"Rough-going" Trials of Britain's War Machines
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Interesting _Demonstration of a Series of War-time Machines' Produced in the Factories of the Rooks Group of Companies. Four-wheel Drive Solves Most
Cross-country Problems
IT is unfertunate for the British motor industry that,for securiky reaSobs, details of much of its war-time activities have to be Withheld from the general public. That it has done and-is dping remarkably good Work goes without saying, and we welcome the opportunity Of dealing with a demonstration recently staged by the Rootes Group of companies, which includes Commer, Karrier, Humber, Hillman and Sunbeam-Talbot, of some of its war-time machines.
'Certain types of vehicle from these factories are still on the`secret list, and, of course, these could not be included. So rapid is pi-ogress under the stimulus• of war, that others are already superseded by later designs, and these, .too, were omitted from the demonstration. Even So, seven different types were put through their paces. • Although; perhaps, of least interest to readers of " The Commercial Motor," the Hillman 'Minx 10 h.p.• saloon, supplied to the Services, is noteworthy as a preLwar private-car design, which, with little modification, is coping ably with military -duties. On ' much the same chassis is the Hilltnan 10 h.p. Utility vehicle, a Mechanical maid-of-all-work which can be used, for carrying personnel, transporting goods or which can be converted in a few seconds to a two-stretcher ambulance.
In all five'of the other types shown, the power unit is almost identical with the pre-war Commer six-cylindered • commercial-vehicle engine. It behaves
equally happily and well in a 3...ton ambulance or a 7-ton armoured car. Leading dimensions, it may be recalled, are:—Bore, 3.35 ins. (85 mm.); stroke, 4,72 ins, (120 inm.): capacity, 2414.23 cubic ins. (4,085.7 'c.c.). As used in these war vehieles, it has a compression ratio of 6.07 to 1, and it develops. 87 b.h.p. 'at 3,300 r.p.ria., ungoverned, 'Except,for the addition Of -frontwheel drive, and certain special equipment, such as a W.D. concertina-type air cleaner, standard peace-time prac-. tiee is followed fairly closely in the chassis used for both the Humber fourwheel-drive Utility model and for the Humber fourswheel-dtiVe ambulance. For normal use, the Commer engine and the 11-in, single dry-plate clutch and fourspeed earbox (synchromesh for top and third gears), -drives to a transfer box, with double helical gears of 1-to-I ratio. This same box also provides a low ratio of 1.47 to through straight-cut -spur gears, and a dog Clutch through which power can be transmitted to the front axle. .
On roads in fair condition only the rear drive is used, the gear ratios being
4.89; 7:16, 12.07, with a reduction ot 18.09 for first or reverse. In such circumstances, the vehicle is very lively and has a maximum speed of about GO
m.p.h, ; •
-For cross-country use, the frontwheel drive and tile lower, ratios are hrolight into action by levershandy to
the driver, These ratios • are 7.24, 10.60, 17:36 and 26.77 to 1. From the demonstration given on , Cannqelc Chase, it would appear that practically nothing can stop this vehicle.
From the transfer box, power is transmitted to each axle by art. open Hardy-Spicer propeller shaft with needle-roller joints. The rear axle is Of conventional design, with banjo casing, 'spiral-bevel gears and semi-floating' half-shafts. It is attached to the frame by .46-in, semi-elliptic springs. A timilar set of bevel and differential gears is housed in a casting at the front, the drive to the front wheels being through short shafts and Tracta ccnstantvelocity joints.
The front wheels are mounted independently, much in the same. way as in the pre-war Humber Even-Keel suspens sion system. There is a single semielliptic leaf spring across the front of the...chassis, mounted rather higher than the wheel centres, and a link below it for each wheel. Luvax piston-type hydraulic shoekabsorbers are used at front and rear.
