REFLECTOR:Vortex Generators on XL
KeithHallsten
reflector@tvbf.org
Sat, 6 Dec 2003 14:05:15 -0800
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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. =20
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
=20
----- Original Message -----=20
From: Alex Balic=20
To: reflector@tvbf.org=20
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:=20
Was said"=20
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). =20
What you want=20
to avoid is sticking the flow to the top of the canard more than =
it was=20
designed to since the canard is supposed to stall before the main =
wing.
.... sticking ... more than it was designed to ...=20
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?=20
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.=20
If the canard becomes more stall resistant (better flow adhesion =
due to well=20
placed VG's), you will have a big problem unless the wing has the =
same or=20
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.=20
since there is some leeway built into the design, you=20
hopefully won't have a problem, but really, you should get the =
situation=20
analyzed professionally before venturing out,
That is what I thought I was doing when I consulted with Dr. Price=20
otherwise, stick to VG's on=20
the mains only......... The VG's will not change the center of =
lift=20
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=20
just move the point of flow separation further back, and allow=20
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?=20
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.=20
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.=20
I can't learn much from unsupported generalities. That's why I went =
to Jim Price .... Jim S.=20
=20
-----Original Message-----=20
From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On =
Behalf Of John Dibble=20
Sent: Friday, December 05, 2003 3:50 PM=20
To: reflector@tvbf.org=20
Subject: Re: REFLECTOR:Vortex Generators on XL=20
Jim Sower wrote:=20
>=20
>If one were to install VGs on the wing or canard and not the =
other, it=20
might "mess up"=20
>the "lift ratio". I used the same VGs in the same pattern and =
location on=20
both=20
>surfaces. No reason to believe that would "mess up" anything.=20
>=20
My SRG is aft cg when I fly solo. Could I install vgs on the main =
wing=20
only to reduce the aft cg situation?=20
John=20
_______________________________________________=20
To change your email address, visit=20
http://www.tvbf.org/mailman/listinfo/reflector=20
Visit the gallery! www.tvbf.org/gallery=20
user:pw =3D tvbf:jamaicangoose=20
Check new archives: www.tvbf.org/pipermail=20
Check old archives: =
http://www.tvbf.org/archives/velocity/maillist.html=20
_______________________________________________=20
To change your email address, visit =
http://www.tvbf.org/mailman/listinfo/reflector=20
Visit the gallery! www.tvbf.org/gallery=20
user:pw =3D tvbf:jamaicangoose=20
Check new archives: www.tvbf.org/pipermail=20
Check old archives: =
http://www.tvbf.org/archives/velocity/maillist.html
--=20
Jim Sower=20
Crossville, TN; Chapter 5=20
Long-EZ N83RT, Velocity N4095T=20
=20
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<DIV><FONT face=3DArial size=3D2>Alex,</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>While your explanation of the effect of =
VGs is=20
correct in the broad outlines, they work by forcing the flow to be =
turbulent,=20
not by maintaining laminar flow. That is, they GENERATE =
VORTICIES! =20
As it turns out, a turbulent flow will adhere to the low-pressure side =
of a wing=20
much better, and the flow separation (stall) will be much less abrupt =
than when=20
a laminar flow jumps to turbulent flow in a less-controlled =
manner. =20
</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>I remember some photographs in my old =
fluid=20
mechanics textbook showing two bowling balls impacting water after a =
significant=20
fall. One of them was a smooth ball, and generated a huge impact =
crater in=20
the water. The other ball had sand glued to the front, and =
generated a=20
wake only slightly larger than the diameter of the ball. The rough =
sand=20
had tripped the flow to turbulent on the surface of the ball. This =
illustrated the difference in flow separation from laminar flow vs. =
turbulent=20
flow.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Keith</FONT></DIV>
<DIV><FONT face=3DArial size=3D2> </FONT></DIV>
<BLOCKQUOTE dir=3Dltr=20
style=3D"PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; =
BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV=20
