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New Nose Gear Leg & Fork Shimmy Issue

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robin1(at)mrmoisture.com
Guest

Posted: Thu Feb 07, 2008 6:05 pm Post subject: New Nose Gear Leg & Fork Shimmy Issue

My 6A just came out of annual with the updated nose gear & fork. Unfortunately there is now a severe shimmy upon landing*. So severe that I was wondering if the tire was rolling off the rim with a good slapping sound. Not a good feeling.  

As part of the annual I replaced both main tires & tubes but the nose wheel tire is the same as before the annual when all was well. I do notice that the front leg fairing is much closer to the nose wheel pant and has caused some abrasions on the top of the pant as they are now probably in contact with my added weight.  

The plane taxi’s well and reasonably high speed taxing did not reveal the shimmy but there is definitely a problem. Any suggestions are appreciated.  

   

Robin  

   

*Perfect landing holding off the nose till I had no more authority.  

      [quote][b]

dale1rv6(at)comcast.net
Guest

Posted: Thu Feb 07, 2008 6:31 pm Post subject: New Nose Gear Leg & Fork Shimmy Issue

My last shimmy was caused by a tire that was slightly out of round. If you hold the nose up till pitch control is gone, you may allow the nose wheel to drop hard enough to start an oscillation from the leg springing, it has happened to me. If you let the pressure get too low I have had the tire slip on the rim and tear the valve stem, and it took 2 days to go flat. If your tire is making noise maybe it developed a bump (hernia). Have someone push the tail down and raise the nose tire 4 inches and release while you watch. Good inspection for fairing clearances.  

Dale  

RV6a 986 hrs  

         

  

From: owner-rv-list-server(at)matronics.com [mailto:owner-rv-list-server(at)matronics.com] On Behalf Of Robin Marks

 Sent: Thursday, February 07, 2008 9:00 PM

 To: rv-list(at)matronics.com

 Subject: New Nose Gear Leg & Fork Shimmy Issue  

  

   

My 6A just came out of annual with the updated nose gear & fork. Unfortunately there is now a severe shimmy upon landing*. So severe that I was wondering if the tire was rolling off the rim with a good slapping sound. Not a good feeling.  

As part of the annual I replaced both main tires & tubes but the nose wheel tire is the same as before the annual when all was well. I do notice that the front leg fairing is much closer to the nose wheel pant and has caused some abrasions on the top of the pant as they are now probably in contact with my added weight.  

The plane taxi’s well and reasonably high speed taxing did not reveal the shimmy but there is definitely a problem. Any suggestions are appreciated.  

   

Robin  

   

*Perfect landing holding off the nose till I had no more authority.   	  Quote: 	
		    http://www.matronics.com/Navigator?RV-List 	
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bobbyhester(at)newwavecom
Guest

Posted: Thu Feb 07, 2008 7:09 pm Post subject: New Nose Gear Leg & Fork Shimmy Issue

Could be that the axle nuts are too tight and not allowing the tire to spin properly.

 Rise the tail and spin the tire by hand you should be able to make it spin at least one complete turn. I have found that they need to be torqued at min torque that is called out on the print. I don't have that handy, thinking it might be 85 in lbs..

  	  Quote: 	
		  ----

Surfing the web from Hopkinsville, KY

Visit my flying RV7A web page:

http://home.newwavecomm.net/bobbyhester/MyFlyingRV7A.htm



	
 

 

 Dale Walter wrote: [quote]         v\:* {behavior:url(#default#VML);} o\:* {behavior:url(#default#VML);} w\:* {behavior:url(#default#VML);} .shape {behavior:url(#default#VML);}  <![endif]-->   st1\:*{behavior:url(#default#ieooui) }  <![endif]-->          <![endif]-->       <![endif]-->         

My last shimmy was caused by a tire that was slightly out of round. If you hold the nose up till pitch control is gone, you may allow the nose wheel to drop hard enough to start an oscillation from the leg springing, it has happened to me. If you let the pressure get too low I have had the tire slip on the rim and tear the valve stem, and it took 2 days to go flat. If your tire is making noise maybe it developed a bump (hernia). Have someone push the tail down and raise the nose tire 4 inches and release while you watch. Good inspection for fairing clearances.   

