Copied from www.20six.co.uk/roadtrafficaccidents

Index and list of Contents

http://www.caravanaccidents2.wordpress.com/

contains paragraphs 1a to 10c
www.20six.co.uk/roadtrafficaccidents and www.itai2005report.wordpress.com
contains paragraphs 10ci to 18b

http://www.caravanaccidents3.wordpress.com/

contains Paragraphs 31 to 50

INDEX
(A) accident statistics 1a : Accident-failure of over run brakes, 3c: Accident-failure of stabiliser, 3c: Acknowledgements, 5d, 5e, 5f, 6b : Air speed indicators, 6c:
Aircraft Stalling Speeds, 7g, 7h, 8a, 8b, 8c:
Alko new brakes; history of: Para 41
Applications of work in these blogs:
Para 32
Air Speed Indicators Para 33
(B)
Blog: aims of, 1d: Bath university on stabilisers, 2e:
Bath University on effect of bow wave of HGV, 9b:
Boat trailer snaking, 4a: Burst tyres (related to centre of mass and stability), 6a, 11e: Boeing 737, 8g:
[D]
Dunwoody; Mrs Dunwoody
MP; Para 38
{C}
Caravan Club, 6a, 6g, 9b, 10, 6h, 6j: Centre of mass calculation, 18a:
Centrifugal force calculation, 12c: Conclusions, 16a:
(E)
Evidence from sailing supports safer towing, 4c,5a,5b,5c:
Electric Brakes, 15b: 42
Equations of motion and stabilisers, 13a:
(F)
Flying caravans, 6h: Formula 1 racing cars, 9e:
(G)
Government Caravan Accident Statistics, 1a:
(H)
Highways Agency Para 31
HGV trailers – summary, 18b;
Handbook for air pilots, 6e, 7a: Head wind and side wind components, 7c, 7d: HGV’s and wind speed needed to over turn them, 7e, 7f: HGV‘s and maximum safe air speed, 9a: HGV‘s effect on caravans, 9c, 9d, 10a, 11a:
(I)
Information on stalling speeds for aircraft, 7g, 8a, 8b: Insurance, 17c:
IVRA over run brake conversion kit; Para 40
(K)
Kinetic Energy and caravans, 11f:
(L)
Length of HGV bow wave related to length of caravan, 11d:
Lobbying Parliament:
Para 34
(M)
Mini Bus/Trailer Accident;
Para 1e to 1g
Maximum legal caravan speed, 3b: Maximum safe caravan air speed, 6f, 6g, 6j: Mini bus accident, 1f, 1i:Marine safety measures applied to road, 14b:
(N)
Newton; GCSE and GCE “A” level work 1b
(O)
Over run brakes – the case against 10cii
Over run brakes, 1e, 1g, 12a: Over run brakes, alternatives, 2a: over run brakes and shock absorbers, 1h: Overloading of caravans, 17b: overloading of tow car, 17d:
(P)
Physics of over turned minibus, 1g: Prevention of snaking, 4b, 2d, 2e: Phase of HGV bow waves, 11d:
Principle of Moments and stabilisers, 13a: Parallelogram of Velocities and vehicle air speed, 14b:
{R}
Research at Bath University, 9b,d,e,& f: 10a & b: References, 10c. Resonance and caravans 11d:
(S)
Snaking tyre marks – evidence produced by, 10ci
Snaking tyre marks, 17a:Snaking, 2b, 11g, 12b: Snaking caravan accident,3a: Snaking prevention and stabilisers, 2d, 13a: Stabilisers and Bath University, 2e:
Stabiliser test on the friction based type (details of procedure), 10ciii;
Stabilisers (design faults with most of them), 2g: South African Mini Bus Accident, 1f, 1i:
Stabiliser test (calculation of centre of mass), 18a:
Stabilsers; Bath University
2003 Report; Para 36
Stabilisers (leaf type)
Stabilisers; Para 39
Para 37
Selby road/rail disaster, 2c, 15a, 10cii: Somersaulting caravan, 3a, 6b: Standen (Bath University) on wind induced snaking, 10b: School Mini Bus, 10d:
Snaking calculations approximated to circular motion, 12b:
(T)
Tyre marks made on the road in a snaking accident, 5g: TV adverts for cars concerning aerodynamic lift, 7h: Trailers-effect of the load on aerodynamics, 8d:
(U)
University mini bus, 10d:
(V)
Ventrui effect, 11b, 11c:
(W)
Wind gusts, 6d: Wind deflectors, 8c, 9d: Wind speed monitoring on road and rail, 9g, 7f: Windy weather, 14a:
Wright: Dr Tony Wright MP
para 35
(Z)
Zero road friction, 6f.

