PFR - Aerospace Engineering Sciences Senior Design Projects ...

Project Final Report – CUDBF April 30 th , 2009
ASEN 4028: Aerospace Senior Projects
To determine the moment of inertia for the airfoil cross-section, a few assumptions were
made. To simplify the cross-sectional shape, the foam was neglected and a thin-walled ellipse of
balsa was selected as seen in Figure 55.
Figure 55: Thin-Walled Ellipse
Since the taper and sweep are not considered, the mean aerodynamic chord of 16.6 inches was
selected as the semi-major axis. The semi-minor axis was defined as the airfoil thickness at the
mean aerodynamic chord. The average thickness-to-chord ratio of 0.9 was used to give the semiminor
axis a value of 0.375 inches (0.75 for the entire thickness). Using the balsa thickness of
1/32 inch, Equation 26 produces the moment of inertia [23] of approximately 0.7 in 4 .
= 4 1 + 3
Equation 26: Moment of Inertial for Thin Walled Ellipse
8.4.2 Wing Material Selection
The wing design materials were selected to minimize overall weight while still meeting the
minimum wing design-to-specifications. A foam-core made of EPS foam (Expanded
Polystyrene Foam) was selected after the foam-core and skin composite construction technique
was selected over the traditional rib and spar construction. Additional analysis was done in order
to select an optimum skin material from balsa, fiber-glass, or carbon fiber. The most significant
resource employed in the skin material selection process was a Young’s modulus vs. Density
Ashby plot [24] .The two significant Ashby charts are displayed within Figure 56 and Figure 57,
the balsa and composites Ashby charts respectively.
84