THE NEED FOR SPECIAL SIS FOR AMBULANCES.
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A Short History of the Growth of the Ambulai With Constructive [ the Metropolitan Asylums Board, Together a Chassis Design.
Fr HE LARGEST fleet of civil ambulances in this
country is that of the Metropolitan Asylums Board, the present fleet consisting of some 160 motor vehicles, mainly ambulances, whilst the absorption capacity for motor chassis is from 12 to 14 per annum. One would think that with such a steady demand here and elsewhere' chassis suitable in every _way would be readily obtainable, but in the experience of the Board that is not the case; in fact, the question of obtaining suitable ambulance chassis is becoming more difficult each year. This is because very few 'chassis are specially designed for ambulance work, most of them being little more than modifications of those for private cars, which are being built much lighter and mostly with smaller engines, points in design which are directly opposed to the requirements of the ambulance.
The wheelbase of an ambulance as required by the Metropolitan Asylums Board should be approximately 12 ft., and at present such vehicles cannot be obtained at a reasonable price, the only chassis available in this category being the Rolls-Royce and the long-wheelbase Daiinler, which may be classified as luxury vehicles.
At the same time, the patients carried should be afforded the maximum possible comfort. The patient may have been in bed for a prolonged period, and he should travel with the same degree of comfort as he experienced in the sick room. Travelling in a recumbent position is an entirely different matter from travelling in a sitting posture ; rapid acceleration for instance, has a most uncomfortable effect, and of course, surgical cases require even more care. We have received from Mr. Charles L. Sladden, .A.. M. M. E. A .M. I. A. E., M. Inst.T'
. M. P. E. , Engineer Superintendent (M.T.) of the Metropolitan Asylums Board, some most interesting information which should prove of great value to designers and users of motor ambulances.
As the result of experience with some 27 different British makes of motor, ambulance chassis, Mr. Sladden points out that he fully endorses the remarks contained in our article entitled "Ambulance Bodies and their Equipment," which appeared in the Special Municipal Issue of this journal published on February 10th, in which it was stated that a chassis of special design is needed adequately to meet the requirements of this exacting form of transport.
Before dealing with the bulk of the opinions expressed by the Engineer Superintendent, it will be of interest briefly to trace the history of the Metropolitan Asylums Board And the progress which it has made in the development of an ambulance fleet.
The Board was constituted in 1867 for the reception
and relief of poor persons suffering from fever or smallpox, or, those insane, and the passing of the Poor Law Act of 1879 empowered the Board to provide and maintain carriages suitable for the conveyance of such persons. The first ambulance station was opened in 1881, horse vehicles then being used. Further stations were erected at New Cross in 1883, Fulham in 1884 and Homerton in 1885, and, later, further stations were erected at Hampstead, Woolwich, Stockwell and Fulham.
From 1903 the Board undertook the conveyance of non-infectious patients of the general public, a charge being made for ambulance hire. The horse. drawn ambulances first employed were of two types-..-. broughams for single stretchers and vans for two stretchers.
The employment of motor vehicles was first decided upon in 1902, when a steam ambulance was put into service for the conveyance of patients to the Dartford Hospitals. This vehicle was built by John L Thornycroft and Co., Ltd. It had a capacity for eight stretchers and a road speed of 5 m.p.h. It was first supplied with steel tyres, but the wheels were, later, converted to carry rubber-band tyres, which, however, gave much trouble. The front springing on this vehicle consisted of laminated inclined springs mounted longitudinally and joined by a transverse spring. To 'give low loading, the whole frame was inclined to the rear.
Various other experiments were then carried out, including some with electrically Rropelled ambulances, which did not give satisfactory results.
The first motor ambulance was a James and: Browne, purchased in 1904 and built by James and Browne, Ltd., at Hammersmith, W. This had a capacity. for one stretcher and a speed of 15 m.p.h. The specification included a four-cylinder, horizontally opposed engine slung under the chassis, a radiator beneath the floorboards and behind the axle, final drive by exposed chains, and 2-in, solid tyres, whilst. the body was of the van type.
In 1905 the general use of motor traction having been favourably reported upon, it was decided to adapt one of the existing stations for the purpose, and by 1908 horse traction for the Western Station had been completely replaced. The remaining stations were dealt with in a similar manner, and the last horse was dispensed with in 1911. The Mead ambulance station at Fulham no longer deals with patients, but has become the central motor works under the name of the Mead Works.
Reverting to the vehicles employed, next in order of date was an Argyll, bought in 1905. This was of more conventional design, having a four-cylindered engine mounted behind the radiator, and final drive by bevel gearing. Incidentally, this was the first vehicle to be fitted with pneumatic tyres. The body was bf the brougham type, the feet of the patient passing under the driver's seat.
In 1910 use was made of a Belsize capable of 20 m.p.h. and with final drive by worm and worm wheel. This was the first vehicle in which an attempt was made to protect the driver.
In 1912 some of the vehicles employed were fitted with cantilever springs at the rear. Detachable rims and electric lighting were now employed for the first time.
Armstrong-Whitworth vehicles with h. capacity for two stretchers and a speed of 25 m.p.h. were placed into service in 1914. The points of interest in these vehicles were the four-cylindered monobloc engines, four-speed gearboxes and multiple-disc clutches ; also three-quarter elliptic springs were employed at the rear.
Daimlers of similar type were employed in 1915, but these had cantilever rear springs.
The first complete vehicle built by the Metropolitan Asylums Board appeared in 1910. This carried two stretchers, ran at :30 m.p.h., and had a six-cylindered power unit combined with the gearbox. Twin pneumatic tyres were employed for the first time at the rear, and the longer wheel base enabled patients to be loaded head first, as it ob viated t h e necessity for passing a part of the stretcher under the ,driver's seat. CI em entTalbot vehicles, used in 1917, were 'notable a s having a speed of 40 m.p.h. and as being the ftrst vehicles to be fitted with heating apparatus.
