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Chase that blaze into rough terrain
Page 75
Page 76
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HIGHER landing speeds, larger aircraft with more passengers aboard and a general increase in aircraft movements have produced an increasing worldwide demand for rapid intervention crash tenders to deal with possible airport emergencies.
These vehicles must be able to reach a crashed aircraft quickly and discharge foam over it before both plane and passengers are consumed by the almost inevitable fire. They must also have the ability to follow a crashing airplane off the tarmac runway and across rough terrain. For this reason the tenders are built with allwheel drive and a high ground clearance.
Just recently, Shelvoke and
Drewry's special-purpose vehicle division has introduced a new chassis suitable for this type of operation. The chassis, which has a gross weight of 27 tons is of 4x4 configuration and CM had the opportunity to put it
through its paces at an airfield in Hertfordshire and at a military proving ground in Surrey.
Performance
The S & D was fitted with a temporary cab, with centre steering, and was powered by a rear-mounted Detroit 8V92T turbocharged V8 diesel driving a transfer box via an Allison HT 750 five-speed automatic transmission. This set-up gave the vehicle a lively performance, even loaded to its maximum gvw, with 50mph obtainable from rest in 45 seconds.
Some axles are used front and rear and the transfer box is of Shelvoke and Drewry's own design and manufacture. This set up has a lockable third diff with 35 per cent front, 65 per cent rear distribution.
On the test track the S&D performed well. It was equally at home on the banked circuit as it was on the one inch stepped surface. However, it was on the airfield that it showed its true
merit. Here it covered rough terrain easily and was able to surmount quite high banks.
Its success here was attributable to the design which incorporates 30° approach and departure angles and gives excellent ground clearance. Enormous 1800 x 25 tyres are used on the Tender which look as if they would take the vehicle through almost any type of going.
Steering
One of the most impressive features of the S&D was its excellent steering. Our test model had centre steering but the chassis can be supplied with either right or left steering.
S&D has cleverly mounted the steering box on the right of the chassis and then used a bevel box with universally jointed
.„ shafts of varying length to give centre or left steering. When right-hand steering. When the column is connected to the box direct.
I found the steering to be light, but extremely positive, writes Steve Gray. Even going over very rough and bumpy grass there was no feedback or snatching to be felt through the wheel.
The Allison five-speed transmission, controlled by a lever nicely placed close to one's right knee, was an excellent match for the huge Detroit power unit. As the engine is rear-mounted, the interior of the cab was amazingly quiet — the turbocharger makes the loudest noise. No doubt when the fire fighting equipment, engine covers and a proper trimmed cab are fitted even this will disappear.