Could anyone help me with a material strenght calculation of this operating horn from crashed plane? 10

[RedSnake]

Picture elevator to the left and stabilizer to the right.

The red cirkel is a tourque tube on the rudder and have a diameter of 38 mm and the thickness is 1 mm.
The operating horn was a welded box design using steel sheet AISI 4130 in condition N thickness is 1 mm welded against the tourque tube.
On the uperside and sides (3/4 of the circumference) has 30% of the normal materiels strenght(severe lack of fusion).
The last 1/4 can be brittle or have been sheared.
The red triangle is the mechanical stop maximum up.
The relationship between hinge, tourquetube and elevetor edge ca..
0 --------1 --------------------7
Can this construction hold for 5,7 G ???


[img [URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1604784211/tips/STABH2_lpxbcz.jpg[/URL]


Properties Metric Imperial
Tensile strength, ultimate 560 MPa 81200 psi
Tensile strength, yield 460 MPa 66700 psi
Modulus of elasticity 190-210 GPa 27557-30458 ksi
Bulk modulus (Typical for steel) 140 GPa 20300 ksi
Shear modulus (Typical for steel) 80 GPa 11600 ksi
Poissons ratio 0.27-0.30 0.27-0.30

 

[waross]

So the aircraft was delivered in 2013 and was in service for six years.

The aeroplane broke up in the air as both the airspeed and the g-forces exceeded the permitted values for the aeroplane. From an altitude of 2,000 metres, the aeroplane fell almost vertically with a descent velocity of around 60 m/s.
The fact that no one was able to get out and save themselves using their parachute was probably due to the g-forces and the rotations that occurred.

Is this the aircraft?
Could the damage have happened on impact?
From the accident report the root cause may have been a lack of discipline on the part of the jumpers.
The pilots limited experience with jumpers may have been a factor in the inability to recover from a probable stall.
That none of the divers were able to overcome the centrifugal forces and exit the doomed craft suggests the extreme forces present during the descent.
I am sure that the crash information will be shared and emphasized by jumping groups world wide.
A tragedy and I am sorry for your loss.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[IRstuff]

I thought these types of sites were for help and understanding, but maybe I was wrong?

This site, in particular, is for helping engineers with their work problems, hence the questioning.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[BrianPetersen]

I thought these types of sites were for help and understanding, but maybe I was wrong?

In order to help, or even to establish whether it is possible to help, it is sometimes necessary to understand why you are asking the question.

Now that the official report for the incident in question has been sussed out, it seems to me (not a crash investigator by any means) that the loss of control happened first (inadequate flight experience by the pilot?), and "breaking stuff" happened afterward.

 

[Alistair_Heaton]

Certified in 2009 then it will be to the proper CS-23 standards and no grandfather specials applicable.

If the mechanical stop is holding it at distance x down the arm then and you apply a force at distance y at from the tube (you would have to get the centre of pressure for that aerofoil) its a simple torsion failure. Which is what the certification load will be.

But you have a fatigue crack in the mix then it would fail before that load and before the design load.

Per say the pilot by physical action would not be able to plastically deform the torsion tube by control input against the mechanical stop and to be honest I wouldn't be surprised if the mechanical stop would fail before the torsion tube starts to yield never mind ultimate failure load.

These torsion tubes on elevators and flaps are meaty and the normal failure occurs at the actuator rods which have a screw thread and locknut to the mount connector bearings. They usually fatigue just above the mount nut due to buffeting in the air and on the ground if parked outside. This is well known and they will be NDT every so often as per the maint manual. There may also be a bit of sacrificial failure mode built in because the links going you can still get the aircraft back onto the ground using trimming and the elevator just floats. If the torsion bar goes then you can get asymmetric elevator or it jammed and unable to float with the trimmer still functioning. There was a series of incidents with some models of piper aircraft in the 80's where this occurred and a few elevator jam's as well.

