REFLECTOR:Trailing Edge
Chuck Jensen
reflector@tvbf.org
Sat, 24 Jan 2004 17:50:03 -0500
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Al,
=20
That shape is close to what would seem to be more eye-pleasing. I =
wonder
though, is all of the top fin is still needed/useful or could the =
radius of
the top corner be increased even more?. And, I assume since you =
extended
the fence beyond the trailing edge, you had a reason, or at least a
hypothesized reason in lieu of terminating the fence at the trailing =
edge?
=20
Chuch.
-----Original Message-----
From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On =
Behalf Of
Al Gietzen
Sent: Saturday, January 24, 2004 4:03 PM
To: reflector@tvbf.org
Subject: RE: REFLECTOR:Trailing Edge
Has anyone made an effort to determine optimum shape/size of the =
fences. In
a post several months ago, there was a discussion that oversized fences =
seem
to inhibit turning but that most of the "gain" from the fences were =
still
realized even with the smaller fences that we are seeing. And, the =
single
most effective fence location was inboard of the ailerons (if I recall
correctly).
=20
Here is my version of trailing edge fence - freshly primed. The height =
at
the trailing edge is 4 =BD". They start about 19" forward of the =
trailing
edge (standard wing), just guessing forward of where flow separation =
may
begin in worst case. The fence extends about 2" back of the edge, and =
the
center of curvature of the back edge of the fence is the aileron hinge =
line.
Seemed to make sense keep the edge a fixed distance back from the =
aileron.
They are aligned with the fuselage centerline.
=20
I based this design on the results of tuft testing on the EZs, and some
looks at Danny's trailer tuft testing. The flow separation crept =
forward
and got thicker as angle of attack increased; and there was spanwise =
flow
outward under the separated flow. Until some folks do some tuft =
testing
with different shapes, and with and without the various aerodynamic
adjusters - fences, vortilons, VGs - on our airplane, it is difficult =
to
know the "best" approach. In some respects, these devices do to same
things; in other respects quite different. Meanwhile, I'll express my
opinion based on study of the tuft tests and what (little) I know about
aerodynamics.
=20
I disagree, at least to a degree, that the vortilons and the VGs play =
very
different rolls. The main function of the VGs is to generate a vortex =
over
the upper wing surface at high angles of attack, thereby breaking up =
the
spanwise flow and encouraging the flow to remain attached. VGs do the =
same
thing, most likely more effectively on a smaller scale. So there is =
some
overlap of function.
=20
The fences provide a means of stopping the spanwise flow, which is the =
worst
coming down off the sides of the fuselage, and heading outward. =
Without VGs
some spanwise flow probably re-establishes outboard of the first fence,
which to me seems the only reason to have more fences outboard of the
aileron. Having them out there probably provides further stability, =
but
would expect to reduce roll rate.
=20
VGs probably cause more drag a high speed than a fence, and the =
vortilons
likely cause negligible drag except at high angles of attack. I'm =
going to
guess that a roughly optimum arrangement for increased low speed =
response,
good roll rate and minimum drag is having a fence inboard of the =
aileron,
and a few VGs forward of the aileron; probably on the outer half of the
aileron length. And leave the vortilons where they are. Like I said, =
it's
my guess.
=20
The tuft testing on the EZs showed little deviation from straight back =
flow
on the underside of the wing at any flyable speed. That leads me to =
wonder
why Klaus suggests that the fence should extend below the wing, but =
wouldn't
disagree. Until there is solid evidence to the contrary, I see no =
reason
not install the vortilons as specified, even with the installation of =
VGs.
=20
And all these conclusions are only worth what it cost you. I didn't do =
any
flight testing on my airplane - yet.
=20
Al
=20
Oh BTW; that aileron fence? Corrugated cardboard core - another =
inovation.
