This report entails the design of a regional passenger aircraft, serving 48 passengers and entering the market by 2035. It is known as the SRP-22 ALAR FOX, however, in general, SRP-22 is used. The propulsion system is designed with hydrogen as its fuel. The hydrogen is converted to electricity with a low-temperature proton-exchange membrane fuel cell, which in turn is used by the electric motors, to power the propellers. There are four electric motors with one six-bladed propeller each. Two propellers are located under the wing near the fuselage and deliver 80% of the total power. The remaining two propellers are positioned on the wing tips, delivering the remaining 20%. The benefit of these wingtip propellers is an expected drag reduction of around 10%, due to the attenuation of wingtip vortices.
The hydrogen is stored in a composite tank, located behind the aft pressure bulkhead. The fuel cell is placed under the cabin floor, just in front of the pressure bulkhead, such that less tubing is required to transport the hydrogen. The boil-off of the hydrogen is used to transform the hydrogen from its liquid state to its gaseous state, through the usage of glass rods. After that, the hydrogen is heated up until about 80◦C, which is the operating temperature of the fuel cell. The control system is controlled through a mechanical-powered hydraulic system. The elevator design includes horns to relieve the hinge moment.
One of the main goals was to reduce the environmental impact of the aircraft. The average temperature response of the SRP-22 is almost 83 times lower than that of the ATR 42 by 2064, which supports this goal. Noise has also been taken into account, which mainly stems from the propellers and airframe. It is found that the noise levels are well below the limits set by ICAO. The unit list price of the SRP-22 will be $19 million when using more optimistic fuel cell prices, while a least optimistic estimate results in a unit list price of $37 million. Moreover, the direct operational cost is around 10% lower than those of the ATR 72. Because of the usage of electric motors, the maintenance cost is expected to be lower than for a turboprop aircraft.

Bachelor Thesis: Design Synthesis Exercise 2023
Group 13: Electric General Aircraft
in collaboration with
Group 10: Mid-Flight Recharging System

Addressing the pressing need for sustainability amid climate change, the aviation sector is under pressure to mitigate its significant carbon emissions. As aviation accounts for over 2% of global emissions, achieving zero-emissions aviation by 2050 is crucial. The challenge lies in finding alternatives to jet fuel. One option is battery-powered electric aviation, but limitations such as range constraints and emissions during production and disposal must be considered.

This report proposes a solution to extend the range of all-electric passenger aircraft. The ElectriFly aircraft can currently fly 600km at 110m/s before requiring recharging. To achieve perpetual flight capability, a mid-flight recharging system is introduced using a drogue and probe system, similar to military refueling technologies. This approach not only increases range but also reduces turn around time at airports.

Powered by four parallel-connected solid-state batteries with an energy density of 600kWh/kg, the ElectriFly aircraft features 14 propellers using distributed propulsion and potential plasma actuators. This setup improves aerodynamic performance, reduces noise, and allows for regenerative braking, easing the burden on the recharging drone. Real-time data sensors enable predictive maintenance, minimizing downtime and providing pilots with crucial flight anomaly information.

This research presents a promising solution for electric aircraft limitations through mid-flight recharging. The proposed ElectriFly aircraft offers extended range capabilities and improved operational efficiency, supporting the goal of sustainable aviation.