WHAT THE HECK IS 'PORPOISING?' by John Crawford

This year changes in F1 rules and regulations forced race teams to come up with new aerodynamic solutions to give their drivers a more competitive advantage.

However, from the first two pre-season test sessions, one thing has dominated discussions among the teams, regulators and drivers. And, this has been dubbed ‘porpoising’

Essentially the previous design of F1 cars utilised a flat floor, with most of the aerodynamic airflow being managed by the design of the body and areas like front and rear spoilers, and various ‘bits’ of carbon fibre appearing in unusual places.

However, this has become an extreme problem for teams and drivers. The designers are working flat out to eliminate this new demon.

Essentially, F1 has said ‘no more flat floors’, and venturi runnels must be created to control air flow under the car.

A quick description of ‘porpoising’ is that the down force pushes the car down to the track, and in order to reduce drag, the driver has to back-off to allow the car height to rise. 

The teams are frantically working to avoid this problem which is causing strain on the driver, and the car.

MOTOR SPORT'S tech editor Mark Hughes has written a more precise definition which I am republishing edited form, from the F1 website.

The venturi tunnels create downforce by inducing a lower air pressure in the underfloor than above, thereby sucking the car to the ground. The lower the tunnels get to the ground, the more powerful the effect is. The faster the car is going, the harder those tunnels suck and the closer to the ground they get… giving a cascading effect.

But if the ride height gets too low, the rear outer corners of the floor from which the tunnels are formed are not stiff enough to prevent those corners from physically touching the ground as the tunnels suck on the car and it sinks on its suspension. When this happens it creates such an effective seal that the tunnel is choked and stops working.

The floor is effectively a big cantilever and it is thus extremely difficult to make the corners stiff enough not to be pulled to the ground at high speed.

It’s relatively easy to cure by increasing the rear ride height so that it never reaches the critical stall point even at high speed, but not without losing a lot of performance.

The images from wet track running in Barcelona suggested the McLaren may be able to achieve good downforce despite its greater rear ride height, because it has more powerful vortices running down the sides – giving the floor a strong seal without having to have it so low that it makes contact with the track at high speed. That makes it apparently more stall-proof.

 

On the final day of Bahrain testing, Red Bull (its RB18 featuring modified sidepods with a bigger undercut at the front) appeared to be running their car with a small degree of rake.

 

This was when the car set the fastest times of the test and during those laps it appeared to be relatively immune to porpoising. Rake helped create downforce under the previous technical regulations because it effectively made the flat floor into a big diffuser, with a small gap between the leading edge of floor and the ground expanding into a bigger area behind.

Clearly, Red Bull and Ferrari think they have a solution

But under the current regulations, with the venturi tunnels in place of the flat floor, the tunnels need to be close to the ground for much of the length of the car and raising the rear will tend to reduce the downforce they create.

But the rake angle could be used as a tuning device to keep the downforce from reaching the stall point which creates the porpoising. This point will vary from track to track and so the rake can be adjusted appropriately simply by adjusting the rear pushrods and/or front pullrods.

There is lap time to be found by running the car low. But it’s a hazardous path to follow, with the onset of porpoising just waiting to ambush the best-laid plans. It’s going to be fascinating watching the teams race to solve the problem.

JOHN CRAWFORD