The chassis frame is of channel section, with a certain amount of. box section near the middle, and a cross brace at the centre, Bueman-Douglas worm-and-nut steering is used in con
junction with .an 18-in, wheel. Lockheed hydraulic brakes operate in 11-in. clrume, and Dunlop 9.25-in. by 16-in. tyres are fitted on 6-in. by 16-in. Dunlop pressed-steel panel (split type) wheels. The petrol tank is at the rear _and has a totalcapacity of 18 gallons, 2 gallons being reserved by a two-leVel tap near the driver. A dipstick to measure the tank contents is included in the tool-kit.
With a seven-seater utility body, this vehicle is gradually superseding the Humber Super Snipe car for staff use, and with the ambulance body by Thrupp, and Maberly it is employed operationaly in the front line, from which it takes casualties rapidly back to the advanced clearing stations.
That it is right on top of its job is shown by the fact that practically the same specification, .even, to the gear ratios, applies also to the (Humber) Mirk III light reconnaissance car, which is armoured and weighs 3f tons. This is a type of advanced scouting car designed to carry three people—the car. commander, the driver and the rear gunner, who is provided with a revolving turret from which hostile aircraft can be persuaded to " lay' off." A second, gun is carried in front. Reliability, is important in any war vehicle, but for this sort of work it is absolutely essential.
Next on the list is the (Humber) Mark III armoured car, which, with its armour and guns, weighs about 7 tons, As the previous model goes• ahead of the infantry, so this one pretecles the Tanks.. Its Corrimer engine is similar.
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to that fitted in the light reconnaissance car, but the transmission is somewhat different. There is a 12-in, single dry-plate cluicb, and a four-speed wides ratio gearbox, with silent helical gears for constant mesh and the-third ratio. The transfer box has an upper ratio of 1.267 to 1 and a lower one of 1.965 to 1. Overall top gears are, therefore, either 8.706 or 13.58, and bottom gears are either 55.84 or 87.18 to 1, the lower reverse being 1.11-..0 to 1.
The suspension on this vehicle is along orthodox lines, with Woodhead semi-elliptic trunnion-ended springs front and rear. Both axles are of the full-floating type with banjo casings and spiral bevel gears, giving a reduction of 6.86 to 1. Hydraulically operated Cowdrey brakes, with shoes 3 ins, wide, work' in 16-in, drums, and Dunlop 10,50An. by 20-in. tyres are enounted on 6-in, by 20-in, divided pressed-steel disc wheels attached by eight studs. There are two-petrol tanks with a total capacity of 30 gallons, of which Eve form a reserve supply. The fifth type seen at the demonstration was the (Humber) Mark IV armoureel car. As it was released from the secret list only that same morning, a complete specification was not available. It is, of course, a later version of • the Mark ITT, which we have already described in detail. There are differences, too, in the automobile parts. hut, broadly, the same specification seems to apply.
All these types—indeed, quite a fleet ofthe four-wheel-drive utility vehicles —were put through their paces for our benefit over a variety of tracks on Cannock Chase. There were long climbs on loose surfaces, shorter but exceedingly steep ascents with really deep ruts, thoroughly rough tracks and a long mud-wallow over land used for Tank testing. At one point, too, a sunken road, with steep banks, was crossed.
To emphasize the value of four-wheel drive, one Utility vehicle attempted to climb out of the sunken road while driving only through the rear wheels, which simply proceeded to dig themselves nicely in. After several such -efforts, during which the machine climbed scarcely a foot upthe bank, front-wheel drive was engaged, whereupon the 3-ton vehicle promptly lifted itself over the top of the bank without fuss or apparent effort.
It has.been intimated that types still on the secret list were not shown, and it may, therefore, be concluded that those which were on view are not the latest designs which the Rootes Group has produced. Nevertheless, it is quite clear that they are extremely useful and serviceable machines. When to that is added the fact that this Group did not start to design a war vehicle until the war had started, it can be still better appreciated that this country and our many allies have been fortunate to corninand the skill, and ability of the British motor industry. •