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  #1  
Old 11-18-2021, 05:41 AM
abuura abuura is offline
 
Join Date: Jan 2006
Posts: 92
Default Bye bye Rocket Steering Link

Upon the last of 5 landings from my post-mx checkout, I felt a strong and prolonged vibration from the rear that continued until I slowed to a walking pace. Inspection revealed that the steering link had sheared off as shown in the picture.
The maintenance I performed before flight simply consisted of cleaning and lubing the tailwheel axle and bronze bushing, and tightening the assembly so the steering arm was tight but the wheel still able to swivel freely 360 degrees - same as I've always done.
Has anyone experienced this before? I plan to return to the original chains-and-door-springs that worked so well before but I'm just curious. Thanks for your input.
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  #2  
Old 11-18-2021, 06:44 AM
Scott Hersha Scott Hersha is offline
 
Join Date: Jan 2005
Location: Cincinnati, OH
Posts: 2,078
Default

Iíve had two of these steering link fractures over the years. I never noticed any vibration or shimmy. I use the door springs now too. I wish the tail lynx was still available.
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  #3  
Old 11-18-2021, 07:17 AM
Freemasm Freemasm is offline
 
Join Date: Nov 2017
Location: Orlando
Posts: 550
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I can't tell for sure from the posted pic but the shape of the fracture surface and apparent lack of necking, etc. would suggest fatigue. Possible overstress but I'm doubting based on the one pic. If you'd like, I can see if our guys in the metallurgical lab can take a quick look.
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  #4  
Old 11-18-2021, 07:31 AM
David Bell David Bell is offline
 
Join Date: Jun 2009
Location: Broussard Louisiana
Posts: 120
Default Rocket Steering

I also recently had the rod end bearing sheer off in the same location. No big deal, ordered and installed a new one. It performed fine for 710 hours. Looking forward to another 700!
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  #5  
Old 11-18-2021, 08:24 AM
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bjdecker bjdecker is offline
 
Join Date: Jun 2005
Location: Georgetown, TX
Posts: 1,042
Default Shimmy...

Quote:
Originally Posted by abuura View Post
Upon the last of 5 landings from my post-mx checkout, I felt a strong and prolonged vibration from the rear that continued until I slowed to a walking pace. Inspection revealed that the steering link had sheared off as shown in the picture.
The pneumatic tailwheel and extended Bell fork seem to be more sensitive to the caster angle of the Van's yoke.

The vibration you felt was the tailwheel shimmy, which caused the rod end to fail.
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  #6  
Old 11-18-2021, 09:06 AM
Freemasm Freemasm is offline
 
Join Date: Nov 2017
Location: Orlando
Posts: 550
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Supports the observation and theory:

Shimmy => cycles => metal fatigue

Sounds like there's plenty of options to make this avoidable.

Last edited by Freemasm : 11-18-2021 at 09:44 AM.
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  #7  
Old 11-18-2021, 10:15 AM
F1R F1R is offline
 
Join Date: Nov 2010
Location: ____
Posts: 925
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TW Shimmy is most often a result of other than ideal castor angle.
Lesser contributors are pivot bushing slop and /or TW spring too soft or loose clamping of the leaf stack.

I have never experienced shimmy with a steering link.

On the other hand I have a Maule TW that is fine on grass, dirt or gravel but on pavement is a holy terror. I generally bring it to a stop with the tail in the air and then set it down to taxi back to the hangar on black top. The castor angle is wrong, and the leaf stack is very soft, but on grass and dirt roads it redeems itself, so I live with it.
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  #8  
Old 11-18-2021, 05:54 PM
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BlakeFrazier BlakeFrazier is offline
 
Join Date: Mar 2016
Location: Evansville, IN
Posts: 66
Default One more for shimmy

I'll second those pointing the finger at a tailwheel shimmy event.

We collected data from a few pieces written by smarter people than me on the topic and put together this article on shimmy and what can be done to fix it: http://flyboyblog.com/2020/06/26/add...shimmy-in-rvs/

Earlier comments about the Condor2 fork presenting a shimmy issue a little more often are not wrong, though there are plenty of them flying with no issues (if it caused problems frequently, we wouldn't sell them!) As near as I can tell the main reason for the correlation is just that the tire is bigger and the fork sits higher, so it raises the tail enough to slightly change the angle into a more shimmy-prone condition.

I've kicked around the idea of making a mounting socket with a shallower angle to make an easy way to correct an assembly with a drooping caster angle, but for now, that project is on hold and the best way to handle a shimmying tailwheel may well be the rod-bending method outlined in the article above.

Cheers!
Blake
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  #9  
Old 11-19-2021, 12:48 AM
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rv8ch rv8ch is offline
 
Join Date: Feb 2005
Location: LSGY
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Quote:
Originally Posted by BlakeFrazier View Post
...
I've kicked around the idea of making a mounting socket with a shallower angle to make an easy way to correct an assembly with a drooping caster angle, but for now, that project is on hold and the best way to handle a shimmying tailwheel may well be the rod-bending method outlined in the article above.
Blake, at a fly-in this summer I spent some time looking at other tailwheel aircraft, and while I'm sure that the RV style is probably the lightest, some of the others look down right space-age in comparison. I think there is room for innovation here, for sure.
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  #10  
Old 11-19-2021, 07:54 PM
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gmcjetpilot gmcjetpilot is offline
 
Join Date: Jan 2005
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Quote:
Originally Posted by rv8ch View Post
Blake, at a fly-in this summer I spent some time looking at other tailwheel aircraft, and while I'm sure that the RV style is probably the lightest, some of the others look down right space-age in comparison. I think there is room for innovation here, for sure.
What do you mean space age?
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