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Author Topic: Landing-Craft accident, Railway Street, Chatham - 1953  (Read 135704 times)

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Offline smiler

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #385 on: May 30, 2013, 07:49:10 »
..... and it takes him 5 seconds to realise what has happened.
      Well thought out Peter but I'd hate to be near any lorry driver who would take 5 secs to realise his brakes were not working  :)

Offline Lutonman

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #384 on: May 29, 2013, 21:11:27 »
Peterchall
Well done, I have kept out of this as I had nothing to add, your latest post does make sense.

Offline Sentinel S4

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #383 on: May 28, 2013, 17:57:11 »
Excellent Petechall, most excellent. No further comments at this time. I will have to read through again  :) :).

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Offline busyglen

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #382 on: May 28, 2013, 15:22:22 »
 :) :) :) :) Well done peterchall!  What an interesting and fascinating thread this has been, mainly between you and Sentinal S4.  The way you have both taken every section to pieces and after checking it out, put it back together again.  It has been a real test of practicality and theory. Thank you both.

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Offline peterchall

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #381 on: May 28, 2013, 15:05:12 »
Having nothing better to do, I’ve been thinking a bit more about this thread:

1.   Looking at photos of the front of the Alex pub, there seems to be an across-road slope of about 1 in 20 right across the road junction, as distinct from the conventional camber. That alone would impose a 1.4 tons sideways force on a 28 ton load.
2.   Looking at a photo of tram tracks at that point, they don’t follow a smooth curve from Maidstone Road to Railway Street, but include a ‘sharpish’ centre bit. If our driver followed a similar path it could mean that the minimum radius of the curve was about 100 ft instead of the 150-160 ft of a steady curve. That would make the turn-over speed about 32 mph.
3.   SentinelS4 suggested that the driver would have tried the hand-brake but it wouldn’t have helped much, so let’s look at that. It would only act on the rear wheels and probably be only half as effective as the foot-brake, so assume its overall effect to be a quarter of the 50% we have assumed for the foot-brake. Taking all other factors into account it would more than halve the acceleration down the hill. Unless the road was very icy it wouldn’t lock the rear wheels, so they would not be sliding. Thus we would have a tractor with an unbraked front axle, braked and still gripping rear wheels, followed by an unbraked trailer. On a straight road it all seems stable to me.

So, still using the data that I’ve used previously, but now including the across-road slope and the tighter turn, does the following make sense?

Driver starts at the top of the hill at 12 mph (the assumed legal maximum) in a middle gear (although engine braking is so marginal that it makes little difference). He applies the foot-brake which immediately fails (more likely then than later under established conditions), and it takes him 5 seconds to realise what has happened, during which time the speed has increased to 17 mph. He then applies the hand-brake and the unit accelerates at about 0.4 mph/second, arriving at the Alex pub at about 35mph (corresponding roughly to the reported speed of 30 mph), just above the turn over speed of about 32 mph.

That is marginal, but even if the unit didn’t tip over due to that, the centrifugal force at 35 mph, plus the side force due to the across-road slope, would impose a side force of 24 tons on the LC. Depending on the ‘grip’ between the LC and the trailer platform – whether it was dry or wet – the resultant force on the load restraints would be between 8 and 19 tons. I imagine that would be enough to break them, allowing the LC to slide across the trailer to the left to make tipping even more likely.

Once it had tipped over at, say, 100 ft before the viaduct at 35 mph it would need a retardation of only 40% to stop under it, I think easily provided by the drag of the LC along the road plus the brushing impact with the bus.

So, ladies and gentlemen of the jury, I suggest that our driver was innocent of any wrongdoing.
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Offline peterchall

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #380 on: May 16, 2013, 08:06:40 »
A bit more information about air brakes, to give background (Internet sources).

The first air brake for road vehicles was designed in 1922 by Knorr-Bremse, a German company now having factories in the UK. By 1926 they were fitted to many larger trucks and were standard on most HGVs and buses by 1949 (but I have reference books showing that many were fitted with vacuum or hydraulic brakes, so question that). Nevertheless, it shows that air brakes were not in their infancy at the time of this incident. Then in 1960 came dual system air brakes with 2 separate systems each operating half the brakes on the vehicle. So we know that our tractor would have had only a single system, making complete failure more likely.

A trouble-shooting chart lists the following causes of complete air brake failure:
1.   No air pressure. (Obvious, but it doesn’t state why!)
2.   Broken tubing or hose. The article from which the chart came explains that the compressor should be able to supply enough air to cope with quite large leaks, so that presumably means complete breaks.
3.   Faulty foot valve (brake pedal integral with a ‘master’ operating valve)
4.   A broken linkage between the pedal and a non-integral ‘foot valve’

Then I found information stating the foot valve fault was likely to be an exhaust leak when the pedal is depressed.

