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<DIV><FONT face=Arial size=2>According to the Ackerman principle having the
clevis hole exactly on the hinge would result in a the cables keeping the same
tension through the entire throw range. Behind the hinge would cause the cable
opposite the pulling cable to create slack. In front of the hole will cause
disastrous effects! </FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Personally I'd like the idea of having the same
tension through the entire throw range, however, for safety sake I set the hole
just slightly behind the hinge (1/64 to 1/32) because it's difficult to see when
it's EXACTLY over the hinge. This results in me having a VERY minor loosening of
the opposite cable.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>So what's the "disastrous effect"?
</FONT><FONT face=Arial size=2>One of the local new pattern guys spent a year
building his first 2M plane and misunderstood the issue of having the control
horn on the hinge line. He thought the *post* of the control horn was supposed
to be on the hinge. He devised an interesting system to get his control post
exactly on the hinge which put the clevis hole around 1/8" in *front* of the
elevator hinge line. On the first flight when in a downline the elevator
fluttered and snapped the stab (though it didn't fall off). The plane was landed
and about two months later he came back with a repaired stab and tried it again.
Again in a downline the stab snapped. After this second occurrence I took a look
at his setup and noticed the clevis hole being in front of the hinge line. After
thinking about it for a bit I realized what had happened. When the hole is in
front of the hinge it will create Reverse Ackerman. This means that as the
pulling cable tries to move the control surface to one side the opposite side
gets tighter. At high airspeeds as the pressure pushes the rudder one
direction the opposite side will tighten and pull the rudder back to the other
side, this in turn will tighten the first side and pull the rudder that
direction. What he'd created was an Ackerman induced flutter.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Sadly after the stab was again repaired and the
hinge problem corrected within the next couple of flights the elevator servo
came loose during a flight and the plane was lost. It's believe that the flutter
from the earlier flights loosened the elevator servo. </FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Therefore, even though I would like the hole
exactly on the hinge line, I give myself a slight safety margin.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Keith Black</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV>----- Original Message ----- </DIV>
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<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=rcaerobob@cox.net href="mailto:rcaerobob@cox.net">Bob Pastorello</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> Monday, November 29, 2004 5:19
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: Elev. Pull pull
Question</DIV>
<DIV><BR></DIV>
<DIV><FONT face=Arial size=2>If we align the clevis attach point with the
hinge line, doesn't that "undo" the desired Ackerman effect that we need?
(Thanks Keith)</FONT></DIV>
<DIV><FONT face=Arial size=2> I agree with stuff over the
hinge line in principle, but would appreciate any informed technical
explanation (go, Dean!!), as I like to understand the "why" of
stuff.</FONT></DIV>
<DIV><BR>Bob Pastorello<BR>NSRCA 199 AMA 46373<BR><A
href="mailto:rcaerobob@cox.net">rcaerobob@cox.net</A><BR><A
href="http://www.rcaerobats.net">www.rcaerobats.net</A></DIV>
<DIV> </DIV>
<DIV> </DIV>
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=d.pappas@kodeos.com href="mailto:d.pappas@kodeos.com">Dean
Pappas</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> Monday, November 29, 2004 10:42
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> RE: Elev. Pull pull
Question</DIV>
<DIV><BR></DIV>
<DIV><SPAN class=494275614-29112004><FONT face=Arial color=#0000ff
size=2>Hello Bob,</FONT></SPAN></DIV>
<DIV><SPAN class=494275614-29112004><FONT face=Arial color=#0000ff size=2>Go
buy some DuBro # 867 control horns. They have almost 3/4" of overhang
between the bolt and the little hole for the clevis, in the little screw-on
pieces.</FONT></SPAN></DIV>
<DIV><SPAN class=494275614-29112004><FONT face=Arial color=#0000ff
