The Rise And Fall Of The Fan Car

The advent of aerodynamic wings in motorsport was one of the most dramatic changes in the mid-20th century. Suddenly, it was possible to generate more grip at speed outside of altering suspension setups and fitting grippier tyres. However, it was just the beginning, and engineers began to look at more advanced ways of generating downforce without the drag penalty incurred by fitting wings to a racecar.

Perhaps the ultimate expression of this was the fan car. Mechanically complex and arguably dangerous, the technology offered huge downforce with minimal drag. However, the fan car’s time in the spotlight was vanishingly brief, despite the promise inherent in the idea. Let’s take a look at the basic theory behind the fan car, how they worked in practice, and why we don’t see them on racetracks today.

The Theory

The equation for dynamic friction states that the friction force generated, or grip in our case, is equal to the dynamic coefficient of friction, determined by the materials involved, and the normal force. For a regular object, this is simply the object’s weight times gravitational acceleration, but a fan car adds downforce to this as well, massively increasing the grip available.

The theory behind the fan car is similar to that of the ground-effect car, in that it involves generating a low pressure region beneath the car, causing the higher atmospheric pressure above to press the car down into the road. This increases the normal force between the tyres and the road surface, thus increasing the available grip. However, unlike the ground effect car, which relies on the car’s forward velocity to generate the low pressure region, fan cars actively do this with, as you might expect, a giant fan.

By fitting a fan to the back of the vehicle with the appropriate ducting, it can suck out air from beneath the car, creating the desired low pressure region underneath, and thus, downforce. In practice, to make the most of the effect, the area beneath the car should be sealed to the ground, like an inverse hovercraft. This limits the amount of outside air that can rush under the car when the fan is operating, ensuring the pressure underneath drops as low as possible. The lower the pressure underneath the car, the more the car will be pressed into the track surface by the atmospheric pressure above.

With only a small gap between the skirts and the track surface, the suction of the fan is able to generate a low pressure region under the car. This sucks the car down on to the track. Pictured is the setup of the Brabham BT46B from 1978; not shown is the engine, which took advantage of the rear-mounted fan for cooling purposes.

This method of generating downforce requires power to run the fan, but doesn’t generate anywhere near as much drag as wings. Additionally, the benefit of the fan car over static aerodynamic surfaces like ground effect venturis and wings is that the fan can lower the pressure beneath the car regardless of how fast the vehicle is travelling. Wings and venturis don’t start doing real work until the car exceeds 100 km/h or so, but the fan can generate huge downforce from a dead stop all the way to the car’s top speed. This is a huge benefit in low speed corners, allowing a fan car to put more power to the ground sooner than a regular competitor who needs to gradually get up to speed before their wings produce sufficient additional grip.

Practical Considerations

The Brabham BT46B featured a pitot tube on the front to measure the pressure difference between the atmosphere and beneath the car. Connected to a modified altimeter in the cockpit, if the pressure gauge was in the red zone, the driver knew a skirt had failed and downforce would be significantly lowered, and slow down to avoid a crash.

It’s not enough to simply whack a fan on the back of an existing car and call it done; like all aerodynamic modifications, careful design and testing is key to ensure success. Perhaps the most difficult feature of building a working fan car is producing viable sideskirts that can reliably seal underneath the car. These skirts need to be able to keep the undertray relatively well sealed to a consistent degree around the whole racetrack, regardless of bumps, pebbles, or other pertubations. If the skirt seal is unreliable, the car could face a sudden loss of downforce when the car hits a bump, as outside air rushes beneath the car, eliminating the low pressure zone underneath.

If this happens midcorner, the car can suddenly spin out as it no longer has enough grip to stay stuck to the track. The consequences for the driver in such a situation can be catastrophic, so designers worked hard to design skirts that would maintain a good seal in most conditions. Various ideas involved sliding skirts, or spring loaded skirts that maintained contact with the track over varying surfaces, and could account for wear over a race distance. Some fan cars, like the Brabham BT46B, featured pitot tubes and modified altimeters that could display the pressure beneath the car to the driver, letting them know if a skirt had failed and allowing them to change their driving style accordingly.

The Chaparrel 2J featured sliding skirts made of Lexan, a cutting-edge material at the time. Connected to the suspension to maintain a consistent seal to the track, they were key to making good downforce with the system.

Another consideration is how to drive the fan. The fan can be driven by its own engine or motor; this has the benefit of providing consistent downforce as long as the speed of the fan stays constant. Alternatively, the fan can be driven off the car’s main engine, with the caveat that the fan speed will change with engine speed. As long as this is predictable, however, it need not be a problem. In practice, drivers of this type of fan car noted they could stick the car to the track by accelerating through a corner, as downforce would increase with the engine speed.

