Given that the gap between the Chinese and Bahrain grand prix was just one, tweaks to the cars were minimal and were mainly aimed at cooling as the two circuits share quite similar downforce characteristics.
However more was learnt about McLaren’s Honda power unit plus a few other additions were also visible over the course of the weekend.
McLaren (Quoted is from my piece for Richland F1)
“A lot has been disputed about the underlying technical details of Honda’s 2015 powertrain. What we have already established is that they are indeed utilising the split turbo concept that Mercedes pioneered last year, with the exhaust driven turbine and the compressor being separated by the MGU-H that sits in the V of the engine.
However, information remained scarce for some time as to how they were cooling the compressed air until the beginning of April, when it was revealed that McLaren run an air-to-air intercooler in the right-hand sidepod. This therefore meant that the radiator – uniquely placed above the engine itself and fed by the top inlet in the airbox – is used to cool the ERS package. This opened up space to pinch the bodywork inwards, tapering tightly into the “size zero” Coke-bottle region at the back of the car.
Recently, more details have been uncovered about just what McLaren are doing with their power unit to allow such tight packaging with relatively little cooling requirements. Although they are still running quite a large central outlet at the back, the overall area of openings made into the car is pretty minimal relative to the rest of the grid.
It transpires that Honda have developed a totally different compressor side to the turbo than any other manufacturer. The regulations do govern this area quite strictly which is why Mercedes, Ferrari and Renault have all converged on the same solution. Honda on the other hand have been a bit different.
The rules state that the compressor must consist of only a single stage, so the general consensus is to use a large centrifugal fan to draw air in through the airbox and onto the intercooler. The larger the fan the higher the boost pressure achieved although this is not such a big tradeoff when considering the fuel flow limit. A smaller fan, though, will spool much faster due to its lower inertia, which improves drivability.
Honda have opted to use a much smaller, axial compressor but without the multiple fan elements that would make the system illegal. Instead there is one elongated fan that stretches across a narrow tube, with perhaps a multitude of increasingly sized blades to guide air through.
There are a number of advantages in doing this: the resulting smaller compressor can be packaged neatly into the V of the engine alongside the MGU-H, removing the blockage created by a large centrifugal fan and bumping the engine up closer to the fuel tank. The emphasis on doing this is to again create more space further behind and improve the weight distribution of the car.
Secondly, a smaller fan naturally spools much faster which places less reliance on the MGU-H to generate boost under acceleration so energy can be saved instead for the MGU-K – a more dominant player in terms of laptime and an area in which Honda have struggled to make inroads in so far. Once reliability problems are sorted in this area we could see the partnership making large strides in energy recovery and deployment later in the year.
To make room for the top mounted radiator, Honda have had to create a low-lying inlet plenum which is made from aluminium rather than carbon fibre. This will have been done to resist the transfer of heat from the radiator above and also to make a more suitable shape in a crowded area. With the introduction of variable-length inlet trumpets, I imagine that this was a pretty tough component to produce.
Overall, it is these detailed changes that Honda have implemented that will eventually aid McLaren’s aerodynamic package. Once the MGU-K seal gremlins have been overcome and the power output rises further, only then will we see the true potential of the MP4-30 chassis.”
Another possible theory is the use of Honeywell’s DualBoost turbocharger, which is technically a type of axial compressor. It also utilises two inlet pipes for the compressor, with the exhaust-driven turbine spooling two fans that face back-to-back of eachother before combining the charge air into one pipe to be fed onto the intercooler. It’s a smaller solution than a conventional centrifugal fan thanks to the dual fans, so it could squeeze into the V of the engine.
Aside from the power unit, the MP4-30 featured some small aerodynamic adjustments.
Gone is the innovative ‘tubercles’ rear wing upper flap and in its place is a traditional straight-cut leading edge. The idea behind the tubercles flap was to improve flow attachment as the DRS closed (more on this here) but clearly – with a host of new faces within the McLaren aerodynamic – there has been a change of philosophy and perhaps some subtle detail work done elsewhere to improve efficiency in this scenario.
Modifications were also made to the rear diffuser. As well as upwash, the diffuser’s outer walls expand airflow out from beneath the floor, too, to suck the car further into the ground. McLaren have tweaked this area to improve this effect, which has also resulted in reducing the number of fences from three to two.
After introducing a new front wing in China, another small tweak was made to the endplate in Bahrain.
The red line represents the China update, with the arched section now more pronounced than before and pushed slightly inboard than the previous specification. The old wing’s arch was pushed right up against the endplate, so this change in philosophy follows more of a Mercedes pathway.
Highlighted is the new addition – a small pressure gradient vane that has become pretty common on the cars this year. The vane will cause a small low pressure zone behind, drawing air out from behind both the underside of the wing and from behind the endplate at a faster rate. This is another outwash aid which, combined with the blown front axle and the underbody effect of the wing, should help improve flow management around the front tyre.