the negative pressure area than would
be possible without this mixing. If you look at a wind tunnel test you
will see the vortices moving wildly back across the wing, but upon close
inspection, there is an energized layer of laminar flow against the
skin. This extended laminar flow is what the vortices make possible,
and what keeps the wing flying at a higher angle of attack.</FONT></SPAN></DIV>
<BLOCKQUOTE dir=ltr style="MARGIN-RIGHT: 0px">
<DIV class=OutlookMessageHeader dir=ltr align=left><FONT face=Tahoma
size=2>-----Original Message-----<BR><B>From:</B> reflector-admin@tvbf.org
[mailto:reflector-admin@tvbf.org]<B>On Behalf Of
</B>KeithHallsten<BR><B>Sent:</B> Saturday, December 06, 2003 4:05
PM<BR><B>To:</B> reflector@tvbf.org<BR><B>Subject:</B> Re: REFLECTOR:Vortex
Generators on XL<BR><BR></FONT></DIV>
<DIV><FONT face=Arial size=2>Alex,</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>While your explanation of the effect of VGs is
correct in the broad outlines, they work by forcing the flow to be turbulent,
not by maintaining laminar flow. That is, they GENERATE VORTICIES!
As it turns out, a turbulent flow will adhere to the low-pressure side of a
wing much better, and the flow separation (stall) will be much less abrupt
than when a laminar flow jumps to turbulent flow in a less-controlled
manner. </FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I remember some photographs in my old fluid
mechanics textbook showing two bowling balls impacting water after a
significant fall. One of them was a smooth ball, and generated a huge
impact crater in the water. The other ball had sand glued to the front,
and generated a wake only slightly larger than the diameter of the ball.
The rough sand had tripped the flow to turbulent on the surface of the
ball. This illustrated the difference in flow separation from laminar
flow vs. turbulent flow.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Keith</FONT></DIV>
<DIV><FONT face=Arial size=2> </FONT></DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=alex157@direcway.com href="mailto:alex157@direcway.com">Alex
Balic</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=reflector@tvbf.org
href="mailto:reflector@tvbf.org">reflector@tvbf.org</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Saturday, December 06, 2003 10:15
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> RE: REFLECTOR:Vortex
Generators on XL</DIV>
<DIV><BR></DIV>
<DIV><SPAN class=159023117-06122003><FONT face=Arial color=#0000ff
size=2>Jim,</FONT></SPAN></DIV>
<DIV><SPAN class=159023117-06122003><FONT face=Arial color=#0000ff size=2>I
used the more simple term of "sticking" instead of "delayed separation of
laminar flow" because I don't want to write a thesis on laminar flow
properties on the reflector, and a lot of the readers here may no be
familiar with some of the the technical terms of fluid dynamics.
I agree, the decision to install or not to install VGs should be thoroughly
simulated and tested before installation. It appears that you have done
that. Just FYI, vortex generators are installed to promote laminar flow, and
thereby DO <U>generally</U> allow a given airfoil section to operate at a
higher angle of attack. This is precisely the effect that allows for a
lowered stall speed, because the wing can fly at a higher angle of
attack. I personally do not know how much laminar flow the canard is
designed to "tolerate", (although I would assume that it is published under
the airfoil number) and that is why I personally would not alter the
flow there withought a through simulation of the modification.
During my undergraduate studies of this subject, we tested several
laminar flow promoting techniques, most notably vortex generating devises,
both passive and active. Sometimes the flow modifications that resulted from
these modifications were unexpected, including some premature
separation of flow in some airfoils at various angles of
attack. There are so many variables involved in the design of
VG's that make their effects extremely difficult to quantify in terms of
generalities except to say that generally they promote laminar flow. For all
I know, the Swings just started adding and moving VGs around until the
aircraft flew the way they wanted, I can not answer that question, like you,
I am not informed on their testing procedures. I am not saying that
you did anything wrong by installing VG's to your canard, as you
probably know, the Starship uses them, but I am certain that the airfoil
design on that aircraft was computer simulated before any actual flight
testing, and that you should not assume that they will have an
identical effect on both the main wing and the canard without such testing.
Maybe your particular arrangement will greatly enhance the low speed
handling and lower the stall speed of the Velocity, I hope it does, please
keep us informed.</FONT></SPAN></DIV>
<DIV><SPAN class=159023117-06122003><FONT face=Arial color=#0000ff
size=2>Alex</FONT></SPAN></DIV>
<DIV><SPAN class=159023117-06122003></SPAN><FONT face=Tahoma><FONT
size=2><SPAN class=159023117-06122003><FONT face=Arial
color=#0000ff></FONT></SPAN></FONT></FONT> </DIV>
<DIV><FONT face=Tahoma><FONT size=2><SPAN
class=159023117-06122003> </SPAN>-----Original
Message-----<BR><B>From:</B> reflector-admin@tvbf.org
[mailto:reflector-admin@tvbf.org]<B>On Behalf Of </B>Jim
Sower<BR><B>Sent:</B> Saturday, December 06, 2003 10:51 AM<BR><B>To:</B>
reflector@tvbf.org<BR><B>Subject:</B> Re: REFLECTOR:Vortex Generators on
XL<BR><BR></DIV></FONT></FONT>
<BLOCKQUOTE dir=ltr style="MARGIN-RIGHT: 0px">Alex Balic wrote: <BR>Was
said"
<BLOCKQUOTE TYPE="CITE">You shouldn't assume that, because the airfoils
are different.</BLOCKQUOTE>The fact that there are nearly twice as many
VGs on the main wing would tend to ensure "balance" (whatever that
is).
