REFLECTOR:Trailing Edge

Al Gietzen reflector@tvbf.org
Sun, 25 Jan 2004 10:55:56 -0800


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Subject: RE: REFLECTOR:Trailing Edge

=20

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

=20

The most eye pleasing and the most effective aerodynamically may not be
the same.  Based on the shape Klaus recommends, he apparently has
concluded that the thickness of the flow separation expands rapidly aft
of the separation point; so on that basis my fence may not have enough
area at the top.  But we are likely both estimating.  The radius I chose
is what looked pleasing to me, but I also recognize that the sharp
corner may, repeat - may result in lower drag.  In some cases where you
want the flow to separate, a sharp separation is better.  But in this
case the drag of the fence is likely negligibly small anyway, so what
does it matter.

=20

 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

Again it is some judgement, and I took the lead from Klaus.  If the
fence is being effective in stopping spanwise flow, there is likely to
be some spill, or turbulence, around the end of the fence.  The idea is
to keep good streamlines past the edge of the aileron.

=20

Al

-----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 class=3DSection1>

<p class=3DMsoNormal style=3D'margin-left:.5in'><b><font size=3D2 =
face=3DTahoma><span
style=3D'font-size:10.0pt;font-family:Tahoma;font-weight:bold'>Subject:</=
span></font></b><font
size=3D2 face=3DTahoma><span =
style=3D'font-size:10.0pt;font-family:Tahoma'> RE:
REFLECTOR:Trailing Edge</span></font></p>

<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D3 =
face=3D"Times New Roman"><span
style=3D'font-size:12.0pt'>&nbsp;</span></font></p>

<div>

<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D2 =
color=3Dblue face=3DArial><span
style=3D'font-size:10.0pt;font-family:Arial;color:blue'>Al,</span></font>=
</p>

</div>

<div>

<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D3 =
face=3D"Times New Roman"><span
style=3D'font-size:12.0pt'>&nbsp;</span></font></p>

</div>

<div>

<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D2 =
color=3Dblue face=3DArial><span
style=3D'font-size:10.0pt;font-family:Arial;color:blue'>That shape is =
close to
what would seem to be more eye-pleasing.&nbsp; I wonder&nbsp;though, is =
all of
the top fin is still needed/useful or could the radius of the top corner =
be
increased even more</span></font></p>

</div>

<div>

<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>&nbsp;</span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>The most eye pleasing and the =
most effective
aerodynamically may not be the same.=A0 Based on the shape Klaus =
recommends, he
apparently has concluded that the thickness of the flow separation =
expands
rapidly aft of the separation point; so on that basis my fence may not =
have <b><span
style=3D'font-weight:bold'>enough</span></b> area at the top.=A0 But we =
are likely
both estimating.=A0 The radius I chose is what looked pleasing to me, =
but I also
recognize that the sharp corner may, repeat - may result in lower =
drag.=A0 In some
cases where you want the flow to separate, a sharp separation is =
better.=A0 But
in this case the drag of the fence is likely negligibly small anyway, so =
what
does it matter.</span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>&nbsp;</span></font></p>

<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D2 =
color=3Dblue face=3DArial><span
style=3D'font-size:10.0pt;font-family:Arial;color:blue'>=A0And, I assume =
since you
extended the fence beyond the trailing edge, you had a reason, or at =
least
a&nbsp;hypothesized&nbsp;reason in lieu of terminating the fence at the
trailing edge?</span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>&nbsp;</span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>Again it is some judgement, and I =
took
the lead from Klaus. =A0If the fence is being effective in stopping =
spanwise
flow, there is likely to be some spill, or turbulence, around the end of =
the
fence. =A0The idea is to keep good streamlines past the edge of the =
aileron.</span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>&nbsp;</span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>Al</span></font></p>

</div>

<blockquote =
style=3D'margin-top:5.0pt;margin-right:0in;margin-bottom:5.0pt'>

<p class=3DMsoNormal =
style=3D'margin-right:0in;margin-bottom:12.0pt;margin-left:
.5in'><font size=3D2 face=3DTahoma><span =
style=3D'font-size:10.0pt;font-family:Tahoma'>-----Original
Message-----<br>
<b><span style=3D'font-weight:bold'>From:</span></b> =
reflector-admin@tvbf.org
[mailto:reflector-admin@tvbf.org]<b><span style=3D'font-weight:bold'>On =
Behalf Of
</span></b>Al Gietzen<br>
<b><span style=3D'font-weight:bold'>Sent:</span></b> </span></font><font =
size=3D2 face=3DTahoma><span =
style=3D'font-size:10.0pt;font-family:Tahoma'>Saturday,
 January 24, 2004</span></font><font size=3D2 face=3DTahoma><span =
style=3D'font-size:
10.0pt;font-family:Tahoma'> </span></font><font size=3D2 =
face=3DTahoma><span
 style=3D'font-size:10.0pt;font-family:Tahoma'>4:03 =
PM</span></font><font size=3D2
face=3DTahoma><span style=3D'font-size:10.0pt;font-family:Tahoma'><br>
<b><span style=3D'font-weight:bold'>To:</span></b> =
reflector@tvbf.org<br>
<b><span style=3D'font-weight:bold'>Subject:</span></b> RE: =
REFLECTOR:Trailing
Edge</span></font></p>

<p class=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
face=3DNimrod><span
style=3D'font-size:11.0pt'>Has anyone made an effort to determine =
optimum
shape/size of the fences. In</span></font></p>

