Scammell's role in drops and clots
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TWO vehicles, a 6 x 6 and 8 x 6, form the basis of a total transport system to supply forward areas with military stores of all kinds, but particularly ammunition, in the event of war, have been developed by Scammell for Britain's Ministry of Defence.
Prototypes will be on show at the British Army Equipment Exhibition at Aldershot from tomorrow, June 17 to 19.
The heart of the system, called the Demountable Rack Offloading and Pick-up System (DROPS for short) is the rack, a 20ft long, x Rft wide, completely flat load stillage with A frame at the front and ISO corner castings so that it can be mounted and locked on a rail wagon or conventional container carrying road goods chassis.
DROPS is only part of the total system, however, and there are other concepts which dovetail into it, notably CLOTS, which stands for Container Loading and Offloading Transfer System. There is other jargon like PLS, or Pallet Loading System, and ULC or Unit Load Container to describe the transport equipment connected with it.
There are two chassis manufacturers involved in the exercise, Foden and Scammell Motors. The body lifting equipment manufacturers are Multilift and Powell Duffryn, and Marshalls comes in as the maker of flat racks as does Multilift.
The Scammells are designed to operate with these bodies, without use of stabilisers, to give a 35 second loading cycle, speed being of the essence in forward areas.
There are container corner castings on the racks to permit storage on rail wagons. These are positioned below the normal level so as to reduce height and thus centre of gravity when mounted on a road vehicle. Should there be problems of onand off-loading wagons what is termed a simplied CLOTS system, which incorporates a side-loading facility, is offered as a back-up.
Scammell developed the two prototype chassis for DROPS following feasibility studies which started in July 1982.
The vehicles are built to meet Ministry of Defence requirements for a 6 x 6 Improved Medium Mobility Load Carrier (IMMLC) and an 8 x 6 Medium Mobility Load Carrier (MMLC). Scammell considered the following factors in obtaining maximum mobility; power-toweight ratios; ground clearance; tyre clearance; tyre ground pressures; tilt table and angle; cross articulation and turning circles.
The difference between the two designs is that the construction of the 6 x 6 is such that it needs special permission to run on public roads. It does not comply in every respect with the Motor Vehicles (Construction and Use) Regulation. The reason is that it is 2.9m (Rft 6in) wide, largely because of the need to fit the 24.00 x 20.5 tyres needed for stability and over-the-ground performance.
Because the 8 x 6 had eight wheels and because of the lower mobility level the vehicle complies with the legal width requirement of 2.5m. Scammell considered it important that as the 8 x 6 represented the bulk of the DROPS vehicles, and as their peace-time role would be mainly on-road, they should conform with C & U Regulations.
Tests with a loaded Scammell oilfield truck suggested that the biggest problem with the 6 x 6 might be side stability. Reducing the centre of gravity of the vehicle was therefore the main objective in evolving the chassis; a low frame height being a critical design aim as were low engine and cab height. Accordingly a special front axle was designed with a well-offset axle bowl. This, along with a chamfered sump, permitted the engine (and cab) to be mounted much lower than in a normal 6 x 6 design.
Scammell decided on a forward control configuration rather than a bonneted one so as to achieve good weight distribution to the front axle and keep overall length to a minimum.
The cab fitted is the sleeper version of the C40 so as to provide plenty of room for equipment and occasional use by additional personnel. Driver position in the forward control design permits better forward visibility than bonneted models, says Scammell, especially when reaching the top of a rise.
The all-steel frame has parallel side members to improve turning circle, side member and flitch being identical in size and thickness to that of the Construc tor 2, 8 x 4 chassis. The DROPS frames have an extended flitch in the cab area to allow for the extra bending moment if bogie blocking is not used.
With the 8 x 6, studies showed that optimum performance over the ground was achieved with the second steer axle lightly loaded. "For obstacle crossing," Scammell adds, "it was essential that the front axle was driven and this provided the best propshaft layout."
The Rolls-Royce Eagle 350 bhp turbocharged and charge-cooled engine is fitted in these vehicles although equivalent Cummins and Gardner engines are regarded as possible choices.
The gearbox is the five-speed Allison HT 750 fully automatic, while hub reduction axles were chosen to provide good ground clearance. Kirkstall was selected as the axle supplier because of its in-service experience with the MoD. Also Kirkstall was willing to develop the offset bowl drivesteer which Scammell felt was critical to the design. Accordingly, the front axle is a Kirkstall SD66 Special and the rear axle a Kirkstall D66 Tandem with a 6.89 ratio for the 6 x Band 5.36 for the 8 x 6.
Suspension in both instances uses Scammell's own taperleaf springs. The reason for their selection is the weight saving in comparison with multileafs. They are conventionally mounted; slipper/shackle at the front and trunnion at the rear.
Scammell points out that the springs of the second axle, whilst stressed to allow the whole front end to be carried on this axle, alone if necessary, are offset upwards to limit the normal load on the axle,to 5 tonnes. This gives a front axle load of 7 tonnes, the optimum, according to Scammell, for normal mobil
ity incl le crossing.