THE " C.M." TESTS A NEM :-WHEELED STEAM WAGON.
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BEFORE laying out a programme for a test of any _vehicle it is always advisable first of all to consider the exact nature of the work for which the machine has been designed. Obviously, a crosscountry tractor is nnsuitable for high-speed main-road work and, conversely, a vehicle intended primarily for fast, heavy haulage over proper road surfaces is not suitable for general use over boggy ground or the type of surface usually associated with pioneer work in undeveloped countries.
It was with the foregoing principle firmly established in our minds that we approached the pleasant task of planning and carrying out a test of the recently introduced Sentinel rigid six-wheeled steam wagon. Now this vehicle has been introduced expressly to cater for the needs of the "heavy haulier" who requires an easily .handled and economical lorry or van, capable of conveying a really big load (both in bulk and
weight) over ordinary roads such as are encountered for the most part in this country. As will subsequently be seen, the vehicle is not, by any means, confined to this class of work, for it successfully negotiated soft ground where the wheels sank to a depth of a foot.
Our test was divided into three sections, the first consisting of a normal main-road run, so that the general performance of both the power unit and the chassis could be noted ; the second involved the negotiation of soft ground, and the third a hill-climbing and braking trial carried out on some of the sharp gradients in the vicinity of Shrewsbury—where, the works of the company are situated.
Throughout the whole of the day of the test a useful load of 12 tons was carried in addition to fuel and water ; the performance, therefore, on half load, or two-thirds load, as the case may be, would probably he very much better, but, of course, the ton-miles per cwt. of fuel, etc., showed to the best advantage with the heavy load. We have compiled a list of interesting figures from our observations, to which reference will be made later on.
Before describing the tests it may be opportune to give a brief description of the vehicle for the benefit of those readers who did not see the detailed description in the issue of The Commercial Motor dated November 15th. Without in any way overcrowding the cab, a platform length of nearly 20 ft. is provided, yet the overall length of the complete vehicle is no greater than 26 ft. 3 ins. ; the wheelbase, incidentally, is 16 overall, i.e., from the front wheels to the rear wheels of the bogie. The height of the platform, laden, is 3 ft. 10k ins. Particular interest attaches to the manner in which the rear wheels are suspended and driven. Actually a hollow, tubular axle is bolted direct to the centre of semi-elliptic springs, the fontwheels being held by two pairs of arms which oscillate about the centre of this hollow axle. Chains are used B32
to convey the drive from the power unit to the forward wheels of the bogie ; thence it is taken by further chains to the rear 'wheels. This arrangement enables the • Unsprung weight to be kept down tothe lowest possible amount.
It is, however, in thOiengine that the chief interest of this new vehicle lies, for " poppet " valves are now used and these, in conjunction with streamlined steam passages, .have made possible an all-round increase in efficiency. Further, economical operation has been enhanced by keeping the cylinder dimensions down to reasonable limits. Three steam cut-off positions and a two-speed ge,ar form a combination which enables the severest gradients to be climbed safely, easily and economically. Low gear, of course, is only required when restarting with an excessively heavy load, on a steep incline, or when negotiating soft ground. The bore of each of the two cylinders is 6 ins, and the piston stroke is 8 ins.; the engine is, as usual, doubleacting and works at a normal boiler pressure of 275 lb. per sq. in.
Looking round the cab we were at once impressed by the very convenient layout of all the controls. Immediately under the rim of the steering wheel is a combined stop-valve and auxiliary valve box, the
throttle lever for which projects upwards, so that it is within easy reach of the driver's left hand. The throttle, of course, controls the speea of the vehicle, but its action is supplemented by a pedal release valve
(actuated by the driver's left foot) which has the effect, when depressed, of shutting off the steam supply to the engine.
On the left-hand side of the driver there are two further auxiliary valves, one controlling the steam to the blower for brightening the fire, and the other operating the water injector. On the right-hand side of the driver's seat are three levers, the innermost one being a pull-on brake which operates shoes within drums attached to both pairs of wheels of the rear bogie. The middle lever controls the "change-speed mechanism, whilst the third regulates the steam cut-off. It allows of three cut-off positions in the forward direction, a neutral or drain position (in which all the engine valves are open) and a reverse position for going astern. The three cut-off positions are important, as they largely control the cost of running the vehicle. The three positions are 89 per cent., 40 per cent. and 30 per cent. respectively of the piston stroke.
Turning now to the trial proper. From cold, 43
minutes elapsed after putting a match to the paraffinsoaked rag in the firebox, until the blower would work satisfactorily, but in four minutes from the time that the blower was put into operation 50 lb. per sq. in. was registered on the steam gauge; in three minutes more the pressure had increased to 100 lb. per sq. in., whilst in a further three minutes 200 lb. was recorded. By this time approximately 48 lb. of fuel had been used to make up the fire and get up to a working pressure.
