Hispano-Suiza 12Y

Hispano-Suiza
Industry	Aerospace, engineering
Founded	1904
Headquarters	France
Products	Aircraft engines

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The Hispano-Suiza 12Y represented a significant aircraft engine developed by Hispano-Suiza for the French Air Force in the period leading up to World War II. It emerged as France’s foremost engine in the 1,000 hp (750 kW) category, powering prominent aircraft such as the Morane-Saulnier M.S.406 and Dewoitine D.520.

Building upon the smaller 12X, the 12Y succeeded it as one of the most powerful aero engines in pre-war France. Progress on its successor, the 12Z, was discontinued following France’s defeat and subsequent German occupation.

Licensed production of the 12Y also took place in the Soviet Union under the designation Klimov M-100, which later evolved into the widely used VK-105 series powering fighters like the Yak-1 and bombers including the Petlyakov Pe-2. Early licensed versions were manufactured in Czechoslovakia (as Avia HS 12Ydrs) and Switzerland (known as HS-77).

Initial development

The 12Y was a traditional 36-litre, water-cooled V-12 configuration, featuring two cast aluminium cylinder banks arranged at a 60-degree angle. Its cylinder heads were fixed and not removable; instead, entire cylinder banks could be swiftly detached from the crankcase—a design praised for its leak-proof qualities and influential on engines such as the Rolls-Royce Merlin.

A notable advancement from the 12X was its use of a master-articulated connecting rod system rather than fork-and-blade rods. The engine employed a single overhead camshaft (SOHC) to operate liquid sodium-cooled poppet valves—one intake and one exhaust valve per cylinder—while many contemporaries utilized multiple valves per cylinder. It incorporated a single-stage, single-speed supercharger, though its intake configuration limited effectiveness at higher altitudes.

First run in 1932, this engine initially delivered 760 hp (570 kW), with clear capacity to reach around 1,000 hp (750 kW). The Hispano-Suiza 12Ycrs variant introduced a hollow propeller shaft enabling a mounted 20 mm cannon to fire through the spinner—a moteur-canon setup adopted throughout subsequent versions. The 12Ydrs series produced 836 hp (623 kW) at sea level with a compression ratio of 5.8:1.

The French Air Force’s Hispano-Suiza 12Y-21 raised compression to 7:1 using 100 octane fuel, increasing output to 867 hp (647 kW). In 1936, the 12Y-31 model refined connecting rod design, maintained a compression ratio of 5.8:1, and boosted power slightly to 850 hp (630 kW). This version became extensively used across French fighter aircraft and prototypes prior to World War II.

Later variants

By 1938, the Hispano-Suiza 12Y-45 incorporated the S-39-H3 supercharger, co-developed by André Planiol alongside Polish engineer Joseph Szydlowski. This larger and more efficient supercharger, combined with use of 100 octane fuel, elevated power output to 900 hp (670 kW) at a compression ratio of 7:1. When paired with the Ratier constant-speed propeller, it allowed the D.520 to compete effectively with contemporary German and British fighters.

The Hispano-Suiza 12Y-49 enhanced performance further, raising power from 850 hp (630 kW) at sea level to approximately 920 hp (690 kW) at around 10,000 ft (3,000 m), reflecting typical altitude performance gains from supercharging during that period.

The last major iteration, the Hispano-Suiza 12Y-51, delivering 1,085 hp (809 kW), entered production shortly before the Armistice. Although approaching the engine’s maximum potential, its single-stage supercharger restricted competitiveness above altitudes of 15,000 ft (5,000 m) compared to British and German counterparts.

Foreign licensed production

During the early 1930s, Czechoslovakia obtained a license to manufacture the HS-12Y engine through Avia (part of Škoda) located in Prague - Čakovice. This engine was designed to serve as the primary powerplant for Czechoslovak military aircraft. Variants such as the HS-12Ycrs and HS-12Ydrs were installed in aircraft including the Avia B-34, B-534, B-71, B-35, B-135, as well as the Yugoslav Rogožarski IK-3.

Switzerland acquired licenses for several 12Ycrs versions, which were utilized in aircraft like the reconnaissance biplane EKW C-35, the versatile EKW C-36, and Swiss-produced Morane-Saulnier M.S.406 derivatives (D-3800 and D.3801). Additionally, Switzerland further developed these engines into the Saurer YS-2 and YS-3 models, which powered advanced French fighter variants such as the M.S.450 (D.3802) and the ultimate D.3803.

