Side mirrors engineer’s nemesis
In the pursuit of aero perfection, Rob Carstairs would scrap wing mirrors on all vehicles. Rob Maetzig reports.
Rob Carstairs hates wing mirrors. Well – he doesn’t really, because he acknowledges they are a very useful motoring safety tool. But wing mirrors do interfere with his job as an aerodynamicist at Ford.
‘‘The first thing I’d get rid of is the side mirrors. Off they go, that’d be great. They are useless for aerodynamics,’’ says Carstairs.
It isn’t just mirrors that are a thorn in the side for aerodynamicists. In his pursuit of aero perfection, Carstairs would scrap and change a lot of the things taken for granted on modern cars in order to create the most fuelefficient vehicle he possibly can by reducing drag.
The dream for an aerodynamicist is a vehicle that directs the flow of air smoothly all the way over the vehicle, without any disturbances.
That dream happens to look like a teardrop. A teardrop shape allows air to flow smoothly, while the long tail solves the problem of vacuums that are created as air leaves the roof and the trunk. A car this shape would easily be the most fuel efficient on the road.
But there are many reasons why these things aren’t solely left up to aerodynamicists, not least because most people don’t want to drive a car that looks like a giant teardrop.
Fortunately, the final look of a car is the result of the different demands of a number of Ford teams, including designers, aerodynamicists and safety engineers. Safety, of course, is why Carstairs’ nemesis the side mirror is a non-negotiable fixture on cars – a fact he agrees is only a good thing.
Compromises like this are a key part of the design development process for Carstairs and his colleagues at Ford. The designers know what customers want vehicles to look like, but this isn’t always good for aerodynamics.
Likewise, Carstairs can make suggestions based on aerodynamics, but if the vehicle won’t sell then they can’t be used. Because of this, a lot of his work involves making subtle optimisations, which can have a surprisingly big effect. ‘‘For example, under the front bumper of the Everest SUV we have added wings on the outer parts to direct airflow. It improves aerodynamics by 5 per cent.’’
Many Ford vehicles now also have a slight flick in the tail lamps to stop the air flow from wrapping round the vehicle and causing added drag – an ingenious and mostly cost-free improvement in aerodynamics.
The work of Ford’s aerodynamicists has been greatly improved by advances in computing.
While wind tunnels are still a crucial part of aerodynamics testing, complex computer models and simulations now allow the aerodynamics team to easily test design tweaks on Ford’s supercomputer cluster. Rather than replacing wind tunnels, the computer models are an additional measure that can replicate hours of testing that would have been unimaginable only 10 years ago. ‘‘If we run tests for two days we can easily complete more than 50,000 hours’ worth of simulations.’’
The look of a vehicle is also affected by the markets it is destined for. Although lower cars are more aerodynamic, the amount of clearance a car has varies by model, and is also heavily dependent on how flat the roads in a region are.
‘‘In India for example, roads can be a bit bumpier so a vehicle might have to sit a bit higher. We have to consider all the different road conditions across the region.’’
However, as more car buyers are demanding fuel-efficient vehicles, the design changes suggested by aerodynamicists are being prioritised.
And in the era of electrification, vehicles are already adopting more aerodynamic shapes.
‘‘On an electric car, demands for powertrain cooling are reduced, so the grille openings can be smaller. Things like that are quite handy for us aerodynamicists.’’