If you are looking for tools to design physical balsa planes rather than virtual ones, the following software is commonly recommended by the hobbyist community:
Balsa Model Flight Simulator is a sandbox experience focused on the design, construction, and piloting of model aircraft. Download Balsa3 dion73 rar
Research indicates that is a known contributor to several flight simulation platforms: If you are looking for tools to design
: Users can build detailed aircraft from scratch, adjusting wing geometry, fuselage shapes, and internal components. adjusting wing geometry
: The user has shared free assets, such as a NASA livery for the AV-8B Harrier. Safety and Downloading Guidelines