The Piaggio P.IX, or Piaggio Stella P.IX, was an Italian nine-cylinder radial aircraft engine produced by Rinaldo Piaggio S.p.A.. Based on the Gnome-Rhône 9K, the engine was rated at 600 hp (447 kW). Production was used to power a number of other aircraft developed in Italy. The main users were the Savoia-Marchetti SM.81 transport and the IMAM Ro.37bis, the main reconnaissance aircraft in the Regia Aeronautica during the Second Italo-Ethiopian War, Spanish Civil War and Second World War, but the engine was also used by other designs, including the prototype Savoia-Marchetti SM.79.