Preliminary sizing of a hybrid-electric aircraft with structural batteries

Electric and hybrid propulsion systems have received a great deal of attention in recent years in various branches of transportation including aviation. The unpredictability of oil price in this era, makes a less-oil dependent source of power more attractive for owners and operators in terms of operating costs. However, the oil price is not only the key driver towards a less-oil dependent solutions. Europe is committed to the ambitious goals of reducing CO2 emissions by 75%, NOx emissions by 90%, and perceived noise by two-thirds by the year 2050 compared to the average new aircraft of the year 2000. This environmental challenge is accompanied by an economic one too: the reduction of carbon emissions will call for radical innovation for all systems and subsystems of the aircraft, offering significant opportunities to reduce aircraft fuel consumption and operating costs. Nowadays, electric motors are generally more reliable than internal combustion engines, and their efficiency in converting stored energy is much higher by the constitution. The main barrier of the electric propulsion is bound to the battery limits in terms of energy and power densities, thus determining a relevant negative impact on payload or aircraft size. It is possible to design and fly an electrically propelled aircraft, as testified by some existing examples, both prototypical and production models, in the categories of ultra-light and general aviation aircraft. A novel technology, which allows the electrification process towards heavier categories of aircraft, is constituted by structural batteries. These are similar in structure to carbon fiber composites, where the matrix features dielectric characteristics, making the structure capable of storing electric energy while retaining the capability to withstand mechanical loads. Despite that, it raises relevant issues concerning aircraft sizing procedures that need to be conceived considering the specific characteristics of such multifunctional technology. This research work aims to evaluate the impact the structural batteries have on the design of a commuter aircraft. According to the envisaged technologies (structural batteries), this work will focus on the determination of the best hybridization factors determining the energy requirements for the typical mission of a commuter aircraft.