Wing spar failure?

[jgarrison]

2 hours ago, DXB said:

Anyone have a link to the J model accident?

 

https://planecrashmap.com/plane/la/N577RS/

[WaynePierce]

27 minutes ago, jgarrison said:

https://planecrashmap.com/plane/la/N577RS/

What a sobering read... Same year and very close S/N of my plane.

 

[carusoam]

If I read that correctly…

All of the parts of the M20J were found at the accident site…. Except the counterbalances for the elevator…

A subtle sign of control flutter prior to arriving at the final resting site…. Where the lead weights don’t want to move as fast as the associated control surface wants to move…

 

PP thoughts only, not an accident investigator…

Best regards,

-a-

[A64Pilot]

Flutter is usually pretty destructive or if your lucky enough to survive flutter it’s usually at least very damaging.

The way flutter is controlled is by those weights, that’s why they exist on most aircraft, if you ever repaint flight control surfaces or repair them, it’s very important to check their balance, the more nose heavy a flight control surface is, the more resistant to flutter it is, so within limits, being nose heavy is a good thing, so if you have to rebalance, do so towards the nose heavy limit. Installing a tail mounted ADSB tail beacon could put the rudder out of limits, depending on how heavy the stock light was.

If God forbid a flight control weight were to separate at higher speed, that ought to guarantee flutter.

Another thing that can start flutter is worn Heim joints in the flight control system or mounting points of the flight control, it seems for whatever reason trim tabs have the most wear, not a concern for us as we don’t have them, I don’t miss them personally. the variable incidence horizontal is a better design. In my opinion.

‘Most that have flown higher performance RC models have seen flutter, often what happens is you see something come off of the aircraft, then hear a buzz sound. May as well set the radio down, cause it’s all over before you even heard it.

[RobertGary1]

Curious to me that so many are wasting time on this based on an accident with almost no objective data currently available. It’s like wondering why captain Picard had a British accent if he’s French. Once the NTSB releases factual data it will be a useful topic to discuss 

[Yetti]

Yes the spar failed,  When it failed (pretty close to the ground), why it failed (corrosion, over stressed on high speed pull up) we will know more about in  a couple of years.    Rear parts of the plane failed and fell off, not long before the impact.

[PT20J]

The procedures for balancing control surfaces on a M20J are in section 27-93 of the Service and Maintenance Manual. Note that all Mooney control surfaces are underbalanced — that is they are trailing edge heavy.

Skip

[DXB]

25 minutes ago, RobertGary1 said:

Curious to me that so many are wasting time on this based on an accident with almost no objective data currently available. It’s like wondering why captain Picard had a British accent if he’s French. Once the NTSB releases factual data it will be a useful topic to discuss 

I dunno - I learned quite a lot from folks here about how structural limits of our planes can be exceeded and corrected a few of my own misconceptions.  Little that's conclusive about that particular crash can be said presently, and yet I suspect most of the potential learning benefit from looking at it has already been extracted in the discussion.

[jlunseth]

In connection with the "Minnesota Crash" thread I searched for prior incidents involving folding of the Mooney wing. I found three, a Mite, a J and the Rocket incident referred to earlier in this thread. If you want to see the references, look at the other thread. Now there is a fourth, the Bravo that went down in Victoria MN. I found another brief reference to a J incident, but there was not enough information to determine whether it was the one I had already found, or a second J. I exclude the Mite from this discussion because the wing construction was different. What was interesting from a forensic point of view about the prior two modern Mooney incidents was that the wings had failed in a negative direction. I tried to explain my understanding of what "negative" and "positive" lift mean to aerodynamics experts and I think I did not do a very good job in the other thread. It is pretty simple. As I understand it, "negative" lift or failure of the spar in the negative direction means toward the belly of the aircraft, regardless of whether the belly is up or down with respect to the earth. "Positive" lift or failure is towards the ceiling of the aircraft, again, regardless of the aircraft's orientation to the earth. As we know, the wing of our normal category aircraft is certified to sustain positive loads a little more than double the certified negative loads. That out of the way, the explanation of the Rocket failure was particularly clear in the NTSB report. Mooney had done an analysis and concluded that the aircraft flipped in the air and the wings failed in the negative direction. The J report was not quite as clear, but the same failure, in the negative direction. 

