F1 Fanatic

The distinctive exhaust slot in the McLaren MP4-27

The FIA has introduced a raft of new rules aimed at curtailing the use of exhaust-blown diffusers.

McLaren have come up with one of the more interesting solutions addressing the new restrictions on exhausts for 2012. John Beamer takes a look at what they’ve come up with for the MP4-27.

2012 exhaust rules

The new 2012 rules dictate the positioning of the final 10cm of exhaust piping. The rules specify that this section must be circular, thin-wall and 75mm in diameter.

Teams can have no entry or exit slots along the length of the exhaust. The exhaust exit must between 250-600mm above the reference plane, 500-1200mm from the real axle and 200-500mm from the car centre line.

In addition, the exhaust exit angle must be at positive 10-30 degrees from the reference plane (i.e., pointing slightly upwards) and plus/minus 10 degrees from the car centre line.

This is all aimed at limiting teams’ abilities to place the exhaust in a position that will increase the power of the diffuser. “The exhaust will still have an effect,” Ross Brawn admitted last week, “but it’s much, much reduced.”

The rules leave three apparent options for where designers may place the exhaust exit:

1. Towards either the rear or beam wing,
2. Over the suspension / brake ducts,
3. Away from the car altogether.

Based on early the first two tests it appears the top teams are blowing the exhaust gases over the suspension. However they are trying to seal the diffuser to replicate the benefits of the exhaust-blown diffuser.

It has been suggested that some teams are pushing the spirit of the rules but the so far the FIA hasn’t stepped in. The sport’s governing body may prefer to let the 2012 solutions pass and clean up the regulations for next year if needed.

McLaren MP4-27 exhausts

McLaren exhaust exit

The first picture shows the new McLaren from above. In the blue circle it is easy to see the exhaust ‘bulge’ and exit channel. The fact it protrudes from the sidepod is the first clue that McLaren is trying to do something clever with the exhaust flow.

There has been a lot of speculation about exactly how the device works but it is likely to exploit the Coanda effect to seal the diffuser.

The Coanda effect is when fluid is guided by a nearby curved surface to modify its direction. As the surface curves away from the flow it creates lower pressure close to the surface. This pulls the fluid towards the surface.

McLaren exhaust exit

The second picture is a side-on view of the exhaust. Again, the exhaust bulge is circled in blue.

From this angle you can see the exit slot is pointing towards the floor. This helps induce the Coanda effect and pulls the exhaust flow towards the floor as indicated by the blue arrow. Also the ‘bulge’ directs airflow coming around the sidepods away from the exhaust plume, protecting this flow to the diffuser.

McLaren exhaust exit

The third picture shows the MP4-27 exhaust from behind with the blue circle highlighting the exhaust exit.

In this diagram the exhaust seems to contravene the regulations which states that it must be circular. The exit appears to have a protruding section and there are also two collars on top of the pipe which appear part of the exhaust. From the published photographs it is hard to see exactly what is going on and the team remains unsurprisingly coy.

There are several possible explanations for why this design may still be legal: these parts may not be attached to the exhaust – they may house sensors to monitor the temperature and flow of the gasses – or they may be an interim solution to allow McLaren to better understand the effect of blowing gasses over the diffuser.

Also in the third picture it is possible to see a number of temperature sensors on the topside of the diffuser – these are circled in yellow. Given we’ve now seen this exhaust solution in two tests and McLaren’s performance looks pretty good it is very likely that the McLaren exhaust solution is working.

What the other teams are doing

Another view of the exhaust outlet on the McLaren MP4-27

Many other teams – Ferrari, Mercedes and Sauber in particular – all had similar but less aggressive solutions. Their exhausts were pointing in a similar directions to McLaren’s but without the bulge and bodywork.

Many teams also added vanes to their rear wing and floor to steer airflow to the diffuser. Don’t be surprised to see an innovative solution from Red Bull too – engine suppliers Renault have indicated the world champions have some exhaust innovations coming.

Despite the FIA’s efforts 2012 will continue to see a lot of work on exhaust and diffuser development. But the early indications are teams have some way to go to recoup the downforce lost due to the new restrictions

Brawn added: “We’re still getting a bit of performance from the exhaust with the new car. Nothing like what was achieved with last year’s regulations and last year’s concept. But once you’ve discovered something you don’t un-invent it.

“All of the engineers, all of the designers in Formula 1 have been looking at how you can still retain some of the performance. But it’s far, far reduced to what we had last year and I think most people designing their new cars would be quite happy if they were able to achieve the overall performance that they achieved last year.

“We were testing in Jerez with the 2011 car and it looked to be the most consistent and fastest car there, in 2011 spec. All the new 2012 cars were a bit behind that.”

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Images © McLaren; Illustrations © John Beamer for F1 Fanatic