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

 

[moon161]

Anna,

There's a lot about aircraft control and upset recovery in the earlier thread segments about the 737 crashes. Good conversation between engineers, pilots and pilot/engineers.

https://www.eng-tips.com/viewthread.cfm?qid=473001

Not a pilot, but what I would say is roll wings level and depending on the aircraft, trim may control the stabilizer angle WRT the plane or a trim tab on the elevator would control what's called in flight dynamics the 'stick free neutral position' to recover horizontal flight. In a banked turn loss of elevator control say a broke cable would probably find the nose pointing down fairly quick because the rudder is steering into the turn to coordinate and this may point the nose down unless the pilot centered the rudder immediately. The sensations of the uncoordinated turn might be disorienting and the artificial horizon might be important for determining what wings level and then level flight were.

And i grew up in volvo 140/240 and SAAB 900 cars but now I have benz W123 cars from the same era, rust is the only thing guaranteed to kill them.

 

[LittleInch]

The issue is going to be if these faults are common enough that anyone has worked out how to fly through them. I suspect not.

I think it's a bit like saying what happens if the track rod on one side breaks on your car as you're going around a corner? Big crash is probable for most of us, but a rally driver might be able to catch it. but so unlikely to happen that no one has a good plan or experience to be sure what is going to happen.

As the 737 disaster has shown, the stabiliser is in fact a much more powerful control surface than the elevator, but in this size of plane??

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

 

[RedSnake]

There's a lot about aircraft control and upset recovery in the earlier thread segments about the 737 crashes.

I'm sure you are right. But since I am not a pilot, it gets advanced pretty quickly and I have a hard time with all the abbreviations.
And a Boing 737 is like a space shuttle compared to this aircraft, even if the principle is the same, it does not feel really comparable.

There is no instrumentation that shows that something is wrong with the elevator, and only the stabilizer can be adjusted and there is an indication for it in the cockpit.
The elevator has no secondary effect it only puts the nos up/down.
So if you do not know that one half do not work and must use it in some position, with large movements it will probably be very strange it will be like getting one more aileron back there and only on one side.

I've talked to a retired civil engineer of flight engineering and flight characteristics, former head of Applied aerodynamics at Saab he explained,
that if you fly with a correct center of gravity, staight ahead, correct speed and right elevator "came of" you can fix it by adjusting the stabilzor and use the ailerons.
If the plane is forward heavy it will go fast left in a steep dive and if it is heavy at the rear i will go left into a spinn.

But this does not answer my above questions.
Or does it ?!?

/A

 

[moon161]

When I looked at it, a glider pilots license would cost me about $2000 USD and my time through a soaring club. With free club instruction, your cost is basically membership and tows to altitude. Maybe that sort of familiarization would yield some direct insight on flight dynamics and aircraft handling. Still want to do it with my youngest.

 

[Alistair_Heaton]

In a balanced banked turn of 60 degs you have to apply a fair bit of back stick to maintain level flight. Your stall speed also increases because of the increase in angle of attack. You root the G which gives 1.41 so your stall speed is 41% greater than flying straight and level.

The G force will be 2g and you wouldn't be doing it with pax onboard normally.

With that far back CoG it would require less back stick than normal.

If one side of the elevators goes during the turn. There will be associated yaw to correct because one side has more drag than the other but as its centre of application is close in it won't be that much and the rudder won't have any issues dealing with it with an appropriate pilot input. But if there isn't enough lift off the elevator the nose will just drop and spiral dive recovery performed.

The turns stuff is exercise 8 and 15 in the ppl syllabus.

Secondary effect of elevator is airspeed with a change in pitch. But different countries have different views on if this is a real secondary effect aka like rudder and roll. It doesn't really matter to be honest.

During level flight if one goes the same thing will happen and the nose will drop or go up depending on what your doing at the time and the trim. But it won't be a sudden departure from controlled flight in side the normal flight envelope as your man from SAAB has explained.

