Stabilisers; Bath University

March 22, 2008

killer-photo-alko-stab.jpg

Advertisements

March 21, 2008
Peter W Jones MInstP
.
Copied from the internet

 

 

 

University of Bath 

 

 

School of Mechanical Engineering 

 

 

THE DYNAMICS OF TOWEDVEHICLES

 

 

 

An experimental study into caravan snakingFinal year project

submitted by Christopher J Killer

for the degree of MEng

of the University of Bath

23 May 2003

Assessor RFN

Supervisor JD

Technician PC

 

 

 

*******************************************************************11 Conclusion

 

 

 

********************************************************************************************The performance of the Alko 2004 tow ball friction damper has been shown to be

very effective at smoothing down snaking oscillations and reducing settling time. But this does not necessarily mean that it makes the coupled combination any safer, i.e. increase the snaking speed. Theory states that this type of damping has little effect on the snaking speed, and tests have shown no evidence to suggest otherwise.

********************************************************************************************

 

 

 

11.1 Practical advice for caravan owners & designers 

 

 

Nothing fundamentally new was discovered in this study, but theoretical factorssuggested in the past have been substantiated by road-tested evidence. The

theoretical advice that is now known to be significant in increasing stability includes

the following points.

For owners:

 

 

 

Make sure car is suitable for the size of caravan 

 

 

Load heaviest items in the car if possible 

 

 

Locate other heavy items in the centre of the caravan, just forward of its axle 

 

 

Make sure tow ball load is adequately high 

 

 

Avoid sharp steer inputs at high speed 

 

 

Never exceed 60mph

for designers: 

 

 

Put the heaviest parts of the caravan, e.g. kitchen, in the centre 

 

 

Consider the distance h between the C.G. and the axle, and its significance in

terms of stability 

 

 

Calculate the new stability coefficient (incorporating h) for each design

and although not tested in this study, other recommendations from mathematicalanalysis include:

 

 

 

Make distance from tow hook to axle as long as possible 

 

 

Move back the C.G. so as not to induce excessive tow ball load 

 

 

Maintain a high tyre pressure to keep lateral stiffness high 

 

 

March 21, 2008

Bath University Report (cont)

.

(extracts)

.

9.5 The effect of using the stabiliser………….., small amplitude oscillations are attenuated considerably more than large ones. Theory also predicted that the frequency of oscillation would decrease when the damper was present, the graph does show this to a very small degree, though frequency was essentially unaffected.

.

………………………….), therefore if the initial one is too large for the friction damper to have any significant effect, thensubsequent oscillations will not decrease in amplitude and the system will become Unstable

Figure 23: Effect of stabiliser shown in blue

.

THE ABOVE  GRAPH HAS NOT APPEARED. IT CAN BE SEEN ON THE BATH UNIVERSITY WEB SITE AND IS NOW ALSO SHOWN AT THE START OF THIS BLOG.

..

Peter W Jones MInstP

.

I have selected the above items from Mr Killers’ work, but as this is displayed on the web it is very easy for interested parties to view the whole document. Mr Killer has made it clear in another section of his report that excessive load on the tow ball can lead to steering deficiencies in the tow car; this is not quite clear from the conclusions.In my view Mr Killer should not, on the basis of his results, suggest never exceeding 60mph. All his results were in the range 30 to 50 mph so it is only justifiable to say that the ALKO stabiliser does not necessarily make the car/caravan combination safer within the speed range 30 to 50 mph.

Standen (Towed Vehicle Aerodynamics 1999) showed in his wind tunnel tests that aerofoils increased caravan stability; my extensive experience towing on the road leads me to believe that aerodynamic lift is a factor over about 50 mph (air speed) and any future studies should investigate this matter in particular. I only have one vote in the caravan club, but I hope that other members will   ensure that the research at Bath University continues and that the results appear on the internet without editing.

I do not agree that sharp steering inputs ( when towing) should only be avoided at high speed. Such in puts are potentially dangerous from about 40mph. However, sharp steering inputs only have a minor effect on caravan/trailer snaking compared with the effect of side winds or the effects of Large High Aspect Vehicles (Standen 1999). When concluding that the ALKO Stabiliser did not necessarily improve safety Mr Killer did not consider the last two factors. The condemnation should have been much stronger.

