Field Day for a 4 x 4
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By Laurence J. Cotton, M.I.R.T.E. BECAUSE of its high pei formance and sturdy build. operators will be tempted to carry on the Austin four-wheel-drive. lorry far more than the 1-ton payload for which it is rated in its military role. This model, which is now available to civilians in specified markets, made such an impressive show under the worst possible conditions at Farnborough, that I returned it to the works at Longbridge and asked to test it again with a much increased payload.
Despite a 3-ton payload, the agility of the Austin was only slightly affected on the steep Farnborough gradients, and the general performance was good for a combination of road and soft-ground operation.
Basically, the chassis is derived from the standard 2-tonner. but to provide the necessary power for off-the road operation, it is equipped with the four-litre engine, having a 6.8-to-I compression ratio, to give an output of 90 b.h.p. and 190 lb.-ft. torque. A six-bladed fan is fitted. The normal close-range four-speed gearbox is used, but a two-speed transfer box is installed amidships, with direct drive to the rear axle. Front-wheel drive is engaged when the lower ratio of 1.47 to 1 is in use.
A live axle having Tracta universal couplings and a spiral-bevel drive, which is interchangeable with the rear axle, replaces the conventional front-axle beam. A standard type of wheel disc is employed on all wheels, but the front track is 9 ins, wider than the rear. Although under certain cross-country conditions it is preferable to have offset tracking, . this system increases the rolling resistance when driving through soft ground with the tyres embedded in the soil.
For the military nominal 1-1i-ton rating, the springing has been revised, and longer leaves are fitted at the front to aid flexibility without increasing the stress. Alternative rear springs are available, depending on load requirements. The addition of H-in.-diameter shock absorbers, as standard at both axles, provides improved suspension on corrugated or rough ground. Special seals have been incorporated in the spring and shackle pins.
There has been a change in the steering gear, which is more robust and of lower ratio to provide lightness of control over the larger and heavier wheels and tyres. Other minor alterations have been made, including reshaping the sump to provide clearance over the driving centre of the axle, a larger petrol tank, and a pressurized radiator. Standard tyres for gross vehicle weights of 6 tons on the road, or 41 tons under cross-country conditions, are of 9.00-20-in. section, which affords sufficient clearance to fit chains. The chassis rear overhang is shortened to 3 ft. 1 in. but there is space for a 9-ft. 9-in. body within the frame length.
a4 In chassis and cab form, the test vehicle weighed 2 tons 11 cwt., but with the military body, the unladen weight was practically 3 tons. For the first test a nominal 1-ton load was imposed, but I added four spare tyres, tubes and flaps, which amounted to 6 cwt. The spare covers were borrowed for a subsequent trial with increased payload. With a flat-rack body in place of the heavy military body, the nominal payload could be raised to l tons for cross-country work with the standard chassis.
After collecting the lorry from West London, I drove to the Staines road for the first acceleration and braking trials, and consumption tests followed on the way to Farnborough and back. It was soon evident that the Austin was geared for fast driving, because it was quick off the mark and held a comfortable 45 m.p.h. where conditions permitted. Using direct drive in the transfer box and second, third and fourth ratios in the gearbox, it reached 30 m.p.h. from rest in an average of 18.5 secs., and accelerated from 10-30 m.p.h. in top gear in 25.2 secs. Such performance is to be expected where the powerweight ratio is in the order of 1 b.h.p. per cwt. Emergency application of the brakes caused complete wheel-locking, so manual effort was reduced. Braking power was certainly not lacking when driving with the nominal 44-ton gross vehicle weight.
In a cross-country vehicle, petrol consumption is of secondary importance to general performance and ability to win through under any ground condition. In the Austin, the high-efficiency engine, coupled with relatively low transmission losses, enables economy to be combined with performance, and on a 17-mile route the average consumption rate worked out to 15.5 m.p.g. at 32 m.p.h. average speed.
