The Lost Wheel Thread

[FiF]

Over in the Lounge there has been a thread about workplace accidents, and one of the posts started a discussion about lost wheels from large goods vehicles, buses and coaches.

In my time have investigated a few of these, but the thing which started the controversy was this, especially bit in bold.

FiF said:

RTB said:

Another truck related story: My dad used to drive oil tankers (4 and 6 wheelers) delivering heating oil. He'd come back from a delivery in south Manchester (to a factory I think) and was coming down the A6 through Hazel Grove and Highlane, with lots of traffic as it was school chucking out time. The wagon steering didn't feel right so he went steady. When he got back to the yard he drove the wagon into workshop and had one of the fitters jack it up to check it. As soon as the fitter touched the front wheel it fell off...

Not sure of the current stats but every year 7 people used to die from wheels coming off large goods vehicles. Here's a sobering quote from the Inst Road Transport Engineers on wheel security "When a wheel becomes detached from a heavy vehicle it may simply come to rest without causing any further damage or harm. However, in the wrong circumstances, when wheels become detached from a moving vehicle, they can accelerate up to around 150 km per hour, going out of control like a bouncing bomb, reaching a height of 50 metres before colliding with other vehicles or road users at an equivalent force of 10 tonnes."

After investigating some incidents and seeing CCTV footage of these things whanging into oncoming traffic I got utterly paranoid about motorway night driving for a time. Thanks to better procedures and improved design it's less of a risk, but even so, one chimpanzee with an air impact nut driver can undo all the good work.

If you follow the thread you will see various discussions.

Now as I've stated on that thread I cannot get my head around the explanations why the wheel should accelerate like that. Some of the circumstances I can understand, eg wheel rolls downhill, gains speed due to gravity, another wheel comes detached when spinning at high speed during drifting event.

Aiui the numbers behind the statement come from post accident analysis where the amount if energy absorbed in the collision has been estimated from damage to vehicles and objects after making allowances for materials, design, modifications and corrosion. From that the speed of objects and impact force has been estimated. I do not know to what extent there has been selective presentation of numbers to generate greater reader impact, sorry about the pun.

There it sits, a big fat don't know about the physics of it here.

What I do know, again said in that thread, it's irrelevant if a wheel accelerates or not, if it detached at 90kph, and even if it slows to 70kph, with your approach speed of 110 kph, you have a combined closing speed which means a very bad day for someone.

Over to you. No conveyor belts, by order.

[FiF]

Sorry, forgot this, bit of background reading in addition to the Lounge thread

https://www.soe.org.uk/downloads/1452081366-Wheel%...

[FiF]

As covered on the original Lounge thread I was always a subscriber to the wheel slows down, vehicle slows down more rapidly, but then there's the trailer argument, and was shown a CCTV footage where the wheel really did appear to accelerate.

But as above, a big fat dunno from me, apart from particular circumstances already mentioned.

[FiF]

I'm not sure that the example of sabot rounds is particularly helpful. Surely the whole principle of those is that the projectile is a much smaller more dense material, the total weight of the projectile being less than a full bore round, but still subject to the same forces from the propelling gas, therefore it accelerates to a higher speed.

The light sabot part is discarded after leaving the barrel in order to reduce aerodynamic drag and thus result in the higher projectile speed being maintained. It's not as if the projectile loses the sabot and then goes even faster from that point.

If I've misunderstood how sabot rounds work then please correct me.

As an off topic aside we have fired sabot rounds from a sniper rifle into armour protected ballistic body gel as part of developments into vital organ plates for vests, bugger me they made a mess even through steel armour.

[FiF]

Appropriate user name for a poster on this subject.

[FiF]

Kawasicki said:

TartanPaint said:

I feel like we're, pardon the pun, going round in circles.

I'm trying to imagine an experiment.


Imagine 3 identical wheels, suspended from an imaginary, static wheel-releasing dropper mechanism of some sort, hanging from the ceiling. Some sort of Barnes-Wallace Lancaster bomb releaser.

Spin wheel 1 forwards.
Don't spin wheel 2 at all.
Spin wheel 3 backwards.

Drop them all. What do they do?

Wheel 1 will roll/bounce forwards and come to rest away from the dropper.
Wheel 2 bounces a bit, wobbles and falls over somewhere directly underneath the dropper.
Wheel 3 rolls/bounces backwards and comes to rest away from the dropper, in the other direction from wheel 1.

I'm stating things here as I imagine them to happen, but feel free to argue if I'm wrong.

Wheels 1 and 3 have more energy because they have a rotational energy component, which wheel 2 does not.

