Effects of Wing Elasticity and Basic Load Alleviation on Conceptual Aircraft Designs

Abstract

Conceptual aircraft design uses in most cases either semi-empirical methods or simplified structural models with a rigid airframe structure and static load cases for wing design. However, only by taking coupled physics effects of the disciplines aerodynamics, structures and flight dynamics into account already at the early design stage, technologies like gust and maneuver load alleviation can be evaluated and their effect on the global aircraft shape can be assessed. By using such an improved model, possible benefits in overall aircraft efficiency can be identified. This paper presents a process for the integration of flight control and aero-elasticity into conceptual aircraft design, using the software ASWING for performing an unsteady lifting-line calculation combined with non-linear Euler beam theory. Results are shown for a long-range transport aircraft design. Maneuver load cases are evaluated. A simplified 2.5D- method sizes the wing box based on a carbon-fiber-reinforced polymer topology and a set of load cases. A five-dimensional planform geometry design space, containing up to 756 aircraft designs is considered. For the design space three studies are evaluated without any load alleviation, with maneuver load alleviation and with an academic approach of a global load reduction factor. The presented process enables the assessment of how load reduction and layouts affect the aircraft design. In the design process loop the wing parameters are fed into an overall aircraft design process. This resulting global aircraft design is, in contrast to the more detailed wing sizing, based on handbook methods. The block fuel for the design mission is the main parameter for evaluating the expected benefits. Certain geometrical constraints for the tank volume, the installation space and the span limit are discussed. The findings reflect a combined maximum load alleviation and shape optimization potential in block fuel of approximately 20 % without further constraints. For the geometrically constrained design space the maximum block fuel benefit is 13.3 % compared to the reference aircraft. The main effect of the load alleviation technology in conceptual aircraft design is to enable more efficient configurations within the constrained design space.