What was a main goal of the Wright brothers when they invented their airplane?

The main goal of the Wright brothers when they invented their airplane was indeed to create a product to sell through patents. They were not just focused on theoretical concepts; instead, they aimed to develop a practical and functional flying machine. Their persistence led to many innovations in aerodynamics and control, which they meticulously documented and patented. This focus on commercialization reflects their understanding of the significance of their invention and the potential market for powered flight. They saw the opportunity for aviation to transform transportation, and securing patents allowed them to protect their work and monetize their invention effectively.

The other options, while relevant to aspects of aviation history, do not encapsulate the primary objective of the Wright brothers' efforts in the same way. They were not primarily focused on creating a cost-effective jet aircraft, as jets were developed much later. Their experiments were rooted in heavier-than-air flight, as opposed to lighter-than-air technology like balloons or airships. While fame and recognition were likely desirable outcomes, they were not the main driving force behind their invention; rather, the Wright brothers were motivated by the desire to solve the problems of controlled flight and commercialize their innovations.