Catch Merc if you can

Clawing back Mercedes’ 2014 performance advantage was the daunting task facing rival teams and engine manufacturers this winter. We present their differing approaches to the challenge
Illustrator Giorgio Piola

Into the second year of the hybrid V6 formula and its associated aerodynamic restrictions, Formula 1 car development leaps on apace. The big gains in performance typical of the early part of a new learning curve are very apparent from lap times, with the cars up to 2sec faster in off-season testing compared with 2014.

Last year Mercedes came up with several key innovations that contributed to the works team’s dominance, but it was in judging the optimum trade-off between aerodynamic and power unit efficiencies that it found its most telling advantage. That has informed the 2015 developments of the other engine manufacturers and teams. The fundamental design choice is between how much aero performance should be sacrificed to gain engine performance – and with fuel flow-limited turbocharged engines that are hugely more power-sensitive to cooling capacities, this is a far trickier equation to solve than with the old normally aspirated V8s. Obviously teams are still chasing gains in both aero and power, but there is now much more of a compromise to be made between them.

Power units

Mercedes attacked this conflict from first principles. Precisely because this type of engine is sensitive to the temperature of the incoming charge, Mercedes prioritised reducing that sensitivity at the concept stage. The Mercedes W05, with its compact water-air intercooler, last year typically ran an incoming charge temperature 20deg C higher than that of the Renault-engined Red Bull. It was able to do this – and gain the resulting aerodynamic benefits of the smaller intercooler – by prioritising the engine’s knock sensitivity. It does not require such a cool inlet charge to prevent knock (spontaneous and uncontrolled ignition) as its rival engines and hence needs less aerodynamically disruptive intercooling. There will still be a power penalty for feeding the engine with a warmer mixture, but a relatively small one.

Fuel composition, combustion chamber and ignition software were designed simultaneously, almost as a single project, to achieve fantastically high resistance to knock. The rest of the engine was then conceived around those three triangulation points. Greater knock resistance will enable a higher compression ratio, and it’s the combination of compression ratio and compressor size that will be so crucial in determining energy efficiency. With a bigger compressor than the others (because it was mounted up front, just behind the cockpit, out of aerodynamic harm’s way) and higher compression ratio, the Merc’s mechanical engine was more potent at both low and high revs. This is at the heart of the advantage – because the recovered energy is only captured from the internal combustion engine, not created independently. The more potent the engine, the more energy can be recovered (or the quicker the same amount of energy can be recovered).

The 2014 Mercedes PU106A V6 set the gold standard for F1 engine design in much the same way as the Cosworth DFV did in 1967, its margin of superiority over everything else similarly vast. But today we have three engine manufacturers – Ferrari, Renault and Honda – reacting to what Mercedes made evident in 2014. Renault and Total have together chased big gains in knock resistance, with changes both to the fuel and combustion chamber shape. However, the fully realised 2015 Renault engine is not expected until mid-season, with a Mario Illien-led upgrade. The revised way in which the engine homologation rules now work has given Renault time for a more considered change. Whether this includes a move to the Mercedes-style front compressor layout remains to be seen. This was a key part of the Merc engine’s advantage last year – bringing packaging, power and aero gains – but it’s an immense engineering challenge to make a small-diameter shaft stretching the full length of the engine run without catastrophic flex at up to 125,000rpm.

Ferrari and Honda have shied away from such a layout too, at least with the engines with which they begin the season. Honda has gone as far as splitting the turbine and compressor, fitting the ersH between, but the compressor resides in the vee of the engine rather than up front. Ferrari has found about 80bhp over its 2014 power unit, partly through being less extreme in favouring aerodynamics over cooling capacity.

Unfortunately for the others, Mercedes has not stood still. A reputed extra 50bhp has been found with the PU106B, partly through now being able to run to the full 500-bar of fuel pressure allowed by the regulations, something that wasn’t feasible last year. This allows greater atomisation of the fuel, significantly improving combustion efficiency.

All the engines, regardless of the improvements made in the energy recovery systems, will be getting more help from them this year. Variable inlet trumpets are allowed back for the first time in F1 since the V10 era, smoothing out natural holes in the torque curves – thereby asking less of the stored energy, which can thus be deployed elsewhere.

Aero developments

Although the Mercedes W06 looks very similar to its predecessor – and its general layout and aerodynamic philosophy is much the same – beneath the skin it is totally reconfigured. The new nose regulations, introduced this year to combat the ugly nose solution of 2014, have totally altered the flow field in the wake of the nose. One of the key aerodynamic endeavours for the front part of the car is in creating vortices (circular currents of swirling air) in the appropriate places – specifically between the front wheels and the sidepods. Generating counter-rotating vortices here draws the airflow through the gap between them at an accelerated rate, in turn pulling the airflow over the front wing harder and thereby increasing downforce. The changes to the nose shape have necessitated front suspension layout alterations in order to keep the vortices forming in the appropriate places. The steering arm is now sited behind the lower front wishbone rather than the upper one. To give a clearer path for the airflow, the lower ‘wishbone’ is again a single piece with just a forked end to provide two attachment points. Because these are more narrowly spaced than on a conventional two-piece wishbone they need to be significantly heavier to give the same load-bearing strength. It’s a challenging piece of engineering, but the team claims it’s a crucial part of the car’s entire aerodynamic concept. The fact that only Ferrari has copied it for 2015 is probably to do with the engineering resource required.

