REFLECTOR:Vortex Generators on XL

Alex Balic reflector@tvbf.org
Sat, 06 Dec 2003 18:45:08 -0600


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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

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        Check new archives: www.tvbf.org/pipermail
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        _______________________________________________
        To change your email address, visit
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        Visit the gallery!  www.tvbf.org/gallery
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        Check new archives: www.tvbf.org/pipermail
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http://www.tvbf.org/archives/velocity/maillist.html

      --
      Jim Sower
      Crossville, TN; Chapter 5
      Long-EZ N83RT, Velocity N4095T


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<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.&nbsp; The reason that laminar flow is lost, is because skin 
friction slows the airflow&nbsp;within about .01&nbsp;or so&nbsp;the 
surface&nbsp;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.&nbsp;&nbsp;Vortex generators are designed to mix the air that still 
contains energy (which fortunately is&nbsp;close to the&nbsp;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.&nbsp; 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.&nbsp;This extended laminar flow is&nbsp;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>&nbsp;</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.&nbsp; That is, they GENERATE VORTICIES!&nbsp; 
  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.&nbsp; </FONT></DIV>
  <DIV><FONT face=Arial size=2></FONT>&nbsp;</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.&nbsp; One of them was a smooth ball, and generated a huge 
  impact crater in the water.&nbsp; The other ball had sand glued to the front, 
  and generated a wake only slightly larger than the diameter of the ball.&nbsp; 
  The rough sand had tripped the flow to turbulent on the surface of the 
  ball.&nbsp; This illustrated the difference in flow separation from laminar 
  flow vs. turbulent flow.</FONT></DIV>
  <DIV><FONT face=Arial size=2></FONT>&nbsp;</DIV>
  <DIV><FONT face=Arial size=2>Keith</FONT></DIV>
  <DIV><FONT face=Arial size=2>&nbsp;&nbsp;&nbsp;&nbsp;</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&nbsp;some of &nbsp;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&nbsp;wing can fly at a higher angle of 
    attack. &nbsp;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&nbsp; there withought a through simulation of the modification.&nbsp; 
    During my undergraduate studies of this subject, we tested&nbsp;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&nbsp;of flow in some airfoils at various angles of 
    attack.&nbsp;&nbsp;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&nbsp; 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. &nbsp;I am not saying that 
    you did anything wrong by installing VG's to your canard,&nbsp; 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&nbsp;that you should&nbsp;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>&nbsp;</DIV>
    <DIV><FONT face=Tahoma><FONT size=2><SPAN 
    class=159023117-06122003>&nbsp;</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).&nbsp; 
      <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?&nbsp; 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.&nbsp; 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.........&nbsp; The VG's will not change the center of lift 
        <BR>appreciably,</BLOCKQUOTE>I disagree.&nbsp; 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.&nbsp; I would really appreciate someone 
      comparing the way I did mine and how, precisely it differs from how "the 
      factory" did theirs.&nbsp; 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.&nbsp; 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.&nbsp; I 
      can't make specific comparisons, and until now, for some reason you folks 
      won't.&nbsp; I feel that further discussion, if it is to be rational and 
      useful, must involve specifics.&nbsp; 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.&nbsp; That's why I 
      went to Jim Price .... Jim S. 
      <BLOCKQUOTE TYPE="CITE">&nbsp; 
        <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>&gt; <BR>&gt;If one were to install VGs on the wing or canard and not 
        the other, it <BR>might "mess up" <BR>&gt;the "lift ratio".&nbsp; I used 
        the same VGs in the same pattern and location on <BR>both 
        <BR>&gt;surfaces.&nbsp; No reason to believe that would "mess up" 
        anything. <BR>&gt; <BR>My SRG is aft cg when I fly solo.&nbsp; 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!&nbsp; 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!&nbsp; 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>&nbsp; 
</P></BLOCKQUOTE></BLOCKQUOTE></BLOCKQUOTE></BODY></HTML>

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