Good things come to those who wait: as far back as the early 1990s, when developing the cabriolet variant of the E-Class of that time (W124), the Mercedes aerodynamicists were looking for ways to reduce turbulence in the interior in order to give all passengers a true open-air experience without the all-too-annoying draught. The project was called KOF4 – from the German for ‘comfortable open-top driving for 4’. They tinkered for some two years before the project was finally shelved in 1992.

People today who see the pictures of the variants tested in the 1990s quickly understand why the company management gave KOF4 the thumbs down: the various draught-stop combinations, which could be mounted on the windscreen and behind the rear seats, looked too clumsy. As ever, the engineers had been very thorough at the start of the project: the basic principles were tested on an A124 prototype in the wind tunnel. The result of these tests is still valid to this day: the only way to achieve the desired effects is to combine a wind deflector at the front, including controlled airflow to elevate the flow, with a draught-stop behind the rear seats. Showing typical Swabian thoroughness, the engineers then tested numerous profiles, louvres and flap solutions to optimise the effect and minimise the amount of installation space required. Their conclusions: satisfactory functioning, but inadequate aesthetics and controllability. The technical design was not yet advanced enough and the components not yet small enough for KOF4 to go into series production.

Shelved but not forgotten: ten years later, in July 2003, the KOF4 project was resurrected for the new E-Class Cabriolet. A specifications book was drawn up, and initial test drives took place as early as November of that year with a louvred variant. The designers tested an active solution, deciding on a pivotable variant. But they were quick to realise that the result did not meet the Mercedes requirements for quality and design.
But Mercedes engineers are nothing if not persistent, and the project was revived again as early as October 2004. This time, they looked at a “snap-on” solution; however, this solution did not deliver the desired success in terms of easy handling. Detailed aerodynamic investigations in this project phase revealed that the KOF4 objectives were achievable: significantly enhanced comfort in the rear seats and no adverse effects for the front passengers when compared with the conventional bracketed draught-stop.

The fourth attempt, which began in late 2005, finally brought the breakthrough: a wind deflector which is retracted into the windscreen frame when not in use, complemented by an adjustable draught-stop between the rear head restraints. A great many design challenges still had to be overcome but, a good four years later and almost 20 years after the first idea, and after non-stop hard work characterised by dogged determination, KOF4 is now going into series production in the new E-Class Cabriolet. Now the roof made of air has a new name – AIRCAP® – to tie in with the name AIRSCARF® used for the neck-level heating system. Now the ‘cap and scarf’ are available as an option for four-seater cabriolets made by Mercedes.

Source: Daimler AG