Mooney spar design

[Igor_U]

13 hours ago, Sabremech said:

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! 

Yes it's true,

all PA28 have NACA 652-415 laminar flow airfoil. So do Comanche's, PA32 and their twin counterparts (some have NACA64A215). This goes for both Hershey bar and later semi-tapered wings. Designer John Thorp and his team wanted to move main spar aft and NACA g series laminar airfoils have max thickness at 40% chord as opposed to 30% for more traditional NACA 4 digit airfoils. Changing the airfoil would not be practical as that would require massive redesign of the wing spar and fuselage attachment points.

I believe Semi-tapered wing has larger wingspan as well as a quick look at Cherokee and Warrior manual would confirm.

Should Pipers be faster?

Well, not all laminar flow airfoils are the same, some are actually designed with gentile stall characteristics in mind. The other wing feature is that Designer chose to use same airfoil at the wing root and the wingtip (NACA 652-415 ). This is normal for rectangular wing but less so designing a tapered wing like Mooney. Mooney wing airfoils are NACA 63-215 wing root and        NACA 64-412 at the tip. Last two digits in the NACA 6 series designation are relative thickness of the airfoil so while Al Mooney decided to use a thinner (12%) airfoil at the wingtip, Piper team decided 15% would do at the tip as well. Also, you can notice the airfoils are different thus having different characteristics; it be safe to say Piper's choice is with more drag, showing constant pressure rise and gentle stall characteristic desirable for training aircraft.

 

How good are these wings in maintaining laminar flow is another question. Build quality of the metal wing with thin skins and wing jigs is something to desire for. Composites are much better in keeping the desired shape of the wing. Even wooden Mooney wing was supposedly much smoother and faster then metal wing after the redesign.

 

Ralph Harmon was designer of the Metal Mooney wing. I am not so sure that Al Mooney hired him, though. As far I remember, Mooney brothers left the company due to (another) bankruptcy at the time first M20s were getting in production and were never around to see them flying. I could be wrong, though as I read the book years ago.

 

 

 

Edited April 19, 2018 by Igor_U

[Igor_U]

2 hours ago, M20Doc said:

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

Clarence

Pipers PA28 do not have a life limit. As far I know, no airplane certified under CAR 3 does; that is something newer designs under part 23 do have, though. I seems to remember Piper Tomahawk has 12,000h limit on wing life...

[Mooney in Oz]

1 hour ago, Igor_U said:

Ralph Harmon was designer of the Metal Mooney wing. I am not so sure that Al Mooney hired him, though. As far I remember, Mooney brothers left the company due to (another) bankruptcy at the time first M20s were getting in production and were never around to see them flying. I could be wrong, though as I read the book years ago.

I have a copy of The Al Mooney Story by Gordon Baxter.  On page 149 it reads that Al left Kerrville in 1955 to work for Lockheed.  The M-20A was introduced in 1958. Later it reads, "In 1960, Ralph Harmon, formerly of Beechcreat, Cessna and McDonnell, joined Mooney Aircraft.  Harmon metallized the wood-winged airplane, creating the M-20B in December 1960."

I also have a hard copy of Larry Ball's Those Remarkable Mooneys. In part it reads Al stayed around until September 1955 when his M20 was certificated, although the M20 prototype first flew on September 3, 1953.

I love reading about Al and Art.  I just wish that they had have been successful at operating Mooney from a business perspective. It's not fair their most successful design, the M20 ended up out of their hands following certification.  I also wish I had the privilege of meeting them both.  

Their legacy lives on.

[cliffy]

I thought that it was Al but it could have been who ever was at the helm at the time (4 decades has a little fog on esoteric information) but the story is correct unless the fog is too thick this far down the road. Updates gladly accepted.

No different than my recollection of why the elevator and stabilizer settings were changed on the C model back in 69 (reference TCDS). I remember reading a small article back then that said there was some discrepancy in stall recovery and it had to be changed (for more down elevator) but I can't find any supporting data today (just my memory). The factory had no information for me when I asked a couple years ago.  Anyone ever noticed this and know why? This is one I really wanted to track down but no one wanted to approach it at the factory.  For me, its an unknown anomaly right now. There had to be a reason why it was done.  

[RobertGary1]

At the factory they would all stand on the wing  Yes, its strong.

 

-Robert

[Guest]

13 minutes ago, RobertGary1 said:

At the factory they would all stand on the wing  Yes, its strong.

 

-Robert

The biggest load a Mooney ever carried!

Clarence

[Cyril Gibb]

I predict a fat lady insertion into this thread....

