VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

  #11  
Old 08-07-2017, 11:02 AM
rleffler's Avatar
rleffler rleffler is offline
 
Join Date: Jun 2006
Location: Delaware, OH (KDLZ)
Posts: 3,540
Default

Quote:
Originally Posted by Dorfie View Post
Bob,
Yes, I am alone for the duration of phase 1. I wish it was easier to get a second pilot on board during phase 1. I will see how it performs during next flight. I was planning on doing the AOA calibration during my next flight. I also thought it might be gain settings that I have to address, but the gain is already at 0.8!! How much lower can you go??
Thanks.
Johan
I don't have or am I familiar with Garmin, so I can't offer specific advice. What does the installation manual show as a range? I suspect it will go down to 0.0.

For example, on my Trutrak Vizion, the range for roll goes from 0 to 24. Trutrak recommended a 3 as the default setting and AFS recommended a 9 for a RV-10. I also have a secondary gain on the EFIS as well, which has a range of 0.1 to 2.0. Mine is set at 0.3. I know it's not a direct comparison, but you get the concept. What it's set at isn't as important as is getting a setting that achieves the desired result.
__________________
Bob Leffler
N410BL - RV10 Flying
http://mykitlog.com/rleffler
Reply With Quote
  #12  
Old 08-07-2017, 11:21 AM
sblack sblack is offline
 
Join Date: Dec 2009
Location: Montreal
Posts: 1,094
Default

roll and yaw are coupled in any airplane. So the yaw servo will impact roll and vice versa. I don't know if that is your problem or not. You have a limit cycle oscillation. I just said that to impress you with my vocabulary. I don't know how to fix it But it is an impressive term to throw around at cocktail parties! We have often seen them get worse when some part of the system, like a control feel spring (which you don't have) is out of tolerance.

I would be looking for gains that were too high, or slop in the system somewhere. When it is rolling is the ball moving very much? That might tell you if it is being induced by the rudder via sideslip. Same with tanks empty and full? It doesn't sound dangerous - only annoying. But check for tightness in the system. everywhere as a precaution.

At your next party you can tell everyone you have a limit cycle issue. Say it casually as though you assume that everyone else knows what that is.
__________________
Scott Black
RV 4, with an engine...and other stuff
VAF dues 2016
Reply With Quote
  #13  
Old 08-08-2017, 06:41 AM
Dorfie Dorfie is offline
 
Join Date: Aug 2009
Location: Lexington, KY
Posts: 378
Default

Quote:
Originally Posted by rleffler View Post
I don't have or am I familiar with Garmin, so I can't offer specific advice. What does the installation manual show as a range? I suspect it will go down to 0.0.

For example, on my Trutrak Vizion, the range for roll goes from 0 to 24. Trutrak recommended a 3 as the default setting and AFS recommended a 9 for a RV-10. I also have a secondary gain on the EFIS as well, which has a range of 0.1 to 2.0. Mine is set at 0.3. I know it's not a direct comparison, but you get the concept. What it's set at isn't as important as is getting a setting that achieves the desired result.
Bob,
After some searching the GAIN setting range for the Garmin roll, pitch and yaw servos range 0.05-10.0, with 0.05 increments. Found this in the G3X install manual (where else!!). So I still have a fair amount of leeway left to fine tune the settings. I love this....every flight I have new things to learn and do!!
Thanks to all for your input.
Johan
__________________
Dorfie
RV10
2017 dues paid with a smile
Reply With Quote
  #14  
Old 08-08-2017, 02:58 PM
BruceMe's Avatar
BruceMe BruceMe is offline
 
Join Date: Feb 2005
Location: Shawnee, Kansas
Posts: 594
Default RV4 & G3X solo high altitude pitch oscillation

Solo > 10K it flies level-ish, but once it gets even a little perturbed it starts a oscillation about 10 seconds peak-to-peek and it just keeps getting worse unless I stop it. So dynamically unstable, statically neutral. Anyone know what to tweak there?
__________________
Bruce Meacham

Built/Own RV-4 254MM
For Sale RV-6 4074V
First RV RV-3 3456B

VAF annual donation on autopay
Reply With Quote
  #15  
Old 08-08-2017, 08:22 PM
rleffler's Avatar
rleffler rleffler is offline
 
Join Date: Jun 2006
Location: Delaware, OH (KDLZ)
Posts: 3,540
Default

Quote:
Originally Posted by BruceMe View Post
Solo > 10K it flies level-ish, but once it gets even a little perturbed it starts a oscillation about 10 seconds peak-to-peek and it just keeps getting worse unless I stop it. So dynamically unstable, statically neutral. Anyone know what to tweak there?
It sounds like the gain for that servo may be set too high.

