SAWE Report - Cal Poly San Luis Obispo

items varies throughout the mission. The fixed equipment aboard the Vendetta is considered in
this case to be everything other than the variable payload.
Vendetta was first balanced it with the fixed equipment and then with the additional variable
payload. This was done by first allowing the configurator to develop an inboard configuration.
The weights engineer then calculated the center of gravity location resulting from this inboard
arrangement. This process was iterative in that the weights engineer and configurator had to
continuously modify the inboard arrangement until the center of gravity location was at the
desired location.
In order to minimize the trim drag on the aircraft, it was opted that the aircraft’s center of gravity
location stay as close to the aerodynamic center as possible. This was a difficult task because of
the dramatic shift, 12% MAC, in the location of the aerodynamic center when transitioning from
subsonic to supersonic flight conditions. A trim tank was considered in order to allow the center
of gravity to follow the aerodynamic center during this dramatic shift in order to maintain a
neutrally stable condition at both subsonic and supersonic flight conditions; however, this idea
was discarded because the trim tank would only require additional fuel volume in an already
congested aircraft. Without a trim tank, in order to minimize drag by keeping the center of
gravity as close as possible to the aerodynamic center the aircraft would have to fly with an
unstable static margin, subsonically, and with a stable static margin, supersonically.
The current arrangement of the fixed payload is such that it provides for a 5% unstable static
margin at subsonic flight conditions. A center of gravity monitor makes use of fuel burn control
in order to keep the aircraft as close as possible to the neutrally stable flight condition.
Furthermore, with full fuel tanks, full weapons load, and subsonic flight conditions, i.e. takeoff,
the aircraft is balanced such that it provides for a 5% unstable static margin. With the empty
weight and takeoff gross weight balanced to provide a 5% unstable static margin, and with an
aerodynamic shift of 12%, the aircraft immediately goes to a 7% stable static margin upon
transitioning to supersonic flight. The center of gravity monitor then controls the fuel burn in
such a way that the center of gravity follows the aerodynamic center and the Vendetta maintains
neutral stability.
Because the fuel load is constantly changing throughout the mission, balancing the fuel load
throughout the mission can be a challenging task. Furthermore, the deployment of various
weapons at any point during the mission makes this balancing process even more difficult.
Because of the complexity involved in developing a center of gravity monitor, a computer code
was developed in order to simulate the center of gravity monitor. The first step in developing
this code was to obtain the best solution to balance the fuel payload throughout the mission. The
code required four inputs including; the weight and location of the fixed equipment, the location
and weight of the fuel at any given time, the amount of fuel burned at intervals throughout the
mission profile, and the desired center of gravity location at that interval. With these inputs, the
code can then determine which tank to burn fuel from in order to obtain the center of gravity
location closest to that corresponding to the desired static margin. The code then outputs the
center of gravity location and the remaining fuel payload. This is done at 10-second intervals
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