Flying after bumping the wing during taxi
Why wasn't the van wearing a Hi-Viz jacket ?
We all know that simple H and S regulation would have prevented all of this
We all know that simple H and S regulation would have prevented all of this
Last edited by Blink182; 25th May 2012 at 22:45.
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Wings arn't designed to take a point load at the wing tips.
I am sure G or IM have the proper data but i would have thought as an ex structural engineer.
The design is for a force loading over the length of the wing design so even if you don't take into account the washout as you get near the tips you can simplifiy that to a point halfway between the support and wing tip. In actual fact it will be alot closer to the support which makes matters worse the nearer the support it is.
Now the support will act as a pivot point so the moment applied from one side with counteract the moment from the other. So in flight the moment acting on the pivot point will be reduced.
By point loading the tip you have doubled the moment acting on the pivot point (in real life it will be more). Yep great the plane is rated at 3g so that not a problem but then you don't have is the balancing moment from lift from the other side of the pivot point. Then the bit of wing inside the pivot point is subject to a negative moment 3 times as a guess more than its designed for which is of course -1g. Then the wing mountings are also getting 3 times more in the wrong direction as well.
Metal doesn't just break when you hit its limit. It has a linear load profile up unto its yield point. Which means it will go back to where it started when the load is taken off, then a nonlinear responce until it fails.
Stress
It could very well be the metal has deformed but not to notice. So what you might say.
Then we get into strain hardening.
Work hardening - Wikipedia, the free encyclopedia
Again so what.
Different strength metals next to each other act as a stress concentrator which means that it acts as a focal point for fatigue cracks to occur.
I reckon it could be a time bomb, it might also not be picked up in a normal inspection unless the engineer knows the history and is looking for it. Until some one sits down and runs the numbers nobody will know. And you certainly wouldn't know with a quick walk round.
Quite alot of industrial failures are caused by none designed loads which have occured while in transport. In fact one of my collegues from my degree course all he does is design loading jigs for transport. And unless the transport jig is certified by DMV etc the equipement ain't allowed to be used.
Now I haven't practised as an engineer for quite some time and I don't have a FEA package to play with or a copy of Roarks. So if this thinking is a pile of poo please correct it.
O and I haven't even started on a point load in the laterial direction
I am sure G or IM have the proper data but i would have thought as an ex structural engineer.
The design is for a force loading over the length of the wing design so even if you don't take into account the washout as you get near the tips you can simplifiy that to a point halfway between the support and wing tip. In actual fact it will be alot closer to the support which makes matters worse the nearer the support it is.
Now the support will act as a pivot point so the moment applied from one side with counteract the moment from the other. So in flight the moment acting on the pivot point will be reduced.
By point loading the tip you have doubled the moment acting on the pivot point (in real life it will be more). Yep great the plane is rated at 3g so that not a problem but then you don't have is the balancing moment from lift from the other side of the pivot point. Then the bit of wing inside the pivot point is subject to a negative moment 3 times as a guess more than its designed for which is of course -1g. Then the wing mountings are also getting 3 times more in the wrong direction as well.
Metal doesn't just break when you hit its limit. It has a linear load profile up unto its yield point. Which means it will go back to where it started when the load is taken off, then a nonlinear responce until it fails.
Stress
It could very well be the metal has deformed but not to notice. So what you might say.
Then we get into strain hardening.
Work hardening - Wikipedia, the free encyclopedia
Again so what.
Different strength metals next to each other act as a stress concentrator which means that it acts as a focal point for fatigue cracks to occur.
I reckon it could be a time bomb, it might also not be picked up in a normal inspection unless the engineer knows the history and is looking for it. Until some one sits down and runs the numbers nobody will know. And you certainly wouldn't know with a quick walk round.
Quite alot of industrial failures are caused by none designed loads which have occured while in transport. In fact one of my collegues from my degree course all he does is design loading jigs for transport. And unless the transport jig is certified by DMV etc the equipement ain't allowed to be used.
Now I haven't practised as an engineer for quite some time and I don't have a FEA package to play with or a copy of Roarks. So if this thinking is a pile of poo please correct it.
O and I haven't even started on a point load in the laterial direction
Last edited by mad_jock; 26th May 2012 at 07:19.
Until some one sits down and runs the numbers nobody will know.
