REFLECTOR:Vortex Generators on XL
Alex Balic
reflector@tvbf.org
Sat, 06 Dec 2003 12:15:04 -0600
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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
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--
Jim Sower
Crossville, TN; Chapter 5
Long-EZ N83RT, Velocity N4095T
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<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></BODY></HTML>
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