Bath University Report (cont)

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(extracts)

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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.

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………………………….), 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

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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.

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Peter W Jones MInstP

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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.

 

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