Junkers Jumo 222
| Industry | Aerospace engineering, aircraft engine manufacturing |
|---|---|
| Founded | 1937 |
| Founder | Ferdinand Brandner (leader of Jumo 222 development) |
| Headquarters | Germany |
| Products | Aircraft engines (including Jumo 222) |
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The Jumo 222 was a powerful German multi-bank inline piston aircraft engine developed by Junkers, under the leadership of Ferdinand Brandner at Junkers Motorenwerke.
Its anticipated performance far exceeded that of contemporaneous engines, prompting numerous Luftwaffe piston-powered aircraft projects during World War II to consider it as a primary or alternative powerplant. Notably, it formed the foundation of the entire Bomber B initiative, which aimed to replace all existing Luftwaffe bombers with a new class of twin-engine planes that were larger, faster, and more heavily armed than any other in service.
Despite extensive development efforts and several significant redesigns, the engine never reached operational maturity. The failure of the Jumo 222 contributed directly to the collapse of the Bomber B program, leaving the Luftwaffe reliant on obsolete aircraft designs during the latter half of the conflict. Production was limited to fewer than three hundred units, all confined to prototype status. Nonetheless, the engine continued to be proposed for various new multi-engine Luftwaffe aircraft concepts long after confidence in its success had waned.
Design and development
Development of the Jumo 222 commenced in 1937. The engine featured six inline cylinder banks arranged symmetrically around the crankcase at equal 60° intervals, each bank containing four cylinders. This configuration gave it a radial-like appearance; cross-sectional diagrams reveal a master connecting rod system akin to single-row radial engines, where one master rod connects to five additional rods pivoting from its crankpin end casting. Internally, however, it functioned more like a series of V engines paired adjacently, each cylinder bank equipped with a liquid-cooled crossflow cylinder head.
Viewed from the front, the six cylinder banks were spaced evenly at 60° increments. Neighboring banks had their exhaust ports positioned at "60°, 180°, and 300°" angles and intake ports at "0°, 120°, and 240°," facing each other to simplify ducting from the rear-mounted supercharger. This arrangement resulted in only three exhaust header sets, likely located at the bottom and upper sides of the engine nacelle for efficient exhaust routing similar in appearance to many Allied upright V-type aviation engines.
The four-cylinder length per bank produced an engine shorter than the Jumo 211 by approximately 80 cm/31.5 in, although it necessitated a larger nacelle cross-section. Similar to the Ju 88, an annular radiator could be used to cool both cylinders and oil. The Junkers Ju 288 was designed with hollow ducted spinners concealing these radiators behind its four-blade propellers.
Each cylinder incorporated two intake valves and a single sodium-cooled exhaust valve—a triple-valve layout inherited from Junkers’ earlier inverted V12 Jumo 210 engine—alongside a high-pressure fuel injector situated between intake valves and dual spark plugs for ignition. With bore and stroke dimensions of 135 mm (5.3 in), the initial Jumo 222A/B variant displaced 46.4 liters (2,831.5 in³), comparable in size to the American Pratt & Whitney R-2800 Double Wasp eighteen-cylinder air-cooled radial developed between 1937 and 1940. The compression ratio was limited to a modest 6.5:1—the same as used on mass-produced Jumo 211C inverted V12s—due to Germany’s low-octane fuel availability. Operating at up to 3,200 rpm, this allowed takeoff power output reaching 1,850 kW (2,480 hp). Though equipped with only a simple single-stage two-speed supercharger—which was somewhat disappointing—the engine still managed 1,641 kW (2,201 hp) at an altitude of 5,000 m (16,000 ft). Its dry weight was 1,088 kg (2,399 lb), roughly 17 kg (37 lb) heavier than the air-cooled Double Wasp.
