F-Duct vs Blown Diffuser

McLaren and Red Bull are the two top teams for a couple of reasons but their success revolve around their unique rule bending technologies that both introduced at the start of the season. McLaren with their F-Duct [a switch that reduces drag on the spoiler to increase top speed] and Red Bull's Blown Diffuser [a reworked exhaust that helps with downforce and grip]. It is now mid way through the season and both teams have now taken on the other's system with varying results. Before I go any further there is a big hill called downforce that needs to be climbed.

*Before I go on you will see me use the terms wing and spoiler interchangeably

Downforce is one of the effects air has any moving object. Lift is the complete opposite of downforce and it is the force that keeps planes in the air. Even a slight amount of lift on a car is dangerous and unwanted [as seen here]. However downforce is always wanted and you can ask any F1 team and they will literally kill to be able to have a downforce advantage. Downforce affects a car by pushing it down to apply force to the tyres, this adds grip to the tyre and more grip = higher speeds the tyre can take and better lap times. Downforce has one flaw however, it reduces top speed. There are two ways however to get the best of both worlds. [Still lost on downforce, watch this]

Active aerodynamics is the best solution where you can have your cake and eat it. Most sport cars take advantage of this with spoilers that pop up above certain speeds and then lowers when the speeds get higher. This however is banned in F1 [actually it is allowed, still new however but adjustments can only be made on the front spoiler]. This brings us to the F-duct system. The F-duct is McLaren's genius idea of blurring the line between active and passive aerodynamics. Unlike traditional methods of active aerodynamics which use actuators to move the aerodynamic pieces, the F-duct uses a channel of that blows on to the spoiler. The way in which they blow air on the spoiler "stalls" it, which pretty much makes the car act as if the spoiler doesn't exist. Now for the active part...... The drivers control this duct by moving their hands to cover another duct which activates the F-duct. Due to the safety risks assosciated with drivers removing their hands from the steering wheel, the F-duct is now operated by their knees. In a race the driver will only activate the F-duct on a high speed straight to reduce downforce, reduce wind resistance and increase top speed. Almost all of the top runners use the F-duct now with Red Bull being the newest on that list [they still experimenting with it though]

This picture shows McLaren's 2009 car [MP4-24] on top and their 2010 car [MP4-25] at the bottom. The most obvious difference is the extension of the airbox towards the rear spoiler, this extension is the F-duct.

This picture is what the F-duct looks like underneath the skin of the car. This is actually Red Bull's system. The 2 red arrows point to the air exists which "stall" the spoiler

Now on to the second way to get the best of both worlds in the world of aerodynamics, The diffuser. Nothing is new about the diffuser, it's actually older than active aerodynamics and also more prevalent. A diffuser acts like a spoiler but it works through the magical act of suction. Because of this wind resistance is little to nothing and does not affect top speed. In the same way a spoiler pushes down a car, a diffuser sucks it down. The most ideal diffuser will have fans underneath to help the suction. After the dominating Brabham BT46B, which used a fan for suction [to bypass the rules they claimed the fan was used for cooling] fans of this type were immediately banned. The blown diffuser followed shortly after. This used air exiting the exausts [which were now placed underneath the cars] to provide a suction effect. The idea is that the exhaust being pushed out by the engine would cause a pulling effect on the air underneath the car causing a slight suction effect. This was prominent in the 90s but was soon abandoned as cars immediately lost grip when drivers lifted off the throttle. In the 2010 F1 season the blown diffuser was reintroduced by Red Bull who are rumored to be using a system which lessens that loss of grip whenever drivers lift off the throttle. Despite being top secret and almost illegal, its also being used by the top runners [McLaren is the newest to use it but abandoned it for the last race]

Brabham's BT46B fan car. The large fan at the back is quite prominent. Weirdly enough this car was designed by a man known for his days at McLaren, Gordon Murray. In fact the McLaren F1 [the road car] has a similar fan system on its diffuser.

These next images show the difference between the conventional top exiting "periscope" exhausts found on last year's Ferrari F60 [top] and the blown diffuser exhaust found on this year's Red Bull RB6. The blown diffuser's exhaust is found right in front of the rear wheel but not directly into the diffuser. If it was in the diffuser, it would be more efficient with downforce but more disastrous on the engine.

Well, fact is both of these systems will be banned for next year so this may be the last we see them at all. The races so far have shown the advantages and disadvantages of each system and its a matter of time before each team refine and use the other's tech.

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