[aviatoreb]

45 minutes ago, Cyril Gibb said:

I predict a fat lady insertion into this thread....

It needs to be two - one on each wing, otherwise the Mooney won't balance.

[KSMooniac]

Some pics of my salvage wing section, with section cuts through the spar.

Sent from my LG-US996 using Tapatalk

[Guest]

On 2018-04-18 at 2:16 PM, 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.

 

 

 

It is easily inspected.  I posted this picture in the other thread as well.  Lift the back seat, removed the carpet from the front of the spar. Insert flash light and mirror or NDT inspection equipment.

[rpcc]

Thanks for the picture and that looks like a robust structure.  

The failure likely began from the bottom part of the spar where the top set of bolts in this pictuer pass through it.   Is it possible to inspect the bottom part of the spar for cracks/corrosion or other signs of weakness?  

When I speak of a design flaw I'm useing a very wide interpretation.  I expect that certified planes, when properly maintained and operated within their intended environment and design limits should never fail.  If the plane fails within its design then the "design" failed.  By design I mean everything, material choice,  inspection access methods and process,  robustness of structure to handle abuse, certification process.   It is simply not acceptable to have a part in a certified aircraft fail when operated within limits and properly inspected.   If it really is a time limited part - then say so.  If it needs to be inspected more carefully then say so.  

I'm not trying to start an argument about one manufactures wing is better than the other.  Reading about the guy who went to get his tank resealed and found the spar corroded under the sealant wasn't good either.

Since the aircraft is certified and properly maintained the wings should never have fallen off on takeoff at 900ft.  

Again thanks for the picture.  

 

[Yetti]

4 hours ago, M20Doc said:

It is easily inspected.  I posted this picture in the other thread as well.  Lift the back seat, removed the carpet from the front of the spar. Insert flash light and mirror or NDT inspection equipment.

I would have lined up the bolt heads on the left, like the ones on the right.  Craftsmanship don't skip it.

[rpcc]

seems like snowmen are very detail oriented

 

 

[kerry]

Mooney's have a reputation for how harsh the ride is in turbulence compared to other planes.  I wonder if this has to with the strength and stiffness of the Mooney wing.  If a wing is not as stiff it seems it would give a softer ride.  A softer ride means more flexing and fatigue in the wing.  I'm not a engineer but my reasoning makes sense to me.  I've heard of many aircraft types with wings coming off for reasons from jet wake turbulence to weather.  Does anyone know of a Mooney wing coming off in flight?

[Mooney in Oz]

7 minutes ago, kerry said:

A softer ride means more flexing and fatigue in the wing

I suppose it would depend whether the wing was designed to flex.  Not a good comparison, but a B787 wing was flexed upwards to 25 feet during testing.

[jetdriven]

only a couple of Mooney’s have broken up in flight. Both I think due to thunderstorm upset and a serious departure from controlled flight. At 300 KIAS anything will break when you pull. 

[bradp]

I thought tail departed one of those due to over stress.  

Past limits or out of spec and all sorts of untoward things happen.  

 

[Yetti]

https://www.facebook.com/gold.standard.aviation.one/videos/1519540618154327/?t=0

[Guest]

2 hours ago, bradp said:

I thought tail departed one of those due to over stress.  

Past limits or out of spec and all sorts of untoward things happen.  

 

The PA 30was used by NASA in flutter testing, it’s very dramatic.  It was flown by astronaut Fred Haise.

“In the video above, astronaut Fred Haise is piloting a Piper PA-30 Twin Commanche during flutter tests NASA conducted with general aviation aircraft in the late 1960s. Once the vibrations are introduced into the tail of the aircraft, in this case a stabilator, the flutter increases dramatically causing tremendous oscillations in the horizontal surface making the stabilator flex as if made of rubber.

According to NASA, Haise said of the experience, “I’m fearless, but that scares me.”

Sadly some years later in private hands it was involved in a fatal accident and lost.

Clarence

[Guest]

5 hours ago, Yetti said:

I would have lined up the bolt heads on the left, like the ones on the right.  Craftsmanship don't skip it.

That’s the way they were aligned when we looked in for inspection.  I’d be more concerned that the washers are installed correctly against the spar.

Clarence

[aviatoreb]

2 hours ago, M20Doc said:

The PA 30was used by NASA in flutter testing, it’s very dramatic.  It was flown by astronaut Fred Haise.

“In the video above, astronaut Fred Haise is piloting a Piper PA-30 Twin Commanche during flutter tests NASA conducted with general aviation aircraft in the late 1960s. Once the vibrations are introduced into the tail of the aircraft, in this case a stabilator, the flutter increases dramatically causing tremendous oscillations in the horizontal surface making the stabilator flex as if made of rubber.

