Drag in Vehicles

by Bill Kuhl

Drag is a major concern with airplanes although much of the drag is created in the process of creating lift. Vehicles such as cars and trucks also need to be concerned with drag if they are to be fuel efficient.

Drag Coefficient - describes the amount of aerodynamic drag caused by fluid flow, the smaller the number the better in terms of fuel economy.  Around 60 percent of the power required at highway speeds is taken up overcoming aerodynamic drag,  this increases very quickly at higher speeds.

Toyota Prius Hybrid has a Drag Coefficient of 0.29	This older pick has a Drag Coefficient considerably higher than 0.29.

  Modern automobiles usually have a drag coefficient of between 0.30 to 0.35, SUV's are in the range of 0.35 to 0.45.   

Notice the streamlined front end of this Toyota Prius Hybrid.		Typical of all cars of this era, this Chevy Chevelle has many drag producing areas around the headlights, bumper, and grill.
Mirrors on newer cars are flared to the car. Door handles are recessed into door.		Mirrors on older cars disrupted the airflow as did door handles which stuck out farther from the door.
Drag Reduction in Trucks Large trucks only get a few miles to the gallon, not very good fuel economy. Substantial drag reduction could increase the mileage enough to account for huge fuel savings.		Bob Englar and his team of researchers hope to reach at least 35% drag reduction. If this were accomplished on the entire US trucking fleet, it could save an estimated one billion gallons of fuel a year.
Good design of truck and trailers can reduce drag by 10 percent.		With no fairing, air pushes directly into flat front of trailer.
Close-up of fairing on truck cab.		Gap between truck and trailer is a source of substantial drag.

The flat rear end of truck trailer is a source of drag that is tough to correct because it is important to use all available space for cargo.	Objects moving through a fluid (ex. air or water) that have a flat surface in the rear, create a turbulence that is a source of drag.

Gradually bringing the rear of an object to a point provides for smoother airflow.	Wheel pants help streamline airflow around the wheels of this airplane. Can you think of  how airplanes reduce wheel drag even further?

Observation Activities

• Be on the lookout for vehicles that have been designed to reduce drag. 
• Look for streamlining in nature.

 Hint: drag can be reduced in water also.

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