Why the 2021 F1 Mercedes W12 is illegal
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Why the Mercedes W12 is illegal ?
Because whenever the Pranching Mercedes collapses the rear suspension, it also - simultaneously - raises the nose, breaching several technical regulations regarding to dimensions thresholds.
Whenever the W12 reaches a given speed in the straights - above the top speed in the fastest curve in the circuit - the rear wing pushes the back of the car down and some damper component w/ dual-action stop resisting the downforce and collapses.
As the rear suspension collapses, the nose raises and delivers a powerful drag reduction effect: reduces the drag coefficient above the front wing [attack angle profile] and reduces the low pressure zone bellow the nose and wing.
Unfortunately no underbelly cam is available in the W12 to measure the effect.
2021 FORMULA 1 TECHNICAL REGULATIONS
3.3.3 Overall dimensions
Front Wing: All bodywork ... must be ... no more than 300mm above the reference plane.
All bodywork situated forward of a point lying 330mm behind the front wheel centre line, and more than 250mm from the car centre plane, must be no less than 75mm and no more than 300mm above the reference plane.
When the rear collapses, the nose raises up and the mandatory limit of 300 mm from the top of the wings to the reference plane [t-tray] is surpassed. Illegal.
The two lines [red & blue] form two inverted square triangles, unite by a pivot point, so is easy to realize that for every millimetre mm the rear suspension/wing collapses; the nose raises by the same measure times X, It depends of the pivot point position.
But let's say 1:1 in the example. For each 1mm lowered at the back; 1mm is raised at the front.
So as the nose raises, the 300mm top front wing limit above the reference plane is surpassed and the rule breached.
3.3.1 Mandatory central section
b. Lower trailing edge point, as defined in Drawing 7, is 86.650 mm above the reference plane...
Also when the nose raises, the bottom part of the front wing also raises beyond the 86.650 mm limit.
But wait, even if the nose goes up, doesn't it arise by the same amount? After all it is all fixed and connected.
No. Using the square triangle resource again, the Lower Trailing Edge point and the Reference Plane [T-Tray] lies at horizontal different lengths from the Pivot Point [acute vertex]. Both points raise in a proportional way, but not linear. So the farthest point [Lower Trailing Edge] from the Pivot Point raises more than the T-Tray [Reference Plane].
ARTICLE 2: GENERAL PRINCIPLES
2.6 Measurements
All measurements must be made while the car is stationary on a flat horizontal surface
The upper car [blue line] represents the FiA static inspection, while the bottom [red line] the car in motion.
When the nose raises due to the cradle effect caused by the rear suspension collapsing, it reduces the attack angle of the front wing, and therefore drag.
Note that the front wing has a much bigger area than the rear wing [yellow area], contributing more than the stall of the rear wing. A matter of cause and effect.
Bottom view, note that the front wing also has a big low pressure zone beneath that also causes drag. When the nose raises, the drag is also reduced, duplicating the benefits.
Less drag above and below the front wing.
The profile view demonstrates the nose height effect creating a low pressure zone under the front wings and the potential rewards in lifting the nose.
Finally the comparison of the low pressure zones [red] on the car in lower speeds [top] and higher speeds, when the collapsed suspension causes the nose to lift.
ARTICLE 3: BODYWORK AND DIMENSIONS
3.8 Aerodynamic influence
Any device or construction that is designed to bridge the gap between the sprung part of the car and the ground is prohibited under all circumstances.
By the diagram its clear that the rear suspension works with the intent to lower the back of the sprung part of the car, by the use of Heave Spring + Damper and Corner damper.
The breaking point to change the behavior of the suspension is the fastest curve threshold, as its not safe for the suspension to collapse when you need downforce the most.
So the two-step suspension is a danger for the own driver and others lying around, as in bumpy surfaces - like in COTA - the behavior is unpredictable, with suspension and wings moving all around.
At Turkey, believe the suspension break-point was around 200 km/h due to the long curve 8.
Why the wing stall effect was so powerful in Interlagos ?
Because the main straight is uphill, which increased the air going under the front wing, extracting the full potential of the stall.
Since the following tracks are mostly plane, the suspension collapse depends on the high speed curves threshold.