The Brabham BT55 was a Formula One racing car designed by Gordon Murray and David North for the Brabham team owned by Bernie Ecclestone.
It used a BMW four-cylinder turbocharged engine tilted over on its side to allow a clear supply of air to the rear wing.
The car competed during the 1986 Formula One season. It was not successful and its introduction coincided with the end of Brabham's time as a competitive team.
Murray left the team and went to McLaren, where his next car, the McLaren's MP4/4, is usually claimed to be based on the same principles and won 15 of 16 races in 1988.
By 1985, Brabham had reached the limit of aerodynamic development of their BT52-BT53-BT54 series of cars. The 1985 car won only one race, and Murray decided that a radical approach was needed. The rear wing of a Formula One car creates much of its downforce, but its effectiveness is reduced by the bodywork in front of it disturbing the flow of air. Brabham's tall, relatively heavy straight-four BMW M12 engine was particularly difficult to package to allow a good flow of air to the rear wing. Designers in the 1950s had addressed the same problem of reducing the cars cross sectional area by tilting the engines around a vertical or longitudinal axis by a small amount. Examples include the 1950s Kurtis-Kraft and Epperly Championship Cars and Colin Chapman's Formula One Lotus 16.Both the Brabham team and their gearbox supplier Weismann lay claim to the idea of doing this with the tall BMW engine in order to create a car with very low bodywork that would allow a large supply of air to reach the rear wing undisturbed and create more downforce. The driver was placed in a lying down position, as had been common in the 1960s, but had become rare by the 1980s. BMW designed a special version of their four-cylinder turbocharged engine with the engine block tilted almost horizontally (18° from horizontal).
Chassis and suspension
The car was also Brabham's first fully composite monocoque. Although the team had been the first in Formula One to make use of carbon fibre composite panels in the structure of the car in 1978, Murray had been reluctant to design a fully composite car until he understood how it would perform in a crash: he eventually persuaded Ecclestone to finance a fully instrumented crash test of a BT49 chassis. He was not happy to employ a two piece composite chassis, preferring to develop a technique which produced a seamless monocoque of carbon fibre/kevlar composite over a nomex honeycomb. This structure was reinforced, like his earlier designs, by machined aluminium bulkheads.
Engine and transmission
At Murray's request, BMW designed a special version of their M10 inline four engine. Differences from the standard upright unit were few, mainly concerning the oil scavenging system and the cradle in which the unit was mounted. Like the upright version the unit was not a stressed component. Mounting the engine on its side meant that the power takeoff from the unit, previously at the bottom, was offset to one side. A special 7-speed gearbox from American gearbox specialists Weismann was produced to deal with this.
The aerodynamic concept worked, in that the car produced plenty of downforce. However, this was matched by an unexpectedly high level of drag which limited the performance of the car. The tilted over engine and specially designed gearbox also produced many reliability problems. The team scored just two points all season, both by driver Riccardo Patrese.
The team's other driver, Elio de Angelis, was the first driver to die in a works Brabham when he was killed in an accident while testing at the Circuit Paul Ricard in France. The car survived the accident relatively intact and de Angelis had only minor injuries. There were very few track marshals at the circuit and he was trapped in the car and killed by oxygen deprivation due to a fire before they arrived. He was replaced by Derek Warwick, reportedly the only top level driver who did not call team owner Bernie Ecclestone to ask about the drive.
Murray has since summarised the reasons for the car's failure: "...I was much too ambitious in how much we lowered it. The rather tall BMW had to lie down so far it produced a heavily offset crank needing a special gearbox and drivetrain, and what I did wrong was to try to do it in the time available.
Secondly, the engine never worked properly in the lay down position. The exhaust and turbo system was a nightmare and it had incurable oil surge and drain problems in corners. One way it was OK, but not the other.
The weight distribution gave dynamic centre of gravity movements that messed up the traction.
And then Bernie [Ecclestone, owner of the team] who is totally non-technical and had always left that side completely to me, started to get involved on the technical side. We had had 16 years with never a cross word until then, and things were changing with his deeper and deeper involvement in [the Formula One Constructors Association]. Then McLaren made approaches to me and I just felt it was the end of the road at Brabham."
Murray left the team at the end of the year to join rivals McLaren. His 1988 car, the McLaren MP4/4 is usually said to have been based on the BT55 concept, although McLaren team manager Jo Ramirez has downplayed Murray's involvement in the design of the MP4/4. The lying down driver position has again become the standard in Formula One since 1988.
Brabham regrouped with the much more conventional BT56, but had to re-use the tilted over BMW engine and gearbox as the German manufacturer, already reducing its involvement in Formula One, had sold the supply of conventional engines to Megatron for use by other teams. BMW pulled out of Formula One altogether at the end of 1987, and the Brabham team missed the 1988 season.
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