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Jim0258
 Post subject: Autopilot Retrofit?
PostPosted: Wed Jun 03, 2020 9:09 pm 
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It's been a long journey getting N7077J back together. I'm getting ready to install Dynon hardware and was planning to install a two axis autopilot down the road. I had assumed that I'd find a good way to retrofit the servos, but now I'm not so sure. The roll servo seems to be the biggest challenge to me. The only idea I've be able to come up with is to mount the roll servo on the inside of the outer wing on the inboard rib. I'd have to add an inspection panel to get in there and add a doubler for the servo. I would pass the control arm through the rib/doubler between the center/outboard wings and run the push rod to the bell crank with a longer bolt to accommodate the push rod from the servo. The total travel of the existing push rod to the aileron is ~2.7 inches (seems OK with the Dynon servo). It looks like the pitch servo could be mounted below the passenger seat with the push rod passing between the aft wing spar BH and the bottom of the seat attaching to a bracket I could add to the right stick fork bolt.

I'm wondering if anyone has added roll and pitch autopilot capability to a T-18 and/or if anyone has any suggestions? I don't plan on making the change until I have the plane flying again, but the immediate issue for me is whether or not to leave space in my panel for the Dynon autopilot control panel. It will be a little tight, but I can make it work. However, if I'll never add it, it would be easier to redesign the instrument panel without it. I just received my first 10 inch Dynon HDX screen and am about to start cutting the IP.

Thanks,

Jim Harter

I tried to attach some pictures, but it didn't seem to work.

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fytrplt
 Post subject: Re: Autopilot Retrofit?
PostPosted: Thu Jun 04, 2020 5:58 am 
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Jim,
Most of us put the roll servo on the panel in the aft part of the spar box under the passenger seat. The arm sticks through a hole. The control rod goes to a longer bolt on the walking beam on the pilot side. A pair of ball bearing rod ends allows for the necessary rotational movement. The pitch servo is under the baggage floor (if you have one) and connects via a link attached to a collar on the push pull tube. Trutrak makes a nice kit for all of this.

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Bob Highley
N711SH
SN 835
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Ryan Allen
 Post subject: Re: Autopilot Retrofit?
PostPosted: Thu Jun 04, 2020 6:55 am 
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I retrofitted a 2 axis Dynon autopilot to my plane. I did as Bob described. One of the best things I ever added to my plane.


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bfinney
 Post subject: Re: Autopilot Retrofit?
PostPosted: Sat Jun 06, 2020 3:35 pm 
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I'm currently installing a Garmin G5 display with 2 axis autopilot.

This is my pitch servo mounting, it's on the aft side of the aft bagage bulkhead -571. The pitch tube collar is 0.063 aluminum lined with 0.032 rubber strip.
Image

The roll servo mount is on the aft side of the -592 bulkhead under the pilots seat. The pushrod attaches to the walking beam on the pilots side.
Image

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Bruce Finney
N18JF T-18C #262
Auburn, WA USA


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Ryan Allen
 Post subject: Re: Autopilot Retrofit?
PostPosted: Sat Jun 06, 2020 4:13 pm 
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Bruce, that looks good. Are those home made straps that bolt around the push/pull tube?


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bfinney
 Post subject: Re: Autopilot Retrofit?
PostPosted: Sat Jun 06, 2020 4:47 pm 
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Yes they are. I didn't know about the Trutrac kit, Bob didn't tell me until after I had done my installation. 8)
Note: I haven't flown with the autopilot yet I'm still doing the install.

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Bruce Finney
N18JF T-18C #262
Auburn, WA USA


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Ryan Allen
 Post subject: Re: Autopilot Retrofit?
PostPosted: Sat Jun 06, 2020 6:04 pm 
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Ha! Well, its looks good. Also better than my solution, so I'm copying you!


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bfinney
 Post subject: Re: Autopilot Retrofit?
PostPosted: Sun Jun 07, 2020 2:18 pm 
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all right, plagiarism the sincerest form of flattery 8)

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Bruce Finney
N18JF T-18C #262
Auburn, WA USA


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fytrplt
 Post subject: Re: Autopilot Retrofit?
PostPosted: Sun Jun 07, 2020 3:13 pm 
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Very similar to mine. Make sure it in no way can go over center. I had use a longer arm, no more than 45 degrees of travel from center position.

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Bob Highley
N711SH
SN 835
KLAL


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bfinney
 Post subject: Re: Autopilot Retrofit?
PostPosted: Sun Jun 07, 2020 3:33 pm 
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Joined: Thu Oct 22, 2009 2:24 pm
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On my Garmin servos with the stop bracket in place and the long crank arm the travel is +-47.6 deg, the short arm is +-50 deg. I have the long arms and the stop brackets are installed. I also have full stick travel in all axis.

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Bruce Finney
N18JF T-18C #262
Auburn, WA USA


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DrParachute
 Post subject: Re: Autopilot Retrofit?
PostPosted: Tue Jun 09, 2020 7:19 am 
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Joined: Tue Nov 27, 2018 9:54 am
Posts: 9
So excited to see this post Jim. I am currently replacing the panel in the 2+2 to remove all steam gauges and replace with GRT EFIS panels. I am working on the panel upgrade now, and will be installing servos next year. Please keep sharing your progress (and thanks all for the input and especially the photos). Can't say enough about how amazingly helpful the Thorp community is!

Travis Fields
N249R (2+2)
KLXT


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dickwolff
 Post subject: Re: Autopilot Retrofit?
PostPosted: Sun Jun 14, 2020 1:08 pm 
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Joined: Tue Nov 24, 2009 7:40 pm
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This looks interesting. Similar to what Andrew Barker (TruTrak) developed at one point but never followed through.

www.xflighttech.com

Assembled in USA.

D


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bfinney
 Post subject: Re: Autopilot Retrofit?
PostPosted: Mon Jun 22, 2020 12:33 am 
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Finally remembered to take a photo of the roll servo push rod connection to the walking beam.
Image

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Bruce Finney
N18JF T-18C #262
Auburn, WA USA


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