 |
|
|
 |
 |
|
A front hood
air duct:
the aerodynamic mechanism for creating
downforce
At the rear, downforce is
easily obtained using a wing-type spoiler. At the front,
though, adding too big an aerodynamic device can negatively
affect minimum ground clearance and/or the approach angle.
Increased aerodynamic resistance resulting in reduced
acceleration is also another example of the many problems
associated with obtaining appropriate downforce in a
road-going car.
The solution we chose was to design the
underbody of the car as flat as possible to encourage smooth
airflow under the car, maintaining airflow speed to create
downforce. This method not only provides for adequate ground
clearance and approach angle but also does not unduly increase
the forward-protruding surface of the body. However, this led
to a new problem: how to extract the airflow through the front
radiator that had previously been channeled underneath the
car?
Taking advantage of the car's mid-ship layout, an
air duct was added in the front hood to provide the necessary
extraction route. Longitudinal fins were also added to the
outer left and right sides of the front under-cover tray to
prevent the air passing under the car from entering the front
wheel wells. Similarly, spats have been added to both sides of
the air ducts to channel air passing through the ducts away
from the wheel wells. The opening ratio under the front bumper
has also been reduced to limit as much as possible the actual
amount of air flowing through. All these innovations result in
a smoother airflow both under the body and through the front
hood, achieving the desired downforce.
No large
aerodynamic appendage was required, helping maintain the
original NSX's overall design and ensure a relatively low
aerodynamic drag. Downforce was thus achieved without
sacrificing top speed.
Wind tunnel tests have shown
that when the car is at an angle relative to wind direction,
the longitudinal fins of the front under-cover tray function
in the same way as the chin spoiler, effectively reducing body
lift and improving transient
characteristics. |
Wind tunnel
testing
|
 |
View of the
underbody
|
|
|
|
|
Cd (Drag coefficient):
0.32
Cl (Lift coefficient/overall): -0.100
Clf (Lift
coefficient/ front): -0.040
Clr (Lift coefficient/rear):
-0.060
Compared to the original
NSX-R, this translates into an increase in vertical force
acting on the front tires of 36.2kgf, and of 25.0kgf on the
rear tires (test results measured at 180 km/h in both
cases).
|
|
Lift reduction measures
(effect measured piece-by-piece)
|
|
|
|
|
|
|
Extensive
circuit testing to determine the optimum
equilibrium
between downforce and front-to-rear balance
The air duct
in the front hood could have been made simply by cutting an
opening and trimming the edges with plastic. But because we
wanted to maintain the beauty of the original design including
the simplicity of line worthy of a car cut for speed like the
NSX-R, and to reach the weight reduction target we had set for
ourselves, we chose carbon fiber instead. The rear spoiler is
similarly a single piece of carbon fiber designed to achieve
the required downforce while maintaining a low drag
coefficient in a simple shape embodying functionality and
beauty.
Both parts are formed using an autoclave, a
method more often seen in aircraft manufacture. Multiple
layers of pre-pregs made of resin-impregnated carbon fibers
are cured in a high-pressure oven to form the parts. The front
hood is made of carbon Aramid fibers for added resistance to
tearing. In the event of an accident, it is designed not to
shatter into small pieces. During the laminating process,
fibers are offset by 45 degrees, with each layer above and
below being symmetrically angled to provide equal strength in
all directions.
Nine to ten hours are required to
complete the laminating process of each single part. After
lamination, the whole lay-up is wrapped in a baking film, and
a vacuum is applied to consolidate the laminate prior to
curing for 2-3 hours in the autoclave at a pressure of two to
three atmospheres. Once in the autoclave, it takes one hour to
bring the part to temperature, while some five hours are
required for the cooling down process. Air released from the
resin when liquefying at high temperature is carefully bled
off to form a strong CFRP (Carbon-Fiber Reinforced
Plastic).
The front hood's outer skin is formed
separately from the inner frame before being glued together.
Glue thickness is strictly maintained at less than 0.5mm. The
resultant strength is superior to that of the base materials.
The rear spoiler is a hollow, one-piece molding made using a
proprietary process developed in cooperation with a parts
supplier.
Durability, a matter not normally emphasized
in aerodynamic carbon fiber parts manufacture, has been
pursued to the utmost. In all aspects of the product,
durability on par with steel is achieved. The painting process
has also been the object of painstaking attention, especially
regarding the undercoating, with both parts undergoing a "5
coat/5 bake" process. For the front hood in particular, paint
has been applied so as to let the roughness of the carbon
fiber surface show through ever so
slightly.
|
|
 |
|
|
| | |
|
