SOFT NOSE, AARDVARK
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Even the Americans are taking aerodynamics seriously. Kenworth's T600A has a rounded 'soft nose' that has led its manufacturers to nickname it 'the Aardvark' ...
• To European eyes, a vehicle like Kenworth's T600A conventional (ie bonneted) truck is hardly at the forefront of design.
It has, after all, the traditional upright vee windscreen with flat glass, small windows and a cramped driving position in its narrow cab. On its home market in the USA, however, the T600A is a revolutionary vehicle. It is the first Class 8 (80,0001bs or 36.3 tonnes) American vehicle to feature aerodynamics as a major factor in its design.
Recently we were able to sample the T600A in its own environment, on the freeways of Washington State on the west cost of the US — and to compare it with its more traditional sister vehicle, the Kenworth W900.
The T600A is a 6x4 tractive unit available with a variety of power units, mainly from Cummins and Caterpillar, with Fuller gearboxes. If there is a standard on such vehicles, the T600A has a standard wheelbase of 4.064m, large by European standards but very short compared to other American conventionals: the traditional W900 has a standard wheelbase more than 800mm longer, at 4.826m. Much of that is due to the setting back of the front axle, which is 410mm farther back than on the W900.
Our vehicle was fitted with Caterpillar's ATAAC (air-to-air after-cooled) six cylinder engine in 261kW (350hp) form. This drove through a Fuller RT014613RC gearbox, with an unusual block on it limiting use of the splitter to top (eighth) speed only. Drive is then to a pair of Rockwell SQ100 single reduction axles, with a final drive ratio of 3.73:1.
Although some 75% of Kenworth's out put of conventionals is fitted with the company's own air suspension at the rear, this particular vehicle was fitted with the traditional leaf spring suspension. The front axle sits on very long (1.62m) triple-taper-leaf springs, while at the rear the tandem drive bogie sits on four multi-leaf springs.
The cab of the T600A is based on that of earlier designs. It is a hand-laid GRP structure with little steel and aluminium reinforcing: the massive Aerodyne sleeper unit behind is an aluminum structure with a GRP roof.
The bonnet and sharply-tapered front wings are formed as one massive GRP structure, hinged at its forward edge. The wings are faired into the cab step structure behind to further reduce drag, which is claimed to be some 22% less than that of a W900.
The steeply-sloped nose is claimed to move the closest point of visible road in front of the vehicle to 5.18m, from the old 14.94m. The low line means a more compact radiator, that on the T600A being 14% smaller than the W900's at 0.77m2. Underneath this nose the setback front axle with a forward-mounted steering box (instead of the usual box mounted back near the scuttle) combine to give a 30% greater maximum turn angle on the wheels. This is claimed to reduce the turning radius between kerbs from 11.6m to 8.8m.
The first impression on entering the T600A's cab, via wide, staircase-type steps, is the smallness of the driving area, which is dominated by the huge steering wheel and a real organ console of a dashboard. The cab is wide enough only for two air-suspended seats: because of the bonneted layout, there is no engine cover to intrude, and the long gear lever goes straight into the top of the Fuller gearbox.
This example had Kenworth's new electronic dashboard, on which the speedometer and tachometer (no tachograph here) are replaced by superb analogue vacuum-fluorescent displays, backed up in each case by digital readouts in the centre of the instrument. Between these instruments are a bar-graph economy meter and digital readouts for temperature, oil pressure and fuel consumption. Beneath are digital readouts of time and distance, plus the output from the trip computer. Sadly reflections from their glass covers made them hard to read in bright sunlight.
The rest of the (conventional) gauges are spread out across the massive mockwood dashboard along with the switchgear, which is arranged in a much more haphazard form than on European trucks. While direction indicators are on a column stalk, the control for the Jacobs brake, for instance, is a rocker switch on the centre panel. An unusual-acting control in our eyes is that for the pneumatic door windows; the windscreen wipers are also air-operated.
Forward visibility on the T600 is a vast improvement over that on the squarebonneted W900, even though the screens are the same size. The T600 nose drops out of sight, giving a clear view of the road as good as that on a Volvo 'N' or Scania 'T' series — though the angle of vision to the sides and upwards is obviously limited by the small glasses. The dropped nose does, however, mean that the useful aiming point of the dummy radiator cap on the W900 is no longer there, making the T600A more difficult to place on the road. Manoeuvring in tight spaces would be tricky, with no indication of the whereabouts of the rounded front.
Under way, the impression given by the ATAAC Caterpillar even at 261kW is that of lazy, insulated power: very little engine noise intrudes into the plushlylined cab, and somehow the perceived hard-working nature of the average big diesel disappears.
The Fuller box is so much more direct in this layout, and once the driver gets used to the ratios, satisfyingly quiet and quick changes can be made. The pedals are well-spaced and all at the right height for those who prefer to heel-and-toe when slowing a vehicle.
Steering is the key area in which American thinking differs totally from the European: the steering wheel of the T600A is as large as that of the muchmaligned Mercedes-Benz item, but is connected to a much-over-assisted mechanism. The T600 is better than its older sister in this respect, but is still woolly compared with a European vehicle.
The ride on this example, even with its long wheelbase, was much inferior to that of the similarly-laden W900 on air which we tried at the same time — and to that of another T600 which we tried, with air suspension, on the confined roads of Paccar's test track.
The brakes — a far cry from the old unbraked-front-axle layouts of traditional American trucks, worked smoothly and powerfully, The 'Jake brake' on this T600 worked well, even in high gears, where that on the 300kW Caterpillar-powered W900 tried seemed much less effective.
Overall, the T600A is a very impressive machine, more at home on American roads naturally than on European-style roads where its length alone would prevent its use with a decent trailer. It nevertheless shows considerable strides towards a European standard of driveability and efficiency. While in ergonomics it might be well behind, in creature comforts it is well ahead — and while the cab itself may look old-fashined against the modern bonnet, the low wind noise suggests that Kenworth does have a very efficient truck on its books.
By Allan Winn