To note meat bombing as we call it in UK pilot circles kicks the absolutely hell out of aircraft. Its loads of short flights high power then low power at near limit speeds with the pilots able to be pretty aggressive without pax during landing. Pulling G to get the airspeed down on the turn onto finals at 500ft while getting bounced around is not uncommon. As you can see by that report loading goes out the window as they will fit as many as they can in.

The BPA training and authorisation and control of jumping in the UK was tight have no clue how it is in Sweden.

With a wing off if it is the Umea accident the loads will be well outside the design limits on the tail. And from my reading it was the control lever arm that failed not the torsion tube. Now my previous comments about a pilot strength being unable to physically break this is out the window in this situation because they are about to die and its well known that people can rip muscles off bones in these sorts of situations. There has been cases of 60-70kg female flight attendants bending aircraft door opening handles on jets. The design codes don't cover this sort of unrecoverable structural failure. To note the aircraft may at some point be going going backwards with the elevator at full deflection acting as an airbrake which is also not covered in the design codes.

 

[verymadmac]

The limiting force on the arm is most likely pilot control forces, not G related at all.
Which just leaves you to find the relative throw between the control column and the control surface (the critical dimensions might be in the Maintenance manual for the GA8).

 

[Alistair_Heaton]

Bare in mind for someone to start researching if the AAIB have got it right or not there is usually a connection with one of the fatalities involved.

Its extremely rare that the structural stuff is wrong, especially on this class of aircraft. Especially with with civilian accidents.

The mil side of things can get a bit political. Basically mil accident investigation is broken in the UK now with several sets fatalities over the years with various causes found which its glaringly obvious that the investigation has been tampered with. And after multiple years of challenges by relatives they have eventually backed down.

Thankfully the civilian UK AAIB hasn't been poisoned in such a manner. The Swedish AAIB did a good job with SAS and the Q400 and this accident has no political pressure as far as I can tell. My gut feel is if there was a problem with it then they would have found it. But to be honest once a wing comes off there is going to be all sorts of failures. And I could quite imagine the pilot pulling or pushing a death grips worth of force on the controls which is way way out of design certification loads.

To the OP if you are close to someone on board I am writing with the utmost respect. Unfortunately over my career I have been to 12 funerals of pilots and I seem to be running out of people I know that fly burning avgas in GA.

 

[LittleInch]

Redsnake,

You have my most sincere condoloneces. As an ex sky diver reading that report before bed wasn't the best idea.

I've jumped many such aircraft and warnings and limits of how many people can be past a certain line are usually painted or stuck inside the cabin, at least on aircraft in the UK. Ditto if you were not supposed to sit on the baggage step this would be visibly marked and maybe even cargo netted off. Unfortunately the desire of skydivers to get out of the door at the same time or very very shortly after often leads to "blurring" of these lines. Those of us that knew what that strange warning noise was would get rather nervous if it started going off, especially if the door wasn't open. Not that that saves everyone, but then at least some people might escape or the load might re-distribute and prevent a spin stall.

I couldn't find the calculation that the report refers to about the arm. Do you have a link or can attach the original?

But to take it any further you really need manufacturing data and also knowledge of the forces the elevator experiences at different velocities.

Having read the report it is not clear how the initial roll and spin occurred. I assume you are thinking that the elevator control arm snapped or partly broke while the elevator was in nearly full nose down position trying to stop the plane from stalling? Maybe, but the slow speed would reduce forces compared to other occasions.

Have you tried contacting the AIB or the manufacturer?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Alistair_Heaton]

I agree likely everyone went to the rear as the door was due to be opened.

It might actually have worked in the past with two up in the front.

This CoG going past the rear limits and putting the plane into negative stability happens to all types. There was crash of a National Airlines 747 in Bastion occurred due to the load shifting to the rear

If everyone has moved to the rear as the door has been readied and then as the plane goes out of CoG control effectiveness limits then it will just continue to pitch up and the parachutists will slide rearwards making matters worse. As the plane pitches up the pilot will put power on to try and get more air over the elevator and speed up. As the controls won't have enough effectiveness the plane will hit the critical angle of attack with max power yaw on which is ripe for a pretty viscous wing drop and accelerate spin entry. We did used to train full power on stalls and spin entries when I did my instructor rating but not during CPL training. And we certainly wouldn't teach them to PPL's I think these days they have banned the practise because it was killing more people during training than it was saving.

