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  #1  
Old 04-17-2017, 06:22 PM
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czechsix czechsix is offline
 
Join Date: Mar 2006
Location: Spring Hill, KS
Posts: 231
Default Issues with Aileron Trim System?

I installed my aileron trim system in my -14 wing yesterday. It uses the same trim kit as the -10, and I'm wondering if anyone has had problems with this setup now that there are quite a few hours on the collective RV-10 fleet. Specifically:

1) When I move the pushrod back and forth I can see the inspection plate and surrounding skin deform under the load where the trim servo is mounted. With enough cycles it looks to me like it's inviting cracks to form in the skin around the inspection opening and/or along the rivets that hold the skin to the ribs on each side of the inspection plate. Anyone seen issues in this area?

2) The springs contact the pushrod adjacent to the attachment brackets. This seems unavoidable because the brackets don't provide enough stand-off from the tube to allow the springs to attach without contacting the tube itself.
Seems like a steel spring chafing against an aluminum tube is eventually going to wear into the tube. It is also going to be difficult to inspect. I'm thinking about wrapping a piece of UHMW tape or something similar around the tube where the springs make contact to provide some protection there. Has anyone else tried this?

Thanks,
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Spring Hill, KS
RV-8A N2D #80583 - built/flew/sold
RV-14A #140017 - wings complete, empacone in progress...
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  #2  
Old 04-17-2017, 09:16 PM
TimO TimO is offline
 
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Location: Wisconsin
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I can tell you this...

I have never heard of anyone having problems with the inspection plate cracking or any other issues of that nature.

I *have* heard from one person that there was rubbing of the parts on the aileron pushrod that caused a gouge to be worn in, which sounds like what you are describing.

I don't know exactly what the difference is between yours/his and mine and many others, but I would guess it is likely the position of the rotation of that pushrod, and perhaps a little bending of the arm on the servo. When you mount the system you have to tighten the rod ends at the right position so that the pushrod can move back and forth without scraping. I would try loosening both jamb nuts on the rod, and when you do that, the rod will be rotated down towards the servo. Then spin it by hand up to a position that does not cause any interference, and have someone tighten the jamb nuts in place.

It is also a good idea to point out that this is a spot that people may want to give extra inspection every year just to verify they aren't getting any rubbing.

Question for you: Can you hear or feel anything that indicates it's scraping right now? I can't on mine and I did make sure that it wasn't scraping when I built it, but I'm personally curious to see if it is detectible.
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RV-10 N104CD - Flying 2/2006 - 1200+ hours http://www.MyRV10.com
RV-14 N14YT - Flying 6/2016 - 150+ hours http://www.MyRV14.com
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  #3  
Old 04-17-2017, 09:21 PM
BobTurner BobTurner is online now
 
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Location: Livermore, CA
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If you adjust the pushrods as above, be sure to stick a piece of safety wire into the 'inspection' holes, to be sure you have minimum required thread engagement.
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  #4  
Old 04-17-2017, 10:31 PM
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czechsix czechsix is offline
 
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Quote:
Originally Posted by TimO View Post
Can you hear or feel anything that indicates it's scraping right now? I can't on mine and I did make sure that it wasn't scraping when I built it, but I'm personally curious to see if it is detectible.
No, I don't hear any scraping when I move the pushrod back and forth...the arm connected to the trim servo is a good 1/2" away from the aileron pushrod. The only place the springs contact the pushrod is the very first coil next to where they connect to the little brackets that are pop riveted to the pushrod. I don't see any way to avoid that contact point...the springs would have to come off of the brackets at something like a 30 deg angle to avoid any contact with the tube, and no amount of rotating the tube is going to achieve that.

So while the springs aren't audibly scraping, they are still in contact and they are going to move/vibrate a little bit at least, with the steel coil pressing pretty hard against the aluminum tube. Not sure if it will take 500 hours or 10,000 hours but eventually it's gonna wear a groove into the aluminum and at some point a hole...

I think I'll put a little piece of UHMW between the spring and pushrod and call it good. Whoever owns my airplane 30 years from now will thank me
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Mark Navratil
Spring Hill, KS
RV-8A N2D #80583 - built/flew/sold
RV-14A #140017 - wings complete, empacone in progress...

Last edited by czechsix : 04-17-2017 at 10:33 PM. Reason: minor wording
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  #5  
Old 04-18-2017, 01:28 AM
TimO TimO is offline
 
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Location: Wisconsin
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Sure, I think the guy that had the scraping problem had a lot more scraping than just the spring ends. As long as you secure the UHMW tape and it can't jam anything I'd say that sounds like a good idea.
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Tim Olson - CFI
RV-10 N104CD - Flying 2/2006 - 1200+ hours http://www.MyRV10.com
RV-14 N14YT - Flying 6/2016 - 150+ hours http://www.MyRV14.com
RV-10/14 Transition Training: http://www.RVCFI.com
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  #6  
Old 04-18-2017, 05:11 AM
Tom Martin Tom Martin is offline
 
Join Date: Jan 2005
Location: Ontario, Canada
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Perhaps a longer bracket is required on the push tube, or a spring with a smaller diameter. I will take a look at this as it is on my to do list.
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CPL & IFR rated
EVO F1 Rocket 1000 hours,
2010 SARL Rocket 100 race, average speed of 238.6 knots/274.6mph
RV4, RV7, RV10, two HRIIs and five F1 Rockets
RV14 Tail dragger under construction #153

Fairlea Field
St.Thomas, Ontario Canada, CYQS
fairleafield@gmail.com
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  #7  
Old 04-18-2017, 10:09 AM
Tom Martin Tom Martin is offline
 
Join Date: Jan 2005
Location: Ontario, Canada
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The hole in the bracket is .300 from the tube. Half the hinge diameter is .340". Thus the contact with the spring and tube. I made a new bracket from 40 thou material, the original was .032 thickness. I moved the hole an extra .100" farther out. This keeps the spring close to the tube without touching.
I may have to move the servo motors he same amount if there are alignment issues.
I agree that the spring should not touch the push tube. However that extra distance out from the tube adds more torque on the new bracket which is why I went up one thickness. This is eyeball engineering only, copy at your own risk.
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Tom Martin RV1 pilot 4.6hours!
CPL & IFR rated
EVO F1 Rocket 1000 hours,
2010 SARL Rocket 100 race, average speed of 238.6 knots/274.6mph
RV4, RV7, RV10, two HRIIs and five F1 Rockets
RV14 Tail dragger under construction #153

Fairlea Field
St.Thomas, Ontario Canada, CYQS
fairleafield@gmail.com
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