In the mid-1930s, Russian engineer Vladimir Klimov secured rights to produce the 12Y locally. Modified for operation in colder environments, production began in 1935 under the designation Klimov M-100, delivering approximately 750 hp (560 kW). Successive improvements raised its maximum RPM from 2,400 to 2,700, boosting output to 1,100 hp (820 kW). The Klimov M-105 (VK-105) emerged as a crucial Soviet wartime engine, powering all fighters designed by Yakovlev.

Variants

Type 73 Hispano 12Y engines specifications. V-12 configuration with a bore of 150 mm and stroke of 170 mm, total displacement of 36.0 litres. Type 77 models include a 20 mm Hispano-Suiza HS.404 cannon mounted between cylinder banks firing through the propeller shaft.
Model	Year	Compression Ratio	Power Output (hp)	RPM	Take-Off Power (hp)	Reduction Gear Ratio	Optimal Supercharger Altitude (m)	Weight (kg)	Cannon Equipped	Notes
12Ybr 650 hp	1932	6.4	785	2,200	785	1.5	0	415	n	Rated power below nominal 785 hp
12Ybrs	1934	5.8	860	2,400	835	1.0625	4,000	470	y
12Ycrs	1934	5.8	860	2,400	835	0.67:1	4,000	470	y
12Ygrs 650 hp	1932	5.8	850	2,400	800	1.5	4,000	430	n	Rated power below nominal 850 hp
12Ydr	1934	6.4	800	2,200	800	1.5	0	440	n	Left-turning variable-pitch propeller
12Ydrs	1934	5.8	860	2,400	835	1.5	4,000	470	n
12Ydrs1	1934	5.8	880	2,400	890	1.5	2,400	470	n	Left-turning variable-pitch propeller
12Ydrs2	1934	5.8	930	2,400	992	1.5	900	470	n
12Yfrs	1934	5.8	860	2,400	835	1.5	4,000	470	n
12Yfrs1	1934	5.8	880	2,400	890	1.5	2,400	470	n
12Yfrs2	1934	5.8	930	2,400	992	1.5	900	470	n
12Y-21	1935	7.0	910	2,400	880	1.5	3,600	470	n
12Y-25		5.8	860	2,400	943	1.5	–	n	Variable ignition timing
12Y-26/27		5.8	900	2,400	950	1.8	850	483	Opposite rotation configurations
12Y-28/29		7.2	920	2,400	910	0.67:1	3,600	475	y	Variants with left and right rotation
12Y-30/31		5.8	860	2,400	830	0.67:1	3,250	468	y	Redesigned connecting rods; LH and RH rotation options
12Y-32/33		5.8	960	2,400	955	0.67:1	2,300	468	y
12Y-36/37		7.0	960	2,400	1,050	0.55:1	1,250	483	y
(38/39)	1936	(7.0)	(1000)	(2,400)	–	(1.5)	(3,400)	–	(n)	Left and right rotation variants
(41)	1936	(7.0)	(920)	(2,400)	–	(0.67:1)	(3,600)	(483)	(y)
(45)	–	(7.0)	(920)	(2,400)	(935)	(0.67:1)	(4,200)	–	(y)	Equipped with Szydlowsky-Planiol (SP) supercharger
(47)	1936	(5.8)	(860)	(2,400)	(830)	(0.67:1)	(3,250)	(468)	(y)
(49)	–	(7.0)	(910)	(2,400)	(910)	(0.67:1)	(5,250)	–	(y)	(SP) supercharger featuring variable ignition timing
(50/51)	1939	(7.0)	(1000)	(2,500)	(1100)	(0.67:1)	(3,260)	(492)	(y)	(SP) supercharger; available in LH and RH rotation versions

Related Models

Hispano-Suiza 12Z
Hispano-Suiza 24Y and 24Z

Variants Produced Under Licence

Czechoslovakia
Avia HS 12Y

USSR: Klimov VK-100; Klimov VK-103; Klimov VK-103A rated at; Klimov VK-104; Klimov VK-105P with take-off power of; Klimov VK-106 at take-off power; Klimov VK-107 with take-off power

Switzerland
Hispano-Suiza HS-77: 12 Ycrs