Alfa Romeo B.A.T.: the Story of the “Berlinetta Aerodinamica Tecnica”

Prof. Grandi looks back over the style genesis of the three prototypes that Franco Scaglione made for Bertone on the 1900C chassis. The aim was to amaze the motor show audience and the Alfa Romeo management with solutions born from the Tuscan designer’s simple mathematical application of principles and solutions to reduce aerodynamic drag

Words and Drawings Massimo Grandi

In 1950, Alfa Romeo made its début with the 1900, a four-door sedan. This was a milestone in the Milan-based company’s history, as it was the first Alfa Romeo mass produced on an assembly line, the first Alfa Romeo ‘unibody’ and the first Alfa Romeo with standard left-hand drive.

  The car met with some success among the specialised press, but some of the Alfa customers wanted more power and the gear lever on the floor. On the other hand, the coachbuilders complained that it was impossible to fit out custom builds because of the unibody frame. Finally, neither coupé nor cabriolet versions were planned.

And so, to meet these needs, less than a year after its launch Alfa Romeo presented the 1900C chassis (the C stands for "Carrozzieri", “coachbuilders”) on which Touring and Pinin Farina built the coupé and the cabriolet which were added to the price list and sold directly by the network of Alfa Romeo dealers, called the 1900C Sprint and 1900C Cabriolet. The same chassis was rebodied by many other coachbuilders, more or less successfully.

The wheelbase on the 1900C was shortened by 130 mm, from 2630 to 2500 mm, and the 1884 cc engine was fitted with a Weber 40 DCA3 dual-body carburettor, larger intake and discharge valves, respectively from 38 to 41 mm and from 34 to 36,5 mm, with the compression ratio increased from 7.5:1 to 7.75:1 to reach 100 HP at 5500 rpm. Axle tracks: front 1320 - rear 1320 mm.

Bertone also worked on the new 1900C chassis, asking Franco Scaglione to design a car on which to experiment new solutions aiming to minimise aerodynamic drag while amazing the motor show audiences, and especially the Alfa Romeo management, with his pioneering design.

Scaglione was an enthusiastic aerodynamic scholar, and his designs were always based on the application of aerodynamic solutions and principles, and here Scaglione’s mathematical approach to design is similar to other great designers of the past, including Jaray, Komenda, Sayer and Savonuzzi.

And thus, the first of three cars marking car design and car history was born, the B.A.T. 5 (Berlinetta Aerodinamica Tecnica no. 5).

The B.A.T. 5 was a revolutionary car, the result of Scaglione’s talent: under the supervision of Ezio Cingolani, head of design development and production, he perfected the concepts inherited from aeronautics that he had previously expressed on the Abarth 1500 Biposto. This car, presented at the Turin Motor Show in 1953, aroused the wonder and curiosity of all the visitors. In fact, it was an authentic mobile experimental laboratory, its fantastic forms being none other than Scaglione’s mathematical application of aerodynamic principles and solutions. No element of its design was a self-referential end unto itself, there was a reason and function for everything in terms of aerodynamic performance. Starting from the main lines marking its side profile, designed based on geometric patterns including ellipsis, parabola and hyperbole, mathematical solutions responding to precise needs of maximum penetration and minimum drag.

But Scaglione’s solutions were already applied to the bonnet design and modelling, characterised by a large double air intake between the extended bumpers, without the typical triangular Alfa Romeo grille, replaced by a metal "nose" built into the body.

Here we see the upturned W solution, previously experimented and applied to the Fiat-Abarth 1500.

In front-engine cars, the air for cooling the radiator water is forced to pass through the grille, filtering through the very narrow gaps in the radiator to be centrifuged by the fan, when forced around all the elements and protrusions in the engine compartment and colliding with the rear bulkhead, leaving through the only exit point at the bottom between the bulkhead and the engine.

  The upturned W design responded to the need to rationally convey the huge flow of intake air in the engine compartment to minimise the turbulence on the front and inside the engine compartment, also through the large air discharge apertures behind the front wheel arch.

  A similar solution would also be applied by Scaglione to his Ferrari-Abarth 166 built by Scuderia Guastalla.

In the B.A.T. 5, the central headlight of the Fiat-Abarth replaced a “nose”, but the design was identical and this arrangement could later be seen in the 1961 Ferrari 246 P and 156 F1 and again in the 2013 Ferrari “La Ferrari”.

The most eye-catching part, however, which captured the public’s imagination, is certainly the tail, which has a huge window divided into two parts by a thin metal strip, a concept later borrowed by the Chevrolet Corvette Stingray.

  And especially the two large fins almost as high as the roof, each with a slit and curving inwards.

In fact, these fins were far from sci-fi or pure fantasy, they were the result of a strict, thorough aerodynamic research. To understand this, we have to start from the beginning, that theoretical shape with CX equal to 0.0, the so-called “ elongated drop”.

