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Cutting-Edge Aerodynamics

Looking at some recently patented aerodynamic technologies.

by Julian Edgar

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This article was first published in 2003.

One area that will see major growth in the next few years is that of movable spoilers. Sure, one version of the R31 Skyline and the RZ Supra ran movable front spoilers, while a variety of Porsche models have used moveable rear spoilers. But when you consider that major changes in drag and lift can be made by using body parts that shift in position, it makes sense to put them into use on a much wider variety of cars. To find out where automotive design is going in this area we've done a search of recent relevant US patents - these cover just-released technologies as well as those still a few years away from commercial application.

Ferrari's Constant Downforce System

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Ferraris' recent patent on movable spoilers highlights what the company sees as the deficiencies in the design of current movable aerodynamics.

"As is known, many high-performance vehicles have spoilers appropriately located on the vehicle body to increase the vertical load on the vehicle in movement and so improve road-holding and traction," says the patent.

"Spoilers, however, have the major drawback of impairing the aerodynamic efficiency of the vehicle, so that considerably more power is required to achieve and maintain a given vehicle speed.

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"By way of a solution to the problem, some vehicle manufacturers have equipped certain models with spoilers which are movable selectively, on command, to assume a... minimum-angle position in which the aerodynamic efficiency of the vehicle is affected as little as possible, or a... a maximum-angle position to increase the vertical load on the vehicle in movement and so improve road-holding and traction. The switch from the minimum- to maximum-angle position is made when the vehicle exceeds a predetermined threshold speed.

"In recent years, the need to reduce pollutant emissions and reduce fuel consumption has induced manufacturers to perfect the movable-spoiler solution by enabling spoilers to be set to any position between the minimum- and maximum-angle positions, thus enabling spoiler position control as a function of vehicle speed. That is, the spoiler angle can be increased in proportion to vehicle speed so as to gradually increase the vertical load on the vehicle as speed increases.

"Though excellent in terms of fuel consumption, particularly at low speed, the above solution seriously complicates high-speed performance of the vehicle."

Ferrari sees the following disadvantages with this traditional movable spoiler approach:

  • As speed increases, the vehicle tends to sink dangerously close to the road surface.
  • As speed increases, the vertical load on the vehicle gradually compresses and distorts the suspensions, thus making the vehicle harder to drive.
  • While improving road-holding and traction, the gradual increase in vertical load also makes steering harder, thus impairing driving comfort at high speed.
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Ferrari's solution is to use movable spoilers at both the front and the back of the vehicle - the front spoiler comprising a movable flap each side of an undercar tunnel, and the rear spoiler being mounted on the trailing edge of the vehicle. These spoilers are infinitely adjustable for angle. The angle of attack of each spoiler is determined primarily on the basis of vehicle sped, but the patent also points out that "other status variables, such as steering wheel rotation angle, longitudinal and transverse vehicle acceleration, accelerator pedal position, etc" could also be input into the decision-making.

An important aspect of the system is that once a given speed (eg 240 km/h) is exceeded, the spoilers are moved so as to maintain the vertical load being developed by them at a constant value, so long as the vehicle remains travelling above that speed. To improve the accuracy of this system, the spoilers use encoders so that the actual angle values can be read by the controller.

The advantages of a vehicle using this system are, according to the patent, obvious. By maintaining a substantially constant vertical load when the speed of vehicle exceeds the preset speed, the bottom of the vehicle is preventing from coming dangerously close to the road surface, and, even more importantly, an excessive vertical load which distorts the suspension - so making the vehicle hard to handle - is avoided. In addition, because current movable spoilers tend to provide more downforce than is needed at very high speeds, such a system gives fuel economy benefits through reduced drag.

The Air Brake Rear Spoiler

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Brian Pettey of Kansas, USA, has recently applied for a patent on his design of moveable rear spoiler. The spoiler can be altered in angle to such an extent that it works as an airbrake! Although looking a full-race design, the inventor suggests that the device is appropriate for aftermarket fitment. However, unlike "many of the fixed spoilers on the market [that] are designed with appearance and styling in mind and produce no aerodynamic benefits whatsoever", this design is intended to work.

The spoiler is automatically moved from its normal position to the air-brake position by the use of the brake pedal, which triggers the actuator through the brake light signal. The movement of the spoiler can be caused by "a screw drive, a hydraulic drive, a solenoid or a pneumatic drive" and the control system can also incorporate a panel on the dashboard allowing the driver to manually select the required spoiler angle.

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As can be seen in this drawing, the normal angle of the spoiler can also be adjusted manually by loosening the bolt and moving it within the spoiler support slot. In this iteration the spoiler is returned to its normal resting position by a spring, but the extensive patent covers pretty well all possible means of actuation of the spoiler.

DaimlerChrysler's Flapping Spoilers!

