Cadillac LMP 02 Technical Insights: Chassis Design And Development
As Cadillac celebrated its 100th birthday in 2002, one of the first presents to be unwrapped was the all-new Cadillac Northstar Le Mans Prototype (LMP). With an aerodynamic new body design, an updated engine package and a performance-driven team, the second-generation Cadillac LMP 02 represented a bold break from the past for young Team Cadillac.
Cadillac launches new Northstar LMP in Centennial year
"Very seldom in racing can you talk about a program in its third year and say that you have an all-new race car, but that is exactly the case with the Cadillac LMP 02," said Herb Fishel, executive director of GM Racing. "The Cadillac LMP 02 marks a new beginning for Team Cadillac with a state-of-the-art race car
"We recognize that Cadillac faces formidable and experienced opponents in the top tier of international endurance racing," Fishel noted. "Now after seeing what Team Cadillac has created, we are optimistic that the 2002 Cadillac LMP will be a credible contender in this fiercely competitive arena. And once you can race side-by-side with the competition, you can begin to look forward to beating them."
b]International Team created Cadillac LMP 02
Designed under the direction of GM Racing by Nigel Stroud, the Cadillac LMP's carbon fibre monocoque chassis and suspension components were fabricated in Brackley, England, and assembled at the team's headquarters near Atlanta. An extensive testing program is planned leading up the 24 Hours of Le Mans on June 15-16, 2002. The Cadillac LMP 02 will also compete in selected American Le Mans Series events in North America.
"The new Cadillac LMP 02 is the culmination of a deliberate step-by-step process," said Jeff Kettman, GM Racing Cadillac LMP program manager. "In the first year of the program, we learned about the level of competition we faced. In the second year, we focused on collecting data and accumulating experience while racing a highly modified LMP 01 chassis. Now in the third year of this program, we are introducing the new Cadillac Northstar LMP 02 - a car that incorporates the lessons we have learned and embodies the knowledge we have gained."
Design Team employed GM's Technical resources for efficiency
"Team Cadillac made use of General Motors resources throughout the design phase of the project," Kettman continued. "Computer simulations allowed us to refine the vehicle's aerodynamics and analyze suspension geometry rapidly. This digital data stream, combined with the trackside data from Le Mans and North American race circuits, enabled Team Cadillac to create an all-new car quickly and efficiently."
The design team utilized the full range of sophisticated tools that are now available to race car constructors: computer-aided design and manufacturing (CAD/CAM), computational fluid dynamics (CFD), finite element analysis (FEA), and three-dimensional solid modelling. Wind tunnel and seven-post tests then validated the Cadillac's performance under carefully controlled conditions.
New chassis designed entirely on computer
The cornerstone of the Cadillac LMP 02 program is a new carbon fibre chassis - designed not on a clean sheet of paper, but on a glowing computer screen.
"While the series rules define many of the car's dimensions, we were able to make significant changes to the chassis within these parameters," said Nigel Stroud. "For example, the move to a shorter wheelbase improves the Cadillac LMP's aerodynamic performance by making the chassis less sensitive to pitch. This results in an overall improvement in stability over the previous car."
Shorter wheelbase produces improved stability
The Cadillac LMP 02's high nose directs airflow under the car while respecting the LMP rules that require a flat bottom between the front and rear wheels. This flat surface can, however, generate significant down force through ground effect - the interaction between the moving vehicle and the fixed track surface. By shortening the wheelbase, undesirable changes in the vehicle's attitude are minimized, allowing the flat bottom to maintain a positive rake angle and produce consistent aero loads. Wind tunnel tests have demonstrated substantial improvements in both lift and drag over the first-generation LMP 01.
The Cadillac LMP design team explored a variety of imaginative body and chassis layouts before finally selecting a shape that is familiar to road racing fans.
"We looked at several concepts that really pushed the limits, but none satisfied all of the requirements for down force, cooling and packaging simultaneously," Stroud said.
New construction method used in Cadillac LMP Monocoque
"Advances were made in the construction of the monocoque by using a different method of bonding the two halves together," he continued. "The side-mounted radiators employ water-to-oil heat exchangers to cool the gearbox, which eliminates the aerodynamic penalty of a separate air-to-oil cooler for the transmission. This system also stabilizes the gearbox oil temperature, especially at the beginning of a race when the lubricant is preheated by the engine coolant."
