Optimum Size and Form.
In essence - a trailer skirt performs in proportion to its area, provided that it does not leave significant gaps in front of the wheel bogie. Taller and longer is better, and the fuel differential between different skirts can be estimated fairly closely just based on their relative surface size. Our skirt length is adjustable to be custom mounted to the preferred wheel bogie setting of the trailer. Our full size skirt saves approximately 6% fuel in average wind conditions.
Advantages of 3D Enclosed Design.
When compared to flat panels - and as with boat-tails, the inner non-airflow surfaces function as a continuous strut and allow for internal pressurization by ram air, such that the skirt will not vibrate or flutter in high cross winds as panel skirts do. It remains true of shape and form over time, and is comparable in weight to the lightest alternative despite larger coverage and therefore performance.
The problem of needing low road clearance for maximum fuel recovery at highway speed, yet needing high clearance to manage slow speed maneuvering in cities and at the docking ramps can be addressed either by compromising on skirt height and accepting traumatic shape alteration and fluttering of a flexible lower portion, and still giving up low clearance and road performance, or by automatically extending and retracting the skirt to optimize performance while avoiding trauma as with the Truck Sail design which deploys to 4" road clearance at highway speed, but retracts in and up for 18" side clearance when maneuvering in cities and at docking ramps. The Truck Sail skirt is designed to serve a dual purpose as a safety guard for cyclists and pedestrians in retracted mode, with deployment to become a full height trailer skirt on the highway.
Optimum Tail Sail Size and Form.
There is no escaping the physics of the boat-tail effect. Basically the surface should follow the arc of a circle with trailer width diameter, cut at the point where the surface angle is 30 degrees to the trailer sides and roof, the angle at which attached air naturally separates off a sphere. Any alternative scheme that deviates from the basic physics is inferior and the only accurate way to compare performance is in the wind tunnel. Test track data can easily exaggerate the device performance unless the control truck was run in identical wind conditions to the test truck i.e. on the track at the same time. The full boat-tail effect is about 10% in drag reduction or 5% fuel reduction on a 53' trailer, and 8-10% fuel reduction on a shorter straight truck at highway speed (the air follows a steeper arc over the shorter vehicle causing greater air acceleration/deceleration and larger boat-tail impact).
Advantage of Enclosed Boat-Tail Design.
The back surface of an enclosed boat-tail design essentially functions as the supporting struts for the top and side airflow surfaces and this allows all surfaces to be ultra-light yet very stable as they do not have to carry local strut loading. All surfaces are then extremely resistant to wind vibration and are shape preserved over time for a clean geometric appearance, as they are ram-air stabilized in high wind. The enclosed/self-contained system also allows for rapid universal (non-customized) installation and maintenance access removal without any need to air seal the perimeter of the trailer (which is necessary to preserve function with an open panel concept). The enclosure also protects internal elements including the automatic deployment mechanism. Total weight of a boat-tail pair including deployment mechanism is around 90 lbs. A boat-tail shouldn't really present structural edges to following traffic and just looks better as a full enclosure.
The basic box geometry facilitates a simple clean folding system using only a single deployment mechanism per side. Deployment and stowage can be manual or speed regulated. Each boat-tail covers the door hinge hardware when deployed for a clean airflow connection, yet automatically swings away from the door hinges when the doors are opened to avoid door binding and allow full door opening at the dock.
Under-ride Deterrent Lighting.
The problem of under-ride accidents has been addressed by the idea of 800-1000 lb steel framing under the trailer. The industry would prefer a solution that does not interfere with the trailer structure and practical operation. Even this added weight displaces payload and requires more miles driven with associated increased accidents and energy used. The Truck Sail Tail-Sail and Side-Sail can be back lit for a soft, even glow which has no distracting qualities. Unlike a roadside digital billboard or oncoming headlights which draws attention off the road or have focal brightness, Truck Sail's unique lighting effect creates high conspicuity from a long distance without annoying brightness or distraction. The effect makes it very difficult to not be aware of the trailer with greater lead time to take evasive action. LED strip lighting is placed strategically beneath the surface for daytime conspicuity as well.