Ducati is often the manufacturer pointed out when it comes to innovations. But they are not the only ones to study new parts concerning aerodynamics. Let's go back to the 2019 Sepang tests, where we saw bi-plane fins on the Yamahas. Looking to one side, you see a first fin at the front and a second, relatively similar one, placed behind and slightly above, with a higher angle of attack, separated from the main fin by a gap visible – the “split”.
Simply flip this system to produce lift instead of downforce, what you see is similar to flap systems that allow airplanes to develop high lift at low speeds, allowing them to take off and land . Without this extra lift, they would have to reach a much higher speed to take off, which would require longer runways and impose dangerously high landing speeds.
But on Yamahas, we can ask ourselves the question of the usefulness of a doubled fin. Why not join the two profiles while keeping the same overall curvature? Wouldn't that work better than having a leakage gap between two fins?
Aeronautical comparison
To get the most out of airflow at low speeds, such as when an airplane takes off or lands, it is essential to rotate the flow at as large an angle as possible. Ascent, after all, is just the reaction to the change in direction of movement of a flowing air mass. In the case of a wing, divert the airflow downward and you get an upward reaction force. But there are limits to what a single wing can do to alter an airflow, which is why modern airliners get up to three narrow subwings carried into the main wing during flight cruise and which are extended rearward and downward to increase wing area and curvature during takeoff and landing. The main wing begins the process of rotating the flow downward and each successive trailing flap element, set at greater and greater angles, rotates the flow further, thereby obtaining maximum lift from it .
If we continue to increase the angle of attack of a single wing, the flow will separate from the low pressure surface (on airplanes, it is the upper surface, but on these support ailerons, which are ultimately inverted wings, this is the lower surface). Once the flow separates, lift decreases, so it is best to divert the flow in the conventional manner with the front wing, then start the process again with an underwing behind, and so on. During the landing approach, the flap system is deflected up to 45 degrees!
Valentino Rossi and his teammate Maverick Viñales regularly test different aerodynamic packages
Flow separation occurs due to the appearance of reverse flow in the boundary layer. The boundary layer is the thin layer of slow-moving air that is closest to the vehicle. It becomes slow because its molecules make myriad collisions with the moving surface, losing much of their original speed in free flow. The further the flow moves over a surface, the thicker the boundary layer.
Just as airlines provide guidelines for carry-on baggage, this template provides a simple method to confirm that MotoGP fairings are within size limits.
On Yamaha's new fairing, the front wing directs the flow upward as much as it can, then its growing boundary layer is dumped into the space between the fins. Higher energy air from ahead rushes through the gap onto the second fin, helping to delay the formation of a thick boundary layer there as it tilts the flow even further upward.
Flow separation occurs because, as the boundary layer naturally flows toward areas of low pressure, it can become thick enough to develop an instability that releases the flow (this is air entering in a “velocity oscillation”).
In the past, MotoGP teams have used up to three wings stacked in a cascade, one above the other rather than one behind the other as in the Yamaha fairing detailed here.
