Downforce After MotoGP Winglets

Last year, led by Ducati, MotoGP teams sought to apply downforce to the front ends of their bikes to keep anti-wheelie systems from having to cut power to maintain tire contact with the pavement. The obvious goal was to increase acceleration. At the time, this took the form of "winglets"—stubby extensions attached to regions of the fairing where air velocity (and, therefore, potential downforce) was highest. This was typically the 10 and two o'clock positions, as seen from above.

Just as this technology was proving its worth, objections were heard. Dani Pedrosa said, “In Argentina, we saw how Andrea Iannone’s winglets cut Marc Marquez’s on-board camera—and that’s pretty strong. If it can break that, it could be much worse if it hits a body. The rider is exposed in general, so we are asking the safety commission to change the curbs, change the grass, the sand of the gravel traps, to increase air fence, and then we put these ‘knives’ on the bike.”

Bradley Smith raised the issue of turbulence. “For me, the number-one issue is turbulence, the fact that bikes become unstable behind other motorcycles at 217 mph and the front starts to shake and blows the brake pads apart [pad knockback, caused by violent front-end motions].”

Now, winglets are banned from all classes, but the concept of downforce is not, as recently made clear by MotoGP Technical Director Danny Aldridge. When Yamaha on Day 2 of the recent Sepang test showed a new fairing with double walls on its flanks, separated by internal downforce vanes, two per side, Aldridge said, "I only control the external shape/profile of the fairing. Meaning, Yamaha can, in theory, change or adjust their inner supports as often as they wish.

“When we discussed the new rules for this year, we had two main options. The first was to be really strict, really confined, with set fairing dimensions. And what we probably would have ended up with is every bike looking the same, which we didn’t want and the manufacturers didn’t want. So, instead, we chose the second option, which was to word the rules very loosely, but give me the opportunity to decide what’s correct and what’s not.”

Speaking of Yamaha’s double-walled fairing, he continued, “For me, it’s allowed because, although the rules say, ‘no bulges,’ the reason I don’t class it as a bulge is because it’s a continuous curve, with a similar radius from the top to the bottom. Safety-wise, it’s perfect. There’s no issue at all. What we don’t want is things coming out of the fairing at 90-degree angles.”

Yesterday at Phillip Island, both Aprilia and Suzuki revealed their next plays in the downforce game. The Aprilia fairing features an undulating wing-like shape above the front tire, forming the underside of the central engine charge air inlet, with two "nostril" openings, one on either side.

Notionally, air flowing around this wing is then ejected upward through the nostrils. Its effectiveness is probably reduced because the airflow above the tire is already slowing as a result of the radiator core behind it—much as airflow decelerates at it enters the nacelle of an aircraft piston engine.

Suzuki’s design was closer to that of Yamaha. Teams are free to test any fairing in the preseason tests, but once they begin with a fairing at the first Grand Prix at Qatar that becomes one of the two fairings permitted to that team for the season (one midseason update is allowed).

Aleix Espargaro noted that Aprilia, with its present six-mph top-speed deficit to the top teams, cannot afford to trade top speed for downforce. “If the fairing gives us a little downforce without losing top speed, great. If we lose even one or two mph in top speed, I will not use it.”

Asked about the Suzuki fairing, Alex Rins said, “We decided to try the new fairing for the last two exits, so I’m happy because Suzuki is trying really hard to improve the bike. The conclusions are not really clear because I just made 10 laps. For sure, it feels different compared to the normal fairing. I feel less wheelie. Tomorrow, we will continue trying this fairing.”

Wings produce lift or downforce by deflecting airflow in the opposite direction. If we could see airflow around an airplane’s wing, we would see the flow turn upward toward the wing, then curve over and under it, then stream downward behind it at an angle to the horizontal. This means that airflow accelerated upward from a downforce wing on a MotoGP bike must have someplace to go.

There is no point in lining up multiple wings like a venetian blind in front of the coolant radiator because there is no upward flow path for the air streaming off the trailing edges. This is why the Yamaha and Suzuki designs place the short winglets or vanes inside double-walled regions on each side of the fairings. Air can easily exit upward from such "pods," as presumably it can from Aprilia's two nostrils.

In thinking about downforce, older enthusiasts will instantly recall Jim Hall’s famous Chaparral “sucker car,” whose body skirts came very close to the pavement on all sides, with a separate two-stroke engine driving two rear-mounted fans that blew out air from under the car. This created powerful downforce (and also usefully blew track dirt and trash into the path of following rivals).

Hall’s design was soon banned, whereupon forests of wings, held above race cars on spindly struts, took its place. When these, too, were banned, “venturi cars” took their place, generating downforce by flowing air through under-car venturi tunnels, helped in some cases by the ejector effect of locating engine exhaust outlets in the rear (diffuser) section of the venturi or venturis.

All this is impossible for motorcycles because they camber or lean over for corners. Winglets proliferated last year and were banned for 2017, leaving us with a rule that now pretty much says you can do all the aero you like, but only within the privacy of your fairing’s interior.