How Do They Work?

See how they work: Watch On YouTube.

Each Airtab® produces two vortices of air, each approximately 4 to 5 times the height of the Airtab® and several feet in length. These tight swirls of air "bridge the gap" between tractor and trailer and lets air flow more smoothly into the vacuum at the rear of the vehicle.


This image shows how the vortices are created.
Click on image to view animation

Aerodynamics of Trucks

The first aerodynamic drag reducing devices were introduced to the trucking market in the early 1980s. To date these devices have been applied almost exclusively to the front of the vehicle in the form of air deflectors or fairing.

Airtabs™ are unique in that they target two drag-producing areas - the tractor/trailer gap and the rear of the trailer, box van or RV.

 

This image shows the airflow and high drag areas around an unfitted unit.

 

Airtabs™ target and reduce drag at two locations: the gap between tractor/trailer and the rear of the trailer.

 

The Tractor-Trailer Gap

The gap size is an important aspect of fuel economy in trucking operations and should be minimized as much as loads allow. If the gap between the trailing edges of the tractor fairing and the front of the trailer is greater than about 18 inches (1/2 meter) increased drag in this region begins to reduce fuel economy. For every additional 10 inches of gap size above about 30 inches, aero drag will increase 2% and fuel economy will decrease by 1%. The operator can reduce this gap with side extenders and/or moving the 5th wheel forward. However, moving the 5th wheel forward can reduce maneuverability and can place more weight on the steering axle increasing steering gear and tire wear. Through the use of side extenders and Airtabs, operators will have the flexibility of setting the 5th wheel more precisely for the load, not add weight to the steering axel and avoid a reduction in fuel economy by using Airtabs to reduce gap turbulence.

 

The Back of the Trailer

Airtabs™ reduce drag at the trailer rear by changing the dominant flow pattern from vertical to horizontal. Airtabs™ change the airflow from the alternating formation of large vertical eddies to a line of dozens of small vigorous horizontal ones. This reduces vehicle sway, improves stability in gusty cross wind conditions and increases fuel economy. By altering the airflow in this manner, Airtabs™ artificially taper the trailer and make the airflow behave as if the trailer was slightly smaller than it actually is. This results in drag reduction and an increase in fuel economy.


Click on image to view animation


Click on image to view animation

Look closely at the image. This is a very accurate depiction of the airflow behavior surrounding a moving trailer without Airtabs™ as viewed from above. Notice how large vertical eddys of air (like small tornadoes) alternately form and "shed" making room for another to form on the opposite side.

Although not visible here, there is an additional eddy that rolls off the top of the trailer as well. These eddys tumble into the partial vacuum formed by the moving vehicle.

A lack of trailer streamlining causes a partial vacuum to form at the rear of the trailer at highway speeds. This causes turbulent air in the form of large vertical eddies to tumble into the partial vacuum and the large alternating eddies cause the trailer to sway. Disturbances from passing vehicles or obstacles tend to amplify these eddies and increase the trailer's tendency to sway, increasing driver work load and fatigue, increasing drag and lowering fuel economy. Streamlining the trailer by tapering would be the best solution but is not practical due to a necessary reduction in trailer capacity and massive changes to docking and loading facilities.

Other functional after-market devices that will reduce drag at the rear of trailers do exist. These are usually devices that physically alter the trailer rear by using inflatable sails, fiberglass boat tails or rigid metal panels that extend to taper the trailer rear. However, these devices can be cumbersome, expensive, heavy and prone to collision damage. These devices can also interfere with loading operations.

 

Wind Tunnel Test Photos

The photos below show results from a wind tunnel trial with smoke generators used to track airflow patterns.

 

This image shows the airflow and high drag areas around an unfitted unit.

 

Airtabs™ target and reduce drag at two locations: the gap between tractor/trailer and the rear of the trailer.

The pictures above were taken in a low speed wind tunnel facility looking down on a simulated tractor-trailer gap. Notice how in one photo the smoke reveals how turbulent air enters the gap and increases aerodynamic drag. The second photo shows how Airtabs™ reduce the amount of smoke, turbulence and drag entering the gap under identical controlled wind tunnel conditions.

* These photos supplied courtesy of the Cranfield University Atmospheric Boundary Layer Wind Tunnel

 

Spray Reduction and Stability

Drivers report an improved view to the rear and sides in wet or snowy weather. They can see other vehicles behind them more clearly, and see if it is clear to pass (or be passed). All drivers of vehicles fitted with Airtabs, even 18-wheelers, report improved stability of handling of the vehicle. Drivers of RVs fitted with Airtabs report consistently better handling when being passed in the same direction by large vehicles. -Improved Safety- Improved stability also means less driver workload to keep the vehicle under control, especially in crosswinds.

 

Road Grime Reduction

Because Airtabs™ alter the airflow at the rear of the vehicle, the partial vacuum there is reduced. There is less accumulation of road grime or snow. Less road grime means advertising remains more visible and the company's image is enhanced. Less snow means less weight to haul and less snow build up that can obscure conspicuity tape reflectors and low heat LED tail lights.

 

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