Otto Aviation (USA) uses the aviation diesel engine from RED Aircraft and an MT propeller from Germany for its Celera 500L, which tries to compete with traditional business jets. The efficient aircraft design (high aspect ratio wing, low drag fuselage) also benefits from a lower engine prices compared to a jet engine. Could this also be a starting point for the design of passenger aircraft? Warning: Mahfouz (2023) showed that Diesel engines with propeller may not be better than turbofans, when their overall efficiency is compared including the propeller.