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601XL rear spar risk mitigation

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a.s.elliott(at)cox.net
Guest

Posted: Mon Aug 27, 2007 1:39 pm Post subject: 601XL rear spar risk mitigation

Gang:

  

 I appreciate all the feedback I have gotten on my idea to mitigate the risk  of rear spar failures by adding a small strap to the lower spar flange in the  area of the aileron pushrod hole.  This was discussed in detail at 

  

 http://members.cox.net/n601ge/drawings/rearspar.html

  

 Many people have other ideas, which is why it's called "experimental"  aviation!

  

 I would like to add some notes:

  

 [1] It should be straightforward to inspect the strap doubler on a regular  basis for working rivets or cracks.  So an additional good characteristic  of this type of risk mitigation is that you can use it to get some real data on  the hypothetical problem.  If people install the strap and report no damage  over time (50 hour intervals?), then either there was no problem there or the  minimalist fix worked like a charm.  If people later report that they are  finding evidence of strap fatigue, then we have identified a "real" problem and  can work out a "real" fix.

  

 [1a] If you install such a strap, you should note it in your builder's log  and consider putting an inspection item in your annual checklist - "Visually  inspect strap doublers on rear spar lower flange in area of aileron pushrod for  any evidence of cracks, fatigue or working rivets."  Over the years, as  evidence builds, you will gain (or lose) confidence in the design and/or  strap.

  

 [3] It was brought up to me by one respondent that for scratch builders,  there is an option to use a 2-piece rear spar, and that this design has a  larger, heavy-duty splice in the same area.  If people with that design  built and flying can inspect the doubler and report its apparent condition,  those would be additional data points.

  

 FWIW,

 Andy Elliott, Mesa, AZ

N601GE (reserved)

601XL/TD/QB, Corvair,  building...

   [quote][b]

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ashontz

Joined: 27 Dec 2006
Posts: 723

Posted: Tue Aug 28, 2007 6:24 am Post subject: Re: 601XL rear spar risk mitigation

Not a bad idea. A better arrangement would have been to place an entire channel inside the spar to span that area like the splice plate that's in there for when the rear spar is made ouut of two spars butted together. Check with Mark Townsend on that. Easy enough to make and even replace where you have that strap and you'll probably like the idea and be more comfortable with it when you see it. What you're really trying to do it beef up the circumference of that hole, albeit mostly at the bottom. A plate that spans the entire hole is more "per the book" than a strap.



Just my two cents.



[quote="a.s.elliott(at)cox.net"]Gang:

  

 I appreciate all the feedback I have gotten on my idea to mitigate the risk  of rear spar failures by adding a small strap to the lower spar flange in the  area of the aileron pushrod hole.  This was discussed in detail at 

  

 http://members.cox.net/n601ge/drawings/rearspar.html

  

 Many people have other ideas, which is why it's called "experimental"  aviation!

  

 I would like to add some notes:

  

 [1] It should be straightforward to inspect the strap doubler on a regular  basis for working rivets or cracks.  So an additional good characteristic  of this type of risk mitigation is that you can use it to get some real data on  the hypothetical problem.  If people install the strap and report no damage  over time (50 hour intervals?), then either there was no problem there or the  minimalist fix worked like a charm.  If people later report that they are  finding evidence of strap fatigue, then we have identified a "real" problem and  can work out a "real" fix.

  

 [1a] If you install such a strap, you should note it in your builder's log  and consider putting an inspection item in your annual checklist - "Visually  inspect strap doublers on rear spar lower flange in area of aileron pushrod for  any evidence of cracks, fatigue or working rivets."  Over the years, as  evidence builds, you will gain (or lose) confidence in the design and/or  strap.

  

 [3] It was brought up to me by one respondent that for scratch builders,  there is an option to use a 2-piece rear spar, and that this design has a  larger, heavy-duty splice in the same area.  If people with that design  built and flying can inspect the doubler and report its apparent condition,  those would be additional data points.

