Wing spar failure?

[Shadrach]

On 9/6/2021 at 1:08 PM, 1980Mooney said:

How do you conclude "The center section of the spar was most certainly compromised by the impact"?  If you believe that the wings folded up vertically outboard of the main landing gear before impact then they were no longer placing any load (or minimal at best) upon the center section of the main spar at the moment of impact.  With no loading or levering of the wings transmitted to and upon the center of the spar at the moment of impact, it does not seem reasonable that the impact alone would cause "The main and rear wings spars were highly fragmented in the center of the airplane between the separated left and right wings."

It’s not that I believe that the wings folded at the station outside the gear, it’s that the NTSB said so in the preliminary:

Both wings were found separated from the fuselage, with the left- and right-wing main and rear spars fractured near the wing rib outboard of their respective main landing gear.

However, looking at the screenshots, it looks like the spar may be compromised in more than two places. It’s hard to tell and even harder to get my head around how that happens. Given the condition of the rest of the fuselage area, it would seem entirely possible to me that portions of the center spar might fracture on impact. I could be wrong. I could be seeing something that isn’t so. Let’s not forget how many of us denied the wings were even folded when the first images were released.

Edited September 12, 2021 by Shadrach

[Chris K]

Tragic.  I missed this story until just recently.  This thread and discussion is interesting but wing spar failure might be jumping to conclusions until all the facts are in. 

This section of the initial report plus the location the pieces were found typical are indications of what failed first.  

Initial examination revealed the left horizontal stabilizer separated about 6 inches outboard of the vertical stabilizer. The three outboard hinge blocks of the left elevator remained attached to the left horizontal stabilizer, with the rivets pulled out and sheared off the elevator. 

I would be amazed as most of you are whether the main spar failure was the cause (instead seems to have occurred after the last sudden descending left turn likely due to the loss of the left stabilizer).  The fact the rivets sheared off only one side of the elevator is something I find amazing  As others mentioned regarding the relatively uniform main spar failures, the failure on the horizontal stabilizers/elevators would occur on both sides, especially if the suspected cause is overspeed followed by flutter.  Instead seems some other load caused the overstress of only one side.  Until both sides of the tail are analyzed, seemingly one side was weaker than the other.  I wonder what sort of past repairs the investigators will find in the logbooks on the tail section or whether there may have been existing hangar rash/and or corrosion that went unnoticed.  

Hopefully we know the answers soon.  In the meantime, safe flying to all.

[Alan Fox]

Couple of things , The spar is NOT a continiuous piece , It is spliced together , It is called one piece (incorrectly) becaues it is fastened together with many rivets and Hi-locs , and is VERY time consuming to seperate .... The eyewittnesses said they heard a loud pop , and looked up and saw the broken plane coming down..... For those unfamiliar with airframe failures , The loud pop IS the spar failure ....  If you play with the video , you can see the wings folded up outboard of the wheels before it hits the ground.... ( when it first enters the frame ) 

 

[PT20J]

I suppose I would be indifferent as to whether an overstress first caused the tail to break off or the spar to fail were I an occupant.

[Shadrach]

On 11/30/2021 at 7:33 PM, Alan Fox said:

Couple of things , The spar is NOT a continiuous piece , It is spliced together , It is called one piece (incorrectly) becaues it is fastened together with many rivets and Hi-locs , and is VERY time consuming to seperate .... The eyewittnesses said they heard a loud pop , and looked up and saw the broken plane coming down..... For those unfamiliar with airframe failures , The loud pop IS the spar failure ....  If you play with the video , you can see the wings folded up outboard of the wheels before it hits the ground.... ( when it first enters the frame ) 

 

It may be an incorrect nomenclature in your opinion but following your logic some spars would be 10 (or more) piece spars.  The reason the Mooney spar is called a one piece design is because the spar and wing are built up in a jig as a single unit and attached to the airframe as a single unit.  Most other Aircraft manufacturers fabricate left and right wings separately.  Unlike most other GA brands you cannot remove one wing from a Mooney (well, perhaps with a Sawsall).  It is indeed a one piece spar as much has a Comanche or Bonanza has a two piece spar.  If you are going to go down the rabbit hole of counting every splice as a piece, that's fine but it is not how the industry classifies various spar designs.  