Some of this is dependant on the trim system how it works. Personally I don't like flying these systems which keep constant force on the elevator trim systems. It feels nicer and also gives you more options if they alter a trim tab which then deflects the elevator with aerodynamic forces. Means the controls don't have any weight on them when your trimmed your always starting a base zero. Where as these screw jack systems your base point is the amount of force you currently have trimmed in. Which also must have an effect on the SN curve for everything in the control run after the force applicator . You can actually land the plane just using the trim tab not touching the Yoke. Its the sort of stupid stuff you do when your doing ferry flights as an instructor when your inexperienced and don't realise your pulling the tigers tail on the risk management front. So yes there is ways of dealing with them worked out. But modern freshly graduated CPL holder won't have been taught them. And won't have been kicking around airfields hearing about stuff like this from the more experienced pilots.

The eye bolt I was on about is the failure in the above post figure 34. They do go usually fatigue and people do survive to tell the tale. I haven't had one personally, although I have spotted cracks in them during walk rounds and put it in the techlog to be fixed before it fly's again. Its meant to be an engineering function not a pilot to look for them. But I always did. Got shouted out once for doing it and then apologised to afterwards once the engineers had swapped the rod out and the school owner and chief engineer got involved.

BTW its chucking it down with snow today!!

The modern 737 are not really comparable but the original 1960's apart from the pressurisation systems and electrical in some ways are less complex than this machine. Certainly less engine controls but more gauges. The Jetstream 31/32 there is very little difference between the two until you have an engine failure but that's more to do with asymmetric flight and having an option and performance to stay in the air when one engine fails. Petrol engines have a lot more failure modes than turbine.

 

[Alistair_Heaton]

People teach and a lot of pilots think that by trimming an aircraft your trimming it for level flight.

Your not actually your trimming it so the control forces at a certain speed are balanced and the plane will naturally come back to the speed.

You can be trimmed out in level flight hands off the controls with say 90 knts of airspeed. If you put more power in the pitch will increase and the plane will climb at 90 knts (there will be some slight differences because you have to adjust your rudder input) if you then put the power back to where it was the nose will lower and you will be flying level again. If you now take power off the nose will lower and you will descend at 90 knts (rudder effects aside) put the power back and you will fly level again.

BTW engineers are dead easy to teach to fly. You basically turn the whole exercise into a energy equation and the controls are the variables. Navigation though sometimes caused issues to the point of how do manage to get to work in the morning.... its just a speed, time vector diagram with a bit a fuel burn thrown in....

 

[LittleInch]

But this does not answer my above questions.
Or does it ?!?

Anna,

Having been in this now lengthy post from the start I think your real questions are:

"What actually happened at 13,500 ft above Umea"?, followed by

"Did the poor welding of the elevator horn create or exacerbate the loss of control of the aircraft"?

With the information to hand I don't think these questions can be answered to the level you, as a partner of someone killed in this, can accept.

The only way forward to be clearer really involves the manufacturer, who is notably absent from the official enquiry document, undertaking some more analysis, trials and inspections of current and existing aircraft.

I don't know what contact, if any, has been undertaken by the accident investigators or by you in this respect, but I believe this is where you need to go from here. In My Honest Opinion (IMHO).

The only other possible way forward to understand the forces and actions is maybe to try a university aeronautics department and see if they are interested in modelling this and spending time doing research. Real life problems and issues can sometimes be very useful for them and the basic design of this airplane will help in that respect.

As said before, you have a huge amount of sympathy and understanding from the community here and I hope we've managed to add to your understanding of the issues involved, though we may have strayed off the strict mechanical path.

Please keep us informed as to any developments as I'm not sure how much further we can go here.
One thing looking at the report again is that after about a 2000 ft drop, at about 11,000ft/3000m, it appears that the pilot may have tried to level out as the vertical speed starts to go down rapidly and the altitude trace starts to level off a bit. However the G forces and overall air speed must have been immense and this may have been when the wing came off or the stabilisers detached as from there it pitches down rapidly.

Good Luck and I hope you manage to get answers to your questions.

LI

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

 

[Alistair_Heaton]

my take is...

1 don't have a clue and glad I wasn't on the controls.

2. don't think the horn design if that's what we will call it would change anything.

The utter shite welding again I don't think would change the outcome.

If you ever on my plane your getting a huge hug if you want one off a hairy Scotsman. On the grand scale of things utterly meaningless I know. But after having buried 12 people due aviation I know I feel a bit of a connection even though we have never met. And if I can do anything to make you feel more at peace I will move heaven and earth to make it happen. I have actually messaged the FDO and he has said message me if she is ever onboard if I don't reply then permission granted unless security goes above yellow . So that means you can fly on the jump seat if I am the Capt and everyone else agrees. But to be honest I can't show you anything with punters onboard.