CARAVAN AND HGV TRAILER ACCIDENTS

Copied from my blog www.20six.co.uk/roadtrafficaccidents

10 ci

The Case Against Over Run Brakes

I wrote about this in my blog
www.caravanaccidents2.wordpress.com
Starting at paragraph 1e, and in
www.20six.co.uk/roadtrafficaccidents
paragraph 12a
The material in these blogs is an update of a paper I produced for the Institute of Traffic Accident Investigators in 2005. This was not published, but most of the material had been well circulated via the private Yahoo web site for Accident Investigators
The Selby Rail Disaster
Some years ago a Land Rover Defender towing a trailer with over run brakes and carrying a fairly large car ran on to the main railway line whilst the driver was sleeping (this was the verdict of the Court) right up to the last short distance to the point of impact with the passenger train.
See para 2c in www.caravanaccidents2.wordpress.com and para 15a in www.20six.co.uk/roadtrafficaccidents
I have owned a Land Rover Discovery for 11 years, as well as a Jaguar 21 Sailing Cruiser with road trailer for 19 years. The latter is comparable in weight with the trailer plus car in the above accident. My Discovery is mechanically almost the same as a Defender and as the latter type was not available to the police for testing the trailer which survived the accident (the train only hit the Land Rover) the police used a Discovery similar to mine to do their tests ( my information comes from an article in the Institute of Traffic Accident Investigators Journal).
I have towed the Jaguar 21 far enough to learn about towing this weighty object; I towed my previous sailing cruiser (a Bradwell 18) around 8000 miles in 12 years, between various coastal harbours and non tidal rivers in Wales and the Midlands.
I have frequently pulled my current sailing cruiser up a steep shingle beech, and of course gone down the same slope when launching. I need to engage the “locking differential mechanism” and use
the low ratio gear box to do this.
(When I had a Rover 3500 SD1 SE V8 I had to use a long rope and block and tackle to pull the boat up the same slope).
I have looked at railway embankments of different types, from the train, and from the top near roads.
I think that if I had woken up some distance down an embankment when I was driving my Discovery but not towing, I could have avoided getting on to the track. I would first of all have turned at about 45 degrees to continue at a slightly reduced speed due to the reduced gradient. When I reached the bottom I also think that I could have turned again to run parallel with the track.
The Land Rover driver who caused the Selby Rail Disaster was an experienced professional tower of trailers and would be even more familiar than I am with the dangers resulting from turning whilst towing such a heavy trailer with over run brakes. He kept the outfit going straight on as I would have done. Trying to turn would have been a worse option as at the time the train was not in view.
The police spent an enormous amount of time testing the trailer that survived the disaster intact, as the train only collided with the Land Rover. The police proved that the trailer met the requirements as laid down by parliament. If their tests had shown otherwise the man may have been given a lighter sentence or even acquitted.
It has been about two years since I wrote my report for the ITAI and I now think that the police should have run additional tests on the trailer as it may have been possible to show that although it did comply with the law, it could possibly be demonstrated that it was dangerous to turn same in such a situation. This would mean, (if demonstrated in the tests), that the trailer was a subsidiary cause of the accident and that this may have given rise to a different verdict/sentence or a “Rider” concerning over run brakes. (Roll bars are common in vehicles used for off road events, as is the use of full safety harness, so non professional testers should be well protected).
This is very much the “Science of Hindsight” many years after the event. I do not think that at the time of the crash any serious doubts had been raised concerning over run brakes. The brake actuating mechanism was first introduced about 1929 and at the speeds most trailers were pulled at in those days I am not surprised that few problems showed up. It is since the development of fast roads and the increase in the popularity of recreational towing that concern about caravan/trailer safety has increased.
If the defence solicitors had seen any evidence that this was the case I am sure they would have insisted that the matter was investigated.
I do not wish to suggest that the police or any one else reopen this case in court.
However, I do think that all road users will wish to have this matter evaluated if the hypothetical case I have outlined above fits the layout of the embankment at the crash site. If there is not a match and it is felt that the gradient at the crash site is too steep for any evasive action to have been taken, I hope that tests will be carried out on a slope more typical of most embankments, as well as on flat tarmac roads in a testing site. (I am not proposing that a railway embankment is used, unless it is a disused railway and disused railways may have great numbers of trees and not be typical of those in use).
These results would also be available as evidence for future court hearings. The Police Accident Investigators could repeat the tests if they thought it necessary.
As far as I know Bath University were not asked to investigate over run brakes.
Members of both Caravan Clubs may wish to fund professional tests.
In my Blogs (see first reference above after main headings) there is a description of a jack knifing accident, and even though I only obtained my information from the TV news and Radio 4 news, I think there is enough to show that there is a serious problem with over run brakes in the case I quote.

