Weight-saving Atkinson Range
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AN important new range of lightweight four-, sixand eight-wheeled .goods chassis is officially announced today by Atkinson Vehicles, Ltd. Important, because the models in the new range—which are to be known as Weightmasters—are considerably lighter than other maximum-capacity chassis currently being made by this concern, whilst the basic specifications have been kept as simple as possible and have the absolute minimum of optional variations.
The range consists of eight basic models—one eightwheeler, two six-wheelers and five four-wheelers—and the fourand six-wheelers are offered with either the Gardner 5LW or Perkins 6.354 diesel engines; the Gardner 6LW is standard in the eight-wheeler and available in the fourwheeled tractive unit to enable it to operate at 24 tons gross train weight (with either of the other engines the tractive Unit is limited to 20 tons gross).
As low chassis weight is one of the prime advantages of the new models, it is interesting to compare the weights of these with typical " heavy-duty" Atkinsons of the old school. For example, the chassis-cab weight of the 24-ton-gross eightwheeled Weightmaster is 5 tons 15 cwt,, whereas the weight of the lightest eight-wheeler of the same wheelbase previously built is 6 tons 8.5 cwt. (chassis only), an LX-engined doubledrive chassis weighing 6 tons 14.75 cwt.
Considering the smaller chassis, a Weightmaster 14-ton-gross four-wheeler with a wheelbase of 16 ft. 0.5 in. weighs 4 tons 4.25 cwt. in chassis-cab form, whilst the original L945L chassis alone turns the scale at 4 tons 5.75 cwt. Taking the sixwheelers, an M1366 weighs 5 tons 18.25 cwt. as a bare chassis, whereas the Weightmaster WM6S(E) has a dry chassis-cab weight of 4 tons 14.5 cwt.
Where has all this weight been saved? In the case of the sixand eight-wheelers, compared with the heavy-duty models much of the weight has been pared off the rear bogie: the total rear-bogie weight of a Weightmaster is 8 cwt. 1 qr. 12 M. (less axles), compared with 11 cwt. 2 qr. 27 lb. for the standard Atkinson eight-Wheeler and 9 cwt. 1 Qt. 2 lb. for a vehicle with Hendrickson suspension. Some of this weight has been saved on the springs themselves, but much of the reduction has been made possible by the use of a lighter balance-beam assembly, and shorter and lighter spring-hangar brackets, the Weightmasters having outrigged rear springs instead of the underslung springs of the heavy models. The spring-centres dimensions of the two vehicles do not differ greatly. however,
(22 partly because the Weightmasters have 36-in.-wide frames, cc pared with the 38-in, frames of the other models.
. Spring weight has been saved by using 2.5-in.-wide springs the front axles throughout the new range and 3-in.-wide spril at the rear axles—the heavier models have 3.5-in.-wide sprit all round—whilst further weight at the rear has been saved the use of an Eaton 18802 two-speed axle (3 cwt. lighter 1.1 the double-reduction type offered in the heavies) and a Rub Owen trailing axle, which is 1.5 cwt. lighter than that of sins drive heavy chassis. .
Although Girling cam brakes are employed instead Kirkstall equipment, 'there is virtually no difference betwf the weights of the two different types, but braking-system wei generally has been reduced by the use of lighter-section hal brake cross-tubes, and so forth. Similarly, a certain amount steering weight has been saved by using 1.375-in. bail-join linkages in place of the 1.625-in. equipment. Hardy Spi 1600-series propeller shafts are used.
. Frame weights have, as might be expected, been cut ei siderably, although no comparative figures are available. 1 Weightmaster eight-wheeler has 9.25 x 3 in. x 0.375 in. s members, compared with the standard chassis' 11 in. x 3 in 0,375 members, or the optional 10.875 in. x 3 in. x 0.31 members (the Weightmaster has thicker imit shallower s members than the optional heavy-duty frame to give increa! rigidity).
