By Fergus Ogilvy
Right at the end of the last century, probably the autumn of 1999, senior R&D man at Renault F1, Dave Hamer, was asked to investigate what could be done to stabilize their wind tunnel model. At that time it was a half-scale model (50 percent) of their current Formula One car and it had a tendency to yaw (move laterally) during wind tunnel testing.
Previous attempts at reinforcing the supporting strut had failed; to their dismay it merely increased its natural frequency of oscillation. “The supporting strut is very under-damped,” explains Hamer, “therefore it was easily triggered into oscillation.”
Could a mass damper stabilize the model in the wind tunnel?
To oppose and kill the oscillating forces, he suggested the use of a tuneable mass damper, similar in concept of those placed at the top of some skyscrapers to protect them from the effects of earthquakes. The Taipei 101 skyscraper uses a tuned mass damper that weighs 800 tons.
“We hired a specialist company to conduct a stability analysis of the model,” said Hamer, “and our drawing office designed some devices. But they didn’t work very well. Confined space within the model was the chief impediment.”
Then four and a half years later, in 2004, another attempt was made. By now the wind tunnel and the work performed within it was more refined. Most significantly, the R&D department had access to a vibration specialist, who was on loan from Renault at the time, and between him and the then Head of the race team’s R&D department they introduced a leaf spring to address the instability of the wind tunnel model. By fixing a mass to one end of the spring, coating its leaves with a damping material, placing it on its side inside the model, and securing the other end to the model’s spine they resolved the problem. As the mass moved sideways it could be tuned to counteract yaw motion. Stability was restored.
Early attempts at curing pitching troubles
Back in their R&D department, Phil Charles, who worked with Dave Hamer on the team’s seven-post shaker rig was inspired by the mass damper concept. He wondered if a bigger version might cure a troubling pitch mode that unsettled the race car.
The pitch mode had been nicknamed “the crocodile” mode, the front of the car bounced up and down as it rotated about the rear wheels. It was perpetuated by high front spring stiffness, which was used to combat high aerodynamic down forces and also to keep the front wing as low as possible at all times. Pitch was measured around 8Hz (8 cycles per second) on the team’s 7-post rig.
The 7-post shaker rig is test equipment used to perform load analysis on race cars. By applying shaking forces it can emulate pitch mode as well as banking loads, lateral load transfer, longitudinal weight transfer and ride height-sensitive downforce. More notably still it can be programmed to simulate the surface of each specific racetrack.
Applying the new device for the first time
Once the idea took hold it didn’t take long for Hamer and Charles to create a bigger, ad hoc version of the mass damper. They installed it in the nose of the rig car and using a replay of the Silverstone race track on the 7-post rig they knew they’d uncovered a decisive edge. The effect was profound: the 8Hz pitch mode was largely cancelled and a proper device was designed and produced that could be tested on the track.
Constructed in the form of a circular carbon container about 12 inches tall and 10 inches in diameter, inside was a central vertical shaft upon which a linear ball bearing operated. This bearing was fixed within an annular ring (like a thick discus) which represented the mass. The mass was held at mid-height by a compression spring on either side of it, so it could freely oscillate up and down.
“But the clever part,” says Hamer, “was that the ring was a close fit to the sides of the container and so we used the air movement as the damping medium. When we tested the device on the 7-post rig we estimated its advantage to be worth about ¼ second a lap at Silverstone.” In the preserve of Formula 1 this was significant and due entirely to the improved mechanical grip as the variation in tire contact patch force was much reduced.
But to confirm the true scale of the achievement they had to wait for a track test. Many in the team were skeptical. “However when Fernando Alonso tested the device at Silverstone,” recalled Hamer, “he confirmed our findings and insisted we have it ready to run at the next race. This wasn’t a trivial task as we had to resubmit the nose to an FIA crash test. However, all was well and Fernando went on to win that year’s (2005) championship.”
F1 championship conquered, device copied then banned
Dave Hamer continued, “Inevitably, the device was quickly copied by other teams, including Ferrari who struggled to make it work properly. We, however, found it very effective; we had the choice of a 5kg, 7.5kg or 10kg (22lbs) mass. For each race track we would find the optimum mass to use at that track, something I doubt the other teams did. We even had a second tuned mass damper fitted in the bell housing. Fernando found he could use much more kerb with the TMD fitted.
“To tune it we changed the spring rate to get the natural frequency correct. Each unit was tested to check its natural frequency and damping. As mentioned the optimum mass was found by trying each unit on the 7-post rig for every track we raced on. Its effect was to improve the mechanical grip. We could convert grip into lap time, so if we were using the wrong mass the lap time would be slower.
“As you can guess, its benefits were extensive. As we were compelled to carry ballast anyway it gave us a performance advantage for free. Meantime we experimented with lead shot damping. Using the Silverstone lap replay this was about half as effective as our air-damped TMD.”
After the Renault F1 team claimed the 2005 World title the FIA, the sport’s governing body who had declared it legal, unfathomably banned the system during the latter stages of the 2006 championship. On the occasion of its banning, opinions ranged from concern to outrage. Read one perspective from the influential f1fanatic.co.uk (see sidebar above).