2014 Analysis: Stepped chassis

Step-bulkhead

If the nose tip regulations have caught everyone’s attentions, probably just as influential but hidden is the front bulkhead regulation. For 2014 the front A-A bulkhead is placed some 100 lower, down to 525mm form 625m. As the bulkhead is a fixed external cross section, this created an unavoidable obstruction for the airflow passing under the raised chassis.

The bulkhead (yellow) is 100mm lower than the old one (dotted). It expected to lead to a gently sloped chassis

The bulkhead (yellow) is 100mm lower than the old one (dotted). It expected to lead to a gently sloped chassis

This change was part of a package of rules around the front end to reduce the overall nose height for safety reasons. It’s understood the FIA wanted an even lower bulkhead height, but this would necessitate completely new front suspension geometry for the teams and it thought this were too big a change alongside the other 2014 regs. Thus a compromise to bring the bulkhead into line with the cockpit sides dimensions, such that the bulkhead is no lower than the cockpit opening for safety in event of a T-Bone crash.
As with the nose tip rules, the rule makers probably envisaged the teams sloping the entire front of the chassis from the cockpit opening down to the front bulkhead. Of course the team don’t think in the same way as rule makers and workarounds have been found to minimise the aero obstruction. For many years the rules have applied a linear taper to the section height between the front and cockpit bulkheads. But this is only specific section height any one point, the overall shape can curve as long the section height tapers linearly. Teams have exploited this in the past by sloping the chassis up from the cockpit opening (550mm) to the maximum height (625mm).

With a stepped chassis, the bulkhead stepped up to the max 625mm chassis height, leaving a step between the nose and chassis

With a stepped chassis, the bulkhead stepped up to the max 625mm chassis height, leaving a step between the nose and chassis

This same loophole is now being applied to the chassis height at the front bulkhead, so the bulkhead is fixed at 525mm but slopes up to the maximum height in the space of 100-150mm, creating a stepped chassis. This approach can be evidenced by the top of the chassis ahead of the cockpit opening being a flat surface running at a horizontal angle.

Although the step on the top of the chassis is most evident, there is a corresponding step underneath too. Doing this creates the maximum height under the raised chassis, with just the step interrupting airflow.
Another benefit of the stepped chassis is that the front suspension mountings can be almost the same as in 2013, as there remains chassis structure in the same places. This extends to the layout of the internal suspension elements and the pedals etc. Rather than the expected lowering of the driver feet, they will remain in the same place as before.

With the stepped chassis, the suspension set and drivers feet can remain in the same place as 2013

With the stepped chassis, the suspension set and drivers feet can remain in the same place as 2013

There is of course a centre of gravity penalty, but the teams have coped with high chassis for many years, so there’s little mechanical disadvantage, compared to the aero advantages of such a set up.
Different teams have treated the step in different ways; most commonly the top step is either left unfaired and simply merges into a sloped nose cone. Other teams have used the vanity panel to cover the step over, the panel being a permanent part of the nose cone.

A vanity panel bonded to the nose cone will cover the step

A vanity panel bonded to the nose cone will cover the step

Underneath its harder to se what teams are doing to cover the step, teams with sloped noses like Ferrari are simply having the step follow the underside of the nose’s contours. It’s likely that more fairing and turning vanes will smooth the aero under the chassis.

This is clearly a ridiculous way of working and the stepped chassis will be outlawed for 2015, where the front bulkhead will remain at the same height, but the slope will subject to a minimum angle, so extreme steps will be banned.

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