Exterior Design and Aerodynamics

Sporty Scandinavian Design

• Well-proportioned, ‘bespoke’ design
• Sporty styling with Scandinavian design flair
• Coupé looks (roof up), roadster-like looks (roof down)
• Fully automated soft-top sets new standards for class
• Unique ‘Surround Trim’ delineates passenger cabin
• Unique ‘CargoSET’ self-expanding trunk feature
• Competitive 0.34 Cd with reduced lift forces

The impressive looks of the Saab 9-3 Convertible radiate power, sporty performance and great strength; all elegantly packaged with a Scandinavian design flair that ensures the lines are clean and flowing, but never cold or clinical.

As an indication of the success of the overall design, this is an open top car that looks like a unique model in its own right, free from any awkward styling compromises. Furthermore, the car looks just as good, top up or top down - effortlessly exchanging the looks of a sporty coupé for those more akin to a roadster.

The automatic soft-top operates entirely at the push of a single button. It incorporates three innovations and new performance standards for the class, including its speed of operation and means of deployment.

Exterior Design
Saab has been a leading player in the premium convertible segment since exhibiting its first open top car as a design study in 1983. It has been a driving force behind the growth of the segment by demonstrating that a car built for the pleasures of open air driving can also accommodate four adults as a practical, all year round means of transport.

The current model; breaks new ground for Saab in being developed as a separate but parallel project to the Sport Sedan, with many of its design team working on both projects in tandem.

Testimony to the essential ‘rightness’ of the final design is that the Convertible and the Sport Sedan share the same frontal bodystyling, even retaining the same rake angle for the windshield and A-pillars.

The deep, prominent evolution of the Saab grille adopts a theme first seen on the Aero X concept car. This is complemented by sweeping headlamp units that incorporate a thin ‘eyebrow’ lighting zone designed as a brand specific ‘signature’ feature. These units culminate in an upswept rear edge, introducing a Saab design theme from the 9-5 range and classic 900 model. The grille’s central wing motif is retained as a reference to Saab’s aircraft heritage..

The frontal styling sees the adoption of another Saab signature feature: a ‘clamshell’ hood, closing across the top of the front wings. The hood pressing incorporates a sweeping, U-shaped styling line, as first seen on the Aero X, which echoes the curvature of the windshield.

The swept-back frontal lines are complemented by a front bumper and splitter assembly with a deep, trapezoidal air intake, even more pronounced on Aero versions. This is flanked by deep black vents which are framed, like the grille, in a matte chrome finish. As with the Aero X concept, these represent a metaphor for the intakes of a jet engine.
In profile, the clean wedge line is typically Saab and, top down, the shape is no longer interrupted by a tower to mount the front seat-belts. The styling of the rear deck is particularly neat because the pop-up roll bars and retractable rear head restraints are beautifully streamlined by twin fairings, giving a subtle hint of the Convertible’s sporty character. The color-keyed tonneau cover is, of course, flush fitting.

Top up, the car assumes the persona of a coupé, an impression reinforced by the extremely smooth, taut lines of the soft-top and its step-less integration with the windshield header rail.
The rear of the car features large light clusters whwith frosted, white lenses, a design theme similar to that used on the Sport Sedan and SportCombi.The glass rear window is heated and the trunk lid opens through 120°, even with the top up, for good trunk access.

A new design feature, never seen before in Convertible styling, is the introduction of a distinctive Surround Trim, marking the transition zone between the car’s exterior and interior. It is a U-shaped line that extends rearwards from the base of each A-pillar, incorporating slim panels along the top of the doors and rear side trims and most of the tonneau cover.

This line integrates the front and rear passenger areas, visually uniting the only top exterior surfaces that ‘come inside’ when the top is up. The Surround Trim is always matched with the external color choice..

Class-leading Soft-top
The Convertible’s soft-top and tonneau mechanism features three innovations: CargoSET automatic storage well retraction, a two-step tonneau action for quicker deployment and a light-colored interior headlining. It is undoubtedly one of the car’s most impressive features.

