Because of the number
of options in the composites world, the field of options had to be narrowed
to bring this project into focus. After research and help from expert
advisors, decisions were made based on the feasibility of each portion of
the project. In this case, a design
matrix was not used because the nature of the project provided enough
constraints to vastly narrow the field. The areas of research were
materials, resin, molding, and curing.
Material
Because of weight
restrictions, the main fuselage shell will have to be constructed from
carbon fiber. Glass fiber and Kevlar
are very strong, but in order to keep the fuselage within 130% of the
weight of the current model, the shell must be made predominantly from
light carbon fiber.
Resin
The first structures
will be constructed with Epon epoxy because of
strength and availability. According
to resources, this is one of the main industry standards for use with
carbon fiber. If weight reduction is
required, less dense epoxy from Epon can be used.
Molding
To increase
aerodynamics and shell integrity, the group will explore the possibility of
creating a female mold. The current
fuselage is constructed from a male mold where the material is wrapped
around the mold. This makes the
inside of the shell very smooth and precise and leaves the outside very
susceptible to imperfections that can cause drag. A female mold would lay the carbon fiber
into a mold with the outside of the shell being formed by the mold. This
increases aerodynamics and efficiency.
Curing
The shell will be
cured at room temperature because of the availability of an autoclave. With proper catalysts, this process
creates a strong part that allows for mass production without the
requirement of a large autoclave.
Focus
The new, narrowed
focus will deal with the construction of more accurate and efficient female
molds. The team will examine the
feasibility of making a mold that can produce multiple shells at one
time. Along with molding, the team
will investigate the most efficient ways to reinforce the carbon fiber
shell with composite foam, Kevlar and other materials. This will increase the MAV’s ability to absorb energy on landing or impact
without structural failure. A new
area of focus is fastening the two molded halves of the fuselage
together. Currently, the fuselage is
assembled with polymer screws so that, on impact, the screws shear instead
of cracking the shell. The group
will investigate other methods of joining these halves to more efficiently
spread stress concentration and reduce weight.