10cii

Evidence from Snaking Tyre Marks
One of my hypotheses is that there must be almost zero friction between tyres and the road during the middle part of each swing of a snaking caravan. (Please also note that a rigid HGV towing a large central axle trailer is the same in principle as a car towing a caravan – except that the former has brakes that can be applied when snaking leading to jack knifing takes place). The only tyre marks seen on the road after a typical snaking accident (see para 5g below from my unpublished report to the ITAI), are on the extremities of each swing. I am publishing this account because from other evidence I am convinced that the person who supplied me with the information concerning the snaking tyre marks is a retired police traffic accident investigator, who still does fairly regular work for the courts as an expert witness.
In addition, any RTAI carrying out a new investigation concerning a snaking trailer or caravan, will be able to compare what I have written with the photographs of the actual marks made in the accident that he/she is investigating.
It follows from my hypothesis of almost zero friction that the caravan/trailer must experience some aerodynamic lift; the fact that this does not fit current theory that one needs a structure shaped as an aircraft wing to achieve lift is a problem for academia.
The aerodynamic lift exists ( see my evidence above) and to make our recreational activity safer we must adapt to make things safer.
Standen, Phd thesis Bath University,1999, “Towed Vehicle Aerodynamics,” as a result of wind tunnel tests with a model car and caravan did show that suitable aerofoils did improve stability. He only failed to solve the problem of devising a legal/practical solution as his final aerofoils were on the side at the front of the caravan. He also is in my opinion also confirming the existence of this aerodynamic lift produced without a wing shaped structure, as a result of his wind tunnel tests.
At the time of writing 1100, 22-10-07, my articles are still being displayed by
www.touringandtenting.com
and can easily be found by typing “Peter W Jones” into their search engine.
I have already posted a prominent “disclaimer” concerning anything attributed to myself as I have no control over editing, particularly as the last time I “viewed” two of my articles had been “locked.”
However, it is still very clear that no substantial evidence has been provided that may refute my hypotheses ( as stated in items in my recent postings), and it is equally clear that a great many have attempted to do so.
Further Information:- See also my blog www.caravanaccidents2.wordpress.com
Para’s 9e, 9d, 10c 10b, and also much further on in this blog
Para’s 10d, 11a to g inclusive, 12b and c, 14a and b, 15a, 17a.

