Oh Look! More anecdotal evidence. Another fuel saving device...

[Skimask]

Looks like this guy threw a whole WEEK of testing into this device.
A whole WEEK!  Talk about heaps of statistical analysis...

https://www.kickstarter.com/projects/910776023/the-first-100-gasblades-ever?ref=discovery

[EEVblog]

And the device covering the number plate can't be legal, surely?

[Dave]

Car manufacturers are designing bonnet mounted airbags to protect pedestrians. This guy put a sharp metal blade on the front bumper.

[deth502]

And the device covering the number plate can't be legal, surely?

not all states require a front plate, but if they do, then im sure that would be a problem. not only that, but there are safety and crash impact regulations that im sure werent considered.

[Skimask]

And the device covering the number plate can't be legal, surely?

Probably not.  But along those same lines, I've got a grille guard covering my front plate on my truck, and I've got a front plate in my state, but not sure if my state requires front plates in the first place.
The guy has a fair idea.  A few car manufacturers are putting open/close air vents on the radiator opening/grille these days.  I assume to assist with engine temps and air flow under the vehicle.
All to squeeze out that last .01MPG...and all they really gotta do is slap everybody with a heavy right foot upside the head a dozen times.
One of the early tricks my Grandpa (worked at Chevy for awhile in the mid 70's) told me about was using stronger throttle return springs.  Whether that's true or not...meh...

[Rerouter]

Bet none of these guys have ever looked into getting new tires, while the difference is small it does slowly add up (only about 1.5 times the cost of the tires over the tires lifetime so not really worth your time in the long run)

still beats spending $100 on a pedestrian blender,

[Wytnucls]

Whether it works or not, it would not be allowed here. SUV owners had to remove all bull bars from their vehicle recently, in the interest of pedestrian safety.

[nihilism]

That would never be legal here. too much of an increased injury risk to pedestrians, as others have mentioned.

i'd also bet you would save more fuel just by going 10km/h slower.

[Wytnucls]

I'd be surprised if that works anyway. All it seems to do is mess up the airflow in front of the car. Any drag coefficient (Cd) improvement would be minimal and would need to be validated by professional testing in a wind tunnel.

[chickenHeadKnob]

Most people don't seem to understand that at the reynolds numbers and speeds of passenger vehicles and their generally unoptimiszed profile that more drag reduction is to be had by "teardropping" the aft end, that is filling in the area in the back that is generating a rotor. I look at many sports cars, particularly the expensive wedge shaped ones with squared off backs and told the young engineer collegues that bought them that they would go better in reverse. It is news that is generally met with disbelief. Minimum drag enclosed area at these reynold numbers is a teardrop shape with a fine-ness (axis) ratio of 3 to 1, bluff end into the airstream.

 Sailplane pilots are kind of the volt-nuts of the skies, looking for any optimization that will get them an improved lift-to-drag. It is a curse, because you see how everyone else is doing it wrong. That goes as far as reprofiling the wings of their gliders, and using inflight leading edge bug scrapers that are deployed whenever they feel they picked up a heavy load. (the bugs trip the laminar flow into turbulent flow and you endeavour to delay that to as far back on the airfoil as you can)

[Wytnucls]

In theory perhaps, in practice, not really.
Kamm effect:

http://en.wikipedia.org/wiki/Kammback

[chickenHeadKnob]

In theory perhaps, in practice, not really.
Kamm effect:

http://en.wikipedia.org/wiki/Kammback

That wiki article says MOST of the benefit of a teardrop so it is a compromise. Paul Macready or any of the knowledgable aerodynamicists working in field of human powered aircraft or land speed record holding bicycles never put a Kamm back on anything I can recall. One of the side effects of winter driving in the cold prairies of Canada is that you can see the airflow around the back of vehicles on the home commute, made visible by exhaust vapour and other ice fog. Most of what is on the road is extrordinarly poor design. I include  the typical squared off trunks on small cars as I have actualy witnessed the rotor on those.

[Wytnucls]

Of course it is a compromise. Manufacturers, like Alfa Romeo, have tried teardrop bodywork in the past, but it was found to be impractical, due to extra weight and prohibitive vehicle lengths. Those cars were produced in very small numbers.



