Piaggio Stella P.IX

Rinaldo Piaggio S.p.A.

Industry	Aerospace, Aircraft engines
Founded	1884
Headquarters	Italy
Products	Aircraft engines, including the Piaggio P.IX

Template:Good article Template:Infobox aero engine The Piaggio P.IX, also referred to as the Piaggio Stella P.IX, was an Italian nine-cylinder radial aircraft engine manufactured by Rinaldo Piaggio S.p.A.. It was derived from the Gnome-Rhône 9K and delivered a power output of approximately 600 hp (447 kW). This powerplant was employed in various Italian aircraft designs, predominantly the Savoia-Marchetti SM.81 transport and the IMAM Ro.37bis reconnaissance plane, which served as key assets in the Regia Aeronautica during conflicts such as the Second Italo-Ethiopian War, Spanish Civil War, and Second World War. Additionally, it powered other models including the prototype of the Savoia-Marchetti SM.79.

Design and development

In 1925, Piaggio secured a licensing agreement with Gnome et Rhône for engines developed from the Bristol Jupiter. A decade later, under engineer Renzo Spolti’s leadership, a refined iteration was introduced in 1933. This nine-cylinder unit was designated P.IX and formed part of Piaggio’s Stella series—radial engines sharing a common architectural foundation.

The construction featured cylinders with steel barrels coupled to aluminium heads. The pistons, crafted from aluminium alloy, connected to a split crankshaft through articulated connecting rods. Valve mechanisms were enclosed within the cylinder assembly. The bore and stroke dimensions matched those of the original Gnome-Rhône 9K, measuring 146 millimetres (5.7 in) and 165 mm (6.5 in), respectively. Despite this similarity, the P.IX offered enhanced power, rated at around 600 horsepower (447 kW) when equipped with a supercharger.

This engine powered aircraft active in several major conflicts including the Second Italo-Ethiopian War, Spanish Civil War, and the Second World War. Notably, it was installed on one hundred and forty units of the Savoia-Marchetti SM.81, an important transport for the Regia Aeronautica, as well as on most of the produced IMAM Ro.37bis reconnaissance aircraft. By 1943, most of these engines had been withdrawn from service.

Variants

P.IX R.

Geared and normally aspirated version.

P.IX R.C.

Geared with supercharging.

P.IX R.C.10

Geared and supercharged variant rated for operations at 1,000 m (3,300 ft) altitude.

P.IX R.C.40

Geared and supercharged model optimized for performance at 4,000 m (13,000 ft) altitude.

Applications

• CANT Z.504
• Prototype of CANT Z.506
• Caproni Ca.131
• Caproni Ca.132
• Caproni Ca.301 (also known as Caproni A.P.1)
• Caproni Ca.305 (Caproni A.P.1 variant)
• Caproni CH.1
• IMAM Ro.37bis
• Prototype of IMAM Ro.43
• Piaggio P.10bis
• Piaggio P.16
• Savoia-Marchetti S.73
• Prototype of Savoia-Marchetti SM.79
• Savoia-Marchetti SM.81