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<DIV><FONT face=Arial size=2>Keith,</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I've been following this thread for the past few
days with great interest. The discussion has been very informative and
interesting, but I have to throw in a concept that has yet to be
mentioned. I suspect everyone has been "to close to the forest to see the
trees" thinking control horns and geometry. I've been using a system for
the past ten years that I developed from an article Gene Rogers, former District
6 VP, covered in the K-Factor back in the early 1990's.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>This system does <U>not</U> use control horns
for the pull-pull setup on the rudder. It uses two equal diameter
pulleys. One on the rudder the other on the servo. I make the
pulleys out of ply, three circles sandwiched together. The two outer
circles of 1/32" ply are roughly 2 - 2 1/2" in diameter. The inner circle
is of 1/16" ply about 1/8" - 3/16" smaller in diameter. I bevel the edges
of the two outer circles so that when I glue the three circles concentrically
together they form a "V" pulley. Also, dremel two notches in the "V" for
the cable ends to pass out and back into the "V" much like a Hanger 9
aluminum servo wheel to enable anchoring the cable to the pulley. Drill
a small hole for a tiny wood screw, no larger than a #2. On the
servo pulley the middle of the cable can duck out of the "V" pass under the
washered wood screw and back into the "V" on the other side of the screw.
The loose ends of the single cable will pass under and around the wood screw of
the rudder pulley.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Install the rudder pulley in a slot cut in the
rudder equal to the thickness of the pulley, 1/8", and a depth of the radius of
the pulley. Make certain that the center of the pulley is centered right
at the edge of the bevel or hinge line of the rudder. This keeps all of
the geometry intact. Epoxy it in place after MonoKoting the rudder but
prior to hinging the rudder to the fuse. Nearly one of the last steps in
the construction of your plane. In preparation for the pulley cut a
similar 1/8" notch, also equal or slightly larger than the radius of the pulley
in the fuselage. I epoxy a balsa block internally in this area if it
is an fiberglass fuse to beef up this area.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>The servo pulley is simply bolted with two 2-56
socket head bolts to a round servo wheel. All tightening of the cables are
done at the rudder pulley outside of the fuse.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>The main advantage of this system is that the servo
is able to maintain constant torque on the rudder through out the entire
deflection of the rudder without any cable slacking or binding issue. Plus
you couldn't get any other system much cheaper. You can also increase the
torque of the servo, at the price of reducing the throw of the rudder, by
making the servo pulley smaller in diameter than the rudder pulley. Or,
increase the throw of the rudder, at the price of reducing the torque of the
servo, by making the servo pulley larger than the rudder pulley. If the
rudder is positioned quite far back in relation to the elevator, such as on a
CAP 232, the rudder could in theory be made to rotate nearly 150 degrees or more
assuming you double bevel the rudder and fuse at acute angles on the hinge
line.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Just another idea to consider. It almost took
longer to write this explanation than it takes to make such a system.
Enjoy.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Buff Miller</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=tkeithb@comcast.net href="mailto:tkeithb@comcast.net">Keith Black</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=discussion@nsrca.org
href="mailto:discussion@nsrca.org">discussion@nsrca.org</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Tuesday, September 02, 2003 9:57
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Control horns, is it just me
or... ?</DIV>
<DIV><BR></DIV>
<DIV><FONT face=Arial size=2>When it comes to control horns for pattern planes
it seems to me that some of the most commonly used choices have a major
flaw.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>On my last plane I used the MK Aluminum
Horns on all surfaces except for the rudder where I used the IM pull-pull
horns. Both of these are nice horns except they have a major flaw when using a
pull-pull setup. The flaw is that the little black plastic arm that screws
onto the horn and connects to the clevis is so short that it doesn't extend
out over the hinge line. I know that with pull-pull systems it isn't
*absolutely* necessary for the connection to be exactly above the hinge, but
the further back it is the more slack there will be in the cable that is not
pulling. In my opinion with these horns the connection point is too far
away from the hinge unless the horn is virtually mounted on the control
surface bevel (especially when it comes to rudder). This can easily be seen in
these "instructions" for installing the MK horns <A
href="http://www.centralhobbies.com/buildingtips/mkhorns/mkhornsinst.html">http://www.centralhobbies.com/buildingtips/mkhorns/mkhornsinst.html</A>.
Notice that in this picture there surface isn't beveled yet and the horn is
almost on the edge.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>On my new plane I wanted to avoid this problem so
I did some searching to find a better solution. To begin with I looked for a
longer arm to connect to the MK horn, one that would extend out to the hinge
line. I found two options from Sullivan but both require too big of a horn
thread (6-32 and 8-32). My search then led me to two other choices that seem
to be good alternatives. The first is the ZNLine aluminum control horns, but
these are apparently only distributed by ZNLine (<A
href="http://www.znline.com/produits.php?langue=english&cle_menus=1025879382&cle_data=1025901639">http://www.znline.com/produits.php?langue=english&cle_menus=1025879382&cle_data=1025901639</A>)
which means an international order. The other solution I've found is by
</FONT><FONT face=Arial size=2><FONT face="Times New Roman" size=3><FONT
face=Arial size=2>RC Model Enterprises</FONT> <FONT face=Arial
size=2>(</FONT></FONT><A
href="http://home.att.net/~rc-enterprises/rcme_014.htm">http://home.att.net/~rc-enterprises/rcme_014.htm</A>)
but these control horns seem very pricey!</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>If anyone could point me to a longer 3mm
connecting arm that will fit on the MK and IM horns I'd be happy (BTW, I've
used the MK BB connectors on the MK horn and they still aren't really long
enough).</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Is it just me, or have others experienced this
dilemma as well?</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Thanks,</FONT></DIV>
<DIV><FONT face=Arial size=2>Keith Black</FONT></DIV>
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