The recent Bravo was the only modern Mooney inflight spar failure that I found, where the wing(s) failed in the positive direction. I know that there was the "artifact" discussion that posited that the tail struck first, then the right wing, and that somehow caused both wings to fold up. I personally think that was a useful discussion even though I disagreed with the theory. However, more than one witness description is now available saying the wings folded in the air. There is video evidence of the right wing after the crash, intact and undamaged at the wing tip. The NTSB says the horizontal stab and elevator departed the aircraft before impact and rendered the aircraft uncontrollable. I think we have all concluded that the wings folded before impact.

We have all been cognizant, if not proud, of the strength of the Mooney wing. These incidents, however, show that we need to be more cognizant of the vulnerability of the horizontal stabilizer and elevator. If there is a flutter failure and the stabilizer departs the aircraft, there will be an abrupt nose-up or nose-down of the aircraft (depending on what direction the wing is generating lift at that moment) that can fail the wing because of the abrupt change in angle of attack. This does not require a sharp pull up by the pilot, it only requires departure of the stabilizer. In my mind the two, a sharp pull up and departure of the stabilizer are not related. Failure of an aerodynamic surface due to an excessive pull-up is a function of knots indicated, angle of attack, lift generated, and the lift capacity of the surface. Failure of an aerodynamic surface in flutter is a function of true airspeed, stiffness of the structure, and harmonics. The stab can be ripped off by flutter regardless of the lift load on the stab or on the wing, or whether there is a lift load on the stab.

The point is that as much as we value the strength of the wing, we need to be very cognizant of Vne and the consequences of exceeding it. Someone said, in the Minnesota Crash thread, that the critical speed for flutter in our airframe is 241 knots. That is not much of a margin over the 195 Vne if you have allowed the slippery airframe to enter an uncontrolled dive in IMC. The information gathered in that thread indicates that the departure from a relatively stable altitude to the moment of impact was between 7 and 11 seconds.

Also, if the stabilizer departs the aircraft, it is not particularly relevant whether the wing survived or not, the aircraft is not controllable.

[Nippernaper]

Richard Collins has addressed this many times, among others. Structural failure after loss of control is a well known, often seen phenomena. It is almost always caused by pilot inputs, usually a big pull either in a spiral dive or after breaking out and trying to avoid the ground. Either the horizontal stabilizers fail first, which will then result in a severe nose down pitch followed by negative direction failure of the wings, or the wings fail first in the positive direction. This looks to be the first for a mooney in the latter sequence. Center of gravity is ahead of the center of lift of the wing, so if you lose the tail down force, your nose is going to pitch down.


Sent from my iPhone using Tapatalk

[Nippernaper]

It may be that for the short and mid-bodies, the horizontal stabilizers are the weak link, but for the long bodies, with the longer moment arm to the tail, the wings become the weak link. Not that it really matters; go fast enough and pull hard and something is going to give.


Sent from my iPhone using Tapatalk

[carusoam]

Sales brochure engineering is fun for conversation….

It takes 100% of the plane to fly the way it is supposed to…

Wrap a simple baggage door around your horizontal stabilizer… you immediately enter the Test Pilot phase of your flying career…

 

Loading the main wing with people makes a memorable conversation…. Even pilots don’t immediately recognize… all that weight is technically simulating negative gs….  Depending on the bending moment and where the main landing gear are… 

 

I was most impressed when I saw a pic of how much weight you need to put on the tail to perform a gear test on jacks…

More or less, that is a similar amount of weight that the horizontal stabilizer supplies in flight…

 

I was most scared when I saw the damaged Mooneys after the mid-air collision…  that could have been a whole lot worse…

 

There are spares and back-ups for everything on a Mooney…. That mostly work if something becomes disconnected… three hinges instead of two…

The first few minutes of flight… the forces are pretty mild… and trim can substitute for a disconnected elevator…

 

Even the parachute plane has learned that at high speeds the plane falls apart…. Without being able to slow down… the chute deployment speed is already exceeded and getting worse…

 

So… if you find yourself at high speed pointing towards the ground… use all of the space available to correct… with all of the brakes deployed… top and bottom if available…

For Robert’s curiosity… I’m in a room full of Mooney pilots having a conversation that is somewhat inspired by recent events…  while we wait to hear more news… the events can’t be overturned… but the discussion is good…  plenty to learn about Mooneys around here…

PP thoughts only, not a cfi….

Best regards,

-a-

[jlunseth]

On 8/10/2021 at 11:34 AM, Jerry 5TJ said:

If you lose your horizontal stabilizer why would you care if your wing spar is intact?  

Exactly.

