The J-9 used a completely new single-engined design. It was to have a top speed of Mach 2.4, necessitating the use of variable geometry inlets and a high-power turbofan engine. Four configurations were considered, all incorporating delta wings. However, each proposed configuration was found to lack agility and experience stability issues at certain speeds. A new configuration was devised, resembling the canard layout of the Saab Viggen. However, just as this major change was made, the Cultural Revolution hit the project, bringing work to a standstill. Meanwhile, Chinese involvement in Vietnam led to rapidly changing requirements, calling for unrealistic range and top speeds higher than originally specified. Work resumed in the 70’s, with a prototype reportedly making a flight. However, the WS-6 turbofan that was to power the aircraft proved a failure, and the competing Shenyang J-8 was not only entering service but was more promising. In 1978 the J-9 was finally cancelled.