THE NEW AERODYNAMIC, FUEL-SAVING TEARDROP TRAILER

(See case studies)

10% extra volume

Annual M&S fleet reduction of 840 tonnes or 20% (6 tonnes per annum per trailer)

DON-BUR Challenges & Objectives

Fuel Consumption: A Basic Guide

Fuel consumption is primarily attributable to 3 things: (1) resistance to inertia, (2) rolling resistance and (3) aerodynamics.

(1) Inertia:

(2) Rolling Resistance

(3) Aerodynamics: As a vehicle passes through air, it creates “drag”, comprising three main factors: parasitic drag, induced drag and wave drag. These main factors can be broken down into sub categories as follows:

Aerodynamics & The Teardrop Shape

As aerodynamics accounts for up to 50% of fuel consumption (especially at cruising/trunking speeds) and, as DON-BUR has little control over points 1-2, this is the area we have focused on with considerable effect.

Aerodynamics applies next to, and around the entire vehicle (Tractor-trailer/ Rigid chassis-bodywork). With this in mind, we not only had to consider the effect created by the trailer, but also had to understand the airflow trailing from the tractor as well.

The key, and most influential aerodynamic factor is Form/ Profile Drag. Air traveling over a smooth, airfoil shaped object will cause less drag than air traveling over an irregular, brick-shaped one. More specifically, the aim is to minimise any turbulence caused by a rapid change in object shape or surface direction. The main areas that cause turbulence on a tractor-trailer combination include: a) the tractor-trailer gap, b) the air “ram” effect caused by the front bulkhead, c) under the chassis and, more importantly, d) the large area of turbulence behind the vehicle. Turbulence is an area of rapid-flow, low pressure air that is created when laminar airflow traveling over a surface leaves that surface (separation point) due to sharp corner or shape change (relative to the initial direction of the air) and flows unevenly, creating vortices and eddies.

By streamlining a vehicle, you minimise the turbulence, reduce drag and lower fuel consumption.

If a liquid droplet is placed on a flat surface and passed through the air, it will naturally form a reverse-teardrop shape as the air moulds it and the forces acting on each surface reach equilibrium. Similar to an aerofoil, the positive-teardrop is an excellent aerodynamic shape is now commonly seen in the automotive industry and often used in sports equipment.

The new aerodynamic "Teardrop" tractor-trailer shape mimics the perfect aerodynamic lines of a teardrop and significantly reduces the co-efficient of drag (CD) by incorporating a specially designed continuous full-length curve on the roof (also considering the tractor). Beginning at a standard 3800 or 4000mm height at the front, the roof gradually curves upwards before gently tapering off at the rear whilst maintaining a generous rear aperture. This actually increases internal volume from a standard 78 to 86m3; an additional 10%.

In addition, the front bulkhead leans forwards slightly (keeping within 2040mm swing radius) to reduce the tractor-trailer gap turbulence and large radius cant rails further minimise vortex effects. The smooth roof lines not only manage linear airflow air well, they are designed to angle the airflow at the rear of the trailer (departure point) to minimise the turbulent area behind the trailer.

Standard 4m high trailer:

Wind-tunnel illustration

Turbulence illustration

Teardrop Trailer:

Wind-tunnel illustration

Turbulence illustration

Aerodynamic Airkits:

Historically, aerodynamic focus (tractor or trailer) has always been on the addition of various independent elements fitted to the existing bodywork and we have seen the inclusion of various designs; all of which have some degree of success and durability in a working environment.

There have been well-documented case studies (Freight Best Practice) regarding the effectiveness of airkits and, in the trials carried out (comparing a tractor-trailer combination without any airkit with a tractor-trailer combination with full airkit), it was found that the tractor cab top deflector alone accounted for 85% of the overall 16% fuel saving acheived; meaning that the remaining 2.4% was attributable to the cab collars, trailer side skirts and other additions.

With this in mind, the Teardrop trailer alone had to achieve significant fuel savings, independant of airkits such as cab tob deflectors, cab collars and trailer skirts, which are now considered by many as standard. Therefore, all Teardrop trailer trials had to be done in comparison to a tractor-trailer combination that already had full aerodynamic styling and airkits.

Due to its snag-free simplicity, the Teardrop bodyshape arguably has greater durability than other aerodynamic alternatives; retaining its fuel saving benefits throughout its life.

Increased Load Space And The Effect on Aerodynamics

Having reached the optimum aerodynamic shape, we are also acutely aware that load-space should not be compromised. To maintain load height and space for a single deck trailer, we had to increase the trailer height at its highest mid-point by 500mm; increasing internal cubic volume by 10%. Overall drag force is calculated using the CD value multiplied by the frontal area and wind pressure.

FD (or CDave) = CD A ½ pV2

In order to reduce drag, the reduction in CD value has to exceed the negative effect of the increased frontal area and wind pressure caused by an increase in height.

The calculation above illustrates how the forces acting on the fronts of both a standard trailer and a Teardrop trailer vary. As shown, the total resistant drag force acting on the Teardrop at 56mph is 35.7% less than a standard trailer, even with an increase in height. As speed does fluctuate (aerodynamic effect becomes less at lower speeds) the averaged fuel saving benefit drops in proportion to the average speed.

CONTACT US NOW TO DISCUSS POSSIBLE TEARDROP SPECIFICATIONS FOR YOUR ORGANISATION

The Teardrop shape is a Registered Design: number 000709423-0001: Patent Application Number 0707243.2

DON-BUR has set aside considerable funding to rigorously enforce both Registered Designs and Patent and will actively seek to claim any/all damages from any party believed to have made, or to be making any infringement, deliberate or otherwise.