DaimlerChrysler has recently patented a number of devices that can be used to alter the flow of air over a car's body. They do this by influencing the vortices (patterns of swirling air) occurring within the aerodynamic wake behind the vehicle. But these moveable vanes aren't just slowly moved from position to position; nope, these ones flap up and down like a bird's wings!

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This diagram shows how it all works. In this example the car already has a passive roof extension spoiler, but an additional active spoiler (green) is also provided. This spoiler can move up and down around a pivot point placed at its leading edge. A stepper motor and crank arrangement is provided so that this spoiler can be flapped up and down. The motor is operated by an electronic controller (purple) which monitors road speed. Using internal maps that correlate road speed with the desired spoiler flapping rate, and "depending on the respective road speed and the resultant flow of the headwind around the vehicle, a corresponding change is made in the frequency of the pivoting movement of [the] spoiler". In another iteration, the distance that the spoiler is moved up and down can also be altered.

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If the idea of flapping spoilers proves too hard to sell to the public, a similar outcome can be achieved in a more subtle manner. Instead of a moving wing, air can be alternately sucked and blown through a slot or tube at the critical body area. In this iteration the stepper motor and crank described above are connected to a piston working within a cylinder. A hose connects the cylinder to "a suitable point on the outer contour of the motor vehicle forming a corresponding air blower and suction opening.

"Pump movements of [the] piston... produces periodic alternating suction and blowing processes in the area of the corresponding outer contour opening. By drawing in and blowing out air in the outer contour area of the motor vehicle... an active influence is exerted in the flow around the motor vehicle which can be varied as a function of road speed..."

DaimlerChrysler are completely serious about this unique aerodynamic approach, with their patent exploring a range of other configurations. Some of these are shown here.

However, an even odder approach than flapping wings is also included in their patent. Expanding membranes that cover suction and pressure holes can be placed strategically on the surface of the vehicle body. Rapidly expanded and contracted, they can be pulsed at the right frequency to appropriately disturb the airflow. These can extend from the rear or roof of the vehicle, being formed into long thin shapes. These stripes can be pulsed in or out of phase, producing a wavelike motion.

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Some of the suggested approaches for these pulsating membranes are shown here.

Anti-Spin Spoiler System

Patented by William Haraway Jr. of the US is a spoiler system for NASCAR-style race cars which is designed to aerodynamically resist lift during a spin. Backgrounding the invention, the patent says:

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"Various types of fixed rear spoilers have been employed for... race cars that serve to spoil or divert air flow passing over the aerodynamic surfaces of the vehicle to thereby reduce, or negate, the aerodynamic lift high speed air flow. These spoilers are normally set at a minimum angle by the sanctioning body controlling race car competition. At this angle, the spoilers located on the deck lid of the vehicles provide positive aerodynamic down forces on the rear end of the vehicle to thereby increase tire traction, enhance directional stability and, as one of several devices employed, to limit maximum vehicle speed.

"Speeds approach approximately one-hundred ninety miles per hour (190 mph) during competition and often, when one race car contacts another aft of the centre of gravity, radial inertia forces causes it to rotate, or spin, through a one-hundred eighty degree arc angle and become airborne while going in the backward direction. The fixed spoiler and aerodynamic design of the race car vehicle exposed to the high velocity aerodynamic air stream lifts the rear end of the car off the ground, resulting in tumbling, cartwheeling and airborne rolls before striking the ground. Extensive car damage and/or driver injury is the result. The hard mounted, or fixed spoiler, at a high angle of attack contributes greatly to the aerodynamic lift effect when travelling in a high speed, backward mode."

However, if the spoiler is designed so that its behaviour changes during a spin, aero lift in this condition can be avoided. This outcome is achieved by using a flat plate spoiler (as required in the formula) that can automatically change its angle of attack when a spin occurs.

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The spoiler uses a split spoiler (green), with the gap between the spoiler sections sealed with tape. The spoiler plates are hinged at their forward edge, and another piece of tape is used to seal this area. A pair of rear pylons (red) support the spoiler plates in their conventional position, serving as limit stops. In addition, a pair of forward supports (purple) are attached to the boot lid. These support the spoiler panels should they be deflected into a forward position.

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As the vehicle reaches the ninety-degree point in rotation in a high-speed spin, one spoiler segment pivots forward. This occurs because of the change in direction of the aerodynamic air flowing over the vehicle. When this occurs, the sealing tape covering spacing between the panels tears, permitting the relative free forward rotative movement of the spoiler segment into contact with its forward support. This spoils the flow of aerodynamic air which is now moving over the rear and towards the front of the vehicle. When the vehicle has rotated a full 180 degrees, the remaining unlifted spoiler segment also pivots to the forward position and further assists in spoiling the aerodynamic air flow over the vehicle. This reduces lift and minimizes the possibility of the vehicle becoming airborne.

Note: Roof flaps that asymmetrically lift are used on current NASCARS to reduce the likelihood of lift being generated during a spin.

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