If you want a break in latvia or Estonia your more than welcome to come over and visit. we can do a summer house swap. And if you want to use the farm house it can sleep 8 so don't worry about bring mates. riga is a bit more limited to 4 and you will have to put up with a 6 year old kid.

 

[RedSnake]

Having been in this now lengthy post from the start I think your real questions are:

I understand that what you are saying comes from a good place.
And I do not expect you to understand how my brain is constructed, there are those who have known me all my life and have no clue

I do not know if it is a Nordic thing or a world problem, but trying to persuade a woman to change her mind or focus is the best way to achieve the opposite.;-)

1. SHK and everyone else I talked to, do a good job of making assumptions about what happened.
So I leave that question to them.
The only ones who really know are dead.

Your question 2 is really my question 3 and 4.

1. Has the strength according to CS-23 been achieved?
The breaking load must be at least +5.7 g and -2.25 g respectively.
According to Gippsland Aeronautic Manual (p51-2) all welded steel tube structure is
deemed to be primary structure. So does the horn hold the measure?
Yes? No?
If the answer is yes .. then I do not have to think about it anymore.
If not.

2.Has the strength of the permissible load factors +3.8 g and -1.5 g been achieved?
If the answer is yes then I probably do not need to think about this anymore,
but if the answer is no...

3.Could the poor welding of the elevator horn create the loss of control of the aircraft?
Then we are back to the assuming part again.
Theoretical, Yes. Probable scenario, maybe not.

4.Could the poor welding of the elevator horn exacerbate the loss of control of the aircraft?
Theoretical, Yes. Probable scenario, maybe.

As I mentioned earlier, I think my approach is different from yours.
I really wanted to set it up as a simple mechanical design with static loads for the 3 ways the lever can have been broken and see what is required then from there add g-force and then flight speeds m.m. if necessary.

I have a harder time accepting that I do not understand how to do the strength calculation.
Than to accept what has happened. Even if it's hard.
I think part of it is that another poorly welded rod broke on the plane a month and a half earlier.

Best regards Anna

 

[RedSnake]

Alister sometimes it's the little things that make the biggest difference.
It already feels like I got one and it really means a lot to me. So thanks for that ..
And I would very much like to accept another big hug from a hairy Scotsman if given the opportunity.
If you do not mind giving one to a fairly/hairy/scary female Swedish one ;-)

My last vacation was in Vilnius.
This year a have just been home inside it feels like it has been raining for four and a half months, it still is :-( and it is +4 degress celcius outside..
If ju ask your friend in Luleå to look for my phone number I can give him my email adress if you like to have it?
Ask him to look for Picea abies in the world champion village.
If he does not understand the clues, I can come up with something else.
But to day thursday it's snowing, probably it wont last long though. But it lights up a little in the dark anyway

Thank you for the invitation, right now with these Corona regulations there will not be much of anything.

My summer cottage is exactly what it sounds like a cottage for the summer ..
No water on in the winter and no insulation ..
And now I also have problems with the sepsis tank!
I got it emptied some time ago, you have to do it every 3 years according to law and then the remnants of hurricane Zeta came in here and it rained and blew so much that the tank has moved out of the ground :-(
And four spruces have fallen over but the cottages survived ...
So now I have more work out there this spring ..

Best regards Anna

 

[LittleInch]

Anna,

I wasn't trying to change your mind, but give you some maybe helpful hints on what to do next and how to get people to do the calculations and tests you desire.

But for your questions

Item 1 really relates to the wings. The only thing keeping an airplane up in the sky is the wings. Everything else just helps them do their job by creating an air flow over them (the engine) or keeping them in the position you want them to be or pointing the airplane in the right direction. Hence the G rating is related to the wings. 5G really means a factor of safety of 5 for the wing construction and fixing to the airplane compared to steady flight. That's a lot.

The force seen by the elevator though is a matter of air flow on a piece of angled metal. The G force on the elevator will be very small compared to the force applied by moving air on an angled plate. As Alastair said before, this will involve a V^2 number somewhere, but how you work out what that force is to move the elevator needs someone in aeronautical engineering to work out (hence my suggestion that you get in touch with a university). But it will involve the velocity, not the G number. I think you will find out that the horn was capable of supplying all the force needed and more to move the elevator all the way up to Vne (velocity never exceed).

