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  #11  
Old 04-02-2011, 03:47 PM
mcencula mcencula is offline
 
Join Date: Jul 2007
Location: Delaware, OH
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Default

I used two washers between the elevator bellcrank and the rod end bearing.
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  #12  
Old 04-02-2011, 09:00 PM
Wayne Gillispie Wayne Gillispie is offline
 
Join Date: Apr 2009
Location: USA
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Default 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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  #13  
Old 04-02-2011, 09:24 PM
D-Dubya D-Dubya is offline
 
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Location: Beaumont, Texas
Posts: 156
Default 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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  #14  
Old 04-02-2011, 10:59 PM
Lars Lars is offline
 
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Location: Davis, CA
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Default 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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  #15  
Old 04-03-2011, 09:27 AM
mcencula mcencula is offline
 
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Here are a few more pics including some that explain how I handled the 3/8 inch side-to-side offset (custom mounting bracket):

http://www.our7a.com/20100424.html
http://www.our7a.com/20100428.html

Good luck.
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  #16  
Old 04-03-2011, 01:15 PM
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DanH DanH is offline
 
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Sure wish everyone would turn those -3 bolts end for end.
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  #17  
Old 04-03-2011, 02:36 PM
Lars Lars is offline
 
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Quote:
Originally Posted by DanH View Post
Sure wish everyone would turn those -3 bolts end for end.
I'll bite- why?
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  #18  
Old 04-03-2011, 07:32 PM
mcencula mcencula is offline
 
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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>
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  #19  
Old 04-03-2011, 10:36 PM
Lars Lars is offline
 
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Quote:
Originally Posted by mcencula View Post
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>
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?
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  #20  
Old 05-20-2011, 05:00 PM
hayabusa hayabusa is offline
 
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Location: Brisbane, Australia
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Default

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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