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MotoGP: Ducati 2017 trickery
Looking at the Ducati 2017 development bike, there are a few specific areas of interest, the front fairing, the rear seat hump and the exhaust.
Ducati have lead aero development since its entry into MotoGP, the 2016 bike ran the most complex winglets and loose bear without them. The mounting points remain on the fairing for the winglet assembly to be bolted to, the dev bike has quite a complex series of split lines around the top fairing bubble. These should allow different shape panels to be fitted into the general fairing shape, most likely to recoup the vertical load lost from the winglets.
The much talked about difference on the new bike is the offset top exhaust outlet, compared to the centered position on the 2016 bike. This repositioning appears to be related a large box-like extension to the underside of the seat hump. The contents of the so-called salad-box are unclear, rumours vary and facts seem in short supply. Many suggest this could be a a secret device means to reduce chatter or wheelies, while less probable is an extended fuel tank for revised weight distribution.
Although my first assumption was high speed data logging (HSL) related. The size of the box matches closely the format of a HSL, which ties in with its appearance at testing, possibly this location chosen as the dense packaging of the bike preclude it being mounted some else less awkward.
Looking at the anti chatter or wheelie options, Leading MotoGP journalist Matt Oxley has suggested it could either be a Tuned Mass Damper, Inerter or even a Flywheel Device. Wheelies are well understood, where the bike rotates about the rear wheel under acceleration. Chatter is much more a bike specific problem, where the frequencies of the tyre, suspension and frame set up a resonant vibration in corners. This shakes both the bike and rider, affecting grip and rider confidence. Being able to reduce either of these traits provides a faster and more ridable bike. So, fitting a new means to tune them out would be competitive advantage. I suspect that any new system is more likely to be an anti-chatter device than anti wheelie, as the science is more complex and harder to tune out with rider style and electronics. What’s needed is a device than can be tuned for a certain suspension frequency to offset that of the chatter. The flywheel is the first solution, having a heavy flywheel spinning inside a casing, driven by an electric motor. Its gyroscopic effect might offset the chatter, if spun as certain RPM, but this the least plausible solution given the shape of the salad box and a legal means to spin the flywheel. A tuned mass damper (TMD) is a more appealing solution, this is a mass supported between two springs, the inertial effect of the mass being acted on by the bikes movement could be tuned to work at the right frequency to negate chatter. The TMD was adopted in F1 in 2006 by Renault for a similar reason, albeit banned for a misunderstanding of its purpose. In F1 the inertial effect of a nose mounted TMD was thought to be reduce dive under braking, rather than working with tyres for more consistent grip. A tail mounted TMD ‘could’ work to reduce wheelies, as the rotational effect under acceleration is resisted by the mass for short period. In which case a mass sliding on bearings between springs could be used. To work with chatter a TMD might need to be oriented differently, depending if the effect is trying to be resolved on the front or rear axles.
If a TMD was required they bike might be better to adopt a Citroen solution used on the 2CV, where mass dampers were fitted to the front suspension, as a can-like add-on fitted to the hub. As the otherwise undamped sprung suspension moved the TMD acted as a damper. Such a ‘canned’ solution would work fitted to the front forks or rear swing arm.
This leaves the possibility of an inerter, these are relatively new suspension devices introduced into F1 by McLaren predating the Renault TMD. Although there are different formats a mass is spun by suspension acceleration, the mass resisting the movement provides the damping effect. But as an inerter is a suspension device operated directly by suspension movement, this counts the solution out as a salad box filler, but does stir debate about inerters use in MotoGP.
A simple implementation could be a small mass mounted atop the forks, operated by a threaded rod connected to the fork slider. As the fork moves the mass initially resists the motion to offset chatter. Different masses being used for different frequencies. Penske Racing Shocks have such a unit combined into a damper body that could easily be implemented into the rear damper on the bike too. We’ll have to wait until the first GP to see if the salad box races, if its left off away from testing it may just be a data logger.
The aforementioned offset top exhaust features a flap-valve near the tail pipe, this being used last season as part of variable back pressure Akropovic exhaust system.
The spec ECU has outputs that allow the valve to be controlled, to close the flap at lower engine speeds to increase back pressure to maintain drivability, then open at higher RPM to free the exhaust of back pressure for better top end power. As always with MotoGP bikes, engine drivability is massively important, even over top end power, so that the rider can finely control grip at acute lean angled.
Although this valve is a standard Akropovic part and race-run solution it piques interest as Ducati have a patent for a jet style variable exhaust outlet, cited as a wheel control system to balance the bike with thrust from the engine, but also provides a variable back pressure solution. One wonders if the patented tail pipe might make an appearance if the under-tail hump disappears and the centered exhaust refitted.