Hispano-Suiza 12M
| Industry | Aerospace, Automotive |
|---|---|
| Headquarters | Spain / France |
| Products | Aircraft engines, Automotive engines |
The Hispano-Suiza 12M represented one of two novel V-12 engine models launched between 1927 and 1928. Delivering approximately 375 kW (500 hp), it was pioneering in its application of gas nitride hardening and the incorporation of wet cylinder liners within Hispano-Suiza’s aircraft powerplants.
Design and development
Prior to 1927, Hispano-Suiza’s propulsion units were developments stemming from the World War I era V-8 Hispano-Suiza 8. During 1927–28, the company unveiled four new engines: two six-cylinder inline configurations and two V-12 variants. The smaller V-12, designated 12M (Type 57), had a displacement of 27.0 L (1,648 cu in), while the larger 12N measured 36.0 L (2,197 cu in). Despite their differences in size and output, both shared numerous design elements.
Both the 12M and 12N featured a 60° V configuration with carburettors, intake, and exhaust ports positioned on the outer sides—each bank equipped with three carburettors servicing two cylinders apiece. A key advancement was the introduction of wet liner cylinders, a concept adapted from Hispano’s automotive division that allowed direct contact between cooling water and steel cylinder barrels, bypassing aluminium jackets. This innovation enhanced cooling efficiency, streamlined assembly processes, and permitted larger bore dimensions without altering cylinder spacing. The cylinders were externally threaded near their upper section to secure the block, with valve seats housed in aluminium cylinder heads; barrel extensions into the crankcase simplified production. The block and crankcase were fastened together by bolts.
These engines were also the first to utilize gas nitriding for surface hardening of cylinder walls, which significantly decreased wear and lowered oil consumption. Additionally, they incorporated a novel main bearing cooling system that improved oil circulation without necessitating increased oil pump speeds.
Designed for rapid installation or removal of epicyclic gearing, unlike earlier fixed-gear designs, the Farman gearing system added 45 kg (99 lb) to the overall weight.
The initial commercial variant, the 12Mb (1929), featured a compression ratio of 6.2 and delivered up to 432 kW (580 hp) at 2,100 rpm. Its geared counterpart was known as the 12Mbr. The following model, the 12Mc (1930), replaced aluminium crankcases with lighter Elektron alloy, reducing mass by 20 kg (44 lb), raised compression to 7.0, and increased output to 477 kW (640 hp). The 12Md maintained the Elektron crankcase but reverted to a compression ratio of 6.2. Both versions had corresponding geared forms designated as 12Mcr and 12Mdr.
To counteract power loss at altitude, the 12Mc operated lean at sea level to reach peak power at approximately 2,000 m (6,490 ft). The final iteration, the supercharged 12Mdsh (1932), employed a Rateau turbine supercharger enabling it to produce 477 kW (640 hp) at 2,250 rpm at an altitude of 2,950 m (9,678 ft), sustaining performance up to 5,500 m (18,000 ft) during test flights aboard a Dewoitine D.32. The evolution of the 12M series culminated in the development of the supercharged 12X (Type 72) engine introduced in 1931.
Operational history
The Swiss authorities, via the KTA (Kriegstechnischen Abteilung or War Technical Department), secured manufacturing rights for the 12Mb engine. In 1932, Schweizerische Lokomotiv- und Maschinenfabrik completed production of sixty units.
On 2 June 1932, a Blériot-SPAD S.91-7 powered by a 12Mc engine established a closed-circuit speed record over 500 km, reaching 308.78 km/h (191.91 mph).
Variants
Source: Hispano Suiza in Aeronautics
- 12Mb/500
- Compression ratio of 6.2; rated power output of 428 kW (575 hp) at 2,000 rpm.
- 12Mbr/500
- Identical to 12Mb, equipped with Farman reduction gearing; rated power of 421 kW (565 hp).
- 12Mc/500
- Compression ratio increased to 7.0; rated power of 477 kW (640 hp) at 2,200 rpm; incorporates Elektron crankcase and components.
- 12Mcr/500
- Same specifications as 12Mc but fitted with Farman reduction gear.
- 12Md
- Compression ratio of 6.2; rated power of 428 kW (575 hp) at 2,100 rpm; features Elektron crankcase and parts.
- 12Mdr
- Equivalent to 12Md with Farman reduction gearing.
- 12Mdsh
- The initial supercharged variant; delivers nominal power of 477 kW (640 hp) at 2,250 rpm and altitude of 2,950 m (9,678 ft).
Applications
- Blériot-SPAD S.91-7
- Dewoitine D.32
- Lioré et Olivier LeO 252, including variants 235, 234, and 236
- Nieuport-Delage NiD 622 and NiD 629