Safety considerations also figured prominently in the design of the Cadillac LMP 02. A Formula 1-style cockpit surrounds the driver while head restraints moulded from shock-absorbing foam cradle the helmet's back and sides. An innovative pedal box assembly provides an extra measure of protection for the driver's lower extremities.
Innovative pedal box enhances driver safety
"The monocoque is the primary survival cell," Stroud explained. "Inside of that is a secondary cell to protect the driver's feet. This 'box within a box' also offers the advantage of a fully adjustable pedal assembly to accommodate different drivers."
The double wishbone suspension employs F1-style cast stainless steel uprights that mount six-piston monoblock brake calipers and carbon fibre discs. The power steering is electronically assisted.
"We have made a large number of small changes in the car that we believe will add up to a substantial overall improvement in Team Cadillac's on-track performance," Stroud predicted. "It comes down to getting the details right in order to produce a great car at the end."
It is said that a journey of a thousand miles begins with a single step. With the introduction of the Cadillac LMP 02, Team Cadillac has taken many steps in its quest to reach a higher level of success - and there are many more steps ahead on the long road to Le Mans.
Pose the question, "What's new?" to GM Racing engineer Ed Keating, and you get a succinct reply: "Everything."
RACE-PROVEN NORTHSTAR LMP ENGINE IS REVISED FOR 2002
Keating leads the team of engineers and technicians that produces the prime mover for the Cadillac LMP 02 - the twin-turbocharged 4.0-liter (244ci) Northstar V8 racing engine. While the changes in the body and chassis of the second-generation Le Mans Prototype are apparent, the modifications to the heavily revised powertrain are virtually invisible.
"We have made substantial changes in internal components and specifications for the 2002 season, but the engine's external appearance is generally unchanged," Keating said. "After evaluating the alternatives in displacement, induction systems, maximum boost and air restrictor sizes, the engine group decided to continue development of the turbocharged Northstar V8 that has proven itself over the last two seasons of competition."
ACO RULES SPECIFY MAXIMUM BOOST AND INLET RESTRICTORS FOR LMP ENGINE
The Automobile Club de L'Ouest (ACO) rules that govern the 24 Hours of Le Mans and the American Le Mans Series (ALMS) achieve performance parity among different types and sizes of engines by specifying inlet air restrictors and maximum turbocharger boost. Under the ACO formula, the 4.0-liter Northstar V8 is limited to 1500 millibars absolute manifold pressure (equivalent to 7.5 psi boost pressure) and its air intake is regulated by two 32.4mm (1.28-inch) diameter orifices.
"The ACO regulations do a very good job of producing equivalency between naturally aspirated and turbocharged engines with a variety of displacements," Keating said. "However, turbocharged V8 engines have enjoyed great success at Le Mans in recent years, and the architecture of both the production Northstar V8 and its racing derivatives is well suited to this particular configuration.
PROVEN ENGINE ALLOWS TEAM CADILLAC TO FOCUS ON CHASSIS DEVELOPMENT
"Another factor in the decision to continue development of the turbocharged Northstar V8 was time management," Keating continued. "There are already enough variables with the introduction of an all-new chassis. The Northstar V8 is a proven, reliable powerplant that will allow the team to focus on car development rather than powertrain issues."
The Northstar LMP engine is a product of GM's global motorsports program. It has close ties to the 4.0-liter naturally aspirated engines used by Opel in the German Touring Car Masters (DTM) road racing series and to the methanol-burning naturally aspirated 3.5-liter Chevy Indy V8 engine that is being introduced in the Indy Racing League (IRL) oval-track series in 2002. All three racing engines are based on GM Powertrain's Premium V platform.
NORTHSTAR V8 BENEFITS FROM IRL AND DTM MOTORSPORTS PROGRAMS
"In 2001, we introduced a 180-degree crankshaft in the Northstar LMP engine that was based on a design originally developed for the IRL series," Keating reported. "This year we are incorporating cylinder head and valvetrain developments from the Opel DTM program that suit the operating range of the Northstar LMP engine.
"We are also pursuing improved performance and fuel efficiency through friction reduction, induction system tuning, refinements in engine calibration and enhancements in oil scavenging to minimize parasitic windage losses," Keating added.
