80mpg SmartCar?

[ERD50]

Originally Posted by jambo101

For those who might think these arent tough little cars..Smart car crash test

Look at this video that samclem and chinaco posted. You might feel differently about that.

YouTube - Mercedes S-Class vs. Smart

look at about 0:55 to 1:10 for the best shot,

discussed at length in this thread - the 'brick wall' test is not the same as the 'hit another, larger vehicle' test.

-ERD50

[Texas Proud]

Originally Posted by ERD50

Look at this video that samclem and chinaco posted. You might feel differently about that.

look at about 0:55 to 1:10 for the best shot,

discussed at length in this thread - the 'brick wall' test is not the same as the 'hit another, larger vehicle' test.

-ERD50

and from what I have seen and heard on other videos... looks can be deceiving....

On a longer version of the first video... they said that more than likely nobody would have survived the 70 mph crash.... but they did reference the video you have and said that the smart punched a hole in the Mercedes before bouncing off.... the car going on its side would hinder rescue, but the passengers would more than likely have survived....

[jambo101]

I guess crash results arent that relevant because i'll never buy one of these little Mickey Mouse cars.

[ERD50]

Originally Posted by Texas Proud

and from what I have seen and heard on other videos... looks can be deceiving....

but they did reference the video you have and said that the smart punched a hole in the Mercedes before bouncing off.... the car going on its side would hinder rescue, but the passengers would more than likely have survived....

I don't know. As samclem was pointing out - the Smart Car had to come to an abrupt stop, and then got pushed backwards. I don't know how fast they were going in that video, I don't think they chopped any time between the :48 and :58 parts, so 10 seconds of acceleration? I'm assuming both cars were going the same speed, so maybe the Smart Car could get to 40mph in 10 seconds?

So the S-class slowed from X to 0 mph in Y feet, the SC went from X to 0 mph in negative Z feet. I don't think you can survive those forces. Anyone want to calculate the G-forces on a 150# occupant in the SC?

-ERD50

[Marquette]

Assuming both cars are parallel to each other and horizontal to the earth and I remember anything from college...

v^2 = u^2 + 2as


edit: I suck at math.

[samclem]

Originally Posted by ERD50

So the S-class slowed from X to 0 mph in Y feet, the SC went from X to 0 mph in negative Z feet. I don't think you can survive those forces. Anyone want to calculate the G-forces on a 150# occupant in the SC?

-ERD50

Back of the envelope computation of the collision:

Total time in contact = .08 seconds (assumes 6 feet of combined crumple space and an average velocity of 50 MPH. This is a wag, and likely conservative. If we assume both cars are going 60 MPH, then they have x number of seconds to cover the 6 feet of crumple space at a combined speed of 120 MPH. I assumed the average speed over this entire time time was just 50 MPH).

If, over that .08 seconds the Mercedes goes from 60 MPH to 0 MPH, then the deceleration forces in the Mercedes are 1100 fps^2, or 34 Gs

In the Smart car (60 MPH to -20 MPH) the deceleration forces are 1466 fps^2, or 46 Gs.

Again, just a wag. I'd love to see the instrumentation reading from the dummies in both cars.

The Smart Car benefits form the generous crumple zone provided by the Mercedes. In a Smart car, riding with your feet very close to the front bumper, hitting anything with less crumple space (truck bumper, another Smart Car, a wall) there's just no way to reduce the acceleration experienced by passengers as can be done in a larger vehicle. That intact body with the doors that open looks impressive on camera, but it's not much good if they find your head snapped off your neck and rolling on the floorboards.

[Later edit: Is see Marquette was crunching numbers, too. 6 G's sounds way too low for the occupants of either vehicle. Still, his approach assumes more distance for the Mercedes to "decellerate", which is probably Marquette's way of accounting for the rearward movement of the Smart car while the vehicle is still crunching. This is probably a more accurate model, and would significantly reduce the accleration in the Merc while also driving up the numbers in the Smart car. So, probably reduce my Gs for the Mercedes occupants by 50%, double the numbers for the Smart car.]

[Marquette]

Originally Posted by samclem

[Later edit: Is see Marquette was crunching numbers, too. 6 G's sounds way too low for the occupants of either vehicle. Still, his approach assumes more distance for the Mercedes to "decellerate", which is probably Marquette's way of accounting for the rearward movement of the Smart car while the vehicle is still crunching. This is probably a more accurate model, and would significantly reduce the accleration in the Merc while also driving up the numbers in the Smart car. So, probably reduce my Gs for the Mercedes occupants by 50%, double the numbers for the Smart car.]

I deleted my math because I think your approach is more sound.

However, I'm not sure I'm getting the same numbers.

edit: Here's my envelope... note, I wasn't adding the two speeds together as I wasn't sure if that was a correct assumption or if it was more correct to treat each car statically.

v^2 = u^2 + 2as
v=final velocity
u=initial velocity
a=acceleration
s=distance

v=0
u=26.82 m/s (60mph)
s=1.82 (6 ft)

Solve for a
a=-197 m/s2

g-force: a/9.80665 = -20 g