Dale   

RV6a 986 hrs   

          

   

From: owner-rv-list-server(at)matronics.com (owner-rv-list-server(at)matronics.com) [mailto:owner-rv-list-server(at)matronics.com (owner-rv-list-server(at)matronics.com)] On Behalf Of Robin Marks

   Sent: Thursday, February 07, 2008 9:00 PM

   To: rv-list(at)matronics.com (rv-list(at)matronics.com)

   Subject: New Nose Gear Leg & Fork Shimmy Issue   

   

    

My 6A just came out of annual with the updated nose gear & fork. Unfortunately there is now a severe shimmy upon landing*. So severe that I was wondering if the tire was rolling off the rim with a good slapping sound. Not a good feeling.   

As part of the annual I replaced both main tires & tubes but the nose wheel tire is the same as before the annual when all was well. I do notice that the front leg fairing is much closer to the nose wheel pant and has caused some abrasions on the top of the pant as they are now probably in contact with my added weight.   

The plane taxi’s well and reasonably high speed taxing did not reveal the shimmy but there is definitely a problem. Any suggestions are appreciated.   

    

Robin   

    

*Perfect landing holding off the nose till I had no more authority.    	  Quote: 	
		     	
0    	  Quote: 	
		   	
1   

    	  Quote: 	
		   	
2 [b]

bobbyhester(at)newwavecom
Guest

Posted: Thu Feb 07, 2008 7:09 pm Post subject: New Nose Gear Leg & Fork Shimmy Issue

Could be that the axle nuts are too tight and not allowing the tire to spin properly.

 Rise the tail and spin the tire by hand you should be able to make it spin at least one complete turn. I have found that they need to be torqued at min torque that is called out on the print. I don't have that handy, thinking it might be 85 in lbs..

  	  Quote: 	
		  ----

Surfing the web from Hopkinsville, KY

Visit my flying RV7A web page:

http://home.newwavecomm.net/bobbyhester/MyFlyingRV7A.htm



	
 

 

 Dale Walter wrote: [quote]         v\:* {behavior:url(#default#VML);} o\:* {behavior:url(#default#VML);} w\:* {behavior:url(#default#VML);} .shape {behavior:url(#default#VML);}  <![endif]-->   st1\:*{behavior:url(#default#ieooui) }  <![endif]-->          <![endif]-->       <![endif]-->         

My last shimmy was caused by a tire that was slightly out of round. If you hold the nose up till pitch control is gone, you may allow the nose wheel to drop hard enough to start an oscillation from the leg springing, it has happened to me. If you let the pressure get too low I have had the tire slip on the rim and tear the valve stem, and it took 2 days to go flat. If your tire is making noise maybe it developed a bump (hernia). Have someone push the tail down and raise the nose tire 4 inches and release while you watch. Good inspection for fairing clearances.   

Dale   

RV6a 986 hrs   

          

   

From: owner-rv-list-server(at)matronics.com (owner-rv-list-server(at)matronics.com) [mailto:owner-rv-list-server(at)matronics.com (owner-rv-list-server(at)matronics.com)] On Behalf Of Robin Marks

   Sent: Thursday, February 07, 2008 9:00 PM

   To: rv-list(at)matronics.com (rv-list(at)matronics.com)

   Subject: New Nose Gear Leg & Fork Shimmy Issue   

   

    

My 6A just came out of annual with the updated nose gear & fork. Unfortunately there is now a severe shimmy upon landing*. So severe that I was wondering if the tire was rolling off the rim with a good slapping sound. Not a good feeling.   

As part of the annual I replaced both main tires & tubes but the nose wheel tire is the same as before the annual when all was well. I do notice that the front leg fairing is much closer to the nose wheel pant and has caused some abrasions on the top of the pant as they are now probably in contact with my added weight.   

The plane taxi’s well and reasonably high speed taxing did not reveal the shimmy but there is definitely a problem. Any suggestions are appreciated.   

