STREAMLINE BODYWORK FOR SPORTS AND RACING CARS.
FOR centuries past, coachbuilders have been regarded as amongst the most conservative of folk, and in. some cases this conservatism is found in the methods of those who have taken up the design and construction of bodies for motor vehicles. Perhaps one of the greatest hindrances to the progress of the motor car has been the lack of co-ordination between the coach-building and engineering industries. Engineers took little pains to consider the essential requirements in a chassis to make it easy for the coach
builder to fit a good body, and in his turn the coachbuilder often did most extraordinary things when carrying out his part of the job. For instance, it used to be a favourite practice for the bodymaker to secrete the petrol tank under large and heavy members of the body frame, another being that of driving nails or fixing screws with a total disregard for such things as electric wires or lubricating pipes. Happily all that is now a matter of the past and the two branches of the great automobile industry now work happily together, and we find consequent improvements in the completed vehicles.
Progress in Body-building.
Perhaps it is no exaggeration of the position. if I state that almost up to the War period, the same By A. P. COMPTON,
Manager, Coachw9rk Department, Messrs. Jarvis & Sms, Ltd., Wimbledon.
methods of body-frame construction were employed as had been used on the original horsedrawn vehicles but, as in the case of engine and chassis design, racing and competition work have had an enormous influence in bringing about the drastic changes that have taken place during recent years.
Indeed, it may be asserted without fear of contradiction, that the modern lightweight body is the direct result of the experience gained in the construction of racing bodies for use on the road and track.
At the same time, much useful information concerning lightness and true streamlining has been derived from a study of aircraft construction, and those coacIlbuilders who have followed aircraft principles have found that it is now possible to make motor-car bodies, which though about one-third of the weight of those built on the old principles, are able to withstand far greater stresses, owing to their scientific construction and to the careful selection of materials. Readers will remember that only a comparatively few years ago, it was the practice of car builders to supply naked chassis, and it was largely left to the purchaser to decide what sort of body he would have fitted. Some customers, who in changing over from horse-drawn vehicles to motor .cars, would hear of nothing else but to
have their motor car bodies built by the firm who had made their family broughams for generations past, so the body-builder became a kind of local despot, and did very much what he liked with regard to design and construction. I am merely stating these facts to draw a comparison between the conditions which had so much influence on the design of bodywork in the past and those under which the modern ultra-light streamline bodies are made.
Nowadays, it is the custom for high class chassis manufacturers to stipulate a definite weight limit for the bodywork, and more than one motor firm issues a very comprehensive instruction booklet as to the points to be observed by the body-builder, in order to make the coachwork conform with certain characteristics of the chassis. The reasons for such precautions are obvious, for the lighter the body, the better the performance of the car generally, especially with regard to speed and acceleration, with the further advantages of improved petrol consumption and increased tyre durability.
How a Sports Body is designed.
The secret of a successful body for sporting car work is a scientific interpretation of the laws of streamlining, which naturally involves an enormous amount of study. As may be observed from the frequent attempts of racing car manufacturers in bringing out modified forms or bodies, we have not yet got to the bottom of this most interesting problem, though for all practical purposes, the advanced designs of to-day are as near perfect as the general lay-out of the chassis will permit. At the same time, car owners will not sacrifice everything to the possession of theoretically perfect streamlining, for the question of appearance is important with the sporting motorist of to-day, so part of the business of the practical body-builder is to combine scientific construction with a pleasing outline, which will look smart and speedy without contravening the laws of wind resistance. In one of the photographs reproduced herewith (Fig. I), the method of designing racing bodies at the
works of Messrs. Jarvis & Sons, Ltd., of Wimbledon, is to be seen. At the back of the shop, a large drawing board will be noticed, upon which the full size chassis is drawn out and the actual lines of the body are actually drawn in the presence of the customer, which besides eliminating the usual drawing office delay, affords the prospective buyer an opportunity of forming an idea of what his car will look like and also enable him to make any alterations to the lines which he may desire.