We started off on a journey through the town of Shrewsbury, and then out along the Holyhead road towards Llangollen. Immediately alter the start the valves were moved into the third cut-off position (where the engine works most economically) ;. it was tonna subsequently that practically all main-road running could be effected on this setting, the engine pulling up moderately steep inclines quite satisfactorily. Indeed, with such a heavy load on board the " topgear" performance (as it might be termed) was surprisingly good, it requiring quite a steep and long gradient to necessitate the intermediate position for the steam cut-off.
Everyone knows that the streets of Shrewsbury are particularly winding and narrow, and form one of the most difficult tasks for a large vehicle, such as this six-wheeled Sentinel model, to negotiate satisfactorily. We were, however, particularly impressed with the manner e driver—no doubt an expert—was able to negotia c. A large steering lock is Wi doubtedlj respons for this ease of handling. We measured the comple e turning circle and found that the wheel tracks measured 62 ft. in diameter from the extreme outside edges when a complete circle had been described.
Running out of the town of Shrewsbury a hill had to be climbed which, with an average gradient in the neighbourhood of 1 in 14, was taken at an average speed estimated at about 10 m.p.h. This must be accredited an outstandingly good performance, for a small calculation shows that something approaching 90 b.h.p. is required to lift the weight of the complete vehicle and load, without taking into consideration any traction losses. Incidentally, the second cut-off position sufficed to maintain the speed of 10 m.p.h. throughout the climb.
Timed from the start at the Sentinel works the village of WittIngton was reached in 1 hr. 7 mins., excluding a stop of some 10 minutes' duration for the purpose of taking photographs. The homeward journey occupied 1 hr. 5 miss.; thus, as the distance out and home is 87i miles, the average speed worked out at slightly more than m.p.h. Despite this comparatively high speed, only one tankful of water (200 gallons) was Consumed, whilst the coal used amounted to 2 cwt 3 qrs. 17 lb. Thus the fuel consumption works out at 12.91 miles per cwt.,or, expressed differently, 155.2 pay-load ton-miles per cwt.
The foregoing results enable a very interesting form of costing to be evolved. For instance, with a 12-ton B34 load and assuming a price of 35s. per ton for the coal, the cost per mile for fuel is approximately 1.63d., an extraordinarily small amount. Reckoning on a 12-ton pay-load basis, 1,770 ton-miles can be run for the expenditure of EL.
Turning now to test section No. 2. The vehicle was taken up to some soft ground, at the top end of the Sentinel works, which is used by the Sentinel engineers for testing the tractor vehicles that have been designed expressly for pioneer work. As might be expected with a vehicle such as the D.G.6 model, we were unable to go ploughing straight across the waterlogged soft ground in the way that the tractors do, nevertheless we were able to run over ground which was• so soft that the wheels sank to a depth of about one foot. Indeed, on one occasion part of the water-feed piping actually dug a groove in the soft earth, so that it is safe to assume that our test was even more severe than was really necessary. It will suffice to say that on every occasion we were able to drive the vehicle without trace of skid or wheelspin, and on several of the worst patches a stop and restart were effected with extreme ease. A glance at the photographs illustrating this article will show the extent to which the driving capabilities of the bogie were tested, and it must be agreed that as the vehicle could negotiate successfully the appalling surfaces encountered during our run, stalling on ordinary road surfaces, however, greasy, should be unknown.
Ease of handling we can vouch for, because we took over the vehicle and drove it ourselves. The act of
steering is similar in all respects to that of the normal touring car, being light, definite and without any sign of the jar or shudder so often associated with steering .heavy vehicles over bumpy surfaces. The gear reduction was, of course, greater than that usual in touringCar practice, but as the average speed of the Sentinel is normally considerably lower than that of a pleasure car the "lightness" amply compensates for any extra movement of t e steering wheel. Attention has already been dra ,n to the manner in which the controls are disposed We found them to be particularly convenient and, a they are all grouped together, the driver is able fu ly to control the vehicle and its anxiliaries, withal t requiring the stoker to do anything other than attend to the fire.
Our final test .onsisted in a demonstration of the hill-climbing powEirs and the braking and accelerating capabilities of th fully laden vehicle. We first made an ascent of Port Iill, in the neighbourhood of Shrewsbury. This particular incline has an average gradient of 1 in 10. is 500 ft. long, and is approached by a turn at the bottom whiCh precludes any possibility of " rushing." At the foot the valve control was moved from the third cut-off "tion to the second, and about halfway up the hill N as again moved, this time into the first position. The engine was then able immediately to accelerate to siiout 6 m.p.h., the steam being held at the normal pressure of 275 lb. per sq. in. throughout the whole of the climb.