As I was ahead of schedule, there was more time for "rough riding." Most of the low-lying sections of the proving ground were waterlogged, and in other parts the wheels were embedded in the sodden surface, taxing 4 tne pulling power to the extreme.
Apart from two occasions when the engine misfired, after an involuntary ducking, there were no moments of apprehension. Because of the relatively high overall ratio, through the transfer-box indirect gear, the engine was pulling hard in low gear when negotiating the soft ground, but on the plains I made full use of second and third gears and found that the suspension was neither harsh nor too resilient.
Some of the approaches to the escarpments were made difficult by soil erosion, which had taken place since my last visit to the proving ground, but the Austin was not spared when the axle centres grounded. Several times the vehicle came to a stop, but by reversing and resorting to bulldozing tactics it eventually cleared a path through all the difficult sections. Although shovels were provided in the tool kit, there was no occasion to use them.
Apart from having a good performance. the vehicle was comfortable to drive. The cab was draughtproof and waterproof, yet under tropical conditions it would B5 not be uncomfortable, because no heat is transmitted through the scuttle or floor boards, and ample ventilation is provided by opening the windscreens and windows and adjusting the quarter vents. For oilfield requirements, it would be possible to extend the nearside seat or introduce a "jump seat" for an additional passenger, without affecting the position of the controls or encroaching on driving space.
After milling in the rough for 17 miles, I stopped to take operating temperatures. When the radiator cap was cautiously released, water spurted over the sparking plugs and stalled the engine. The water temperature was 146 degrees F., against an ambient reading of 41 degrees F. I found some difficulty in reaching the engineoil dipstick, because the military-pattern air filter occupied most of the available space under the near side of the bonnet, and. I had to crouch below the wing and reach between the spring and frame to insert the thermometer. With the civilian-type filter fitted the dipstick would be more easily accessible.
The base-oil temperature registered 128 degrees F., indicating that cooling was equal to tropical conditions. The trailing edge of the bonnet is upswept to prevent heat build-up or hot-air pocketing. Plug-type spanners, which were not available in the vehicle tool kit, are required to remove the fillers of the axle and transfer cases, so temperatures were not taken of the transmission components.
B6 The concrete and pebble-surfaced gradients were tackled with zeal. On the 1-in-2/ concrete slope, the Austin almost made the grade in second gear at the first attempt, and was held stationary while bottom gear was selected for the stop-start trial. There was no carburetter flooding when the engine was stopped, both uphill and downhill, and the braking was adequate for effective stopping and there was sufficient power for smooth starting.
With normal control, and the spare wheel between the body and cab, the weight distribution between axles was not equal on level ground, and on the steeper Farnborough gradients the transfer of load to the rear axle was considerable. The result was a tendency towards front wheelspin when negotiating the loose pebbles on the steeper slopes.
The Austin managed the 1-in-3 gradient without trouble, but wheelspin developed on the next slope, and four attempts, gaining a few yards each time, were required before it reached the brow. I think the wider front track was of assistance under these conditions, because both rear tyres did not fall into the ruts made by the front wheels.
Although a little more difficult, the 1-in-21 loosesurfaced gradient was also climbed after several attempts, success finally coming after the tyre pressures were lowered from 40 lb. to 30 lb. per sq. in. I optimistically tackled the 1-in-2.48 pebble-covered slope, but since it was resurfaced, ['have never seen any vehicle reach the top. The Austin was claimed as another victim.
As the performance was nearly perfect with the nominal load, the vehicle, with the permission of the manufacturer, was loaded to approximately 6 tons gross for extended trials. Many operators will carry such loads both on and off the road, and to meet this increase, special rear springs were installed and 11.00-20-in. tyres were fitted. I selected the 11.00-in. tyre because it is the largest that can be fitted without fouling the chassis or wings.
Fitting larger tyres and changing the rear springs added 21 cwt. to the unladen weight, and with the addition of 3 tons of sand in the body, the gross vehicle weight registered 6 tons 21 cwt. When the sand was level in the body, the weight distribution was 4 tons 1 cwt. on the rear axle and 2 tons 11cwt. on the front. With single tyres all round, it would be preferable for the spare-wheel carrier to be removed from its present position, and the body and load shifted forward.
