Aerodynamic blade design with multi-objective optimization for a tiltrotor aircraft

Abstract

Purpose -The purpose of this paper is to present the aerodynamic blade design of a tiltwing aircraft with a multi-objective optimization procedure. The aerodynamic design of tiltrotor blades is a very challenging task in the project of this type of aircraft. Design/methodology/approach -Tiltrotor blades have to give good performance both in helicopter and aeroplane modes. According to the design parameters (the chords, the twists and the airfoils along the blade), as the optimization objectives are different from one operating condition to another, the blade is the result of a multi-objective constrained optimization based on a controlled elitist genetic algorithm founded on the NSGA-II algorithm. The optimization process uses a BEMT solver to compute rotor performance. To avoid negative effects due to compressibility losses in aeroplane mode, the blade shape has been refined following the normal Mach number criterion. Findings -It has been found that the optimized rotor blade gives good performance both in terms of figure of merit and propulsive efficiency if compared with experimental data of existing rotor (ERICA tiltrotor) and propeller (NACA high-speed propeller). Practical implications -The optimization procedure described in this paper for the design of tiltrotor blades can be efficiently used for the aerodynamic design of helicopter rotors and aircraft propellers of all typology. Originality/value -In this work, advanced methodologies have been used for the aerodynamics design of a proprotor optimized for an aircraft which belongs to the innovative typology of high-performance tiltwing tiltrotor aircraft.

Aerodynamic Interaction between Rotor and Tilting Wing in Hovering Flight Condition

“…This value is slightly lower than the thrust coefficient C T = 0.0215 considered for the hovering condition in the design of the blade shape (Ref. 39).…”

“…The tip Mach number was M tip = 0.32, which corresponds to half the tip Mach number of the full-scale aircraft at design point in hover (Ref. 39). The range of C T /σ values during the tests varied from 0.001 to 0.093 and was achieved by controlling the collective pitch of the rotor head.…”

Experimental investigation of the rotor-wing aerodynamic interaction in a tiltwing aircraft in hover

“…However, the maximum value of C T achieved during the experiments was 0•0180 because a further increase of collective pitch angle leaded to a power requirement over the motor capability. This value is lower than the thrust coefficient C T = 0•0215 considered for the hovering condition in the design of the blade shape (21) .…”

“…The design of the aerodynamic blade shape was carried out making use of a multi-objective optimisation procedure adopted in the frame of genetic optimisation techniques. A detailed description of the shape optimisation procedure is given in Droandi and Gibertini (21) . The main geometrical parameters of the rotor blade are summarised in Table 1.…”

Aerodynamic shape optimisation of a proprotor and its validation by means of CFD and experiments

“…To avoid premature algorithm convergence and lack of genetic information, a well-distributed initial population was created by selecting the best individuals included in the final population given by single-objective genetic optimisations carried out previously on each objective. Further details on the implementation of the multi-objective optimiser can be found in the paper by Droandi and Gibertini (32) and in Droandi's doctoral dissertation (33) .…”