Dynon certified install on a Cessna 172- Auto pilot roll slip and other frustrating issues...

Douglas

New Member
Joined
Sep 21, 2019
Messages
4
I recently spent a great sum of money to have an absolutely beautiful dual screen Dynon HDX panel with all the bells and whistles installed in my 1977 Cessna 172. I must say, although it is beautiful to look at and I am pleased with many of the awesome features, I have been plagued with problems from the moment we powered up the system.
First let me say I feel like I chose a reputable shop with many years of Dynon experience to do the install. In fact, I chose this particular shop not because they were on Dynon’s “certified” installers list, but because they were the biggest proponents of Dynons equipment. Their sales pitch was refreshing in that they did not try to talk me into installing Garmin equipment like two of the big “high volume installers” that were on Dynons approved list...
My objective here is not to talk poorly of anyone, but to instead just to give you some interesting background info and let you know that I was a believer in Dynons stuff after trying it out at Sun N Fun this year. After researching it online and talking to a few current experimental owners and A&P’s, I wanted a dual screen Dynon system, nothing else...
After going through the research process, I do find it odd that some of the bigger
high volume certified installers Dynons choosing to work with are not always actively promoting their equipment...It’s really kind of weird... and thinking back, I hope I made the best choice...
Anyway,
After talking to 3 different shops I chose the one that although was not the least expensive, was the most knowledgeable of the task ahead. It seems like this was the type of shop that should be a “certified dealer”. Just my opinion...
Fast forward a couple of months and the panel is in and ready to go...
So the 1st issue was a faulty com radio, after days of phone calls with dynon my tech literally built a test bench for the radio and together they came to the conclusion Dynon had sent a faulty radio...
Fine, no big deal, in my opinion poor quality control, but Dynon overnighted a new radio, problem solved.
Simultaneously my tech discovered that one of the soft keys located at the bottom of HDX screen #1 was also faulty and dynon quickly overnighted a new screen, again, come on guys, where’s the quality control? At least they were quick to respond and send a new screen. I do appreciate that...
That brings me to the auto pilot...
After carefully following Dynons calibration booklet, flying multiple flights and spending hours literally raising and lowering, torque, gain, sensitivity, and the rest, I’m still gettting the roll slip indication a couple times a minute, the auto pilot will track a course but basically methodically rocks back and forth and this is the best I’ve been able to get it to do. The high point is the vertical guidance has been good since day one.
This brings me to my biggest question...
Given my brief experience with Dynon components and what seems to be weak quality control, is it possible I’ve got a bad servo? I guess the part I don’t understand, is that Dynon has spent all this time and effort certifying this system for 172’s and Cessna 172s are all rigged basically the same, shouldn’t the pre determined settings sent to upload with the new system just work right out of the box? I’ve spent hours reading on this forum about people with RVs trying to figure out many of these same roll slip and tracking issues but it just seems like when you pay $2000 extra for an STC this stuff should be somewhat ironed out...
Anyway, has anyone on this forum experienced similar issues with a 172 install? If so any recommendations?
I apologize for the long intro but thanks in advance for taking the time to read it...
Sincerely, Doug
 

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Raymo

I love aviation!
Joined
Apr 25, 2016
Messages
682
Location
Richmond Hill, GA
Sorry to hear of your dilemma.

A couple thoughts. First, the radio is a re-branded Trig and are very solid. Could the shop have accidentally hit the transmit button while not connected to an antenna? If they did, it likely fried the transmitter. Second, does your plane have roll trim and does it fly level without the autopilot? It should and must for proper functionality. If it does, I'd suspect the shear pin in the servo may be broken, which could also have been caused by the shop. The shear pin can be easily replaced and Dynon's support will help.

I've had the system installed in my RV-7A for 3.5 years. It took a while and lots of flights to tweak the pitch servo settings but roll has never been a problem from day one. That said, the control forces are much greater in your plane than mine.
 

Douglas

New Member
Joined
Sep 21, 2019
Messages
4
Hey Raymo,
Thanks for the info.
No Transmit buttons installed at radio installation so no chance of a accidental transmit...
Plane flys nice and straight, so im hoping the shear pin may be the answer...
Putting it back in the shop tomorrow to examine the servo a little closer.
I appreciate your response.
 

Dr.M

New Member
Joined
Jul 25, 2019
Messages
8
Douglas - I have just finished my certified Dynon install on my C172L. So far, so good on infant mortality issues (knobs, screens, etc - I didn't use the Dynon comm). But I do agree with you on autopilot settings (gain, sensitivity, etc.). Dynon should provide those as part of their research for the STC. I, like you, had to fiddle-fart with those settings in-flight to get reasonable autopilot tracking behaviors. It is ok now...but I am not sure that my autopilot performance is optimal. Still tweaking.
 

kellym

I love flying!
Joined
Sep 29, 2013
Messages
93
Douglas - I have just finished my certified Dynon install on my C172L. So far, so good on infant mortality issues (knobs, screens, etc - I didn't use the Dynon comm). But I do agree with you on autopilot settings (gain, sensitivity, etc.). Dynon should provide those as part of their research for the STC. I, like you, had to fiddle-fart with those settings in-flight to get reasonable autopilot tracking behaviors. It is ok now...but I am not sure that my autopilot performance is optimal. Still tweaking.
I agree that default settings from the certification aircraft should be supplied. However, recognize that the fleet of C-172s varies widely on force and travel needed in the controls...both by model and age/wear/tear. Earlier models needed much less force and IIRC somewhat less travel than later models. Later models had significantly higher forces required as options and weight increased. Control cable tensions and pulley condition all affect what is needed. In the mid-70s flight schools often had both old high time early model C-172s and some brand new ones. Moving between them from day to day as availibility dictated would be eye opening as to the differences. Thus it is not surprising that some tweaking is required for the calibration.
 
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