Couldn't locate any thin foam, and knew that mostly what was needed was =
to
maintain airspace between the fine BID plys until they cured. After =
cutting
out I recessed and filled around the edges with micro. After glassing =
to
the wing they are very rigid, very light, and just under 3/16" thick. =20
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<DIV><SPAN class=453264222-24012004><FONT face=Arial color=#0000ff
size=2>Al,</FONT></SPAN></DIV>
<DIV><SPAN class=453264222-24012004><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=453264222-24012004><FONT face=Arial color=#0000ff size=2>That
shape is close to what would seem to be more eye-pleasing. I
wonder though, is all of the top fin is still needed/useful or could the
radius of the top corner be increased even more?. And, I assume since you
extended the fence beyond the trailing edge, you had a reason, or at least
a hypothesized reason in lieu of terminating the fence at the trailing
edge?</FONT></SPAN></DIV>
<DIV><SPAN class=453264222-24012004><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=453264222-24012004><FONT face=Arial color=#0000ff
size=2>Chuch.</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>Al
Gietzen<BR><B>Sent:</B> Saturday, January 24, 2004 4:03 PM<BR><B>To:</B>
reflector@tvbf.org<BR><B>Subject:</B> RE: REFLECTOR:Trailing
Edge<BR><BR></FONT></DIV>
<DIV class=Section1>
<P class=MsoPlainText><FONT face=Nimrod size=2><SPAN
style="FONT-SIZE: 11pt">Has anyone made an effort to determine optimum
shape/size of the fences. In</SPAN></FONT></P>
<P class=MsoPlainText><FONT face=Nimrod size=2><SPAN style="FONT-SIZE: 11pt">a
post several months ago, there was a discussion that oversized fences
seem</SPAN></FONT></P>
<P class=MsoPlainText><FONT face=Nimrod size=2><SPAN
style="FONT-SIZE: 11pt">to inhibit turning but that most of the "gain" from
the fences were still</SPAN></FONT></P>
<P class=MsoPlainText><FONT face=Nimrod size=2><SPAN
style="FONT-SIZE: 11pt">realized even with the smaller fences that we are
seeing. And, the single</SPAN></FONT></P>
<P class=MsoPlainText><FONT face=Nimrod size=2><SPAN
style="FONT-SIZE: 11pt">most effective fence location was inboard of the
ailerons (if I recall</SPAN></FONT></P>
<P class=MsoPlainText><FONT face=Nimrod size=2><SPAN
style="FONT-SIZE: 11pt">correctly).</SPAN></FONT></P>
<P class=MsoPlainText><FONT face=Nimrod size=2><SPAN
style="FONT-SIZE: 11pt"></SPAN></FONT> </P>
<P class=MsoPlainText><FONT face=Verdana size=2><SPAN
style="FONT-SIZE: 11pt; FONT-FAMILY: Verdana">Here is my version of trailing
edge fence - freshly primed. The height at the trailing edge is 4 ½".
They start about 19" forward of the trailing edge (standard wing), just
guessing forward of where flow separation may begin in worst case. The
fence extends about 2" back of the edge, and the center of curvature of the
back edge of the fence is the aileron hinge line. Seemed to make sense
keep the edge a fixed distance back from the aileron. They are aligned
with the fuselage centerline.</SPAN></FONT></P>
<P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN
style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana"></SPAN></FONT> </P>
<P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN
style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana">I based this
design on the results of tuft testing on the EZs, and some looks at Danny's
trailer tuft testing. The flow separation crept forward and got thicker
as angle of attack increased; and there was spanwise flow outward under the
separated flow. Until some folks do some tuft testing with different
shapes, and with and without the various aerodynamic adjusters - fences,
vortilons, VGs - on our airplane, it is difficult to know the "best"
approach. In some respects, these devices do to same things; in other
respects quite different. Meanwhile, I'll express my opinion based on
study of the tuft tests and what (little) I know about
aerodynamics.</SPAN></FONT></P>
<P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN
style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana"></SPAN></FONT> </P>
<P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN
style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana">I disagree, at
least to a degree, that the vortilons and the VGs play very different
rolls. The main function of the VGs is to generate a vortex over the
upper wing surface at high angles of attack, thereby breaking up the spanwise
flow and encouraging the flow to remain attached. VGs do the same thing,
most likely more effectively on a smaller scale. So there is some overlap of
function.</SPAN></FONT></P>
<P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN
style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana"></SPAN></FONT> </P>
<P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN
style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana">The fences provide
a means of stopping the spanwise flow, which is the worst coming down off the
sides of the fuselage, and heading outward. Without VGs some spanwise
flow probably re-establishes outboard of the first fence, which to me seems
the only reason to have more fences outboard of the aileron. Having them
out there probably provides further stability, but would expect to reduce roll
rate.</SPAN></FONT></P>
<P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN
style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana"></SPAN></FONT> </P>
<P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN
style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana">VGs probably cause
more drag a high speed than a fence, and the vortilons likely cause negligible
drag except at high angles of attack. I'm going to guess that a roughly
optimum arrangement for increased low speed response, good roll rate and
minimum drag is having a fence inboard of the aileron, and a few VGs forward
of the aileron; probably on the outer half of the aileron length. And
leave the vortilons where they are. Like I said, it's my
guess.</SPAN></FONT></P>
<P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN
style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana"></SPAN></FONT> </P>
<P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN
style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana">The tuft testing
on the EZs showed little deviation from straight back flow on the underside of
the wing at any flyable speed. That leads me to wonder why Klaus
suggests that the fence should extend below the wing, but wouldn't
disagree. Until there is solid evidence to the contrary, I see no reason
not install the vortilons as specified, even with the installation of
VGs.</SPAN></FONT></P>
<P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN
style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana"></SPAN></FONT> </P>
<P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN
style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana">And all these
conclusions are only worth what it cost you. I didn't do any flight
testing on my airplane - yet.</SPAN></FONT></P>
<P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN
style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana"></SPAN></FONT> </P>
<P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN
style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana">Al</SPAN></FONT></P>
<P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN
style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana"></SPAN></FONT> </P>
<P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN
style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana">Oh BTW; that
aileron fence? Corrugated cardboard core - another inovation.
Couldn't locate any thin foam, and knew that mostly what was needed was to
maintain airspace between the fine BID plys until they cured. After
cutting out I recessed and filled around the edges with micro. After
glassing to the wing they are very rigid, very light, and just under 3/16"
thick. </SPAN></FONT></P></DIV></BLOCKQUOTE></BODY></HTML>
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