style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black"><B>From:</B>=20
<A title=3Dalex157@direcway.com =
href=3D"mailto:alex157@direcway.com">Alex=20
Balic</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>To:</B> <A =
title=3Dreflector@tvbf.org=20
href=3D"mailto:reflector@tvbf.org">reflector@tvbf.org</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Saturday, December 06, =
2003 10:15=20
AM</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Subject:</B> RE: REFLECTOR:Vortex =
Generators=20
on XL</DIV>
<DIV><BR></DIV>
<DIV><SPAN class=3D159023117-06122003><FONT face=3DArial =
color=3D#0000ff=20
size=3D2>Jim,</FONT></SPAN></DIV>
<DIV><SPAN class=3D159023117-06122003><FONT face=3DArial =
color=3D#0000ff size=3D2>I=20
used the more simple term of "sticking" instead of "delayed separation =
of=20
laminar flow" because I don't want to write a thesis on laminar flow=20
properties on the reflector, and a lot of the readers here may no be =
familiar=20
with some of the the technical terms of fluid dynamics. I =
agree,=20
the decision to install or not to install VGs should be thoroughly =
simulated=20
and tested before installation. It appears that you have done that. =
Just FYI,=20
vortex generators are installed to promote laminar flow, and thereby =
DO=20
<U>generally</U> allow a given airfoil section to operate at a higher =
angle of=20
attack. This is precisely the effect that allows for a lowered stall =
speed,=20
because the wing can fly at a higher angle of attack. I =
personally=20
do not know how much laminar flow the canard is designed to =
"tolerate",=20
(although I would assume that it is published under the airfoil =
number) and=20
that is why I personally would not alter the flow there =
withought a=20
through simulation of the modification. During my undergraduate =
studies=20
of this subject, we tested several laminar flow promoting =
techniques,=20
most notably vortex generating devises, both passive and active. =
Sometimes the=20
flow modifications that resulted from these modifications were =
unexpected,=20
including some premature separation of flow in some airfoils at =
various=20
angles of attack. There are so many variables involved in =
the=20
design of VG's that make their effects extremely difficult to quantify =
in=20
terms of generalities except to say that generally they promote =
laminar flow.=20
For all I know, the Swings just started adding and moving VGs =
around=20
until the aircraft flew the way they wanted, I can not answer that =
question,=20
like you, I am not informed on their testing procedures. I am =
not saying=20
that you did anything wrong by installing VG's to your canard, =
as you=20
probably know, the Starship uses them, but I am certain that the =
airfoil=20
design on that aircraft was computer simulated before any actual =
flight=20
testing, and that you should not assume that they will have =
an=20
identical effect on both the main wing and the canard without such =
testing.=20
Maybe your particular arrangement will greatly enhance the low speed =
handling=20
and lower the stall speed of the Velocity, I hope it does, please keep =
us=20
informed.</FONT></SPAN></DIV>
<DIV><SPAN class=3D159023117-06122003><FONT face=3DArial =
color=3D#0000ff=20
size=3D2>Alex</FONT></SPAN></DIV>
<DIV><SPAN class=3D159023117-06122003></SPAN><FONT face=3DTahoma><FONT =
size=3D2><SPAN class=3D159023117-06122003><FONT face=3DArial=20
color=3D#0000ff></FONT></SPAN></FONT></FONT> </DIV>
<DIV><FONT face=3DTahoma><FONT size=3D2><SPAN=20
class=3D159023117-06122003> </SPAN>-----Original=20
Message-----<BR><B>From:</B> reflector-admin@tvbf.org=20
[mailto:reflector-admin@tvbf.org]<B>On Behalf Of </B>Jim =
Sower<BR><B>Sent:</B>=20
Saturday, December 06, 2003 10:51 AM<BR><B>To:</B>=20
reflector@tvbf.org<BR><B>Subject:</B> Re: REFLECTOR:Vortex Generators =
on=20
XL<BR><BR></DIV></FONT></FONT>
<BLOCKQUOTE dir=3Dltr style=3D"MARGIN-RIGHT: 0px">Alex Balic wrote: =
<BR>Was=20
said"=20
<BLOCKQUOTE TYPE=3D"CITE">You shouldn't assume that, because the =
airfoils=20
are different.</BLOCKQUOTE>The fact that there are nearly twice as =
many VGs=20
on the main wing would tend to ensure "balance" (whatever that =
is). =20
<BLOCKQUOTE TYPE=3D"CITE">What you want <BR>to avoid is sticking the =
flow to=20
the top of the canard more than it was <BR>designed to since the =
canard is=20
supposed to stall before the main wing.</BLOCKQUOTE>.... sticking =
... more=20
than it was designed to ... <BR>What exactly does "sticking" mean =
and how=20
much "sticking", precisely, was the canard designed to =