What AP do you have?
__________________
Bob Leffler
N410BL - RV10 Flying
http://mykitlog.com/rleffler
Reply With Quote
  #16  
Old 08-11-2017, 11:00 AM
KeithB KeithB is offline
 
Join Date: Mar 2014
Location: Granbury, TX
Posts: 84
Default

I have a G3X in an RV-14A (but with no yaw damper) and am experiencing the same roll oscillations when on autopilot in Nav mode - so you are not alone. In my experience, Heading mode is rock solid. Garmin's suggestion (booth at Airventure) was play with the gain settings as others have suggested. I have tried some experiments but have not yet come up with a final satisfactory setting. It is definitely only an inconvenience and I would recommend to put it on a list to do after your Phase I tasks are complete - i.e. play with when you are boring holes just to fly off the 40 hours.
__________________
Keith Brown

RV-14A Builder - kit #136
N314KC - First flight Mar 8, 2017, Phase I compl Apr 3, 2017
RV-6A sold
Sport Pilot (weight-shift control) - Airborne XT912
Dues paid 12/2016
Reply With Quote
  #17  
Old 08-15-2017, 03:09 AM
kai kai is offline
 
Join Date: May 2011
Location: Berlin, Germany
Posts: 83
Default

Oscillations around the longitudinal axis can also happen when the aircraft is slipping or skidding. Check if your ball is centered.
I had a customer in the past with a Beech Duke, he complained the aircraft is rolling. During a test flight we trimmed the roll channel and the rolling stopped immediately.

cheers,

Kai
__________________
Kai

flying RV-9a, O-320, G3X Touch
a father&son project
Reply With Quote
  #18  
Old 08-15-2017, 06:32 AM
Walt's Avatar
Walt Walt is offline
 
Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 4,328
Default

Quote:
Originally Posted by KeithB View Post
I have a G3X in an RV-14A (but with no yaw damper) and am experiencing the same roll oscillations when on autopilot in Nav mode - so you are not alone. In my experience, Heading mode is rock solid. Garmin's suggestion (booth at Airventure) was play with the gain settings as others have suggested.
Just curious, are you getting full throw of the roll servo? Which hole did you end up using in the arm? The middle hole works good on the 7/8 but not sure on the 14.
__________________
Walt Aronow, Dallas, TX (52F) RV7A, IO360, C/S, 1500+hrs

EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154
Reply With Quote
  #19  
Old 08-15-2017, 08:06 AM
868RM 868RM is offline
 
Join Date: Oct 2009
Location: lena, il.
Posts: 246
Default nav rolling

I have a Garmin touch and Garmin auto pilot in another airplane. Had the same issue of rolling in nav mode. Someone posted earlier that the gain was maybe on the high side. I lowered the gain from 2.25 to 1.85 in .05 increments and problem is gone. On previous attempts I bounced around changing gain in larger increments. That did not work. .05 steps about 2 minutes between changes worked. My numbers will have NO reference on your plane.
Reply With Quote
  #20  
Old 08-16-2017, 05:05 AM
Brantel's Avatar
Brantel Brantel is online now
 
Join Date: Mar 2006
Location: Newport, TN
Posts: 6,656
Default

Quote:
Originally Posted by 868RM View Post
I have a Garmin touch and Garmin auto pilot in another airplane. Had the same issue of rolling in nav mode. Someone posted earlier that the gain was maybe on the high side. I lowered the gain from 2.25 to 1.85 in .05 increments and problem is gone. On previous attempts I bounced around changing gain in larger increments. That did not work. .05 steps about 2 minutes between changes worked. My numbers will have NO reference on your plane.
I agree, you have to use small adjustments and sneak up on it. When you find the magic number for your plane, it will be awesome.
__________________
Brantel (Brian Chesteen),
RV-7/TU, #72823, N159SB
Lyc. O-360 carbed, HARTZELL BA CS Prop, MAG/P-MAG, Dual Garmin G3X Touch
Track N159SB (KK4LIF)
Like EAA Chapter 1494 on Facebook
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 06:55 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.