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Empennage SBs SWAG

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rwstracy(at)gmail.com
Guest

Posted: Mon Feb 10, 2014 4:03 am Post subject: Empennage SBs SWAG

Might I propose (with tongue only slightly in cheek) that the problem is on the other end of the airplane.   The only conceivable root cause of HS / Elevator spar cracking is a resonant vibration of these parts excited by that throbbing thing at the nose.   Possibly primary engine frequency during operation (aggravating factor being prop imbalance) or the tail shaking violently during startup and shutdown, in which case problem may be related to number of start/stop cycles rather than hours or aerobatic stress.

RV-4  1850 hours

RV-8    220 hours

(Both   - Mazda rotary engine powered)



Sent from my iPad



On Feb 10, 2014, at 1:57, Jack <n81jg(at)aol.com (n81jg(at)aol.com)> wrote:

[quote]RV7A  781JG

466 hrs

No aero

No cracks HS or E



Sent from my iPhone



On Feb 9, 2014, at 10:41 PM, vanremog(at)aol.com (vanremog(at)aol.com) wrote:

 	  Quote: 	
		   Might I suggest as you all go about your SB inspections, that you report back to the lists with your a/c type, TTA, inspection results (no cracks, cracks, extensive cracks) and your flying profiles (no aero, mild aero, hard aero) to help us understand the overall fleet condition and assess the airframe life of these designs under the normal range of conditions.  Some of you are quite easy on these airframes while others I'm sure are yank and bankers.

   

  As for my RV-6A situation at 1130 TTA, no cracks or distress found in either the horizontal stab or elevator, with a history of mild to no aerobatics, a few dozen hours in mountain wave conditions during cross countries and only one time to +6gs during botched maneuver. 

   

  -GV

   	  Quote: 	
		  

	






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st"">http://www.matronics.com/Navigator?RV-List

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//forums.matronics.com

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[b]

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vanremog(at)aol.com
Guest

Posted: Mon Feb 10, 2014 6:01 pm Post subject: Empennage SBs SWAG

You could propose that, Tracy but, aside from there being zero evidence for that assertion, we would need to see more than just your word on it.  As they say, "Extraordinary claims require extraordinary evidence". ;o)

   

  -GV 

  

  

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flying-nut(at)cfl.rr.com
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Posted: Mon Feb 10, 2014 6:13 pm Post subject: Empennage SBs SWAG

I doubt that vibration up front causes       the HS/rudder spar cracking although lack of dynamic prop balance       does play hell with the front end .... instruments, especially       gyros.  However, I think the more logical culprit is the HS/rudder       banging against the stops in the wind.

       IMHO, of course!

       Linn

       

       On 2/10/2014 9:01 PM, vanremog(at)aol.com (vanremog(at)aol.com) wrote:

     

     [quote]         You could             propose that, Tracy but, aside from there being zero             evidence for that assertion, we would need to see more than             just your word on it.  As they say, "Extraordinary claims             require extraordinary evidence". ;o)

          

         -GV 

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ceengland7(at)gmail.com
Guest

Posted: Mon Feb 10, 2014 6:22 pm Post subject: Empennage SBs SWAG

On the other hand, there appears to be       zero evidence of *any* cause, at least from Van's A/C, yet the       cracks are there, on some airframes. And Tracy isn't the 1st to       mention it as a possible source of the problem. What's so       extraordinary about the assertion? Many have commented about major       'tail shake' at startup & shutdown. 

       

       Charlie

       

       On 2/10/2014 8:01 PM, vanremog(at)aol.com (vanremog(at)aol.com) wrote:

     

     [quote]         You could             propose that, Tracy but, aside from there being zero             evidence for that assertion, we would need to see more than             just your word on it.  As they say, "Extraordinary claims             require extraordinary evidence". ;o)

          

         -GV 

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vanremog(at)aol.com
Guest

Posted: Mon Feb 10, 2014 6:28 pm Post subject: Empennage SBs SWAG

Let's follow this line of thinking to its logical conclusion.  If the rudder banging back and forth were a cause of the HS and elevator hinge mount cracking phenomena in the SBs then we would expect it to be worse in the A airframes, since they are not restrained from motion while parked as are the non-A airframes.  Once we get more data, we will see if there is even a correlation, much less causation.

   

  I will withhold judgment until such time as I have more data, but I find the possibility unlikely.

   

  -GV 

  

  

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vanremog(at)aol.com
Guest

Posted: Mon Feb 10, 2014 6:51 pm Post subject: Empennage SBs SWAG

Charlie-

   

  You misunderstand me.  I would love to see the evidence, even if it was extraordinary.  Neither am I arguing against dynamic balancing, as mine was dynamically balanced by Dave Morss before it even flew the first time.

   

  It could be aerobatic motor mounts, the horizontal stab going into resonance, flutter or any other dynamic force.  As with Occum's razor, I am looking for the most likely causes.  Horses, not zebras, although I admit it may turn out to be zebras...

   

  -GV

   	  Quote: 	
		  On the other hand, there appears to be       zero evidence of *any* cause, at least from Van's A/C, yet the       cracks are there, on some airframes. And Tracy isn't the 1st to       mention it as a possible source of the problem. What's so       extraordinary about the assertion? Many have commented about major       'tail shake' at startup & shutdown 	


  

  

  

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rwstracy(at)gmail.com
Guest

Posted: Tue Feb 11, 2014 1:03 am Post subject: Empennage SBs SWAG

GV,  the only point I would disagree with you on is that resonant vibration is the horse rather than the zebra.  

Tracy



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On Feb 10, 2014, at 21:48, vanremog(at)aol.com (vanremog(at)aol.com) wrote:

[quote] Charlie-

   

  You misunderstand me.  I would love to see the evidence, even if it was extraordinary.  Neither am I arguing against dynamic balancing, as mine was dynamically balanced by Dave Morss before it even flew the first time.

   

  It could be aerobatic motor mounts, the horizontal stab going into resonance, flutter or any other dynamic force.  As with Occum's razor, I am looking for the most likely causes.  Horses, not zebras, although I admit it may turn out to be zebras...

   

  -GV

   	  Quote: 	
		  On the other hand, there appears to be       zero evidence of *any* cause, at least from Van's A/C, yet the       cracks are there, on some airframes. And Tracy isn't the 1st to       mention it as a possible source of the problem. What's so       extraordinary about the assertion? Many have commented about major       'tail shake' at startup & shutdown 	


  

  

  

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