There’s a good reason why fan cars have been banned in motorsport. Cars sucked to the ground will always produce astonishing cornering accelerating and braking performance but any disruption to the skirt contact with the ground – such as running over a kerb – is likely to see a very rapid accident under way. Of course, a car that literally scrapes along the ground can only be used on very smooth race tracks and would be impractical for the road. The engineers at Original Twist don’t entirely agree and think a new approach is called for. Here is the Original Twist fan car design. The usual idea is that flexible skirts on the car scrape along the ground to maintain a seal, the air pressure inside the skirt is reduced with a fan and the pressure differential forces the car down. The Original Twist idea deviates by separating the skirt from the car; an independent suction pad is held under the car and with its lightness and agility this pad is free to track the road contours even if the car is in more vigorous motion.
The suction pad is circular in order to keep the air bleeding edges to a minimum. A 60” diameter area with a 1 psi pressure drop will produce 2,800lbs of downforce; about the weight of a car then.
The suction pad is not directly attached to the car. Instead it rides on 4 small wheels like a circular go-kart which is towed under the car.
The skirt edge is held very slightly off the ground so there is no horrible scraping noise as you move along. The skirt is different too and employs hovercraft principles in reverse. Apart from the main extraction fan air is blown out of slots round the edge against the air that is trying to get in and that makes an inertial barrier. The blowing can be done with an extra fan in the nose of the car for example. The extractor fan probably won’t double up as the blower because the pressure/flow characteristics are different but it would be worth investigating. A concertina bellows connects the skirt edge to the underside of the car floor and the seal is complete. The skirt/kart is pressed lightly to the ground by the trailing links that locate it and although the relatively heavy car might be jumping and jiggling the skirt will tend to remain flat on the ground and unlikely to reveal a sudden and potentially deadly pressure change.
With an electrically driven fan the downforce on the car can be tightly regulated and as aero downforce comes with speed the fan speed can be decreased accordingly until eventually there is no need for it and the whole underkart can even be retracted. The retraction feature makes the fan car suitable for the road; a fan car that can cope with humps and farm tracks and then pop round the Nürburgring in 5 minutes has got to rewrite the book somewhat.
While all this is alluringly simple there is one complication. Cornering with 8 wheels instead of four is going to be out of this world but the kart wheels will need to be steered unless they are on castors. A supermarket trolley under the car won’t add much dynamically but a steered go kart, pushed down very slightly by the trailing arms, will make a major contribution to the cornering forces.
The potential for electric sports cars has been examined in
but the main point is that all the performance extremes of current supercars, in terms of acceleration, cornering and braking , can be exceeded by a factor of two or more. That means forces on your body, and head, of over 2g. It’s like doing press ups with someone sitting on your back so you’d need to be immensely strong to try the brakes without a full harness seat belt on. Cornering and braking at the same time would see you clawing your way out of the passenger footwell.
Formula One drivers experience forces like this but now a moderately priced sports car will be able to deliver the same. Headline figures of 0-60 in 1.5 seconds and 120mph in around 3 or 4 seconds will reset the performance bar in a shocking way. A 5 minute ring time is technically possible – just a question of who and when?
Note: Suck is a concept for when the force of atmospheric pressure – or other – acts against an object with lowered pressure on the opposite side. Really there is no such thing as a sucking force; when you ‘suck’ on a straw it is atmospheric pressure pushing your drink into your mouth.
With any fan car it is the weight of the atmosphere above the car which is pushing it down.
Atmospheric pressure is 14.7 psi at sea level so this sets the theoretical upper limits of our skirt with a total vacuum on one side. That would be about 18 tons in this case so the 1 psi pressure drop that equals the weight of the car is not too much to aim for and might easily be exceeded.