Who's winning F1's crucial diffuser war?

On September 1 2017 the EU banned the sale of vacuum cleaners that used more than 900W of energy. This was down from somewhere around 2000W, so most people felt that was a bit harsh and it is possibly one of the reasons the UK is now trying to manoeuvre its way out of Europe!

The reason for all this was that most people felt this new regulation of using less power would mean the vacuum would be less powerful. But it turned out this was not so, as companies like Dyson just put extra effort into the detail design of the airflow and motor and came up with new machines that clean just as well using less power. The negative is they cost a lot more to purchase.

Bear with me, this is relevant to Formula 1.

Vacuum cleaner requirements are all fairly similar: you want them to clean up any dirt that is on the floor. To do that, the motor and fan system generate a suction and they suck in that dirt and dump it into a container. If you open up any of the slots that are on the suction tube, the suction effort at the cleaning head reduces and it lifts less dirt.

That's good for getting it untangled from the curtains but that's it. Simple, you might say, but no, there are good ones and not so good ones and I have yet to see one that tries to push the dirt up the tube - they always suck.

F1 is no different from the big world of vacuum cleaners (I don't mean it sucks, although some might disagree). An F1 car is actually very similar, it is the rear of the car that makes the rest of it all work. Without the suction from behind, the front wing could be made from double the amount of elements and it still wouldn't make up for an inefficient diffuser.

I have said on many occasions that getting the outer corners of the diffuser to connect to the low pressure behind the rear tyres is vitally important to its overall performance. If you look at the Red Bull, Ferrari or Williams, they are very similar in design. They use the maximum height and width with a very square upper outer corner.

The Mercedes still has a little bit of room to go with the upper outer corner detail, but rear brake duct design has an effect on this area, so this may need a change there before it can optimise the diffuser (after all, who am I to criticise Mercedes?).

For a comparison to teams that have a long way to go with diffuser design you can look at the Toro Rosso and the Haas. Their upper outer corner detail just allows airflow through inside the rear tyre into that low pressure area behind the rear tyre. Doing this does nothing for the performance of the underfloor and in effect just reduces the overall downforce potential.

The rest of the car is there to service the requirements and performance of the diffuser. The Coke bottle sweeping inwards and downwards does this to allow the mass flow that is being pulled down into that area.

James Allison, technical director of Mercedes, made the bold statement that by sweeping it inwards and downwards as tightly as possible the team's sidepod design for this year was worth a quarter of a second alone. If that is so then the Red Bull packaging must be worth 0.5s. I don't think I have ever seen a sidepod Coke bottle package so neatly defined.

The undercut area at the front of the sidepod is there to make sure that low pressure suction from behind the car is maximised at the trailing edge of the bargeboard area. All of the cars are fairly similar in that they all have an undercut sidepod design, but I think the McLaren shows what I mean best.

It might be just because it is orange and stands out better than the others but I do believe McLaren has maximised this undercut and by having a small letterbox style radiator inlet it has also got maximum height. This in turn allows the bargeboards to pull more airflow out from underneath the front of the chassis.

I don't think I have ever seen a sidepod Coke bottle package so neatly defined as Red Bull's

The front section of the sidepods are different from car to car and it depends on how you have packaged the side impact structures. Some like Mercedes and McLaren still have them incorporated in the sidepod package. Others like Ferrari and Red Bull have them in separate or partly separate aerodynamic structures.

I think the best way of recognising who has what is the detail of the outer vertical vanes.

On the cars with the leading edge of the sidepods further rearward, Red Bull and Ferrari have more dramatic vertical vanes because they have that little bit more room to manage the turbulent airflow coming off the low pressure area behind the front tyre.

The McLaren and the Renault have less dramatic components in this area mainly because they just don't have the room. To manage the turbulence the vertical vanes need to be positioned relative to the rear of the front tyre.

The bargeboards themselves vary dramatically in design, and again this is because of the space that regulations allow them to be in - the extra space that the rearward sidepod design opens up.

I don't think anyone would argue with the fact that the Mercedes in this area has the most detailed package. It is akin to watchmaking in its detail and as every component is working in conjunction with each other, the hours of CFD research in this area must be astronomical.

McLaren and Renault are a close equal second on this front with Red Bull being probably the most sophisticated of the rear sidepod leading edge brigade. The Ferrari is a bit more robust, with fewer components, all a bit more bold, and a bit more agricultural. But this might be no bad thing, as I'll explain later.

From there it's on to maximising the low pressure area behind the trailing edge of the front wing. If all the components from the diffuser, forward, are doing their job then the front wing will work more efficiently and more consistently, and that is why we have seen more and more slot gaps being opened up on the front wing main plane and flap assemblies.

Some of the details on the Ferrari are a little agricultural. Well, in some cases that might not be a bad thing

You need to be able to feed this low pressure area behind the front wing consistently otherwise the aerodynamic flow structure of the whole car falls down and you get massive losses of downforce from every area.

Front wing wise all the cars have now got finite detail on every component, but the McLaren, Red Bull and Mercedes have really pushed the boat out on that detail.

One of the interesting features is how the flaps originate at their inner ends. Some cars, such as the Mercedes, start the flap from a very short chord, which curves upwards. This reduces the vortices that are created in this area. The Red Bull doesn't do this quite as much.

In the past this vortex, which was called Y250 vortex because that's how far it was from the car centre line, was very important, but now, with more room for bigger and better bargeboards, it is not as important and can actually do more harm than good.

The McLaren and the Ferrari have more of a pronounced tunnel in the front view of the flap design. They sweep downwards again as they go outwards. This will mean that they are pulling more airflow from the FIA defined central wing section, which is a neutral aerodynamic section.

Teams do different things with their wing mount structures. Mercedes is probably the shortest and least dramatic and McLaren the longest and most detailed. All of these areas have to work together, you can't entice the airflow to go in two directions at once.

Initially pulling it in under the raised section of the chassis is the objective, so getting the maximum direction change out of it early on is very important. After that, it is up to the vertical vanes under where the driver's feet are, and the bargeboards, to scavenge that mass airflow back outwards across the leading edge of the underfloor. From there, it is down to the diffuser pulling it under the floor, creating a low pressure underneath the car.

I said above that some of the details on the Ferrari were a little agricultural. Well, in some cases that might not be a bad thing when a car is running in traffic. After all, on many occasions last year Lewis Hamilton was fairly vocal about how difficult it was to follow another car in the Mercedes.

He wasn't used to it because up until then the team had a car that normally would qualify on pole and disappear into the distance. Last year, on a few occasions it was a little different, but both Ferrari drivers had to endure running among other cars as well, so perhaps the Ferrari aerodynamic design is just that little bit more robust and will perform better in traffic.

Get that all working together and you have a car that produces lots of downforce. Oh, and the other thing is sealing the sides of the floor as best possible. Failing to sort this is like opening that slot on the vacuum cleaner suction tube - you just lose suction, and losing suction is the same as losing downforce, and in turn grip.