Isotta Fraschini Asso XI

Isotta Fraschini

Industry	Aerospace, Engine manufacturing
Founded	1900s (exact date not provided)
Headquarters	Italy
Products	Aircraft engines (including Asso XI series)

The Asso XI represented a series of supercharged, water-cooled V12 piston engines developed during the 1930s by the Italian firm Isotta Fraschini. These powerplants were installed in various aircraft models produced by companies such as CANT, Caproni, among others.

Design and development

Isotta Fraschini manufactured an extensive lineup of engines under the Asso designation (meaning Ace in English). The Asso XI R.C. was a liquid-cooled V-12 engine delivering peak power outputs ranging between 670–725 kW (898–972 hp), contingent on supercharger performance. Two primary variants existed, distinguished solely by their supercharger rotational speeds: the R.C.40 featured a supercharger speed slightly exceeding ten times the crankshaft speed, enabling it to sustain a rated power of 623 kW (835 hp) up to an altitude of 4,000 m (13,000 ft); in contrast, the R.2C.15 maintained 655 kW (878 hp) at 1,500 m (4,900 ft) with a gearing ratio of 7 for the supercharger.

The R.C.40 models shared many design elements with the earlier Asso 750 R.C., although they incorporated two banks of six cylinders instead of three, and utilized four valves per cylinder rather than two. The cylinder barrels were crafted from carbon steel and featured flat-topped heads with integrated valve seats; each barrel was enclosed by an individual sheet steel water jacket. Cast aluminium heads were affixed to each cylinder bank, providing passages for valves, guides, coolant flow, and camshaft supports. Pistons were made from aluminium castings as well. The crankshaft employed a six-throw configuration supported by eight plain bearings, complemented by a double row ball thrust bearing located between the foremost two bearings. Connecting rods included bronze bushings at the little ends and white metal bearings at the big ends. The crankcase consisted of two cast parts, with the upper section housing the crankshaft bearing supports.

Variants

Asso XI R

(R - Riduttore, indicating reduction gear)

Asso XI R.C.

(C - Compressore, denoting supercharged)

Asso XI R.C.15

Supercharger speed at 75/7 times crankshaft speed; rated power specified at 1,500 m (4,900 ft).

Asso XI R.2C.15

(2C - second supercharger gearing) Supercharger rotates at 7 times crankshaft speed; rated power measured at 1,500 m (4,900 ft).

Asso XI R.2C.16

(2C - second supercharger gearing) Supercharger speed set at 7 times crankshaft speed; rated power defined at 1,600 m (5,200 ft).

Asso XI R.C.40

Supercharger speed maintained at 75/7 times crankshaft speed; rated power recorded at 4,000 m (13,000 ft).

L.121 R.C.40

A derivative of the Asso XI producing 671 kW (900 hp).

A.120 R.C.40

An inverted configuration based on the L.121 model.

Applications

• CANT Z.501
• CANT Z.505
• CANT Z.508
• CANT Z.1007
• CANT Z.1011
• Caproni Ca.124 idro
• Caproni Ca.134
• Caproni Ca.135
• Caproni Ca.405
• Caproni Campini N.1
• IMAM Ro.45
• Piaggio P.32
• Piaggio P.50
• SAI Ambrosini S.S.4
• Savoia-Marchetti SM.79 (initially)