2) See item 1 - The G factor is about the wings, not the elevator.

3) No, I really don't think it had any impact at all. The pilot basically was flying too slow and too level. Given his conversation with the ATC, he was clearly concerned about the cloud and whereas normally you expect the plane to go into a shallow dive as they throttle back to let you get out, he didn't do that. The skydivers may well have all been in the correct place, but if the plane isn't flying fast enough it will stall. The biggest issue with stall recovery for a plane like that is the fact that the weight and CofG was very mobile and large moving. When that happens even large cargo planes crash.

4) Again no. The horn only works in one plane where the welds were good. The poor welding only became an issue when the stabiliser came off the plane and this was the only thing left holding it to the body of the aircraft.

I did a bit of thinking about the apparent partial climb out of the dive at 11,000 ft and there is a potential scenario here where the pilot had managed to stop the spin he was in and was trying to pull out of the dive. However he was trying to overcome very high velocity, a nose down stabiliser, plus all the aircraft weight was almost certainly at the front end forward of the Cof G envelope as all the skydivers were now at the front and hence he couldn't make it stick. He may even have blacked out - once you go past 3-4G for more than a few seconds without a G suit you'll just faint and slump forwards on the controls. Either that or that's when a part of the aircraft fell off as he was beyond Vne.

I really do wish you all the best and hope you can find the answers you're searching for.

Please keep us appraised, even it's months from now - the threads only become inactive after 6 months of no posting.

LI

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

 

[RedSnake]

Thanks for the advice.
I have started on a simple strength model that I thought I would post on the correct forum, just so I can find out if it is okay so far.
Then maybe I can develop it more with what you suggest.

As written in the metal report, the elevator's metal structures must also maintain the standard as no exceptions have been made for this.
So even if the surface area and weight are small, it should still be able to withstand these G-forces.
But I have to take that into account when I get there.

This elevator has a very flat surfaces no curvature. Should be "pretty" easy to calculate air resistance and such when I get there.
But one thing at a time.
As they say, you have to learn to walk before you can run.

There's something you might be able to help me with .. found a program to do strength calculations on beams.
But there's a demand for Young's Modulus?
I think I've seen it somewhere for MIL-4130 N but I can not find it again and I'm not really sure what it means.
The lever is made of 1 mm cold-rolled sheet.

To something completely different I had a workmate who had almost the same nickname as your alias, he was called Half-Inch, because he was so short.
At least until he drove off the road and tipped over with a cross kart at a department party.
After that he got the nickname TipOver in Swedish Tippen

Guess LittleInch doesn't really have to do with inch, but I'm not really sure.

Best regards Anna

 

[LittleInch]

https://www.engineeringtoolbox.com/young-modulus-d_417.html

Steel it's generally around 210 x 10^9 Pa or GPa

Aluminium is lower.

"LittleInch" is a long story....

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

 

[RedSnake]

In the Description it says Elastic modulus. Defaulted to 200,000 MPa or 29,000,000 psi, for structural steel.
And I use the metric system so it should be in MPa..
Found this for AISI 4130 Steel, normalized.
Modulus of Elasticity 205 GPa 29700 ksi Typical for steel.
It's the same thing, right?

/Anna

 

[waross]

"LittleInch" is a long story....

Does that long story involve a very high length/diameter ratio? grin.

Spoiler

Definition of big inch
: a very long oil or gas pipeline 24 inches (or greater) in diameter
Little Inch is undefined although the "Little Big Inch pipeline" is 20 inches in diameter.

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

 

[LittleInch]

Kind of.

Yes anna, it's the same thing. Around 200 000MPa for steel

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

 

[RedSnake]

And do I use
Tensile Strength or Yield Strength ??
or
Tensile Strength, Ultimate or Tensile Strength, Yield ??

Guess there are different names for the same thing?

Best regard A


“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[LittleInch]

Tensile or ultimate is when it breaks

Yield is when it starts to go plastic

For your case use yield. If that horn starts to bend and keeps bending then it's not doing its job

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

 

[Eufalconimorph]

Good video about stress & strain, with humor & decent analogies. Explains yield, Young's Modulus, etc. Might be helpful for understanding, maybe just good for a laugh.