Motogp - What Do Motogp Winglets Do?

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    What Do MotoGP Winglets Do?

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    Explaining how MotoGP racer winglets make racers faster.
    By Kevin Cameron May 7, 2020

    MotoGP bikes are still accelerating strongly at 200 mph. At that speed, wind pressure—aerodynamic drag—on the front of the machine has taken substantial weight off the front tire, and adding acceleration to this can result in instability, or even front-wheel liftoff.

    Doesn’t the anti-wheelie system take care of this? Anti-wheelie doesn’t push the front end down against the pavement; it works by reducing power enough that the front end falls back onto the pavement. Reducing power slows the bike’s acceleration. Long ago, Valentino Rossi said, “The wheelie is the enemy.”

    To solve these twin problems of high-speed instability and wheel lift, teams in 2016 appeared with fairings whose forward cheeks bristled with tiny downforce winglets. On aircraft, wings produce lift with which to fly, but on surface vehicles, inverted wing systems make downforce precisely to prevent flying. In 1978, as rider Mike Baldwin crested the back straight rise at Canada’s Mosport circuit on a TZ750 Yamaha on full throttle, the front end came up so fast that he had to go for the back brake to return it to Earth. MotoGP bikes of the present day make more than twice the power of Baldwin’s TZ yet weigh only 12 percent more. They need downforce—not in corners, as in Formula 1—but when upright.

    In the old days, the only purpose of bike aerodynamic development was to cut drag, thereby increasing top speed. The production of downforce is a new job for aero.

    Riders saw danger in the new winglets. Dani Pedrosa called them “knives.” Bradley Smith and Cal Crutchlow called for their prompt removal. FIM tech director Danny Aldridge a year later noted that neither he nor the manufacturers wanted rules so restrictive as to force all fairings to look alike. Therefore, rules interpretation has been left to his discretion.

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    The stubby winglets of 2016 are no longer knives, but now have end plates or have begun to extend themselves around fairing noses, extending rearward. Stubby wings are inefficient because the high pressure on their upper surfaces spills off the tip, curling around it into the low pressure beneath the winglet, producing a “tip vortex” that reduces lift and downforce while disturbing the air behind the bike. At the time, I made a rough estimate of how much downforce the winglets in use might produce at 200 mph: around 40 pounds. That’s enough to be useful but hardly decisive. Rider comments since then have covered a range from “I couldn’t tell the difference” to “They make turning a bit more difficult” to “I think there is some benefit.” Downforce is useful or it would have been abandoned, but it is hardly a revolution.

    As air flows around a moving object, it must accelerate because the flow path around the object is longer than its length. This accelerated flow around the curving nose of a fairing is a great place for winglets because the potential for producing lift increases at the square of airspeed.

    It looks as though a fresh concept is being applied to the downforce problem, that of vortex lift. On an aircraft such as an F-16, rapidly rotating vortices stream back and outward over the wing from forward extensions of the wing called glove vanes. Such vortices, with quite low pressures at their cores (a tornado is just a dangerous natural vortex), by lowering pressure above the wing, can roughly double lift at high angles of attack such as 30 degrees. This lift isn’t free—it takes power to push the angled wing and vortex system through the air.

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    In the case of F1 cars at high speed, as much as 60 percent of engine power is consumed in downforce generation, leaving 40 percent to overcome the drag and rolling resistance of the car itself. This is the price of the downforce that enables such cars to corner so fast at extraordinary G-forces. On MotoGP bikes, the horsepower cost is much less because the goal of downforce is different and quite limited—stability enhancement and the ability to continue accelerating at very high speed. (This is why MotoGP bikes have higher top speeds than F1 cars.)

    Electronic rider aids have been a great gift to a motorcycle industry presently lacking the sales income to tool the entirely new models that used to excite us every two years; exciting us by adding a few electronics chips and colored handlebar buttons is much cheaper than new crankcase die-casting molds.

    Similarly, adding swoopy and mysterious-looking winglets to high-end production literbikes may set styling off in new directions and get hearts pounding, even though few buyers spend time above 200 mph. We have become technology addicts; our fix is the next phone and the next bike. For us, Norton’s OHV Model 18 500cc single, introduced in 1922 and little changed through 41 years of production, is impossible to understand.

    Source: Cycle World 7 May 2020
     

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