10ciii
SUMMARY 3
Testing Friction based Stabilisers for Caravans and Trailers
I am strongly in favour of modifications to over run brakes to convert them to electronic/electric operation. I also wish to draw attention to the fact that if you put “electric brakes” into the Google search engine you will be introduced to the range of these available in the USA and Australia. In particular you will also be able to see that electric brakes would cost considerably less than over run brakes plus stabiliser and electric brakes have been in use for around 30 years. It is possible to apply electric brakes when a trailer is snaking and this application of the brakes will in most cases control the snaking (but see also Bath University Wind Tunnel Research showing the need for aerofoils to create down force).
I hope that Caravanners and Trailer towers will test their friction based stabilisers. You do not need qualifications in Mechanical Engineering to make a reliable rough estimation.
I previously wrote that you need to evaluate the amount of friction available from your stabiliser by moving it with the aid of a 2 metre length of tubular steel or timber. I also wrote that to perform this task accurately the length of timber must be equal to the distance from the tow hitch to the centre of mass of the trailer or caravan.
It is possible that by looking at a caravan/trailer and its load any reasonably intelligent person can estimate the distance of the centre of mass from the tow hitch almost as accurately as I can calculate same. It will be seen therefore that for a small trailer the stabiliser test lever will be less than 2m long, but for a large twin axle van it will be very much longer.
The Centre of Mass is the point where the whole of the mass acts.
If the centre of mass is over the axle the caravan is balanced on its axle and zero force is needed to lift the caravan by the handle on the tow hitch.
In theory the centre of mass could be found experimentally by balancing the van on a strong length of tubular steel placed under the van on axle stands. This is not advisable as the steel may damage the chassis.
If the van is correctly loaded the centre of mass will be a short distance in font of the axle/axles.
Calculations
I have explained how to calculate the position of the centre of mass in Para 18a of this blog.
The first solicitor who wishes to use this method of testing a stabiliser in connection with any legal proceedings will need to engage the services of a Forensic Engineer to evaluate the method.
However, if it were not for the size of the apparatus required this test could be carried out in a school or FE College as part of the Physics course for either GCSE or GCE “A” level. (The theory behind my formula may still be in some schemes of work for GCSE if Physics is taken as a separate subject.)
As a previous Head of Science I would not have thought it justifiable for lab technicians to spend time on this construction, but if a member of staff with a caravan and stabiliser made the apparatus in their own time it would be a different matter.
Physics teachers are always on the lookout for practical applications of the work they teach.
If any school or College did carry out this procedure, as long as the teacher/lecturer in charge had a sufficiently high academic qualification in Physics or Engineering to satisfy the court, it could well be that this would be accepted as a validation of my method.
In simple terms, by moving the stabiliser with the constructed lever the operator is just asking themselves the question : Does this amount of force stand any chance of having any effect at all on a caravan or trailer snaking at 50mph?
According to the Haynes Caravan Manual (by John Wickersham) my stabiliser needs adjusting so that a force of 27kg is needed to just turn the arm of 0.7 m length. This gives 270N x 0.7 = 189 Nm.
Similar design specifications for stabilisers which obtain their friction from a device fixed over a dry tow hitch, have never been disclosed (to the best of my knowlege).
If readers look at the www site for the “Advertising Standards Authority” they will find some interesting reading. In 2003 the Swift Caravan Group took a whole page in the Caravan Club Magazine to advertise the ALKO stabilisers on their caravans, but they included a picture of a gyroscope in the advertisement.
The details will be found on www.asa.org.uk
Put “SWIFT CARAVAN GROUP” into the search engine in the top right hand corner, and then click on the extract that appears, to see the full “adjudication.”
Other methods of testing stabilisers have been used. The Fratilla Phd thesis of 1994 used a computer model; see para 2e, 9b and 10c of my blog www.caravanaccidents2.wordpress.com
and para 18a of this blog.

Peter Jones MInstP

I have set up this extra blog to hold work transferred from my

20six.co.uk blog as this is so often “off line”

. Wave Theory

An Explanation of why trailers “snake”, based on well established Laws of Physics and 26 years experience of towing sailing cruisers and caravans.

A number of phenomena studied in School Physics exhibit resonance. When something is made to vibrate it will only vibrate excessively when the frequency of vibration is the same as the natural or resonant frequency . Musicians have to be familiar with this but moving closer to caravans I would point out that if a company of troops marched over a wooden bridge were not to “change step” every few minutes there would be a probability that they would set the bridge resonating and cause it to collapse. I have several times shown a TV “Physics for Schools” programme which depicts an approx 1930′s USA road supension bridge collapsing when set in resonance by a strong wind.

