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After the oil shortage of the 1970's, truckers started attaching windbreaks on top of their cabs to make the front end of the trailers more wind resistant. This made a noticeable difference to anyone on the side of the road. But, when a body moves through a fluid with a viscocity as low as that of
air, it is more important to streamline the rear of the body, and trucks are still squared off with vertical doors. I suggest inflatable aerodynamic rear ends attached to the back of the truck which can be deflated for unloading. The bumpers would have retractable extensions.
Rear fairing
http://www.atdynamics.com/trailertail.htm
Here's one [lurch, Jan 28 2011]
Same idea
Inflatable_20aerodynamic_20add-ons
[MisterQED, Jan 31 2011]
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Annotation:
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[+] Does this windbreak make my ass look big ? |
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Why just trucks though ? You could have an auto-inflatable bag on a car for extended highway travel... have to work your way 'round the tail-lights, and be careful changing lanes. |
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Cool concept but I think that it got debunked not too long ago. Something to do with vortices reducing drag.
I didn't really buy it though...otherwise there would be box ended fish right? (+) |
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I think this could take the form of a spring-loaded
mechanism that is inflated by air (a la parasailing) at
highway speeds and is pulled out until the truck
slows and it is retracted. |
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//more wind resistant// I think [tony] means less affected by wind. A confusing choice of words. |
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Deep breaths, [Ian]. I agree with you. That's why I speculated on what [tonybe] meant, rather than what those particular words mean. |
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A plant that is more insect resistant is less affected by insects. By a false analogy a more wind resistant trailer could be thought to be less affected by wind; although if anything it would seem to imply that wind does not penetrate or damage the trailer. |
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'Wind resistance' is not a technical term anyway; also 'windbreaks' are usually intended to slow air flow by increasing drag, such as in an orchard. I would have said 'truckers started attaching fairings ... to reduce drag...'. |
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Those wind-fairings on top of the cabs do increase the wind-resistance of the *tractor*. This is especially noticable when they are running "bob-tail" without a trailer behind them. (A good invention would be a fold-down fairing for those times.) |
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The fairings direct the air up over the bluff front of the trailer, decreasing the wind resistance of the unit overall. Which has diddly to do with what someone would feel while standing at the side of the road. |
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Putting a fairing at the back end of a trailer isn't nearly as advantageous as streamlining the front ... |
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Thanks spidermother, I did mean "aerodynamic" when I said "wind resistant". |
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No worries. (That's Australian for "she'll be right".) |
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Check out the Dymaxion car for a vehicle that is streamlined front and back. For some reason, aerodynamics does seem to be a little neglected in motor vehicles. In the case of long distance trucks, aerodynamic drag is probably the main cause of fuel consumption. |
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An inflatable rear end will need to be rather rigid, which implies high pressure, or it will create drag itself by fluttering. |
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The problem with this concept is the size of the tail extension required. To prevent the formation of energy draining vortices, flow must not be allowed to detatch from the surface. There is a critical angle at which flow remains attached. In air, this is typically around 15°. For a 2.4m high container this requires a tail at least 4.5m long. |
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This won't work well as an inflatable. The high pressure drops created by that angle will quickly induce rippling of the surface, sending off vortices and generally defeating the object of the excercise. This would need to be a rigid attachment. |
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So, the question is, would the cost and inconvenience of a large, rigid tail be offset by the fuel saving? |
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One of the wonderful things about the English language (and possibly other languages, but I'll stick to what I know for now), is its marvellous ambiguity. Whatever you say can almost always be explained away later as meaning exactly the opposite to what you said; ask any politician. So, for example, the phrase 'windbreaks...make...trailers more wind resistant', can be taken to mean either that windbreaks increase the drag effect of the wind or that they make the trailers more resistant to the effects of the wind and so decrease drag! |
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//but I'll stick to what I know for now// - <gasps!> |
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It's a radical strategy, I know, but one that I thought that I'd adopt, just to see what it feels like. |
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I was going to talk about superconductors' being highly resistant to electricity - you can run thousands of amps through them and they don't even get warm - just to get a rise out of [IanTindale], but decided to use my powers for good, not evil. |
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Sorry, I thought of this a while ago (link). |
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My hat is off to you Mr QED. It's a relief to know that someone else besides me thinks of such stuff. |
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For goodness' sake! All these annotations and no fart jokes? |
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