A completely new cooling layout brings further efficiencies over the 2014 W05, while at the rear the log-style exhaust has given way to a more conventional ‘spaghetti’ layout. With the improved combustion of the new engine, more heat is generated for the ersH to use, making it no longer advantageous to have the more heat-retaining log style.

Contained within the McLaren MP4-30’s Red Bull-like contours is a remarkably compact Honda power unit, so small that the gearbox is out of reach of the rear suspension wishbones that are instead mounted to the crash structure. Williams, with its FW37, has also focused on changing the location of its rear suspension arms and it’s all to do with getting the airflow between the diffuser exit and wing endplates linked up.

The Red Bull RB11 is even more aggressively packaged than its predecessor and probably leads the way in integrating every detail part with the overall aerodynamic concept. Even the plate joining the top rear wishbone to the wheel upright is contoured to work the adjacent brake ducts aerodynamically harder.

The Ferrari SF-15T is more conventionally packaged than its predecessor and apparently blessed with a much better aerodynamic balance. Uniquely retaining pull-rod front suspension, in combination with its Mercedes-like single lower wishbone arm this has given the aerodynamicists scope to work those vortices. With Sebastian Vettel and Kimi Räikkönen on board – two drivers who absolutely need to be able to lean on the outer front tyre to do their best stuff – it’s important for the team’s prospects that the SF-15T has the front end that Ferraris of the last few years have lacked.

Ferrari is one of several teams pushing on with development of ‘blown front axles’ whereby air is routed through the centre of the wheel purely for aerodynamic effect in controlling front wheel wake. The concept isn’t new, but teams have struggled to perfect it.

Lotus has built a much more aerodynamically conventional car around its new Mercedes V6 than last year’s Renault-powered twin tusk machine. But there is very clever detailing in the E23’s multiple inlet airbox. This has been shaped to work in conjunction with the driver’s helmet to induce low pressure just ahead of the main engine inlet, increasing the incoming flow. Off to the side are three smaller inlets feeding the oil cooler and electrical components.

Like the other Mercedes-engined cars, the Lotus features a short, wide nose. Because of the dimensional requirements in the rules, the longer the nose – because of the way it has to droop – the further it blocks the airflow to the underside and thence the rear. So the challenge has been to minimise the nose’s length but still get it through the crash test. Ferrari had the longest nose at the time of writing, but was expected to shorten it.

Ferrari F14T

By moving the oil tank from within the gearbox casing (where it was in the F14T) to the conventional position between the cockpit and engine (where it is located in the SF-15T), Ferrari has fundamentally changed the plan view shape of the entire rear body section, which now extends farther back. The wheelbase is also slightly longer as a result of the change (the difference shown in yellow behind the F14T’s rear tyre).
The engine now has to be mounted further rearwards to create space for the oil tank. Although this will have reduced the venturi area of the diffuser (increasing it led Ferrari to locate the tank in the gearbox in the old car), it was found that the theoretical advantages of the greater area could not be realised, as adequate flow could not be provided. The effects on the weight distribution of moving the engine back slightly are countered by that of moving the oil tank and its contents much farther forwards. This and further rearranging of components and ballast has allowed the weight distribution to remain much as before. The smaller angle of the SF15-T’s upper wishbones from the wheels to their attachment points on the gearbox is another visual indicator of the engine/gearbox having been relocated rearwards.

McLaren MP4-30

Honda has not, as originally believed, copied Mercedes’ front-mounted compressor layout. However, the Japanese manufacturer has split the turbine from the compressor, which resides in the vee about half way along the length of the engine, with the ersH device between it and the turbine. Uniquely, it has mounted the intercooler (blue block in this drawing) above the engine. In the Mercedes it is forward of the engine, integrated into the chassis. In the Red Bull it is in the sidepods. In the Ferrari it resides between the vee of the engine. The Mercedes turbine-compressor layout (the middle of the three circled drawings) remains as in 2014 with the compressor (in blue) up front and only the turbo (red) at the rear, linked by a long shaft through the vee, with a triangulation cage (yellow) to prevent catastrophic flex for both the shaft and the bearings of the shaft-mounted ersH. Renault and Ferrari (left) share a conventional layout of a single unit turbine-compressor at the rear.

Red Bull RB11

Without the beam wing (banned since last year) to join up the various airflows off the back of the cars, the rear corners are now much more aerodynamically sensitive, hence the proliferation of slots in wing endplates and ahead of the rear tyres. There is a lot of performance to be found in the aerodynamic interplay between the diffuser, rear wing endplates, rear wheels and rear brake ducts. Because of this, the attachments between rear suspension arms and wheel uprights are becoming integral to the aerodynamic packaging. In the Red Bull RB11, the plate fixing the wishbone to the upright is wider and shaped to work in aerodynamic conjunction with the brake ducts to extract air around the rear tyres. The red arrows in the inset circle indicate extraction of hot air from the brakes to inboard of the tyres, keeping it from creating drag.