engineering

Semi-trailer aerodynamic device

Semi-trailer aerodynamic device is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Semi-trailer aerodynamic device rather than just read about it. In short: Semi-trailer aerodynamic devices are devices affixed to semi-trailers, for the purpose of reducing aerodynamic drag caused by air turbulence. The two major types of device in use are trailer skirts (or side skirts), affixed to the underside of trailers, and trailer tails (or boat tails, or rear fairings), affixed to the rear.

Key takeaways

Semi-trailer aerodynamic device belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Semi-trailer aerodynamic device to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Semi-trailer aerodynamic device from memory before moving on to harder problems.

Reference excerpt

Semi-trailer aerodynamic devices are devices affixed to semi-trailers, for the purpose of reducing aerodynamic drag caused by air turbulence. The two major types of device in use are trailer skirts (or side skirts), affixed to the underside of trailers, and trailer tails (or boat tails, or rear fairings), affixed to the rear. Several such devices have been recognized by the U.S. Environmental Protection Agency's SmartWay Transport Partnership, making them eligible for funding under the Diesel Emissions Reduction Act.

Trailer skirts

Construction Trailer skirts comprise a pair of panels affixed to the lower side edges of a trailer, running most of the length of the trailer and filling the gap between the forward and rear axles. Trailer skirts are typically constructed of aluminum, plastic, or fiberglass, with plastic the most resistant to damage from side or bottom impacts. Skirts may have a modular design, allowing installation on a variety of trailer lengths. Skirts generally weigh between 70 and 160 kg (150 and 350 lb). Installation typically requires three to five person-hours.

Cost As of 2009, a set of trailer skirts cost between C$1500 and C$3000 (US$1300 to $2700). Standard trailer skirts have an estimated payback period of ten to eighteen months, while "advanced" skirts (those that improve fuel efficiency by over 7%) are estimated to pay for themselves in seven to fourteen months.

Performance A 2012 investigation by SAE International of nine trailer skirt designs found that three provided fuel savings greater than 5%, and four provided savings between 4% and 5%, compared with an unmodified trailer. Skirts with reduced ground clearance offer greater fuel savings; in one instance, reducing ground clearance from 16 in (41 cm) to 8 in (20 cm) resulted in an improvement in fuel savings from 4% to 7%. One 2008 Delft University of Technology study found fuel savings of up to 15% for the particular design studied. Sean Graham, president of a major supplier of trailer skirts, estimates that in typical use, drivers see fuel savings of 5% to 6%. Trailers with skirts fitted have also demonstrated reduced tire spray, and drivers have reported improved stability in crosswinds.

Adoption As of 2018, over 60% of new trailers produced in Australia are equipped with skirts, whereas the figure is over 50% for the North American market. A 2014 study by the North American Council for Freight Efficiency on adoption of fuel efficient technologies and practices found trailer skirts to be the most widely adopted technology of those studied, having been adopted by seven of the ten major shipping fleets in the study. Since the wide adoption of trailer skirts, incidents of them becoming detached and colliding with other vehicles have increased. On October 18, 2018, a trailer skirt came off of a tractor trailer traveling East in Knoxville, Tennessee and hit a westbound car, killing its driver.

Trailer tails

Trailer tails, boat tails, or rear fairings comprise a set of panels, usually collapsible, which fold out from the rear of the trailer, creating a tapered shape that reduces drag from the low-pressure wake created behind the trailer. Trailer tails alone have demonstrated a fuel savings of 1%–5%, and in concert with trailer skirts, 9% improvement has been demonstrated. TrailerTail is a registered trademark of STEMCO.

SuperTruck project At least one model of trailer tail, trade named TrailerTail, is part of Navistar's SuperTruck project, which will use $37 million of US Department of Energy grants to build next generation trucks and tractor trailers.

See also Teardrop trailer (truck), an aerodynamically shaped trailer in use in the UK

References

Illustrations

Worked examples

Example 1 — a first encounter with Semi-trailer aerodynamic device

Start with the simplest possible case. Write down what Semi-trailer aerodynamic device claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Semi-trailer aerodynamic device before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Semi-trailer aerodynamic device ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Semi-trailer aerodynamic device

In research: Semi-trailer aerodynamic device appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Semi-trailer aerodynamic device in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Semi-trailer aerodynamic device is common in secondary-school and first-year university syllabi. It links to neighbouring topics Automotive technologies, Energy conservation, Shipping and the environment, so understanding it makes those chapters shorter.
In everyday life: Look for Semi-trailer aerodynamic device outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Semi-trailer aerodynamic device in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Semi-trailer aerodynamic device means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
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Frequently asked questions

What is Semi-trailer aerodynamic device in simple terms?

Why does Semi-trailer aerodynamic device matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Semi-trailer aerodynamic device?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Semi-trailer aerodynamic device.