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Additional NTSB Documents

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dougsire

Joined: 10 Jan 2006
Posts: 37

Posted: Thu Oct 29, 2009 8:17 am Post subject: Additional NTSB Documents

John Clark, Chief Scientist, Office of Aviation Safety at the NTSB has posted three additional documents to the public docket of the Polk City, FL accident.   They include photos of “compression buckling” on the upper and lower rear spar caps for six 601XL accidents: Markermeer, Netherlands, Antelope Island, UT, Polk City, FL, Oakdale, CA, Barcelona, Spain, and Yuba City, CA.   The three separate documents are attached (hopefully).



It is interesting to note that the builder of the Antelope Island aircraft apparently drilled the hole in the rear spar incorrectly on one wing, and then put a patch over it.   The buckling is in the same place on both the upper and lower spar cap on that wing.



What could have caused this damage, and why would Mr. Clark post these documents at this point?   



I’m reminded of the cartoon which shows a dog furiously writing a long mathematical proof on a classroom chalkboard.   One of the human observers exclaims, “I think Lassie is trying to tell us something!”

REAR SPAR DAMAGE Spain Yuba City 102109.pdf

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REAR SPAR DAMAGE Polk City Oakdale 102109.pdf

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REAR SPAR DAMAGE Dutch Antelope Island102109.pdf

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Doug Sire 601XL
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Stephen Smith

Joined: 02 Jul 2009
Posts: 13
Location: Santa Rosa, CA

Posted: Fri Oct 30, 2009 7:54 am Post subject: Re: Additional NTSB Documents

Interesting information.  The location of failure is for sure a weak spot on the wing.  I noted this weakness before my plane even flew.  I always thought it odd that such a large hole would be placed in a critical component but I figured someone knew that it was OK; maybe not...



The PDFs are careful not to say the deformation occurred in flight.  They even suggest that the deformation may have occurred on impact.  However should the deformation occur in flight the aileron and flap would lock together so that the aileron would no longer move.  A crash would result without a doubt.



I have looked at the PDFs three times.  I conclude that if the NTSB knew what the deformation "meant" in the crash investigation, they would say something more definitive. I think this is a symptom, not a cause; probably not interesting nor an area to fix on our planes.  I would not fault anyone for adding a bit a aluminum in that spot to make it stronger however.  I wonder what the 650 looks like in this area.



Steve

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Steve Smith
N601WF
Zenair Zodiac XL
Jabiru 3300
600+ hours
Sensenich composite - ground adjustable

ter_turn(at)yahoo.com
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Posted: Fri Oct 30, 2009 10:10 am Post subject: Additional NTSB Documents

This is what I did to beef up that area. I'm not advocating this for anyone else..use your own discretion.Terry Turnquist



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sabrina

Joined: 15 Jun 2009
Posts: 170

Posted: Fri Oct 30, 2009 11:51 am Post subject: Re: Additional NTSB Documents

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Last edited by sabrina on Wed Nov 04, 2009 4:20 pm; edited 1 time in total

aussiech650

Joined: 04 Oct 2009
Posts: 25
Location: Sydney, Australia

Posted: Fri Oct 30, 2009 11:54 am Post subject: Additional NTSB Documents

The rear spar on a CH650 has this hole positioned 92mm outboard of RR#7 and

20mm up from the bottom radius. The hole is 38mm OD and therefore we have

2mm edge distance to the bottom radius and is 36% of the 106m rear spar web.

Is it necessary that this hole be so large or could it be reduced?

Greg Cox

Zenith Zodiac CH650, VH-ZDC

Sydney, Australia (Cecil Hills)



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sonar1@cox.net

Joined: 02 Oct 2007
Posts: 55
Location: Santa Barbara, Ca

Posted: Fri Oct 30, 2009 3:25 pm Post subject: Re: Additional NTSB Documents

I didn't like the looks of this hole when I built my 601, but didn't make any changes. I am actually happy that this inspector has followed up on this. Seems that this could be a problem especially with any quick aileron inputs with the piano-hinged ailerons. 