In hang-gliding we always used to inspect the spars for wrinkles or dents following a 'whack' or crash, and that was about it. Hang-gliders are abused substantially yet structural failure is very rare.
For this accident, I find it interesting that the pilot didn't seem to notice it. At the end of the day, if you push against a wingtip you have a huge amount of leverage and if the wing rode over the van without causing the pilot to require substantial amounts of differential brake, I can't imagine the forces were terribly large?
Even if the pilot did require substantial brake, there would be a limit on how much force he could apply through the wheel, which I guess could provide some measure of the force on the wingtip. Perhaps I'm answering my own question..?
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Opps sorry just realised your completely correct but I will leave the post anyway. I was on day 5 of 6 sector days on earlies.
The youngs modulus doesn't change and after yield there is residual stress in the structure and the hardness changes. It is one of the of the ways you test that something has yielded. And as the metal becomes harder it becomes more brittle which effects its post yield behaviour.
For abdg, its a rockwell hardness tester PCE-2000 (type D impact) hardness tester that we use and the change in hardness tells you how much its yielded by. You can also acid etch the surface and look at the metal grain. And if you really want to get fancy you stick a x-ray diffractometer on it and that will give you a real reading of the residual stress in the metal.
Basically the stress strain curve shifts to the right but it never returns to the original zero strain. The yield point increases which is sometimes used to work harden for use so the strength is increased. The classic example of this is high pressure piping systems and the teeth on digger buckets. Both cases the metal is quite mallable when installed but after the work up in the pipe system and using it after the install the metal properties change allowing alot higher pressures to be carried. The digger teeth you can grind them and weld them before using them but after a couple of hours work you can't touch them with a grinder and if you weld them they will just shatter.
For a given load you first have to over come the residual stress then you will start deflecting. The material next to that will be deforming as it did before which will set up a discontinuity which will act as a stress concentrator.
So if you deflect a yielded bit of metal by say 5mm it will require a different force to deflecting a none yielded bit of metal by 5mm. So I would call that a change in stiffness but to be honest its more a discussion on definitions than anything else and the US engineers do use different terminology to european ones.
Stiffness - Wikipedia, the free encyclopedia
The youngs modulus doesn't change and after yield there is residual stress in the structure and the hardness changes. It is one of the of the ways you test that something has yielded. And as the metal becomes harder it becomes more brittle which effects its post yield behaviour.
For abdg, its a rockwell hardness tester PCE-2000 (type D impact) hardness tester that we use and the change in hardness tells you how much its yielded by. You can also acid etch the surface and look at the metal grain. And if you really want to get fancy you stick a x-ray diffractometer on it and that will give you a real reading of the residual stress in the metal.
Basically the stress strain curve shifts to the right but it never returns to the original zero strain. The yield point increases which is sometimes used to work harden for use so the strength is increased. The classic example of this is high pressure piping systems and the teeth on digger buckets. Both cases the metal is quite mallable when installed but after the work up in the pipe system and using it after the install the metal properties change allowing alot higher pressures to be carried. The digger teeth you can grind them and weld them before using them but after a couple of hours work you can't touch them with a grinder and if you weld them they will just shatter.
For a given load you first have to over come the residual stress then you will start deflecting. The material next to that will be deforming as it did before which will set up a discontinuity which will act as a stress concentrator.
So if you deflect a yielded bit of metal by say 5mm it will require a different force to deflecting a none yielded bit of metal by 5mm. So I would call that a change in stiffness but to be honest its more a discussion on definitions than anything else and the US engineers do use different terminology to european ones.
Stiffness - Wikipedia, the free encyclopedia
Last edited by mad_jock; 27th May 2012 at 08:05.
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ABGD - you think he may not have noticed?
Take a look at the end photos on this site, where some youths are standing by one they built. Rans Build Pages [This aircraft has nothing to do with the incident, it is just a good photograph]
I don't know the clearance under the wing of a Rans 6, but I do know that youths are rarely available equal to the height of the van roof - 2225mm. The contact point was not on the wing tip, but approx 15cm inboard from there. You will appreciate the angle of bank that creates for the Pilot, which continued for the length of the van. When the wing "fell off" the van rear, the Rans lurched to the right so hard I thought the Pilot was pulling over. The Rans wheels left the taxi-way and the Pilot corrected for that and rejoined.
