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  #11  
Old 11-12-2015, 06:14 PM
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N941WR N941WR is offline
 
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Before you do anything to the rudder, remove the wheel pants and gear leg fairings. Then go fly and see if it flies with the ball centered.

If it does flight with the ball centered, then the issue is with the alignment of those fairings and wheel pants.

If it still flies 1/2 a ball out, check the wing tips, ailerons, and flaps.

If after all that it still doesn't flight straight, then play with the rudder.
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  #12  
Old 11-12-2015, 06:27 PM
Captain Avgas Captain Avgas is offline
 
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Quote:
Originally Posted by N941WR View Post
Before you do anything to the rudder, remove the wheel pants and gear leg fairings. Then go fly and see if it flies with the ball centered.

If it does flight with the ball centered, then the issue is with the alignment of those fairings and wheel pants.

If it still flies 1/2 a ball out, check the wing tips, ailerons, and flaps.

If after all that it still doesn't flight straight, then play with the rudder.
Top advice from Bill. A trim tab on an RV rudder is like a sign on the plane that says: "THIS AIRCRAFT HAS NOT BEEN BUILT PROPERLY".
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  #13  
Old 11-12-2015, 06:30 PM
alpinelakespilot2000 alpinelakespilot2000 is offline
 
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Quote:
Originally Posted by Captain Avgas View Post
A trim tab on an RV rudder is like a sign on the plane that says: "THIS AIRCRAFT HAS NOT BEEN BUILT PROPERLY".
Van's RV-9 demonstrator has (or at least had in 2006) a trim tab on the bottom side of the left aileron. Must not have been built properly.
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  #14  
Old 11-12-2015, 07:27 PM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by alpinelakespilot2000 View Post
Van's RV-9 demonstrator has (or at least had in 2006) a trim tab on the bottom side of the left aileron. Must not have been built properly.
Isn't that an early prototype? If so, a trim adjustment wouldn't surprise me.
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  #15  
Old 11-13-2015, 09:22 AM
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The left/right alignment of the vertical stabilizer is critical, it would take VERY LITTLE to be off to require some rudder trim. It would be very easy to inadvertently build in a little skid......
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  #16  
Old 11-13-2015, 10:04 AM
Bill Dicus Bill Dicus is online now
 
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Thanks for information on the -4 using a Gurney flap. If you have any details that come up in the future please let me know. Thanks.
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  #17  
Old 11-13-2015, 10:51 AM
Far North Texan Far North Texan is offline
 
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Quote:
Originally Posted by Captain Avgas View Post
Top advice from Bill. A trim tab on an RV rudder is like a sign on the plane that says: "THIS AIRCRAFT HAS NOT BEEN BUILT PROPERLY".
Darn it, there is a lot of certified airplanes out there that must not be built properly.
Better get Cessna, Beech, Piper, Boeing, etc. on the phone and let them know.
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  #18  
Old 11-13-2015, 04:35 PM
Captain Avgas Captain Avgas is offline
 
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Quote:
Originally Posted by Far North Texan View Post
Darn it, there is a lot of certified airplanes out there that must not be built properly.
Better get Cessna, Beech, Piper, Boeing, etc. on the phone and let them know.
I will reiterate what I said again. A trim tab on the rudder of an RV is a sure sign that the the plane is poorly rigged and is experiencing asymmetrical drag. What else could it mean.

The problem with a rudder trim tab is that you are simply introducing more "equal and opposite" drag to counter the asymmetrical drag you already have. And adding drag to counter drag just robs you of speed. It's not an ideal situation but it appeals to people who are looking for a quick and dirty fix.

Bill Repucci's advice is still the best plan proposed. Take off the wheel/gear fairings and see if that fixes the problem. If it does then the OP will know where the problem lies and can address it in the correct manner rather than adopting the bandaid approach of using a trim tab.
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  #19  
Old 11-13-2015, 07:22 PM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by Far North Texan View Post
Darn it, there is a lot of certified airplanes out there that must not be built properly.
Better get Cessna, Beech, Piper, Boeing, etc. on the phone and let them know.
Have you ever seen how Cessna, Beech, and Piper built planes? (The same probably goes for the early Boeings too.)

They have (or had) big templates that they would lay over the raw aluminum, trace it and use it as a hole template. They were built very much like the RV-3's, 4's, and 6's, in a jig and a lot shimming.

The match hold technology that is used in the -7, -8 (later 8's), -9, -10, -12, and -14 make it virtually impossible to build an airframe that isn't straight.

Production techniques for certified aluminum airplanes may have changed and I hope they have but most of those planes flying were built with a lot of craftsmanship and not much technology.
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  #20  
Old 11-14-2015, 02:17 AM
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curtis curtis is offline
 
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Quote:
Originally Posted by Captain Avgas View Post
The problem with a rudder trim tab is that you are simply introducing more "equal and opposite" drag to counter the asymmetrical drag you already have. And adding drag to counter drag just robs you of speed. It's not an ideal situation but it appeals to people who are looking for a quick and dirty fix.
No airframe is perfect and by moving gear leg fairings, wheel pants, flap positions, wing tips, etc.. to correct the yaw in flight is just hiding the correction that an external trim tab provides. Now if you actually find one of the listed items actually out of the proper position that is one thing, but to just move them around until you don't need a trim tab is just hiding the fact. A trim tab does not mean the aircraft is unsafe or even built out of tolerance. Staying within the allowed plans tolerances over the length of an RV aircraft could require a tab to correct for straight flight even thought the aircraft is built per print.

I don't have an issue if someone wants to spend their time rebuilding or reglassing fiberglass parts to eliminate a small trim tab on the rudder, however in my opinion I have elected to add a safe trim tab to my rudder and enjoy flying. Life is too short for me to stay in the building and tweaking phase forever.
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