The History

The first fan car built for competition was the Chaparral 2J, entered into the largely no-holds-barred Can Am series. The brainchild of Jim Hall, it debuted in 1970 featuring two massive fans from the cooling system of the M109 Howitzer on the back. Its slab-sided design absent of any wings was surprising at the time, but its competition quickly realised the threat the car posed.

With the fan system powered by a two-cylinder snowmobile engine, the sound of the car was a constant piercing whine at rest, and even louder when its Chevrolet V8 roared into life.Β  Hunkering down two inches when the fans turned on, the car used sliding skirts connected to the suspenison to maintain a consistent one inch gap to the track all the way around, maintaining good downforce without destroying the skirts too quickly. The car had incredible grip, giving it huge corner speed and excellent braking ability. However, reliability proved to be a problem. Despite qualifying up to a full two seconds faster than the field, the car never won a race, often due to the fan engine failing before the finish. The car was outlawed for the following season after concerted protests from other competitors, who felt the fan design was an unfair advantage and constituted a “movable aerodynamic device”, already outlawed under FIA rules. There were also allegations that the system blew dust and rocks at other competitors, a potential hazard on the track.

The Brabham BT46B only competed once, but it did bring home the trophy in its single outing with Niki Lauda behind the wheel.

The Brabham BT46B followed a similar story in Formula 1, eight years later. A development of the existing BT46, the fan car design was chosen when the team realised they couldn’t modify their existing car to use ground effect venturi tunnels like the dominant Lotus cars due to their flat-12 engine. Instead, Gordon Murray designed the BT46B with a large fan to generate downforce. The rules at the time stated that any device whose primary function was aerodynamically related could not move; thus, over 50% of the fan’s flow was designed to cool the engine, thus making its primary function a cooling device. The scrutineers ruled it legal for the 1978 season, but alas, the car was to have a short-lived career. In its first appearance at the Swedish Grand Prix, Niki Lauda brought home the win in the BT46B, after sandbagging much of qualifying to try and placate those opposed to the new design. Regardless, other teams protested, most notably Colin Chapman of the Lotus team, whose cars were otherwise in the box seat to take the championship. Initial attempts to argue that the device was dangerously flinging debris at other cars were shouted down when the team pointed out the outlet velocity of the fan was just 55 mph. Not wiling to relent, the opposing teams threatened to pull out of the Formula One Constructor’s Association, a powerful body led by Bernie Ecclestone, then head of the Brabham team. Ecclestone agreed to pull the car from competition after just one race, in order to preserve his own position. While the BT46 design failed to win without its party piece, the deal paid off for Ecclestone – who eventually parlayed his position with FOCA into leading Formula 1 for decades.

The T.50 is designed by the same hand that penned the Brabham fan car, though it works somewhat differently.

Since then, fan cars have been absent from the motorsport world, as FIA regulations clamped down strongly against any form of movable aerodynamic device. However, the fan car concept has had one last gasp, with Gordon Murray this time penning a road car with the technology instead, by the name T.50. The design differs somewhat, however, with the intelligently-controlled electric fan used more to maintain flow to the car’s steep underbody diffuser, rather than outright generate downforce through its own suction. The fan is used in a variety of modes to reduce drag and maintain downforce, with flaps used to vary the flow underneath the car depending on the flow regime. Powered by a 48V motor, it’s highly reminiscent of the BT46B from the rear, even if it works somewhat differently.

Looking Ahead

Ultimately, we won’t be holding our breath for fans to make a reappearance at the racetrack anytime soon. Worldwide, regulations against movable aerodynamic devices have remained in place and only gotten more restrictive as teams pushed the boundaries in various ways. The complaints about debris will remain, and as with the ground effect era, it’s likely such devices would lead to corner speeds getting high enough to test the limits of human endurance. Regardless, the technology remains a fantastically interesting one, for the sheer performance it promises and the manner in which it burned so brightly for such a short time.

47 thoughts on “The Rise And Fall Of The Fan Car

  1. That reminds me, I would like to have a “Dustbuster on a stick”.
    Pretty much a regular Dustbuster with an attachable handle so I wouldn’t have to stoop when spot cleaning a floor. (My back gets cranky at times). A regular Dustbuster costs about $30-40, but a rechargeable upright “electric broom” costs over $100.

    1. Movable as in capable of changing angle relative to the body of the car while the car is in motion beyond a very small range, this outlaws active aero (like airplane ailerons) and intentionally flexible wings, but allows adjustment of the angles from outside the car when it’s stopped.