This is the racing TZ with the Kamm back:


http://en.wikipedia.org/wiki/Alfa_Romeo_Giulia_TZ

[deth502]

streamlining the ass end of a vehicle only works well IF it is a "sleek" desin like a sports car that will have attached air flow all the way to the back. most cars are not smooth enough to keep the flow attached to the back, and once the flow has detached, there is no appreciable benefit to anything other than a blunt cutoff.

another thing to consider. how many people will start to have overheating issues once they install this because they are diverting the airflow from the radiator??

[EEVblog]

I can remember an interesting test Mythbusters did with a ute. IIRC it got better mileage with the tailgate UP. Aerodynamics can work in mysterious ways.

[deth502]

I can remember an interesting test Mythbusters did with a ute. IIRC it got better mileage with the tailgate UP. Aerodynamics can work in mysterious ways.

At the risk of appearing pedantic (which I am )perhaps counter-intuitive is more accurate than mysterious. Aerodynamics I hope rigidly follows the laws of Physics.

I had the same reaction when I found out that dimples on a golf ball improve its aerodynamics  (travel further and better control). Same with the spoilers on a boot at the rear of cars. All involve a trapped layer or pocket of air that alters and improves the streamlining contours of the vehicle (or ball).

In a very childlike reasoning I wondered if putting dimples on racecars would make them faster.

iirc, mythbusters did that as well, and iirc, the "dimpled" car, actually did preform better.

[IanB]

Car designers and manufacturers test car body shapes in a wind tunnel and work out the drag coefficient (c_d). Clearly the drag coefficient has to be traded against many other practical factors, but they certainly don't mindlessly increase the drag when they are trying to optimize the fuel efficiency or performance.

[scientist]

If this guy was driving his ugly Ford at supersonic speeds it might make a difference in the volume of his sonic booms. But his little piece of garbage is plastic, of course, so it would melt.

[scientist]

Not very long after a couple of trips and repositioning the angle, the "aircutter" as I called it at that time proved its value by increasing my performance from 38 to 44 mpg!

 

Off the charts!

[matkar]

Another fuel saving device is a lit candle under the gas pedal and a barefoot driver. Works like a charm. Patent pending of course.

Seriously, This device has no effect and makes the car ugly. If anything it disrupts laminar air flow and increases drag. To reduce drag you have to keep the laminar layer as long as possible over car surface.
Here are a few free (and already well documented) solutions that would actually work but I guess they are not worth the trouble.
By covering the bottom with a smooth surface aerodynamics will improve. This is the area most car producers neglect in terms of making it more aerodynamically efficient.
Another idea is to blow (or suck) air through the surface in the region where turbulent layer starts to form. This is a method gliders use to minimize wing drag.

[Legit-Design]

I think someone should make kickstarter with MAGNETS



http://knowyourmeme.com/memes/troll-science-troll-physics


Video where they test it Mythbusters style, looks like it's working!

[Skimask]

iirc, mythbusters did that as well, and iirc, the "dimpled" car, actually did preform better.

My truck ('01 Dodge 1/2 ton) got drilled back in '05 with hail.  All panels, except for right side doors, got replaced.
Maybe I should've left the truck as it was after the hail storm.  Might have brought my average MPG from 8 to 8.01 !

[keethrax]

I can remember an interesting test Mythbusters did with a ute. IIRC it got better mileage with the tailgate UP. Aerodynamics can work in mysterious ways.

At the risk of appearing pedantic (which I am )perhaps counter-intuitive is more accurate than mysterious. Aerodynamics I hope rigidly follows the laws of Physics.

I don't follow you. By your logic absolutely nothing is mysterious, since everything follows the laws of physics.  Mysterious was a perfectly cromulent word. So was counter-intuitive, but that doesn't make mysterious wrong.

OED has definition #1 difficult or impossible to understand, explain, or identify. Note that impossible is not a requirement.

As far as tailgates go, there was a test similar to the mythbusters one ~10 years ago using  the big 3 american truck manufacturers. Tailgate  up or down being more efficient depended on model and manufacturer. 

Sidetrack to a sidetrack: I'm somewhat disappointed by cromulent not making it through spell checking. That would have made me happy.

[Noise Floor]

I wonder if the aerodynamic engineers at vehicle and airplane manufacturers find this stuff funny or insulting.

[deth502]

well, hes got 10 ppl interested.....