Edited December 6, 2021 by Shadrach

[Blue on Top]

1 hour ago, Shadrach said:

It may be an incorrect nomenclature in your opinion but following your logic some spars would be 10 (or more) piece spars.  The reason the Mooney is called one piece design is because it is built up in a jig as a single unit and attached to the airframe as a single unit.  Most other Aircraft manufacturers fabricate left and right wings separately .  Unlike most other GA brands you cannot remove one wing from a Mooney (well, perhaps with a Sawsall).  It is indeed a one piece spar as much has a Comanche or Bonanza has a two piece spar.  If you going to go down the rabbit hole of counting every splice as a piece, that's fine but it is not how the industry classifies various spar designs.  

Well put, @Shadrach.  The airplane was obviously well outside the operating envelope.  The fact that one side of the stabilizer departed the airplane will give the NTSB a lot of information.  Data on whether the airplane was rolling may also be available (or reasoned from ADS-B data ... or radar returns).  Further up the chain, the elevator departed the stabilizer, which was still attach at that time.  Analyzing those parts and how they came apart will also be used.  The fact that the elevator was only 600 feet away (and stabilizer 300 feet) says they departed very, very late.  Control surfaces will "fly" a long way from where they depart the airplane.  They will also go further up the chain.

Another point I've heard is about what should have failed first.  Remember that ALL airplanes are designed with a MINIMUM safety margin of 50%.  Composite airplanes are normally very close to this value (ply schedules are changed to get the lightest structure).  Small, GA, aluminum airplanes normally stick with standard material thicknesses.  IOW, if an 0.032" skin is marginal (or fails), the designer will go to an 0.040" skin which may give much more than the required 50% margin.  We all know that Ralph Harmon designed a really, really beefy airplane! 

Bottom line:  There's A LOT of data the NTSB has to sort through.  There's a reason it takes them so long to put out a final report.

[Mooney in Oz]

17 hours ago, Shadrach said:

Unlike most other GA brands you cannot remove one wing from a Mooney (well, perhaps with a Sawsall).

 

15 hours ago, Blue on Top said:

We all know that Ralph Harmon designed a really, really beefy airplane! 

A few weeks ago I was discussing the strength of the Mooney spar with an airframe engineer who will be doing the required metal work for my GFC500 install. He told me that years ago he was part of a team who had to retrieve a wrecked 201 that crashed into a heavily wooded area necessitating breaking the aircraft up into pieces to effect the wreckage removal.

As part of the breakup, the spar had to be cut in half using some type of electric saw. He said it had taken him 3 whole days to do so.

[Jerry 5TJ]

1 hour ago, Mooney in Oz said:

As part of the breakup, the spar had to be cut in half using some type of electric saw. He said it had taken him 3 whole days to do so.

Perhaps he used a Dremel tool.  

[Alan Fox]

On 12/4/2021 at 7:20 AM, Mooney in Oz said:

 

A few weeks ago I was discussing the strength of the Mooney spar with an airframe engineer who will be doing the required metal work for my GFC500 install. He told me that years ago he was part of a team who had to retrieve a wrecked 201 that crashed into a heavily wooded area necessitating breaking the aircraft up into pieces to effect the wreckage removal.

As part of the breakup, the spar had to be cut in half using some type of electric saw. He said it had taken him 3 whole days to do so.

I do it in about 6 minutes , There is a video on here somewhere , of that very task

[Alan Fox]

On 12/3/2021 at 1:33 PM, Shadrach said:

It may be an incorrect nomenclature in your opinion but following your logic some spars would be 10 (or more) piece spars.  The reason the Mooney spar is called a one piece design is because the spar and wing are built up in a jig as a single unit and attached to the airframe as a single unit.  Most other Aircraft manufacturers fabricate left and right wings separately.  Unlike most other GA brands you cannot remove one wing from a Mooney (well, perhaps with a Sawsall).  It is indeed a one piece spar as much has a Comanche or Bonanza has a two piece spar.  If you are going to go down the rabbit hole of counting every splice as a piece, that's fine but it is not how the industry classifies various spar designs.  

It is indeed NOT a one piece wing , It is halved and has a seam in all the parts , right down the center , and held together with aluminum splice plates and Hilocs .... I have taken enough of these things apart , they also splice outboard of the second skin , OIts actually a 4 piece spar , The stringers and caps , may overlap on the outer splices , I dont know if they do , or do not , But the two halves are spliced right in the middle , Look in the parts manual....