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Old 09-09-2019, 06:27 AM
Reflex Reflex is offline
Join Date: Jan 2015
Location: Kansas
Posts: 144
Default Question on Bellcrank/Autopilot

When installing my roll servo, I discovered a discrepancy between Van's instructions and Garmin's instructions. Drawings are below:

Van's has you put a nut plate in the bellcrank for the bolt that holds the autopilot pushrod. This means that the head of the bolt is on the bottom of the assembly and therefore has gravity as an enemy. In addition, I'm not sure about using a nutplate and threads to hold a bolt that is responsible for holding a moving/rotating part. However, I've found that Van's usually has a pretty good reason for nearly everything they design. Drawing below:

Garmin has the bolt inserted from the top and is capped with a nylock nut on the bottom. This allows the bolt to rotate (if needed) and seems proper. I hesitate to install using this method until I understand why Van's has a different approach. Drawing below.

Most of the web sites I've visited for the RV-14 have the bellcrank/pushrod installed as per the top picture. Seems to me that the Garmin design is better.

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Old 09-10-2019, 02:13 PM
Jake14 Jake14 is offline
Join Date: May 2014
Location: Seattle
Posts: 262

I wondered about the suitability of a nut plate for that application as well, mainly due to the moment applied by the servo pushrod to the extended arm of the connection to the bellcrank. I considered using a 1/2 in diameter spacer instead of the thin sleeve to make a more rigid connection to the bellcrank, but decided against it.

So far it's worked ok (250 hours)

Here's the Dynon version (for an RV-10, but very similar to a 14). See pgs 7-10 in this pdf:
RV-14A #140158 flying

Last edited by Jake14 : 09-10-2019 at 02:32 PM.
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Old 09-10-2019, 08:43 PM
PCHunt PCHunt is offline
Join Date: Feb 2007
Location: San Diego, CA
Posts: 1,610

In both the Garmin and Vans installations, the bolt and nut are tightened down to proper torque specs, and the bolt does not rotate, and shrould not rotate. Both installation methods use friction locknuts, in one case it is a platenut, and in the other case it is a regular nyloc.

The rotation occurs in the bearings of the rod end.

If the bolt needed to rotate, you would need a cotter pin and castle nut.

I suspect that the Vans installation will be easier to both install, and later remove if necessary.

My 2 cents. [BTW, why can't we do away with pennies and nickels, and round off to the nearest ten cents.....]
Pete Hunt, [San Diego] VAF #1069
RV-6, RV-6A, T-6G

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Old 09-11-2019, 06:57 AM
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Walt Walt is offline
Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,386

Personally I would have a bit more confidence with the nut than the nutplate. The cyclic load on the bolt/nut will be more than just tension.
Walt Aronow, DFW, TX (52F)

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