size=2>Use those pieces, but set the bolt and nut aside, and see if the
little holes line up with the center of the hinges.</FONT></SPAN></DIV>
<DIV><SPAN class=494275614-29112004><FONT face=Arial color=#0000ff size=2>If
not, then drill new holes in the black plastic bits so that they do
line up: one straight line through both holes and the center of the
hinge.</FONT></SPAN></DIV>
<DIV><SPAN class=494275614-29112004><FONT face=Arial color=#0000ff
size=2>Now when you get the horns all the same length, it will be much
easier to get the throws matched in both directions.</FONT></SPAN></DIV>
<DIV><SPAN class=494275614-29112004><FONT face=Arial color=#0000ff
size=2>This is absolutely necessary for matching two elevator halves
properly, but is also a good idea for rudders.</FONT></SPAN></DIV>
<DIV><SPAN class=494275614-29112004><FONT face=Arial color=#0000ff
size=2>The problem with the stock setup is that the cables slacken at
the ends, and tighten at neutral.</FONT></SPAN></DIV>
<DIV><SPAN class=494275614-29112004><FONT face=Arial color=#0000ff
size=2>While this might sound like a good thing, it is awful: the servo has
to fight the tightening cables as the surface comes closer to
neutral,</FONT></SPAN></DIV>
<DIV><SPAN class=494275614-29112004><FONT face=Arial color=#0000ff
size=2>then as it gets there, the surface may try to "spring" to the
opposite direction.</FONT></SPAN></DIV>
<DIV><SPAN class=494275614-29112004><FONT face=Arial color=#0000ff
size=2>The servo and gear train will prematurely beat themselves up chasing
this problem.</FONT></SPAN></DIV>
<DIV><SPAN class=494275614-29112004><FONT face=Arial color=#0000ff
size=2>You want the cable tension to be almost constant throughout the
throw.</FONT></SPAN></DIV>
<DIV><SPAN class=494275614-29112004><FONT face=Arial color=#0000ff
size=2>There will be pictures of this when I get the Excelleron review out
the door.</FONT></SPAN></DIV>
<DIV><SPAN class=494275614-29112004><FONT face=Arial color=#0000ff
size=2>One of the previous posts pointed to a website that showed the proper
geometry.</FONT></SPAN></DIV>
<DIV><SPAN class=494275614-29112004><FONT face=Arial color=#0000ff
size=2>DuBro and Rocket City both make parts that are useful, for this
problem.</FONT></SPAN></DIV>
<DIV><SPAN class=494275614-29112004><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=494275614-29112004><FONT face=Arial color=#0000ff
size=2>Check DuBro.com and put #867 into their search engine, you can see
the lonng overhang part. It's either 5/8" or 3/4" from bolt to clevis
hole.</FONT></SPAN></DIV>
<DIV><SPAN class=494275614-29112004><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=494275614-29112004><FONT face=Arial color=#0000ff
size=2>Later,</FONT></SPAN></DIV>
<DIV> </DIV>
<P><FONT face="Times New Roman">Dean Pappas</FONT> <BR><FONT
face="Times New Roman">Sr. Design Engineer</FONT> <BR><FONT
face="Times New Roman">Kodeos Communications</FONT> <BR><FONT
face="Times New Roman">111 Corporate Blvd.</FONT> <BR><FONT
face="Times New Roman">South Plainfield, N.J. 07080</FONT> <BR><FONT
face="Times New Roman">(908) 222-7817 phone</FONT> <BR><FONT
face="Times New Roman">(908) 222-2392 fax</FONT> <BR><FONT
face="Times New Roman">d.pappas@kodeos.com</FONT> </P>
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<DIV class=OutlookMessageHeader dir=ltr align=left><FONT face=Tahoma
size=2>-----Original Message-----<BR><B>From:</B>
discussion-request@nsrca.org [mailto:discussion-request@nsrca.org]<B>On
Behalf Of </B>Bob Pastorello<BR><B>Sent:</B> Friday, November 26, 2004
8:58 AM<BR><B>To:</B> NSRCA<BR><B>Subject:</B> Elev. Pull pull
Question<BR><BR></FONT></DIV>
<DIV><FONT face=Arial size=2>May seem obvious, but I could use some help
here....setting up my Excelleron, centers are okay, cable tensions are
pretty close, centering is good. Up elevator is fine, on Down
elevator, ONE elevator moves farther, but they track together except at
the endpoint, as close as I can tell.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Anyone have suggestions on how I'd fine tune
this out...??</FONT></DIV>
<DIV><FONT face=Arial size=2>Hope everyone had a great
T-day!!</FONT></DIV><FONT face=Arial size=2>
<DIV><BR>Bob Pastorello<BR>NSRCA 199 AMA 46373<BR><A
href="mailto:rcaerobob@cox.net">rcaerobob@cox.net</A><BR><A
href="http://www.rcaerobats.net">www.rcaerobats.net</A></DIV>
<DIV> </DIV>
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