A well-engineered roof is essential for good weatherproofing, insulation and noise refinement. It must be strong, snug-fitting, quiet when up, quick and easy to operate, good looking and extremely reliable.

For its latest Convertible, Saab specified a completely automatic, ‘state of the art’, soft-top operation, requiring no manual involvement beyond pressing a button. The roof is hydraulically-powered, with automatic self-latching to the windshield header rail, and deploys fully in just 20 seconds with the engine running, making it among the fastest in its class. It can be reliably operated in strong winds and, in an emergency, can even be raised while on the move at speeds up to 30 kph (20 mph).

The materials for the triple-skinned soft-top are also improved, with the addition of a thicker, fleece middle layer for good heat and noise insulation. The outer skin is made of an extremely tough, canvas/butyl(rubber)/canvas, weatherproof, woven fabric and the inner textile skin forms the interior headlining. There is an exterior color choice of black, blue or beige.

To save weight, the soft-top’s frame, the swivelling braces and the large padded front rail which connects to the windshield header, are all made from magnesium. To ensure robustness, steel is used only for the soft-top's pivoting side brackets.

Great attention has been given to effective sealing in order to prevent drafts, water leakage or intrusive wind noise. A small gutter has been sewn into the side of the fabric to prevent any water droplets dripping down on to the seats when a door is opened. Excellent sound insulation means that occupants can listen comfortably to the audio system or chat easily with the top in position at speeds up to 200 kph (125 mph).

Looks in this class of car are even more important than functionality and the soft-top has a taut and smooth appearance, more like that of a fixed roof on a coupé. This has been achieved by the use of six, instead of five, swivelling braces (or bows) on which the fabric is mounted. As the distance between each brace is reduced, there is less sagging of the material and, once in position, the whole soft-top is finally tensioned by locking braces at the rear, instead of the front, which helps stretch the fabric even tighter.

Interior looks have not been overlooked, either. With the roof up, convertibles are often criticised for being rather gloomy or claustrophobic inside because of the usually black headlining. Saab has now addressed the issue and the 9-3 Convertible is first on the market to offer a light colored headlining for all interiors.

The operation of the tonneau cover - made in aluminium to save weight - is another Saab ‘first’. Automatic soft-top systems have previously required the tonneau cover to be hinged at the rear. For quicker roof deployment, the Convertible's tonneau now features an extremely elegant, two-stage operation, being completely raised horizontally and then moved rearwards, parallel to the top of the trunk.

Whilst it is an action that is intriguing to behold, it offers real benefits. Tests have shown this to be a quicker and more efficient means of allowing clearance for deployment of the soft-top. Pulling the tonneau down flat, instead of hinging and latching it closed, is also a more robust operation that contributes towards improved reliability and better seating and sealing.

The final innovation is a practical feature: raising the roof automatically raises the capacity of the trunk. The CargoSET (Self-Expanding Trunk) feature directly links the soft-top’s rearmost hinge mechanism to the flexible, ‘concertina’ storage well in the trunk. When the roof is in position, the well is therefore fully retracted, releasing useful additional storage space. It is a simple mechanical action that eliminates the need to manually hitch up the well with straps or rods. When the roof is stowed, there is still enough room in the trunk to accommodate two golf bags.

The design and operation of the Convertible’s soft-top is a masterpiece of precision engineering. As an indication of the demanding requirements involved, the roof, which is more than two meters long when fully extended, locates at the windshield header to a lateral tolerance of just ± 2 mm, equivalent to a remarkable 0.001 per cent margin of error!

Real World Aerodynamics
In the field of aerodynamics, the performance of Saab products is optimized for real world conditions, in the same way as Saab has developed its ‘real life‘ safety strategy.