My conclusion is that on the basis of Fratilla 1994, Killer 2003 and my further analysis of the ALKO stabiliser below, any friction based stabiliser failing the simple test I have outlined also below should only be sold in the UK with a clear “large type” summary of the Fratilla and Killer conclusions.

This action would encourage the caravan/trailer industries to seriously consider using the electric brakes which have been in use elsewhere for over thirty years and are cheaper than over run brakes plus stabiliser. Pneumatic and hydraulic brakes are also feasible; an example of the former was successfully tested for over 12 months by a journalist from Practical Caravan Magazine. Furthermore enterprising companies would develop aerofoils following the public attention given to friction based stabilisers, and HGV trailer manufacturers would also have to consider aerofoils as well as electronic brakes to improve safety.

 

March 20, 2008

Para 37

 

Peter W Jones MInstP.

Photograph of Stabiliser and Tow Ball

Below is a photograph of the  same stabiliser that I published on >

.. 

March 9th.

.. 

This time I have removed the tow ball cover so that the size of the

.. 

 tow ball relative to the circular part of the stabiliser can be

. 

.seen.The tow ball is a standard 50mm in diameter.

Inside the circular part of the stabiliser are TWO friction pads of
100mm diameter, with a circular space in the centre of 50mm

diameter where there is no friction material.

Readers who have remembered their GCSE Maths will be able to calculate the area of the friction material available in my now obsolete Scott stabiliser ( but similar stabilisers are still on sale) and compare that with the area of friction material available inside the ALKO stabiliser which is still on sale as a “retro fit” and as a standard item on most of the used caravans in dealers’ show spaces.

However, do not give up if you lack a GCSE Maths textbook because the difference in size between the area of friction available with the Scott Stabiliser and the ALKO stabiliser is so great that it is apparent from my photograph below and it is hardly worth doing the calculations.

For readers who are not familiar with ALKO stabilisers I must point out that this device uses friction between a tow ball free from grease and a “cup like” device which fits over the tow ball.

The force of friction generated by your cars’ brakes is not only in direct proportion to the area of your discs (on the brakes), but in direct proportion to the force applied to the brake pedal (this is of course not quite true if you have abs or a similar electronic system.)

My Scott stabiliser has a nut which can clearly be seen in the photograph and this is used to take up wear and keep the correct force on the friction plates. To the best of my knowledge the only way that owners of the ALKO friction based stabiliser can allow for wear on the friction pads is to replace them.

If ALKO engineers had viewed the matter in the above light they would not have made this type of stabiliser as it is clearly inferior to the type it has now managed to almost completely replace. I would give the ALKO device full marks for smartness of design and appearance, but very low marks for effectiveness in reducing snaking of trailers/caravans with over run brakes.

Details of my test for friction based stabilisers are in

www.20six.co.uk/roadtrafficaccidents Section 18a.They are also further on in this blog (or in the archives). The duplication is due to the fact that 20six.co.uk seems to be “off line” a great deal of late.

 

 

March 20, 2008

stabiliser-tow-bal-001.jpg

Letter to the Hon Mrs Dunwoody MP

March 11, 2008

Para 38

Dear Mrs Dunwoody,

Thank you for your prompt reply to my e mail.

I am publishing your reply in www.caravanaccidents3.wordpress.com
together with my e mail to Tony Wright MP
and my reply to yourself.

_________________________________________________________________________________________

The following is a reply to my e mail concerning the recent closure of
the West Coast Main Railway line due to Containers weighing up to 4
tonnes being blown off a freight train.
This reveals the fact that Network Rail, like the Highways Agency, do
not accurately monitor wind speeds.
Railways have always had strict regulations concerning the max safe
speed for particular stretches of track, but they seem to think that
all their tracks are safe at any wind speed.

I also mentioned in my e mail that I wished to complain about the conduct of a Senior Engineer at the DfT (Trading Standards) who did not adequately advise Birmingham Trading Standards when they asked for advice in 2006 concerning my test for caravan stabilisers.

——————————————————————————————————————————————

I HAVE DELETED MY HOME ADDRESS FROM THE FOLLOWING LETTER, BUT
OTHERWISE IT IS AS I RECEIVED IT.
THE ERRORS IN THE LETTER ARE DISTORTIONS PRODUCED BY MY SCANNER,
PARTICULARLY THE FACT THAT MRS DUNWOODY’S SIGNATURE HAS BEEN
ERRADICATED.