As a rule, customers who own sporting chassis have very definite ideas on the question of streamlining, though naturally these have sometimes to be controlled by practical constructional details, in order to make the finished article capable of withstanding the stresses of the road or track.
The use of ” Plasticine ” Models.
Long experience of bodywork has proved that lines drawn upon a flat surface, though they may be perfectly accurate, do not always give an exact impression of the appearance of the finished body, and this drawback can be overcome by constructing scale models in Plasticine. Two of these models may be seen in the photograph reproduced as Fig. 2, and the nature of the material permits of alteration to any required degree by pressure of the fingers. Besides affording an ocular demonstration of the real shape of the proposed body, these models, which are one-fifth actual size, serve as a guide for the panel beaters and wood workers, so that in conjunction with the full-sized drawing these useful little models facilitate the constructional work in numerous ways.
Having determined the actual shape of the body with regard to streamlining and appearance, we now have to consider the constructional details, for in this department the whole secret of successful racing bodywork lies. The system employed in producing an ultra-lightweight body embodies a framework constructed of very light ash members, strengthened by ash cross-struts and
straining wires. Whereas, in the older methods of construction, the -rigidity of the whole body was provided by the use of heavy bottom runners, the modern sports body relies upon light but very rigid box girders, and the heavy body irons originally adopted are now substituted by light angle steel, which is actually much stronger. The streamline body is usually constructed of an extremely light framework of English ash, the longitudinal members and. cross hoops being cut and spliced to obtain the curves, instead of being bent in. the usual way. Where angles occur in the framework, the body is strengthened by corner chocks and by three-ply where curves exist. This forms a very rigid construction in readiness for the panelling, which in its turn gives additional strength, 20 S.W.G. aluminium usually being employed for the purpose. A body so constructed is exceedingly light and strong, and possesses the quality known as “liveliness,” which means that if the chassis whips, the body whips also and returns to its normal position with the chassis. The shell, or all-metal
body is liable to become distorted and strained, developing breaks and cracks after a very short life, when run at high speeds. It is desirable to arrange the seating position in relation to the height of the scuttle dash, so that the top of the latter is almost at the level of the driver’s eyes, and as close as possible to the steering wheel. This means that it is necessary to scoop out the last few inches of the scuttle, which has the effect of deflecting air currents over the driver’s head and down the head fairing, thus eliminating irritating “back neck” draught. The cut-away of the cockpit should be as small as the leg length of the driver will permit, and the sides cut to the shape of the arm when the steering wheel is held. It is important that this will allow a rest for the right arm of the . driver, and allow easy access for the gear and
brake levers. The staggering of the passengers seat is another point, and this should allow the passenger to sit nine inches behind the driver, so that his right shoulder is immediately behind the left shoulder of the driver.
Streamlining is not solely concerned with the bodywork proper, and the term ” streamlining ” as applied to sports cars is frequently a misnomer. ” Streamlining ” is quite a speciality and calls for accurate study not only of bodywork, but also of chassis details. This study happens to be a particularly pet subject of mine, and as the result of a somewhat extensive experience with racing bodies, I have found that big improvements have been obtained by extending the streamline effects to the undershield, front axle and wings. The results of fitting an undershield from the front to rear of a racing car give a most remarkable increase in all out speed, which could hardly be credited unless the tests were observed by the aid ‘of a stop watch. With regard to wing design, the Continental pattern of ” flaired ” wing appears to give the best results, but
at the same time, one has to bear in mind the necessity of keeping the occupants of the car normally clean. An alternative from the ” flaired ” pattern is the very narrow wing, having a distinct reverse curve at the back, which is now becoming very popular with certain types of sporting cars. These are only a few of the many features of the modern ultra-lightweight body, and can be employed with equal success for all types of body, from the single seater racing shell to the full-sized Pullman limousine. Thus it is possible for the sporting owner to improve the performance of his car to a remarkable degree by investing in a new body of modern design, which practice is frequently adopted by owners who have reached the zenith of tuning, and yet want a little more speed,