The Weightmaster six-wheeler has 9 in. x 3 in. x 0.25 members, the same section being used for the two 101 wheelbase four-wheelers: the equivalent heavy-duty models IN 9.25 in. x 3 in. x 0,375 in. frames. The four-wheelers intent for tipper applications have 9.125 in. x 3 in. x 0.125 in. fran arid the tractive unit has Sin. x 3 in. x 0.25 in. members: 8.25 x 3 in. x 0.375 in. frames are employed on the heavy mock En all cases the frames are bolted, but -instead of chann section cross-members being used throughout, sonic tubu members have been introduced at the rear of the frames.
Compared with heavy chassis powered by Gardner 61 engines, 2.25 cwt. has been saved by fitting the smaller 61 engine as standard in the eight-wheeler, and there are p portional savings in engine weight throughout the Weightmas range—even 28 lb. has been. saved by fitting a 32-gal. fi tank on the eight-wheeler in place of the 54-gal. unit of .heavier chassis—whilst a valuable 1 cwt. has been knocked.. the weight of the cooling system by using' a Morris-block ty of radiator in place of the normal Atkinson detachable-41 unit, and a very effective moUlded-plasties radiator-cc
ound (painted to look like polished aluminium and deceptive t at close range) in place of the traditional cast-aluminium mind.
he same plastics-panelled, timber-framed cab as is used on heavy models has been adopted for the Weightmasters, so e is no weight saving here, but a slightly lighter though e expensive light-alloy cab can be fitted if the very last x of weight must be saved.
ealing specifically with the individual models in the new ge, the two normal load-cariying four-wheelers are the .45(E) 13-ft. 5.75-in.-wheelbase and the WL.45L(E) 16-ft. in.-wheelbase versions. The tipper chassis are the WS.45(E), a wheelbase of 10 ft. 8 in,, and the WM.45(E), which has heelbase of 12 ft. 4.75 in. The basic specifications of these models are virtually identical, and include the Gardner
✓ five-cylinder diesel engine (94 b.h.p. at 1,700 r.p.m. and lb.-ft. torque at 1,300 r.p.m.), with the option of the Perkins 4 six-cylinder direct-injection engine (112 b.h.p. at 2,800
m. and 260 lb.-ft. torque at 1,450 r.p.m.). The standard gear: is the David Brown 550 five-speed constant-mesh unit, h forward ratios of 7.81, 4.86, 2.76, 1.596 and Ito 1, reverse ng 8.03 to 1, and the standard rear axle is the Eaton 18802 .-speed unit with ratios of 5.14 and 7.02 to 1-this axle . the same set of ratios are standard throughout the range. Vith the standard 10.00-20 (14-ply) tyres, these ratios give 5LW chassis a maximum speed of 38 m.p.h. in high ratio I a maximum grade ability of 1 in 3.8 in low ratio: with Perkins engine axle ratios of 6.5 and 8.87 to 1 are standard. I the maximum speed becomes approximately 46 m.p.h. (at ,erned speed), whilst the maximum gradient ability would be the region of 1 in 3. Additional optional ratios are 5.57
1 7.6 to 1, and 4.5 and 6.14 to 1.
Chroughout the complete range the standard front brakes Girling 15,5 in. x 4.25 in. cam-operated unit, whilst the rears )f the same make and type-have dimensions of 15.5 in. x in. These give respective frontand rear-axle lining areas 256 sq. in. and 422 sq. in. respectively, so the four-wheelers .re a total lining area of 678 sq. in. Brakes are air-pressure !.rated, and the handbrake lever is of the usual Atkinson Iti-pull type. The same front springs are employed throughthe Weightmaster range also, and these are 42-in, long.
e four-wheelers have 48-in.-long rear springs, whilst the ings of the sixand eight-wheelers are 44-in. long. Manes n and double roller steering is employed.
-Istimated chassis-cab weights of these four-wheelers are as lows: WL.45(E), 4 tons 3.5 cwt.; WL.45L(E), 4 tons 4.25 cwt.; >.45(E), 4 tons 2.5 cwt.; and WM.45(E), 4 tons 3.25 cwt.