This solid allowed the fluid stream to flow perfectly adhering to the surface, without creating any turbulence. The problem of practically applying this shape to a car lies in its proportions, which require a length around five times the width. Starting from the minimum width of a two-seater car, the final length of the car would be at least seven metres. The engineer Kamm had solved this problem if only in part using the famous K-tail, while Scaglione sought a solution for the pavilion of his B.A.T. 5 using these large fins.

  In this drawing we can see how the pavilion of the B.A.T. is shorter than the virtual pavilion (in red), causing the fluid stream to become detached more or less at the height of the rear pillars. Introducing these large concave fins, the fluid stream was forced to realign to the virtual profile of the elongated drop.

The operational diagram of these fins is even clearer in the second drawing.

So these amazing lines and shapes were merely the result of an aerodynamic solution that obtained a Cx of 0.23, which allowed the car to reach a maximum speed of 200 km/h, over 30 km/h more than the 1900 C SS with the same 100 hp engine. At that time, Bertone didn’t have a wind tunnel, and to obtain the precious aerodynamic information necessary for the design, they used a system commonly used at the time based on some woollen yarns. These were applied to the bodywork of the cars driven on the road at different speeds and photographed by another car driving alongside to observe the movements of the woollen yarns in the wind.

In the second experimental car, the B.A.T. 7, the solutions adopted in the B.A.T. 5 were developed further.

In the B.A.T. 7, the general profiling of the whole front part was further extended and lowered by 70 mm. Here too we see the double front air intake which had the task of “guiding” the air flows in the engine compartment in a more regular manner. As seen for the B.A.T. 5, the air flows have an escape route through two apertures on the sides of the car just behind the wheel housings and in front of the rear bulkhead. In the B.A.T. 7, having eliminated the fan, given the exceptional nature of the car, Scaglione adopted two continuous tunnels running from the front air intake to the side discharge vents.

The radiators were placed in the tunnel in order to avoid parasite turbulence in the engine compartment. As with the B.A.T. 5, the four wheels were completely faired, the finned air vents of the radiator cooling tunnels were integrated into the front casings, while those in the rear had the profiled shape of the air intakes for the brakes.

As concerns the design of the side of the B.A.T.  7, with the casing integrated flush to the body, the inevitable “weight” of the side panel is resolved exceptionally by a balance of solids and voids, a perfect hyperbole drawing the finned air vent of the radiator cooling tunnel here too, a hyperbole that splits into smaller parts in the shaped profile of the rear air intake for the brakes.

The upper arm of the first hyperbole runs perfectly horizontally along the whole length of the door, recalling the horizontal arm of the smaller hyperbole running along the rear mudguard to draw another hyperbole represented by the opening for the exhaust pipe.

The curved design of the large windscreen is also very interesting, joining the 45° angle of the side windows to the 30° inclination of its midline.

Also in the B.A.T. 7, the most eye-catching part is the rear, where the concave fins are even larger and rounded, indeed in the collective imagination they are reminiscent of the huge wings of the manta ray.

In fact, the increase in surface area and therefore the size of the fin terminals is due to the fact that, increasing in height in the front, these had unwillingly moved the centre of pressure forwards, and this could only be compensated by increasing the rear surface area; in any case, in the B.A.T. 7, the function of the fins in the reconstruction of the virtual elongated drop was even more evident, and this further aerodynamic development of the rear fins gave it the lowest Cx value of the B.A.T. series, 0.19.

  The B.A.T. 7 was presented at the 1954 Turin Motor Show, and like the B.A.T. 5 it aroused great amazement and admiration. Two years after the B.A.T. 5 and one after the B.A.T. 7, the 1955 Turin Motor Show saw the launch of the B.A.T. 9.

For this car, Nuccio Bertone asked Franco Scaglione to develop the aesthetic concepts of the B.A.T. 5 and 7, again on the Alfa Romeo 1900C chassis, to try to make it more similar to a car suitable for mass production, without however ceasing to amaze the motor show audiences and Alfa Romeo, which that year had planned to launch the Giulietta sedan and had begun working with Bertone to build the Giulietta Sprint bodies.

The B.A.T. 9 of 1955 was in some way different from the formal and conceptual path of the previous models. Here too, due to the direct intervention of Nuccio Bertone, the project aimed mainly to show how the developments of the B.A.T. project could lead to large-scale car production.

Although developing the style code of the previous models, the B.A.T. 9 had far more subtle lines, just think of the rear fins: on the B.A.T. 5 and B.A.T. 7, these were very large and ostentatious, while here they were reduced to two far more discreet metal strips. Bertone abandoned all the most extreme features of the previous two cars, turning them into features that were more suited to normal road use: the non-retracting front headlights were now located on the bumpers. For the first time, the classic Alfa Romeo badge adorned the front of the car.