The impact left red dye from the Dacron cover along the edge of the van roof.
The pilot "did not notice"? If that's true, how can he possibly fly the aircraft! His sense of balance is shot, as is his observation of the horizon / bank angle.
It seems likely that you will read more about this event in later months.
Take a look at the end photos on this site, where some youths are standing by one they built. Rans Build Pages [This aircraft has nothing to do with the incident, it is just a good photograph]
I don't know the clearance under the wing of a Rans 6, but I do know that youths are rarely available equal to the height of the van roof - 2225mm. The contact point was not on the wing tip, but approx 15cm inboard from there. You will appreciate the angle of bank that creates for the Pilot, which continued for the length of the van. When the wing "fell off" the van rear, the Rans lurched to the right so hard I thought the Pilot was pulling over. The Rans wheels left the taxi-way and the Pilot corrected for that and rejoined.
The impact left red dye from the Dacron cover along the edge of the van roof.
The pilot "did not notice"? If that's true, how can he possibly fly the aircraft! His sense of balance is shot, as is his observation of the horizon / bank angle.
It seems likely that you will read more about this event in later months.
Last edited by John R81; 27th May 2012 at 09:20.
Thanks Mad Jock...
So you do the tests, then presumably use the FEA to work out how much the initial strength of the spar has been compromised, and whether it's still got an acceptable fatigue life ahead of it?
So you do the tests, then presumably use the FEA to work out how much the initial strength of the spar has been compromised, and whether it's still got an acceptable fatigue life ahead of it?
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What a cracking project for the youngsters to have done.
Seems like someone has taken an interest then. It will be interesting to know what the engineering report is afterwards.
How fast was it going?
So far we have only spoken about a static lift of a wing tip. Add in speed as well and the forces applied go through the roof.
You tend not to use FEA like that unless your doing an experiment to find out whats happening. Then you are using the data to tweek your model so you can predict whats going to happen with other loads etc. Once your into yield points and large deflections your into nonlinear FEA which was my skill set.
The linear side of things is pretty much intergrated now into all the CAD packages and will spit out some very pretty pictures. It was just changing as I was leaving engineering. I hope things have improved since then there was alot of people using it that didn't realise that von mises stress is always positive and not really a real stress and only of use for working out the failure point. Which led to some interesting designs. And they would force solutions through with "ill conditioned matrix" errors. I am sure though that the software packages have got more protective so instead of ill conditioned matrix the error is now "your boundary conditions are a pile of ****e" instead.
What are von mises stresses exactly in laymans language? - Yahoo! Answers
Most engineering is done by reference to codes and the codes will have acceptable limits and if your outside that its scrapped unless you can do a full analysis. Huge structures which are worth it then tend to get instrumented with strain gauges in high stress regions . They will then take a series of zero load readings then ramp the load up and see how the structure responds. Give it a dynamic wack to seem what its frequency responce is like. There are engineers that can tell you all sorts of things about whats going on by the structures natural frequency. Then basically they monitor it and watch for any changes.
Its actually the fun side of engineering which is quite specialised, completely different to the office code bashing side of things.
And yes thats about the sum of it in laymans terms but there are only a few structures out there that they do this for. The prime example is a nuclear reactor which they check ever 6 months or so to see whats changed. But that has alot more factors effecting the metal than just load. You have load creep, Neutron creep, thermal gradient effects and no doudt more that slip my memory (its been 20 years since I did that course at uni)
It seems likely that you will read more about this event in later months.
How fast was it going?
So far we have only spoken about a static lift of a wing tip. Add in speed as well and the forces applied go through the roof.
You tend not to use FEA like that unless your doing an experiment to find out whats happening. Then you are using the data to tweek your model so you can predict whats going to happen with other loads etc. Once your into yield points and large deflections your into nonlinear FEA which was my skill set.
The linear side of things is pretty much intergrated now into all the CAD packages and will spit out some very pretty pictures. It was just changing as I was leaving engineering. I hope things have improved since then there was alot of people using it that didn't realise that von mises stress is always positive and not really a real stress and only of use for working out the failure point. Which led to some interesting designs. And they would force solutions through with "ill conditioned matrix" errors. I am sure though that the software packages have got more protective so instead of ill conditioned matrix the error is now "your boundary conditions are a pile of ****e" instead.
