Tech: Mercedes' twisted wing explained

Spa-Francorchamps is technically a low-drag track. It's not that it doesn't require downforce, just that the most demanding corners are taken at high-speed and at those elevated speeds small wings will easily create the downforce required. The smaller wings therefore provide a drag benefit to aid top speed along the straights.

Thus we see teams bring elements of their Canadian Grand Prix packages to Belgium and also test parts ahead of the even lower drag demands of the Italian GP.

Quite how low teams can afford to go on the wing size varies. Most teams will even bring two different wing sets to compare, the drivers' confidence at these low wing levels being as important as the simulations conducted at the factory.

So in Friday's practice sessions we saw every team with smaller wings and detailed aero parts in a bid to find the ideal set up for the Belgian GP.

As the key factor in setting the car's top speed, the rear wing is the main aero change for most teams. The usual route is a wing somewhere between a normal level and the extremely shallow version needed for Monza.

With engine power also being a factor in top speed, teams with the Renault engine have found themselves running at the skinniest end of rear wing levels, both Red Bull and Toro Rosso having distinctly flatter wings than their rivals.

Rear wing designs can either be shallower versions of the usual straight rear wings or twisted wing shapes such as the Mercedes design, development time and the overall aero philosophy steering teams in either direction

Then front wings are simply trimmed to balance the lesser downforce created at the rear. With the high speeds, the outwash effect of the front wing and other aero devices are not as critical, so we will see front wing cascades, endplate details and sidepod furniture removed to suit the car's set-up.

MERCEDES

Rather than merely running a shallow rear wing for Spa, Mercedes has developed a completely new rear wing, distinctive for its twisted shape.

Extreme rear wing shapes have been a feature of the Spa and Monza races for years, however Mercedes has not run one before even in its BAR/Honda/Brawn incarnations.

This Spa specification wing follows the approach of reducing downforce by having a shallower angle of attack for part of the wing's span.

The outer spans are also shallower, to reduce drag. It's these outer sections that induce a lot of drag where they meet the endplates, as a shallower angle in this area means the vortices - which are sometimes seen as vapour trails in the wet - are reduced. That leaves the deeper middle section working hardest at creating downforce.

So why do teams such as Mercedes choose to create such complex wings, rather than a simpler shallower rear wing?

Both options will create the required amount of downforce and similar drag levels, but it's the wake structure that differentiates the two designs.

The twisted shape will feature a stronger upwash along the centreline. This is a flow structure Mercedes already works hard, with the exhaust plume, monkey seat and diffuser. Therefore the twisted shape fits in better with its aero philosophy than the straight wing shape.

FERRARI

Flushed with its success from Hungary, the very different demands of Belgium have pressed Ferrari into taking an aggressive approach to its car set-up this weekend.

It's a mix of old and new on the SF15-T, with the pre-Spain sidepods, revised front wing from the British GP and a new rear wing.

By using this blend of old, updated and new parts, Ferrari hopes to find the ideal mix of drag and downforce.

The more rounded sidepods seen in the first four races presumably create less drag, and this is more important at Spa than the downforce benefit the latest sidepods provide.

While the front wing is a modified version of the Silverstone spec, to reduce the downforce the wing provides over the standard version the two element flaps are replaced with a single angular shaped flap.

Then, as we saw at Monza last year, the cascade winglet is removed leaving just a pair of r-shaped vanes.

The shape of the flap reduces the downforce it creates, by being shallower at the tips, but the steeper inner section allows it to still create the powerful Y250 vortex that pushes the front tyre wake from the bodywork, which serves to reduce drag.

But most influential to the Spa set-up is the rear wing. Unlike Mercedes, Ferrari has opted for simple straight low-drag wings, the updated front wing merely needing to balance the downforce produced by the rear wing.

Ferrari brought two rear wings specs to Spa, being distinguishable by the different DRS pod mounted above the wing.

McLAREN

Belgium has proven to be another milestone for the McLaren-Honda MP4-30's development, as finally the engine received a major makeover and the chassis was adapted to suit - although results do not reflect the scale of the changes.

What Honda is calling the 'version three' spec of the V6 motor has required the use of three of its in-season development tokens.

The most productive use of development tokens is the combustion upgrade. This effectively allows most of the top end of the engine to be updated, making the most of the limited fuel available under the current regulations.

Changes to the combustion efficiency means that both power, cooling and fuel consumption should be improved, all having been weak spots of the package so far.

With these changes on top of the ERS updates earlier this year, Honda has been able to improve the heat rejected from the power unit and with this McLaren has repackaged the engine installation.

Part of the 'size-zero' rear end packaging on this year's car was the trademark top-mounted radiator.

Cooling the ERS is a water cooler mounted high up over the engine, and while this location allows slimmer sidepods, it does add bulk to the top of the engine cover and increases the centre of gravity height.

Now McLaren has positioned this to a more conventional location, by having the long narrow radiator switched to a more triangular shaped cooler mounted over the gearbox.

The relocated radiator required revised ducting inside the bodywork and as a result the bodywork itself is now even tighter.

So the engine cover now sports a fin along its spine, the external shape allowing for a cleaner flow of air to the rear wing and adding to the 'size zero' philosophy.