I would therefore suggest that one reason caravans snake excessively is that an overtaking HGV or the wind happens to have set them oscillating at their resonant frequency.

I have many times demonstrated, using a water ripple tank, in GCSE Physics lessons, that when waves are “in phase” they will reinforce each other and produce bigger waves, and that when they are in “anti phase” two identical waves will cancel each other out and have zero effect. It is reasonable to suppose therefore that this also applies to vibrating caravans being affected by the bow waves of HGV’s. If the bow wave of a HGV is in phase with the slight vibrations of a caravan a dangerous snake could be induced as the HGV overtakes. If another HGV is following too closely behind (as is often the case) and it also has a similar bow wave it could make the situation even worse for the caravaners, but if the wave happened to be in “anti phase” with the caravan vibrations it would dampen them down.The above also explains why you are less likely to get a dangerous snake on a crowded motorway than on a quieter one. Waves from various vehicles will interfere with each other and be less likely to cause trouble for trailers.

I had always thought that the length of a trailer (with a high aspect) had almost as much influence on stability as the tow car/trailer weight ratio, but after I purchased a twin axle caravan ( just over 19ft long) I became more convinced of this. I was therefore not at all surprised when I found that wave theory also explained this phenomena.

If L= length of bow wave of HGV, and T= average body length of high aspect part of trailer, the bow wave will have the maximum turning effect (giving rise to snaking) on the trailer when T=L/2; ie when the length of the trailer is half the length of the HGV bow wave. Wave theory shows that the pressure created by the wave is such that it will tend to push the front of the trailer in one direction and suck the opposite end in the other direction ( or vice versa). This will create the twisting effect which sets the trailer in oscillation. It is when T=L/2 that this occurs, but it should also be taken into account that as these effects are felt at the ends of the trailer they will have greater turning effect on a longer trailer than a short one.

Similarly, wave theory shows that this effect is also felt when :- T=3L/2, 5L/2, 7L/2 ……and so on.

In the cases mentioned above the overtaking HGV travelling at 60mph will pass the trailer (travelling for example at 50mph) at a relative speed of 10mph. A 20ft trailer will therefore be under the influence of the first and most energetic part of the bow wave for approx: 1.6 secs. When one is travelling on an ordinary class A road HGV’s will pass close by going in the opposite direction at a relative speed of 100mph (assuming that both vehicles are moving at 50mph.) I would speculate that in this case the HGV has no unpleasant effects on the trailer because the interval of time that the latter is subject to the worst effect of the bow wave is only approx: 0.15 secs.

(11e)

It is well known that a “blow out” on a car tyre can have a serious destabilising effect on a car, and often leads to an accident. It has therefore been assumed that the same thing applies to trailers. I do not think that this is correct. If a trailer tyre suddenly deflates there will be an increase in friction between wheel and road on that side of the trailer. This will exert a steady force which will cause the trailer to be slightly out of line with the tow car, but the trailer should continue without snaking, at a slightly skewed angle with respect to the tow car. Similarly, the fact that the trailer is slightly lower on one side should not have any effect. It is the tow car that is steering the trailer and the outfit should hold a steady course so that it can be slowed down gradually, only gently applying the brakes for the final halt. I was towing an Ace Pioneer Caravan (about 12 ft long) with a Morris Marina 1800cc at approx: 50mph, on the M5, when I had a “blow out.” I managed to stop in a controlled manner as outlined above. (see photo of van in caravanaccidents2.wordpress.com).

(11f)

You cannot ignore the Laws of Gravity. Whereas you can shut off the power of the car engine simply by taking the pressure off the accelerator pedal, you cannot shut off gravity. It is to remind drivers of this Law of Physics, amongst other things, that the Highways Agency has errected large signs on “fast roads” at the start of steep down gradients stating “TOWING VEHICLES SLOW DOWN”.

The other basic law of Physics which is applicable here is the one that leads to the equation for calculating the amount of energy your outfit has because it is moving (Kinetic Energy).

