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Mooney spar design

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One thing that I did learn about the Mooney spar from my recent repair to the wing is that the spar is not one contiguous single piece of metal but several individual pieces which are spliced together.

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2 hours ago, flyboy0681 said:

One thing that I did learn about the Mooney spar from my recent repair to the wing is that the spar is not one contiguous single piece of metal but several individual pieces which are spliced together.

Yes. our spar is built from many pieces, riveted solidly together into one piece.

Piper spars are similarly built from many pieces into three large pieces that bolt together, designed to be removable. The failure was at the bolt location . . . which we don't have. Spar design is different; the built up shape is different; size, number and location of rivets is different; otherwise, just say they are both low wings and can both fail like this. But ours won't, there are no bolt holes, no wear from removing a single wing panel, no stress concentration at the wing joint bolts, no possibility of a wing joint bolt being overtorqued and causing problems, nor loosening and damaging the hole, etc., etc., etc.

I am sorry for these guys . . . an awful thing to happen on a beautiful day to fly.

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Yeah - its a design flaw in the piper wing.  Should have been inspectable at annual and at preflight if its capable of failing catastrophically.  If its not inspectable then it should have been reinforced or redsigned so it cant fail.  

Wings should not fail in normal flight.  

This plane was intended to be used in a training environment.  It was properly inspected, yet there are two dead people as a result of this.

 

 

 

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2 hours ago, rpcc said:

Yeah - its a design flaw in the piper wing.  Should have been inspectable at annual and at preflight if its capable of failing catastrophically.  If its not inspectable then it should have been reinforced or redsigned so it cant fail.  

Wings should not fail in normal flight.  

This plane was intended to be used in a training environment.  It was properly inspected, yet there are two dead people as a result of this.

 

 

 

If it’s a design flaw, why aren’t more falling out of the sky?  And why hasn’t the FAA grounded them all pending a re-design?  

The area is able to be inspected just not easily.

Clarence

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Its a design flaw because the plane was being flow within its design limits and the wing fell off.  It was a plane intended to operate in a training environment so saying it had some tough landings is no excuse.  If 7000 hours is too much use, it should time limited.  

Who knows what the FAA will do - I'd like to hear them ground the planes until they have been inspected. 

I don't believe as aviation consumers we should accept events like this.  We should demand better performance from manufactures, designers, FAA certification process and maintenance professionals.  

I know - I'm not living in reality - but this type of event upsets me.   These guys were just enjoying a beautiful day.

Sad

We can demand better.

 

 

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37 minutes ago, rpcc said:

Its a design flaw because the plane was being flow within its design limits and the wing fell off.  It was a plane intended to operate in a training environment so saying it had some tough landings is no excuse.  If 7000 hours is too much use, it should time limited.  

 

The airplane had over 7000 hours on it, so a design flaw would have shown up a lot earlier, and would be exhibited in other aircraft of the same type.

Since the airplane wasn't anything close to new, had changed hands a few times, and had a LOT of hours on it, the storage, use, and maintenance history can play a big part in the condition of the aircraft.   It is far more likely that the airplane had an age- or storage- or maintenance-induced- or whatever- related condition that had been missed in previous inspections.   It's not like that hasn't happened before, to any make or type of aircraft, including Mooneys, including Mooney cases that have been archived here.

 

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55 minutes ago, rpcc said:

Its a design flaw because the plane was being flow within its design limits and the wing fell off.  It was a plane intended to operate in a training environment so saying it had some tough landings is no excuse.  If 7000 hours is too much use, it should time limited.  

Who knows what the FAA will do - I'd like to hear them ground the planes until they have been inspected. 

I don't believe as aviation consumers we should accept events like this.  We should demand better performance from manufactures, designers, FAA certification process and maintenance professionals.  

I know - I'm not living in reality - but this type of event upsets me.   These guys were just enjoying a beautiful day.

Sad

We can demand better.

 

 

By extension we should ground all Boeing 737’s pending redesign of the engine and it’s containment because it failed and all windows should be strong enough to stop engine shrapnel.

Clarence

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4 hours ago, rpcc said:

Yeah - its a design flaw in the piper wing.  Should have been inspectable at annual and at preflight if its capable of failing catastrophically.  If its not inspectable then it should have been reinforced or redsigned so it cant fail.  

Wings should not fail in normal flight.  

This plane was intended to be used in a training environment.  It was properly inspected, yet there are two dead people as a result of this.

