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  #1  
Old 08-19-2021, 07:44 PM
MVPILOT MVPILOT is offline
 
Join Date: Aug 2014
Location: Mount Vernon, WA
Posts: 97
Default Jerky Ground Taxi

I've owned two RV-12 SLSA a 2015 and a 2020 RV-12iS. I have over 300 hours in factory built RV-12's. Recently I noticed a very jerky response and over response when using brakes to control direction while taxing. It feels like when I touch a brake for steering anywhere from about 1-10 kts, the wheel over reacts and then when I correct using the other brake it repeats almost like a bearing is shot and the wheel is flopping from side to side but when I elevate the nose wheel and test it by hand I don't get this affect. Anyone else noticed. I took it to a mechanic and they looked at it with any disassembly and didn't see the problem...
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  #2  
Old 08-19-2021, 08:14 PM
skydiverlv skydiverlv is offline
 
Join Date: Jul 2008
Location: kansas
Posts: 359
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Have you recently completed the nose gear replacement? I have found mine needing increased brake pressure to control, resulting in "jerkiness".
The angle at the lower bend is greater than the original leg so steering geometry is different. With the original leg I had a uniform 3/16" clearance between the front wheel pant and the leg shroud. Now the clearance begins at 3/16" and widens to about 3/8" indicating the bend angle is greater. Just yesterday I unscrewed the gear nut 1 face to see if it helps. Have not flown.
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  #3  
Old 08-19-2021, 11:20 PM
seagull seagull is offline
 
Join Date: Dec 2019
Location: San Bernardino
Posts: 391
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Quote:
Originally Posted by skydiverlv View Post
The angle at the lower bend is greater than the original leg so steering geometry is different. With the original leg I had a uniform 3/16" clearance between the front wheel pant and the leg shroud. Now the clearance begins at 3/16" and widens to about 3/8" indicating the bend angle is greater. Just yesterday I unscrewed the gear nut 1 face to see if it helps.
I had Vans replace my original SB leg and a friend went through 2 to get a straight one. You will also notice your nose wheel pant is not sitting level. My nose wheel would chatter (not caster properly) at higher speed on roll out with the forward canting leg.
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  #4  
Old 08-20-2021, 02:02 AM
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Piper J3 Piper J3 is offline
 
Join Date: Nov 2014
Location: Hinckley, Ohio
Posts: 2,523
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Breakout friction needs to set correct with Belleville washers on nose strut pivot. Too much friction will prevent centering. Also, pivot bushings need to be well lubricated. Its surprising how grease gets squeezed out of the close-clearance bronze bushings. I added a grease fitting problem solved.

See.... https://vansairforce.net/community/s...9&postcount=29
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Jim Stricker - EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 717

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father - CFI) - USAAF 1st Lt. Captain B-17H
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  #5  
Old 08-20-2021, 07:02 AM
MVPILOT MVPILOT is offline
 
Join Date: Aug 2014
Location: Mount Vernon, WA
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I believe my 2020 SLSA came with the new nose and it worked fine for the first 100 hours so I don't think that is the problem.
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  #6  
Old 08-20-2021, 07:03 AM
MVPILOT MVPILOT is offline
 
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Location: Mount Vernon, WA
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Thank you however I have about 100 hours and it was fine until recently. It seems to be getting worse.
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  #7  
Old 08-20-2021, 07:18 AM
JFCRV12 JFCRV12 is offline
 
Join Date: May 2015
Location: Liberty Township OH
Posts: 216
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Sure sounds like breakout force isn't properly set. Have you or your mechanic checked the breakout force? Takes two minutes with nose lifted so worth a shot.
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  #8  
Old 08-20-2021, 07:19 AM
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Piper J3 Piper J3 is offline
 
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See my post #29 listed above. No disassembly required. Drill small hole - chips will follow drill bit and be extracted during drilling process. Follow with 1/4" drill x 1/4" deep c'bore. Use a small socket to protect the drive-type grease fitting and tap in with hammer. Pump grease until it extrudes from top/bottom of bushings.
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Jim Stricker - EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 717

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father - CFI) - USAAF 1st Lt. Captain B-17H
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  #9  
Old 08-20-2021, 07:37 AM
MVPILOT MVPILOT is offline
 
Join Date: Aug 2014
Location: Mount Vernon, WA
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Thank you. The mechanic didn't mention break out force so I'll check with him again.
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  #10  
Old 08-20-2021, 07:39 AM
MVPILOT MVPILOT is offline
 
Join Date: Aug 2014
Location: Mount Vernon, WA
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Thank you Jim. Your solution seems like a good one. I'm not all that handy and might screw it up but I'll check with the mechanic.
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