Development of Methodologies for the Aerodynamic Design and Optimization of New Regional Turboprop Aircraft

Abstract

The Development of Methodologies for the Aerodynamic Design and Optimization of New Regional Turboprop Aircraft is presented proposing innovative procedures and tools to improve the aerodynamic of this aircraft category. Nowadays the increase in oil price, the huge growth of air transport traffic and the increasing attention to the aircraft environmental footprint led to considerable interest of specialists in new configurations of regional transport aircraft. Airlines and aircraft industries forecast in the next twenty years about 12000 turboprop aircraft will be delivered. Of these aircraft about 7000 will replace the older turboprop which reach their product life-cycle, while the remaining amount of about 6000 aircraft will be new turboprop aircrafts to satisfy market needs. The 61% of new turboprop delivered expected to be under 70 seats category (20% under 50 seats and 41% of 70 seats), while the new 90+ seat segment is a strong percentage of the total, i.e. the 39%. For these reasons this work aims to provide some guidelines in the aerodynamic design of future regional turboprop aircraft with about 90 or more passengers. Currently there are no configurations on the market of this type, so a typical 70 passengers turboprop aircraft is taken as reference starting point to put in evidence those aircraft components which particularly affects the aerodynamic, especially in terms of aerodynamic drag. Particular emphasis is posed on aircraft performance, to highlight how a more accurate aerodynamic design can improve aircraft performance and so give aerodynamic guidelines in the design of new turboprop aircraft configurations. Research work can be divided into three main topics:i) airfoil design and optimization, ii) aircraft components design and optimization and iii) vertical tail design. Airfoil design and optimization is a typical aeronautic topic, which involves several aspects such as parameterization techniques, optimization algorithms and aerodynamic solvers. These aspects have been analyzed and put together into a user friendly code which allows to design and optimize a generic airfoil geometry choosing i) the parameterization technique, ii) the optimization algorithm and iii) the aerodynamic solver. Constraints and multi-objective optimization have been performed, highlighting the crucial features in the design and optimization of a regional turboprop airfoil. The second topic aims to provide an optimization procedure for several aircraft components, fast to use also in a preliminary design phase. By coupling non uniform rational b-spline (NURBS) and a panel code aerodynamic solver, the geometry of a regional turboprop nose, wing-fuselage junction and undercarriage vane have been optimized to reduce aircraft aerodynamic drag. Particular emphasis has been also posed on the winglet design, highlighting how an accurate design can give an improvement in the whole regional aircraft flight envelope. The last topic involves the design of vertical tail plane for turboprop aircraft. This is a crucial topic for all twin-engine commuter aircraft because of all the ground performance are strictly related to the minimum control speed (VMC) which mainly depends from the engine failure speed (VEF), clearly related to vertical tail design. As a matter of fact both Part 23 and Part 25 of the aircraft regulations relates the certification speeds (especially for ground performance) to the VMC; the lower will be the last, the better will be the performance. Moreover a performance improvement also means the commercial success of an aircraft, given the capability to be more competitive in several scenarios respect to competitors. In this research work, using a Navier-Stokes aerodynamic solver, a new method named VeDSC (Vertical tail Design Stability and Control) to design a vertical tail and a rudder has been carried out. More than 300 Navier-Stokes runs have been performed to accomplish with the objective. Particular care has been posed to the software set-up and several test-cases have been performed to validate the methodology. Finally the new method has been applied to several turboprop and twin-engine commuter aircraft and compared to typical semi-empirical methodologies to highlight the capabilities and reliability.