With the start of the Formula One season upon us, all eyes are on McLaren and its drivers, reigning world champion Jenson Button and former world champion Lewis Hamilton. But the attention isn’t exclusively on the champs. Everyone’s talking about the creative aerodynamics of the MP4-25 cars they’re driving.
Nobody outside the team is sure of specific details, but an ingeniously simple system allows Button and Hamilton to control the amount of downforce generated by the rear wing during the race. The wing has generated howls of protest, but the rulemakers at the Fédération Internationale d l’Automobile have approved it, so the cars are set to race Sunday in Bahrain.
McLaren’s wing addresses a paradox of racing: How to maximize downforce in the corners while minimizing drag on the straights. It’s always been a compromise, one that traditionally has required teams to continuously adjust the front and rear wing on a car during practice until they find the right balance.
Ideally the amount of downforce would be variable — increased in the corners and decreased on the straights. But F1 prohibits the use of movable parts to manage airflow, so no one’s been able to find a way to do that.
McLaren’s solution appears to combine an aerodynamic principle common in aviation with the mechanics of a flute.
Downforce operates on the same principle as lift, which is of course imperative to flight. At low speeds — actually, high angles of attack — airflow over the wing of an airplane begins to detach from the upper surface of the wing. When this happens, the wing is less effective at generating lift. That can impair control or, worse, result in insufficient lift to maintain flight.
To generate more lift at low speed, aircraft designers often use slats and other devices to increase airflow over the wing. Look out the window of an airliner and you’ll see slats along the leading edge of the wing that deploy when the airplane is landing. Boeing and others have even experimented with putting the jet engines over the top of the wing to increase the energy of the airflow and the lift of the wing.
In a Formula One car, the wing works upside down. Instead generating lift, it creates downforce that pushes the car into the ground. The added downforce allows the driver to carry more speed through a turn. The rules say McLaren can’t use movable devices like the slats of an airplane to control airflow, but nothing says it can’t use a passive device.
McLaren’s system is brilliant in its simplicity.
It is believed that a small air scoop in the nose of the car — you can see it just below the steering wheel in the pic below — allows air to enter a tube that runs through the cockpit and the air intake above the driver’s head to the rear wing. From there it flows to the wing and passes through small slots to the back side of the wing, where the added energy can aid the airflow like the slats on a plane. This increases downforce in the corners.
The downside of increased downforce is, of course, increased drag — in this case induced drag, a byproduct of lift.
To minimize this drag, the driver can close the vent with his knee (or elbow, no one outside of McLaren seems to know for sure), halting air flow to the rear wing. Button and Hamilton can thus control the airflow to the rear wing in much the same way flute players control the flow of air through their instruments. When the driver closes the vent, it essentially stalls the rear wing, thereby reducing drag and increasing speed on the straightaways. Some accounts put the increase at 6 mph.
Strictly speaking, there are no moving parts on the car to control the system. That, of course, has not kept several teams from complaining that McLaren’s novel approach violates the spirit of the rules if not the letter. But the FIA has deemed McLaren’s air-management system legal, and team boss Martin Whitmarsh expects other teams to adopt similar setups.
That, of course, depends upon whether the interesting idea actually works. We’ll find out Sunday in Bahrain.
Photos of the McLaren MP4-25 car: Vodafone McLaren. Photo of the aircraft wing: Arpingstone/Wikimedia Commons
Here’s how it works, in pics:
Air enters a vent — that’s it just below the steering wheel — on the nose of the car…
…then flows through a tube through the cockpit and air intake behind the driver’s head to the rear wing…
…where it passes through small slots to the back side of the wing. The driver controls the airflow by opening or closing a hole in the tube.