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04-02-2011, 03:47 PM
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Join Date: Jul 2007
Location: Delaware, OH
Posts: 435
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I used two washers between the elevator bellcrank and the rod end bearing.
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Mike Cencula
RV-7A (fuselage)
www.our7a.com
Betcha my pile-o-scrap is bigger than your pile-o-scrap.
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04-02-2011, 09:00 PM
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Join Date: Apr 2009
Location: USA
Posts: 1,499
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Also install a spacer in the bellcrank
I don't know why this is not mentioned in the instructions. I mentioned it in a previous post and got no replies. In your picture it is easy to see the bowing inward due to torquing the bolt to specs. You want to torque down most hardware onto a spacer/bearing/washer and not a 1/16" gap. It won't hold the torque and will loosen over time especially on something with so many load reversals even though it is a relatively small load.
On the issue of the nut hitting...on mine the hole was drilled about 1/4" from the centerline and has about a 5/16" spacer. Of course the RV-10 has the torque enhancer so slightly different design.
In any case, you could install equal length spacers made from 5/16" tubing and longer bolts.
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Good judgment comes from experience, and a lot of that comes from bad judgment.
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04-02-2011, 09:24 PM
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Join Date: May 2009
Location: Beaumont, Texas
Posts: 156
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I agree!
I think you've answered your main question, as the two washers should do the trick. But others have chimed in with two more concerns regarding the spacer between the bell crank halves and the thread engagement on the rod. I agree with their concerns.
Just a suggestion, but I replaced the Van's designed spacer with a slightly larger one that was essentially a triangular shape. That let the two original rivet holes hold the spacer in place, while allowing the bolt for the A/P arm to go through the tip of the triangle spacer sandwiched in there. Not sure if that makes sense, but picture a triangle pointing down. Just a suggestion.
Regarding the arm length, make a new longer aluminum arm if you don't have proper thread engagement. I would think TruTrak sent the proper length material, but there's always an outside chance that it wasn't measured correctly. Not trying to insult your building skills or TruTrak, but it's worth checking. Even though I've never cut something to the wrong length! 
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David Welsh
Beaumont, TX
RV-7 N413WD
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04-02-2011, 10:59 PM
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Join Date: Nov 2005
Location: Davis, CA
Posts: 1,156
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some pix of an RV-7 installation
Not the greatest, but hopefully a bit of help. Link is set to TruTrak spec length. I spaced both ends to get it reasonably parallel to the longitudinal axis of the fuselage with minimal standoff distance.

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Lars Pedersen
Davis, CA
RV-7 Flying as of June 24, 2012
960+ hours as of June 30, 2020. Where did the time go?
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04-03-2011, 01:15 PM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Sure wish everyone would turn those -3 bolts end for end.
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Dan Horton
RV-8 SS
Barrett IO-390
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04-03-2011, 02:36 PM
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Join Date: Nov 2005
Location: Davis, CA
Posts: 1,156
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Quote:
Originally Posted by DanH
Sure wish everyone would turn those -3 bolts end for end.
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I'll bite- why?
__________________
Lars Pedersen
Davis, CA
RV-7 Flying as of June 24, 2012
960+ hours as of June 30, 2020. Where did the time go?
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04-03-2011, 07:32 PM
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Join Date: Jul 2007
Location: Delaware, OH
Posts: 435
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If I recall Dan's previous post on the subject, I believe his argument is that the bolt is being used as a cantilever beam and the strength of the bolt is better using the grip diameter than the minimum diameter of the thread.
Although he is correct that the bolt strength is best in the grip range, I don't think the concern is applicable in this case. As long as the bolt is tight, the bolt won't be in bending...it'll be in (single) shear.
Even if the nut were to loosen up, causing the bolt to be cantilevered, it'll still be cantilevered on the grip diameter by the edges of the holes in the bellcrank. Of course the aluminum would get wallowed out by the bolt, but I don't think the threaded portion could ever see anything but the tension due to tightening.
Maybe I misunderstood Dan's point, though. <shrug>
__________________
Mike Cencula
RV-7A (fuselage)
www.our7a.com
Betcha my pile-o-scrap is bigger than your pile-o-scrap.
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04-03-2011, 10:36 PM
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Join Date: Nov 2005
Location: Davis, CA
Posts: 1,156
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Quote:
Originally Posted by mcencula
If I recall Dan's previous post on the subject, I believe his argument is that the bolt is being used as a cantilever beam and the strength of the bolt is better using the grip diameter than the minimum diameter of the thread.
Although he is correct that the bolt strength is best in the grip range, I don't think the concern is applicable in this case. As long as the bolt is tight, the bolt won't be in bending...it'll be in (single) shear.
Even if the nut were to loosen up, causing the bolt to be cantilevered, it'll still be cantilevered on the grip diameter by the edges of the holes in the bellcrank. Of course the aluminum would get wallowed out by the bolt, but I don't think the threaded portion could ever see anything but the tension due to tightening.
Maybe I misunderstood Dan's point, though. <shrug>
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Makes sense, in principle, though I fear as much for the cantilevered shaft of the servo as for the bolt that's transmitting the load to the shaft. But I also have no sense of the loads involved, this being my first experience with an autopilot and related servos. I'll admit to looking at the whole thing with a somewhat jaundiced eye. Sure hope it works...
In my case I selected fasteners long enough that a washer was required under the nut to prevent it from bottoming on the thread. That doesn't quite prevent the thread, as opposed to the shank, from being subject to a bending load. I s'pose if that's the issue though, not hard (except on my feeble back) to turn them around.
How much torque can a servo such as these develop?
__________________
Lars Pedersen
Davis, CA
RV-7 Flying as of June 24, 2012
960+ hours as of June 30, 2020. Where did the time go?
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05-20-2011, 05:00 PM
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Join Date: Feb 2011
Location: Brisbane, Australia
Posts: 37
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Post removed due to the issue already being raised in this thread. Computer glitch didn`t show page two.
Last edited by hayabusa : 05-20-2011 at 05:02 PM.
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