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RV4 Autopilot Servo bracket

Scott Hersha

Well Known Member
I have a not quite new, to me, (Aug 2019) RV4, and I would like to add a 2 axis autopilot. I have GRT avionics installed, so I’m looking at their servos. Unfortunately, I haven’t been unable to find a bracket for my roll control Servo. I have researched and found numerous installations for this, and have concluded that mounting the Servo in the cockpit area is the best solution. The wingtip install seems a little too difficult, and less robust/serviceable. I’m considering the Servo mount under the seat area, but I have footwells, so moving it aft creates difficulties with access, but it’s doable. However, this type install requires a bracket for the roll torque tube - basically two half circle brackets that capture the torque tube and supply a connection to the autopilot control rod. I haven’t been able to find anyone that has this torque tube bracket. Stein doesn’t have it. I contacted TruTrak/Bendix/King and they sent me to Mid-Continent Avionics. They sent me to their “TruTrak Expert”. I had to leave a message, and he/she hasn’t gotten back to me. So, what I am seeking is someone that has one of these torque tube brackets, or knows where to get one. If I have to, I’ll fabricate my own, but it sure would be easier if someone here has one they don’t need. The bracket supporting the Servo is easy enough to make, but the round bracket that captures the round torque tube is a bit more challenging.

I would also consider a roll Servo attachment forward of the wing spar, as has been done on other RV4’s, and a couple Rockets, but not sure how this connects to the torque tube. This has been done before, but the posts are so old that the pictures are no longer available. If anyone has a picture of this installation, please forward it to me.

Thanks for your help/recommendations. This is the part of homebuilding that I really enjoy, but since it involves critical flight controls, I want to be safe and not do something that might be unsafe ( I understand the autopilot over center limitations).
 
Jim,
Thanks for the response. I have that diagram, and that?s what I?m looking for. The control arm is easy to make, I?ve made several. What I need is the round two part bracket that attaches to the torque tube. I don?t think anyone makes it anymore. I?m sure I can make it - not easy for me - but I would rather buy one if its available somewhere. TruTrak, who used to make this, is no more. They are now Bendix/King, and their focus on EAB seems a little disconnected.

Thank you for responding. If you know where I could get other installation parts, please let me know.
 
Tom,
Wow!! That is way better than what I was looking for. If my tube is 1.5?, I?m getting it. I?ll ?whittle? mine down a bit too, but it looks like the perfect solution. Did you drill a hole through it and the tube for a pulled rivet to secure it? This looks like a better solution than the TT solution.

Thanks
 
I recently made mine, it is a single piece. I took the circumference of the tube I made the 90? bends first about a 16th of an inch shorter than what was needed so that I knew it would be tight. The metal does not need to be overly thick so it's easy to wrap around a pipe the same size and it will easily flex enough to get around the torque tube. I chose to do 2 tabs with the link end between. After finding the spot I wanted I added a pop rivet to keep it from moving. It was a lot smaller job than I figured it would be.
 
Tom,
Wow!! That is way better than what I was looking for. If my tube is 1.5?, I?m getting it. I?ll ?whittle? mine down a bit too, but it looks like the perfect solution. Did you drill a hole through it and the tube for a pulled rivet to secure it? This looks like a better solution than the TT solution.

Thanks

I drilled through the bracket and the torque tube and tapped the bracket with a 10-32, used a drilled head bolt for safety wire. If you go this route, be warned the bracket is a lot bulkier than it looks. Whittling might not be the best choice of words....I had to take a lot of material off of it. It turned out nice though.
 
Tom,
What material did you use to make this bracket? I assume a mild steel. What thickness? This sounds easier, and close to what has worked in the past.

Thanks
 
In the installation picture, below, the torque tube fitting is located so that you'd get asymmetric results.

cR2iMMe.jpg


Normally, both control arms, the torque tube one and the servo one, ought to be close to perpendicular to the pushrod.

As it's shown, it could easily go over center and even drive it backwards.

Dave
 
My installation is IAW the drawing in the previous post using Tru Track supplied torque tube attachment fitting. Works like a champ--can't over-center based on geometry. It is necessary to relieve the 6060 angle slightly to cut the hole for the arm, however the amount of material removed is within repair margin. I don't have footwells, however. Some folks have put it further aft and that will work as well (I believe Axel did that, so he has more SA), but the floor would have to be screwed in place (or an access panel built) to provide access to the servo at that location.

Cheers,

Vac
 
Thanks Vern. I was thinking about trying something like this, but wasn?t sure what it would look like. Now I know. This would be the easiest place to mount the Servo in my airplane. I?ll have to see if I can get that torque tube out of my finished airplane to modify it. Not sure if the opening in the spar web is large enough to remove it.
 
Actually, after studying your pictures some more it looks like this is mounted at the aft end of the torque tube, at the co-pilots stick location. I was thinking about the same thing mounted at the forward end of that torque tube. Having access to that area would require me to drill out that area of the floor and make it removeable, which I may have to do anyway.

Thanks.
 
Finn and Vince - that’s what I was hoping to get a picture of. It’s a little crowded there, but very accessible and easy to wire. These pictures are worth a thousands words. The bracket drawing helps a lot too. And I like the bent stick too, since I moved my front seat back almost 3”.

Thanks
 
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