The VAC-221, derived from the MiG-15, was a jet fighter that used the new TX-470 turbojet engine. Having 4 rockets on its wing, the jet engine made it extremley unstable for powered flight. However, it was not all like that. A plastic model, tested in a wind tunnel, proved its stability in flight. An unweaponized model flew at the Póris Altaís Airshow and showed its capabillities. Before the airshow, workers suggested a tandem arrangement of the engines, which failed. Other workers suggested a single engine placed in the rear, and failed but was fixed by adding fuel to the main fuselage. After its weaponization, the VAC-221 was heavier and its STOL preformance was worse than expected. This, a glider model, was the plastic model used in the wind tunnel.