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Tufnol bearings clearances

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asarangan(at)gmail.com
Guest

Posted: Sun Aug 28, 2011 8:10 am Post subject: Tufnol bearings clearances

Looking through the email archives, the alignment of the front and

rear tufnol bearings/bushings with the aileron torque tube appears to

be a critical step in preventing control stiffness.



There are no specific guidelines about this on the manual. I am mostly

concerned about thermal expansion since the cockpit can see 70C

difference from summer to winter. The torque tube is about 24" long

and looks like zinc plated steel. For 70C, the thermal expansion will

be about 22 mils. So I am thinking I need to insert 12mil shims on

either side of the tufnol bearing before bonding the fork and the

bushing, and then removing it after cure.



Then there is also the question of tufnol expansion due to moisture.

There is a chart on tufnol.com on how much tolerance should be allowed

for water absorption. This is for prolonged immersion so it can be

considered a worst case scenario. For the 1/2" bearing, this

translates to about 0.8mm, or about 32mils.



So putting both factors together, I am thinking of inserting 25mil

shims on both side of the tufnol, for a total of 50mil play. Does this

sound right?



All of this could turn out to be a moot point if the flex in the

cockpit module is a greater factor.



Comments are welcome.

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grahamsingleton(at)btinte
Guest

Posted: Sun Aug 28, 2011 2:47 pm Post subject: Tufnol bearings clearances

Andrew

You are right about the problems of thermal expansion etc. I had a problem due to the clearances being too close. Going from a warm hangar to cold air (flying) the roll control stiffened up, due to the aluminum contracting quickly and the rest of the airframe  slowly.  After an hour the controls had loosened up again.

Graham



From: Andrew Sarangan <asarangan(at)gmail.com>

To: Europa List <europa-list(at)matronics.com>

Sent: Sunday, 28 August,  2011 17:07:32

Subject: Tufnol bearings clearances



--> Europa-List message posted by: Andrew Sarangan <asarangan(at)gmail.com (asarangan(at)gmail.com)>



Looking through the email archives, the alignment of the front and

rear tufnol bearings/bushings with the aileron torque tube appears to

be a critical step in preventing control stiffness.



There are no specific guidelines about this on the manual. I am mostly

concerned about thermal expansion since the cockpit can see 70C

difference from summer to winter. The torque tube is about 24" long

and looks like zinc plated steel. For 70C, the thermal expansion will

be about 22 mils. So I am thinking I need to insert 12mil shims on

either side of the tufnol bearing before bonding the fork and the

bushing, and then removing it after  cure.



Then there is also the question of tufnol expansion due to moisture.

There is a chart on tufnol.com on how much tolerance should be allowed

for water absorption. This is for prolonged immersion so it can be

considered a worst case scenario. For the 1/2" bearing, this

translates to about 0.8mm, or about 32mils.



So putting both factors together, I am thinking of inserting 25mil

shims on both side of the tufnol, for a total of 50mil play. Does this

sound right?



All of this could turn out to be a moot point if the flex in the

cockpit module is a greSearch & Download, 7-Day Browse, Chat, gt; http://forums.matronics.com

_;                   -Matt Dralcontribution" =======



    

 [quote][b]

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Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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