First to explain how the foot valve should work. As the pedal is depressed the valve allows air to flow from the reservoir to the brakes, the pressure being proportional to the pedal movement. When the pedal is released air passes from the brakes to atmosphere via the exhaust port of the valve, thus releasing them. That is the ‘whoosh’ of air that can sometimes be heard from an HGV or bus.

When faulty, the air from the reservoir passes straight through the foot valve to atmosphere when the pedal is depressed, without applying the brakes. With a modern dual system, having 2 foot valves operated by the one pedal, half the vehicle’s brakes would still work, but on our tractor it would result in complete brake failure.

The source does not explain what happens inside the valve, simply stating the remedy to be “Replace foot valve”. I can only find an indistinct illustration of the internals of a foot valve, which appears to consist of a shuttle system to maintain proportionality between pedal movement and brake pressure, and an exhaust valve. But most importantly, it contains SPRINGS, which can break at any time.

So is that a plausible cause of the brake failure?
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Offline DaveTheTrain

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #379 on: May 14, 2013, 21:42:48 »
PM sent.
DTT

Offline peterchall

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #378 on: May 14, 2013, 21:01:08 »
Would that shed in Kent be near Dartford, because that's where one of them was first delivered?

I just wondered how much their design influenced the design of the CD45, but detailed discussion is probably off-topic so I'll just post the link to my source, for those interested:
http://www.historicroadways.co.uk/scammell-100-tonner.html
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Offline DaveTheTrain

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #377 on: May 14, 2013, 20:26:27 »


I’ve found what seems to be a progenitor of the CD45. In 1929 Scammell built two (yes, two!) ‘100 tonners’ designed to do just that – pull 100 tons


The 100 tonners are quite unique machines peterchall, built, if I recall correctly specifically to serve construction of the electricity network, hauling transformers and the like.  Of course previously this would have been the work of heavy steam haulage.

You may be interested to know there is still one in Kent, sat nicely in a shed not too far from me. 

DTT

Offline peterchall

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #376 on: May 14, 2013, 16:28:25 »
If by ‘blowing up’ a gearbox you mean damaging it by over-speeding, bear in mind that only rotary motion is involved, so there are no inertia forces due to reciprocating parts starting and stopping, as in an engine. I suppose there must be a speed at which a steel gearwheel will fly to pieces due to centrifugal force, but it must be colossal.

I asked whether there was an auxiliary box or whether just using some of the gears was the norm in order to modify my previous assumptions about transmission drag, but now realise it was pointless question, because just a few extra gears would have made no substantial difference anyway.

I’ve found what seems to be a progenitor of the CD45. In 1929 Scammell built two (yes, two!) ‘100 tonners’ designed to do just that – pull 100 tons

The engines were initially Scammell 7094cc units giving 86 bhp, but they were replaced in 1932 by Gardner 6LW diesels of 102 bhp. They had 4-speed gearboxes with a 2-speed final drive, giving 8 speeds in all, but the final drive ratio was changed by external levers behind the cab, so only 4 gears were usable at one time. They could pull a 100 ton load up a gradient of 1-in-10.

16 inch drum brakes were fitted to the shafts from the diff to the driving sprocket of the chain drive (not at the wheels) and could be operated by a foot pedal or a hand lever, enabling the driver to manipulate throttle and clutch while braking at the same time; the parking brake was operated by a hand wheel, so could not be used for hill starts.

Both vehicles were finally retired in 1953. I’m not suggesting that a CD45 had those features, but they were contemporary and probably more akin to the ‘100 tonner’ than to today’s HGVs.

The torque of a Gardner LW was over 95% of its maximum from 700 rpm to 1500 rpm, and assuming my recent graph is correct with a governor cut in at 22mph (1700 rpm), that equates to a speed range of 9 to 19 mph in top gear.  With that torque spread the force needed to pull the load up a 1-in-10 slope (about 6 times that on the level) could be achieved with a 4-speed gearbox. Because of its more ‘peaky’ torque curve a petrol engine would need more gears, but I think 6 would be adequate and would also give a diesel more flexibility regarding gear change speeds. So there seems no need for a range-change box in this case.

Once brake failure occurred (if it did) it wouldn’t matter if the trailer had been braked or not – its only significance was as a source of failure.