At first I thought the braking might be inadequate for the heavier load, as there ism° assistance to manual effort and the frictional area is about 40 sq. ins. per .ton. Undoubtedly the driver has to use more force on the foot brake than in most modern vehicles, but I was able to lock the wheels with a 200-lb. pedal effort. During the braking tests the vehicle was stopped in 32 ft. from 20 m.p.h. and 63 ft. from 30 m.p.h.
By coincidence, the larger-section tyres aided acceleration, because of the increased speed in the intermediate gears. The time to reach 20 m.p.h. was still 9.3 secs. but only 22 secs. were required to attain 30 m.p.h. in third gear. The fuel-consumption test was made over the same course as before, and the efficiency of the vehicle was again proved by covering the route at a rate of 12.1 m.p.g. and an average speed of 29.6 m.p.h.
Apart from calling for a little more care in driving in traffic, because of the lower braking power, the performance was comparatively little impaired by the additional load and larger tyres. With but little more weight on the front axle, there was practically no change in the steering and only a slight tendency for tail woh*le at speeds exceeding 40 m.p.h. on a wet road.
Before arriving at Farnborough, I doubted whether the lorry would climb the loose gradients. In this I was mistaken, because, starting from the "shallow end," it romped up the 1-in-4 slope and then repeated the measure on the next hill. Three attempts. with a short start on the flat. were needed before the 1-in-31 was conquered. A failure was recorded on I in 2.94, because of a rut with shingle I-ft. deep half-way up the escarp
ment. The 1-in-2,1 hill was in better condition, and by dint of perseverance, taking a 50-yd. run on the flat and changing from second to low gear when the engine speed started to fall, success came on the eighth assault.
It was noticeable during the trials that there was no wheelspin. All failures were caused by lack of power with the load and tyres used. I place great value on the large-section tyres, which helped over the pebbles and prevented bogging down.
The lorry would not quite reach the brow on the l -in-4 concrete slope, using second gear, but stop-start tests were made on this gradient with bottom gear engaged. Attacking the 1-in-21 concrete gradient at speed, the vehicle just succeeded in breasting the crown.
A six-wheel-drive recovery lorry was standing by to give assistance should the Austin fail on the Tank proving ground, but there was no need for its services. The flotation of the large tyres, inflated to 35 lb. per sq. in., prevented the wheels from sinking deeply below the surface, and, judged by the engine behaviour, there was little difference between carrying 6 tons on 11.00-in. tyres and 41tons on 9.00-in. tyres. Apart from a stop caused by the engine being swamped when nosing through a pool, the performance was exemplary.
To wind up the off-the-road trials, the vehicle was driven over the drastic kerbstone circuit, where the suspension, steering and frame took severe punishment. After five miles at 15-35 m.p.h., a head lamp, doorlining panel and lock worked loose, and a pin was dislodged from the hand-brake trigger. Considering the severity of the test, with tyres re-inflated to normal road pressure, causing one or both front wheels to leave the ground at frequent intervals, the Austin sustained remarkably little harm. After six miles one of the driving mirrors worked free, but there was no mechanical failure.
With both military and uprated loads, the Austin proved its ability to overcome practically any obstacle. The results of the second trial suggest that performance with military load might be improved, "in the rough," by employing a 10.00-in. tyre. With a gross vehicle weight of 6 tons 9 cwt., which was the loading complete with crew and equipment when testing for the second time at Farnborough, none of the components was overloaded when judged by the temperatures of the engine and transmission.
After an hour's continuous low-gear work, in fourwheel drive, the temperatures were: Water 156 degrees F., engine oil, 136 degrees F., front axle, 82 degrees F., transfer box, 84 degrees F. and rear axle, 86 degrees F. The ambient reading was 46 degrees F.