The next hill was situated on a narrow lane known as Roman Road, which runs off to the left of the road leading from the top of Port Hill. This particular gradient is somewhat steeper than Port Hill and has a very much he vier surface. As a matter of precaution the Towel gear was engaged at the foot, but the ease with wl ich the incline was tackled showed conclusively that t would take a very steep hill indeed to stall the engin . With only 230 lb. per sq. in. of steam 5 m.p.h. to 6 m.p.h. could be maintained, whilst a restart on any part of the gradient proved to be a matter of extreme simplicity.
On our way back to the Sentinel works "The Kopp" (actually in Shrewsbury itself) had to be negotiated. Anyone familiar ith this hill will realize that to climb
• it with a load of 9 tons on top gear at about 5 m.p.h. is no mean perfo ance, yet this is what the Sentinel did without any fins whatever.
This, then, shcuid give some idea of the extraordinary capabilitie of this latest Sentinel product. It only remains to slow how the vehicle performs against the stop-watch. A separate test had to be made in order to obtain th4 two acceleration and braking curves, which are publish d. The vehicle then carried a useful load of about 31 tons. We should have preferred to have had these tests also carried out with the full load, but, unfortunately, the vehicle could be released from service for only a short time following the main test, and the necessary loading facilities were not then available.
Brief Specification.
TyPE.—D.G.6 model Sentinel wagon. Price 11,150, with fiat platform body.
LOAD CA.P.Aerrr.-10-12 tons.
PLATFORM A.REA.-133 sq. ft.; length, 19 ft. 9 ins.; width, 6 ft. 9 ins.
PLATFORM HEIGHT.-3 ft. 10; ins. (loaded).
CHASSIS DivinNsioNs.—Wheelbasc, front to middle wheels, 12 ft. 14 ins.•, middle to rear wheels, 3 ft. 10 his. Track (front), 5 ft. 3 ins.; (bogie), 5 ft. 9i ins. Overall length, 26 ft. $ ins.; overall width, 7 ft. 6 ins.; overall height (loaded), 8 ft. 71 ins.
ENGINE.—Twa cylinders, 64n, bore, 8-in. stroke. Doubleacting. Poppet Valves. Automatic lubrication.
,Bornxii.—Water-tube type. Firebox replenished with
fuel from the top. Normal working pressure 275 lb. per sq. in.
GEARS.—Two-speed type. Approximate engine speed at 6 m.p.h. (top), 195 r.p.na.; bottom, 595 r.p.m, FINAL DRIVE.—By chains throughout CAPACITY OF BUNKER.-10 Cwt.
CAPACITY OF WATER TANK.-200 gallons.
TURNING CIRO' E.-62 ft. diameter.
Figures of Performance.
TIME TO RA/SE STEAM (FULL PRESSI'RE) .-53 ming.
rum, REQUIRED TO RAISE STEAM.-48 lb. Wimber steam coal.
ITsgyun LOAD CARRIED THROUGHOUT TEST,-12 tons.
LENGTH OF CONSUMPTION TE.9T RUN'.-37/ miles.
NET TIME OCCUPIED FOR CONSuMPTION TEST RUN.
2 hrs. 12 reins.
AVERAGE SPEED DURING TEST.-17.05 m.p.h.
WEIGHT OF 'VEHICLES COMPLETE AR 'Pus:mm-21 tons 7 cwt. 8 qrs.
COAL CONSUMED.-2.9 Cwt.
AmO,UNT OF WATER EVAPORATED.-240 gallons.
VEHICLE MLLES PER CWT. FUEL.-12.9i.
NET TON-MLLES PER CWT. FUEL.-155.2.
COAL PER VEHICLE-MILE.-8.66 lb.
COST OF FUEL PEP, Vrancr.,n-min.--1.63d. (35s. per ton).
COST OE FUEL PEP. NET TON-MILE,—.135d.
NUMBER 'OE NET TON-MILES PER .11 OF FUEL.-1,770.
WATER EVAPORATED PER LE: OF COAL:-6.15 lb.
WATER CONSUMED PER MILE.-53.3 lb.
COST OF COAL PEE, GROSS TON-MTLE.—.0767.1.
ViArEn. PER NET TON-MTLE.-4.44 lb.
RANGE OF ACTION ON TANKFUL OF WATER.-37.5 miles.
ArAKIAIUM C4RAD1ENT CLIMBED ON TOP GEAR,-1 in O.