Feasibility of morphing aircraft propeller blades
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The aim of this study is to assess the feasibility of variable geometry aircraft propeller blades, the main focus being on the aerodynamic performance. A number of objectives are established to reach this goal, with the development of an aerodynamic model and a blade optimization scheme being among these. The choice of the blade element method coupled with vortex theory and the use of calculus of variations for optimization is the result of an extensive literature review. This review also covers smart materials and their capabilities, and presents a number of structural morphing concepts. The propeller aerodynamic model is presented in detail along with the developed airfoil model and compressibility corrections. Predicted propeller performance parameters are compared with experimental data to validate the model. Both unconstrained and constrained twist optimization are considered and the derivations of the Euler- Lagrange equations are given. Unconstrained twist optimization results show that, regardless of the operating condition (takeoff, climb, or cruise), maximum efficiency occurs at lower thrust and power coefficients than required for those conditions. Constrained optimization supports this observation by showing that a constraint lowers the propeller efficiency. Twist distributions obtained from constrained optimization for the three operating conditions differ significantly but the effect on performance is insignificant. This leads to the conclusion that variable twist is not viable for a typical aircraft mission. Further analysis, however, reveals the possibility of variable twist for a loiter-dash type mission. A study of such a mission profile shows that a morphing propeller would offer a significant performance boost and is indeed feasible. Estimates of actuation power requirements show the required power to be less than the performance gain from a morphing propeller. A structural analysis of a variable camber concept shows the viability of shape memory alloys as an actuator material.
Thesis (Ph.D.)-- Wichita State University, College of Engineering, Dept. of Aerospace Engineering