Tractor-trailer Buses
Page 35
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built for a
Desert Service
THE peculiar difficulties encountered on the route between Baghdad and Damascus have led to the design of a special type of motor vehicle for the Nairn Transport Co., which operates the passenger service between these two points. The vehicles comprise tractors with semi-trailers and the principal characteristics of their design are low load per wheel, extreme flexibility of springs and the employment of exceptionally large 1 o w pressure tyres. In addition, in view of the unusual conditions met on the journey, maximum comfort for pas. sengers was kept in mind as a
predominating factor. _ Each semi-trailer, built by the Budd concern, in stainless steel, is 37 ft. 6 ins, long, and provides accommodation for 28 passengers, although, in order to ensure the greatest possible comfort, the seating capacity is rarely used to its fullest extent. The seats have metal frames, supporting canvas hammocks, and Dunlopillo cushions.
In addition to the passenger compartment, occupying the centre of the semi-trailer, a small lavatory compartment is provided at the rear. Space at the front is fitted out as a snack bar, whilst the extreme forward compartment houses the air-conditioning apparatus, which is worked by a small petrol motor, operating a compressor unit and cooling coil. Methyl-chloride is used as the cooling liquid and is compressed and liquefied in the compressor and coil, over which air is blown by fans fixed to the shaft of the motor operating the cooling unit.
Air for the trailer is forced through a dust filter by another fan and is cooled by the cooling unit before being admitted by ducts at various points inside the compartment. The operation of the unit is controlled by a lever in the cab, to buzzer signals from the steward in the trailer.
The body of each trailer is built up of spot-welded stainless-steel sheets, -the windows and doors being fitted in rubber to provide the maximum pro
tection against dust, The constant pumping of air into the vehicle maintains the interior air pressure slightly above that outside the bus, so that any leaks serve for the escape of air rather than for the entry of dust.
To provide efficient insulation against heat and sound, a layer of kapok has been inserted in walls and floors. Further insulation ,against sound is provided by the generous use of rubber, notably on the under sides of the mudguafds, to avoid the noise created by large stones thrown up by the wheels.
The axles and wheels of the vehicles are of normal type, but to ensure easy riding over the extremely bumpy desert tracks the springs are 70 ins. long and designed for a deflection of 9 ins, under normal load. An additional 8 ins, deflection is allowed for passing over irregularities in track surfaces. The tyres have . been specially
constructed and require only 25 lb. pressure to carry 2,500 lb. each.
The tractor has also been specially designed, a 240-in, nickel-steel doubledrop chassis being used, with special chrome-vanadium steel springs of nearly as great a deflective capacity as those of the semi-trailer. The engine is a Cummins 150 b.h.p., oiler, with an oversize radiator designed to maintain a difference of 28 degrees C. between the water and the ambient air, The gearbox is a Fuller five-speed unit and connects with a double-reduction rear axle. The engine speed of 1900, r.p.m. allows road speeds of 65 m.p.h.
Like that of the trailer, tlie tractor body is provided with kapok insulation and spongy rubber sealing of all joints, to prevent the penetration of dust. All instruments on the dashboard are luminous, sothat no dashlight is required. The head lights are fitted with locomotive-type 250-watt bulbs in parabolic reflectors, and are fed from a *volt battery, which also provides current for the interior lighting.