MythBusters: Does Drafting Semis Improve Fuel Economy?

[Hockey4mnhs]

damn sounds good to me

[TheSSG]

Originally Posted by Snax

There seems to be a misconception, perhaps from NASCAR announcers, that an effective draft needs to be done at arms length from the next vehicle. Considering they are referring to cars that are supposed to be slippery, that would make sense. Conversely, a big box trailer aint slippery, and multiple trailers actually accelerate the air the direction of travel, creating a current.

You can generalize drafting as dangerous if you want to, but consider that the benefits of it can be exploited as far back as 200 feet from a triple trailer doing 60mph. Even cutting that distance in half is hardly walking the tightrope of safety.

This is a good point.

People Imagine that Drafting works because you slip in "below the radar" of the current of air; that you sneak in to just under the current of air as it descends off the back of the trailer.

This is not necessarily WHY drafting works.

Air Resistance creates Drag. When Air is undisturbed, you car has to "slice" through a "solid block" of air Molecules. This can take a decent amount of energy.

Now, when a truck barrels down the highway, it is actively "cutting" this block of air. Behind it, the air is not swooping down quickly, and returning to a blissful, calm state. The air is violently and almost randomly whipping about.
What the truck has done is it has disturbed the air.

Now, we can make use of this. It is easier for us to "slice" through moving, disturbed air; air that is not in a dense, "solid" formation. Since the air behind the truck is already swirling and ebbing, it is much easier for us to go through; the initial change of the air from a "solid" "at rest" state to the aggitated state is already done.

Drafting is not about slipping UNDER a slipstream. That's NASCAR. When you and I are drafting a Semi, we are saving energy. The energy we are saving is the energy it takes to INITIALLY agitate the air as we move through it.

All we have to do is be within the space limit that this air is agitated to gain SOME benefit.

I'm sure slipping UNDER the slipstream would be best, but this is unsafe. I just want to point out that we can BOTH reduce wind drag AND be safe.

Though, there DOES tend to be a "sweet spot" where the slipstream violently cascades down, HARD. This "sweet spot" tend to not be a good place to be It'd say, try to stay just ahead or just back of this area.

[Dynamically Aero]

Just a reminder for those who are interested; the show is on tonight.

[Dynamically Aero]

Twenty minutes...at least in some time zones.

[Bubba Bob]

Originally Posted by Dynamically Aero

Twenty minutes...at least in some time zones.

LoL. Excited?


BTW, yall should click here for what truckers think about drafting. They don't seem to be too fond of it...

[DrivenByNothing]

I've always wanted to attach a remotely control arm to the front of my vehicle that can attach to big rigs so I can put the car in neutral and shut it off. They've got the torque even at cruising speeds, so it won't make a noticeable difference to them and a rigid arm would prevent collision.

Lol. They just said 'improve fuel efficiency' with drafting. That I'd like to see.

[Snax]

Ok, so far:

100' behind = 11% improvement
50' = 20%
20' = 27%

[Hockey4mnhs]

watching it now!!

[DracoFelis]

Originally Posted by OdieTurbo

Yay! I love that show! Though I sometimes doubt their methods

Sometimes?

Seriously, I really really think their "scientific tests" leave a lot to be desired! They seem to not care one little bit as to how accurate their "tests" reflect reality.

This was (most forcefully) driven home to me, when "Myth Busters" did their (so-called) tests about "zombies". Now, anyone who has actually studied what happens with this grizzly process (and out of morbid curiosity, I have followed some of the reports done by respected researchers that have looked into this), knows what is really going on is this:

1) Someone pisses off a local (Haitian?) "Witch Doctor" (who is really the local poisoner).

2) The "Witch Doctor" poisons the victim with a powerful nerve toxin. Now the exact formula of this "zombie powder" is still a well kept secret. However, it has been discovered that the main "active ingredient" in this "powder" is the venom of the puffer fish (which is known to be an EXTREMELY POWERFUL nerve toxin). In fact, the puffer fish venom (which has been studied a lot under controlled scientific conditions), is so powerful of a paralyzing agent, that it can easily kill. Furthermore, it's known that in controlled quantities, the puffer fish venom can induce a powerful coma that slows the body's vitals down so much, that it does a close simulation of death (to all but very careful tests for "death"). So all the "witch doctors" have figured out, is a controlled way to use the puffer fish venom to simulate death (with their "zombie powder").

3) The now (supposedly) "dead" victim is buried alive (because everyone thinks they really died).

4) Due to the nerve toxin, the victim needs much less air than a normal awake (or even a normal sleeping person) would. This allows them to live many times longer (on the air supply in the coffin) than an awake (or even a normally sleeping) person would.

5) Some hours (or in some cases days) later, the witch doctor digs up the "body", and now has a nice slave who everyone thought was dead (so nobody is looking for the "missing person"). Naturally, the "witch doctor" can continue to drug the victim, to keep them nice and helpless (and agreeable to any slave labor that is desired). Also, sometimes (even with the nerve toxin slowing their need for air), the victim still suffers some brain damage (while they are in the coffin) due to loss of air to the brain. This also often works for the "witch doctor", as the "zombie" is now more stupid (due to brain damage), and therefore even easier to control.

OK, that's what the scientific research on "zombies" actually says is going on.

So what did "Myth Busters" do? They put one of their crew AWAKE (with no drugs in their system) into a "coffin" (made out of clear plastic), and then watched how quickly they were using up air, and dug him out when the air got to a "dangerous" level (where brain damage could occur). They then concluded in a very loud voice, that they had "Busted" the "Myth" of "zombies" (because their reasoning said that someone would suffer brain damage (or be dead) long before the "witch doctor" would be able to return).

Never mind that honest research on this subject knows about the nerve toxins (and the coma they induce), that can greatly lower the body's need for air (to a small fraction of the air needed for the "normal respiration" that "Myth Busters" was testing). And also never mind that "zombies" don't necessarily make it out of the process without brain damage. So "Myth Busters" totally ignored 2 different key factors, that made their test pointless, as a test for the validity of this "Myth". And yet, they still happily proclaimed "Myth Busted"...

Personally, I find "Myth Busters" to be more show, than science. Yes, they may sometimes "luck out" and actually do a little real science. But in general, their "methods" are so suspect, that I take anything they say with a huge salt mine...

[Snax]

Yeah, the tire tread launcher is along the same vein. Sending an 'alligator' at a fixed car side window at 40mph does not mimick reality very well. In order to replicate that experiment in real life, the tread would have to be thrown forward through the rear window of a car on end or be relatively stationary relative to the roadway as a following vehicle runs into - again, on end.

Anyway, I already forgot the final numbers for following at 10' and 2', but it was in the mid-40% range at 10' and dropped to the low 40% range at 2' - supposedly because Harry was ineffective at modulating his speed. Still, they prove what any nitwit with a sense of observation has been able to figure out: Drafting works. Duh . . .

They do however confirm what has already been said here, that being as far back as 100' generates a measureable improvement.