Aileron Servo placement

U2fletch

U2fletch

Well-known member
Right wing is a good place to locate aileron autopilot servo, so I would like to see any pics of their installation. I have a convenient spot in mind, but a clean attachment to the bellcrank is eluding me. Would be nice to use the same hole in the arm as the pushrod, but there is a clearance issue with the support tube.
 
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I mounted mine under the copilot seat. It is a very accessible place and a good place to tie into the Skyveiw network.
 

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Brilliant! I initially dismissed the capstan idea because I thought I needed to get to both cables. Nope, it’s a closed loop you just need to grab one.
 
I know Virgil is working on a adapter plate to mount the servos. Not sure the status as I am not to that point.
Travis
 
This is the pitch and yaw servo locations, at the last fuselage station. Pitch is a pushrod to the elevator bellcrank and Yaw is bridle cables to each rudder cable.
 
Thanks for sharing the photos! I'm planning to follow this general approach on my BH4 build. A couple of questions:
1. Do you know material thickness and spec for the mounting plate? 2024-T3 or ???
2. I was planning on a capstan + pulley approach for connecting the yaw servo to the rudder cables, using one bridle cable with a ball in the center and bridle clamps (Vans CS-00022) to connect the bridle cable to the rudder cables. What I see here is one long arm, which I imagine is long enough to line up the bridle cables at each end with the rudder cables as they exit the fairleads. I think this is quite elegant, but I'm wondering if the GSA28 servo will have enough torque to overcome the air loads on the rudder in my application. The RV-10/14 installation is similar, with a total arm length of about 4.75" according to https://vansairforce.net/threads/vans-yaw-servo-mount.153870/post-1258276 . In my BH4, the arm would be 9" long to line up with the rudder cables. The max torque spec of the GSA28 Servo is 60 in-lb (from the G3X Install manual), yielding 60/4.5=13.3 lb maximum "pull" on whatever rudder cable needs pulling. The rudder pedals give a ~2:1 advantage, so 13.3 lb of cable force is equivalent to 6.7 lb of pedal force. Does anyone know if this is sufficient for actual control surface loads the autopilot will encounter in flight?
 
Here is a pic of my final installation of the aileron servo. 20250705_122130_resized.jpg 20250705_121944_resized.jpg

I used .062" plate that I had sitting around. Probably 6061. With the flanges and riveting to the ribs, it is very strong.
 
I just received the 3 axis ap mounts from Bearhawk. Nicely made. Haven't installed yet.
Travis
 

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Travis' picture shows the setup that Virgil used for both Erin and Paul's plane as well as John McCardle's. John's BH5 is the one that Virgil took a ton of BH5 completion photos and put them up on the Bearhawk website. It shows the detail for the aileron, pitch and yaw servos. Aileron in the right wing, pitch and roll in the rear fuselage. You can buy his CNC'd kit now for $900.

I'm still debating where to put my servo's - under the pilot / co-pilot seat (for pitch and roll) with yaw on the firewall OR using a similar approach as Virgil's current system. Note that Virgil put them under his seats for his BH5 build several years ago.

Question to those that put them under their seats - how has it been performing? Any issues with kids / dogs kicking on them or stuff getting crammed into them under the seat? Would it do it again?

The two downsides of the wing / rear fuselage are running the wire and maintenance (yes, there are access panels but still a hassle for preflight checking).

What say ye all of our autopilot friends?

Thanks much!
 
We have tried several locations and arrangements for the autopilot servos. The current location is yaw and pitch in the tail roll in the right wing. We have a full bracket kit for this and have been very happy with it so far. The under seat mounting tends to lag pretty bad due to the length of cables in the system. Our current configuration is extremely precise and we have been really happy with it, we now have four of these systems out flying with good results. The servos are direct pushrod to the aileron and elevator and a small cable loop for the yaw damp.
 
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