Tech blog: Merc's passive DRS returns

With development rates slowing as 2014 looms ever-larger, many Formula 1 teams are introducing the last of their major updates.

But amid vastly improved race performances, thanks to improved tyre management, Mercedes is in a far more competitive position than it once was, which gives it the chance to invest more heavily in this year's car to achieve a better championship finish.

While some teams have already stopped 2013 development, Mercedes is well-placed for a strong end to the season.

It turned up for its home race in Germany with several upgrades to the front wing of the W04 and to the rear. Most striking of these is the new nose design, but it is the passive drag reduction system that is most important.

The system outlets at the back of the Mercedes © XPB

Having pioneered what was then called the 'double DRS' previously, Mercedes tested a passive version last year and tried it out again during Friday practice at the Nurburgring.

The W04 was designed to accommodate this as the version seen at the Nurburgring was a far tidier package compared to last year's, with the ductwork neatly integrated into the roll hoop and the problems associated with the duct under the rear wing resolved.

The device works by diverting airflow through a ductwork system, once a certain speed is reached, to stall the wing at high speed. Unlike DRS, this can be used every lap and on sections of the track that are above the standard system's activation speed.

To allow better packaging of the system, this year's Mercedes has more of the roll hoop formed by the removable bodywork. This allows Mercedes to incorporate the inlet ducts for the system neatly just behind the airbox inlet.

One large duct feeds high pressure air into the system while the smaller inlet further back down the engine cover acts as the switch for it.

Exiting the engine cover are the two exit ducts. One larger duct passes out under a modified monkey seat wing while the other one passes up under the rear wing.

Linking all this pipework is a fluid switch. While it is basically the same solution as the f-duct, it is legal under the current rules because there are no moving parts and it requires only a change in airflow from the control inlet to flick the device from a neutral state to stalling the rear wing.

But unlike Lotus, which uses the engine airbox pressure to activate the switch, Mercedes appears to simply use increasing air speed over the bodywork.

Rear view of the Mercedes system © XPB

As soon as the car reaches a certain speed, the fluid switch sends the flow up under the rear wing. This is likely to be at over 200km/h, so that even when stalled the car has enough downforce to take any fast kinks.

The duct under the rear blows upwards to upset the laminar flow under the wing and this stalls the wing. Stalling reduces both downforce and drag and this will increase top speed by some 8-10km/h.

In testing passive drag reduction systems last year, teams found the switch will still leak airflow under the rear at lower speeds.

Both Lotus and Mercedes now have extra outlets in the wing stalling duct to bleed off this unwanted flow at lower speeds. Now, only when the switch is fully activated and blowing hard, does the effect stall the wing.

Mercedes will not race the system this weekend, but it likely to appear at upcoming circuits where downforce is needed for slower sections along with good speed on the long straights.

FRONT-END UPDATES

At the other end of the car is a new nosecone set-up. This is more streamlined and features larger wider-spaced wing mounting pylons. It also sports the Silverstone-spec front wing and revised turning vanes.

Mercedes has front-end updates too © XPB

Since last year, the Mercedes nosecone has featured a very slim rounded nose fairing in to meet the square front bulkhead. This abrupt section change has been smoothed by a larger vanity panel, allowed under the 2012 rules, to streamline the nose.

Underneath, the section of the nose's impact structure will be unchanged and just the bonded nose tip, mounting pylons and vanity panel are new. This means the new set-up does not have to pass crash tests again.

The reshaped upper nose section probably doesn't add much aero performance, but the underside does. The slightly higher nose tip and wider mouth formed by the pylons will direct more airflow to the new turning vanes under the car, which in turn drives better flow under the floor.

As a result, the new nose may actually create more rear downforce because the diffuser is working more effectively.