You would then take the power off and take it out of the spin using rudder. But then you would have everyone at the front accelerating very fast vertically and forward CoG and needing to pull back to lift the nose and decrease the speed. It would be seconds before you were through Vne and this case wing and tail came off. But to be honest there is no way of knowing when the arm broke it could have been on the initial pitch up or more likely in my opinion during the pull up after stopping the rotation of the spin and un stalling the wings.

As littleinch says the BPA are extremely strict with both parachutists and pilots. There is a twin channel qualification endorsement for pilots. You get signed off by another pilot training and also by a jumpmaster. Jumpmasters have several grades the top two I think can sign off a pilot and supervise them for the first 20 jumps or something like that. They may go out the door last or stay until landing again for the next batch. Per say there is no EASA rating for being a drop pilot and all the control is done through the BPA for civilians. There is a similar process and control for glider towing. For both pilots and parachutists there is a black list and you won't fly or drop in the UK if you don't play the game.

There was a crash in Finland under similar circumstances about 5 years ago, the elevator control was lost during the pull out of a dive and the plane accelerating fast through Vne.

https://turvallisuustutkinta.fi/mat...nta/2014/JlA5YOXyJ/L2014-02_Jamijarvi_eng.pdf

 

[Alistair_Heaton]

Its the V sqrt part of the lift equation which gets you.

Its got a Vne of 160knts apparently normally cruises about 120 knots.

Exceeding 160knts by 10 knots increases the load by 36 % and by 20 knts by 156%.

Sorry earlier i was using Vmo which is a JAR25 certification limit which maybe for several reasons not only structural.

This type use Vne which is structural.

 

[RedSnake]

The only political thing about this is that the Accident Investigation Board seems to have decided early on what the cause was.
No really thorough investigations have been made of the so called "scrap".
Although their conclusion about what happened is based on well founded assumptions, there is no concrete evidence to support it.
I am not saying they are wrong.
But when they can not present a more thorough examination in the technical parts, I can not feel that their conclusion is the only one that remains.
I have no objection to their recommendation as such.
The parachute club "claims" that the procedure described in the report is incorrect.
Which was pointed out to SHK that did not take this into account.

I'm neither a sky diver nor a pilot, but as a partner to someone on board, I have reseved a lot of information and documents that are not included in the report.
I am still waiting for more.
The calculation is not in the report, I received it from the head of the investigation.

A report by those who conducted the material investigations states, among other things

Visual inspection of the corner welds indicated areas of severe lack of fusion in the
longitudinal and the circular part of the weld. This was confirmed using radiographic
examination. LOF is regarded as critical and is normally not accepted in any welding class.
The weld defect will reduce the load carrying ability and the stiffness of the elevator
operating horn.
The fracture mode was overload in tension transverse to the welding direction. No signs of fatigue were evident.

I would like to emphasize that the head of the investigation in particular and the Accident Investigation Board have been very accommodating and that this is not a criticism of any individual employee's competence or the like.
Perhaps more a lack of clarity and working methods.

And the reason why I was not so clear in my questions in the begining was because I did not want this to be about the Accident Investigation Board or become a general discussion about the accident itself.
For me, it is part of my mourning work, and something I try to understand and need answers to, in order to move on.

I have not been offended by anything written here, I am too much of a fact person for that

Best regards A

 

[Alistair_Heaton]

The problem with these aircraft is they don't carry any data recorders. Although quite a bit of data can be derived from Garmin radio/gps stacks and the like. And they seem to have used the parachutist altimeters quite a bit. And also the engine management system to see power settings.

