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  #1  
Old 02-04-2019, 02:35 PM
scsmith scsmith is offline
 
Join Date: Jan 2008
Location: Ashland, OR
Posts: 2,968
Default New steering link geometry

Some of you will have seen the thread that I started several years ago after a surprise groundloop occurred in a strong starboard cross wind when the steering link unexpectedly and suddenly released.

That thread stimulated a lot of good discussion on several related topics, one of which is the asymmetry of a "rocket link" steering link in the release points when steering left and right. The asymmetry is caused by the angle at the rudder horn from the rudder hinge axis to the attach point for the steering link being a different angle than the angle at the steering arm from the tail wheel pivot axis to the attach point for the steering link.

After some discussion with Darwin Barrie at JD Airparts, he arranged to make a modified steering arm. I spent a little while doing some trig and analytic geometry to come up with a length and sweep angle of the steering arm that would produce a symmetrical release action to the left and right, and have both directions cause release of the tail wheel lock just at the extreme deflection of the rudder. Darwin sent me the the new steering arm and a longer steering link to test out. Here are some pictures of the installation.

I have not been able to fly this installation yet because of weather, ongoing condition inspection, and some other activities. But I will report back here as soon as I can fly with it. I can tell you that on the ground, if you pull the rudder all the way to the stop, and put pressure on the tail wheel in the direction it would feel if steering, it does NOT release. Same left and right. If you put the rudder all the way to the stop and put pressure on the tail wheel in the direction to make it swivel intentionally, it does release. Same left and right.




You can also see that I substitute a normal rod end with an AN3 bolt and AN970 washer, plus some of the rod end spacer washers that Vans sells, in place of the integral rod end + stud that is supplied. This insures that the rod end stays captive in the very unlikely event that the bearing fails.

So I am pretty optimistic that this will be a nice improvement to the steering link system for those that like it. The steering link system is quicker steering than chains or cables with springs and a little slack, and arguably not as rugged as cables with springs. So there is still room for personal preference here. But for those of us that like the quick, positive steering feel, this new steering arm should give you symmetrical behavior.
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Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet" Flying since Sept. 2009
Hobbs 700
also
1/4 share in 1959 C-182B (tow plane)
LS6-15/18W sailplane SOLD
bought my old LS6-A back!!
VAF donation Dec 2020
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  #2  
Old 02-04-2019, 02:51 PM
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rocketbob rocketbob is offline
 
Join Date: Jun 2006
Location: 8I3
Posts: 3,759
Default

I make my own steering links out of titanium components. It achieves the same result, which is for the rudder to go to either stop without unlocking the tailwheel. It takes a tap of the brake to get the tailwheel to swivel. Simply a function of spring rate and travel. No change in arm geometry required.

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Bob Japundza CFI A&PIA
N9187P PA-24-260B Comanche, flying
N678X F1 Rocket, under const.
N244BJ RV-6 "victim of SNF tornado" 1200+ hrs, rebuilding
N8155F C150 flying
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  #3  
Old 02-04-2019, 03:12 PM
scsmith scsmith is offline
 
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Location: Ashland, OR
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Default

Bob, if you check carefully, you will see that you have a different tail wheel deflection for the same rudder deflection left and right. It is 5 degrees or more different from left to right. So you can't get the same release behavior left and right with an unswept steering arm.

Very pretty work though!
__________________
Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet" Flying since Sept. 2009
Hobbs 700
also
1/4 share in 1959 C-182B (tow plane)
LS6-15/18W sailplane SOLD
bought my old LS6-A back!!
VAF donation Dec 2020
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  #4  
Old 02-04-2019, 03:21 PM
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rocketbob rocketbob is offline
 
Join Date: Jun 2006
Location: 8I3
Posts: 3,759
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That is correct, the travel is not equal. Its hardly noticeable when swiveling, in fact I've never noticed it. The important thing is it wont break the tailwheel loose going down the runway, in either direction.
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Bob Japundza CFI A&PIA
N9187P PA-24-260B Comanche, flying
N678X F1 Rocket, under const.
N244BJ RV-6 "victim of SNF tornado" 1200+ hrs, rebuilding
N8155F C150 flying
N7925P PA-24-250 Comanche, restoring
Not a thing I own is stock.
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  #5  
Old 02-04-2019, 06:09 PM
scsmith scsmith is offline
 
Join Date: Jan 2008
Location: Ashland, OR
Posts: 2,968
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Quote:
Originally Posted by RV8JD View Post
Steve,

Time to break down and buy the JDAir ball bearing fork assembly (delete the standard steering arm!). Expensive, but you'll love it!

https://www.jdair.com/tailwheel-assembly-for-vans-rv/

That is good looking. A little less drag and maybe easier to install a fairing too.
Does it have the same ground clearance as the Bell fork?
__________________
Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet" Flying since Sept. 2009
Hobbs 700
also
1/4 share in 1959 C-182B (tow plane)
LS6-15/18W sailplane SOLD
bought my old LS6-A back!!
VAF donation Dec 2020
Reply With Quote
  #6  
Old 02-04-2019, 06:10 PM
scsmith scsmith is offline
 
Join Date: Jan 2008
Location: Ashland, OR
Posts: 2,968
Default

Quote:
Originally Posted by scsmith View Post
That is good looking. A little less drag and maybe easier to install a fairing too.
Does it have the same ground clearance as the Bell fork?
Also wondering about the attach hole alignment. Mine have been reamed for taper pins. So as long as the holes line up, I can ream the holes to match.
__________________
Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet" Flying since Sept. 2009
Hobbs 700
also
1/4 share in 1959 C-182B (tow plane)
LS6-15/18W sailplane SOLD
bought my old LS6-A back!!
VAF donation Dec 2020
Reply With Quote
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