In the Moto GP 2015 pre season testing, Ducati
introduced a new Winglet design on their fairings,
which they updated several times during that
season.
Other manufactures took notice, and by the
2016 season, all of them had winglet designs
in use.
During that 2016 season, safety concerns about
the winglets were raised by riders to the
FIM, who before the beginning of the 2017
Moto GP season implemented a ban on dangerous
winglet designs, with the following rule:
"Anything not integrated into the bodies streamline,
that may provide aerodynamic effect, including
downforce, are not allowed.”
This rule was shorty after its announcement
dubbed to be “a winglet ban” and controversy
ensued, with some fans blaming the FIM to
consciously be trying to remove Ducatis advantage.
Calling the rule a complete ban proved to
be wrong, as by the 2018 season, the Technical
director of Moto GP Danny Aldrige, now approved
updated winglet designs, where the wings have
been integrated into the fairings, and are
according to Aldrige no longer a safety concern.
Updated versions of these designs are expected
to be seen at the first race at Qatar in March.
So in todays episode of Speed & Noise, we
are going to explore the often misunderstood
subject of Motorcycle aerodynamics.
——
Motorcycle aerodynamics were a hot topic as
early as in the 1930s, when manufacturers
such as Zündapp & BMW were experimenting
with fairings shaped almost like a torpedo,
often referred to as Dustbin fairings.
They discovered that by shaping the fairings
in that way, they could increase the top speed
of their motorcycles without adding additional
power.
These dustbin fairings were used in GP racing
into the 1950s, with the Moto Guzzi V8 being
clocked at an incredible 301 km/h (187 mp/h)
at the MIRA test track in France, 1957, and
286 km/h (178 mp/h) at the Belgian GP the
same year.
The bike produced only 75 bhp, weighting in
at 135 kg.
Considering the low power output, the speed
is astounding.
For comparison an unrestricted 2012 Suzuki
Hayabusa, weighting in at around 264 kg wet
with 197 hp, clocks in at 327 km/h (203 mp/h).
Only 26 km/h faster than the 1957 Guzzi.
So why is that?
Well, an important factor affecting the top
speed of a motorcycle is the gearing, but,
consider that the Moto Guzzi could reach 286
km/h in a Grand Prix race, or in other words,
it was geared for a race and not for a top
speed run, which means that the gearing is
not the full answer.
The most important factor affecting the top
speed of the Guzzi was its dustbin fairing,
which provides an astounding CdA value of
0.186 m2.
The CdA value is the combined Drag coefficient
& Reference area of an object moving through
a fluid, and yes, air is a fluid.
Where the Drag coefficient is a dimensionless
quantity of the resistance of the object,
and the Reference Area is the projected frontal
area of the rider & motorcycle.
So to get a small Cd value, you want a streamlined
shape of the object, and to get a small reference
area, you try to minimize the frontal area
of the object.
The smaller the number, the less drag force.
For comparison, the 2012 Suzuki Hayabusa has
a CdA value of 0.27.
(Moto Guzzi GP V8 CdA: 0.186.)
So the Guzzi would be exerted to 30 % less
drag force at any speed as compared to the
Hayabusa.
Interestingly, if you would put the Dustbin
fairing on a Hayabusa, its top speed would
increase to 353 km/h (219 mp/h).
That speed increase would require an additional
75 hp at the rear wheel without the fairing.
This gives us a perspective on how big influence
the CdA value of a motorcycle has on its top
speed.
So why isn’t dustbin fairings used in todays
Moto GP racing?
Well, these types of fairings were, surprise
surprise, banned from racing by the FIM in
1958, because of safety concerns.
These safety concerns were related to the
fact that the very thing that made dustbin
fairings so efficient at cheating wind head-on,
also made them dangerously unstable.
This is because the Center of air pressure
on a dustbin fairing, is ahead of the center
of gravity, which introduces a strong yaw,
or left/right turning force on the motorcycle.
Have you ever tried to carry a large cardboard
sheet on a windy day?
When the wind is blowing towards you, nothing
happens, but if it comes in at an angle, you
are both pushed and pivoted to the side.
In fact, side winds are a concern also in
modern racing, where many teams drill holes
into the fairings to reduce lateral pressure
at especially windy tracks, such as Philip
Island in Australia.
But what exactly did the Dustbin fairings
do, that modern sport bike fairings don’t
do?
They covered up the enemy of smooth laminar
flow: The rider.
The rider of a motorcycle is the cause of
most of the turbulent flow, which increases
the Cd value significantly and thus increases
the drag force.
Since fairings cannot cover up the rider entirely,
because of issues with instability, the focus
of most manufacturers have been to minimize
turbulent flow around the riders without covering
them entirely.
Turbulence around the rider is important not
only because of the drag it creates, but also
because it requires more physical effort from
the rider.
This is a very important factor, because a
tired rider is not a fast rider.
So to minimize turbulence around the rider,
manufacturers have borrowed several solutions
from the aerospace industry, such as Strakes,
Turbulators, Pressure ducts, Winglets & Vortex
generators.
These devices cause controlled turbulent channels,
that add small amounts of drag, but effectively
create an invisible air wall over the riders
body, protecting them from turbulence.
The manufacturers have been experimenting
with these solutions for quite some time,
for instance the 1999 Aprilia RSV Mille had
Vortex Generators implemented into the fairing.
Most spectators just did not take notice.
So what happened in the 2016 Moto GP season
was simply that it became more evident for
the average spectator that the manufacturers
are experimenting with aerodynamics, since
the winglets on the fairings were such an
obvious deviation from previous fairing designs.
The winglets they were experimenting with
had two major advantages:
Anti wheelie at high speeds, which provides
more acceleration, since modern Moto GP bikes
tend to wheelie at speeds well above 200 km/h.
Front tire grip when braking from long straights,
where the winglets provide downforce pushing
the front wheel down
There were three downsides with winglets:
In effect the winglets were airfoils fastened
to the sides of the fairings.
These airfoils needed to be very stiff in
order to provide predictable flow.
This led to designs which were effectively
small, stiff and sharp fins, which could be
very dangerous if they hit a rider.
Turbulence for riders that were behind bikes
with winglets, which made their bikes front
ends start to shake violently
Exhausting the rider physically, since the
downforce requires the rider to use more strength
to steer the bike & because of turbulence
around the riders themselves
The two safety concerns were raised by riders
to FIM, who as you know implemented a ban
on those dangerous winglet designs because
of this.
The updated fairing designs for the 2018 season
looks promising, both in providing downforce
but also minimizing turbulence around the
rider.
We shall see what the outcome is, but we are
surely in for an exciting season!
I hope that the video helped you understand
motorcycle aerodynamics a bit better, and
that you are now prepared for heated debates
with your friends over the different manufacturers
design choices.
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