SAWE Report - Cal Poly San Luis Obispo

The extra 10° cant resulted in a substantially larger pitch coupling term. In addition to the
complications of canting more, a 30° angle would mean that a more complex mixer and control
system would be required. This would add to the cost and is avoided.
It is important to note that the previous static methods do not take into account the dynamic
characteristics or modes of this aircraft. With such a large amount of the fuselage in front of the
center of pressure, the Vendetta may require a complex yaw damper or larger vertical to
compensate.
The size of the vertical could potentially be driven by the one engine inoperative (OEI) control
power requirements. Because the engine nozzle centerlines are mounted considerably offset from
the centerline at 3 feet (0.9144 m), a large yawing moment will be created if the Vendetta loses
an engine during takeoff. The engines produce roughly 45,000 pounds of thrust and would
generate a 135,000 foot-pound moment. Table 10.III shows the results of the rudder control
power analysis for this critical OEI condition.
Table 10.III - Rudder Control Power Results for OEI Condition
PARAMETER NOTATION VALUE
Side Force due to Rudder C yδr 0.0105
Rolling Moment due to Rudder C lδr 0.0072
Rudder Effectiveness C nδr -0.0070
OEI Critical Yawing Moment
135,000 ft-lbs
Rudder Deflection Required in OEI Condition at Takeoff 13.6°
With a rudder effectiveness of -0.0070 (1/deg), a 13.6° rudder deflection is required to keep the
aircraft flying straight in the OEI condition on takeoff. This is not too large, and would suffice by
allowing approximately another 10° of rudder deflection for the pilot to yaw the aircraft beyond
the straight condition for controllability. In this condition, the aircraft would be susceptible to
large amounts of sideslip, β.
This rudder deflection would be substantially higher if a higher cant angle were used. In these
critical situations where the aircraft is in danger, the added drag created by the mixing is desired
to be as little as possible.
A separate 4 surface empennage was now made necessary because going to a purely V-tail was
shown to be ill-advised at this stage because of the aforementioned studies. If a pure v-tail was
chosen, it would have to be full-flying due to the demand placed on the surface and hinge lines in
supersonic flight. This would require a large actuator and large structural members in the aft
portion of the aircraft. This would considerably drive the configuration away from initial RCSfriendly
layouts as well as increasing complexity and cost.
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