      Red Bull F1 team once mounted a rigid wing with rigid mounts to a flexible car nose because flex was being measured from the wing mount to the wing elements :-)

      1. Couldn’t you simply install this device with the exhaust flowing over the engine and say it was part of the cooling system? (“Yes, sure it sucks the car to the road but that’s not it’s function, just a side effect.”)

    2. It comes from the 1966 Chaparral2 with an automatic transmission and a foot pedal to change the angle of attack of a high wing. The moveable wing and I think the connected devices that blocked ducts in the front were outlawed because no one could compete. The cars were incredible. The same happened when someone ran a turbine powered Indy car. In fact there were several turbine teams in the 2 years after the Chaparral. They were 1-speed and rather amazing. The USAC banned turbines and 4-wheel drive shortly after. One can see why. Oil companies might sponsor turbine cars but the car makers would not, and they did not want to see turbine winners. Racing would become Polo instead of Soccer. Is that a good analogy?

  2. Safety is the biggest issue. All active suction downforce can be lost suddenly and easily by breaking the seal with the ground, potentially sending drivers on a surprise off-track excursion the likes of which only a wing spontaneously snapping off could otherwise produce. The next biggest issues are track safety and driver endurance – on a given track higher cornering speeds are inherently more dangerous, and the only way to mitigate this would be to increase runoff room, putting the cars at binoculars-needed-distance from any spectators or walls, like on the Bonneville salt flats. And finally the G-forces a sucker car can pull would be too much for even a very fit F1 driver, cars have even become unbearable to drivers with nothing but Indycar-legal wings and very sticky tires on a grippy track already.

    1. I don’t think the G forces would be massively higher. Right now they are peaking at 4.7g lateral, with quite high downforce from the wings. A fan could only add about half an atmosphere vacuum underneath, probably less at speed, so I think it would only add another G to the peak loads, but it could improve low speed corners from 1.5G to maybe 3G.

      1. GameboyRMH is correct. I remember hearing about driver “grey out” at the Texas Superspeedway a couple decades ago. They were experiencing the same effects as a fighter pilot because of the G-forces. Surviving those kinds of forces is not kind to the body. Even a lot of young men aren’t healthy enough to take that very long, or often.

      2. Niki Lauda always stated the FIA were right to ban it in F1 as quickly as they did. On the F1 car the fan was connected to the engine camshaft . The higher the engine revs the higher the fan speed, the greater the downforce. If you lifted off going around the corner you lost downforce and were then in real trouble because of the cornering speed you had already committed to. In those days F1 racing was already very dangerous

  3. It was about that time that I realised that both wrestling and racing were so artificial that they were not worth my attention. I look forward to driverless racing with no limits on the technologies deployed.

        1. You guys are way, way low.

          If you compare *velocities*, the mass matters: which means you’re looking for the highest Lorentz factor, which are going to come from *neutrinos*, since it’s the ratio of energy to mass. A PeV neutrino, for instance, has a Lorentz factor of at *least* 1E15 (because its mass has to be less than 1 eV), and more likely near 1E18 (because its mass is likely in the milli-eV range). And for electron neutrinos it could be 100 times more than that, too.

          A Lorentz boost of 1E18 means you’re only ~1 part in 10^18 away from the speed of light. Or
          0.999999999999999999c, assuming I can count. I chose PeV because PeV neutrinos have directly observed already.

          Because neutrinos are produced via interactions with the CMB, since we know *particles* up to 10^20 eV exist, it’s virtually guaranteed that *neutrinos* are fairly plentiful at 10^18 eV, which is 1000 times more energetic than the PeV neutrinos already observed.

          1. Oh, eff me, even *I’m* way wrong: I forgot the square. A Lorentz factor of 10^18 means that beta squared = 1 – 1E-36, and that would be within 1 part of ** 10^36 ** of the speed of light. Which is waaaaay too many 9s to put on.

          2. For it to be a real race though, you have to accelerate your car-particle from rest, and stop it again afterwards, ad go around a track, or possibly a straight line if you’re just thinking of a drag strip. So SLAC would count too.

    1. I’m sorry, but that’s hogwash. The constantly increasing restrictions in F1 are the *primary driver* for innovation. A team with a new technique gets an advantage over the competition… but only a temporary one.

      And the advantage is temporary regardless of whether it’s banned or not. Either every other team copies it for the next season, eliminating the advantage of having it, or it’s banned (which is almost always in response to lobbying from the other teams who don’t want to use it) which is effectively the same result.

      To be competitive, every team has to be constantly trying new things, searching for something to give them that one season advantage. And while they often get banned for use in F1, the techniques then become fair game for automotive makers in their commercial products, driving improvements in performance and safety for the whole industry.