It is extremely hard to get concrete evidence of timeline events during a inflight breakup. They can trace things back down the failure tree but then hit forks of it could have been that or that that happened first especially if everything is fast fracture faces with no ductile tearing or obvious buckling.

To be honest this is a rather regular occurrence in parachute dropping operations.

Figure 17 with the sudden drop then a brief climb followed by more decent has been seen many times before unfortunately. And when linked to figure 21 paints an all to familiar picture. And then look at what the power settings were and that then confirms the suspicion.

I don't disagree with you that a poor quality weld will degrade the performance but with the flight profile indicated in those 2 figures its way past the structural limits. It was descending at over 100 m/s which is over 190 knts which is a 350% increase in load from V sqrt. I can't work out where that fracture surface comes from. Is it from the region of the weld or is it from some other part of the horn as you call it? i thought it was 25-27 point but confused now.

Remember that ultimate load is when it actually breaks. Before that it can and does plastic yield a bent horn is pretty useless for deflecting a primary flight control and applying corrective inputs.

BTW I am a Scottish ex FEA engineer now commercial pilot for 17 years now. And flown a lot in Scandinavia. The reason I know about the Finnish crash was because my brother inlaw was the first on the scene fire fighter and knew the people on board.

 

[LittleInch]

Redsnake I do feel for you. Air crash investigations for small private planes are often inconclusive and the best the investigators can do is find probable cause.

The problem with the damage caused by the failure of the parts of the plane is not knowing which part failed first. It would seem that the damage to the control arm is equally likely to have happened during the failure of the stabiliser as it was wrenched from the body of the aircraft.

The only way you will get any meaningful data I think is by replication of the parts and some physical testing of the parts to destruction with various weld fails. That though may be beyond any private individual without close cooperation of the manufacturer and the relevant government organisations

I would agree that the lack of fusion of the part isn't mentioned somewhere a bit more prominently and what the manufacturers input into that aspect of the investigation were are a little troubling.

I have no idea what the failure rate or accident statistics are for that particular aircraft type, but if this was really a one off failure then it becomes equally difficult to show that it was a primary cause of the crash.

As Alastair says though, the investigators have limited resources and will look at similar incidents world wide where skydivers have caused crashes due to the moveable nature of people in small aircraft having very bad impacts on the flying characteristics of the aircraft. Also far too often, the pilots are relatively inexperienced, doing it as a hobby or trying to establish hours on a plane and getting low pay. The planes themselves get a fair bit of abuse and have many more landings and take offs than other planes of similar flying hours.

It is unfortunately a fact that you stand a similar chance of dying in the air craft before you get out as you do from hitting the ground at speed afterwards. After an emergency exit from a helicopter I vowed never again to loosen any part of my rig or not do it up until inside the plane as you never know when you need to get out. Similarly an old antonov biplane had no holds in the hold and as a taildragger we all ended up at the back of the plane having slid down until the tail lifted up and we could scramble back up the plane. I did that once and never again.

If you want to take something form this to prevent it again, I think a far better way would be to promote proper aircraft packing, hand holds and ensure that this aspect (preventing it from stalling) is part of a regular set of briefings to skydivers about the importance of the lines painted inside the aircraft. Just because you have a rig on doesn't mean you will get out alive.

If you can release any more technical data, photos of an undamaged connection, drawings showing how it is put together then we can help you here. Good luck.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Alistair_Heaton]

Actually Redsnake if you want I can put you in touch with a Swedish friend who is also an Engineer and a pilot based in Lulea he was my examiner on the Jetstream for years. In fact he is what's called a TRE which is a type rating examiner. Come to think of it he made me land the aircraft with out using the yoke and only the trim and rudder which isn't a normal test item. He will also more than likely know all the AAIB people you have been speaking to.

The other option is to contact the pilots union in Sweden who will put you in touch with someone locally who would be willing to sit down and go through it all with you. If Ander's isn't willing to talk to you I am sure he will have a contact for you for the union. And to be honest they have a huge amount of power in Sweden if things haven't been done correctly.