<p class=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
face=3DNimrod><span
style=3D'font-size:11.0pt'>a post several months ago, there was a =
discussion that
oversized fences seem</span></font></p>

<p class=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
face=3DNimrod><span
style=3D'font-size:11.0pt'>to inhibit turning but that most of the
&quot;gain&quot; from the fences were still</span></font></p>

<p class=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
face=3DNimrod><span
style=3D'font-size:11.0pt'>realized even with the smaller fences that we =
are
seeing. And, the single</span></font></p>

<p class=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
face=3DNimrod><span
style=3D'font-size:11.0pt'>most effective fence location was inboard of =
the
ailerons (if I recall</span></font></p>

<p class=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
face=3DNimrod><span
style=3D'font-size:11.0pt'>correctly).</span></font></p>

<p class=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
face=3DNimrod><span
style=3D'font-size:11.0pt'>&nbsp;</span></font></p>

<p class=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
face=3DVerdana><span
style=3D'font-size:11.0pt;font-family:Verdana'>Here is my version of =
trailing
edge fence - freshly primed.&nbsp; The height at the trailing edge is 4
=BD&quot;. &nbsp;They start about 19&quot; forward of the trailing edge =
(standard
wing), just guessing forward of where flow separation may begin in worst =
case.
&nbsp;The fence extends about 2&quot; back of the edge, and the center =
of
curvature of the back edge of the fence is the aileron hinge line. =
&nbsp;Seemed
to make sense keep the edge a fixed distance back from the =
aileron.&nbsp; They
are aligned with the fuselage centerline.</span></font></p>

<p class=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
face=3DNimrod><span
style=3D'font-size:11.0pt'>&nbsp;</span></font></p>

<p class=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
color=3Dblack
face=3DVerdana><span =
style=3D'font-size:11.0pt;font-family:Verdana;color:black'>I
based this design on the results of tuft testing on the EZs, and some =
looks at
Danny's trailer tuft testing.&nbsp; The flow separation crept forward =
and got
thicker as angle of attack increased; and there was spanwise flow =
outward under
the separated flow. &nbsp;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 &quot;best&quot;
approach.&nbsp; In some respects, these devices do to same things; in =
other
respects quite different.&nbsp; 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=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
face=3DNimrod><span
style=3D'font-size:11.0pt'>&nbsp;</span></font></p>

<p class=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
color=3Dblack
face=3DVerdana><span =
style=3D'font-size:11.0pt;font-family:Verdana;color:black'>I
disagree, at least to a degree, that the vortilons and the VGs play very
different rolls.&nbsp; 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. &nbsp;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=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
face=3DNimrod><span
style=3D'font-size:11.0pt'>&nbsp;</span></font></p>

<p class=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
color=3Dblack
face=3DVerdana><span =
style=3D'font-size:11.0pt;font-family:Verdana;color:black'>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.&nbsp; 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.&nbsp; =
Having
them out there probably provides further stability, but would expect to =
reduce
roll rate.</span></font></p>

<p class=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
face=3DNimrod><span
style=3D'font-size:11.0pt'>&nbsp;</span></font></p>

<p class=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
color=3Dblack
face=3DVerdana><span =
style=3D'font-size:11.0pt;font-family:Verdana;color:black'>VGs
probably cause more drag a high speed than a fence, and the vortilons =
likely
cause negligible drag except at high angles of attack. &nbsp;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.&nbsp;
And leave the vortilons where they are.&nbsp; Like I said, it's my =
guess.</span></font></p>

<p class=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
face=3DNimrod><span
style=3D'font-size:11.0pt'>&nbsp;</span></font></p>

<p class=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
color=3Dblack
face=3DVerdana><span =
style=3D'font-size:11.0pt;font-family:Verdana;color:black'>The
tuft testing on the EZs showed little deviation from straight back flow =
on the
underside of the wing at any flyable speed. &nbsp;That leads me to =
wonder why
Klaus suggests that the fence should extend below the wing, but wouldn't
disagree.&nbsp; 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=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
face=3DNimrod><span
style=3D'font-size:11.0pt'>&nbsp;</span></font></p>

<p class=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
color=3Dblack
face=3DVerdana><span =
style=3D'font-size:11.0pt;font-family:Verdana;color:black'>And
all these conclusions are only worth what it cost you.&nbsp; I didn't do =
any
flight testing on my airplane - yet.</span></font></p>

<p class=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
face=3DNimrod><span
style=3D'font-size:11.0pt'>&nbsp;</span></font></p>

<p class=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
color=3Dblack
face=3DVerdana><span =
style=3D'font-size:11.0pt;font-family:Verdana;color:black'>Al</span></fon=
t></p>

<p class=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
face=3DNimrod><span
style=3D'font-size:11.0pt'>&nbsp;</span></font></p>

<p class=3DMsoPlainText style=3D'margin-left:.5in'><font size=3D2 =
color=3Dblack
face=3DVerdana><span =
style=3D'font-size:11.0pt;font-family:Verdana;color:black'>Oh
BTW; that aileron fence?&nbsp; Corrugated cardboard core - another
inovation.&nbsp; 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.
&nbsp;After cutting out I recessed and filled around the edges with
micro.&nbsp; After glassing to the wing they are very rigid, very light, =
and
just under 3/16&quot; thick.&nbsp; </span></font></p>

</blockquote>

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