    

Robin   

    

*Perfect landing holding off the nose till I had no more authority.    	  Quote: 	
		     	
0    	  Quote: 	
		   	
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2 [b]

ronlee(at)pcisys.net
Guest

Posted: Thu Feb 07, 2008 10:05 pm Post subject: New Nose Gear Leg & Fork Shimmy Issue

The two most likely issues are out of balance and out of round.   Since

 it is a new tire I would guess out of balance.  It is easy to tell the  difference

 between one or both of those and shimmy from the outside while  taxiing

  

 Ron Lee

    [quote][b]

robin1(at)mrmoisture.com
Guest

Posted: Thu Feb 07, 2008 10:16 pm Post subject: New Nose Gear Leg & Fork Shimmy Issue

[quote]I am fairly sure the shimmy is unrelated to a tire issue as I have had zero issues with the exact same tire before the annual (0.2 hours ago). I will test the rotation in the AM. I have read about the axel nut torque in the past so I will check that too. When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. Thanks,Robin  [b]

Vanremog(at)aol.com
Guest

Posted: Thu Feb 07, 2008 10:54 pm Post subject: New Nose Gear Leg & Fork Shimmy Issue

In a message dated 2/7/2008 10:18:26 P.M. Pacific Standard Time,  robin1(at)mrmoisture.com writes:

  	  Quote: 	
		   	  Quote: 	
		  I am fairly sure the shimmy is unrelated to a tire issue as I have had zero issues with the exact same tire before the annual (0.2 hours ago). I will test the rotation in the AM. I have read about the axle nut torque in the past so I will check that too. When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. 	
	


 

 ===============================================

  

 And your castoring "breakout" force is still the same?  Did you  over grease the pivot joint?  Is the mounting hole to the engine mount  getting sloppy?

  

  

  

 N1GV (RV-6A, Flying 883hrs, O-360-A1A, C/S, Silicon  Valley) 



Who's never won?  Biggest Grammy Award surprises of all time on AOL Music.

dale1rv6(at)comcast.net
Guest

Posted: Fri Feb 08, 2008 4:48 am Post subject: New Nose Gear Leg & Fork Shimmy Issue

OK, then remove the tire and fly the plane. If the shimmy is still there you have proved your case. BTW, except for the hub, the tire is the only moving part at the end of the leg unless your tire is not perfect. The wheel fairing will not create shimmy, it is always the victim. Tires change, and can go bad any time; forget about how it was before the shimmy. The poster who questioned greasing has a good point. Also, maybe that super landing of yours got grease on it (greaser).  

Good luck,  

Dale  

         

  

From: owner-rv-list-server(at)matronics.com [mailto:owner-rv-list-server(at)matronics.com] On Behalf Of Robin Marks

 Sent: Friday, February 08, 2008 1:14 AM

 To: rv-list(at)matronics.com

 Subject: RE: New Nose Gear Leg & Fork Shimmy Issue  

  

    	  Quote: 	
		  I am fairly sure the shimmy is unrelated to a tire issue as I have had zero issues with the exact same tire before the annual (0.2 hours ago). I will test the rotation in the AM. I have read about the axel nut torque in the past so I will check that too. When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. Thanks,Robin    When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. 	
0 	  Quote: 	
		  When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. 	
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		  When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. 	
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		  When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. 	
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		  When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. 	
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		  When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. 	
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		  When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. 	
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		  When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. 	
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		  When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. 	
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		  When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. 	
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robin1(at)mrmoisture.com
Guest

Posted: Fri Feb 08, 2008 8:28 am Post subject: New Nose Gear Leg & Fork Shimmy Issue

 	  Quote: 	
		  And your castoring "breakout" force is still the same?  

I doubt as it’s a new gear leg & fork. I will have to check & re-set.  
	


   

 	  Quote: 	
		  Is the mounting hole to the engine mount getting sloppy?  

No, this is a new gear leg and the drilled hole is perfect.  
	


   

 	  Quote: 	
		   Did you over grease the pivot joint?  

