UWE Bristol Engineering showcase 2015

Mathew Swinburne
Mechanical Engineering MEng – Part B
Project Supervisor
Neil Larsen
“When Competition Aerodynamics Fail” – Part B
Literature Survey
This paper’s empirical research consisted of two methods for measuring the pitch of the vehicle regardless of the gradient of a slope;
using an accelerometer with a mathematical model and using a laser displacement sensor to measure the displacement between the
front of the vehicle and the surface of the track. It found that both were viable options however concerns were raised over both
methods which could not be resolved without further investigation; the accelerometers mathematical model requires the change in
acceleration not to equal zero, the laser displacement sensor would require testing on a track surface to determine if the described
preventions such as polarised filter and focused beam would suppresses errors associated with measuring the displacement to a rough
surface.
Accelerometers are found all around the home, from inside your smart phone, to your Nintendo Wii’s remote, even
in the ignition device associated with airbags, but what are they? An accelerometer is a device, which can either be
mechanical or electromechanical used to measure acceleration or deceleration. A mechanical version of the device
uses a mass, spring and damper system. An electromechanical device can be either a slide wire, strain gauge,
variable inductance or a piezoelectric or similar device that can measure the effects of acceleration.
A mathematical model was derived that could calculated the pitch of the vehicle regardless of the gradient of the
hill from the z and x components of the accelerometer.
A laser displacement sensor (LDS) works by firing a laser beam at the object under study, the beam is fired at a slight angle,
this beam bounces off the target object, where it then strikes a charged couple device (CCD). Unlike traditional
displacement sensors, because there is no physical contact with the object, a LDS is not prone to wear and tear.
A change in the displacement of a target object is recorded as a change in position on the charged coupled device pixels.
the laser displacement sensor would require testing on a track surface to determine if the described preventions such as
polarised filter and focused beam would suppresses errors associated with measuring the displacement to a rough surface.
Proposed Concept
Finally a design was proposed that took into consideration all relevant design constraints. The design
consisted of two bars riveted to the flap with an arm on the bar at an angle of 20 ° to the horizontal
axis. When this arm was pulled by an actuator contracting, it forced the flap open to 20 °, the optimum
flap angle as discovered in the Part A paper. The design itself is simplistic and therefore has the least
potential for failure.
Project Abstract
Part A validated the concept of using roof
mounted flaps to prevent the phenomenon of
lift-off, as experienced by a number of world
endurance championship prototypes over the
years. Part B looks at potential methods for
measuring and calculating the pitch by using
an accelerometer or the innovative concept
of using a laser displacement sensor. This
paper briefly looks at a control system for the
deployment of the flap in the event of such
an incident and finally a design is proposed
that takes into account the stated design
considerations. It was concluded that
although either the accelerometer and laser
displacement sensor were viable options in
measuring or calculating the pitch further
investigation was required before either could
implemented with an acceptable level of
error. The control system was produced in
MATLAB using a simple ‘if’ function,
determining the critical pitch before lift-off at
a given velocity and comparing it to the pitch
obtained from one of the chosen sensors,
calculating whether the flap should be
deployed or not. Finally a potential concept
was designed in SolidWorks, composing of
two bars riveted to the flap, which was
opened by the contracting of two actuators.