[jlunseth]

22 hours ago, RobertGary1 said:

Curious to me that so many are wasting time on this based on an accident with almost no objective data currently available. It’s like wondering why captain Picard had a British accent if he’s French. Once the NTSB releases factual data it will be a useful topic to discuss 

There is quite a bit of factual information, see the Minnesota Crash thread. The NTSB has stated that the aircraft was on an instrument flight plan from AXN to FCM, and was on the ILS 10R into FCM. See the NTSB interview in the Kathryn’s report. At page 10 of the Minnesota Crash thread is a graphic by 1980mooney using ADSB data and showing the flight path. The aircraft was inside the intermediate fix, ZAMUD, at an altitude of 3000-3100 and slightly left of course. Intercept altitude for the approach is 2700 and at ZAMUD the pilot is supposed to descend to 2600 at STUBR, which is the FAF, which is at that point roughly three miles away. The plotted course data shows that the pilot turned southbound and descended to 2600-2700. This would suggest he was correcting to get on the final approach and at the correct altitude at STUBR to intercept the glideslope. At the end of the southbound turn, the aircraft turns abruptly northbound and altitude variations begin. The plane at that point is 7-11 seconds from impact. The descent rates from that point to impact were very high. There was a cloud deck about a thousand feet thick, from about 2700 to around 1100 or 1200, according to a recent RAOB. The ATC record suggests the pilot was either distracted or impaired, as his responses to tower were delayed and nonstandard. One side of the horizontal stabilizer and elevator departed the aircraft. The wings folded in the positive direction. The aircraft fell to the ground uncontrolled in a shuttlecock descent. Two separate eyewitnesses said that the wings folded in the air and the aircraft spiraled to the ground. The two wings were found on the ground essentially intact except torn off at the roots. There was no damage to the right wingtip, indicating the aircraft did not tip to the right and impact right wing first. It pancaked. The stabilizer and elevator were found two blocks further back on the flight path. These things are uncomfortable, certainly, but they are in the record. It would be good to get time-stamped information for the communications from tower, and the communications with approach before that. It would be good to know the engine data, was it running and how fast, which the NTSB will tell us. There was an engine monitor onboard, which the NTSB says they have. It would be good to know the state of the AP, whether engaged or disengaged and in what mode. It would be good to know whether there was an incipient gyro failure. The state of the AP, the vacuum pump, and the gyro we may never know because of the fire.

[BKlott]

On 8/8/2021 at 11:44 AM, PT20J said:

I've never seen one actually documented. The story related to me years ago by a factory engineer is that the Bonanza had a few spar failures on Ralph Harmon's original design and so when he metalized the Mooney, he way over-built it. I was told that more modern calculations showed it would fail at around 10 g, but I have no idea if Mooney ever tested one to destruction.

Skip

In early 1980 Aviation Consumer published a report on the Beech model 35 V-tail Bonanzas. The report indicated that through 1978 seventy one (71) of the fifteen hundred (1500) original model 35 Bonanzas had been involved in a fatal in flight airframe failure. That represents 4.8% of the original, straight model 35 aircraft produced.

Subsequent improvements to the airframes during the production run lowered this percentage on later models closer to 1%. None of the various models of the V-tail Bonanzas were immune to airframe failures. The only exception was the model 35R of which there were only thirteen (13). These were early model Bonanzas that were returned to the factory for numerous modifications to beef up the airframe based on what Beechcraft had learned from earlier accidents. The modification program was discontinued as it cost nearly as much as the entire airplane.

The report indicated AT THAT TIME (thru 1978) there had been a total of 208 fatal in flight airframe failures amongst the V-tails. There have been more since.

The early Bonanzas, the straight 35, A35 and B35 had what is referred to as the narrow chord tail. These aircraft tended to experience wing failure before the tail would fail. That is why they have no cuff on the leading edge of the tail surfaces. They don’t need it. The later models, those with the wide chord tail, tend to experience tail failure before the wing would go. They have the cuff on the leading edge of the V-tail.

One reason that the wing failed in the early model Bonanzas was that the outboard portion of the wing, outboard of where the main gear attached and the landing light was located in the leading edge, there was no spar web. This is where the wing typically failed in the early Bonanzas. That was corrected later in the production run in the much newer models. They also increased the thickness of metal used in the leading edge of the wing.

I often think of this report whenever I see an old model 35 for sale at a very affordable price.

Mooney pilots take heart. At least your airplane was structurally sound in the first place.

[jlunseth]

I have to correct one thing. I stated that there was an engine monitor on board. There was a dial-type JPI in a panel picture when the aircraft was sold. It is in a picture on aircraft.com.  However, I reviewed the panel photos in the Kathryn’s Report and there is a blank where that JPI is in the other panel picture, so I cannot verify whether there was a JPI or another monitor. I don’t know which photo was taken when. However, the NTSB rep says in the Kathyrn’s Report interview that they have engine data that they will review.

