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Shimmy vibration?

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motoadve

Joined: 23 Apr 2009
Posts: 123
Location: Seattle

Posted: Sat May 02, 2020 4:49 am Post subject: Shimmy vibration?

It had happened twice, once landing on grass strip that transitions to pavement, the nose wheel got back in the air a bit and when it touched down, got lots of vibration, whole plane shaking.



Second time I did a landing and bounced, (short field and wanted to be down before I should , had too much energy) when it touched down again lots of vibration, whole plane shaking.

Both times I thought I had a flat tire.



Take offs , no vibration , and regular landings no vibration, seems to be the nose wheel does not likes to come back up in the air because the second time it touches down generates a lot of vibration.



Any ideas what causes this (apart from lousy landing )

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threein60

Joined: 04 Feb 2016
Posts: 51
Location: Everett Wa

Posted: Sat May 02, 2020 6:36 am Post subject: Shimmy vibration?

Service shimmy dampener 

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On Saturday, May 2, 2020, 05:59, motoadve <larry(at)motoadventuring.com> wrote: 	  Quote: 	
		  --> Yak-List message posted by: "motoadve" <larry(at)motoadventuring.com (larry(at)motoadventuring.com)>



It had happened twice, once landing on grass strip that transitions to pavement, the nose wheel got back in the air a bit and when it touched down, got lots of vibration, whole plane shaking.



Second time I did a landing and bounced, (short field and wanted to be down before I should , had too much energy) when it touched down again lots of vibration, whole plane shaking.



Both times I thought I had a flat tire.



Take offs , no vibration , and regular landings no vibration, seems to be the nose wheel does not likes to come back up in the air because the second time it touches down generates a lot of vibration.



Any ideas what causes this (apart from lousy landing ) 



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Cessna 182 P



CJ -6



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dougsappllc(at)gmail.com
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Posted: Sat May 02, 2020 9:55 am Post subject: Shimmy vibration?

Could be several things:

Linkage worn

Scissors worn

Splined shaft (in damper) sheared

Damper needs overhauled

My guess is that the splined shaft is sheared.  I have o/h kits and new splined shafts if you discover you need them.

Best,

Doug

On Sat, May 2, 2020 at 5:53 AM motoadve <larry(at)motoadventuring.com (larry(at)motoadventuring.com)> wrote:



 	  Quote: 	
		  --> Yak-List message posted by: "motoadve" <larry(at)motoadventuring.com (larry(at)motoadventuring.com)>

 

 It had happened twice, once landing on grass strip that transitions to pavement, the nose wheel got back in the air a bit and when it touched down, got lots of vibration, whole plane shaking.

 

 Second time I did a landing and bounced, (short field and wanted to be down before I should , had too much energy) when it touched down again lots of vibration, whole plane shaking.

 Both times I thought I had a flat tire.

 

 Take offs , no vibration , and regular landings no vibration, seems to be the nose wheel does not likes to come back up in the air because the second time it touches down generates a lot of vibration.

 

 Any ideas what causes this (apart from lousy landing ) 

 

 --------

 www.Backcountry182.com

 Cessna 182 P

 CJ -6

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=496160#496160

 

 

 

 

 

 

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motoadve

Joined: 23 Apr 2009
Posts: 123
Location: Seattle

Posted: Sat May 02, 2020 2:38 pm Post subject: Re: Shimmy vibration?

Thanks Doug, good to hear from you, will keep you posted.

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romaine_richard(at)yahoo.
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Posted: Sun May 03, 2020 3:20 am Post subject: Shimmy vibration?

..also check NW side/side uneven tire wear and sufficient (33 psi) inflation.  Both will make shimmy damper work harder.  Low inflation will induce wear on outer tread, significant uneven wear there will make it more likely to shimmy off-balance.  If you have any yaw on touchdown, the bounce may still have the NW displaced on second touchdown getting more of the uneven wear.



Cheers, Rich 



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woodja51

Joined: 13 May 2015
Posts: 40
Location: MELBOURNE AUSTRALIA

Posted: Wed Aug 05, 2020 8:45 pm Post subject: Re: Shimmy vibration?

Another area that can cause apparent shimmy is if there is wear in the extension actuator upper/lower attachment points. I had no end of trouble with shimmy -to the point I replaced the entire nose leg, tried to balance the tyre with lead, changed the tyre, noise wheel bearings  - you name it. 



Lift the nose wheel and see if there is any movement in the fore aft direction. You might notice this when you taxi as a pronounced clunking from the nose/firewall etc. 



If there is any significant wear in the upper actuator attach  point you might be able to take it out with adjusting the lower rod ( the over centre scissor) but be very careful not to overdo it otherwise the down stay won't stay over centre and the nose gear can collapse. In my case, about half -one turn fixed the majority of the issue. All the other points may contribute of course. Matt

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stephen.hayne

Joined: 01 Nov 2013
Posts: 59
Location: United States

Posted: Wed Sep 09, 2020 3:29 pm Post subject: Re: Shimmy vibration?

This is probably too late, but I was experiencing shimmy at 60+ knots, that I just couldn't seem to fix.  Balanced tire, rebuilt dampener, rebuilt strut, rebuilt torque links (with new brass bushings - reamed to perfect tolerance) and fore/aft movement non-existent.  There was just a TINY click in the links at the lower attach point... 



So, I bought some 0.001 M8 ring shims from McMasters (https://www.mcmaster.com/stainless-steel-shim-washers/ring-shims-7/) - jammed 2 in the bottom, and managed to get 1 in the top (very tight!), and voila - shimmy sorted!  Yay!



BTW, I am/was also exploring using the "Balance Masters" Cleveland wheel balance ring (http://www.balancemasters.com/aircraft.html) - not the prop stuff.  I will report back when/if I actually install it.  FYI - the owner of Balance Masters is a pilot and a great guy to talk to!



Stephen

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