Now do the same thing again, but with the imaginary wheel-dropping Lancaster bomber device flying along above a road at 70mph.

Drop them all. What do they do?

Wheel 2 first. It has some kinetic energy, but no rotational inertia, because it's not spinning. It bounces along at 70mph and slows down as air resistance and friction get the better of it and it'll fall behind the dropper.

Wheel 3 doesn't keep pace with the dropper at all. Although it has more energy than wheel 2, it's angular momentum is directional (momentum is a vector). It'll go shooting off backwards relative to the dropper. Every time it touches the road, its "backspin" will slow it down sharply. That's sort of intuitive, right?

Wheel 1 has a load of additional rotational kinetic energy, the same as wheel 3. But its angular momentum is acting in the opposite direction this time. In other words, in the direction of travel of the dropper.

I think that because wheel 1 and wheel 3 have the same amount of energy (total, kinetic plus rotational), wheel 1 will shoot forwards just as hard as wheel 3 shoots backwards.

Edited by TartanPaint on Friday 5th October 16:18

whether the wheel gets a forward boost of acceleration depends on the direction of the force at the contact patch upon first contact, if the wheel circumference is moving at a speed less than the ground contact speed it will get a braking force...and if it is moving at a speed higher than the ground it will be accelerated forward...so even the forward spinning wheel could get a jolt backwards if the circumferential speed is lower than the speed of the ground upon contact.

the length of time this braking or accelerating operates for is related to the stored rotational energy in the wheel

the wheel dropped from an airplane is way more complicated than a car losing a wheel...but it is a nice experiment all the same

i did all these experiments thousands of times...with lego technic as a kid...has anyone ever tried to make lego technic fly? I failed.

OP here, breaking my own rule, reckon you could simulate the wheel dropped from an aeroplane experiment very easily using a conveyor belt. Oh no I've said it now.

I agree with your analysis essentially, that if the speed of the contact patch at first bounce is higher than the speed of the whole wheel then it will accelerate, viz the example of a lost wheel during a drifting competition.

[FiF]

otolith said:

That claim appears to come originally from a 2006 Transport Research Laboratory report, by the way. Can't get my hands on the report to see where it got it from.

If you are referring to 2006 report PPR086 I have a pdf of the report and nowhere does that refer to any increase in wheel velocity.

Obliquely they reference as one of the data sources as the HVCIS fatal database which is an analysis of the STATS19 form completed by police collision investigators, there may be something in there.

Equally the bibliography references another TEL report from 2006 PPR085, but that's just a rdgulatory impact assessment so possibly not from there. I don't have a copy of that.

Other references include collision investigations from around the world, which would be a large task to survey, but seeing as they don't make the claim in the report.

Suspect we have to trawl back through old IRTE stuff, thrown all mine away in a clear out.

[FiF]

I can understand the argument from otolith, it requires an impact which rapidly slows the wheel rotation but without applying a restriction to further lateral movement, as say an Armco barrier would restrict it. So perhaps a kerb which would also help to launch it into the air.

I'd like to see the numbers.

[FiF]

otolith said:

Kawasicki said:

Nothing unusual there, nothing freaky either.

Would you say that it’s usual for a bouncing object to bounce higher each time it hits the ground? The transfer of energy from rotation to translation is very obvious there.

Off topic but I'm thinking of a cricket delivery from a decent spinner, lots of rotation, and occasionally the ball really grips "something" and spits upwards off the wicket. Poor analogy I know, but another one where, to my eyes holding the bat, it appears to increase speed having converted rotational energy and thus an increase in lateral energy.

[FiF]

TheDrBrian said:

FiF said:

otolith said:

Kawasicki said:

Nothing unusual there, nothing freaky either.

Would you say that it’s usual for a bouncing object to bounce higher each time it hits the ground? The transfer of energy from rotation to translation is very obvious there.

Off topic but I'm thinking of a cricket delivery from a decent spinner, lots of rotation, and occasionally the ball really grips "something" and spits upwards off the wicket. Poor analogy I know, but another one where, to my eyes holding the bat, it appears to increase speed having converted rotational energy and thus an increase in lateral energy.

But the surface rotational speed of that ball is faster than linear speed the person has flung it.
The surface rotational speed of the tyre is only ever as fast as it’s linear speed and it can’t go any faster.

• unless you were doing burnouts.

That's why I said it was off topic, and was simply an illustration of rotational energy being converted into linear energy, plus the ball bouncing more than it would naturally. Also in case you missed it the possible reason for wheel acceleration due to wheel spinning faster than speed of travel was covered in the original post, i.e. during a drifting competition.