Energy coefficients for comparison of aircraft supported by different propulsion systems

Abstract

Stakeholders envision introduction of electric and hybrid-electric aircraft into operation by 2035. First developments meet a series of challenges caused mostly by deficiencies (like low specific energy) of battery technology. Due to this, electric aircraft will have unacceptably large take-off weight or significantly reduced range. Energy factors (energy used per unit of work performed adapted to electric and hybrid-electric aircraft can support the evaluation of aircraft with different propulsion systems, and prediction of required battery technology and electric energy generation. Using the recommended energy factors, aircraft with different propulsion systems are comparable at the concept inspiration and conceptual design stages of new aircraft design. The results are clear and understandable. Energy intensity (evaluating the “aerodynamic goodness” at cruise flight) is about 10–60% lower (better) for full electric aircraft, but such aircraft have 50–80% less range and 40–230% greater take-off mass than comparable conventionally powered aircraft. Analysis of the used energy factors shows that the full electric small 4-seater aircraft may use less energy for flights up to 750 km range. Total energy used per unit of work done is 15–20% greater than total used energy during aircraft operations.