F1 2009-13 part three: the f-duct

When the 2010 McLaren MP4-26 broke cover pre-season, rival teams' attention was immediately drawn to the letterbox intake on the top of the front of the chassis. This was the first glimpse of the f-duct, which became the big technical topic of discussion that season and played a part in the introduction of the DRS in 2011.

The concept of the f-duct was elegantly simple. The intake was used to channel air through the car and directed to the rear wing. But when a hole in the cockpit was covered - in the case of the McLaren by the driver's elbow - this airflow was used to blow across the upper element of the rear wing to stall it, slashing drag.

While there was some strong public opposition to the f-duct on the basis of the oft-referred to ban on moveable aerodynamic devices, it wasn't illegal.

The regulation in question simply stopped bodywork itself moving. There was nothing stopping the driver influencing the aerodynamics until a simple rule was brought in for 2011 stating that "with the exception of the parts necessary for the adjustment described in Article 3.18 [the DRS], any car system, device or procedure which uses driver movement as a means of altering the aerodynamic characteristics of the car is prohibited".

The bottom line is that the driver moved to influence the aerodynamics, but did not move any aerodynamic devices directly. That's what made it so brilliant, and so legal.

"The driver was the moveable part, which is now against the rules but wasn't in 2011," says Sam Michael, now sporting director of McLaren but then the technical director of Williams. "I remember seeing it in winter testing and my opinion was that it was legal and never took issue.

Michael, then at Williams, had no problem with future employer McLaren's breakthrough © XPB

"I rarely do with things like that. In F1, ideas do come up and my default position is that teams have usually done their homework properly. To invest time in such a device, you have to be pretty sure about it. I'm not always right about that because sometimes people do have to change their designs but my impression was that there was nothing wrong with it.

"I remember seeing that postbox thing at the top of the chassis and thinking it was too big for a cooling scoop, especially as it was running at Valencia in the cold winter. Obviously, there was the connection up to the rear wing and from the rear of the car you could see the profile where they had cut out the separation point, so the flap had that little slot in it."

A group within McLaren headed by Mike Brown worked on the f-duct concept and the decision was made to integrate it fully into the 2010 design. Don't underestimate how much work it took to optimise the f-duct, which had been tossed around in McLaren for some time and was at one stage considered for trial in '09.

"We could have tested it but I don't think it was really ready," says Paddy Lowe, technical director at McLaren in 2010. "It was one of those projects that if you don't know it's going to work, you don't put 15 people on it, you have one or two. So that takes quite a long time.

"The project had actually been going for perhaps 18 months and it came to a point that winter where we told the individual who was running it 'we're going to go with it, it's got to deliver now and we're not going to have any fallback option'. That's what focused the effort on it and a much bigger team attacked it and it was launched with the car.

"It was a fantastically elegant solution to a clear loophole in the regulations, unlike the double diffuser. It was a great bit of lateral thinking by one or two people at McLaren. Mike Brown was the technical guy on it but I'm not totally sure whether he was the one that found the idea because there are a number of elements to it.

McLaren's f-duct neatly fitted within the rules © XPB

"It started off with identifying a switching device without moving parts. Then you have the idea of stalling a wing by blowing the slot. Then you've got the problem of how do I put that together within the regulations and how do you control it legally?

"Mike certainly worked on the switch and slot aspect but I'm not quite sure who said 'ah yes, here's how we will put it together because Article 3.15 [of the technical regulations, covering moveable aerodynamics] doesn't mention the driver."

At Red Bull, chief technical officer Adrian Newey watched the f-duct situation with interest. Today, he admits that he had no particular doubts about the legality of the design, although at the time Red Bull was among the teams that rushed to demand clarification of the rules.

"We certainly missed the f-duct and there's no doubt that it was legal," admits Newey.

"The only grounds on which you could argue about it was that of safety. There were at least two accidents during the year that were caused by a driver only having one hand on the wheel.

"To get the most out of the f-duct, you want to be on it as soon as possible, which means the drivers are taking their hand off the wheel just when the car is most unstable at the corner exit. [Sauber's] Kamui Kobayashi had an accident and there was another case that year. So in terms of safety, you could possibly argue that the f-duct was of slightly dubious legality.

Sauber was among the first to copy McLaren © XPB

"But hats off to the guy at McLaren who came up with it."