———————————————————————————————————————————————–

MRS GWYNETH DUNWOODY MP.

HOUSE OF COMMONS
LONDON SW1A OAA
Tel: 020 7219 3490 Fax: 020 7219 6046

Peter Jones, Esq
4th March 2008
Dear Mr Jones
Thank you for your email of 3rd March 2008. I am grateful to you for
keeping me up to date, but as I was caught up in the problems over
the
weekend, I am only too aware of the
situation.
I understand your worries about the evidence that was presented and
we
do, of course, try to get as broad a cross section as possible to
give
us accurate information.
At the moment, we are not looking at the caravan/trailer points that
you raise and I am afraid that we do not have sufficient trained
staff
which would enable us to undertake the sort of inquiries that would
be
of interest to you.
I have, however, noted your views and will make sure that we keep
them
on file for the next time we meet the Secretary of State and the
Permanent Secretary to discuss them.

Yours sincere!

hon. mrs GwVNETH dunwoody MP
www.gwyneMi dunwoody.co.uk
Constituency Office: Tel. 01270 589132 Fax. 01270 589135

——————————————————————————————————————————————-

From Peter W Jones
Retired Head of Science in a Birmingham Comprehensive School.

I hope that Mrs Dunwoody means that she will not only be pressing for
monitoring of wind speeds on our main roads and railways, but will be
seeking an investigation in to the conduct of the Senior Engineer at
the DfT that I drew attention to.

I thought that civil servants at the DfT had a duty to provide
advice
and support when asked for same by colleagues in Birmingham.
I retired before OFSTED came into being, but if any one senior to
myself thought that I was not performing my duties satisfactorily I
would expect to see an HMI at the back of my laboratory observing how
I conducted myself when teaching a class of 16 year olds ( for
instance). I think some thing similar should apply at the DfT to
Professional Engineers.

My stabiliser test
( see www.20six.co.uk/roadtrafficaccidents Section 18a and
www.caravanaccidents3.wordpress.com)
is quite simple (in the Physics world), and it only
supports the results on caravan stabilisers produced by Bath
University
Department of Mechanical Engineering in 1994. (see a small section
of
Fratilla’s Phd Thesis ).
Exact quotes in section 2e of www.caravanaccidents2.wordpress.com

When the Caravan Club received this thesis in 1994 I think they
should have pressed for the banning of these stabilisers. In other parts of
the world electric brakes were in use and they are far more effective
as caravan/trailer stabilisers. If the Caravan Industry felt that
EU/UK
regulations on caravan/trailer brakes were unduly restrictive they
should have urged the authoriites to change the wording of the
regulations.

__________________________________________________

Para 39 PHOTOGRAPH OF A STABILISER

March 9, 2008

stabiliser-and-old-trailer-001.jpg

Information Concerning Stabilisers for those reading this blog

with no experience of caravanning or trailer towing. 

This stabiliser is several years old, but it still meets the specifications prescribed for a new item.

Similar items of the same type are still on sale in large caravan dealer’s show rooms, but under a different brand name.

The rather grubby spherical item of maroon colour is the cover over the tow ball. I keep the latter well greased.

The approximately circular item to the right of the tow ball contains the friction pads held between plates of metal.

The nut in the centre of the circular item can be tightened or slackened in order to obtain the prescribed amount of friction.

To measure the friction  place a set of accurate bathroom scales against the right hand end of the lever and apply pressure. The reading should be taken just as the stabiliser arm begins to move.

The amount of frictional force is laid down by the manufacturers, but according to the caravan club’s advice section for members it is almost exactly the same for all types. In my view the limiting factor is the amount of torque the towing bracket of the tow car will stand.

The caravan club did not give the specified torque for the ALKO stabiliser, presumably because it can not be adjusted

In use on the road the right hand end of the  stabiliser arm ( as shown in the photograph above) fits into a plastic mounting on the front of the caravan chassis, so that if the caravan oscillates from side to side  ( snakes) when being towed the friction between the sections of the circular part of the stabiliser should dampen down the oscillations.

For details of how to test whether the stabiliser is likely to be of any use on the road go to  section  18a by scrolling to the end of this blog and then clicking on “Older Entries,”  and scrolling further.

To read the 1994 Bath University result on Stabilisers

 go to section 2e

www.caravanaccidents2.wordpress.com

The 2003 Bath University report on stabilisers supports the 1994 result.