tolerate? Is=20
there a report somewhere in the Velocity archives that you can quote =
or I=20
can read? <BR>The canard airfoil does have more chamber than the =
main wing,=20
precisely to make it stall at a lower AoA than the main wing. =
I don't=20
believe VGs alter that.=20
<BLOCKQUOTE TYPE=3D"CITE">If the canard becomes more stall resistant =
(better=20
flow adhesion due to well <BR>placed VG's), you will have a big =
problem=20
unless the wing has the same or <BR>better =
improvement,</BLOCKQUOTE>Which is=20
why I used the same placement of VGs on the canard and wing - =
neither is=20
more "well placed" than the other.=20
<BLOCKQUOTE TYPE=3D"CITE">since there is some leeway built into the =
design,=20
you <BR>hopefully won't have a problem, but really, you should get =
the=20
situation <BR>analyzed professionally before venturing =
out,</BLOCKQUOTE>That=20
is what I thought I was doing when I consulted with Dr. Price=20
<BLOCKQUOTE TYPE=3D"CITE">otherwise, stick to VG's on <BR>the mains=20
only......... The VG's will not change the center of lift=20
<BR>appreciably,</BLOCKQUOTE>I disagree. It may not move the =
CL of the=20
wing, but by increasing the lift of the wing, will move the CL of =
the=20
airplane aft, having the effect of a forward CG and defeating the =
purpose of=20
installing the VGs=20
<BLOCKQUOTE TYPE=3D"CITE">just move the point of flow separation =
further=20
back, and allow <BR>the airfoil to fly at a higher angle of=20
attack.</BLOCKQUOTE>If you move the point of separation further =
back,=20
doesn't that <B>cause</B> the CP to move back? <BR>What I would =
appreciate=20
hearing is less unsupported generalities and vague terms like =
"sticking" and=20
"balance" and all and more specific engineering and hard science.=20
<P>A lot of folks have been alluding (rather vaguely) to "factory =
approved"=20
placement of VGs. I would really appreciate someone comparing =
the way=20
I did mine and how, precisely it differs from how "the factory" did=20
theirs. We could then have a rational discussion as to what =
effect my=20
departures from the "gospel according to Duane" might have on the =
flight=20
characteristics of my airplane. I am at quite a disadvantage =
here in=20
that I have no specifics at all on how the factory does this, but =
you folks=20
have all the details on my approach. I can't make specific=20
comparisons, and until now, for some reason you folks won't. I =
feel=20
that further discussion, if it is to be rational and useful, must =
involve=20
specifics. Absent details and some engineering principles =
applied to=20
them, it's all bullshit and black magic.=20
<P>I can't learn much from unsupported generalities. That's =
why I went=20
to Jim Price .... Jim S.=20
<BLOCKQUOTE TYPE=3D"CITE"> =20
<P>-----Original Message----- <BR>From: reflector-admin@tvbf.org =
[<A=20
=
href=3D"mailto:reflector-admin@tvbf.org">mailto:reflector-admin@tvbf.org<=
/A>]On=20
<BR>Behalf Of John Dibble <BR>Sent: Friday, December 05, 2003 3:50 =
PM=20
<BR>To: reflector@tvbf.org <BR>Subject: Re: REFLECTOR:Vortex =
Generators on=20
XL=20
<P>Jim Sower wrote:=20
<P>> <BR>>If one were to install VGs on the wing or canard =
and not=20
the other, it <BR>might "mess up" <BR>>the "lift ratio". =
I used=20
the same VGs in the same pattern and location on <BR>both=20
<BR>>surfaces. No reason to believe that would "mess up"=20
anything. <BR>> <BR>My SRG is aft cg when I fly solo. =
Could I=20
install vgs on the main wing <BR>only to reduce the aft cg =
situation?=20
<P>John=20
<P>_______________________________________________ <BR>To change =
your=20
email address, visit <BR><A=20
=
href=3D"http://www.tvbf.org/mailman/listinfo/reflector">http://www.tvbf.o=
rg/mailman/listinfo/reflector</A>=20
<P>Visit the gallery! www.tvbf.org/gallery <BR>user:pw =3D=20
tvbf:jamaicangoose <BR>Check new archives: www.tvbf.org/pipermail=20
<BR>Check old archives: <A=20
=
href=3D"http://www.tvbf.org/archives/velocity/maillist.html">http://www.t=
vbf.org/archives/velocity/maillist.html</A>=20
<P>_______________________________________________ <BR>To change =
your=20
email address, visit <A=20
=
href=3D"http://www.tvbf.org/mailman/listinfo/reflector">http://www.tvbf.o=
rg/mailman/listinfo/reflector</A>=20
<P>Visit the gallery! www.tvbf.org/gallery <BR>user:pw =3D=20
tvbf:jamaicangoose <BR>Check new archives: www.tvbf.org/pipermail=20
<BR>Check old archives: <A=20
=
href=3D"http://www.tvbf.org/archives/velocity/maillist.html">http://www.t=
vbf.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></BODY></HTML>
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