Banned from motorsports half a century ago, variable aerodynamic devices were simply too effective to bury. Like practically every engineering advancement born of racing, manipulating air flow for improved performance was destined to trickle down to production cars.
In 1989, Porsche equipped its redesigned 911 Carrera 4 with a hinged air-inlet grille serving double duty as a rear spoiler. Above 50 mph (80.4 kph), an electric motor lifted the panel 30° into the air stream, returning it to a flush position below 10 mph (16 kph). This rising spoiler achieved three ends: Rear axle lift fell to zero, air flow to the engine was doubled and a large and unsightly grille opening was avoided.
Since that seminal 911 feature, Alfa Romeo, Audi, Bugatti, Ferrari, Ford, McLaren, Mercedes-AMG and Porsche have all bent the wind to their will with adjustable flaps, shutters, spoilers and wings. (See AE November 2015 cover story: http://magazine.sae.org/15autp11/). Two additional strides for the 2018 model year described below suggest that moveable aerodynamic surfaces could become core features in every new sports car’s design—and potentially in more mainstream vehicles as well.
Lamborghini’s innovative application of this science is part of a comprehensive upgrade of its Huracan V-10 supercar encompassing chassis improvements, the addition of 29 hp (22 kW), and a 90-lb (41-kg) mass reduction. Venturing off the standard path to higher performance, Lamborghini also improved its $274,390 Huracan Performante with an approach bearing the acronym ALA. While ala is Italian for wing, here it stands for Aerodinamica Lamborghini Attiva, or Lamborghini Active Aerodynamics. The key components are a front air splitter and a rear wing, both manipulated by a control computer to benefit acceleration, braking, cornering and top speed.
Engineering an optimized wing
Two motor-operated flaps are built into the front splitter. In the closed position, air flows above and below the splitter to augment front-tire loading; opening the flaps redirects the upper flow beneath the car, diminishing both downforce and drag.
The rear of the Huracan Performante is adorned with what appears to be a conventional high-flying airfoil. The issue with such devices is that there’s no free lunch in the aero world. Wings, especially those of this magnitude, generate substantial traction-improving downforce, but they also inflict drag. In the worst case, the relationship between downforce and induced drag is a squared function: For every 10 lb (4.5 kg) of downforce produced, there’s a 100-lb (45-kg) drag penalty.
That relationship can be improved by maximizing the aspect ratio (wing width versus cord length) and by adding winglets (end plates). The most common approach is to simply flatten the wing’s angle of attack when the down force isn’t needed. Lamborghini engineers learned of the plusses and pains inherent to conventional wings grooming Huracan Super Trofeo racers for GT3 competition. Those lessons drove them to develop the ALA strategy which avoids the complicated gear needed to alter a wing’s height and/or angle of attack. Instead, two pylons support the Huracan Performante’s forged-carbon-fiber rear wing rigidly in place.
An air duct covered by a small flap is located at the two points where the hollow support pylons meet the surrounding bodywork. The wing is also hollow and its bottom surface is pierced with holes that vent the air flowing up each pylon into the wing. Each flap is commanded by the Piattaforma Inerziale computer which is in touch with the car’s powertrain and chassis systems. Opening a flap routes air up the pylon, through the wing cavity, and out the wing’s underside to eliminate the pressure differential between the top and bottom surfaces, thereby significantly diminishing both downforce and drag.
With the flaps closed, the wing and the front splitter provide 770 lb (349 kg) of downforce at 193 mph (311 kph) according to Lamborghini aerodynamics engineer Antonio Torluccio, greatly enhancing cornering and braking performance. Opening all four flaps shifts the car into low-drag mode for improved acceleration and top speed.
The most ingenious ALA touch is splitting the wing cavity in half to enable side-to-side differences in downforce and drag—what Lamborghini calls “aero vectoring.” During left turns, using only the left half of the wing enhances the inside rear tire’s traction, diminishes body roll, and raises drag at the left-rear corner to increase yaw torque.
Because ALA can switch flap settings in only .5 s, it’s able to benefit acceleration, cornering, braking, and top speed on road or track. Torluccio adds that this approach saved 31 lb (14 kg) over using electric motors or hydraulic actuators to vary the wing’s orientation.
Proof that the Huracan Performante’s active aero approach is effective came last October at Germany’s Nürburgring Nordschliefe circuit, when factory driver Marco Mapelli beat the previous production-car lap record held by a Porsche 918 Spyder by five seconds.
GM patents active-aero control package—for a super Corvette?
While Chevrolet is thus far mum on the subject, there’s rampant speculation that a 750-hp (559 kW) Corvette ZR1 will break cover this fall. Beyond the spy photos of camouflaged mules adorned with a towering rear wing, the best evidence of what’s afoot is GM’s U.S. Patent Application 2017/0080770 A1 dated March 23, 2017. The document is titled Vehicle Ride-Height Determination For Control of Vehicle Aerodynamics.
All six of the annotated illustrations in this patent show a current Corvette Stingray adorned with “a plurality of adjustable aerodynamic elements and various sensors mounted to the vehicle body…” Background statements clarify the reasons for this pursuit: “to reduce drag and wind noise…and to prevent undesired lift forces and other causes of aerodynamic instability at high speeds” and “to achieve down force in vehicles in order to improve vehicle traction, high speed stability, and cornering.”
The list of adjustable devices includes a spoiler, an air dam, a shutter with moveable louvers, a specialized wing, an airfoil and a dive plane. The patent description says that these devices may be located at both ends of the vehicle and be adjusted by an electric motor or other types of actuators. In addition to an accelerometer to quantify acceleration and braking dynamics, laser and ultrasonic sensors are noted for ride height determination.
To vary the position of the aero elements relative to the body, electric, mechanical, electro-mechanical, and pneumatic actuators are specified plus “any other type appropriate for the specific packaging, efficiency, and cost constraints…” CPUs responsible for managing ride-height, body pitch angle, and aerodynamic component settings are mentioned.
Now that the Lamborghini and Corvette supercars are about to demonstrate what can be achieved with active aerodynamics, this technology will likely continue trickling down to mainstream models with a performance bent.Continue reading »