Application of Thrust Vectoring to Reduce Vertical Tail Size

Abstract

The vertical tail size of a multi-engine aircraft is typically driven by the directional control requirement during one-engine-inoperative flight. This results in the vertical tail being over-sized for most regularly occurring flight conditions. By adding thrust vectoring technology to an aircraft, the vertical tail can be designed to cope with regularly occurring flight conditions rather than the one-engine-inoperative flight condition. A modern aircraft was redesigned such that it would have thrust vectoring capabilities and an unconventionally small vertical tail. The redesigned vertical tails had areas which were 85\%, 70\%, 60\%, and 50\% of the original vertical tail area, which corresponded to reductions in the vertical tail area of 15\%, 30\%, 40\%, and 50\%, respectively. By reducing the vertical tail area, an aircraft's parasite drag may be reduced, and a reduction in parasite drag would allow for a reduction in the aircraft's fuel consumption. Analyses showed that the redesigned vertical tail and change in aircraft inertia due to the addition of thrust vectoring technology had a negligible impact of the aircraft's roll mode dynamics. It was also shown that the reduction in vertical tail area resulted in a degradation of the aircraft's spiral mode flight qualities. With regards to the Dutch roll motion, a reduction in vertical tail area resulted in a reduction of Dutch roll damping coefficient and Dutch roll frequency. Based on the analysis of the Dutch roll mode, it has been recommended that a compromise between the 85\% and 70\% vertical tail area would likely produce an acceptable compromise between the reduced vertical tail area and Dutch roll flight characteristics; however, the aircraft design would required a yaw damper. It is predicted that trimmed flight with one-engine-inoperative can be achieved by simultaneously using thrust vectoring technology and an unconventionally small vertical tail. Through the use of directional thrust vectoring, an aircraft's rudder deflection angle, aileron deflection angle, and bank angle may reduced during the one-engine-inoperative flight condition. Analysis of the one-engine-inoperative and crosswind flight condition shows that using thrust vectoring for directional control may allow for a reduction in trim drag; however, additional analysis of this flight condition should be completed. A vertical tail mass estimation was completed, and it has been shown that the reduction in vertical tail mass resulting from a reduction in vertical tail area is of the same magnitude when compared to the engine mass increase due to the addition of thrust vectoring technologies. Lastly, it has been shown that an aircraft's mission fuel consumption can be reduced if the aircraft's vertical tail area is reduced and thrust vectoring flight control is implemented into the aircraft design. Reductions in mission fuel consumption greater than 1\% are unlikely; however, there are feasible reductions in mission fuel mass for the proposed thrust vectoring aircraft design.