I completely understand why you need to know. Your not the first or unfortunately I think last relative who I have been through this sort of stuff with. Normally its due to controlled flight into ground though which is invariably the pilots fault.

In this case it was a 27 year old sub 300 hour pilot who is no where in the same league of grumpiness and intolerance to the meat bombs behaviour in the back as some one like myself who is nearly double their age and 28 times more experience. The chief pilot at Edzel was brutal with both the bombs and his pilots some would say he had tourette's but to my knowledge they have never had a incident at edzel apart from a few airpox's which after the investigation was firmly pointed at the crew of the commercial plane coming into Dundee being idiots. I can just imagine 27 swedish bloke in his first job with a load of blokes 10 year older than him in the back. Swedish female pilots from the ones I know it wouldn't have been a problem with crowd control. The male youngsters from the south I have my doubts they would be assertive enough single crew.

My personal thoughts is its very rarely only a machine issue, its usually a human factors issue. This case the loading or crowd control in the back, and pilot experience. Which then creates a situation which then leads to a fatal spiral which may bring other hardware factors into play.

But please don't hate the pilot I can still remember the day I took my first student up with 210 hours under my belt. 200 hours later I was a different pilot. We all have to go through that first 1000 hours... And even after 8.5k I am still learning everyday both about flying and human interactions.

 

[Alistair_Heaton]

I have to apologise I have realised that I have presumed you are female. Which is partly because of your requirement to know and knowing Swedish lady's. And also the excellent Swedish lady engineers over the years.

The option that a northern Swedish lady is actually more likely later on in life to take up sky diving than a male has just hit me. It has been a few years since I worked in Pajala but I should have know better.

Anyway one of my favourite pictures from my time working up there.

 

[RedSnake]

No need to apologize you were right ;-)

I have no problem with the pilot!

My problem is that I am a fact and excel sheet kind of person.
I am educated in all technical subjects in school such as welding, mechanics, electricity, building, chemistry and hydraulics.
But in the end I became an electrical engineer with an extra year of computer electronics but I have worked as an automation programmer and maintenance electrician/technician on our hydraulics and eccentric presses for more then 33 years.

They are more advanced than the aircraft, the only difference is, that our presses do not fly

And my experience and my way of working is to troubleshoot methodically and logically and if there is one thing I have learned, it is that assumptions are the origin of all fuck ups.

For me, it has never been an option to make assumptions if you can check something out no matter how improbable it is.
As in this case.
If I seem to be persistent, it's probably because I have worked as a single woman in a man's dominated workplace from the very beginning.
It leaves its mark ;-)

They have the physical lever, but still they choose not to make a proper calculation with values they should ask for from the company that has research the material, instead they make an assumption that it is not likely that this has affected anything and make a simplified calculation instead.

It bothers me..
Especially since I know that another poorly welded rod broke a month and a half earlier and my partner had to hold the door shut so they could land the plane because the door could not be locked.

And that the company that did the material examination has been in contact with the manufacturer and told them that they must review their welding routines and quality controls because the welding is substandard.

They also say that it is not possible to determine whether the brake took place in 1, 2 or 3 steps, for example a part at the first landing, a part at the second landing and the last bit at the third lift the same day.

What I really want to know is, if it is possible that the lever broke at too low a load and made it impossible for the pilot to sort out the situation..

Best regards Anna
And I am not a sky diver.

 

[Alistair_Heaton]

I would say they are more advanced than that aircraft....

The persistency is cultural and a fundamental nature of being a good engineer. Although I would say the female Swedish ones are pretty scary in my male Scottish experience.