GM PREMIUM V ENGINE FAMILY PROVIDES PLATFORM FOR LMP, DTM AND IRL RACING ENGINES
The LMP, DTM and IRL racing engines share their fundamental design with the family of production Premium V engines that power Cadillac Seville, Eldorado and DeVille models. The production and racing engines have similar attributes, including lightweight aluminum block and cylinder head castings, four-valve combustion chambers, chain-driven dual overhead camshafts and electronic engine management. They also share the same architecture, including a 90-degree V angle and 102mm cylinder bore centerlines. In the Cadillac LMP and IRL applications, the engine is a fully stressed chassis member that is subjected to suspension and aerodynamic loads.
COMMON ENGINE ARCHITECTURE IS KEY TO EFFICIENT USE OF RESOURCES
"The Premium V engine program demonstrates how General Motors is able to marshal its global resources to adapt a common engine platform to the unique requirements of three different racing series," said Joe Negri, GM Racing IRL/Road Racing Group manager. "Using a common engine architecture in several racing series allows GM Racing to respond quickly to new opportunities while controlling overall costs.
"The common elements in the ALMS, DTM and IRL engine programs also promote synergy between GM operating units in North America and Europe," Negri added. "This engine program demonstrates how GM uses motorsports to achieve its business objectives in specific markets."
NEW SIX-SPEED SEQUENTIAL TRANSMISSION
The Northstar LMP engine is paired with a new six-speed sequential gearbox in 2002. Paddles mounted on the steering wheel activate gear changes through a pneumatic shifting mechanism. This system allows the driver to shift gears without moving his hands from the wheel.
"The pneumatic shifter is completely self-contained," said chassis designer Nigel Stroud. "Unlike many hydraulically operated systems, it does not require oil pressure from the engine. Consequently we believe this air-operated system offers advantages in both reliability and maintenance."
Two years of continuous engine development have pushed the Northstar V8's output to 600+ horsepower.
ENGINE DEVELOPMENT PROGRAM FOCUSES ON POWER, RELIABILITY AND FUEL EFFICIENCY
"The Northstar engine program has made impressive progress, and we fully expect this steady improvement to continue," said Cadillac LMP Program Manager Jeff Kettman. "Working with our development partners, Ed Keating and his group have produced an extremely reliable engine package. With the enhancements that they are introducing this year, we anticipate further improvements in outright speed while maintaining the reliability and fuel efficiency that are absolutely essential in endurance racing."
From the winding road courses of the DTM and the high-speed ovals of the IRL to the magnificent sweeping turns of Le Mans, GM's extended family of Premium V-based racing engines is turning fast laps - and turning heads.
Construction:Carbon fiber monocoque with aluminum honeycomb core Weight: 900 kilograms Length: 465 cm. (193 in,)
Width: 200 cm. (78.75 in)
Height:102 cm. (40.15 in.)
Bodywork: Carbon and Kevlar with Nomex honeycomb Suspension: Double wishbone front and rear with pushrods Dampers: 4-way adjustable gas-filled
Brakes:AP 6 piston monoblock calipers - carbon fiber discs Steering: KYB electric power steering
Wheels: BBS one-piece forged magnesium custom designed for Cadillac Front diameter: 18 in. width: 13.5 in.
Rear diameter: 18 in. width: 15 in.
Tyres: Michelin Pilot
Gearbox: Xtrac 6-speed sequential
Clutch: AP four disc carbon diameter 5.5 in. (160 mm) Fuel cell: Capacity: 90 liter (23.7 gallon)
Data Acquisition: Pi Sigma with Bosch telemetry
Type: Twin turbocharged and intercooled 180 degree V8 Displacement: 4000 cc (4.0 Liter - 244 cu. In.) Bore x Stroke: 93 mm. (3.66 in.) x 73.4 mm. (2.89 in.)
Lubrication: Dry sump with oil to water heat exchanger Fuel system: Bosch
Engine controllers: Bosch
Intercoolers: Secan air-to-air
Restrictors: Twin 32.4 mm diameter
Maximum rpm: 7500
Brake horsepower: 600+
Top speed: 200+ mph (322+ kph) in LeMans trim
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