View Full Version : TruTrak pitch servo installation -- a new solution?

07-13-2009, 06:22 PM
As others have noted on the forums, the TruTrak pitch servo installation in the RV-7A results in the push rod having a pretty substantial sideways angle. I'm told this is ok. But I'm also finding that even still, I'm having to add spacers between the push rod and the servo arm as well as the bell crank, to prevent the push rod from rubbing on the bell crank. I understand TruTrak recommends against adding spacers at the servo arm due to added stress on the servo. So...

I have another solution to propose, and I'd like to solicit some feedback, especially from TrutrakTech (Lucas?). My proposed solution is to connect the push rod on the opposite side (i.e. the left side) of the servo arm and the elevator bell crank. With no spacers on the servo side, and just one washer serving as a spacer on the bell crank side, the geometry actually works out very nicely, except that the push rod just barely rubs on the servo mounting bracket at the top of the flange where it's diagonally cut. (I'll venture a guess that this was actually the intent when the bracket was designed, but it just wasn't quite enough clearance.) I think I can make it work by trimming just a bit more from the mounting bracket, maybe 1/8 inch deeper, at that diagonal-cut area of the flange. I think that would provide ample clearance for the push rod, and shouldn't significantly affect the strength of the mounting bracket. Any thoughts?


Proposed solution:

07-13-2009, 07:38 PM
Roee, puzzled as to why yours would not line up. All 7s are cut from the same cloth if the spacing(ers) on the bellcrank center bolt is correct. According to the install instructions, Tru-Trak has both ball ends on the outside and shows only two #10 washers as a spacer on the bellcrank. Bolt needs to come through from the other side on the bell crank which means it has to be put on first. Mine is perfect per the instructions and I can't really fathom why yours would not be as well. There just aren't any dimensions that can vary much unless the bellcrank is not centered.


If I remember correctly, the push rods for roll and pitch are not identical in lenght but very close,.. perhaps that might make a difference.

Not sure this helps and still puzzled ??

Bill S
7a finishing with TT DII VSVG

POST SCRIPT OOPs found old picture and I have two washers under BOTH ball ends! You right ,... me wrong!


07-14-2009, 08:33 AM

Good timing on your post. I installed the pitch servo for my -7A last night, and actually did it the way you show in your picture before I realized that wasn't what the plan called for. I took it apart and mounted it per the instructions, and found I needed five washers between the servo arm and the bearing to keep the pushrod from rubbing.

I like your plan better, but I haven't checked to be sure I can get full up elevator travel before the pushrod contacts the universal head rivet in the elevator bellcrank...

Any thoughts from others?

Flying RV-4
Building RV-7A

07-14-2009, 09:48 AM
I hope this helps. http://trutrakap.com/forum/showthread.php?p=354#post354

07-14-2009, 10:04 PM
I had to put a couple of washers in there to take the angle out of the TT pushrod. A point in the TruTrak pic link.... aren't the big O.D. washers supposed to go on the OUTside of the rod ends? I thought their purpose was to keep the rod end safely in place if the rod end fails ...i.e. comes apart?

pierre smith
07-15-2009, 05:39 AM
....That's exactly the purpose you describe and the pictures from Lucas show an incorrect position for the big washers.


07-15-2009, 10:35 AM
Pierre, I second that!

Lucas, that was a bad example!

07-15-2009, 11:55 AM
My apologies on that everyone. They are the only PHOTOGRAPHS we have on hand of an RV6/7/9 pitch installation. They were sent to us by a customer. Roee is correct, it is an RV6. Our own RV9 is not here for me to take photographs of or I would have snapped some better shots. I posted these just to show on which side the pushrod was attached. I'll make a disclaimer about the washers. ;)