Posted on 05/14/2007 11:59:24 AM PDT by antiRepublicrat
Find a picture of a commercial jet that has blunt rear surfaces like a semitruck, instead of tapered tails. The kamm effect and toyota engineers...those japanese engineers will believe anything. There’s the story of how we let them steal a certain ship design from US in WWII, knowing they would copy it. Of course in the plan the center of gravity was above the center of buoyancy, what happened then when it slid out of dry dock? They’ll believe anything....
As to extensive wind tunnel testing, fish, birds, even airplanes flying in the real world have VAST experience in tapered vs blunt tails, you’re just trying to be cute or the devil’s advocate. Maybe you can hire on at airbus(airbust)and introduce them to the kamm effect and blunt tails.....
Sadly though, here the public whines about “freedom from foreign oil”. It should be “freedom from stupidity” as semitrucks roll on, pulled back into the suction zone of the hole they blow thru the air. A TAPERED TAIL would eliminate most of that rear aerodrag(fish tail)just as the aeroshell does over the cab(fish head).
Again, a box has 14 times the aerodynamic drag of an equal cross section torpedo, that’s right there in every physics book. In the movie : Flight of the Phoenix, the tail of the box is a tapered clam shell. Now if it works in a 300 mph aircraft, why not a 70 mph semitruck?
No, I’m not suggesting a solid shell tapered tail, it would either be a curved pyramid form made by an inflated balloon or open weave parachute, on a hinging frame, that deploys at high speed(above 35 mph), then retracts back onto the rear doors as the truck slows to a stop(below 15 mph). You could also have two (on each back door)that joined via magnetic zippers(top and bottom furrows to the rear point).
If this tapered tail boosts energy efficiency of the truck by 3 mpg, then on a 7 mpg rig : 7+3=10 mpg. With an annual fuel bill of $50,000, that’s about $15,000/year that stays in the trucker’s wallet instead of becoming the gov’t/big oil’s cash cow. So maybe you’re a front man for them with your kamm effect, or just intellectually lazy...
Today, truck length is specified by law. Truckers know that economically the increased amount of cargo space with a Kamm-back far outweighs the fuel efficiency gains of making a streamlined tail within the legally permissible length.
There are designs that try to pressurize the area behind the chopped-off tail and many of them use NACA ducts to achieve this effect. See http://en.wikipedia.org/wiki/NACA_Duct
But, these designs do not lower drag much at automotive speeds, so they are usually left for race cars and aircraft.
Seriously, before you accuse the engineering world of plotting against your inflatable cones, please check out a book on aerodynamics from the library and learn the physics involved.
I do not think it is appropriate to use FreeRepublic’s bandwidth to educate you further.
Said like a true pharisee. The good is the enemy of the perfect. Your kamm guy is a pedant/academic. Who CARES if a 10’ long aerotail ONLY reduces rear drag by some 50%, with still some residual turbulence? If that ONLY works out to $5,000/year for the trucker’s annual fuel bill savings, that’s CASH left in his pocket instead of the gov’t/big oil pocket!
Truckers driving 18 wheelers are the backbone of our economy, imagine life WITHOUT them. Thus I’m trying to HELP them with the other half of the aerodynamic “fish story”, the tail to go with the head, what have YOU ever done for them?
Since science and the law do not seem to matter to you, why don’t you visit a truck freight terminal such as J.B. Hunt or Yellow Freight and speak with some truckers and warehouse workers about your idea.
Period, Paragraph, Over and Out.
End XMIT
They see but do not PERCEIVE. There is a world wide war over oil, tinhorns like chavez and putin jerk us around because of our addiction to it. Semitrucks are the backbone of our economy and any increase in their efficiency would be beneficial to everyone.
Aeroshells began in AL as simple plywood sheets, evolving into the boutique designs of today, as the fish head. Even if a short 10’ to 15’ long tail reduced rear drag to 50% of what it is now, that’s money that stays in their pocket instead of swelling gov’t coffers. The gas tax is a hot issue in congress and state legislatures right now as prices rise for the summer driving season. This isn’t some minor academic question as to the kamm effect, that’s the perfect being the enemy of the good.