So provided complete brake failure was possible, all the ingredients are there: The runaway down the hill with little resistance, the attainment of enough speed to tip over on the bend at the bottom, the drag of the LC along the ground, plus the brush with the bus, being enough to stop it under the viaduct. The liquid seen by Signals99 could have been engine oil, suggesting that the engine was still in gear and that something broke. The ‘assistance’ of an AEC Matador could mean that it took over the tow because our tractor was damaged. All it needs is a reason for that complete brake failure - an air line parting or the pedal becoming disconnected. As S4 says, he could have tried the parking brake and it wouldn't have had much effect, but could it have prevented the speed reaching that necessary for it to topple?
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Offline Sentinel S4

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #375 on: May 13, 2013, 18:49:25 »
Back to the first point. If I gave my neighbour’s car a tow with mine, I probably wouldn’t be able to get into top gear (although, to the best of my memory, that could be done with the works Hillman Minx van when towing a similar sized vehicle), and I wondered if it was accepted in heavy haulage that the topmost gears would not be usable with a heavy load.

Sorry Peterchall but all gears High and Low range would be used. Hence my question about blowing up a gear box. With the speed range of this vehicle He would certainly be in the upper ratios at 12 mph. For comparison I drive a 4 over 4 gear box. That is to say 1 to 4 are low range and 5 to 8 are high. I am regularly in high range at 20 mph, I am allowed to go a lot faster than these men and I have a better rev range and power output. However seeing that top speed was in the range of 35 mph I would expect the range change to be around 8 to 10 mph. That is why I ask about the gear box and accept that he would be changing down from High to Low, two levers and two movements, High - Low and 7 to 6. Complicated and if rushed a lot of potential for missing gears.

The relevance of the trailer being braked is not to the driving (although it might mean the driver being less cautious on down grades), but to making brake failure more likely due to there being another ‘weak point’ in the system - that is the tractor/trailer brake connection becoming parted.

The early system used on these relies on pressure being maintained. No pressure no braking effort. Today with no pressure the brake fail to release, on these they fail to go on. To put every ones mind at ease they have been modified to meet current standards on those that are still running. If the coupling should part, palm couplings perhaps as they are very easy to part, then he would loose all of his effective braking effort  and would be left with a ratchet parking brake.

More grist for the mill there Peterchall. On the parking brake he would have held for a while, along with engine braking, but would not have been able to stop her. He needed the bridge abutment to stop. Sadly the bus got kissed in passing and wiped out the ropes and allowed the load to drop............

Just a thought.

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Offline peterchall

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #374 on: May 13, 2013, 11:39:05 »
To answer your last bit first, the short answer is a qualified ‘no’, but it’s not easy to explain without a diagram (which non-technical readers might find helpful in other contexts), so here is a 4-speed sliding mesh (crash) gearbox:

It consists of:
A Primary Shaft (P) driven by the engine via the clutch.
A Layshaft (L) driven by P via the Constant Mesh Gears (C). The layshaft and its gears all rotate as one unit.
A Mainshaft (M) with gearwheels on splines so they can slide along it but must rotate with it. Its left end is carried in a bearing in the end of P but, despite appearances, they are separate shafts able to rotate at different speeds.
P, L, and the right end of M are carried in bearings in the gearbox casing.
Lubrication is by ‘splash’ caused by the bottoms of the wheels on L dipping into oil in the bottom of the gearbox casing.

The unit is shown in neutral, and to engage 1st gear the wheel 1 on M is slid by the selector mechanism (Red) until it meshes with the wheel 1 on L. The drive is then via gears C , shaft L, and gearwheels  1, to M. To engage 2nd, the pair of wheels is slid until gearwheels 2 engage, and similarly with 3rd. 4th (top) is engaged by sliding the mainshaft gear 3 until its ‘dogs’ (the little black squares) engage with those on P, thus locking P and M together.

Additional ratios are provided by additional pairs of gearwheels on L and M.

In the situation you envisage, P and L would be turning at engine tick-over speed and M would be turning at the vehicle’s road speed. To engage a gear – say 2nd – the driver would have to increase the engine speed until the speeds of the wheels 2 on L and M matched and could be slid silently (we hope!) into mesh, and if he then engaged the clutch it would be no different to a normal gear change.

That highlights the difference between a diesel and petrol engine. If the speed needed to engage the gears was above the governed speed of the diesel, it couldn’t be done, but the speed of an unloaded petrol engine is limited only to that at which it runs out of breath or (more likely) something breaks.

However, if having engaged the gear, the driver kept the clutch disengaged and took his foot off the throttle for long enough, the whole gearbox would be turning at ‘vehicle speed’ and the engine would just be ticking-over. If he then engaged the clutch suddenly something nasty would happen:
1.   Umpteen miles worth of clutch lining wear while the engine speed was forced up, &/or
2.   Centre torn out of clutch plate, &/or
3.   Broken axle shaft, &/or
4.   Teeth broken off gearwheels in gearbox or final drive (although probably not all 'stripped' off)

So your scenario is possible, but begs the question: would a professional driver be such an idiot?

