P'art of the day: Chaparral 2J "Vacuum Cleaner"

Todays p'art gave the team that invented it such an advantage over the rest of the field that it was banned after 1 season of racing.

The 2J was the maddest in a long line of progressively madder racing cars by Chaparral. It's party piece was a 45bhp snow mobile engine that powered a pair of 430mm fans at the rear of the car. These fans sucked air out of a large compartment below the car. This compartment was sealed from the atmosphere by sliding skirts made of lexan, which minimised ingress of air at atmospheric pressure.

This produced a partial vacuum under the car equivalent to 1/5th atmospheric pressure. As force is pressure divided by area the total downforce produced by this arrangement was about 500kg. This meant that while the engine only had to accelerate 820kg of car the force which forced the tires onto the road was 1320kg. This was also true during braking and cornering which allowed the 2J to lap a few seconds faster than its closest competitors, every lap. (The sliding skirts can be seen above and below)

Unlike typical racingcars which generate downforce relative to speed (an increase in downforce is the square of an increase in speed), the 2J generates nearly all of its downforce stopped because the snowmobile engine runs independently to the main engine. This graced the 2J with prodigious traction during standing starts, allowing the full might of its 700bhp engine to be unleashed with negligible wheelspin off the line.

Despite being far faster in qualifying and racing in general, it suffered from reliability issues, mainly overheating of the fan engine. These problems could have been solved through development over the course of the following seasons. Unfortunately the competition didn't like being hammered and complained about the use of the fans, saying that they were "movable aerodynamic devices" which were outlawed by the FIA although the car had already been approved. There were also claims that the fan threw up debris on the track, but these were largely unsubstantiated.