KE=1/2MV(where V is squared)

M= mass and V= velocity ( for the purposes of this explanation it can be assumed that velocity = speed and mass = weight.)

Even if everyone reading this suddenly has a “flash back” to school Physics, my observations tell me that not many people remember that the effect of the weight of the trailer on the amount of energy is the same at 30mph as at 60mph, but as the speed in the above equation is raised to the power of two (ie squared), an increase of speed from 30 to 60mph (ie x2), will increase the energy by x4 (ie 2 squared).

Also, when going downhill it should be remembered, that not only is it not possible to shut off the force of gravity, but if your caravan starts to snake, as previously explained, you effectively have no brakes if you are relying on an “over-run” brake actuating mechanism and almost no brakes if it does not snake due to overheating as down hill over run brakes will be “on” all the time.

(11g)

The energy required to set off a snake comes from the bow wave of the overtaking vehicle ( assuming the wind is neglible), but once the snake is established it can often increase in size due to another effect. As the trailer is snaking it will be travelling a greater distance than the tow car and will have to move at a higher speed to keep up with the car. This will lead to the tow car exerting a considerable force on the trailer, particularly as it reaches the outer edge of its swing; it is at this point in particular, that the trailer will be increasing its speed and this fact must give rise to the snake increasing in severity.

However, all other cases are likely to be “emergency” stops so these small number of cases are the really vital ones. If you are on only a very slight bend when the brakes are applied there is a probability ( for instance) that your trailer will turn your car round through 180 degrees. The probability of this disaster taking place is low if your speed is low, and vice versa. Also, the probability of disaster is low if your trailer/car weight ratio is 50% ( as is the case if you are towing a small caravan with a heavy 4×4 ), but very high indeed if the previously mentioned ratio is 100%. As can be seen from the diagram (see

) this can happen in two ways; the force of the trailer pushing on the tow car may be insufficient to apply the trailer brakes adequately, but in a situation when the tow car will be close to starting to slide in any case it may only need a slight extra push to send the tow car spinning further out of control. Alternatively, the momentum of the effectively “unbraked” trailer may cause it to jack knife ( ie swing round in an arc with the tow hitch as the centre of the arc.) Again, it is important to study the trailer’s tyre marks The absence of tyre braking marks for the trailer in my view confirms that an “offence” has been committed because the law is that trailers between 750kg and 3500kg must have brakes, and this means that they should work at all times. If a post accident investigation shows that the brakes are in working order the absence of tyre braking marks is strong evidence that all over run brakes are likely to have the same problem and be ineffective in this situation.

The left hand diagram (see

) indicates the condition I found the over run brake mechanism in for my current boat trailer after the Winter of 2003/4. The boat plus trailer had been stored in a line of similar boats, on shingle, above the high water level, well up a sheltered creek, near Falmouth. Something quite big had obviously “bumped” my trailer. It would be a serious and most unusual accident on the road that caused this much damage, but the incident did remind me of the fact that every time a tow car brakes in the situation shown in the right hand diagram mentioned above there will always be a tendency for the mechanism to distort very slightly ( perhaps by such a small amount that the mechanism would recover its original shape), but the slight distortion would ensure that the telescopic item would “stick” and the brakes would not be applied. The size of the effect that either of the above actions will have on the tow car depends on the distance of the car’s rear axle from the tow hitch . The greater this distance the greater will be the leverage on the tow car and the larger will be the probability that the car will be swung round or even turned over.

(See photograph in

)

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An updated copy of my 2005 report to itai.





At the beginning of May 2003 I received a very
valuable item of evidence that an experienced and qualified AI did not wish to have attributed to him. He told me that it represented the typical marks you can expect to see on the road after
a caravan snaking accident. The marks below are the best approximation using a PC.




(

(


If you ignore the full stops, necessary for the Blog software to reproduce this diagram,
it would appear to me that these marks on the road are produced when a trailer is snaking that violently that it is on the point of turning on its side. As the centre of mass of a caravan is quite low (if it is correctly loaded), it will have to lift a very considerable amount before it eventually topples over.

See

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