Body Shape Evolution

  The body style evolution has had a strong impact on aerodynamic performance，andtherefore maximum speed.

    We must avoid, first of all，the prejudice that aerodynamic performance was neglectedon the first cars, as the squared shapes of older vehicles seem to suggest.

    The problem of reducing aerodynamic drag was already studied by ship engineers; as amatter of fact the first experiments were not made in wind tunnels but in water channels.The shapes developed were very ingenuous for the lack of suitable experiments.

    Many old cars witness attention to aerodynamic drag；among them the JamaisContente（speed record of 106 km/h in 1899）and the Alfa Romeo 40/60 HP of EarlRicotti，are shown in Fig. 2.17. Both bodies were designed according to the slender bodyshape that presents minimum drag at a large distance from the ground. Later ．it wasdemonstrated that ground proximity requires the body shape to be slightly curved. Theseshapes were premature, in consideration of effective needs and aesthetic tastes of thosetimes；in addition they were completely unsuitable to build-up a vehicle and were notfollowed by similar examples. To document the evolution of shapes we will refer forsimplicity to a single manufacturer, looking at different sedans produced by FIAT.

    A first period of time may be identified at the beginning of the motoring era, from1899 to 1915，where shapes were squared，especially in the front area，where the hoodjoined with a flat dash board and windshield without any kind of rounding；an example ofthis form is the 35/45 HP of 1908，in Fig. 2.18 at upper left.

    This form is partly influenced by the fashion, coming from horse-driven coaches andexisting fabrication technologies，that did not allow very rounded shapes; in addition, afully functional approach did not consider yet the integration of engineering solution andtechnologies.

    The next period may be set between 1915 and 1930 and the 501 of 1919 can beassumed as its emblem；this car is shown in the same figure at upper right. Shapes arenotably more rounded and show an aevolution coming from the adoption of steel sheetsworked essentially with roll or bending press.  A‘torpedo’shape provides foruninterrupted lines，connecting the radiator with the car back.

    Fenders assume an aesthetic value and are made with round shapes integral withrunning boards；in addition, they are used to cover mechanical parts under the floor，stillpositioned at a notable height. Fenders are produced by beating steel sheets on openwooden stamps manually. The hood is part of the same surface of the body sides；theradiator also is rounded at its edges. Frameworks surrounding body panels have alsodisappeared because of the abandonment of the wood.

    The overall aspect still recalls the horse-driven coach，but details do not. This style isstill present at the beginning of the 1930s；a breakpoint might be represented by the 1934508 sport； this body is the result of the first aerodynamic experiments，partly performed inan airplane's wind tunnel，partly on the road directly. It was determined, for example,that a slight inclination of the windshield could increase vehicle top speed by 5%，around avalue of 100 km/h.

    Similar.otudies were performed in other parts of the world during this period；weremember in particular the experimental studies of Lay，published in 1933 in Germany,about the influence of different  shapes on aerodynamic drag.  The  famous，butunsuccessful，1934 Chrysler Airflow is the starting point of this new style.

    We see in the middle of Fig. 2.18 at left the appearance of the 508 Sport. Hood，passenger compartment and trunk are integrated in a single volume；windshield andradiator grille are inclined. Also windshield frame is rounded. The body is tapered in theside and upper view and shows a very long tail；fenders start merging with body sides. Forthe first time the drag coefficient is well below 1. 0. This is also one of the first examplesof the integration of trunk with body；in previous cars it was an add-on attached to theback of the body. A further evolution of styling rules developed for this sport car was theirapplication to a series produced car，the 1，500 sedan of 1935，in Fig. 2. 18 in themiddleright. To stylistic features of the 508 more details were added，as head lights built intofenders and rounded disc wheels. The drag coefficient of this car was about 0. 5，less than0.7，the average value obtained with former more traditional shapes.

    The passenger compartment is wider and has replaced part of the space previouslytaken by running boards，that now are a style decoration only; they are no morenecessary，because the adoption of central beam chassis frames and independent frontsuspension have notably lowered the floor height.

    Lowering the body has also made the body more vulnerable；the increased trafficdensity suggests introducing bumpers at the front and rear ends. We can identify the‘ponton'body shape in the 1，400 of 1950，at the bottom in Fig. 2.18，still in use onpresent bodies. Characteristics of this new style are the disappearing of separated fendersand running boards and the full integration of head lights. The passenger compartmenttakes all the space available between the wheels and the very rounded shapes，con cealinghighly efficient space frame structure；the reduction of drag coefficient is not so high as forthe previous generation.

    The reduction of drag coefficient in connection with evolution of the body style isdocumented by the diagram in Fig. 2. 19，where the best and worst measured values are

reported as function of the model year decade. The measurement was made recently onfull-scale cars in the same wind tunnel.

    The following body styles have not always brought big reductions. The 1970s oilenergy crisis has renewed the interest about more stream lined forms；the performanceincrease is not only caused by an evolution of the base form of the body but due to theoptimization of many small details of the external surface and the underbody.

    The most showy feature of new styles is the integration of bumpers and the alignmentof the glass surface of side windows with the body surface; this last feature is the result ofa totally different organization of body shell components in the roof area.

    A notable improvement was introduced in the 1970s and diffused gradually on allsedan bodies; it is still adopted in contemporary cars. It is shown on the right of the figureabove.

    The roof is welded along a section more inside of the body side surface；thereinforcement is welded along the same section and the wending is concealed by anaesthetic coverage.

    The door side is now aligned to the roof without discontinuity.

    The glass weather strip is completely modified (please notice that weather strips arerepresented with their natural shape，not deformed by the closure of door or side windowglass) and allows the glass to be almost aligned with the body side surface.