While much attention has inevitably been focused on the new hydrid engines F1 introduced this year, other changes in the 2014 rule book aimed to reduce the amount of downforce being generated at the rear of the car.
Perhaps the most significant of these concerned the positioning of the exhaust. In previous seasons teams have exploited exhaust gasses for aerodynamic gain, directing the hot air around the diffuser in such a way to make it perform better.
In 2014 this trick was effectively banned as the positioning of the exhaust is now tightly controlled. The 2014 technical regulations dictate that the exhaust exit but be between 170-185mm behind the rear axle line, 350-500mm above the floor and along the car centreline.
This has led some teams to get creative at the back of the car and exploit other means of generating downforce. The rear of the car is still hugely important aerodynamically and is responsible for about 40% of the downforce generated. The drawing below shows the back of the McLaren MP4-29.
The exhaust is positioned above the rear crash structure along the car centreline. Although the rules are clearly written to limit the extent to which teams can use their exhausts to generate downforce, what is learned is never forgotten, and designers have deployed aerodynamic structures around the exhaust exit to try to use the gasses for aerodynamic gain.
In the case of the MP4-29, a flap behind the exhaust serves this purpose. The high-speed exhaust gasses create a low pressure zone below the flap, which helps create downforce. In addition the plume is directed upwards where it will interact with the flow structure from the rear wing, again adding to downforce (although this interaction will be small as it occurs some way aft of the rear wing).
Another source of downforce at the back of an F1 car is the brake ducts. Ostensibly for brake cooling, in recent years the inner wheel area has seen a proliferation of carbon fibre in the name of grip.
The MP4-29’s has five distinct aerodynamic surfaces that are clearly not designed to help cool the brakes. One advantage of the brake ducts is that the downforce is generated on the unsprung part of the car so is transmitted straight to the rubber (as opposed to being transmitted through the suspension arms).
The final part of the downforce equation is the diffuser. The dimensions of the diffuser is tightly regulated but teams do have choices as to the shape. McLaren have opted to have rounded outer edges in an attempt to keep the airflow inside the diffuser attached, which helps with downforce – turbulent air in the diffuser kills downforce.
The MP4-29 also sports ‘fat’ suspension arms. The intent of the fat suspension is to block airflow above the diffuser. This creates a low pressure area above the diffuser thereby reducing the pressure gradient the diffuser has to work against. Air in the diffuser is more likely to stay attached and generate grip.
This comes at the cost of considerable drag from the suspension, and it appears the trade-off may not be worthwhile. No other teams have copied the McLaren design and the performance of the MP4-29 suggests the invention will not be retained for the 2015 campaign.
The last detail to note is the location of the cooling exit. With the advent of the turbocharger the thermal footprint of the 2014 formula has increased. Like many F1 teams McLaren vents hot air out of the rear of the car. This comes at the cost of having slightly expanded bodywork at the rear of the car, although the McLaren engineers have raise the vent to ensure a reasonably deep sidepod undercut.
With all the focus on engines, one of the unspoken successes of the 2014 regulations has been neutralisation of exhaust blown diffusers. Unlike the front wing and nose, which will change for 2015, there are few regulation changes at the rear of the car. That won’t necessarily stop some clever teams doing something inventive in an attempt to get an edge.
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Image © McLaren/LAT