[1980Mooney]

23 hours ago, jlunseth said:

The NTSB says the horizontal stab and elevator departed the aircraft before impact and rendered the aircraft uncontrollable. I think we have all concluded that the wings folded before impact.

Also, if the stabilizer departs the aircraft, it is not particularly relevant whether the wing survived or not, the aircraft is not controllable.

Except that is not what the NTSB has said.  They said "portions of the left elevator and left horizontal stabilizer" were found 2 blocks away.  They did not clarify what "portion" of the left stabilizer or left elevator departed...a "portion" implies part but not all.  That also implies that the right stabilizer was attached and intact with elevator.

When pressed the NTSB spokesman said that an airplane is not controllable without an elevator and stabilizer.  He was clear that he was not going to comment on the specific causes (the "why" as he put it) of the N9156Z crash.  I took his comment as a generic response to the loss of an entire horizontal stabilizer and not the consequences of losing "a portion" of the left stabilizer in this particular case.

I think we have to be careful and stay factual.  Others are now commenting on the loss and consequences of the entire horizontal stabilizer when that is not the case in this accident. 

Additionally if you think about it, the loss of part or all of the left horizontal stabilizer will create a clockwise roll force .  The horizontal stabilizer is an inverted wing that pulls down slightly.   If left and right horizontal stabilizers were there there the left and right side pull down with equal force imparting a stress on the airframe - at the point of attachment on the airframe the right h-stab transmits that force as a lever and creates a clockwise force. and the left creates counterclockwise .  The twisting forces cancel and the result is just a downward force.  The loss of part or all of the left stab only will unbalance the forces creating a roll.  

The loss of the entire horizontal stabilizer results in loss of pitch control.

Reacting to an uncommanded or uncontrollable roll is different than reacting to the loss of pitch control.

[jlunseth]

I agree with what you say 1980mooney, it was the left stab and elev that were missing. I don’t see any significant pieces left in the crash video or photos. However, the NTSB rep says unequivocally in the interview, twice, that the aircraft was uncontrollable after departure of the stab. I don’t agree with your thesis that there was some kind of control, the NTSB says there was not.

[Raymond J1]

Before France awarded an ICAO-level certificate of airworthiness and by recognition of the equivalence of foreign standards, there was the passage to the CEV (centre d'essais en vol) to find that the type of aircraft for which a certificate of airworthiness was applied met the national standard "AIR" 2003 or 2004. For the Mooney M20, this procedure was followed and several models went through the CEV of Bretigny sur Orge near Paris. Today, our national archives keep documents on this subject : One concerns the prevention of flutter on an M20 C (report 116 of 1961). There is a supplement for the " F " in 1966. Maybe the same is available in the FAA or manufacturer archives ?

Transports ; Direction générale de l'aviation civile ; Service de la formation aéronautique et du contrôle technique ; Sous-direction des affaires techniques ; Bureau entretien des aéronefs (1945-1972)

 

 

 

1 sur 2Résultat suivant

Cotes : 19760069/546, 23 T 565

23 T 565 - Avions Mooney (américains)

 

RéserverPlus d'actions

Description

- Correspondance concernant l'avion Mooney M 20 n° 1078 appartenant à M. Tranchant, 1958
- Correspondance concernant la certification française des avions Mooney, 1966-1967
- Correspondance concernant un avion Mooney accidenté le 16 juin 1965 sur l'aérodrome d'Annemasse
- Model M-20 C. Weight and balance, 1961 (report n° 113)
- Model M-20 C. General design data, 1961 (report n° 114)
- Model M-20 C. Flutter prevention data, 1961 (report n° 116)
- Model M-20 F. Tir and addendum, 1966

[Cruiser]

can someone explain the aerodynamic forces required to place the airframe in such a huge nose up attitude as shown in the image of the plane hitting the ground tail first. ? 

The long body M20 is very nose heavy, without lift, it seems the nose would drop and the plane would be in the opposite attitude. 

[A64Pilot]

22 hours ago, Cruiser said:

can someone explain the aerodynamic forces required to place the airframe in such a huge nose up attitude as shown in the image of the plane hitting the ground tail first. ? 

The long body M20 is very nose heavy, without lift, it seems the nose would drop and the plane would be in the opposite attitude. 

