Tuesday, September 26, 2017
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Control Horn Basics

Mechanics Made Easy

This months Primary Training is in response to an email sent to our Editors Inbox (editors@flyrc.com) from Rick Breckwoldt. Rick writes:

I was hoping that you would include an article about the best way to install the aileron, rudder, or elevator control horns that come with most kits. I have been building for over 30 years, and this remains my least-favorite portion of the build. The screws always seem to be just a little off when I try to put them through the aileron to fasten the horn to the plastic attachment on the other side. Thanks in advance for your help. I thoroughly enjoy each and every issue of Fly RC.

Always trim off the excess length of the exposed screw shanks. It cleans up the models overall appearance and makes post-flight cleaning less of a hassle.

Rick Breckwoldt

Its quite a coincidence that Rick wrote to us about this problem around the same time as I was building a J-3 Cub with floats. The only frustrating part of the entire build was, as Rick writes, installing the control horns so that the screws passed through the aileron control surfaces and into the keeper plates as they should. I took comfort from hearing that Rick, a 30-year-veteran of the hobby, shares my frustration.

A Du-Bro EZ-link connector is used at the servo side of this 2-56 control linkage while a Du-Bro Qwik-Link is used at the control horn. Notice how the control rod fits very tightly through the servo arm. Remember that slop is your enemy.

WHAT OTHERS SAY

We bounced the idea around the office about the best solutionone that would work well and serve as a universal guide to installing control horns. We realized that because control surfaces differ, creating a jig for drilling the holes wouldnt be a solution. This is because the control horns are typically installed after the control surfaces have been hinged and installed.

To avoid building differential into your control linkages, install your control horn so that the pivot point, where the clevis is attached to your control horn, is directly over your hinge line.

To further complicate things, some modelers I spoke with said that they dont worry if they dont get the holes through control surfaces absolutely perfect. Some said that they do try to get the holes perfect by drilling through the control surface while keeping the bit as perpendicular to the surface as they can. One modeler even suggested drilling the hole slightly oversize and epoxying a short section of brass tubing into the control surface to strengthen the structure. Several modelers said that they work the screws into place if they are slightly off and then apply CA to the underlying wood to strengthen around the screw holes.

These standard control horns are a subset of those available from Du-Bro, and they indicate the broad range of available sizes and styles.
 A      B  

 

 

C

 

 

 

D