Ultimately, that was pretty much the attitude the whole paddock had to take. The battle was on to copy the f-duct. Much to McLaren's surprise, it did not take long for the clones to start to appear. The first non-McLaren f-duct was tried by Sauber during the opening race weekend of the season in Australia, while Ferrari trialled its design for the first time in race three in China.

"There was a realisation by the other teams of the gap that had been found and there was a bit of push-back and argument," says Lowe. "But they seemed to roll over quite quickly and accept that a flank had been pulled!

"What was depressing was how quickly everyone managed to bring out their own versions given it involves some quite tricky aerodynamics. We thought it would take the best part of a season for everyone else to catch up. It was rather depressing to see how quickly alternative solutions arrived."

Red Bull's f-duct made its first appearance in the fourth race in Turkey. But like all those who adapted their cars to it, it was reliant upon bodging together pipework using whatever hatches in the chassis happened to be available. All sorts of different parts of the body were employed for this. In the case of Red Bull the driver's leg was used, but others had to opt for a hand-off-the-wheel approach.

"We were lucky because one of the things that was central to an f-duct was to be able to duct air in and out of the monocoque," says Newey.

"We had sufficiently big holes in the side of the chassis for the wiring loom we could put the duct through afterwards. That season, the chassis was homologated for the season so if you didn't have that, you couldn't put an f-duct on.

Red Bull's f-duct arrived for Turkey © XPB

"I guess everybody must have been in a similar position because almost everybody managed to get it in some shape or form. But it was not an easy piece of technology to get to work even though we could see what McLaren had done. Certainly, our first attempt at it in Turkey didn't work very well at all.

"But the definitive version actually worked very well and was more powerful than the McLaren system because we went one step further and put the slot in the main plane rather than the flap of the rear wing, which had a bigger benefit. Lotus did the same and, subsequently, McLaren copied that towards the end of the season."

It was clear that the f-duct was not long for the world of F1. The decision to outlaw it was as rapid as it was wise, given that it could have led to all sorts of multi-stage switches for drivers to trim downforce levels for specific corners as well as stalling wings for straightline speed.

As Michael puts it, "the driver could effectively be playing a musical instrument in the cockpit while driving".

"We had some interesting discussions," says Lowe. "At that time, FOTA was quite active so what would happen is that there would be a FOTA technical meeting before the technical working group meeting. Generally, we agreed a joint approach to things going into the TWG.

"In the FOTA meeting, all of the teams ganged up on McLaren - or at least it felt like that - and said we're going to ban this because it's got no business being in the sport. I felt it was more that they were fearing they were behind and being opportunistic.

Kobayashi was caught out by the need to drive one-handed © XPB

"It's not an expensive activity. You were just making carbonfibre parts from windtunnel tests and that's what F1 teams do anyway! Arguably f-duct-type devices are cheaper to make than many things.

"There was a safety aspect. We had gone to some effort at McLaren to produce a solution where the driver didn't take his hands off the wheel, so there was no loss of control. Other teams came out with things where they took the hand off the wheel.

"We did have quite a lot of debate with Charlie Whiting to say they're just not doing it safely. But that didn't seem to get anywhere. You can see on the in-car footage, these other teams were moving their hand off the wheel so then you've only really got load on one hand. OK it wasn't too far to travel back but still if you had a puncture, blow out or something you're not actually in full control..."

Teams did attempt to recycle the effect using passive f-ducts based on fluidic switches, while the so called 'double DRS' - used by Red Bull - flowed air across parts of the rear wing to increase the drag reduction when the DRS was deployed before being outlawed.

At the same time, the regulations for the DRS were also being discussed, with its arrival part of the rationale for outlawing the f-duct.

HOW THE F-DUCT WORKS
By Craig Scarborough

Pictured is the internal workings of the Force India f-duct. The f-duct is formed as a Y-shaped duct ,where the central connection is a fluid switch.

This fluid switch has no moving parts and is controlled by a small control duct running from the cockpit. Airflow enters the duct around the roll hoop and normally the flow passes straight through the switch and out of the lower exit duct for zero aero effect.

When the driver closes off the cockpit duct with his hand or knee, the air now coming through the control duct alters the fluid switch and the flow passes out of the other exit duct. This sends a jet of air out of a slot in the rear wing, which is enough to break up the airflow under the wing. This loses downforce and, more importantly, drag, which aids top speed.

NEXT WEEK: Exhaust-blown downforce