      1. And imagine how much more advanced racing as a whole would be if that silly mindset went right out the window, along with the draconian rules it provides.
        Saying that squashing innovation increases innovation is like saying that up is down, it just makes no sense. Yes, teams have to dodge and weave their ways through an ever increasingly ridiculous book of rules just to make a car that can “legally” compete, but that’s not innovation and it does not improve the sport. All it does is ruin it.

        Anyone else remember when “stock car” racing was ACTUALLY stock car racing? Remember when F1 cars roared and snorted their way around the tracks instead of farting and wheezing their way around with the weed-whacker engines they’re using now? I do, and racing was far better then.

          1. ‘Fraid I agree with DainBramage, F1 hasn’t had decent racing for most of my lifetime… The current rules are garbage, particularly the tyres that ‘must’ be crap to be allowed so the cars will actually pit, now refuelling is banned… means they cruise around keeping a good gap 90% of the race, because they can’t actually get stuck in, the tyres won’t last if they do..

            Then there is the DRS system, the one moveable aerodynamic device allowed, that is just a push to pass button or pointless depending on the track.. The number of actual honest interesting overtakes on track since refuelling was banned is probably just now getting on to the second hand…Sure there are lots of overtakes now, but most of them are push the magic DRS button and win, no great skill or tactics required.

            Where when I was little you’d get such wildly different strategy you might end up with one of the fastest cars being overtaken by the worst car on track, entirely on merit, tactics and skill – and even sometimes finishing the race that way as the safety cars, clear track and pit windows play out for them… Usually it would be similarly good cars really racing but with different tactics that lead to pivotal overtakes for the outcome, but there have been some minnows getting lucky in the end.. And you can see the drivers hammering at each other trying to find the opening far more often and far longer, now they have to either make it quickly or give up so they can manage the crap tyres..

            Just look at the win % now, the No1 driver for the team in the best car wins every race near enough, where Schumacher’s (early) career and before you could win championships not even winning half the races, and almost never having it as easy tactically as they do now (all you have to do now most of the time is pit at around the same time as everyone else, preferably a touch earlier so you can perhaps get the undercut)….. Plus the raggedy edge they were running the cars at meant some retirements for mechanical failures that upset the championship… The whole ‘green’ F1 is a nice idea, but does mean they are not pushing the envelope on the engine, gearbox much at all…

            I just about remember watching some rallycross on tv, that was real racing, or the touring cars – BTCC and its support races are full of real racing, with cars pushing the limits of their grip and each other all damn race, and in the case of the BTCC itself with wildly different cars…

          2. Also look at what happened to Ferrari just recently, they ‘cheated’ in a annoyingly undefined way, which gave them engine performance enough to actually be competitive, perhaps they deserve to have it taken away, as its actually really against the rules, perhaps not, we are not allowed to know…

            Where if the rules were just a bit less restrictive maybe they would have remained competitive, as whatever they were doing would be legal…

            Personally I don’t care much who’s doing well, as long as there is some actual competition.. and recently the only racing in F1 has been for something like 5th place most races, the midfield battle has been interesting, but poorly televised.. because it matters so much less apparently than watching the top 3/4 cars cruise around getting a little closer/further apart each lap, but rarely actually doing something that resembles racing…

  4. I understand the ‘fairness’ factor of the ‘movable aerodynamic device’ ban-rule. But if they were to remove that rule for a few certain races or classes of races, that could lead to some very interested innovation that would benefit more than just the racing industry. And I rather like watching new, unique, and different types of races. (Was recently watching School Bus races.) NASCAR and F1 is boring.

  5. I once saw a Corvette (nicknamed the Cheaparral) run with an active fan. The skirt used a rectangular frame on casters to stay near the ground, and like its namesake, a snowmobile engine drove the fan. The entire car dropped over an inch when the fan started, and the car could grip like nothing else on the course that day.

  6. Interesting! I know that Elon Musk has claimed the next Tesla will optionally feature a cold gas jet to increase acceleration because apparently they are close to the theoretical limit of what the contact patches of four tyres can achieve. I would have thought a fan could be an option to increase the coefficient of friction on the tyres and potentially allow the motors to deliver more power without losing traction.

  7. It is interesting to know this isn’t just an idea that was floating around in my brain.
    Semi trailers have all kinds of modifications to reduce drag and improve fuel economy. One of the better modifications is a plastic “scoop” right in front of the tires. It is supposed to channel air to the tandems and decrease drag. I’ve always wondered if a fan system could be added to improve fuel economy even more.

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