Control horns, is it just me or... ?

[davel322 at comcast.net]

Keith,

Independantly developed and implemented, I have been using a similar system to 
what Buff described.  There are several pictures of my EMCs on Xavier Mouraux's 
website at http://pattern-canada.mouraux.com/glen.html - one of the pics 
towards the end shows the plywood disc / control "horn" mounted in the rudder.

Regards,

Dave Lockhart
DaveL322 at comcast.net
> Do you have pictures?
> 
> Keith
>   ----- Original Message ----- 
>   From: Buff Miller 
>   To: discussion at nsrca.org 
>   Sent: Friday, September 05, 2003 8:42 PM
>   Subject: Re: Control horns, is it just me or... ?
> 
> 
>   Keith,
> 
>   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.
> 
>   This system does not 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.
> 
>   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.
> 
>   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.
> 
>   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.
> 
>   Just another idea to consider.  It almost took longer to write this 
> explanation than it takes to make such a system.  Enjoy.
> 
>   Buff Miller
>     ----- Original Message ----- 
>     From: Keith Black 
>     To: discussion at nsrca.org 
>     Sent: Tuesday, September 02, 2003 9:57 PM
>     Subject: Control horns, is it just me or... ?
> 
> 
>     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.
> 
>     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 
> http://www.centralhobbies.com/buildingtips/mkhorns/mkhornsinst.html. Notice that 
> in this picture there surface isn't beveled yet and the horn is almost on the 
> edge.
> 
>     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 
> (http://www.znline.com/produits.php?langue=english&cle_menus=1025879382&cle_data
> =1025901639) which means an international order. The other solution I've found 
> is by RC Model Enterprises (http://home.att.net/~rc-enterprises/rcme_014.htm) 
> but these control horns seem very pricey!
> 
>     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).
> 
>     Is it just me, or have others experienced this dilemma as well?
> 
>     Thanks,
>     Keith Black
> 
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