AP Servo Push Rod misalignment.

ZK-LCM

Member
Joined
Aug 26, 2010
Messages
36
Location
New zealand
I am nearly finished my RV6 which has a D100, D120 & a Dynon Autopilot . This has been a very slow project, way down in new Zealand, & I installed the Dynon AP hardware approx. 6 years ago to Dynon document 101046-001 Rev D. Page 7 of said document specifies that the Aileron servo is 5.875" aft of the Fuselage frame web. The drg isn't clear exactly which face of the frame this 5.875" dimension applies to & I see that this drg has been eliminated from later versions of the document.
Having only recently fitted the wings and aileron pushrods I found that the pushrod outer bolt rubbed against the aileron pushrod at full aft & RH stick.
Hence I moved the servo approx 0.25" further aft, which gives me a min clearance between pushrods of 0.25" over a wide range of travel.
Unfortunately this also results in a pushrod misalignment of approx. 10.4 degrees at full aft & RH stick travel. See photo.

Does Dynon have any figures for the maximum misalignment that these pushrods are allowed? My experience is that they are designed for about + 7.5 degrees.

Also, I believe that my elevator pushrod is too short, being 4.0". Dynon's instn drg that I worked to shows the overall pushrod length as 6.0" center to center, which agrees with my measurements. But IMHO that leaves only 0.5" of thread engaged at each end. That may well be satisfactory but i would prefer 3/4" of thread engagement at each end, i.e. a 4.5" to 5" long pushrod. Your feedback would be highly appreciated Thank you.
 

davedubb

Member
Joined
May 10, 2010
Messages
69
According to the rod end spec sheet, the allowable off axis angle is 13.5° so your angle of 10.4° is within the tolerance. Verify that the rod end does not bottom out on washers or any other hardware before considering it an acceptable installation. If you are still not comfortable with the clearance you could consider inserting the AN3H-10A bolt from the opposite direction and get more clearance or use a low profile AN364-1032A nut and a shorter AN3 bolt.

As far as the elevator pushrod, if you are not comfortable with the amount of thread engagement then simply screw the rod end into the pushrod until you are comfortable. Your additional 1/4" does not seem unreasonable. There is no requirement for the servo arm to be perpendicular to the servo body when the flight control is neutral. You will need to verify that the arm does not rotate past the +/-60° limit (a properly installed limiting bracket will help here) and that there is no other interference with the installation. Some builders have had issues with the rod end contacting the elevator pushrod here but with some adjustment they get the desired clearance. As a side note, there are hundreds...if not thousands of pitch installations on RV6, 7 & 9's using that installation set up with tens of thousands of flight hours on them. You should be fine.
 

ZK-LCM

Member
Joined
Aug 26, 2010
Messages
36
Location
New zealand
Thank you for the excellent & prompt reply.

Is it possible to obtain a copy of the Rod End spec sheet??

Thanks
 

kellym

I love flying!
Joined
Sep 29, 2013
Messages
272
Be sure that you are testing with some one at the controls. w
With the seat empty you will get results that can't happen in real life.
 

davedubb

Member
Joined
May 10, 2010
Messages
69
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