A still further advance was made in 1922, when war arrears were made good by placing into service a large number of ambulances of a much improved design, which in its turn is giving way to the latest type built by the Board in 1924, which was described not 'long ago in the columns of this journal. It carries, two stretchers, has a speed of 40 m.p.h., and is designed to give ample riding comfort, to assist which it has flat springs with gaiters, shock absorbers and 7-id. Palmer cord pneumatic tyres. The interior is warmed by the cooling water from the engine, the heat being controlled by a thermostat. The body has a clerestory • roof., and an enclosed cab for the driver. The equipment includes dipping headlights and a pneumatic stretcher, whilst three folding steps give easy access to the interior, although the floor could not be built so low as was desired owing to the necessity for using standard components.
We will now proceed with the opinions expressed by Mr. Sladden. He points out that the Metropolitan Asylums Board is continually being asked by medical officers and public bodies for advice on the transportation of the sick in a manner to avoid all distress and discomfort, and they realize that a satisfactory ambulance will not be a cheap article. The usual, comment is that the riding qualities of an ambulance are worse than those of a touring ear, which is not to be wondered at when the conditions are analysed.
A touring car has tyres of ample dimensions for the weight to be carried, flexible springs—in most cases' nearly flat—encased in gaiters, with shock absorbers or snubbers, and, in a few cases, bodies mounted on rubber blocks. As a final insulation against vibration there is about 10 ins, of cushion made up of small springs well upholstered ; sometimes air cushions are provided, and it must be remembered that all this comfort exists for a person considered, normally, to be in good health.
Now take the case of a recumbent patient. The fact that he is lying down makes the question a much more difficult one. The ambulance chassis will, as a rule, be that of an ordinary touring car. The tyres, due to the weight to be carried, can no longer be claimed to be of ample dimensions and will necessitate the employment of high air pressures. The springs will be stiffene 1 to take the increased load and to overcome the excessive roll due to the fitting of large, high bodies, and, in many cases, no provision is made to jacket springs or to control the rebound.
The bodies are, ordinarily, mounted direct on to the frame, and in the place of the 10-in, spring cushion is substituted a stretcher, which still, in many places, consists o f two poles and a piece of canvas and, generally, without any means of attachment to t h e vehicle. It will thus readily b e seen that the person in good health is much
better provided for than a patient.
It would seem that the ambulance of
to-day should be classified with the lifeboat and fire-engine and designed accordingly for special duty, and Mr. Sladden has reason to helieve that this is being done on the other side of the Atlantic, where special• chassis are being made with large, powerful engines allowing a small final reduction axle, which enables the floor to be brought low ; also a number of ambulances is fitted with four-speed gearboxes having direct drive on the third speed, the idea being to enable the vehicle to proceed quickly to a case and, having once loaded the patient, to proceed on thq third gear. The experience of the Metropolitan Asylums Board, shows that the engine should be very powerful— ambulances are not taxed, so high power is no drawback on that account—silent, and as free from vibration as possible. A six-cylindered engine is preferable, and this should be complete with lighting and starting equipment.
As to whether the speeds should number three or four is not of importance, but what is vital is that the gears should be silent in operation and the changes effected with ease. The clutch should be progressive in action and designed to allow clean gear changes: A thermostat should be employed in the cooling system to enable tile engine to warm up quickly. Worm gearing should be employed for the final drive, for the reason that this will remain quiet throughout the useful life of the chassis. It is important that the ambulance should be capable of starting on top gear on a level road when fully laden, and at the same time be capable of reaching a maximum speed of 45 m.p.h. ; starting on top means a reduction in the rapidity of acceleration which occurs on the lower gears and thus enhances the comfort of the patient'. A low centre of gravity is most desirable, and a wish for this is expressed by all interested in the transportation of the'sick. The frame should taper from the front to the rear, thus enabling the body to be as wide as possible and at the same time obviating somewhat the tendency to roll when cornering. The springs should be long, of ample width and with low periodicity, preferably of the half-elliptic type enclosed in spring gaiters and with the rebound effectively controlled. Seven-inch pneumatic tyres are desirable and these should be of the low-pressure type. Brakes on all wheels are a necessity in these days of fast traffic in busy centres. The rear axle must be of such design as to allow low loading at the rear and Mr. Sladden thinks that this could be satisfactorily arranged by offsetting the differential easing, thus bringing the axle casing beneath one of the wheel arches of the body. The floor level can then he lowered to the requisite clearance for the vertical movement of the axle tube.
A wheelbase of approximately 12 ft. must be provided to allow the fitting of a body of adequate dimensions, and the steering should be well designed and easy to operate with one hand, leaving the driver's other hand free to use the warning bell and to give signals.
We include amongst our illustrations a drawing showing the lay-out and principal dimensions of the chassis recommended by Mr. Sladden. The details are not arbitrary, and the chassis has been designed ' with a view to the use of components of standard type. For instance, the alteration in the axle is not nearly so drastic as may be first thought ; the only new parts required are tubes of different length and new axle shafts. The engine and gearbox are mounted centrally, and the drive is taken through a cardan shaft which has movement in to planes, the vertical and the horizontal, and by making the sixcylindered engine as a unit with the gearbox this shaft can be of such length as to give comparatively small angularity. However, to prevent trouble, it is recommended that universal joints of the ball-race type be employed. It is immaterial whether central or side positioning of the controls is adopted.
The employment of a clerestory roof gives satisfactory headroom, whilst the positioning of the dash forward of the rear of the engine makes up for the length of the six-cylindered unit.