A methodology to implement agility as a tradeoff parameter into multi-disciplinary optimization of a helicopter rotor is proposed. Being a qualitative evaluation measure and having no clear definition, agility is tried to be quantified through utilization of "ease", "speed" and "precision" metrics. The developed methodology utilizes a non-linear model predictive control approach to generate trajectory and control input history specifically to track the agile maneuver of interest. Deviation from reference path, state and input history and quickness are managed to determine integrated agility score. Then effect of rotor primary design parameters on agility characteristics is studied. A sensitivity analysis is performed to identify driving parameters and agility simulations are performed for four different maneuvers that are commonly used in nap-of-earth flights/missions. Slalom course, acceleration & deceleration, hurdle-hop and teardrop turn maneuvers analogous with ADS 33 Mission Task Elements are selected as the agile maneuvers to be considered and response surface analyses are performed to study the tradeoff between primary design parameters.
Aerodynamic shape design of the helicopter tail boom is aimed for anti-torque power requirement alleviation at hover and improvements on sideward flight characteristics. Oval type basic tail boom cross section, whose camber can be modifiable with organic shaped strakes, is proposed to supersede conventional symmetrical tail boom profiles. Performance of several contour shapes is investigated with systematically varying the position and alignment of the strakes through the 2-D RANS simulations. Cross-section shapes that shows highest potential are utilized on tail boom design and to evaluate the resulting hover performance, 3-D CFD analyses are conducted with both of RANS simulations using the actuator disk approach and URANS solutions where blade motions are modeled with overset method. The assessment of the design concept outlined that, utilizing proper design decisions on position, size and alignment of the strake shapes on properly designed oval type cross section, it may be possible to reduce significant amount of power requirement on hover while enhancing the lateral controllability margins at sideward flight or hover at cross wind conditions.
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