Rear Elevator Pushrod length?

[VentusA]

With the elevators and the control stick assembly mounted, it appears that the rear elevator pushrod is about 1.5" too short to allow the elevators to be in neutral with the control sticks centered in their travel, even with the rod ends extended to their maximum. I suspect that I'm overlooking something that should be painfully obvious. Can anyone send me the correct length of the rear pushrod as a check, and/or point out the obvious error I've probably made in the assembly?

[N3UW]

Check the length of your push tube against the length called out in the Plans. Mine was too short and mike sent me out a coupler to extend it out an inch or so I think. It was just a grade 8 threaded rod and coupler. I welded it so that it would not unthread. I can take a photo if you would like

[Bcone1381]

An Engineering notice was published because "....The pushrod is not discussed in detail..." in the plans. Below is a link with that information.

http://bearhawksafety.com/Patrol/changeoct10a.html

With that being said, length given is "... to fit" .

I'm curious, if you install the pushrods with the threads inserted at the minimum acceptable thread engagement to maximized the pushrod length, then what is the result you are seeing?

Another question....what is the minimum thread engagement for rod end bearings?

[N3UW]

Here is a post where the issue was discussed in the past.

https://bearhawkforums.com/forum/bearhawk-patrol-quickbuild/69866-elevator-rigging-issue

this was an issue with some quick build fuselage kits.

this was the email I received from Mark Goldberg at the time regarding this issue.



“Hi John. The reason your long push tube seems too short is because it is too short. Bob made a mistake on the plans and specified the wrong rod end bearing. GMM-3M-680. .500 wide ball.

When we changed to the correct rod end bearing, GMM-3M-670, (7/16 wide ball) the shaft on the correct rod end was 1/2" shorter than the other one. Times two. So the pushrod which had worked well for a long time all the sudden was too short.

I will send you a piece of Grade 8 threaded rod in 3/8"-24. And a female threaded rod end bearing. Use the threaded rod and rod end on the forward end of the push tube. Extend it as much as needed with the threaded rod with a jam nut on both ends of the threaded rod. I should take about 1" or a little more of additional length.

Bob has approved this fix. There is another option but it involves welding. Let me know if that interests you rather than what I described above. Sorry for the problem John. You are the 3rd Patrol customer to find this. So me and Bob have kicked around this subject. Mark”

[VentusA]

Thanks N3UW and Bcone1381 for the quick responses that pretty much completely answered my question.

Bcone1381: With the rod ends installed with the proper thread engagement, the pushrod assembly about 2.0 inches short.
I've always used 1.5 shank diameters as the minimum thread engagement for a rod end, with 1.0 diameters as a minimum in low load/non critical locations. I think the "real" minimum engagement length to develop the full load carrying capability of the assembly depends on both the thread pitch and the material properties of two mating parts...

[Dpearson]

Regarding minimum thread engagement: I was pondering this very topic while working on flap and aileron linkages a few days ago. On the A model (and maybe others?) the male rod end screws into a nut welded to the end of a hollow tube. I believe the ID of the tube is > the major diameter of the rod end thread. So any thread engagement beyond the thickness of the nut adds no additional strength. Dissenting opinions welcome!