“We’ve literally designed this vehicle from the back forward, because there is a fundamental principle in aerodynamic design that says until you clean up the back of the truck and the trailer, you’re going to be limited by what you do in the front,” explained Navistar’s Dean Opperman, chief engineer, advanced vehicle technologies.
“Fundamentally, the design of the trailer and tractor impact each other. We worked directly with Wabash National, and were able to optimize our design around their specific technologies—and we will continue to do that with all different types of trailer aerodynamics technologies,” Opperman said. “In a perfect world, we would like to be in control of both systems, but that’s never going to happen. But once we knew where we were going, it solidified a lot of things we wanted to do up front.”
Among the special touches on the CalalIST trailer by Wabash National, for instance, are the skirt design, the “ball and socket” passive gap treatment, a bogie treatment on the tandem axles, and an extended boat tail design, Opperman pointed out.
Most significantly, the overall shape of the trailer is the key to developing a more optimum, wing-like airflow by lowering the front and rear of the vehicle.
As the CatalIST reaches highway speed and “changes shape,” the load bias also shifts forward more toward the tag axle and the low-rolling resistance single tires.
Because of the improved aerodynamics and reduced rolling resistance, the CatalIST needs only about 80 h.p. to cruise at 65 m.p.h., Opperman noted.
The laptop displays telematics data from the various systems, including engine speed and downspeeding performance, horsepower in use, hybrid charging and discharge, solar power input from the trailer roof, and the vehicle height controls down to the axle and the corresponding load bias.
For the SuperTruck program, Wabash National likewise leveraged some existing advanced designs and materials to improve fuel efficiency.
In order to give the tractor-trailer the airfoil shape without exceeding height limits, the project trailer utilized smaller wheels and tires as well as the hydraulic control mechanism.
The CatalIST trailer’s skirt is based on the new Wabash Ventix DRS (Drag Reduction System), in which segmented side panels manage air flow across the entire underbody.
Navistar continues to refine, searching for the ideal aerodynamic shape for a working heavy-duty commercial vehicle.
Among the aero touches, a camera system replaces and improves upon traditional mirrors.
A new LED headlamp system reduces lamp size for a more aerodynamic shape and cuts electrical power requirements by greater than 80 percent.
Along with the tight gap, the tractor and trailer fairings are mutually optimized, using computational fluid dynamics, to minimize drag.
A polycarbonate windshield allows for "a more aggressive curvature" that, in turn, better manages the airflow around the cab, Opperman noted. Combined with the camera system that replaces mirrors, the result is a significant reduction in noise and buffeting at highway speeds.
Low rolling resistance tires and aero wheel covers are also part of the package.
If the sun is just right, you might notice that the CalalIST is based on the International ProStar.
But the CatalIST project is aimed squarely at Navistar International's future products.