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Rudder post & hinges

Neil

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Being engineer minded, I like seeing how different designs accomplish similar end results.

The difference between The Acro Sport and Skybolt relating to the rudder horn is between how they transmit torque to the spar. Skybolt welds directly to the spar and to one rib, with the rib acting as a lever. I'm guessing the spar of the Skybolt is at least .058" wall.

The Acro Sport uses a spar of .035" with a sleeve of 1"x .058" tube cut at a long angle welded on in the area of the rudder horn. There is no rib in this area so all the torque is transmitted through the sleeve to the spar.

This area on the Skybolt is also helped by a center hinge that absorbs the pull of the rudder cables when the pilot gets heavy feet.

Acro Sport uses two hinges with the horn just above the lower hinge.

All any of this really means is that they are two different airplanes, yet very similar.

The rudder horn is virtually identical in design and the flange that turns down on the front edge is not actually intended to be welded to the rudder post. Doesn't hurt a thing if you do, and nearly all of them are. The flange is a stiffiner and the flat area is for the stops to work against.


The Acro uses Pitts style strap hinges and I have seen these on Skybolts.
I don't know if the plans offer the option.

The bushing and pin hinges shown on another thread are simple to make but you can't just weld bushing stock to the spars. These were made by welding a length of bushing stock to an equal length of .058 wall material that fits the rudder post, then sawing them into individual pieces. You must also remember to slip them on to the spar before you weld the ribs. And yes, I've done that. If you find yourself in that position, just cut off the back half of the ring.

The thing to remember about hinges is not to weld them in place until all other welding is done. On stabilizers, start from the inboard end and work out. If you weld the hinges in place without rigging the stabilizers to the airframe with flying wires, the hinges will bind up when you do rig the tail. This is especially true with strap style hinges! Yep, did that too.

These are things I have encountered over the years and since so many are working on tail groups, I felt compelled to pass along. Hope it helps.
 

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