Nature is perhaps the quintessential optimisation engineer, and birds in flight are an excellent example. From Daedalus and Icarus with their feathered wings to the morphing airplane wings patented and used by the Wright brothers for their Wright Flyer, humans have attempted to emulate the optimised wings of birds. While the Wright brothers had the right idea, over the years demands for increasing speed, payload, and distance resulted in more rigid aircraft structures that are unable to adapt to changing aerodynamic conditions. As the industry comes full circle, it is vested in the development of the next generation of morphing wings to enhance flight efficiency and reduce energy requirements and emissions. To do so, it requires better design tools. The EU-funded OPTIMOrph project has responded to industry demand.
Current optimisation methods are not optimal
Current design of conventional aircraft wings considers aerodynamic and structural factors separately, tweaking one and then the other. Iteration of the cycle continues until a design is converged upon that allows the plane to fly under a range of flight conditions with acceptable, although not optimal, performance. While the accuracy of the algorithms increases with inclusion of increasing degrees of freedom and complexity, so does the ‘weight’ of the software at the expense of speed. As project coordinator Rita Ponza explains, “The OPTIMOrph project developed an integrated aerodynamics and structural optimisation methodology that includes the constraints and capabilities of the selected concepts and materials in the aerodynamic optimisation from the outset. Thus, it delivers optimised target shapes that can be practically realised. The result will be significant savings of time and money associated with the design and development process.”
Efficient algorithms for efficient airplanes
OPTIMOrph targeted the optimisation of a high-lift and cruise condition. Aerodynamic objectives for the former were maximisation of the maximum lift coefficient (CL) and the simultaneous maximisation of aerodynamic efficiency (lift-to-drag ratio or L/D ratio) at 70 % of maximum CL. For the cruise condition, maximisation of aerodynamic efficiency at a fixed angle of attack was selected. The team investigated two different morphing strategies. In the first, the morphing region was set between 0 % and 15 % of the airfoil chord, an imaginary straight line joining the leading and trailing edge of an aerofoil. The second provided an additional level of deformability to the skin. In both morphing scenarios, for both high-lift and cruise conditions the morphing wing outperformed the reference airfoil. In addition, the morphing wing with greater complexity and deformability resulted in a substantial drag reduction at maximum CL, leading to an even greater aerodynamic efficiency enhancement. Ponza concludes, “We have provided a useful tool ready to be applied to morphing wings with tangible effects on the efficiency of the aircraft design process. The combination of bio-inspired wings with engineering tools can provide exciting new results for next generation aircraft.” Europe’s largest application-oriented research organisation, Fraunhofer, has received the OPTIMOrph software for optimisation and use in future projects, particularly with its partner Airbus. This winning combination could lift morphing wings from the lab bench to the friendly skies.
OPTIMOrph, morphing, wing, optimisation, aerodynamic, morphing wing, efficiency, lift, aircraft, cruise, algorithm, high-lift, maximum lift coefficient (CL)