  

 FWIW,

 Andy Elliott, Mesa, AZ

N601GE (reserved)

601XL/TD/QB, Corvair,  building...

    	  Quote: 	
		  [b]

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planecrazydld(at)yahoo.co
Guest

Posted: Fri Aug 31, 2007 1:30 pm Post subject: 601XL rear spar risk mitigation

Another thing to emphasize would be to "polish" the hole edges as well. Since the necked down area of concern near the flange in the original spar is now occluded by the strap doubler, it could crack without being detected. perhaps add a strip of this along the lower edge after polishing to avoid notching or dinging during asembly?

   

  http://www.devicetec.com/DTIProducts/SpringFast/Default.asp



"Dr. Andrew Elliott" <a.s.elliott(at)cox.net> wrote:

  [quote]  BODY {   BACKGROUND-POSITION: left top; MARGIN-TOP: 10px; FONT-SIZE: 11pt; MARGIN-LEFT: 10px; COLOR: #000000; BACKGROUND-REPEAT: no-repeat; FONT-FAMILY: Courier New  }        Gang:

   

  I appreciate all the feedback I have gotten on my idea to mitigate the risk of rear spar failures by adding a small strap to the lower spar flange in the area of the aileron pushrod hole.  This was discussed in detail at 

   

  http://members.cox.net/n601ge/drawings/rearspar.html

   

  Many people have other ideas, which is why it's called "experimental" aviation!

   

  I would like to add some notes:

   

  [1] It should be straightforward to inspect the strap doubler on a regular basis for working rivets or cracks.  So an additional good characteristic of this type of risk mitigation is that you can use it to get some real data on the hypothetical problem.  If people install the strap and report no damage over time (50  hour intervals?), then either there was no problem there or the minimalist fix worked like a charm.  If people later report that they are finding evidence of strap fatigue, then we have identified a "real" problem and can work out a "real" fix.

   

  [1a] If you install such a strap, you should note it in your builder's log and consider putting an inspection item in your annual checklist - "Visually inspect strap doublers on rear spar lower flange in area of aileron pushrod for any evidence of cracks, fatigue or working rivets."  Over the years, as evidence builds, you will gain (or lose) confidence in the design and/or strap.

   

  [3] It was brought up to me by one respondent that for scratch builders, there is an option to use a 2-piece rear spar, and that this design has a larger, heavy-duty splice in the same area.  If people with that design built and flying can inspect the doubler and report its [quote][b]

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dforney(at)bctonline.com
Guest

Posted: Sat Sep 01, 2007 4:45 pm Post subject: 601XL rear spar risk mitigation

Most of the guys in my local EAA chapter are real RV advocates.  Several are building RV9As.  I am the only one building a Zenith 601XL in my chapter.  I wanted to take advantage of the “Sport Pilot” rating for medical and flying longevity, even though I am currently “Private Pilot” rated.  I chose the 601XL after doing what I felt was in-depth investigative due diligence.    

   

One of the members brought up and made a point of noting at one of our club meetings the other day, the two NTSB fatal accident reports (LAX06LA105 & DFW07LA102) regarding in-flight breakups & wing failures.  At that time I was unaware of the incidents and did not respond.  Since then, I have read the official reports on the NTSB web site, but they are far from conclusive.  I found it interesting that one of the aircraft had just had some work and modifications done by an aircraft repair facility two weeks earlier and the other incident appeared to be during some very foul weather.  I was wondering if anyone had any additional information on these two incidents, or knows of any more details and information that I could access regarding them.  

   

I realize that there are many factors that could contribute to these incidents such as build quality, maintenance quality, flying procedures, etc.  I am building from standard 601XL kit and trying to do everything exactly as the plans and assembly guides instruct.  Since I have never built an aircraft before I just want to make sure that I don’t unknowing do something that could contribute to in-flight failures and want to feel that I am building and flying a safely engineered aircraft.  

   

All feedback or reassurance is welcome.  

   

Thanks!  

   

   

       [quote][b]

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