Some stability and control problems with trailed farm tankers on slopes

Abstract

Trailed farm tankers in Britain, which are generally used either for slurry spreading or crop spraying, have become very large in recent years. The fluid contents, which may be three times as heavy as the towing tractor, will move under gravity inside a partly full tanker and this introduces problems while driving on slopes, which have not been recognised previously. The fluid movement will affect both the stability of the tanker and the control of the tractor and trailer combination. Recent accidents where tankers overturned due to loss of stability, and where tractor and trailer combinations slid downhill due to loss of control, led to extensive research on tankers. In this paper, the centre of gravity analysis of fluid in tanks and the stability analysis of tankers are both reviewed, a full treatment being given elsewhere. The control analysis of tractor and trailer combinations is presented, and this is followed by a discussion of the problems facing tractor drivers with trailed tankers. Tankers behave unpredictably because the characteristics change continuously while the contents are emptied, for example during slurry spreading. The most dangerous condition for working on slopes may be when the tanker is nearly empty, unlike other trailers which are normally safe when nearly empty.