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Old September 10th 19, 06:30 PM posted to rec.aviation.soaring
Bob Kuykendall
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Default Discus 2 rudder stiff help please

On Sunday, September 8, 2019 at 6:51:03 PM UTC-7, India November wrote:

...The rudder on this ship is kept in place by an M8 metal locknut and washer on the lower pivot pin. On disassembly, the nut was hard to turn at first. After loosening by 1/2-turn the rudder moved freely...

...On reassembly after cleaning and lubrication and with a new metal locknut my AME could reproduce the issue by tightening the nut against the bearing. After backing off the nut slightly to give slight clearance the rudder moves freely...

Very interesting. In the US, that arrangement would probably never pass muster for 14CFR Part 23 certification. AC43.13 requires that a nut on a pivot bolt subject to rotation must be secured with a cotter pin.

Relying on the self-locking feature of a nut to prevent overtightening or loss of the nut (and failure of a primary flight control system) is quite suboptimal. As you have already observed, relatively little deterioration of the nut or the pivot bolt is required to result in failure of this connection.

--Bob K.