When compared with contemporaries such as the BMW 801 and Daimler-Benz DB 605, the Jumo 222 represented a significant performance advance. Its displacement slightly exceeded that of the BMW 801’s 41.8 liters (2,550.8 in³) and was about one-quarter greater than the DB 605’s 35.7 liters (2,178.5 in³), yet it delivered substantially higher power: 1,850 kW (2,480 hp) versus 1,193 kW (1,600 hp) for the BMW and 1,119 kW (1,501 hp) for the Daimler-Benz unit. This equated to approximately 40 kW per liter for the Jumo compared to only about 29 kW/L for the BMW and 31 kW/L for the DB 605. Its power-to-weight ratio stood at roughly 1.7 kW/kg (1.04 hp/lb), outperforming both competitors—the DB 605 delivered about 1.4 kW/kg (0.88 hp/lb) and BMW’s engine about 1 kW/kg (0.60 hp/lb). Dimensionally, it was similar in size: approximately 1.16 m (3.8 ft) wide compared to 1.27 m (4.2 ft) for the BMW engine and about 2.4 m (7.9 ft) long versus 2.3 m (7.5 ft) for the DB unit.
The Jumo’s advantages became even more evident against other high-output engines under development at that time. For example, BMW’s enlarged eighteen-cylinder radial—the BMW 802—was based on their successful fourteen-cylinder BMW 801 but began work only in late 1939; it weighed around 1,530 kg (3,370 lb) and first ran in 1943 without entering production. Another attempt by BMW involved coupling two BMW 801 radials into a twin-engine configuration called BMW 803, which proved unsuccessful. Additionally, there was Daimler-Benz’s DB 606—a pioneering “high-output” powerplant composed of two DB 601 engines coupled together—producing around 1,790 kW (2,400 hp) but weighing approximately 1,515 kg (3,340 lb) with dimensions measuring roughly 2.1 \times[convert: unknown unit] (feet). Its problematic installation in Germany’s sole heavy bomber production model—the Heinkel He 177A—led Reichsmarschall Hermann Göring to disparagingly nickname them “welded-together engines” during late summer of 1942.
In contrast, the Reich Air Ministry (RLM) viewed both the compact layout of the Jumo 222 and Daimler-Benz’s X-configuration DB 604—featuring twenty-four cylinders with similar displacement but lower specific power—with enthusiasm. The Bomber B program was built around twin installations of these engines aiming to produce bombers matching Heinkel He177’s payload but surpassing Junkers Ju88’s speed capabilities—a versatile concept.
The initial prototype ran on April 24th, 1939; subsequent flight tests involved mounting it on a Junkers Ju52 nose position. Production targeted two main variants: 222A and 222B, differing solely by rotation direction intended for left-wing (port) and right-wing (starboard) use on twin-engine aircraft employing counter-rotating propellers. Nevertheless, persistent testing issues led Junkers to halt development of these “Series I” models in favor of redesigned “Series II” variants: 222A-2 and B-2. These featured slightly larger cylinders with a bore increase to 140 millimetres (5.5 in), raising displacement to approximately 49.88 liters (3,043.86 in³), while operating at reduced rpm but maintaining equivalent output levels; further upgraded versions A-3 and B-3 incorporated improved superchargers optimized for higher altitudes. One example each of A-3 and B-3 were reportedly installed on the ninth Junkers Ju288 prototype airframe for flight evaluation purposes.[citation needed] Despite these enhancements, reliability remained poor and these uprated models saw only experimental use.
By late 1941 Junkers pursued more substantial modifications resulting in 222C and 222D versions featuring increased bore and stroke dimensions of [convert: invalid number], expanding displacement further to around 55.5 liters (3,386.8 in³)—slightly exceeding that of contemporary American Wright Duplex Cyclone R-3350 eighteen-cylinder radials which were themselves experiencing developmental challenges partly due to magnesium-alloy crankcase issues. Operating again at original maximum speed of about 3,200 rpm, these variants approached nearly 2,200 kilowatts (3,000 hp) output when first tested mid-1942; however persistent technical difficulties meant only limited numbers were produced before RLM abandoned reliance on this design after three years’ delay and cancelled Bomber B altogether later that year.
Despite setbacks Junkers persisted by returning to original A/B displacement figures while introducing new two-stage superchargers combined with three aftercoolers—one per adjacent cylinder bank pair—for enhanced high-altitude performance yielding variants 222E and F. Although sea-level power remained unchanged, altitude rating improved significantly producing up to 1,439 kilowatts (1,930 hp) at about 9,000 metres (30,000 ft) altitude as testing progressed toward resolution of earlier issues; unfortunately Allied bombing raids severely disrupted manufacturing capabilities at Dessau facilities impeding production scale-up efforts entirely. Further attempts included turbocharged 222G and H models developed solely as testbed prototypes.