I shall add further comments on this within the next few days.

Para 40 The IVRA conversion for O/R Brakes

February 28, 2008

ivra-brochure.jpg

Peter W Jones AMInstP

I would like to draw attention to the efforts of Charles Irving of Preston Lancs who has for  over 30 years endeavoured to improve caravan stability, but in the past has  mainly been  side lined by the Caravan Industry.

The IVRA system depicted in this brochure was tested and approved by the Caravan Club’s experts whose account was published on page 80 of the July 2000 Caravan Club Magaazine. It can just be seen that Charles Irving is named at the end of the brochure and the IVRA system had been developed from Charles Irving’s original design.

In spite of this approval the Managing Director of a  Caravan Group told a large meeting of Caravan Club members (Thistle Hotel, East Midlands Air Port) in February 2004 that he had never been so frightened in his life as when he was given one of these systems to test on the motor way.

However, he failed to tell the meeting whether the person who fitted the system had been trained for this new type of work and whether he himself had been advised by an expert of the different nature of the response compared with over run brakes. The CC, CCC, and the NCC control the quality of the work in a large number of the Caravan Workshops in the UK and training in electrical/electronic braking systems will only be given when the former give approval.

Further on is a Short History of the New ALKO braking system; this short item is an introducton.

Para 40 IVRA Conversion Kit

February 28, 2008

ivra-brochure-2.jpg

February 28, 2008

ivra-brochur-3.jpg

Para 41

 

A Short History of the New ALKO Brakes

 

Peter W Jones AMInstP

 

The above type of system was “invented” by Charles Irving of Preston, Lancs, about 30 years ago.

Charles Irving was first brought to my attention in 2003 by several members of the Institute of Traffic Accident Investigators (ITAI) communicating via a private e mail system.
I had circulated an out line proposal for an electric/electronic device to make over run brakes safer. I was immediately told that Charles Irving had already demonstrated his similar device at an ITAI conference some years previously. ITAI members had been very impressed. I spoke at length by telephone to Charles Irving in 2003; in April 2007, after I had published my results on the web, we had a further telephone conversation and decided to meet at Keele Services on the M6 to discuss this and other matters in more detail.
Charles Irving’s electronic device was later developed and marketed by www.ivra.nl and it was under this label that the Caravan Club’s experts tested same and published their approval in the CC magazine some considerable time ago. IVRA have now been taken over by Reich Benelux.Charles Irving told me that he had also “invented” another system for making caravans and small trailers safer, and this system had been tried out very successfully for 12 months by a journalist working for Practical Caravan Magazine. (Charles Irving later sent me all the technical details by post). This ingenious device was pneumatic, the air pressure needed to operate the system being produced by an electric pump, and being electric the system could apply the brakes as soon as the tow car driver operated the brake pedal. (Over run brakes only work when and if the trailer catches up with the tow car. When a trailer is snaking this will never happen as the trailer is travelling further then the tow car. Drivers are advised not to brake whilst snaking is taking place, because the trailer would then very rapidly catch up and if it was not in line with the tow car when the trailer eventually “pushed” on the brake lever the whole out fit could be spun round out of control.)

I understand that ALKO are only fitting their device to new caravans. Charles Irving had been fitting his invention to existing caravans for some years.
If “electric brakes” is put into the Google search engine it will take only a few minutes to establish that ALKO Australia has caravan electric brakes available for caravans of comparable size to those in the UK. When some years ago a Caravan Club member wrote to the CC magazine to inform us about the extensive use of electric brakes “down under,” the editor informed the members that the Australian brakes were only suitable for larger vans and were very expensive.
If the results from Google are examined a little further it will be seen that currently in the USA caravan electric brakes are being sold that would cost less than the over run system plus the ALKO friction based stabiliser ( at current rates of exchange).
Clearly part of the solution to caravan and trailer instability is electric brakes for new caravans, not an electric/electronic adaptation of the 1929 over run brake. ALKO’s latest device must be fitted to existing caravans and trailers.

Caravanners and trailer towers will have to drive more slowly to remain safer until this business is resolved and in this respect it should be remembered that the legal speed limit was 50 mph when I started towing boats in 1976 ( my boat towing light board still has a “50” sticker on same). It can be seen from my other reports on the web that this matter is far more complicated than originally realised; it is air speed which should really be considered.