  It is important to underline this “diversity of intentions” to better understand the formal solutions of the three cars in a comparative analysis. In the B.A.T. 9 we find all the elements characterising the two previous models, but in a more reduced form. The rear ellipsis is more open, and the shorter side profiles, originating from the rear cut of the door and with a constant progression parallel to the belt line.

A particular feature of the B.A.T. 9 is the ribbing and beading running along the whole side of the car, at the rear maintaining a straight horizontal line deviating from the narrow profile of the fairing, almost as if forming other horizontal fins. Setting out to maintain a low aerodynamic drag, the bodywork kept the large front and rear overhangs, faired wheels (only at the front), a very sleek “drop-shaped” passenger compartment with less angled side windows compared to the body and a large panoramic windscreen with an upturned pillar integrated perfectly into the almost-flat pavilion.

The large air vents behind the front wheel arches also disappeared. One curious thing about this car was Bertone and Scaglione’s decision to eliminate the fairing on the rear wheels but not the front ones. In fact, doing the opposite would have significantly narrowed the front of the car where the fairing, having to leave room for the wheel movements on the vertical axis, caused an inevitable swelling. The two solutions are compared in this drawing.

  Of course, there must have been objective reasons for this peculiar solution, but to be honest I have no idea what they might have been. At this point we can look at these B.A.T.s for a comparison of their similarities and differences.

  We have already examined the more general aspects the three models have or do not have in common, but it is perhaps interesting to underline the different solutions Scaglione applied to the front headlights. Aiming to eliminate sources of air flow disturbance at the front of the car, in the B.A.T. 5 and 7 the headlights are fully retracting in the B.A.T. 5, incorporated in the internal face of the bumpers. In the B.A.T. 7 they are again retracting, but are placed inside the two air intakes near the central “nose”. In the B.A.T. 9 on the other hand, the headlights are fixed and on show, but integrated into the bumper profile with a Plexiglas casing.

Another special aspect marking the three designs is the pavilion. Talking about the pavilion design, Scaglione stated, “It is certainly the hardest part, both due to the insufficient elongation ratios and the interference that this creates in the fluid stream on the main fairing”. The solutions on the rear of the pavilion are particularly interesting, with the window and the central stabilizer fin with a different design for each of the three cars. As with the Fiat-Abarth 1500, the window is again very wide and divided into two parts. In the BAT5, the rear pavilion is particularly long, and tapers to create a kind of thick central fin with the two parts of the rear window running from the rear pillars almost to the top of the pavilion.

In the BAT7, on the other hand, also in the longitudinal section the pavilion forms a more specific drop shape, connecting to the main fairing with a concave profile that continues onto two large curved fins which, separating the two parts of the rear window, create a thin yet evident central crested fin, limiting the formation of parasite turbulence created by the meeting of the two masses of air running along the sides of the pavilion as far as possible. In the BAT9, these forms are “normalised”, recalling more the BAT5 solution but in a smaller size. The pavilion follows the drop shape to the rear, regularly tapering into a just-hinted thin fin shape, with the two trapezoidal rear windows on the two sides.

As explained above, the drop-shaped pavilion requires rear fins to overcome the insufficient length of the pavilion. As we can see, this special function of the fin requires that it be located in the point in which the fluid stream becomes detached from the curve of the pavilion, but in fact it is also necessary for the fin to be progressively aligned along the side of the pavilion both before and after the point in which the stream becomes detached.

These aspects can be perceived immediately when looking particularly at the B.A.T. 5 and 7. In both profiles, the fins start at the height of the front edge of the door, rising progressively and following the sides of the cars and ending on the edge of the rear coupling. The concave-convex section of the fins creates a channel between the fins and the sides of the pavilion, drawing a kind of open ellipsis at their ends, which in the specific case of the B.A.T. 7, seems almost to close definitively. In the B.A.T. 9 we find all these elements, yet in a reduced form. The rear ellipsis is more open, and the shorter side profiles, originating from the rear cut of the door and with a constant progression parallel to the belt line.

So, as we have seen, while the B.A.T. 5 and 7 seemed to be two authentic mobile experimental laboratories, with the B.A.T. 9 the designers attempted to translate these experimental elements into a formal synthesis suited for a car produced on an industrial scale.

Clearly an experiment, the B.A.T. 9 was never produced in series, but overall these three technical aerodynamic berlinettas contributed enormously to aerodynamic studies applied to cars, and the ability of these applications to generate new and advanced formal languages, as all Franco Scaglione’s works demonstrated to the full.

--

Massimo Grandi, architect and designer, previously director of the Car Design laboratory at the Design Campus of the Department of Architecture at the University of Florence. Member of the ASI Culture Commission. Among his published works: “La forma della memoria: il progetto della Ferrari Alaspessa”, “Car design workshop”, “Dreaming American Cars”, “Ferrari 550 Alaspessa: dall’idea al progetto”, “Quando le disegnava il vento”, “Il paradigma Scaglione”, “La più veloce: breve storia dei record mondiali di velocità su strada” (with others).