Ultimately regarded as an expensive failure project-wise, only approximately two hundred eighty-nine Jumo 222 units were built without entering operational service; meanwhile Luftwaffe piston-powered aircraft development stagnated between roughly 1940–42 as numerous engineers within military testing establishments such as Oberst Edgar Petersen’s Erprobungsstelle network awaited functional results from this engine’s protracted development cycle. Proposals advocating conversion from twin-engine configurations powered by Jumo 222s into four-engine alternatives were rejected over concerns regarding strain on Germany’s aviation engine industry capacity; consequently no tangible advancements arose from this initiative leaving Luftwaffe largely dependent on minimally updated pre-war designs well into late stages of conflict.
Variants
None of the Jumo 222 engine versions were ever introduced into active service.
- Jumo 222 A / B-1: The initial model featured a bore and stroke of 135 × 135 mm, resulting in a displacement of 46,380 cm³ and delivering 1470 kW (1970 hp) at 3200 rpm. It was equipped with a single-stage, two-speed centrifugal supercharger and underwent flight testing as part of the "service-test" A-0/B-0 series.
- Jumo 222 A / B-2: This enlarged variant had increased valve cross-sectional areas with a bore and stroke of 140 × 135 mm, totaling 49,880 cm³ displacement. It produced 2500 hp at 2900 rpm, retained the single-stage two-speed centrifugal supercharger, and was tested in the zero series during flight trials.
- Jumo 222 A / B-3: Similar to the A/B-2 but incorporated an enhanced centrifugal supercharger, allowing operation up to a full pressure altitude of 6000 meters. This pilot series was also flight-tested.
- Jumo 222 C / D: Further increased in size with bore and stroke dimensions of 145 × 140 mm, yielding a displacement of 55,480 cm³. It generated 3000 hp at 3200 rpm and was designed for operation at full pressure altitudes up to 10,000 meters. V-series experimental models were assembled based on this design.
- Jumo 222 E / F: Comparable to the A/B-3 but fitted with a two-stage, two-speed centrifugal supercharger alongside three aftercoolers. This pilot series achieved a full pressure altitude of 9400 meters and underwent flight testing.
- Jumo 222 turbo: Based on the A/B-3 configuration but equipped with a turbocharger and intercooling system, enabling operation at a full pressure altitude of 12,300 meters and producing 2400 hp at 3200 rpm. This variant was only tested on the bench.
- Jumo 222 G / 225: A conceptual lengthened model featuring six banks of six cylinders (totaling 36 cylinders) with bore and stroke dimensions of 135 × 135 mm, resulting in a displacement of 69,570 cm³. It was projected to deliver 3500 hp at 3000 rpm with adjustable speed charging.
The propeller shaft’s rotation direction was designated by letters: A, C, and E variants rotated counterclockwise (to the left), while B, D, and F rotated clockwise (to the right). The crankshaft itself always turned clockwise; variations in propeller rotation were achieved solely through different gearing mechanisms.
With its six cylinder banks, the Junkers Jumo 222 is classified as a Hexagon engine. Such configurations are uncommon; other examples include the water-cooled Dobrynin VD-4K with 24 cylinders and the air-cooled Curtiss H-1640 Chieftain with twelve cylinders. Similarly rare are octagon engines like the Bristol Hydra, which featured eight cylinder banks.
Applications
- Aircraft projects designed to be powered by the Jumo 222 included:
- Dornier Do 435 (in cases where the rear piston engine was not replaced by a jet engine)
- Focke-Wulf Fw 300
- Heinkel He 219 B & C variants
- Heinkel He 277 (proposed in late July 1943 as an alternative for the Amerikabomber project to replace six BMW 801 radial engines)
- Hütter Hü 211
- Junkers Ju 288
- Prototype concepts that planned to utilize Jumo 222 powerplants:
- Arado E.340 (a twin-engine Jumo 222 design competing in the Bomber B contest)
- Focke-Wulf Fw P.195 (a very large transport aircraft concept powered by six or eight Jumo 222 engines)
Specifications (Jumo 222A/B)
See also
References
Bibliography
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