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25 April 2015
McLaren-Honda RA615H powerunit

McLaren in search of a new works partnership have got back into bed with their Japanese friends at Honda and although the going has been tough thus far the future could be much brighter, should they start to unlock some performance, having seriously curtailed maximum power in the opening rounds.

Ron Dennis has already alluded to the fact that a 'works' style collaboration is the only way forward under the new regulations and in fairness he is accurate in his assessment.  Mercedes led the way in 2014 and although Williams kept apace with the Silver Arrows their chances of beating them was always slim.  Mercedes HPP power 4 of the teams on the grid, including their own team and so many have questioned why the likes of Williams, Lotus and Force India are unable to challenge for victories.  As I've already shown the installation of the powerunit within each of these cars is very different and as a by-product performance is affected in differing ways too, with the 'works' team having the benefit of working with HPP to tailor the package in their direction they have been able to unlock more performance.

Credit to RaceCar Engineering as always as they got the first clear shots of the RA615H:

The images don't clear up everything but help to paint a clearer picture of the powerunits architecture of which I'll try to cover here.

The question that comes up more than any when discussing the layout of the powerunits is the positioning of the turbo, mostly owing to Mercedes application of the split Turbine and Compressor at either end of the ICE.  The few pictures that had surfaced of the McLaren thus far seemed to indicate that Honda had also followed this path too, with the boost pipes Siamesed on the air-air cooler (below) suggesting that the compressor was located at the front of the ICE whilst the exhaust manifold swept to the rear.
The new pictures contradict this though as it is clear that the compressor is not housed in the front face of the ICE, with the boost pipe (marked in purple) disappearing into the V.

So where is the compressor?

It appears to be inside the V, it's actual longitudinal location has yet to be ascertained, although ScarbsF1 concluded in a piece for Autosport ( that Honda were using an axial flow compressor rather than a traditional centrifugal compressor, which could reduce the diameter of the unit, placing it and the MGU-H at almost the full length of the V.
Ordinarily the diameter of the compressor is reduced in an axial configuration as you aren't reliant on just one rotor but a selection of rotors and stators which help to create the same compression ratio as the larger single centrifugal rotor.  However, the problem with using an axial flow compressor setup is that the regulations only permit a single stage (ie a stator and rotor) and so getting this same compression ratio may be difficult, although it will have the potential to be more efficient at lower speeds.

5.1.6 Pressure charging may only be affected by the use of a sole single stage compressor linked to a sole single stage exhaust turbine by a shaft assembly parallel to the engine crankshaft and within 25mm of the car centre line.  The shaft must be designed so as to ensure that the shaft assembly, the compressor and the turbine always rotate about a common axis and the same angular velocity, an electrical motor generator (MGU-H) may be directly coupled to it.
Undetered and pursuant of this line of thought I remembered the Honeywell dual boost turbocharger, which on the compressor side utilises two air inlet chambers (A&B), feeding a double sided compressor wheel.
Although it's still not axial in the standard sense having the double sided wheel (albeit not a stator (stationary) and rotor (rotary) at least contributes toward calling it an axial design.  Honeywell are proud of the fact that the design allows for the overall size of the compressor to be reduced as obviously the wheel (rotor) could be roughly half the size of its standard counterpart to achieve similar performance.  McLaren could easily split the airbox as it enters the V in order to provide airflow to either side of the wheel. 
Honda have, like Mercedes did in 2014 opted for log style exhaust maniold (marked in red), whereby the short primary pipes converge on an elongated 'log' collector.  This feeds around to the rear of the ICE where the Turbine can be found.  A metal inlet plenum (marked in yellow) has been employed to enclose the inlet trumpets, which contradicts the carbon fibre plenums being used by the other 3 suppliers.  The use of the metal plenum may be supersceded at some point in the season but I don't believe in coincidences and so the plenum may well be serving its own purpose, paramount of which is serving as a load bearing structure, given two (saddle) coolers are mounted upon it (marked in yellow, below).

With the top of the plenum off we can see that the upper section of the variable inlet trumpets are bent over 90 degree's (only marked the rearward one, in green to retain clarity on each trumpet), maximising flow conditions, whilst saving space.  You'll also note I have marked the exhaust outlet in red at the rear of the engine, which appears to be quite large in diameter, sweeping abrubtly upward from the turbine that is located much lower in the V.

Up until now the location of the MGU-K had remained a mystery with speculation pointing toward its installation in the V.  It would appear however that the MGU-K remains in a similar location to what we have become accustomed to, under the left hand cylinder bank (circled above).

As I've already said the pictures still don't tell us everything and the turbo architecture is most puzzling, Honda had already seen what was being used by the others and have instead (seemingly) opted for a different strategy. From an architectural point of view I think we've already seen the best possible installation from Mercedes but is there something to be gained by using un-conventional methods in a fuel limited formula?  It seems Honda believe so and I look forward to seeing just how they've achieved their goals when the details emerge.  I know many people are eager for me to expand on my thoughts about the turbo but frankly it'd be guesswork at this stage (some of which I have covered above), suffice to say there are many ways to go about it, even with the limiting diameter factor.  Everything from an elongated compressor wheel with slots (to prevent stall) to a rotary vane compressor are in play, with many other options in between.  As alway, as and when I'm able to I will update you with my findings.
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16 April 2015

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