Spoiler (automotive)

A spoiler is an automotive aerodynamic device whose intended design function is to 'spoil' unfavorable air movement across a body of a vehicle in motion. Spoilers are often fitted to race and high-performance sports cars, although they have become common on passenger vehicles, as well. Some spoilers are added to cars primarily for styling purposes and have either little aerodynamic benefit or even make the aerodynamics worse.

Spoilers for automobiles are often incorrectly confused with, or even used interchangeably with, wings. Automotive wings are devices whose intended design is to generate downforce as air passes around them, not simply disrupt existing airflow patterns.

Operation

Spoilers generally function by disrupting or diffusing the airflow passing over and around a moving vehicle as it passes around the spoiler. This is accomplished by increasing the amount of turbulence flowing over the shape, "spoiling" the laminar flow and providing a cushion for the laminar boundary layer.Fact|date=April 2007 Applications are varied, including using body panels, or most typically by adding an extruding attachment.

Occasionally spoilers are added solely for appearance with no thought towards practical purpose.

Passenger vehicles

The main design goal of a spoiler in passenger vehicles is to reduce drag and increase fuel efficiency. While many often imitate wings and airfoils, these serve mostly decorative purposes. Passenger vehicles can be equipped with front and rear spoilers. Front spoilers, found beneath the bumper, are mainly used to direct air flow away from the tires to the underbody where the drag coefficient is less. Rear spoilers, which modify the transition in shape between the roof and the rear and the trunk and the rear, act to minimize the turbulence at the rear of the vehicle. Sports cars are most commonly seen with front and rear spoilers. Even though these vehicles typically have a more rigid chassis and a stiffer suspension to aid in high speed maneuverability, a spoiler can still be beneficial. This is because many vehicles have a fairly steep downward angle going from the rear edge of the roof down to the trunk or tail of the car. At high speeds, air flowing across the roof tumbles over this edge, causing air flow separation. The flow of air becomes turbulent and a low-pressure zone is created, increasing drag and instability (see Bernoulli effect). Adding a rear spoiler makes the air "see" a longer, gentler slope from the roof to the spoiler, which helps to delay flow separation. This decreases drag, increases fuel economy, and helps keep the rear window clean.

Other vehicles

Heavy trucks, like long haul tractors, may also have a spoiler dome on the top of the cab in order to lessen drag caused from air resistance from the trailer it's towing, which may be taller than the cab and provide a very non-aerodynamic effect. These spoilers primarily increase fuel economy instead of improving handling, however.

Trains may use spoilers to induce drag (like an air brake). A new prototype Japanese high-speed train, the Fastech 360 is designed to reach speeds of 250 mph. Its nose is specifically designed to spoil a wind effect associated with passing through tunnels, and it can deploy 'ears' which act to slow the train in case of emergency by increasing its drag.

Related terms

* Diffuser, which creates downforce by accentuating a low pressure zone beneath a car.
* Wing (automotive)
* Aerofoil
* Tail fin