aerothrust on semitrucks

January 28th, 2007, 2:37 pm

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Yes, most of you are right, aerothrust to PULL air off the front and PUSH it onto the back with rows of propellers would take MORE energy than it's worth, considering generator/motor inefficiences + blade drag losses. But neither are you Edisons.
N Harris has it right, a companion form to the aeroshell, (the "fish head") : a "fish tail" : a torpedo form on the rear surface. It could be inflatable OR it could be self inflating. A perforated rubber sheet, like stretchable nylon stockings, that is a pyramidal gum drop shape when fully extended by the rearward tensile stress.
Thus at 70 mph it pokes out some 10 ft to 20 ft to a point allowing the air to collapse in the laminar mode rather than the violent turbulence on flat truck back doors. Then when the truck stops it pulls back on the back doors like a sagging nylon stocking. Or it could be an accordian-fold.
The 9'x10' frame is piano-hinged on one side and swings 180 deg onto the box side when loading/unloading. Of course you'll need some kind of latch to securely hold the frame during travel, either magnets or physical latches.
Cost? Oh maybe $1K to $2K installed, something like the cost of the aeroshell. And the mpg improvement should be about equal to the aeroshell aerodynamic improvement.
Another aspect is alternating Karman Vortices(how fish "walk") : solid tail vs inflatable vs the loose perforted rubber sheet(permeable FABRIC in the generic sense) : how will each perform with those side motions if and when they occur?
Generally speaking though, how many FISH are there with SQUARE/FLAT tails? Or BOX shapes? And yet all objects moving through a fluid are sort of "fish", even semitrucks. They've already done the "head", now we need to add a "tail". HEY, any FISH can tell you THAT....

January 28th, 2007, 3:53 pm

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Mr-914
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When I saw the topic to this post, I initially thought of the Mercedes Bionic concept car form a couple of years ago. They used the boxfish as their inspiration:

http://www.worldcarfans.com/news.cfm?ne ... ountry/gcf

Image

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aerothrust on semitrucks

January 28th, 2007, 6:44 pm

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That blowfish looks like a tasty little morsel to a FAST barracuda. How does it stack up aerodynamically with other designs? That high rear end looks like LOTS of SUCTION.

No, nature has evolved fish to be as fast moving and energy efficient in a fluid as possible, or get EATEN. Unless the blow fish has some other defense, it's going to be some faster fish's FOOD.

Aerodynamically, semitrucks are "fish" moving in an ocean of air. The fastest and most energy efficient ones SURVIVE, the others....fall into the lawyer's hands, a kind of SHARK...

January 28th, 2007, 8:53 pm

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Despite its boxy, cube-shaped body, this tropical fish is in fact outstandingly streamlined and therefore represents an aerodynamic ideal. With an accurately constructed model of the boxfish the engineers in Stuttgart were able to achieve a wind drag coefficient of just 0.06 in the wind tunnel.

DaimlerChrysler utilised the findings from this research during the development of the Mercedes-Benz bionic car, a fully functioning and roadworthy compact car with a length of 4.24 metres and space for four occupants plus luggage. With a Cd value of just 0.19, this concept vehicle is among the most aerodynamically efficient in this size category.

aerothrust on semitrucks

January 28th, 2007, 10:35 pm

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Sorry, but I just can't see how the square, flat back of a semitruck is in any way, shape, or form aerodynamically efficient. Why do fish have tapered-to-a-point tails and bullet noses? The reason dust piles up on the back doors is the tensile stress from the HOLE that the box blows in the air. That tensile stress = a partial vacuum = drag = energy loss. Semitrucks need fish TAILS as well as fish HEADS(aeroshell over cab).

aerothrust on semitrucks

February 8th, 2007, 8:39 pm

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Yes, N Harris has it right. Aerothrust with propellers doesn't work, not even with paper calcs.

Edison : Plan B : a FISH TAIL. Aeroshells are now standard equipment on truck cabs, but where is the companion TAIL that allows laminar rearward flow instead of the turbulence from explosive decompression around the rear edges?

A SOLID shell, like a clam shell with vertical plane-joint and hinges to the side...I once saw on a long, towed trailer in Utah. But a SOLID shell like that wouldn't work on your standard semi. Safety issues, still sticking out at slow speeds/stops, wider radius on backing turns, narrow loading ramps and a 4.5 solid shell swung to the sides....wouldn't work as a practical solution.

So, plan C : either a balloon tail like a curved pyramid or an open weave fabric parachute on a 9'x10' frame, 3"x3" steel tube, with edge umbrella ribs. The inner surface of the balloon presses against the back doors and the outer surface pooches out into the curved pyramid form. It has to be a THICK fabric though, thin balloons POP. At slow/stop it sucks back against the rear doors.

On loading/unloading the frame is swung 270 deg on side hinges to the side of the truck, or swung 90 deg and shoved forward on top and bottom rails on the truck side.

With the parachute the fabric is stretched rubber like a nylon stocking and upon stopping pulls back against the rear doors like a sagging stocking. It should have umbrella ribs at the edges. At 70 mph the natural low pressure pulls it into the curved pyramid shape.

Now, why do this? The SUCTION on the rear doors(dust layer = BIG CLUE)costs a BOX blowing a HOLE through the fluid maybe 1 to 3 mpg in extra fuel costs, from that turbulence from explosive decompression. This TAIL would eliminate most of that loss with LAMINAR flow.

Cost? About the same as the front aeroshell. I just sent this idea off to 8 semitruck manufacturers yesterday, with the sentence : FISH whisper : swish, swish...tapered tail, tapered tail...swish, swish...tapered tail, TAPERED TAIL.....

February 8th, 2007, 11:04 pm

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with the sentence : FISH whisper : swish, swish...tapered tail, tapered tail...swish, swish...tapered tail, TAPERED TAIL.....

I see where you're going with this... but you gotta get out more, man.
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