As to legal length limits, that disappears in a flash, with the stroke of a pen, when a turbulence/suction reducing tail proves itself in boosting diesel powered truck’s mpg on freeways. Buckminster Fuller had it right in 1933 with his dymaxion car/fish design. Now 74 years later semitrucks are 1/2 way there, the tail is the other half still to be added; as it swims upstream to “spawn”.
You imply that fish actual understand and knew about turbulence and aerodynamics 2 million years ago and then call 2 people on this thread dummies because their understanding of fluid flow and drag doesn't equal yours. Did the fish design themselves this way? I hear they attend school, so who knows for sure.
The curved hoods atop most cabs these days don't do anything compared to what having a real fix to the back of the vehicle would do. Exactly as you suggested. Problem is, that the fin/tail needs to be much longer than is practable to drive around trailing behind you or an alternate design would wipe out over half your carrying capacity to maintain the same length. Either way, it's not going to work and that is why we don't see tail or wing shaped cars and trucks on the road everywhere.
Again, the PERFECT is the enemy of the GOOD. A short tail in the 10’ to 15’ range would eliminate MOST of the rear drag, even though a 30’ to 40’ long tail would be perfect as per this kamm effect. Truckers don’t care about PERFECT, improving their mpg is all important to them, even a 50% reduction is GOOD NEWS.
Like all the other critics here, you try to mask laziness with our know-it-all brickbats. The simple truth is that you and yours do NOTHING for the energy picture. I and others like me are trying to HELP truckers and our ecomony in general by improving the aerodynamics of inefficient semitruck boxes; the aeroshell is a GOOD start, now the bookend TAIL.
You people remind me of what Jesus said : Lawyers, liars, pharisees, hypocrites; you load burdens on other men’s backs but won’t lift a finger to help. And as it is said : no one ever built a monument to honor a critic. If YOU and yours are ever going to ever be WORTH anything, get off your dead ***** and DO something worthwhile.
I remember doing some of these calculations in college, but that was over 20 years ago.
Question, what do you mean by 50% reduction? I assume 50% less drag. How does that translate to fuel consumed?
Real world question: Which will get better gas mileage:
A) An open bed pickup truck with the tail left down,
B) or the same open bed pickup truck with the tail up in the closed position?
Final question: what chapter/verse is your Jesus quote from?
As a side note, it’s usually not wise to patronize anonymous posters over whether or not that person does anything to help our economy or truckers.
I flash truckers into my lane nearly every single trip to and from work. That should count for something.
I build products vital to our national defense and our allies national defense (devices that find enemy submarines). You likely do not. Certainly this doesn’t imply do NOTHING to support our nations defense. Nor would criticizing parts of our military imply that either.
Oceans ahead of you in the marine transport field : private post following. As to the biblcal verse, read your bible. As to the aerotail, SOMETHING would be better than nothing; even boxfish have tails. Damn kamm, these truckers are real world people not ivory tower academics. Even a 1 mpg improvement is JOY to their ears, and pocketbooks.
Again, the clam shell-tapered tail on the skytruck in the Flight of the Phoenix movie worked for a 300 mph aircraft, don’t try to tell me it won’t work for 70 mph semitrucks. I KNOW it will even if it results in only a partial rear drag reduction. It may not be PERFECT, but GOOD enough = energy saved to do the same transport job.
As to the up or down tailgate on a pickup, come on already...
OR you can buy a VW Jetta Diesel that gets 40 to 45mpg and has no batteries to pollute(mining) and replace every 7 to 10 years. And the diesel will get an easy 300,000 mile life on the engine. Plus it’s sporty and fast. I really think it’s a NO BRAINER choice. But the American consumer doesn’t think diesel, AND diesel is now cheaper than regular unleaded gas. Strange world!!
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.