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Airborne
Vehicle Dynamics
A study into the background, viability and accuracy
of airborne speed estimating
By
Weston Brown
Abstract:
 The
evidence at a traffic homicide is rarely ever spelled out in black
and white. As a reconstructionist we are often looking for new
and innovative ways to determine the speed of a vehicle involved
in a collision. It is known that a reliable speed estimate may
be made from a vehicle which becomes airborne during the collision
sequence. Many schools teach airborne speed estimating but the
occasions to use it are few and far between. The dynamics of a
vehicle which becomes airborne are complex and multifarious.
The first
concepts of the effect gravity has on the motion of an object
were developed by Galileo and were later further researched by
Sir Isaac Newton. Galileo determined that objects experience constant
acceleration while under the effect of gravity. This he proved
with experiments at the Leaning Tower of Pisa. It is said that
Newton first began to ponder the effect of gravity on objects
in motion while, "he sat in a contemplative mood," against
a tree and observed an apple fall to the ground. Newton not only
made amazing leaps in physics but also in mathematics by developing
what has commonly become known as calculus. Incredibly most of
what a reconstructionist uses to reconstruct a collision are based
on the principles Newton developed in the 17th and 18th century
both during and after his studies at Cambride University.
This paper's
content is designed to review the concepts of uniform projectile
motion then apply those concepts to a vehicle which becomes airborne.
The paper offers examples of what to look for at the scene of
a collision where a vehicle has become airborne as well as a basic
algorithm for collecting evidence at an airborne scene and processing
that data to determine the speed of a vehicle. As well the paper
will demonstrate through repeated testing that concepts 300 years
old apply to the vehicles we drive today.
Introduction:
The concepts
that we use today are based on the principles that Galileo, and
Newton developed. Although we have developed many new technologies
since the days of Newton and Galileo, gravity has remained constant
as has the effects of gravity on objects in motion. When dealing
with a vehicle in freefall, it is crucial to understand the compound
dynamics involved.
This form
of speed estimation is often left in the classroom and rarely
used to estimate the speeds of vehicles. The reason for this is
multilateral. First, this genus of speed estimation is left as
a side note to many reconstruction courses, leaving the students
understanding vague and uncertain. Second, the basic physics principles
can be difficult to understand and conceive. Many reconstructionist
just want to be able to "plug and chug" and this is
not always the case when dealing with airborne vehicle dynamics.
Third has to do with the complexity of doing practical examples.
Skid tests are easy to set up and administer, jumping cars presents
liabilities and expense. It is important to not only understand
the physics principles but to also explain them in layman's terms
to a jury.
Download
the entire study
pdf document
(647k)
Contact
Information
West Brown
Accident Investigation Unit
Traffic Enforcement Section
Phone: (480)-312-2666
E-Mail: wbrown@ci.scottsdale.az.us
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