Haulage in High Altitudes
Page 39
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New-type Garrett Oil-engined Tractors for the South Rhodesian Gocernment
XP14:RIENCE in tractor construe don for work in many parts of the world has been the lot of the Richard Garrett Engineering Works, Ltd.; of Leiston. No doubt this was largely instrumental in securing for that company an order for three oil-engined tractors for haulage work for the roads department of the South Rhodesian Government.
The hatch is now nearing completion, and we have inspected and tested the first of three, tuned for work under English conditions. ActuaBy they will operate in Rhodesia at an altitude of 5,000 ft.; to this end the Gardner engines will be equipped with special pistons to give a compression ratio suited to the atmospheric pressure concerned.
One of the conditions of the order is that the ground clearance must not be • less than 14-11 ins.; this accounts for the somewhat unusual appearance of these entirely new models, which are fully sprang. Including the 18 cwt of ballast in the body, the total weight is 5 tons 4 cwt. (rear-axle weight 4 tons). Turning now to constructional details, we start with the channel-steel frame ; the cross-members arc riveted in position, but all brackets are held by fitted bolts in reamed holes. Semielliptic springs connect both axles to the frame; those at the rear have their eyes working on single shackles carried on slippers; the axle location is effected by an A frame articulated to a cross-member. This spring mounting allows the whole rear axle and A frame to be removed in toto after uncoupling the ball joint and brake connections.
In this frame may be installed a Gardner 4L2 engine or a 3LW engine of the same make; the latter unit is specified for the Rhodesian order. At the front a single mounting point embodies a rubber pad, whilst the two Tear points have Silentblocs working on vertical bearers. To the bell-housing of the Gardner engine is bolted a Meadows four-forward-speed gearbox, with a Borg and Beck single-plate clutch.
The drive is carried rearward by a short propeller shaft with Hardy-Spicer joints to an overhead worm assembly with a differential. To the differential casing are bolted the castings forming the A frame, the rear ends of which house secondary spur-reduction gears. The twin-tyred wheels run on a dead axle and their brake drums contain side-by-side shoe sets, one pair per wheel being hand operated and the other pair operated by the pedal.
This A frame takes all the torque and drive stresses to a ball-and-socket joint, and thence to a frame crossmember. At the rear of the frame is an adjustable drawbar, giving height variation from 14i ins. to 27 ins, from the ground. A ballast box forms the rear of the body, which is surmounted by a tropical awning.
• In regard to the engine there are certain specially interesting features. A belt-driven fan is prbvided and the radiator is of three-piece construction to facilitate cleaning when bad water only is available. The air filter takes the form of a box containing a " mattress " of wire wool dipped in oil.
A point indicative of practical ex perience is the fact that both front and rear tracks are the same, thus facilitating handling on rutted roads; steering is by worm and wheel, and the turning circle is 35 ft. in diameter. Between the driver and his mate is the trailerbrake control wheel. The dash of the driver's compartment is formed by a 16-gallon fuel tank ; feed is by gravity.
The gross haulage capacity of the Garrett tractor is given as 12 tons on a level surface and 8 tons up 1 in S. Our test was carried out over the hilly route from Leiston to Aldeburgh and return (8.4 miles). The round trip was accomplished lin 53 mins. (9.5 m.p.h.) on half a gallon of oil fuel. The laden trailer weighed 12 tons 9 cwt., so the gross ton miles per gallon were 296.52.
First gear (80.05 to 1 overall) gave easy restarting on 1 in 8, and the other ratios appeared to be well graded for the work (69.61, 24.02 and 11.2 to 1; the last named is intended primarily for light running). The change was easy and the clutch progressive and free from slip. On the southward trip there was a strong head wind; wet tarmac was the surface throughout.
Dynamometer pulls (average) re corded were as follow, the maxima being given in parentheses :—First gear, 4,700 lb. (5,500) ; second gear, 2,300 lb. (2,750) ; third gear, 1,500 lb.
(1,750). At sea level the engine delivers 51.1 b.h.p. at the governed speed of 1,550 r.p.m.. At 5,000 ft. it delivers 41.8 b.h.p.