What are von mises stresses exactly in laymans language? - Yahoo! Answers
Most engineering is done by reference to codes and the codes will have acceptable limits and if your outside that its scrapped unless you can do a full analysis. Huge structures which are worth it then tend to get instrumented with strain gauges in high stress regions . They will then take a series of zero load readings then ramp the load up and see how the structure responds. Give it a dynamic wack to seem what its frequency responce is like. There are engineers that can tell you all sorts of things about whats going on by the structures natural frequency. Then basically they monitor it and watch for any changes.
Its actually the fun side of engineering which is quite specialised, completely different to the office code bashing side of things.
And yes thats about the sum of it in laymans terms but there are only a few structures out there that they do this for. The prime example is a nuclear reactor which they check ever 6 months or so to see whats changed. But that has alot more factors effecting the metal than just load. You have load creep, Neutron creep, thermal gradient effects and no doudt more that slip my memory (its been 20 years since I did that course at uni)
Last edited by mad_jock; 27th May 2012 at 09:38.
John_R81...
Your initial post didn't have most of that information, and I got the impression that the wing just rode up a few inches then dropped down again - not that the pilot was fighting to keep the aircraft on the taxiway.
I don't find your pictures terribly helpful, because I don't know how tall the van was other than that it was 'a few inches' higher than the tips of the wing.
'A few inches', as you originally stated, applied to a wing half-span of 5 metres wouldn't have produced more than a degree or two of bank which the pilot may not have noticed, or could have ascribed to unevenness in the taxiway. From the fact that the aircraft lurched to the right after the (presumably) left wing dropped implies to me that the pilot was probably using a lot of right brake, and therefore must have noticed that something was wrong. I assume the conditions weren't gusty on the day?
Your initial post didn't have most of that information, and I got the impression that the wing just rode up a few inches then dropped down again - not that the pilot was fighting to keep the aircraft on the taxiway.
I don't find your pictures terribly helpful, because I don't know how tall the van was other than that it was 'a few inches' higher than the tips of the wing.
'A few inches', as you originally stated, applied to a wing half-span of 5 metres wouldn't have produced more than a degree or two of bank which the pilot may not have noticed, or could have ascribed to unevenness in the taxiway. From the fact that the aircraft lurched to the right after the (presumably) left wing dropped implies to me that the pilot was probably using a lot of right brake, and therefore must have noticed that something was wrong. I assume the conditions weren't gusty on the day?
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Not gusty at all. Van height stated in the post with a link to the pictures. If someone can share the wing clearance of a Rans S6 it would help.
Last edited by John R81; 27th May 2012 at 09:10.
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S-6ES Coyote II Aircraft Kit
So 7'4 if its a trike or 6' if it was a tail dragger.
Usually the compact vans are under 6 ft so they can get into car parks.
But I don't doudt your description of the wing getting lifted.
So 7'4 if its a trike or 6' if it was a tail dragger.
Usually the compact vans are under 6 ft so they can get into car parks.
But I don't doudt your description of the wing getting lifted.
Last edited by mad_jock; 27th May 2012 at 09:31.
Well, it certainly sounds as if he should have noticed...
I think it was a point worth clarifying though.
The engineering does sound fun, MJ. Methinks I shall have to sit down and read up on it a bit more.
I think it was a point worth clarifying though.
The engineering does sound fun, MJ. Methinks I shall have to sit down and read up on it a bit more.
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It is bloody good fun but unfortunately very specialised and hard to get into.
O and the reason why they monitor the frequency is they can tell when a crack is starting by the frequency signature and then how far it has extended by the change.
O and the reason why they monitor the frequency is they can tell when a crack is starting by the frequency signature and then how far it has extended by the change.
Last edited by mad_jock; 27th May 2012 at 09:59.
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OK - I understand 350mm too short to go over the van. The van is a good deal over 6ft high. I am 5ft 11 and I needed to stand on to the van floor to get height to see the witness marks.
Mad Jock - I think your nmumbers are total height which for the Trike would be top of the tailplane (it was a trike). For the tail dragger the height would be for top of the wing leading edge or cockpit so you would still need to subtract the depth of the wing to get the clearance. Clearance for the trike I understand to be 1875.
John
Mad Jock - I think your nmumbers are total height which for the Trike would be top of the tailplane (it was a trike). For the tail dragger the height would be for top of the wing leading edge or cockpit so you would still need to subtract the depth of the wing to get the clearance. Clearance for the trike I understand to be 1875.