I don’t have the repairman’s certificate on this plane so the annual was performed by a mechanic. I will go out to the airport and check today.  
	


   

Thanks for everyone’s help so far.  

   

Robin  

       

From: owner-rv-list-server(at)matronics.com [mailto:owner-rv-list-server(at)matronics.com] On Behalf Of Vanremog(at)aol.com

 Sent: Thursday, February 07, 2008 10:47 PM

 To: rv-list(at)matronics.com

 Subject: Re: New Nose Gear Leg & Fork Shimmy Issue  

  

  

       

In a message dated 2/7/2008 10:18:26 P.M. Pacific Standard Time, robin1(at)mrmoisture.com writes:  

   	  Quote: 	
		   	  Quote: 	
		  I am fairly sure the shimmy is unrelated to a tire issue as I have had zero issues with the exact same tire before the annual (0.2 hours ago). I will test the rotation in the AM. I have read about the axle nut torque in the past so I will check that too. When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. 	
	
  

    

======================  

    

   

    

And your castoring "breakout" force is still the same?  Did you over grease the pivot joint?  Is the mounting hole to the engine mount getting sloppy?  

    

   

    

   

    

   

    

N1GV (RV-6A, Flying 883hrs, O-360-A1A, C/S, Silicon Valley)   

  



 

         

  

Who's never won? Biggest Grammy Award surprises of all time on AOL Music.  

   	  Quote: 	
		    When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. 	
0 	  Quote: 	
		  When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. 	
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		  When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. 	
2 	  Quote: 	
		  When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. 	
3 	  Quote: 	
		  When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. 	
4 	  Quote: 	
		  When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. 	
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		  When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. 	
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		  When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. 	
7 	  Quote: 	
		  When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. 	
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		  When I let the front wheel down it was not a drop but rather a near perfect landing right before the violent shimmy. 	
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      [quote][b]

mike109g6(at)insideconnec
Guest

Posted: Fri Feb 08, 2008 8:56 am Post subject: New Nose Gear Leg & Fork Shimmy Issue

Change tire is good idea-eliminate the  obvious.  Bearings go bad also, especially if too much or too little  grease.  Try one thing at a time, you'll find the issue as to why,  hopefully it will be sooner then later.

 Mike H

 [quote]   ---

pitts_pilot(at)bellsouth.
Guest

Posted: Fri Feb 08, 2008 9:08 am Post subject: New Nose Gear Leg & Fork Shimmy Issue

I don't think so.  Out of round will cause the nose fork to bounce, not shimmy.  Shimmy being a side to side motion.  Tighten up on the nut that holds the nose fork on.  The Grummans use belleville washers to create the drag necessary to prevent the shimmy.  I don't know about the RV gears.  To adjust the Grumman nose gear, you apply a spring scale to the wheel axle and torque the nut 'till the spring scale exerts at least 25 Lbs pull before the gear swivels.  With the tire off the ground, of course!   

 Linn

 

 Ron Lee wrote:

 [quote]         (at)font-face { 	font-family: Cambria Math; } (at)font-face { 	font-family: Calibri; } (at)font-face { 	font-family: Consolas; } (at)page Section1 {size: 8.5in 11.0in; margin: 1.0in 1.0in 1.0in 1.0in; } P.MsoNormal { 	FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New Roman","serif" } LI.MsoNormal { 	FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New Roman","serif" } DIV.MsoNormal { 	FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New Roman","serif" } A:link { 	COLOR: blue; TEXT-DECORATION: underline; mso-style-priority: 99 } SPAN.MsoHyperlink { 	COLOR: blue; TEXT-DECORATION: underline; mso-style-priority: 99 } A:visited { 	COLOR: purple; TEXT-DECORATION: underline; mso-style-priority: 99 } SPAN.MsoHyperlinkFollowed { 	COLOR: purple; TEXT-DECORATION: underline; mso-style-priority: 99 } P { 	FONT-SIZE: 12pt; MARGIN-LEFT: 0in; MARGIN-RIGHT: 0in; FONT-FAMILY: "Times New Roman","serif"; mso-style-priority: 99; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto } PRE { 	FONT-SIZE: 10pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Courier New"; mso-style-priority: 99; mso-style-link: "HTML Preformatted Char" } SPAN.HTMLPreformattedChar { 	FONT-FAMILY: Consolas; mso-style-priority: 99; mso-style-link: "HTML Preformatted"; mso-style-name: "HTML Preformatted Char" } SPAN.postbody { 	mso-style-name: postbody } SPAN.EmailStyle21 { 	FONT-WEIGHT: normal; COLOR: #1f497d; FONT-STYLE: normal; FONT-FAMILY: "Arial","sans-serif"; mso-style-type: personal } SPAN.EmailStyle22 { 	FONT-WEIGHT: normal; COLOR: #1f497d; FONT-STYLE: normal; FONT-FAMILY: "Arial","sans-serif"; mso-style-type: personal-reply } .MsoChpDefault { 	FONT-SIZE: 10pt; mso-style-type: export-only } DIV.Section1 { 	page: Section1 }       <![endif]-->       <![endif]-->   The two most likely issues are out of balance and out of round.  Since

   it is a new tire I would guess out of balance.  It is easy to tell the difference

   between one or both of those and shimmy from the outside while taxiing

    

   Ron Lee

    	  Quote: 	
		  

	
 [b]

ronlee(at)pcisys.net
Guest

Posted: Fri Feb 08, 2008 9:26 am Post subject: New Nose Gear Leg & Fork Shimmy Issue

Ok, listen closely. You need to have someone observe your tires while you  get 

 what you call a shimmy.  Look from the front and from the side.   A competent

 observer will be able to tell if it is shimmy or out of balance/out of  round.

  

 Once that is determined you can determine which of the possible fixes  works.

  

 Ron

 [quote]   ---

ronlee(at)pcisys.net
Guest

Posted: Fri Feb 08, 2008 9:45 am Post subject: New Nose Gear Leg & Fork Shimmy Issue

Linn, the problem is that whenever someone gets a vibration of any sort the  immediate

 assumed problem is SHIMMY.  Unless someone confirms visually that it  is a shimmy

 the original poster may be chasing the wrong problem.  I have had  these problems and

 chased shimmy causal factors until I had someone videotape the nose wheel  and it 

 was immediately obvious that it was not shimmy, but out of round/out of  balance.

  

 Heck it may be a main wheel/tire so the simple step of visually seeing what  is happening

 when the problem is felt can save a lot of time.

  

 Ron

 [quote]   ---

hooverra(at)verizon.net
Guest

Posted: Fri Feb 08, 2008 6:27 pm Post subject: New Nose Gear Leg & Fork Shimmy Issue

Troubleshooting 101 says that if you change one variable and something 

bad happens change it back!! In this case the most likely change was the 

drag on the fork to strut bearing. The tire although it could have 

changed probably not likely. Shimmy is more related to geometry and the 

damping in the system it appears. I'm not an expert so look at this NACA 

study on the subject and draw your own conclusion. The first thing I 

would do is check the fork drag is to Van's spec



http://tinyurl.com/399cjn



Stability of castering wheels for aircraft landing gears 

<http://ntrs.nasa.gov/search.jsp?R=849502&id &qs=Ntt%3DShimmy%26R%3D849502%26Ntk%3Dall%26qs%3DNo%26Ntx%3Dmode%2520matchall%26Ns%3DHarvestDate%257c1%26N%3D0%26id%3D2>



Author(s): Kantrowitz, Arthur

Abstract: A theoretical study was made of the *shimmy* of castering 

wheels. The theory is based on the discovery of a phenomenon called 

kinematic *shimmy*. Experimental checks, use being made of a model 

having low-pressure ...

NASA Center: Langley Research Center

Publication Year: 1940

Added to NTRS: 2006-11-06

Accession Number: 93R21053; Document ID: 19930091763; Report Number: 

NACA-TR-686



-- 

Ralph C. Hoover

RV7A 

hooverra at verizon dot net

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