REFLECTOR:Vortex Generators on XL

Jim Sower reflector@tvbf.org
Sat, 06 Dec 2003 13:39:01 -0600


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OK.  This is much better.  We find ourselves, I think, in
violent agreement.
<... 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 ...>
I had thought they were to prolong attached (but not necessarily
"laminar") flow, and delay separation thereby allowing ...  But
for our purposes here that would be nit picking anyway.  Jim P
left me with the belief that turbulent flow that stays attached
to maybe 80% MAC is better than laminar flow that detaches at
40% and that's what VGs do - keep the flow attached longer.
<... I personally do not know how much laminar flow the canard
is designed to "tolerate" ...>
Nor do I.  What I have done does not depart that much from what
I've seen on other Velocitys that as far as I know were done
with the "approved kit" whatever that might be.

<... (although I would assume that it is published under the
airfoil number) and that is why I personally would not alter the
flow  there without a through simulation of the modification
....>
As I said, I believe my excursions from the standard are minor

<... 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 ...>
Agreed (except that I would substitute "attached" for "laminar"

<... 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 ...>
Exactly.  Absent specific information on why they did what they
did (and just as important, why they didn't do what they didn't
do) I have no way to evaluate their result or compare it in any
meaningful way to my own.

<... I am not saying that you did anything wrong by installing
VG's to your canard ... maybe your particular arrangement will
greatly enhance the low speed handling and lower the stall speed
....>
Like I said, I talked rather extensively with the champion.  He
went to a lot of trouble designing and testing the setup he used
on his record setting flight(s) - he had to in order to get the
results he did - and I used what he told me.  I am completely
confident that within the envelope I am operating, his stuff is
quite transferable from his Long-EZ to my Velocity.  Absent
compelling information to the contrary, I am assuming that he
put a lot more quality engineering effort into his scheme than
the Swings or Danny or whoever did to theirs.  This is not meant
as a slam at anybody's research efforts, but just an observation
(and an undocumented one at that).  The fact that my scheme is
as effective as it seems to be validates to me Price's efforts.
I wish I had better "before - during - after" data than I do,
but conditions and situations didn't lend themselves to
extensive testing and documentation of results.  I am very
pleased.  I truly believe I got an honest 10 kts reduction in
landing speed, and at least 5 kts reduction in takeoff/rotation
speed.

<... please keep us informed ...>
You will be the first to know :o)  I'm always looking for more
and better information.  The minute I find a better reason to
change my setup than I had to adopt it in the first place, I
will adopt the new scheme.

Any and all useful input is welcome ... Jim S.



>  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-

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OK.&nbsp; This is much better.&nbsp; We find ourselves, I think, in violent
agreement.
<br><font face="Arial"><font size=-1><font color="#0000FF">&lt;... 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 ...></font><font color="#000000"></font></font></font>
<br>I had thought they were to prolong <b>attached</b> (but not necessarily
"laminar") flow, and delay separation thereby allowing ...&nbsp; But for
our purposes here that would be nit picking anyway.&nbsp; Jim P left me
with the belief that turbulent flow that stays attached to maybe 80% MAC
is better than laminar flow that detaches at 40% and that's what VGs do
- keep the flow attached longer.
<br><font face="Arial"><font size=-1><font color="#0000FF">&lt;... I personally
do not know how much laminar flow the canard is designed to "tolerate"
....></font><font color="#000000"></font></font></font>
<br><font face="Arial"><font color="#000000"><font size=-1>Nor do I.&nbsp;
What I have done does not depart that much from what I've seen on other
Velocitys that as far as I know were done with the "approved kit" whatever
that might be.</font></font></font><font face="Arial"><font color="#0000FF"><font size=-1></font></font></font>
<p><font face="Arial"><font size=-1><font color="#0000FF">&lt;... (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 without a through
simulation of the modification ...></font><font color="#000000"></font></font></font>
<br><font face="Arial"><font color="#000000"><font size=-1>As I said, I
believe my excursions from the standard are minor</font></font></font>
<p><font face="Arial"><font size=-1><font color="#0000FF">&lt;... 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 ...></font><font color="#000000"></font></font></font>
<br><font face="Arial"><font color="#000000"><font size=-1>Agreed (except
that I would substitute "attached" for "laminar"</font></font></font><font face="Arial"><font color="#000000"><font size=-1></font></font></font>
<p><font face="Arial"><font size=-1><font color="#0000FF">&lt;... 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 ...></font><font color="#000000"></font></font></font>
<br><font face="Arial"><font color="#000000"><font size=-1>Exactly.&nbsp;
Absent specific information on why they did what they did (and just as
important, why they didn't do what they didn't do) I have no way to evaluate
their result or compare it in any meaningful way to my own.</font></font></font><font face="Arial"><font color="#000000"><font size=-1></font></font></font>
<p><font face="Arial"><font size=-1><font color="#0000FF">&lt;... I am
not saying that you did anything wrong by installing VG's to your canard
.... maybe your particular arrangement will greatly enhance the low speed
handling and lower the stall speed ...></font><font color="#000000"></font></font></font>
<br><font face="Arial"><font color="#000000"><font size=-1>Like I said,
I talked rather extensively with the champion.&nbsp; He went to a lot of
trouble designing and testing the setup he used on his record setting flight(s)
- he had to in order to get the results he did - and I used what he told
me.&nbsp; I am completely confident that within the envelope I am operating,
his stuff is quite transferable from his Long-EZ to my Velocity.&nbsp;
Absent compelling information to the contrary, I am assuming that he put
a lot more quality engineering effort into his scheme than the Swings or
Danny or whoever did to theirs.&nbsp; This is not meant as a slam at anybody's
research efforts, but just an observation (and an undocumented one at that).&nbsp;
The fact that my scheme is as effective as it seems to be validates to
me Price's efforts.&nbsp; I wish I had better "before - during - after"
data than I do, but conditions and situations didn't lend themselves to
extensive testing and documentation of results.&nbsp; I am very pleased.&nbsp;
I truly believe I got an honest 10 kts reduction in landing speed, and
at least 5 kts reduction in takeoff/rotation speed.</font></font></font><font face="Arial"><font color="#000000"><font size=-1></font></font></font>
<p><font face="Arial"><font size=-1><font color="#0000FF">&lt;... please
keep us informed ...></font><font color="#000000"></font></font></font>
<br><font face="Arial"><font color="#000000"><font size=-1>You will be
the first to know :o)&nbsp; I'm always looking for more and better information.&nbsp;
The minute I find a better reason to change my setup than I had to adopt
it in the first place, I will adopt the new scheme.</font></font></font><font face="Arial"><font color="#000000"><font size=-1></font></font></font>
<p><font face="Arial"><font color="#000000"><font size=-1>Any and all useful
input is welcome ... Jim S.</font></font></font>
<br><font face="Arial"><font color="#000000"><font size=-1></font></font></font>&nbsp;
<br><font face="Arial"><font color="#000000"><font size=-1></font></font></font>&nbsp;
<blockquote TYPE=CITE>&nbsp;<span class=159023117-06122003><font face="Arial"><font color="#0000FF"><font size=-1>Jim,</font></font></font></span><span class=159023117-06122003><font face="Arial"><font color="#0000FF"><font size=-1>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&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 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 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.&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 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></font></font></span><span class=159023117-06122003><font face="Arial"><font color="#0000FF"><font size=-1>Alex</font></font></font></span><span class=159023117-06122003></span><span 
class=159023117-06122003></span><span 
class=159023117-06122003></span><font face="Tahoma"><font size=-1>-</font></font></blockquote>
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