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  #11  
Old 01-20-2019, 06:26 AM
BigJohn BigJohn is offline
 
Join Date: Nov 2008
Location: Gloversville, NY
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Quote:
Originally Posted by bobg56 View Post
I believe what your saying but it doesn't make sense to me, most of all my GA experience is Cessna and Piper.
Good Morning Bob,

If you think about it this way, it is easier to understand what the others are saying.

As long as you are not applying any pressure to one rudder pedal or another, the rudder will center aerodynamically in flight. That is why to change the trim on an RV-12 rudder a wedge or trim tab is required. The cable length does not come into play.

But, the cables including the links do need to be of the correct length so that the pedals are in the same positions when the rudder is centered, and they do not contact the firewall when fully deflected. That is why Van’s has the builder construct a simple wooden jig to use when doing the final fit of the cables.

If you are unsure of the rigging in the airplane you purchased, you could check this out by clamping the rudder in the center, and running staright edge across the pedals with them gently pushed forward. They should be equally deflected. Then remove the clamp and check full defelction of each pedal to be sure neither one contacts the firewall.

Hope this helps,

John
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RV-12 N37JP 120176 Flying since 2012.
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VAF paid through 10/2019.
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  #12  
Old 01-20-2019, 06:37 AM
BigJohn BigJohn is offline
 
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Originally Posted by rvbuilder2002 View Post
Not entirely true.

If the links are too long the rudder pedals will be bumping the firewall when the rudder hits the travel stops. If the links are excessively long, you will never get full rudder travel before the rudder pedals get stopped by the firewall.
And, the cables dont have to be very much too long to hit the firewall. When I built my 12 I didnt leave enough clearance between the fully deflected rudders and the firewall, even though the rudder itself was hitting the stops. After a couple of years I noticed these little bumps appearing on the front side of the firewall. (The firewall material is pretty soft.)
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One Week Wonder Build Team, OSH 2018.
VAF paid through 10/2019.
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  #13  
Old 01-20-2019, 07:24 AM
bobg56 bobg56 is offline
 
Join Date: Nov 2018
Location: Peachtree City, GA
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I'm familiar with metal tabs, but when rigging I would set neutral to either pedals or control wheel/stick with a straight edge and clamps, then adjust the flight control to neutral using cable adjustments. If a tab was needed it wouldn't take much input/bend...My RV12 as a hefty wedge on the LH side of rudder and in level flight the ball is still off to the right a little. With the pedals in neutral the rudder TE is slightly to the left. I figured if I had cable turn barrels
I could adjust it more to center and possibly install a smaller tab.
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  #14  
Old 01-20-2019, 08:42 AM
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Tony_T Tony_T is offline
 
Join Date: Dec 2008
Location: Lacey, WA
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Quote:
Originally Posted by bobg56 View Post
I'm familiar with metal tabs, but when rigging I would set neutral to either pedals or control wheel/stick with a straight edge and clamps, then adjust the flight control to neutral using cable adjustments. If a tab was needed it wouldn't take much input/bend...My RV12 as a hefty wedge on the LH side of rudder and in level flight the ball is still off to the right a little. With the pedals in neutral the rudder TE is slightly to the left. I figured if I had cable turn barrels
I could adjust it more to center and possibly install a smaller tab.
You might consider removing the wedge and installing the Van's rudder trim tab available as a retrofit kit. Search the web store for "12 Rudder Trim Kit". It costs only 7 bucks.
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  #15  
Old 01-20-2019, 09:30 AM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
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Quote:
Originally Posted by bobg56 View Post
I'm familiar with metal tabs, but when rigging I would set neutral to either pedals or control wheel/stick with a straight edge and clamps, then adjust the flight control to neutral using cable adjustments. If a tab was needed it wouldn't take much input/bend...My RV12 as a hefty wedge on the LH side of rudder and in level flight the ball is still off to the right a little. With the pedals in neutral the rudder TE is slightly to the left. I figured if I had cable turn barrels
I could adjust it more to center and possibly install a smaller tab.
As John already tried to explain, the rigging of the rudder cable lengths has no bearing on whether an RV-12 flys with the slip/skid ball centered. The purpose of any trim tab (rudder or others) is to induce a trimming force when there is no pilot force induced into the control circuit.

The whole purpose of a trim tab is to make the airplane fly in trim so that the pilot doesn't have to constantly hold some control presssure for it to do so.
The RV-12 rudder pedals move relatively freely. With no foot pressure on the pedals, the rudder will move to it’s aerodynamically balanced position. If that position happens to be with the ball displaced (out of trim) the rudder pedals will move where ever the rudder moves them (via the cables).

The only way rudder cable length would change yaw trim is if in straight and level flight the pilot always kept his feet on the rudder pedals with the pedals centered. That would be an airplane that was not considered to properly fly in trim.
Possibly your concern is that if an aerodynamic trim tab is holding the rudder deflected, that in level flight the rudder pedals are then no longer aligned. This doesn’t seem important and pilots don’t notice because it is generally a very small displacement. What is most important is that when the pedals are aligned, that the pilot knows that the rudder is centered / neutral.
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  #16  
Old 01-20-2019, 02:22 PM
bobg56 bobg56 is offline
 
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Location: Peachtree City, GA
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Thanks guys, that makes sense now...the rudder will fare aerodynamically, the tab will work to center the ball.
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  #17  
Old 01-20-2019, 02:56 PM
DHeal DHeal is offline
 
Join Date: Sep 2006
Location: Windsor, California
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BTW, when I received the factory trim tab plate it was pre-bent. When installed it perfectly centered the ball and there was no need to tweak it.
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