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Discus 2 rudder stiff help please



 
 
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  #21  
Old August 28th 19, 04:42 PM posted to rec.aviation.soaring
India November[_2_]
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Default Discus 2 rudder stiff help please

On Tuesday, August 27, 2019 at 8:41:54 AM UTC-4, Dave Nadler wrote:
On Tuesday, August 27, 2019 at 8:17:45 AM UTC-4, India November wrote:
I had heard of corrosion issues from Dave Nadler et al...
I didn't imagine the internal parts could be affected...


Ian, internal corrosion is shown in the video:
https://www.youtube.com/watch?v=QEJJb_ufo8A


Thanks Dave, yes I see you holding what looks suspiciously like a S-H rudder horn.
Ads
  #22  
Old August 28th 19, 11:53 PM posted to rec.aviation.soaring
Frank Whiteley
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Default Discus 2 rudder stiff help please

On Tuesday, August 27, 2019 at 6:40:25 AM UTC-6, Dave Nadler wrote:
On Tuesday, August 27, 2019 at 1:24:06 AM UTC-4, wrote:
When you disconnect the rudder cables, be sure to attach a section
of safety wire as the cables are spring loaded and may retract into
the fus which will make retrieval of the cables difficult.


Really now, don't go spoiling the entertainment value for onlookers...


Dang, ran out of popcorn, but put it on the shopping list. Doesn't look like Amazon.com has one day delivery yet.
  #23  
Old August 29th 19, 06:16 PM posted to rec.aviation.soaring
jo[email protected]
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Default Discus 2 rudder stiff help please

I’ll second Karl’s remarks. I remember a pilot at a Nationals that had a tow hook that was jammed........wouldn’t budge! I told him to pull the seat and we found a tow pulley that was sitting in water from a leaky wing bag..........he said the bag had always leaked. The problem comes from situation known as dissimilar metal corrosion. Usually, the brass bushing and steel bolt + water will set up an electrolytic action..........aka a little battery! Our little battery needs water to make it work and it works even better if it finds salt water or urine. The little battery hates lubrication, so inspect and lube everything you can git to, every year!
JJ
  #24  
Old September 9th 19, 02:51 AM posted to rec.aviation.soaring
India November[_2_]
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Default Discus 2 rudder stiff help please

Thanks to everyone who posted suggestions. I appreciate your help.

Having now disassembled the rudder with my AME, the answer seems to be that the retaining nut was too tight.

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. Upon removing the rudder the bronze bushing and washer on the lower pivot had bright mating faces showing sliding contact.

Not so clear is why the nut had become overtight. The rudder never been taken off. One theory is that the nut worked itself tighter through friction as the rudder moved.

No significant corrosion was seen on the rudder horn, bearing or mounts.

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.

Some pics here if anyone wishes to take a look. https://1drv.ms/u/s!Al9GDrAowZRAi59D...aIqCA?e=jhOKn8

Ian IN
  #25  
Old September 10th 19, 05:08 PM posted to rec.aviation.soaring
Nyal Williams[_3_]
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Default Discus 2 rudder stiff help please

On Monday, August 26, 2019 at 7:55:09 AM UTC-4, India November wrote:
The rudder on my D2b has become very stiff on its hinges during this season. I disconnected the cables at the rudder horn, and it's clear the problem is in the rudder not elsewhere in the control circuit. Removed mylar seals without effect. No visible damage to the rudder, and no foreign objects visible between rudder and fin. Before I remove the rudder, has anyone out there encountered a similar problem? Glider has 650hrs TT, always hangared.

Thanks in advance for all suggestions!
Ian IN


Do you have a bladder relief exit on the fuselage behind the gear? Urine can run backward and up to the first hinge point and cause problems there. If that is the case, move the exit from where it is and to one side of the landing gear structure and have the tube clear the ground a couple of inches. This means you must lower the gear before urinating.
  #26  
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.
  #27  
Old September 10th 19, 08:07 PM posted to rec.aviation.soaring
[email protected]
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Default Discus 2 rudder stiff help please

As delivered, the ship came with Schempp-Hirth standard brass bushing and brass washer which allows the self-locking nut to be tightened up completely and the rudder will still move freely. Not uncommon to find the brass washer installed upside-down or missing and replaced with a standard washer. In either case, tightening the nut will produce a stiff rudder.
JJ
  #28  
Old September 11th 19, 11:52 AM posted to rec.aviation.soaring
krasw
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Default Discus 2 rudder stiff help please

On Tuesday, September 10, 2019 at 10:07:23 PM UTC+3, wrote:
As delivered, the ship came with Schempp-Hirth standard brass bushing and brass washer which allows the self-locking nut to be tightened up completely and the rudder will still move freely. Not uncommon to find the brass washer installed upside-down or missing and replaced with a standard washer. In either case, tightening the nut will produce a stiff rudder.
JJ


I was a bit amazed that op, provided with necessary knowledge about lower hinge bushing, managed to not get it replaced by proper part, and still get it signed off by AME.
 




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