Back to the first point. If I gave my neighbour’s car a tow with mine, I probably wouldn’t be able to get into top gear (although, to the best of my memory, that could be done with the works Hillman Minx van when towing a similar sized vehicle), and I wondered if it was accepted in heavy haulage that the topmost gears would not be usable with a heavy load.

The relevance of the trailer being braked is not to the driving (although it might mean the driver being less cautious on down grades), but to making brake failure more likely due to there being another ‘weak point’ in the system - that is the tractor/trailer brake connection becoming parted.
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Offline Sentinel S4

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #373 on: May 12, 2013, 18:50:49 »
If she had a range change that could well have been a separate lever, to a separate box giving the difference between High and Low range, a common feature on Land Rover's. However unlike those this would have been available whilst in motion. Today it is a switch on the gear lever. This would have gone 1st to 6th, range change, back to 1st position giving 7th to 12th. He certainly would have needed all of the gears to move this load, even if he block changed (missed gears out, 1st to 3rd to 5th for example, it is common practice).

If the trailer was braked then it would have had positive pressure air (not the fail safe items we now have) with either a wind down or ratchet hand/parking brake.

Could he have shredded the gear box? Peterchall this one is for you; If he had been coasting out of gear, speed building, and finally got a gear but in low box not high and dropped the clutch on an idling engine. Would an over speeding input shaft be enough to blow the rest before the engine caught up? Or would the engine just spin up and let go?

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Offline peterchall

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #372 on: May 12, 2013, 17:48:24 »
Thanks Smiler. I think I remember from a previous post that it was a gate-change 6-speeder which, I suppose, could be used effectively as a ‘range change’ box by using, say, 1st to 4th when laden and 3rd to 6th when running light.

The RR 7.7 litre engine (actually 7668 cc) was a straight 6 and in its final version had a cross-flow cylinder head – the most efficient petrol engine design – so presumably produced much more power than the 97 bhp of the 1927 model. However, it ceased to be used in a RR car (the Phantom II) in 1935 so, unless our tractor was made before then or the engine continued in production for ‘out-sales’, it couldn’t have been fitted with it. I didn’t twig it until yesterday that you can’t make a 4 cylinder 7.7 litre engine out of a 27 litre V12 Meteor engine by just cutting it down, so it can’t be that. Actually, I’m surprised that a diesel was not used because of its more suitable characteristics, given that they had by then become well established. Many, but not all, photos I have seen of the CD45 carry a ‘Gardner’ badge.

However, power output is irrelevant to this thread, apart from obviously being ‘adequate’, because we are concerned with stopping. On the over-run a petrol engine acts purely as a vacuum pump, so its effectiveness depends on its size, regardless of whether it is a 1920s side-valve engine producing 20 bhp/litre or the latest multi-valve, high-compression ‘super-duper’ special producing over 100 bhp/litre. So, for the reasons I’ve stated previously, I’m confident that engine braking, whether from petrol or diesel, couldn’t have held back a runaway to any significant degree.

Signals99 has PM’d me to say that he visited the site that day and saw workers putting sand on a pool of liquid behind the tractor. He can’t say whether or not it was engine oil, but if it was it suggests that a gear was engaged at the end of the run and the engine over-sped and spewed bits out. If the tractor had been a forward control/cab-over-engine design there would probably have been reports of injury to the crew, but with the engine out in front that would be unlikely. If not engine oil, what else could it have been?

DaveTheTrain’s Reply#224 of 28th February suggests the trailer might have been an ex-tank transporter, and if it was the same type as the ones used in Ted Ingham’s video (Reply#285 of 20th March) it was braked – see photo of one carrying a tank in Reply#297 of 26th March, in which a brake pipe can be clearly seen. So could the trailer have been braked after all? If so, it was unlikely to have been like the complex systems of today, and a breakage of that connection could have caused complete brake failure, more plausible than the pedal becoming disconnected.

A new line of enquiry, perhaps?
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Offline smiler

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #371 on: May 12, 2013, 08:08:17 »
http://www.youtube.com/watch?feature=player_detailpage&v=Fe-3Kdt7J7s
Scammells pulling a real load. How would you fancy this S4
Sorry PC, can`t remember anything about gearbox, mine would have been different gearing I'm sure as the Scammells I worked on were mainly tankers belonging to Thomas Allen. Any older drivers remember that name?

 

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