According to NASA, Haise said of the experience, “I’m fearless, but that scares me.”

Sadly some years later in private hands it was involved in a fatal accident and lost.

Clarence

That is generally how flutter onsets in any aerofoil / the onset can be sudden and dramatic - the key is to stay below futter limits rather than to try and engineer a mild flutter.

[Yetti]

3 hours ago, M20Doc said:

That’s the way they were aligned when we looked in for inspection.  I’d be more concerned that the washers are installed correctly against the spar.

Clarence

Yep.  I was referring to the installer, not the inspector. 

[carusoam]

See if this helps calm some fear of unseen oxidation between aluminum layers...

 

Oxidation between layers of aluminum, when it gets to an important level, is often detectable to the eye...

Aluminum oxide is a higher volume than the solid aluminum.  In other words the volume increases significantly...

Volume increasing between layers has a tendency to pry the layers apart, stretching and breaking the fasteners that are holding the layers together... the fasteners are designed to stretch really far before they can break in a tensile mode...

It is not possible for the fasteners to keep the corrosion from expanding...  the chemical expansion is a very powerful force...

The oxidation can’t seep out. If it does it will leave a trace... (smoking rivet style trace) even though smoking rivets are an abrasion/wear effect and not-corrosion related...

 

So...

If you look at the spar and all the fasteners are still there... that is a good sign...

On the other hand.... If you see a row of rivets, and you notice one (or two or more) is missing...  that is a sign to look for what made that guy get away...

or, you look and see the nice flat, straight, layers of aluminum are looking expanded enough to have a non-uniform gap or curvy layer in an area... that is worthy of closer inspection....

It is not likely to get the interlayer oxidation to occur, as something has to let the oxygen in there to begin with, and have the catalyst near by, water, relative humidity can be a catalyst as well...

 

One may need to have an actual investigation before claiming the failure is a design flaw...

There is a lot of design put into these things... with Plan Bs to each design step...

• Materials that are used.
• procedures and processes for making the parts.
• Assembly procedures.
• maintenance procedures.
• Documentation procedures.
• Serialization procedures.
• There is often, acceptable depth of oxidation that can be repaired and or re-used when treated properly.

All of this gets done every time a plane gets built and maintained...  when the rules are followed.

Modern manufacturing Science has left very little to be a surprise...

Computer science has made it incredibly easy to cross check serial numbers all the way back to the day each part was made, from which batch of raw materials the part was made from... and a complete record of inspection  for each part...

The first thing owners would want to know... does this failure possibly affect the plane I own/fly...?

The second thing some owners want to know... does my maintence get done properly, down to the last documented detail...?

The FAA and user groups are pretty good at narrowing down the causes of such failures, and, ruling out, the larger population on technical reasons...  and unfortunately (sort of), ruling in, certain planes that have shared a common maintenance procedure or part...

 

Is this enlightening?

PP thoughts only. Not a mechanic... may have designed and or built non-flying machines in another lifetime... 

Best regards,

-a-

 

[rpcc]

@carusoam As always, thank you for your thoughtful posts.  

My posts regarding the accident  plane are from my perspective which is at best,  little more than a naive aviation consumer and in no way an engineer, examiner or maintenance person .  From my perspective  I'd like to believe that through the hard work of all the smart and diligent people involved, that wings should stay attached to planes provided the the plane is being flown within its limits.  So again, no offense to anyone and you all have your right to your opinion, but I believe the system of designs on this plane are flawed because the wings fell off.   

Regarding the mooney wing and corrosion - again from my naive consumer position - this thread I've provided a link too below is an interesting read - good news is it ended well.  However, the design choice to use  the spar as one side of the wet wing fuel tank requiring sealant that covers the rivets and gaps between aluminum layers makes the inspection you are suggesting very difficult.   

 

[cliffy]

Every metal wing Boeing is designed the same way as our Mooneys, wet wing technology. Even 50 year old 727s have wet wings so the design style is well proven as doable. As mentioned, the difference "may" be in inspection technique and interval to find corrosion. 

I have always found the mind set we exhibit toward 50, sometimes 60, year old airplanes (when viewed from the position of maintenance) and how we view automobiles quite interesting. We invariably drive cars that are less than 6-10 years old (FOR RELIABILITY) yet we think  nothing of jumping into a half century old airplane with lots of "deferred" maintenance or with maintenance we as amateur mechanics have done (when a lot of times we don't even work on our own cars, hangar fairies?) and fly across the country over hostile terrain. Its mind boggling. Probably needs another thread here.