ALL, well almost all as there are a very few exceptions standard configuration aircraft have their CG forward of the center of lift, now while the center of lift in an asymmetric airfoil does shift with angle of attack, it will always be forward of the CG in an aircraft loaded within its CG limits, regardless of angle of attack.

When you load aft CG enough you get to the stick force neutral point, which means no force required to push or pull the yoke and of course an aircraft is unstable there and it’s very easy to overstress an airframe, that’s about when the CG and center of lift are in the same place. Go further aft in CG and control forces actually reverse, but of course your WAY out of CG then. Then CG is behind center of lift.

‘Therefore to maintain level flight the horizontal provides a down force, or negative lift if you will, this is done so that if the tail were to ever stall, the nose of the aircraft will drop all on its own and regain flying speed. If the tail provided lift and stalled, it’s not likely to be recoverable.

So to pull very high positive G force the tail will be under tremendous pressure downwards, just the opposite of the wing. You don’t really lift the nose, your really pushing the tail down and the airplane rotates about its center of lift.

‘In order for what we see here to happen I believe the tail and the wing pretty much failed simultaneously, it’s not a case of one failed and that failure caused the other to fail, in my opinion.

With half of the horizontal gone, assuming control integrity still exists, I believe there woud be some control, I think maybe enough to even maintain level flight at normal airspeed and CG, have to land fast though but who knows? Yes there would be some roll, but I don’t believe it would be excessive as it’s so close to the fuselage, once the main spar folds  nothing matters then of course.

I can’t find an example of a aircraft with a lifting tail, but I know it’s been tried in the past. I doubt any GA aircraft does though

Edited August 16, 2021 by A64Pilot

[carusoam]

14 hours ago, A64Pilot said:

 

I can’t find an example of a aircraft with a lifting tail, but I know it’s been tried in the past. I doubt any GA aircraft does though

The closest thing we may see of that type of layout… would be a canard… where the front wing produces lift…

Being in the lead position, when it stalls… the nose drops… 

So… the canard airfoil is selected to stall first…

 

PP thoughts only, not an airfoil designer…

Best regards,

-a-

[jlunseth]

On 8/15/2021 at 10:48 AM, Cruiser said:

can someone explain the aerodynamic forces required to place the airframe in such a huge nose up attitude as shown in the image of the plane hitting the ground tail first. ? 

The long body M20 is very nose heavy, without lift, it seems the nose would drop and the plane would be in the opposite attitude. 

The aircraft is not flying in the photo. The wings are folded, the left stabilizer and elevator are gone, and it is shuttlecocking into the ground. The aerodynamics in that photo have no relationship to the aerodynamics of a flying aircraft. Think of it as hanging from a string, with some upward drag because the wings are still attached although upward folded. Remember, there is a passenger and luggage in the back, upward drag on the wings about a center of drag that no longer has anything to do with the classic center of lift of a wing, and practically no upward drag at the tail.

People keep trying to relate that image to classic, flying aircraft, aerodynamics. The aircraft is not flying. There is no lift from the no-longer-existing elevator, which is on a lawn two blocks away or working at arriving on that lawn.

[A64Pilot]

10 hours ago, carusoam said:

The closest thing we may see of that type of layout… would be a canard… where the front wing produces lift…

Being in the lead position, when it stalls… the nose drops… 

So… the canard airfoil is selected to stall first…

 

PP thoughts only, not an airfoil designer…

Best regards,

-a-

There have been in the past aircraft whose tails provided lift too. in the search for greater efficiency, range etc. Military aircraft, and I believe they got the moniker Widow maker. But yes a reduction in total lift required and therefore drag etc is one of the advantages of a Canard design. 

Many Airliners fly at cruise with the CG so far aft that the tail provides little downforce and the lost stability is controlled by computer, of course us little guys just live with the increased drag.

Last aircraft I worked to Certify we proved that as long as you stayed within its airspeed envelope, you couldn’t over G the wing, it would stall first, but that was assuming that the G load was slowly or at least built up in a controlled manner, God knows how high the G load could go if you were at or above VNE and a rapid full control movement applied, and I believe that’s what we have here.

Anything man made can be broken by a man, add however many other sexes you believe there are to be PC.

If flown well behind design limits, any aircraft can be broken.

[PT20J]

Some sources say that the Stearman has a lifting tail. I don’t know if that is true or not, and my aerodynamics guru friend Dave Lednicer didn’t know either. But we both observed that the horizontal stabilizer is positively cambered, and there wouldn’t seem to be another good explanation for that. Maybe @Blue on Top knows.

Skip