Pilot wise one of your famous model air ambulance pilots I trained coming into the industry. Bit skinny for my tastes and young enough to be a grand child. Her dad fly's rotary in Greenland. She is forever in the newspapers as the face.. Had a few run ins with her and was a bit concerned when I was to meet her parents at the summer solstice party in Pajala. End up getting getting very drunk with her dad who was lovely bloke and consummate aviator. Who then ran through all my classic comments with his daughter over the last 3 months... Which she wasn't happy with but he said wind your neck in he is doing his job and doing you a favour listen... what's it like to flying with someone that's not interested into getting into your knickers or that's not gay for once? she is an uttley great aviator, operator and pilot. I think she now owns most of the wood in Northern Sweden through her husband not that would change her dealing with a load of meat bombs not behaving in the back.

This one though I would say the aircraft was in a situation which is way over the design specs and the weld quality has no effect on the outcome.

As for the failure even if it failed above the load I suspect I would be extremely unlikely to be able to deal with it... Much like the 737 MAX situation. I am just being honest.. I might have prevented the situation occurring in the first place being a grumpy intolerant twat but after the situation progressed I don't fancy my chances. That said from my heart with no ego or wish to fluff you.... I actually feel rather sorry for the pilots mum being put in this situation. I count it as a understandable pilot screw up due inexperience. The argument about if he should have had enough rope to hang himself is worthy of discussion with your CAA.

 

[Alistair_Heaton]

BTW I am first a dad, then a pilot, then an engineer. The risk assessment of any flight centre's round being a dad and seeing the wee man at the end of the day. Some say the responsibility of being a Captain/pilot must be immense.....

I really don't find that... there is only one person that I care about onboard and that's me the rest get there as a bonus. There are more than a few in piloting circles that would take issue with that statement. I really don't care. There is zero changes to my professional standards be it 146 on board (my current type A220) or just me.

In fact if you ever fly out of ARN on a green engine machine and you hear my name on the PA please please introduce yourself. Unfortunately due to 9/11 rules we can't take you on the jump seat even though we would really love to. But I am more than game for a big hug and/or show you the office.

 

[RedSnake]

Okay Thanks
I'll remember that.
And I would really need a big hug.

We took a road trip in Scotland in 2015 it was very nice there and you have my favorite whiskey, quarter cask.
But we didn't se Nessi :-(

Best regards Anna

 

[Alistair_Heaton]

that's my favourite nip but I can't drink more than one because it effects my inner ear balance for days afterwards.

If you can bare it please try and speak to the pilots mum she will be feeling very remote and lonely in the grand scale of things. And if you don't have a grudge to bare it maybe help both of you come to terms with the whole thing.

Its only a suggestion after meeting other pilots mums at funerals. And there have been 12 of them so far in my career.

She will be just a mum with a child that has departed before her and not really understanding what's happened. I presume you will understand the reason for a closed and locked coffin but she won't and if you don't I won't go into the technicality's of it all even though I have briefed my wife I don't want want her or my child going near my coffin if I meet my maker in an aviation accident. Not that there will be much of me in it anyway.....

The mums really suffer in my experience and if you can manage it and you have it in your heart please reach out to the lady if you can.. it won't change anything but maybe make an old lady more at peace in this world.

 

[hpaircraft]

I have designed and fabricated several very similar control surface drives made from welded 4130N steel. The ultimate strength and stiffness of such weldments is rather difficult to evaluate without using finite element analysis. Even then, the maximum capacity is subject to a variety of factors relating to the welding and installation of the part. The general practice is to include a healthy margin in such parts, since it comes at a relatively trivial price in extra mass.

Looking at the picture in the accident report, I am inclined to accept the probable cause arrived at in the report. Had the part actually had inadequate strength, it would have been far more likely to undergo a fatigue failure, while the photos appear to show something much more akin to a simple overload.

Control system forces for small aircraft are determined by either the maximum force required to deflect the control surface, or the maximum force the pilot can apply at the control handle, whichever is greater. Typical practice would be to calculate the hinge moment required to deflect the control surface to its stop while the airplane is at Va (maneuvering speed), and then design the control system for at least 125% of that value. For small airplanes with small control surfaces, the maximum hinge moment developed by aerodynamic loads might be smaller than could be applied by the pilot. In which case the system is generally designed to 125% of the maximum pilot input load.