Will Gray

Tech Talk: The new ‘double diffuser’?

Will Gray

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The pre-season questions posed over McLaren's unique rear
wing concept smacks of the fuss made over Brawn's double diffuser last year -
but what's it all about, and will it make such a difference?

There's no smoke without fire, and the fact that several
teams have called for a clarification over the design treatment at the rear end
of the new McLaren means the team has simply created a clever concept or
discovered a new loophole that others failed to spot.

Last year, Brawn got the jump on their rivals by spotting
a gap in the regulations that allowed the double diffuser - and while their
concept met the letter of the law, other teams felt the design pushed the
spirit boundaries to the limit. Brawn broached the subject previously, trying
to ban it because he knew what would happen, but he failed and so he ran with the
double diffuser and they became standard equipment.

McLaren's innovation, it seems, is a similar matter. They
have cleared it with the FIA once already, but just as happened with the double
diffuser, the design is under investigation as the teams head to the opening
race of the year.

But what have they done?

The design, according to popular perception, revolves
around the concept of aerodynamic stall.

Racecar wings work because the shape forces air to flow
faster under the element than it does over the top, creating a pressure differential
and a downwards force. Steeper wing angles create more downforce but only to a
certain point, after which the flow underneath separates from the surface and
becomes turbulent, slowing down and ruining the downforce. To stop this, the
rear wings on an F1 car use two elements with a gap between them to allow air
to merge in and regenerate the underside flow, allowing it to flow at greater
angles before it separates and stalls.

With high downforce, however, comes high induced drag
that slows the car down - and it is here where McLaren's concept is understood to
be focused.

It appears the McLaren has a flow channel in which air
enters at the top of the airbox above the driver's head and travels through the
inside of the engine cover all the way into the upper plain of the rear wing,
where it exits through a slot gap at the rear. In theory, this would inject
additional air into the underside flow on the rear wing, allowing the air to
stay attached on the steeply angled wing.

If the flow through this gap could somehow be stopped at
high speeds on the straights, then the underside flow would become turbulent
and the drag would drop. If this is, indeed, the concept, the only way it could
be done is without a moveable aid (as these are banned), and without that any
design that enables it to work
only on straights and not on high speed corners would be a real design

And the big gain to all of this?

With refuelling banned, fuel efficiency is a real focus
this season - and with drag having to be overcome by fuel-sapping engine power,
if the drag can be reduced the engines can run leaner and fuel will last
longer. And that could be a crucial factor in race strategy.

Of course, it could be much simpler that that, but until
the teams work out the concept behind it, their only solution is to protest and
see if they can get it outlawed...

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