Kestrel Airfoil Pro
IDE Upgrades The KM40
In 1999 IDE first brought Computer Aided Design capabilities to Kestrel's family of carbon fiber bicycles with it's design of
the KM40 Airfoil Triathlon bike. This has proven to be a success for everyone involved;
Kestrel, IDE, and the Triathlon Community:
economically, by shortening the development cycle and bringing a higher degree of precision to the process: commercially,
in the form of increased sales and exposure: aesthetically, in that the KM40 has received a number of prestigeous design
awards: and athletically by providing a superior product that has outperformed all previous models.While it has remained the preferred bicycle for many world-class triathletes, an update of the KM40 was needed to integrate new technologies and formal attributes with it's classic features. IDE has used new research in aerodynamics and bonding techniques to help transform the rest of Kestrel's product line, and these could now be applied to the weight-and wind-cheating needs of the triathlon market.
The Airfoil Pro is intended for use in races against the clock where aerodynamics and speed are the primary goals
and advantages. Kestrel's carbon fiber bikes are unique in that the appearance and external form factors are inseparable
from the performance attributes of the frame. It must be strong, stiff, and use proven geometry, while reducing weight
over conventional 3-tubed metal frames. The reduced weight along with the vibration-absorbent properties of carbon fiber,
equal a predictable and stable ride quality. Kestrel's goal was to offer a triathlon bicycle that would be aerodynamically
sound, look and ride fast, and still weigh less than the competition.
IDE's designers referenced the history of transportation in the details they created. The shape of the head tube was intended
to convey speed and strength, and is reminiscent of Henry Dreyfuss' 1936 'Mercury' locomotive. The rear half of the frame
references the XB-70 Valkyrie, a Cold-War era supersonic jet, in the angular wing sections and smoothly blended main
fuselage. Overall the frame can be understood in terms of it's purpose by the flowing, softer, more aerodynamic lines
of the front section, and contrasted with the relatively more mechanical and efficient struts and wings
of the rear end.A Unique Advantage
IDE was able to achieve Kestrel's goals with a blend of aerodynamic efficiency, modular construction, and striking form by
refining the KM40's unique seat tube-less mainframe. This feature eliminates a large measure of aerodynamic drag from
the frontal profile. The absence of a seat tube gives the rider a more comfortable, compliant ride through the subtle
flexing of the frame. In place of a traditional, "double-triangle" frame, the Airfoil Pro has a large bond junction
connecting the rear seat stays with the top tube. This large bonding area continues down to the rear axle in a nearly
parallel-lined, wing form. This wide area takes advantage of a phenomenon called 'center of pressure', which allows
the rear end of the Airfoil Pro to function as a sail in a crosswind, actually propelling the rider down the road.
Using the spontaneity and freedom of hand drawn sketches, IDE's designers began by exploring the possibilities for innovation
inherent in the seat tube-less profile. These preliminary ideas were then refined and developed further in Adobe Illustrator
and Photoshop in order to integrate accessories and parts and maintain accurate geometry and scale. Dozens of these
profiles were explored and reviewed with Kestrel until the desired combination of aesthetics and function were achieved.
IDE used actual NACA airfoil sections wherever possible on the frame design to ensure maximum aerodynamic effect, and these
'teardrop' sections became distinctive ornaments over the surface of the frame. At the headtube and downtube junction, these
teardrop sections are apparent in the way we shrouded the headset bearing cups within the frame, blending a horizontal
teardrop shape back into the downtube. A similar treatment is seen at the top of the seat stays, where the transition
was handled by creating a teardrop section in horizontal profile, and translating that section with a straight line into
the abbreviated seat tube.
From Profiles To Teardrops
3D development was begun with preliminary surface studies done quickly in Rhinoceros 3D surfacing software. From these
surface studies, cross-sections were extrapolated and transferred to Pro/ENGINEER, where a new set of parametric surfaces
were developed to define the exterior geometry of the frame. Final renderings were then created in Cinema for Kestrel's
approval.
The Airfoil Pro features all new, forged metal parts for cable management and high-friction surfaces. These black-anodized
aluminum cable stops and guides are integrated to fit flush into the body of the carbon fiber frame, for the least amount
of aerodynamic drag, and are common to all frame sizes. Cables are routed behind the leading edges, or within the frame
body to further decrease drag, and exit the frame at a slight angle to prevent wind-induced rattling. This internal routing
also simplifies assembly and maintenance for service personnel. The steering fork is held in place with an integrated
headset, which ensures long-term durability and reliability since all the parts are replaceable. The 1 1/8" bearing
cups seen on the frame's head tube are 'faired in', shrouding the parts from the wind and creating an aerodynamic,
'teardrop' profile. Careful engineering resulted in a set of forged aluminum rear dropouts that are 75% lighter than
originally projected.
Custom Fitting Becomes A Reality
Once IDE had completed the 3D design engineering for the 56" model of the Airfoil Pro, they used the data base as a template
to convert the design into six unique sizes of front frame, and two sizes of modularly designed rear stays. These size
combinations will allow triathletes of all sizes to ride a precisely fitted bicycle, and now, along with the Airfoil Pro's
reduced weight and aerodynamic advantages, riders will be able to go faster and longer than ever before.
