Norbert puts double-deck longer semi to the test
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By Hayley Pink FOLLOWING DELIVERY OF its irst 15.65m longer semi-trailer, Norbert Dentressangle (ND) put the double-decker through a challenging trial at Millbrook Proving Ground to ensure its roll stability safety.
The trailer forms part of the irm’s 131-unit order for longer semis – the biggest allocation issued by the Department for Transport (DfT) under its 10-year trial – of which 67 are the longer 15.65m version and 64 are the 14.6m type.
ND head of UK leet John Matthews says: “The longer unit provides scope for increasing volumes. But irst the trials will provide a clearer picture of the beneits and possible limitations.” The objective of the tests, conducted by Mira, was to conirm that the roll stability of the 15.65m trailer, itted with a ratchet second deck system, was within the safe limit of existing 13.6m trailers with high centre of gravity loads.
The trailer was a triaxle unit itted with a rear steering axle but, to comply with European Commission turning circle regulations, the axle coniguration was not an even spread: the steer axle was set at greater spread than the front two axles. For the test, the ratchet deck was lifted to its highest position – 2.1m from the top of the main deck, or 3.5m from the ground. The top deck was loaded to its maximum capacity of 10,000kg and the bottom deck to 16,000kg, giving a 44,000kg GCW (45,800kg with Mira equipment itted).
Two tests were carried out to establish the semitrailer’s roll stability: a steady state circular test and the roundabout test. The irst was designed to deine the roll stability and limiting conditions of articulated vehicles. It involved driving around a 33m radius clockwise and anti-clockwise, gradually increasing speed until a ‘limiting’ condition was reached. These included trailer wheel lift, signiicant payload movement, electronic stability control (ESC) cut-in, tractor traction loss or tractor reaching the limit of its available power.
ND says there is no legal requirement for the limits of roll stability, however, vehicles with a high centre of gravity and effective payload restraint system typically achieve lateral acceleration levels of 0.31g, compared with vehicles with low centres of gravity that can achieve levels as high as 0.44g.
The roundabout test was conducted to conirm roll stability in transient manoeuvres. It was carried out on a simulated roundabout with crossroads, commonly found on A roads. ND says the results indicated that neither the vehicle nor the trailer displayed any unstable characteristics during the tests and the combination acted in a stable manner with the intervention of the ESC. Both sets of results showed roll stability is well above the levels typically achieved for standard trailers with high centres of gravity.
The longer semi’s driver reported that he felt in control of the vehicle at all times, ND adds. ■
Steady circular test Lateral acceleration 0.37g Maximum roll angle 3.5 degrees Maximum speed 35km/h Limiting condition ESC cut in reducing speed Roundabout test Lateral acceleration 0.35g Maximum roll angle 2.8 degrees Maximum speed 34km/h Limiting condition ESC cut in reducing speed