The first question about the aerodynamics of a new car always relates to its coefficient of drag. Important, of course, but in everyday driving conditions it is seldom a major factor for long enough. A shape that cleaves the air as efficiently as possible is, of course, important but good high speed stability, excellent weatherproofing, low wind noise inside the car and optimised fuel consumption are also areas where the aero team has an input. Simply quoting a Cd value hardly does their work justice.

For instance, a great deal of time was spent testing for yaw behavior and stability in cross-winds at different speeds and angles. It is also important to know how a car behaves when passing or being passed closely at speed by large vehicles, as well as how much and where any grime builds up on the car. Questions that are best answered by testing in real road conditions, outside the laboratory.
The Convertible’s roof-up drag coefficient is a class competitive 0.34 but, probably more important, major strides have been made in improving high speed stability by keeping rear lift forces low and consistent.

Smooth airflow
A smooth airflow over, around, through and under the car is important, with particular attention paid to points of flow separation at the rear in order to reduce the size of wake turbulence and improve stability. Here the focus was on the shaping of corner radii and the curvatures at the rear of the roof and the sides of the car..

The behavior of the Convertible’s roof, particularly its effectiveness in resisting ‘ballooning’ at speed and in its seating on the side windows was closely studied. As there is no monoside upper door closure for a Convertible, the effect of the windows being ‘sucked’ outwards, by the difference in outside and inside air pressure, with undesirable consequences for wind noise, had to be addressed. It is actually the same effect that causes 'ballooning' or flapping.

At the front, the rear edge of the hood lid ‘kicks up’ to smooth the passage of air on to and around the windshield. Its traditionally deep curvature also reduces the acceleration of the airflow as it approaches the A-pillars, which have a flattened radius where they connect to the windshield to minimise airflow disturbance and wind noise. The bottom edge of the door mirror casings is also extended rearwards by 5 mm to help reduce the likelihood of road grime build-up on the mirror surface.

Good airflow management even plays a safety role. The ‘wraparound’ rear light clusters have an optimized corner radius that gives a distinct separation for airflow from the side of the car. Careful shaping of the angle actually helps the air ‘turn the corner’ first before it separates. This creates a flow over part of the light clusters, helping to reduce the build up of road grime, which can impair the visibility of the lights.

Airflow is also designed to keep the windows of the car as free from grime as possible. For example, the door mirror casings have a small spoiler-like profile in the bottom surface to reduce contamination of the side windows.

Underneath the car, airflow management is becoming an increasingly important area for ‘fine tuning‘ and the aero team concentrated their efforts where the return is greatest. A small spoiler ahead of the front wheels has been carefully shaped in the wind tunnel to reduce drag and the forward lower link of the rear suspension has also been aerodynamically shaped to reduce wind resistance and minimize the accumulation of road grime on the wheel rims.

Airflow under the hood, within the engine bay and at the bottom of the front footwells was also closely scrutinised. Shielding of the ‘exhaust’ air from the cabin air conditioning reduces disturbance where it exits behind the rear wheel-arch.

Testing
As evidence of the close liaison between the aero and design teams during development, it was possible to test up to 70 different body variations in one-fifth scale during a single eight hour shift in the Stuttgart University wind tunnel, where most of the optimization work was carried out. This is only possible by having a modeller on hand and a number of moulds prepared in advance. In this way, a large number of suggested changes can be investigated quickly to meet aerodynamic targets.

After this work was completed, the team moved to full-scale testing on a rolling road. Further wind tunnel work was also carried out at the Motor Industry Research Association (MIRA) in the United Kingdom and in Detroit in the United States, for wind noise suppression.

Advanced CFD (Computational Fluid Dynamics) modelling now replaces a great deal of laborious work in the wind tunnel and also allows faster, more effective communication between project team members. For example, CFD played a vital role in the visualization of airflow and speeded up optimization work in the wind tunnel.

CFD was also the main tool for managing internal airflows: in the engine bay to control heat build-up and in the passenger compartment for best possible comfort.

Next page: Interior