A W.D. CHASSIS FOR VANS AND AMBULANCES.
Page 15
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A Precis of the Specification for a Pneumatic-tyred Model Suitable for, 15-cwt. Loads or the Carrying of Four Stretchers.
TDERE HAS just been published by the War Office a complete specification for a pneuntatie-tyred chassis suitable for a 15-cwt. van or a four-stretcher. ambulance. This chassis is not to be subject to a War Department subsidy, lett it is of interest both to the manufacturer and to the general public in that the specification calls for a strongly built vehicle comparable in service •and, to some extent, in constructional detail, with the subsidy-type light lorry running on pneumatic tyres.
In the main, it differs but little from the standard 20-25cwt. British-built commercial vehicle, and the principal features specified are those referring to cooling, clearance, hill-climbing and brake power, all points which should be of value to the owner of commercial vehicles operating in hilly districts at home and to the Colonial user abroad. In order to make the specification more concise, we have shortened the phraseology, but all the salient points have been retained.
What is Required.
Enginc: Minimum 2,500 c.c., four cylinders. If gudgeon .pins work lease, these must not score the cylinders.. Adjustment for wear and stretch must be provided for timing chains, if employed. The efficient oil filter must be accessible for withdrawal, and this should not involve the loss of the main body of oil. A .high-level test cock and dipper rod are required for the sump, and a lubrication indicator of the tench type must be close to the driver's hand.
A 12-volt dynamo, 41 ins, diameter, with standard flanged fitting and the necessary appurtenances, must be positively driven. Ignition to be by high-tension magneto of standardized type with spark control. Timing must be marked on flywheel to fixed peinter. A locking device must keep the starting handle vertical when not in use. Provision must be made to .reduce the cooling capacity of the radiator when required, and the drain cock must be of not less than I-in. . bore.
The radiator to be of the vertical-tube type with detachable tanks and protected by a bar or tube at least 1+ ins, diameter, supported from the frame. The filler cap opening to be at least 21 ins, diameter, with a hinged cap secured by a screw. Petrol must be fed by gravity and a two-way cock fitted to retain two and a half gallons in the normal position, this being released in the third position. An accessible filter of ample Size to be fitted between tank and carburetter, so arranged that leaking petrol cannot fall on the exhaust pipe. • The engine must pass Professor Dalby's sengine test. It must be possible for one man to decarbonize piston tops and cylinder heads in five hours ; also this time muse not be exceeded for examination of big-end and main bearings, including removal and replacement of caps. Petrol consumption must not exeeed 20 m.p.g. with full load. It must be possible entirely to drain the cooling system. The water in the radiator must not at any time exceed approximately 100 degrees E. above atmospheric temperature.
Utittelt Ifultiple-disc or leather-faced clutches not acceptable. A clutch stop must be provided. It Must he possible to start the loaded vehicle on top gear on a level road.
gearbox.: Four speeds forward and a reverse with safety eateh on change-speed lever for reverse. The gate must be marked or a diagram of the speeds mounted on the dashboard. An approved speedometer must .be 'positively driven from the transmission •(preferably the gearbox). The instrument to be mounted on the dash. A test plug or cock is required to indicate the oil level in the casing.
The vehicle, fully loaded, will be required to climb a gradient of 1 in 41 without clutchmanipulation and with a speed of approach approximating that of the climb. It must be capable of stopping and restarting on a gradient of 1 in 5 in forward and reverse gear and climb an average gradient of 1 in 10 at 8m.p.h. for a quarter of a mile. On level roads it must be capable. of 30 m.p.h. for one mile and 22 M.p.h. for a period of two hours. Where governor gear is fitted, this may be removed for the trials.
'Final Drive: hear axle to be fully enclosed and without Chain drive not acceptable. .
. • -3-17heelr:. Front and rear hubs and etude to. accordwith standard W.D. hub fitting and suitable for wheels of 20 ins.
diameter, with rims of S.M.M. and T. standards, suitable for tyres i:12 ins. by 6 ins. Wheels and tyres will be supplied by the -War Department, and tyree will be of the giant, straightwall type Jack Platforms: Both axles must have suitable platforms near the ends to receive the bead of a jack, unless the shape is such that, in the opinion of the C.I.M.T., they are unnecessary. Minus tyres, the jacking point must not be less than 7+ ins, from the ground.
Tyre Puritp; This must be positively driven, with pressure gauge and oil filter, and must form an integral part. It must be capable of inflating a tyre to its correct pressure in five minutes.
Steering: Stops must be provided to prevent tyres from fouling the chassis. The gear must be capable of easy control under all normal conditions, and the minimum turning circle must not exceed 45 ft. diameter.
Brakes: , All wearing surfaces to be of large dimensions and easily renewable. Brakes on the driving wheels must be compensated and must not be operated by wire rope or chain. Either brake
must stop and hold the vehicle, fully loaded, on a gradient of 1 in 5 in either direction, and must permit of continuous application for a distance of half a mile on an average gradients of 1 in 12, and aka speed of not less than 8 m.p,h„ the gear lever being in neutral.
Adjustment must be carried out in five minutes without tools.
Controls: Clutchpedal on left, brake pedal on right. Throttle pedal required. Clutch and brake pedals must work independently. Brake lever to pull on and be well clear of change-speed lever. . The preseure required to operate the pedals and their range of travel must permit of easy control by a driver of average height and strength. The hand levers for throttle and ignition must have their movement independent of that of the steering wheel. Both levers to move forward to increase engine speed and to be provided with a rack and index plate marked to show what the movements wilt effect.
Lubrication: Oil lubrication throughout the chassis is desired. Consideration will be given to an injector system.
Loess; caps must be avoided. The engine lubrication system must have a capacity for at least 200 miles. Both the engine and gearbox must work efficiently with W.D. lubricants.
Chassis: As light as possible, with fitted and driven bolts in place of rivets for parts liable to replacement. Minimum road clearance 91 ins. The frame to take W.D. towing hook attachment. Engine and gearbox units three-point suspended. Maximum overall width 7 ftFrame braced against horizontal distortion due to diagonal pull up to 20 degrees. Permanent dashboard approximately 3 ft. 2 ins. wide required.
• The Chassis Tests.
Tests: The tests to include jacking up one front wheel until the other is off the ground with the vehicle fully loaded.
It mustthen be possible to operate without difficulty the steering wheel, clutch, brakes, Change speed, starting handle and engine hand controls.
TestSOn rough ground include running on soft sand up •
to 8 ins. or 10 ins. depth and ,through unmetalled lanes with soft surfaces. These will be mainly to test the application of non-skids and their attachments, heating of the water and spring-mounting arrangements. Driving thiough water 15 ins, deep with a hard bottom must not affect the running of the engine.
Equipment: All standard tools, jacks, etc., will be supplied by the War Department, but' the, makers must supply all special tools and equipment needed in addition to these.
The specification includes a number of appendices. 'Ile first of these is a general note which points out the desirability of employing B.E.S.A. standards, particularly for ball and roller bearings, -screw threads and materials, and that
due consideration must be given to the question of facilitating repairs and -maintenance. Appendix B is a table of the
main properties :of W.D. lubricating oils. Appendix.0 gives details of the dividing line between chassis and body. It 'al deals with the W.D. equipment. Appendix D gives details of PrefeeSer DalbyS engine. acceptance test, and appendix*, standard sections for steels for laminated spring's.,