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Tuesday, 13 September 2016

Ariel's Thinking About a Vacuum Car

Ariel Atom AERO-P research car
It's not just large car companies that like to push the boundaries of automotive technology, you know. Small British sports car companies are doing things their own way and many of those things are of distinct intrigue. TVR is punching its way out of its coffin with an all-new car using Gordon Murray's ingenious new construction and manufacturing techniques dubbed "iStream." BAC, makers of the Mono one-seater, have successfully made body panels out of graphene, the upcoming wonder material that's just one atom thick (although they used more than one layer of course!). Oh, and speaking of atoms, let's look at Ariel's latest news...

Despite still looking oh-so cool after over a decade, the Ariel Atom isn't particularly aerodynamic. The nose cone and little plastic headlights may have a tiny frontal area but airflow needs to be smooth and an exposed tubular frame just isn't. Faster versions can be had with "F1-style" wings, but as Ariel themselves point out, "conventional aerofoils and aerodynamic devices give downforce at speed – the higher the speed, the higher the downforce.  However the negative aspect of this is that downforce is not required for most of the time, particularly for road based cars during normal driving, and is not available at slow speed or when stationary."

"The ensuing drag of fixed aerofoils also not only reduces a vehicle’s top speed but has a marked negative effect on its fuel consumption as well as emissions.  On the Atom drag can be increased by as much as 15% by adding conventional aerofoils with the resultant effect on fuel use and tailpipe emissions."

So you see, it's dirty downforce, only working at speed and holding back certain aspects of the car's potential, plus wings make you look like a bit of a chav sometimes.


The small Somerset-based company is thus on a quest for a better solution. The one it's testing now allegedly guarantees downforce from a standstill without any real drag penalty. I'll give you a hint: look at the picture above and atop this article. See how it looks like the car has a surfboard glued to the bottom? It's closely related to that, which isn't on normal Atoms.

The large flat floor conceals two fans which suck air up from underneath the car through two small tunnels, thus generating a low pressure area under the car. The reason this matters is that with low pressure below and high or unaffected pressure above the car, the air going underneath is accelerated as it tries to equalise the pressures. This causes the car to be sucked downwards. The effect can be guaranteed by sealing the floor and using a wing-shaped underside to generate "ground effect," but cars using fans to generate or greatly increase the effect are generally known as "sucker cars" or "fan cars." Ariel have nicknamed their prototype "The Vacuum Cleaner" for obvious reasons!


Of course, a vacuum car is nothing motorsport hasn't seen before, both in sports cars and single seaters. Naturally the F1 solution was more complicated, but the earlier American machine had a simpler setup; the 1970 Chaparral 2J featured a two-cylinder snowmobile engine running completely independently of the big-block 680hp Chevrolet V8 powering the wheels, instead running at a constant speed to spin the fans and generate a consistent aero platform. It looks a bit like someone plonked the air conditioning unit from a skyscraper on the back of a fairly basic Can-Am car - although its aluminium construction was itself actually quite advanced at the time - but combined with Lexan skirts connected to the suspension (thus creating a seal around the underbody) the 2J was as much as two seconds per lap faster than the opposition... when it wasn't suffering mechanical problems. Oh, and in case you were wondering it does have a pair of rear wheels under there! I imagine pit stops took a while...


In the 1978 Brabham BT46B Formula 1 car designed by Gordon Murray, the enormous central fan system was connected directly to the 520-horsepower, 3.0 flat-12 Alfa Romeo engine via "a series of clutches" and drew air from both underneath and partially through the top-mounted radiators, the latter so that Brabham could pass it off as a legal and innocuous engine cooling device (Spoiler Alert: this did not work). One giveaway was that this setup caused the car to squat down when the driver revved the engine, so strong was the suction! It required a different driving style involving hitting the throttle as early and as hard as possible, thus generating the downforce to carry major speed through a corner. It worked so well that the car was banned after a single dominant race at the Swedish Grand Prix, at which point Brabham had to revert to the previous, fan-less spec. Niki Lauda later said of the experience that it would become very tiring for the drivers to be subjected to cornering forces of that magnitude, which has a byproduct of making the steering heavier as well as throwing the driver around more.


