A vertical-takeoff-and-landing (“VTOL”) aircraft including a non-VTOL aircraft equipped for forward takeoff and flight and a modular boom system interoperably coupled to the non-VTOL aircraft. The modular boom system includes a first modular boom and a second modular boom. The first modular boom includes a first rocket-turbine engine. The first modular boom is mounted to a first wing of the non-VTOL aircraft. The second modular boom includes a second rocket-turbine engine. The second modular boom is mounted to a second wing of the non-VTOL aircraft.