VansAirForceForums  
Home > VansAirForceForums

-POSTING RULES
-Advertise in here!
- Today's Posts | Insert Pics

Keep VAF Going
Donate methods

Point your
camera app here
to donate fast.

  #1  
Old 05-06-2016, 05:07 AM
Derek Derek is offline
 
Join Date: Jan 2011
Location: Sydney, Australia
Posts: 86
Default Dynon AP Servo Issue- maybe

I've be chasing an AP altitude hunting issue for a while, i won't bore you all with the details, but I will say it's caused me a phenomenal amount of frustration trying to fix it, more so because for the first 30 hours of my aircrafts life the AP worked faultlessly. Additionally, I can trick the AP into holding altitude by trimming in 3 clicks of pitch trim.

Today I decided to check for slop in the linkages, once again. All my linkages are good ( no slop) not surprising since my aircraft is new 100hrs TTIS, however on closer inspection of the AP Servo arm I found some slop.

I'm guessing (hoping) that this amount of slop is unacceptable ??

http://www.youtube.com/watch?v=g2zZxFoLaj0&sns=em
Reply With Quote
  #2  
Old 05-06-2016, 05:19 AM
Jesse's Avatar
Jesse Jesse is offline
 
Join Date: May 2005
Location: X35 - Ocala, FL
Posts: 3,683
Default

There should be absolutely no slop in that position at all. It should be tight. I don't know that that would cause it to porpoise in flight, though. Usually a porpoise is caused by an activity setting being a little off. If it is a "twitchy" hunting, then turn down the activity. If it is a "wallow" hunting, then turn it up a little.

Sorry for the use of such technical terms.
__________________
Jesse Saint
Reply With Quote
  #3  
Old 05-06-2016, 05:43 AM
blueflyer's Avatar
blueflyer blueflyer is offline
 
Join Date: Nov 2008
Location: Shreveport, LA
Posts: 1,050
Default

did the shear pin break in the servo arm (giving you the slop)?
Reply With Quote
  #4  
Old 05-06-2016, 05:45 AM
Jesse's Avatar
Jesse Jesse is offline
 
Join Date: May 2005
Location: X35 - Ocala, FL
Posts: 3,683
Default

No, you can see the shear screw in the video. The nut holding the arm on the servo is loose.
__________________
Jesse Saint
Reply With Quote
  #5  
Old 05-06-2016, 10:29 AM
dynonsupport's Avatar
dynonsupport dynonsupport is offline
 
Join Date: Jun 2005
Location: Woodinville, WA
Posts: 1,499
Default

As Jessie correctly says, there should be no slop there. That will cause hunting for sure, since when the servo changes direction, the first few moves are just taking up that slop. So I think you found your culprit.

We've looked at the video, and we're pretty sure that shear screw is broken. The head is stuck in the output arm, so it's still there, but it's likely sheared. It appears to tilt with the arm which it should not. The simple test is to engage the AP on the ground and see if you can move the pitch controls up and down without the servo really fighting you.

Once the shear screw breaks, then other wear occurs, and you get some of that tilting.

Give us a call or email and we can get you a new shear and instructions on how to tighten it all up.
__________________
_______________________
Dynon Avionics
support@dynonavionics.com
425-402-0433
www.DynonAvionics.com

Last edited by dynonsupport : 05-06-2016 at 11:09 AM.
Reply With Quote
  #6  
Old 05-06-2016, 01:25 PM
Derek Derek is offline
 
Join Date: Jan 2011
Location: Sydney, Australia
Posts: 86
Default Thank you

for all the replies to my AP issue.

Here are my next steps:

Perform the AP ground test as suggested by our good friends at Dynon Support and if it fails, remove the AP arm and replace the shear pin.

Thinking out loud here. We all know now that the servo castle nut needs tightening, whilst I'm down there doing this can I just remove the servo output arm and visibly check if the shear pin is broken ?
Reply With Quote
  #7  
Old 05-06-2016, 01:44 PM
blueflyer's Avatar
blueflyer blueflyer is offline
 
Join Date: Nov 2008
Location: Shreveport, LA
Posts: 1,050
Default

Yes, you can do that to check if the shear pin is broken. When you take the servo arm off, the head of the shear pin will fall out (or come out with the servo arm). Then, replace the shear pin in a new hole, reinstall the servo arm, rotate it all by hand to be reconnected in same orientation as before, tighten the castle nut, install cotter pin and you're done.
Reply With Quote
  #8  
Old 05-07-2016, 12:56 AM
Derek Derek is offline
 
Join Date: Jan 2011
Location: Sydney, Australia
Posts: 86
Default Looks like I'll be needing a new Shear Screw



I removed the servo output arm today, and yes the shear screw has snapped.

The fix / solution is quite simple, but I'm wondering what has caused the screw to break in the first place ?
Reply With Quote
  #9  
Old 05-07-2016, 06:58 AM
Jesse's Avatar
Jesse Jesse is offline
 
Join Date: May 2005
Location: X35 - Ocala, FL
Posts: 3,683
Default

The shear screw most likely broke at least partially because the arm was loose. Beyond that sometimes they just break. I don't know how many I have replaced, but it's dozens probably, and sometimes they just break. If/when you break your second or third, it's time to really try to figure out why. On the first, just out a new one in and move on.
__________________
Jesse Saint
Reply With Quote
  #10  
Old 05-09-2016, 03:19 AM
Derek Derek is offline
 
Join Date: Jan 2011
Location: Sydney, Australia
Posts: 86
Default Thanks Jesse

I've just just reset all the Skyview AP settings back to their defaults. Once the new shear screw turns up fingers crossed my altitude hunting issue will be a thing of the past.
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 04:16 PM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.