REFLECTOR:Rudder Shim

Sun, 10 Aug 2003 20:46:01 -0600

Chuck,

I just don't know how much if any is acceptable. I do know that as soon 
as I told the factory A&P that I had shimmed a rudder inboard he 
immediately said that was the cause of the flutter and he was right.

My right rudder is shimmed inboard a thin 1/32 of an inch, my left is 
shimmed outboard a fat 1/8 of an inch to get the ball dead center and 
also to get even fuel consumption. I had the right one shimmed inboard 
about an 1/8 and got the flutter at 180 knots.

I've flight tested the thin 1/32 to 215 knots indicated. No flutter 
jabbing any and all of the flight controls.

But for all I know that much inboard shim would induce flutter in some 
planes, I just don't know.

That was why I said that if you were to try it to shim it a very small 
amount and test it to redline. Then shim it an additional very small 
amount and flight test again.  Maybe its worth it, probably not.

Your definitely pushing the outside of that envelope.

Scott

Chuck Jensen wrote:
> Scott,
> 
> Let me see if I have this right.  I unshim the left side about a 1/32 inch
> which will deshim the right side an equivalent amount.  If this works, then
> I progressively unshim the left rudder in 1/32 inch increments until I get
> high speed flutter and the winglet falls off??  Then I know I went too far
> and unloaded the left rudder!
> 
> I hate to be picky and difficult, but is there perhaps a way of determining
> when I'm getting close to unloading the rudder....before I do?
> 
> I really like the idea of being able to reduce the shim out on the right
> rudder by shimming in the left rudder.  Less opposed control surfaces in the
> wind, less resistance, more speed.  I like it.  We just need to work out a
> few details on that scary part about the high speed flutter!!  Sounds like
> nose wheel shimmy, only scarier.
> 
> Scott, your mission, should you decide to accept it, will be to inform the
> rest of us how the heck we do that!
> 
> Chuck
> 
> 
> 
> -----Original Message-----
> From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
> Behalf Of Scott Derrick
> Sent: Sunday, August 10, 2003 6:48 PM
> To: reflector@tvbf.org
> Subject: Re: REFLECTOR:Rudder Shim
> 
> 
> Chuck,
> 
> I had exactly the same result as you did, ball in the middle, fuel flow 
> just a purty as you could ask for, and I also thought I imagined a 
> couple of extra knots!!
> 
> My only problem is with all the couple knot speed increases I've made so 
> far I should be way up over 200 knots, but I'm still dragging along at 
> 175. :-(
> 
> Now, about driving tricks.... ;-)  Nah, I'll let that dead dog(I hope!!) 
> lie.
> 
> 
> Chuck, you can try this to even out the rudder shimming, but approach 
> this with due caution.  I created a wicked winglet flutter by over doing 
> it.  It scared me and my wife out of a year or two and took lots of 
> phone calls and help from a good friend and A&P to get it resolved.
> 
> I'm not really recommending you do this but you may think of it and try 
> what I did and not realize it could bite you bad if you brought the 
> other rudder to far in.
> 
> You have now shimmed one of your rudders "out" and the other is as you 
> originally set it up.  If you "unshim" or bring the other rudder in, no 
> more than a tape thickness, you can remove some of the tape from the 
> outshimmed rudder.  BUT DON'T UNSHIM TO MUCH!!!  If you unshim to much 
> the winglet will unload at high speeds, my flutter happened at 180 knots 
> indicated.  So the way to do it, if you want to try it, is to unshim a 
> 1/32 or less.  Fly the airplane and take her up to indicated redline to 
> verify the winglet is still loaded up. Do this every time you unshim a 
> rudder inboard.
> 
> 
> Scott
> 
> 
> 
> 
> 
> Chuck Jensen wrote:
> 
> 
>>Oh, Reflectorites, I bow before your great wisdom!  A couple weeks ago, I
>>started the string about uneven fuel flow.  Scott Derrick, the trick
> 
> driver,
> 
>>and always reticent to express his opinion, opinionated that "you're
>>probably unbalanced" to which I had difficulty disagreeing.
>>
>>Others joined the chorus so, rather than swimming against the current
> 
> (heck
> 
>>I can hardly swim at all), I started shimming out the right rudder with
> 
> duct
> 
>>tape from my National Emergency Preparedness Package.  Sure enough, the
>>third effort and slightly over 1/4" thickness, the ball is dead center
>>between the lubbers.  
>>
>>Not only does my fuel flow evenly now, never more than a 2 gallon
> 
> variation,
> 
>>but I believe I actually gained a couple knots of cruise; proving the
> 
> theory
> 
>>that it's less than optimal to fly through the sky sideways.
>>
>>Life is good!
>>
>>Chuck
>>_______________________________________________
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> 
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> 
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>>
> 
> 
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