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Old 01-05-2009, 04:45 PM   #6 (permalink)
Master EcoModder
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WonderWagon - '94 Ford Escort LX
Last 3: 51.52 mpg (US)

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Said I'd get back to you about the deer impact in your build thread, but decided that might lean to much toward thread jacking and let it slide. You're analysis is basically correct, but here's how I see it ...
Originally Posted by basjoos View Post
The traditional flat bumper is designed to absorb and transmit the energies of collision when you run into something. It mostly absorbs it when impacting a immovable object or when running into an object heavier than your vehicle and mostly transmits it when you run into an object lighter than your vehicle.

So if you are traveling in your car at 60mph when you run into lightweight object such as a pedestrian, the bumper first impacts their legs, shattering them as they are instantly accelerated from 0 to 60mph. Next the torso is rotated and accelerated from 0 to 60 in a leisurely fraction of a second as it is thrown onto the hood, which may hold them in place until the car brakes or corners. Its even worse with a truck or SUV where the flat bumper and flat grill combine to make a chest high battering ram that instantly accelerates their legs and torso to 60mph, shattering legs and crushing the chest in the process. Then, once up to vehicle speed, they drop off the front and go under the vehicle where more damage can occur; ba-bump ba-bump.
The bumper first impacts one or more of their legs (closer to the knees, than to the ankles) most likely breaking/shattering one or more leg bones near the 6" to 8" tall zone of initial impact. Various sorts of damage may be inflicted on the knee(s) depending on various factors such as weight supported and the angle of impact. As the legs are accelerated to 60 mph (88 ft/sec), the torso begins falling (32 ft/sec *sec) and rotational energy is imparted to the center of gravity (torso) via the legs which act as a lever. The induced rotation of the torso means the upper portions of the torso will be accelerated towards the vehicle and the lower portions of the torso will be accelerated in the direction of the vehicles travel. The lower the hood, the more closely the rotational speed of the lower edge of the torso will match the forward speed of the vehicle. The lower the hood, the greater the downward force induced by the falling torso, but since the impact of the torso on the hood occurs about .02 - .07 seconds after initial impact this may not be all that much. The slope of the hood (and possibly the windshield) will impart upward momentum in addition to any effects induced by air flow over the vehicle.

With my ecomodded vehicle it is different. With its sloped nose and a stagnation point one foot above the ground, when hitting lightweight objects the transmitted collision energies are redirected upward rather than straight forward as with a traditional bumper. So when hitting that pedestrian, their legs would be knocked out from under them and they would be scooped upwards, passing over and landing on the ground behind my vehicle while traveling at a maximum speed (mostly vertical) of around 25mph rather being accelerated to 60mph as with a traditional bumper. Needless to say, much less damage would occur as they were accelerated more gradually to a much lower speed.
Since the nose of your vehicle (zone of initial impact) is smaller than the stock bumper, bones are more likely to break, but less likely to shatter. Since the point of impact is lower, less trauma is induced on the knee(s) and more trauma is induced on the ankle(s). Because the point of impact is lower, you have a longer lever acting on the center of gravity (torso) which means rotational speed of the torso when it contacts the hood will be closer to the car's forward speed.

But my bumper is two mode. When colliding with an object heavier then about 500 lbs, the rounded nose would absorb energy while crushing down to the car's stock flat bumper still in place under the aerodynamic nose, which would then function as a traditional bumper.
Think you may be assuming that the impact against the 500 lbs object is at the height of the 500 lbs object's center of gravity. For 500 lbs think calf. For 1500 - xxxx lbs think full grown cow or horse. Don't think your nose piece will absorb all that much of the impact. The main force of impact will occur on your hood and/or windshield. You're nose piece makes the point of initial impact: smaller, lower, further forward.

The gist of it? The nose piece means you're less likely to suffer serious damage to the vehicle when hitting a deer, sheep, dog ... . The nose piece probably won't help all that much when hitting a cow, horse, moose ... and may even adversely affect operator safety??? (Haven't decided if those sorts of animals are more or less likely to come through your windshield. Probably far too many factors to make it predictable)
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