<BLOCKQUOTE TYPE="CITE">What you want <BR>to avoid is sticking the flow
to the top of the canard more than it was <BR>designed to since the
canard is supposed to stall before the main wing.</BLOCKQUOTE>....
sticking ... more than it was designed to ... <BR>What exactly does
"sticking" mean and how much "sticking", precisely, was the canard
designed to tolerate? Is there a report somewhere in the Velocity
archives that you can quote or I can read? <BR>The canard airfoil does
have more chamber than the main wing, precisely to make it stall at a
lower AoA than the main wing. I don't believe VGs alter that.
<BLOCKQUOTE TYPE="CITE">If the canard becomes more stall resistant
(better flow adhesion due to well <BR>placed VG's), you will have a big
problem unless the wing has the same or <BR>better
improvement,</BLOCKQUOTE>Which is why I used the same placement of VGs on
the canard and wing - neither is more "well placed" than the other.
<BLOCKQUOTE TYPE="CITE">since there is some leeway built into the
design, you <BR>hopefully won't have a problem, but really, you should
get the situation <BR>analyzed professionally before venturing
out,</BLOCKQUOTE>That is what I thought I was doing when I consulted with
Dr. Price
<BLOCKQUOTE TYPE="CITE">otherwise, stick to VG's on <BR>the mains
only......... The VG's will not change the center of lift
<BR>appreciably,</BLOCKQUOTE>I disagree. It may not move the CL of
the wing, but by increasing the lift of the wing, will move the CL of the
airplane aft, having the effect of a forward CG and defeating the purpose
of installing the VGs
<BLOCKQUOTE TYPE="CITE">just move the point of flow separation further
back, and allow <BR>the airfoil to fly at a higher angle of
attack.</BLOCKQUOTE>If you move the point of separation further back,
doesn't that <B>cause</B> the CP to move back? <BR>What I would appreciate
hearing is less unsupported generalities and vague terms like "sticking"
and "balance" and all and more specific engineering and hard science.
<P>A lot of folks have been alluding (rather vaguely) to "factory
approved" placement of VGs. I would really appreciate someone
comparing the way I did mine and how, precisely it differs from how "the
factory" did theirs. We could then have a rational discussion as to
what effect my departures from the "gospel according to Duane" might have
on the flight characteristics of my airplane. I am at quite a
disadvantage here in that I have no specifics at all on how the factory
does this, but you folks have all the details on my approach. I
can't make specific comparisons, and until now, for some reason you folks
won't. I feel that further discussion, if it is to be rational and
useful, must involve specifics. Absent details and some engineering
principles applied to them, it's all bullshit and black magic.
<P>I can't learn much from unsupported generalities. That's why I
went to Jim Price .... Jim S.
<BLOCKQUOTE TYPE="CITE">
<P>-----Original Message----- <BR>From: reflector-admin@tvbf.org [<A
href="mailto:reflector-admin@tvbf.org">mailto:reflector-admin@tvbf.org</A>]On
<BR>Behalf Of John Dibble <BR>Sent: Friday, December 05, 2003 3:50 PM
<BR>To: reflector@tvbf.org <BR>Subject: Re: REFLECTOR:Vortex Generators
on XL
<P>Jim Sower wrote:
<P>> <BR>>If one were to install VGs on the wing or canard and not
the other, it <BR>might "mess up" <BR>>the "lift ratio". I used
the same VGs in the same pattern and location on <BR>both
<BR>>surfaces. No reason to believe that would "mess up"
anything. <BR>> <BR>My SRG is aft cg when I fly solo. Could I
install vgs on the main wing <BR>only to reduce the aft cg situation?
<P>John
<P>_______________________________________________ <BR>To change your
email address, visit <BR><A
href="http://www.tvbf.org/mailman/listinfo/reflector">http://www.tvbf.org/mailman/listinfo/reflector</A>
<P>Visit the gallery! www.tvbf.org/gallery <BR>user:pw =
tvbf:jamaicangoose <BR>Check new archives: www.tvbf.org/pipermail
<BR>Check old archives: <A
href="http://www.tvbf.org/archives/velocity/maillist.html">http://www.tvbf.org/archives/velocity/maillist.html</A>
<P>_______________________________________________ <BR>To change your
email address, visit <A
href="http://www.tvbf.org/mailman/listinfo/reflector">http://www.tvbf.org/mailman/listinfo/reflector</A>
<P>Visit the gallery! www.tvbf.org/gallery <BR>user:pw =
tvbf:jamaicangoose <BR>Check new archives: www.tvbf.org/pipermail
<BR>Check old archives: <A
href="http://www.tvbf.org/archives/velocity/maillist.html">http://www.tvbf.org/archives/velocity/maillist.html</A></P></BLOCKQUOTE>
<P>-- <BR>Jim Sower <BR>Crossville, TN; Chapter 5 <BR>Long-EZ N83RT,
Velocity N4095T <BR>
</P></BLOCKQUOTE></BLOCKQUOTE></BLOCKQUOTE></BODY></HTML>
--Boundary_(ID_HYtk9MF6OnZoWbO0h6FdEw)--