[he tractive-unit four-wheeler has two gross-train-weight ings: with either of the two units fitted in the standard foureelers the gross weight is 20 tons, but with the Gardner 6LW 2 b.h.p. at 1,700 r.p.m. and 358 lb.-ft. torque at 1,300 r.p.m.) : rating is increased to 24 tons. This model-type WT.45(E) has a dry chassis-cab weight of 3 tons 17 cwt. in standard an and its wheelbase is 8 ft. 9 in. When the Gardner 6LW gine is installed, David Brown 557/480 or 657 gearboxes are fitted, and the standard tyres in all cases are 9.0020 (12-ply).
Both the Weightmaster six-wheelers are restricted by Atkinsons to a gross weight. of 18 tons. The two models are the WM.65(E)-wheelbase, 15 ft. 1.5 in.-and the WL.65(E), the wheelbase of which is 36 ft. The quoted dry chassis-cab weights are 4 tons 14.5 cwt. and 4-tons 16 cwt. respectively. As with the four-wheelers, the Gardner 5LW is the standard unit in both these vehicles, but the 61_,W and the Perkins 6.354 are offered as optional equipment. With the 5LW and the Perkins engine the David Brown 550 gearbox is standard, but the David Brown 557/480 box is fitted with the 6LW.
Similarly, the standard Eaton axle has the normal ratios of 5.14 and 7.02 to 1, but with the Perkins engine ratios of 6.5 and 8.87 to 1 are employed, optional sets of ratios being as already detailed. Because 9.00-20 (12-ply) tyres are used on the bogie wheels, the maximum speed of the six-wheeled Weightmaster is just over 1 m.p.h. lower than that of the fourwheelers, whilst the higher gross weight results in a slightly reduced maximum gradient performance, though not to any greatly significant degree. The standard front tyres are 9.00-20 (14-ply).
Whereas the four-wheeled Weightmasters have air-pressure brakes, the six-wheelers have a vacuum-hydraulic system, although the same brake units are used, giving a total frictional area of 1,100 sq. in. The brakes are actuated by Lockheed hydraulic cylinders, and boost is given by a Lockheed 9.5-in.diameter tandem suspended-vacuum servo. Full air-pressure braking is, however, offered as an alternative.
The new eight-wheeler, a road-test report of which appears on pages 916-919 of this issue, has the Gardner 6LW without option, whilst the standard gearbox is the David Brown 557/480 constant-mesh unit with forward ratios of 7.95, 4.7, 2.78, 1.56 and 1 to I, reverse ratio being 7.95 to I. This gearing gives a maximum governed speed of 38 m.p.h. and a maximum gradient ability of 1 in 5.5 when the standard 9.00-20 (12-ply) tyres are fitted: 9.00-20 (14-ply) tyres can be specified at no extra cost, although these raise the unladen weight by at least 50 lb.
The eight-wheeler is offered with one wheelbase only-17 ft. 8.25 in.-and its chassis-cab dry weight is 5 tons 15 cwt. As with the six-wheeler, vacuum hydraulic braking is employed, with the option of air-pressure actuation, and because only the first, third and fourth axles are braked, the lining area is the same as that of the six-wheeler-----1,l00 sq. in.
In addition to the plastics-panelled de luxe cab (which weighs 5.75 cwt.), other standard equipment throughout the Atkinson Weightmaster range includes a chromium-plated front bumper bar, flashing direction indicators, cab heater and demister and a quilted engine-cowl cover. The electrical system is 12 v., double pole, and the batteries arc stowed outside the cab, except on tanker chassis. Optional equipment offered includes a gearbox power take-off and a front towing member.
The seven load-carrying chassis are suitable for the following lengths of body: WS.45(E). 11 ft.; WM.45(E), 12 ft. 6 in.; WL.45(E), 17 ft. 6 in.; WL.45L(E), 20 ft.; WM.65(E), 18 ft. 3 in.; WL.65(E), 22 ft.; and the WL.86(E), 24 ft.