Abstract

Pipistrel, an aviation & aerospace company based in Slovenia, has its DNA in designing the next generation aircraft meant to be highly efficient and hybrid-electric. The work was part of the EU funded project MAHEPA (Modular Approach to Hybrid Electric Propulsion Architecture), that had the aim of advancing two variants of a low emission, serial hybrid-electric propulsion architecture to TRL (Technology Readiness Level) 6. The challenge resides in designing a propeller, driven by hybrid-electric propulsion system taking into account the different conditions the aircraft meets during the four flight phases: takeoff, climb, cruise and descent. Considering speed, power and thrust requirements changing during the flight, the objective is to maximize takeoff thrust and recuperation power during descent and minimize power during climb and cruise phase. The propeller design exercise involves three stages: the preliminary propeller optimization, the irfoil optimization, and the final propeller optimization. Within this multi-phase optimization project, modeFRONTIER coupled with CHARM (Comprehensive Hierarchical Aeromechanics Rotorcraft Model) and XFOIL were used. With the first propeller optimization, Pipistrel optimized the chord and twist distribution to get the maximum thrust and minimum power for a given set of airfoils. The results were then used as requirements for the airfoil optimization considering a number of specific geometry constraints (thickness, curvature or leading-edge radius), while increasing the lift and reducing the drag. At last, Pipistrel used the optimum airfoil for the final propeller optimization. Within this process thousands of designs were evaluated within a very limited time frame and the overall propeller performance has been increase over 30% with respect to its initial design. The presentation will describe how at Pipistrel the development process of the propeller could be automated reducing significantly the development time while maximizing the thrust during takeoff and not requiring prototypes to confirm the propeller performance.