Inspired by these two cars, Ariel's philosophy is somewhere between them. The fans run separately from the engine, like the 2J, but they don't run all the time and you can switch them on and off to make the car squat down only when it needs to, a bit like the 46B. There are two 100mm electric fans, one at each end, powered by a dedicated battery pack. In the photos of the prototype there is no clear exit point for the air - certainly no enormous turbine-looking thing like the '70s cars - but on this CFD simulation image of theirs, there appears to be an additional banana-shaped pipe between the rear wheel and the main body, just ahead of the suspension wishbones. Maybe it's that? They don't seem to say in their press release [EDIT: There's a Y-shaped one-into-two pipe between the seats/under the engine air intake - it's that]. In any case, the reason they've made the fan system switchable instead of running permanently is because when you're cruising on the motorway, you don't need the tyres to be forced so hard into the road. Turning the fans off would mean less force on the tyres, therefore less friction and rolling resistance and thus slightly better fuel economy than if the fans were on. Ariel say that this version 1.0 vacuum car is already making three times more downforce than a normal Atom with wings on while adding no drag, the benefit of which is much more grip and stability when stopping and steering, not to mention better traction under acceleration, without losing any top speed or significantly affecting economy.

But you may be wondering, if we came up with this stuff in the 1970s, why has it not been on road cars before? Not even Adrian Newey's crazy new Aston Martin does it. Well, there is some evidence to suggest the McLaren F1 road car had front and rear(?) fan systems with a switchable "high downforce mode" to help cancel out all the lift naturally generated by any car body shape, while also blowing cool air strategically onto the hot bits like the engine, ECU, brakes etc. However, McLaren themselves are very quiet about it, only saying in the original 1992 press release that "two powerful electric fans remove boundary layer air from the rolled S-wave of ‘reflex’ diffuser sections, helping to control movement of the Centre of Pressure" and never explaining further. It sounds like it's more for balancing the car's handling than for outright grip.

McLaren F1 road car
Red Bull X2010 Gran Turismo concept on its side, revealing where the air gets sucked in
At any rate, even if we put aside the added complexity of a fan car, there are a few practical issues with the concept. Some F1 teams claimed that Brabham's car was picking up dirt and stones from underneath it and chucking them out the back of the car along with the air, which wouldn't be ideal in any situation with multiple cars close together (or a bike following). While some speculate that this was merely an attempt to get the car banned on safety grounds, it would nevertheless be interesting to know what McLaren's solution to this problem was, if indeed it's a real problem. Would the suction effect be weakened if the intakes had grilles on them to filter out grit and leaves?

Secondly, the reason the Ariel Atom AERO-P research car has a big rubber platform on the underside is the same reason the Chaparral 2J had sliding skirts connected to the suspension; for the effect to be fully realised, you need to 'seal' the floor onto the road surface. This is fine on most race tracks, but if the car hits a big kerb or rises up as it drives over a big crest in the road, the seal is lost and so is the downforce. Suddenly you'd have significantly less grip to play with than you did a second ago - I read that the 2J could make a tonne (1000kg) of downforce just with the fans - which could easily lead a rather significant accident. Again, if McLaren or the F1's designer Gordon Murray opened up about their system we could find out what they did about this (maybe it was as simple as giving the driver a toggle switch like Ariel has done and then telling them to only use it on a track).

Ariel will find out all this and much more - including how to retract the rubber skirts when they aren't needed - as their research continues. The AERO-P will also be used to study other, passive aerodynamic concepts and to study "the particular requirements of new technology powertrains, not yet released and still under development."

If they keep us informed, it will be fascinating to follow the development of this notorious, immensely effective, yet scarcely utilised aero effect and find out whether it really is feasible for road cars on a more everyday basis... or whether drivers could handle an Atom track car making over a tonne of downforce!


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1 comment:

  1. That's a great explanation of a complicated subject!

    ReplyDelete