A fatigue fracture through 80% of the wing spar at 7000 hours is not a design flaw, it's a manufacturing defect or external factor such as corrosion or maintenance damage.  If it was a design flaw, wings would be falling off at 7000 hours everywhere, and they're not.  There must have been a stress riser early on to cause such an extensive fracture--my understanding is that the loads and frequency of stresses on an aluminum wing spar should give them 20,000 hours of life or more.

OTOH, just because it's a manufacturing defect does not mean there won't be an AD. 

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The airplane had over 7000 hours on it, so a design flaw would have shown up a lot earlier, and would be exhibited in other aircraft of the same type.
Since the airplane wasn't anything close to new, had changed hands a few times, and had a LOT of hours on it, the storage, use, and maintenance history can play a big part in the condition of the aircraft.   It is far more likely that the airplane had an age- or storage- or maintenance-induced- or whatever- related condition that had been missed in previous inspections.   It's not like that hasn't happened before, to any make or type of aircraft, including Mooneys, including Mooney cases that have been archived here.
 


It will be interesting to see how they proceed. It is unlikely the fleet will be grounded unless they changed their views on these matters. The 737 uncommanded rudder accidents are a good example of how they have proceeded in the past.

https://en.m.wikipedia.org/wiki/Boeing_737_rudder_issues


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12 hours ago, Igor_U said:

What you see on that picture is just a T shape Wing spar cap that failed, not the whole spar. Spar is build up "I" beam (upper and lower caps plus web) similar to Mooney's and you can see it on the Isometric view attached to the report. Wing shapes are, of course different with early PA28 having Hershey bar wing while later one have outboard portions of the wings tapered.

Similarly to Mooney, PA28 have laminar wing profile so the main spar is at maximum airfoil thickness (40% of the chord) and passes aft of the pilot's seats.

I'd be interesting to read the final accident report and more about history of the aircraft. Making a left crosswind definitely didn't break the spar; previous flights did.

 

PA28 has laminar flow wing profile? Never saw that on my PA28 Cherokee that I owned. Should have been a heck of a lot faster! 

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only the hershey bar wing was a laminar profile. but it wasnt built close enough to smooth to make it that way in practice.

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it is very much a design flaw - 7k hours on an airframe should be nothing.  just crappy design that killed a couple of guys.  

 

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13 minutes ago, jetdriven said:

only the hershey bar wing was a laminar profile. but it wasnt built close enough to smooth to make it that way in practice.

That plus the honking landing gear sticking out probably creates an issue <_<

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I understand that the Mooney has a laminar flow wing, and understand why it is; that is, the airflow over it acts a certain way. But how does one make a wing "laminar flow". Is it shape, thickness to chord ratio, or some other factor(s). Can one tell by looking at a wing? Or do you have to test it in a wind tunnel to know.

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3 minutes ago, M20Doc said:

From Piper SB 978A The wings have quite a long life in regular use.

 

63,000 hours?  Wow...

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From Piper SB 978A The wings have quite a long life in regular use.
614BD73E-A753-4B0A-A4ED-3811E5AA74B9.thumb.png.3a682b15860639bd3331ac6871e621fc.png


I’ve seen that SB elsewhere and I’m curious whether ERAU applies the Class A requirements unless it can be determined Class C applies.

While flight training is considered by this SN as normal (Class A), reading the definition for Class B makes me hope ERAU uses the Class B intervals.

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Just a couple of items to add-

Mooney has a laminar flow wing back to about the 40% chord line IIRC. Piper Comanche and Twin Comanche also have a laminar flow about the same IIRC. Laminar flow is where the boundary layer of air stays attached to the wing surface for an extended period of time as it flows aft toward the trailing edge. Generally these wing airfoils have a more streamlined thinner shape than say the airfoil on a Cessna wing. Full laminar flow would stay attached all the way to the trailing edge. Very difficult to achieve. 

As far as Mooney wing strength goes, the same engineer that designed the Bonanza wing designed the Mooney wing. If you recall, several Bonanzas were lost to wing failure early on and many "fixes" were incorporated into later Bonanza wings to strengthen them. 

When Al Mooney hired that engineer to design the metal wing on the Mooney the engineer would only accept the job if Al let him design it the way he wanted  as he said he didn't want to have another design coming apart because Walter Beech kept having him "lighten" the structure to save weight. That is why we have such a strong wing in a Mooney. 

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14 hours ago, jetdriven said:

thats not a life limit, its an inspection interval.

You’re correct, the life limit would actually be longer, you wouldn’t inspect the wing if the life were shorter.

Clarence

Edited by M20Doc
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