Better by design
Our man gets beneath the skin of this year’s Formula 1 cars, pinpoints the key differences between the three engine manufacturers’ approaches… and explains exactly why the Mercedes V6 has won the power battle
Illustrator Giorgio Piola
Formula 1’s adoption of the 1.6-litre V6 hybrid format has radically altered the competitive pecking order. Hand in hand with fairly swingeing aerodynamic restrictions, which rendered obsolete the accumulated advantage of fruitful development programmes, the complex new power units made it far from obvious where the optimum balance would lie between conflicting aero and mechanical demands. Plotting the points of triangulation between downforce/drag, power/fuel efficiency and driveability was a major challenge, even for the best funded and resourced teams, when the hybrid part of the equation was new territory. The lead teams of the three engine manufacturers – Mercedes, Ferrari and Red Bull-Renault – produced for this season three designs that, while looking superficially similar, diverge considerably beneath their skins. Here, with the illuminating aid of Giorgio Piola’s drawings, we show the inner layouts of the Mercedes W05, Ferrari F14T and Red Bull RB10 and the impact they have had on the season’s competitive shape.
Central to Mercedes-Benz’s philosophy has been the engine’s split turbo concept, with the compressor mounted at the front, connected to the turbine via a long shaft that runs through the engine vee. This was a feature originally suggested by the Brackley chassis side of the team, with the Brixworth-based engine department then confirming after research that it was feasible from an engineering standpoint.
The benefits this has conferred are significant. Moved to the front of the engine, the compressor is in a far less aerodynamically sensitive part of the car and, as a result, is physically bigger and more powerful than the conventional rear-mounted compressors of the Ferrari and Renault engines. It allows the intercoolers, which are cooling the charge air that has just been compressed, to be mounted closer to the compressor. This means there is less inherent lag in the system and the associated plumbing takes up less space. Old-fashioned turbo lag is effectively non-existent in these hybrid engines because any delay in mechanical power delivery can be compensated by brief bursts of electrical energy – as the electrics can be used to spool up the turbo instantly. But by taking inherent lag out of the system, the battery’s energy store is called upon less – and that saved energy is then available for accelerating the car or saving fuel. There is also a small but significant benefit in having the compressor in ambient air rather than close to the very hot exhausts.
From a combustion perspective, fuel and lubricant supplier Petronas was part of the concept right from the beginning. Between the engine designers and the fuel chemists, the focus was very much on delivering an engine/fuel combination that had exceptionally high knock ceilings. The further the onset of knock can be postponed, the weaker the mixture can be, giving a more potent power/economy potential and – critically – the less cooling the incoming air needs and therefore the smaller the intercooling capacity can be.
The combined effect of an engine with exceptional combustion characteristics and a big compressor has been much more power and significantly better fuel economy than any rival. There was even scope to surrender some of the mechanical grunt for electrical gain, by introducing flat exhaust collectors rather than the conventional ‘spaghetti’ shapes that tune the engine’s torque curve by allowing the exhaust gas freer exit. The flat collectors and short stubby primaries lost the engine about 15bhp, but the greater heat build-up within the engine boosted the power capacity of the heat-driven motor generator (MGUh) by more than that. The MGUh can either spool up the turbo or feed any excess through the kinetically driven motor generator (MGUk) and into the crankshaft – and there is no regulation limit on that. The flat pipes also conferred a small aerodynamic advantage.
The packaging benefits of both the front-mounted compressor and the relatively small intercooling requirement have made possible further aerodynamic gains. Opting for a water-air intercooler rather than the bulkier (but lighter and more efficient) air-air unit allowed the intercooler to be incorporated into the chassis, again saving vital packaging millimetres and plumbing.
With the compressor up front, fed by the closely adjacent airbox, the design team was able to sweep the back of the W05 down very sharply, within a much shorter space than either the Red Bull or Ferrari. This is evident by the bodywork blisters towards the bottom of the engine cover, which are there only so the bodywork meets the regulatory dimensional requirements. Because the hot turbine unit at the back was so much smaller without the associated compressor, it was possible to bring the gearbox significantly forwards, reducing the car’s polar moment of inertia – thereby making it more responsive to direction change and taking less from the delicate rear tyres.
The shaft between turbine and compressor is conventionally just a few centimetres long. When the two components are at opposite ends of the engine rather than joined, however, the shaft is massively longer and subject to exponentially greater axial loads. A triangular cradle was devised to eradicate potentially catastrophic flexing.
Red Bull RB10
Using a conventional turbo-compressor layout, the Renault V6 imposed certain limitations upon Adrian Newey and designer Rob Marshall, something the Mercedes designers didn’t face.
Furthermore, the best evidence suggests that the Renault engine does not have anything like the Mercedes V6’s resistance to knock. Quite aside from the negative implications this has on power and fuel consumption, it has meant that the intercooler requirement is significantly higher. The car uses a conventional air-air intercooler, because the engine needs more charge cooling to keep the dreaded knock of detonation at bay: an air-air intercooler typically delivers air to the engine about 20deg C cooler than the more compact
water-air intercooler. This, though, has impacted upon the packaging of the car, with an intercooler significantly bulkier than that on the Mercedes – and mounted towards the back, so as to be near the rear-mounted compressor.