This is certainly a lot easier to fix than  counter-weights on the ailerons. 

The strength is in the top and bottom (like an I beam) so an extra plate on the top and bottom of the wing would be all that would be required.

Fred Sanford...N9601....

zenithlist(at)yahoo.com
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Posted: Fri Oct 30, 2009 7:09 pm Post subject: Additional NTSB Documents

I used the leftover outboard rear spar cut-off to "double-up" the rear spar aileron rod hole area.  The holes do not need to be that large but they need to be close to the bottom of the rear spars to clear the aileron rods.

         [quote][b]

sabrina

Joined: 15 Jun 2009
Posts: 170

Posted: Sat Oct 31, 2009 6:10 am Post subject: Re: Additional NTSB Documents

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Last edited by sabrina on Wed Nov 04, 2009 4:19 pm; edited 1 time in total

dougsire

Joined: 10 Jan 2006
Posts: 37

Posted: Sat Oct 31, 2009 8:00 am Post subject: Re: Additional NTSB Documents

I think the real question to be answered here is not where the compression buckling occurred, but rather why did it occur.   What physical force caused this damage?   Personally I think this area is in need of strengthening and some of the suggestions are very good.   After seeing these photos for the first time a couple of weeks ago I had the same thought  as Sabrina regarding extending both the spar side of the aileron and flap hinge so they overlap.



But the compression buckling alone did not bring these aircraft down; it is just the result, or signature, of some other force.   I would say that the damage either had to have been present on the ground before the aircraft took off and the pilot did not notice it (not likely), or it occurred during flight, or it occurred as it hit the ground or water.   Take a closer look at the damage to the left wing in the photos of the Markermeer (Dutch) accident (pgs  2-5).   In this accident, the right wing folded over the aircraft, and the left wing was “relatively straight”.   Could this damage have occurred as it hit the water?   You can see from the damage to the leading edge D cell which is crushed that it took the bulk of the impact energy, so it likely hit somewhat parallel to the water.   



The skin on both the top and bottom of the wing is indented outward at the damage spots.   Conceivably if the wing had hit the earth at the wing tip just right, it might have caused this type of buckling, but that clearly did not happen.   Maybe if the wing hit the water primarily at the outboard end of the leading edge, that would have bent the outboard end of the rear spar back some and caused it.   However, if it did that, we would expect to see the aileron angled back and hitting the flap.   The photo at the bottom of page 4 shows that not to be the case.   There is a consistent gap between the aileron and flap.



So what might be the most plausible explanation?   Well, since it is well documented that flutter can occur in unbalanced ailerons, and that it could easily cause an upward and downward motion of the outboard end of the wing which could cause the damage shown (at the weakest spot on the rear spar), I would have to say that flutter is the most likely force which caused the compression damage.   And of course since it is also well known that left unchecked, flutter can quickly destroy an aircraft, I don’t see any explanation other than flutter as the cause.

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psm(at)att.net
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Posted: Sat Oct 31, 2009 8:17 am Post subject: Additional NTSB Documents

Hi Sabrina,



I don't get it.



Why use a hinge part instead of just cutting some aluminum to 

reinforce the rear channel?



Also, why not reinforce both sides of the rear channel - both the top 

and bottom?  After all, the web has been essentially removed in that 

area.  Perhaps it is the web that should get a doubler rather than the flange.



Paul

XL Awaiting engineering changes

At 07:10 AM 10/31/2009, you wrote:

 	  Quote: 	
		  Looking back on it, an easy fix would be to purchase flap hinges 

that are about a foot longer than the flaps, using the forward 

portion of the outboard last foot of the flap hinge to reinforce the 

lower rear spar cap, discarding the aft portion of this new flap 

hinge extension.

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