Schultz Engineering Project: Building an Electric Streamliner
BugE Chapter 7 - Ultra-Light Land Vehicle Safety

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Ultra-Light Land Vehicle Safety: August 23, 2009

Land Vehicle Safety things to think about:
  • Physics of Moving Bodies
  • Crashworthiness of Human Body - What can the human body take?
  • Crash Avoidance
  • Crashworthiness of Vehicle
  • Things to include in building an ultra-light
  • Things to do when driving an ultra-light
Are you a Bug, or a Windshield? When a car hits a Bug, the resulting mess is unpleasant for the car driver, but catastophic for the insect. It's a little ironic that my test platform is a BugE.

I hope not to become a bug in the bug/windshield equation, but the physics are not in my favor.

PHYSICS OF MOVING BODIES

The physics behind the collosion are interesting. Let's start with the basics. Newton's laws of motion are three physical laws that form the basis for classical mechanics. They are:
  1. In the absence of net external force, a body either is at rest or moves in a straight line with constant velocity.
  2. Force is proportional to mass times acceleration (when proper units are chosen, F = ma). Alternatively, force is proportional to the time rate of change of momentum.
  3. Whenever a first body exerts a force F on a second body, the second body exerts a force -F on the first body. F and -F are equal in size and opposite in direction.
Therefore, when two identical cars (equal mass and equal velocity) run head on into each other, they come to a complete stop where they impact. This is a balanced equation. Both cars experience the same amount of acceleration. Let's say for the sake of argument that both cars were traveling at 35 miles per hour when the crash occured, each car weighed 3,500 lbs and each cars front end crushed in 1 foot during the crash. This means that both cars experienced enough acceleration to decrease their speed from 35mph to 0mph in 1 foot. From this example, and using Newtons laws of motion equations, we can calculate the force and acceleration involved.

With these things in mind, we can also play around with the scenario and exchange one of the vehicles with one that weighs exactly 1/2 of the other vehicle or 1/10th of the other vehicle (as is the case with my BugE and a typical Mini-Van). As it turns out, keeping all things equal except for the mass of the moving object, the acceleration experienced by the lighter vehicle is inversely related to the ratio of the vehicle masses. In lay terms, if your vehicle is 1/10th the weight of the other vehicle your vehicle will recieve 10 times the acceleration as the other vehicle.

CRASHWORTHINESS OF THE HUMAN BODY

There is a threshold for how much acceleration the Human body can recieve without dying (things like your neck breaking and/or your brain bouncing off the inside of your head). The threshold is...more to come...

But don't despair. Just because your vehicle recieves 10 times the acceleration doesn't mean the human inside needs to recieve 10 times the acceleration. Things like crumple zones, air bags, stretchy seat belts, etc. can increase the distance and time the acceleration takes place in, and reduce the acceleration...more to come...

COMMON SCENARIOS OF ACCIDENTS:
  • -----Caused by other drivers:-----
  • Being backed into in a parking lot
  • Being run off the road by an oblivious driver
  • Being T-boned by car that did not stop for a cross street
  • Not being seen
  • cars pulling out directly in front of you
  • cars rear ending you when you are stopped to make a left hand turn
  • cars clipping you when they are passing you
  • --
  • --
  • -----Caused by you:-----
  • Being t-boned because you pulled out in front of another car
  • Driving too fast for conditions
  • Loss of Control due to slippery roads
  • Loss of control due to mechanical failure
  • Loss of control due to poor steering and or braking systems - vehicle unstability
  • Unable to see due to fogging of windshield, fog or rain resulting in a forward collosion
  • Following too closely to car in front
  • Unable to stop for a street light
  • --
  • --
  • Types of impacts:
  • Ramming a stationary or moving object
  • Hitting a building or a tree
  • Hitting another car or truck (bumper height is a concern)
  • Being Rear ended
  • Being T-boned
  • Roll Over
more to come...in the mean time go to You Tube and type in Motorcycle Crash and/or type in crash testing for the make and model of the car you drive. Watching these videos is a sobering reminder of the power of inertia and how far we've come in improving vehicle safety.