Without having anything like the same leeway as Mercedes to minimise the length of the installation, Red Bull instead concentrated on its traditional strength of tightly packaging the rear end. Seen from above in plan view, the RB10 has by far the slimmest waist aft of the cockpit. The exaggerated ‘coke bottle’ bodywork profile will accelerate the airflow over the brake ducts, diffuser top and rear wing, increasing downforce. But to achieve this has demanded greater length between cockpit and rear wheels. The implication is for a more rearward-biased weight distribution and a less centralised mass.
Routing the inlet air to the compressor at the back of the engine has necessitated a visibly longer engine cover than the Mercedes and the siting of many major components can be seen to be further rearwards. However, the bodywork’s enhanced coke bottle profile has increased the airflow around the side radiators sufficiently to allow them to be smaller than those on the Mercedes, clawing back valuable lost ground.
The 2014 regulations banished Red Bull’s former policy of mounting the battery outside the car (instead, this must now be situated beneath the fuel tank), but Red Bull itself manufactured the battery pack and is believed to have engineered an advantage in maximum duration of full power deployment by the simple expedient of making the battery physically bigger. The RB10 seems able to deploy the maximum permitted power deployment for longer than other cars before overheating its battery.
The core mission of the F14T’s configuration within the constraints of the new regulations was to maximise aerodynamic performance – even if that meant some compromise in the potency of the power unit. To this end, the design team was quite radical in opting to move the oil tank from what since the late ’90s has been the conventional place, between cockpit and engine, and relocating it to within the gearbox casing. This allowed the engine to be moved significantly forward within the car and, together with the biggest wheelbase increase of all the cars since 2013 (about 15cm), this made possible a bigger diffuser area and enhanced coke bottle bodywork profile to speed up airflow. The gearbox and exhaust were shaped according to this ‘long and narrow’ philosophy.
To help achieve aero gains, the engine department was tasked with producing an engine in less than its ultimate state of tune and, accordingly, downsized wherever possible so that the radiator sizes were minimised. From the respective radiator sizes of each car, the unknown variable of flow velocity around the radiators makes it impossible to determine visually which has the best heat rejection figures. It is suspected, however, that the Ferrari engine’s heat rejection figures are the smallest, overturning the tradition of the normally aspirated era.
In combination with an energy recovery system that for much of the season lacked efficiency in both deployment and harvesting, the engine configuration has left the car badly down on power – sonic analysis suggests by as much as 40bhp to the Mercedes. In pre-season testing at Bahrain the team rid itself of its power deficit by increasing the fuel flow beyond the maximum permitted 100kg/hour. This was in order to assess the state of competitiveness of the car’s aerodynamics. The results suggested that, despite having been configured heavily in favour of aerodynamics, when given power parity with the Mercedes the car was still about 0.25sec adrift.
Like the Mercedes, the F14T utilises a water-air intercooler – again indicative of the design team’s deliberate decision to sacrifice power for aerodynamic performance. In the case of the Ferrari it nestles within the engine vee rather than in the chassis (Mercedes) or sidepods (Red Bull). This, and the desire to move the engine as far forward as possible, would have made it impossible to adopt the Mercedes front-mounted compressor concept, even if they had wanted to. The size of the compressor has, just as with Renault, therefore been limited. The smaller compressor essentially means that the Ferrari has a power shortfall to the Mercedes for a given fuel consumption. As the fuel consumption is limited by regulation to a maximum of 100kg for the race, it effectively means the Ferrari and Renault are always behind on power.
While the Mercedes W05 has been the dominant car of the season by dint of a power advantage and a very good chassis, the Red Bull RB10 has shown itself capable of splitting the Mercs in wet qualifying, when its power shortfall wasn’t so costly. GPS analysis suggests it’s usually as quick, sometimes quicker, than the Mercedes through the corners.
The Ferrari F14T fares best on long-corner circuits where its relatively high downforce can keep it in play. Its over-abrupt electrical deployment and traction shortfall make it a mediocre machine on tight tracks. The efficiency of its braking energy harvesting was improved significantly by Barcelona, but its ersH remains a weak point. A thermal covering around the turbo was introduced in Hungary and allowed the MGUh more heat.
Although the Red Bull’s Renault V6 cannot compete with the Mercedes in how much extra power is fed from the ersH to the crankshaft (via the ersK), its ability to deploy maximum battery power for longer has played its part. The Red Bull drivers were able to do two consecutive qualifying laps early in the season, when others had to intersperse with a harvesting lap, and this also allowed Sebastian Vettel a run on Lewis Hamilton’s Merc at Spa on the first lap.
Braking stability and tyre temperatures work hand in hand with efficient energy harvesting in this formula – and here the Mercedes W05 has been outstanding. Its more forward weight distribution has probably been influential in this, giving a stable braking platform as the electronic brake distribution systems vary the load front-rear according to the energy harvesting levels from the rear axle. The Ferrari has been notably poor in this regard, something with which Kimi Räikkönen, in particular, has struggled.
In summary, the new regulations triggered a re-assignment of design priorities – and that was best understood at Mercedes.