John
Last edited by John R81; 27th May 2012 at 10:18.
It is bloody good fun but unfortunately very specialised and hard to get into.
Seriously, if anybody can suggest any good alternative careers for a technically minded medic, I'm open to suggestions!
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Well actually there are specialist engineering courses for medics. Mainly run by Bio engineering university units round the country. Some medics do them as a Phd in bio engineering and others do them as a MSc.
FEA is used alot in orthopedic implants.
You start off with this.
Then you test it with this.
Bio engineering FEA is a bit of a bitch to be honest though. Virtually all the material properties are non-linear and every bone is different. For all its challanges it also is bloody good fun. I think mainly because you have to verify by experiment then loop back to regig your engineering and then try it again.
And medics especially surgeons who have engineering savy can make a whole heap of money. I met a ortho surgeon who also had a full BEng who had been told that it was a bit late in life etc to be studying medcine, but he was banging out the patents much to the disgust of all his consultants. They were very good designs as well with high success rates and minimal fannying around getting them approved. He apparently was **** hot with a knife hammer and power tools in theater as well.
Then you get into replacement limbs and stump grips etc. Not as much money in it but they all seem to have a good time of it with alot of job statisfaction getting a better quality of life for the person.
One of the medics at Gatwick is right into his modifcation engineering to aircraft for disabled pilots.
FEA is used alot in orthopedic implants.
You start off with this.
Then you test it with this.
Bio engineering FEA is a bit of a bitch to be honest though. Virtually all the material properties are non-linear and every bone is different. For all its challanges it also is bloody good fun. I think mainly because you have to verify by experiment then loop back to regig your engineering and then try it again.
And medics especially surgeons who have engineering savy can make a whole heap of money. I met a ortho surgeon who also had a full BEng who had been told that it was a bit late in life etc to be studying medcine, but he was banging out the patents much to the disgust of all his consultants. They were very good designs as well with high success rates and minimal fannying around getting them approved. He apparently was **** hot with a knife hammer and power tools in theater as well.
Then you get into replacement limbs and stump grips etc. Not as much money in it but they all seem to have a good time of it with alot of job statisfaction getting a better quality of life for the person.
One of the medics at Gatwick is right into his modifcation engineering to aircraft for disabled pilots.
Last edited by mad_jock; 27th May 2012 at 11:07.
Hmm... I'll have to look into that... I'd always thought of it as being medical-physics territory but it seems I'm wrong. I already have a PhD in neuroscience (colour perception), but could really do with more mathematics.
It gives insights into odd things such as the best form of lighting to do medical procedures under, or colour-vision in aviation, or slight improvements to 3d endoscopy... Part of the problem is that when you're working very long hours it's very difficult to innovate, even though I have a few ideas that I would otherwise pursue.
Was your orthopod acquaintance working in the UK or elsewhere?
It gives insights into odd things such as the best form of lighting to do medical procedures under, or colour-vision in aviation, or slight improvements to 3d endoscopy... Part of the problem is that when you're working very long hours it's very difficult to innovate, even though I have a few ideas that I would otherwise pursue.
Was your orthopod acquaintance working in the UK or elsewhere?
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UK , I met him at an engineering conference but it was 15 years ago now. BUt I suspect he is abroad now working for surgicraft or the like.
The bio-engineering units sometimes have a medical-physics attached or they are attached to or they don't. Some have quite a large cross discipline groups from Medics right through to software engineers, or they are just a load of engineers depending where there focus is.
I wouldn't be suprised if you could find something that would allow you to combine the vision stuff with engineering. For example the robotics for nuclear decomissioning etc.
Its one of the good things about engineering if you enjoy it. You can get something between Finance and law right the way through to flying planes or high energy physics experiments.
The bio-engineering units sometimes have a medical-physics attached or they are attached to or they don't. Some have quite a large cross discipline groups from Medics right through to software engineers, or they are just a load of engineers depending where there focus is.
I wouldn't be suprised if you could find something that would allow you to combine the vision stuff with engineering. For example the robotics for nuclear decomissioning etc.
Its one of the good things about engineering if you enjoy it. You can get something between Finance and law right the way through to flying planes or high energy physics experiments.