Bundesarchiv Bild 101I-332-3096-12, Russland, Entladen eines Lastenseglers Go 242

A power-egg is a complete "unitized"

modular Broadly speaking, modularity is the degree to which a system's components may be separated and recombined, often with the benefit of flexibility and variety in use. The concept of modularity is used primarily to reduce complexity by breaking a s ...

engine installation, consisting of engine and all ancillary equipment, which can be swapped between suitably designed equipment, with standardised quick-changing attachment points and connectors. In aircraft so designed the power-egg is typically removed before

mean time to failure There are several kinds of mean in mathematics, especially in statistics. Each mean serves to summarize a given group of data, often to better understand the overall value ( magnitude and sign) of a given data set. For a data set, the ''arithm ...

is reached and a fresh one installed, the removed engine then being sent for maintenance. Spare power-eggs may be stored in sealed containers, to be opened when needed. The power-egg or ''Kraftei'' format was used in some German Second World War era aircraft, particularly for twin or multi-engined airframe designs. It existed in two differing formats – the initial ''Motoranlage'' format which used some specialized added components depending on what airframe it was meant for use on, and the ''Triebwerksanlage'' format, a more complete unitization format usually including exhaust and oil cooling systems.

Applications

Germany

Inline and radial engines were both incorporated into the ''Kraftei'' concept: the

Junkers Jumo 211 The Jumo 211 was a German inverted V-12 aircraft engine, Junkers Motoren's primary aircraft engine of World War II. It was the direct competitor to the Daimler-Benz DB 601 and closely paralleled its development. While the Daimler-Benz engin ...

was a pioneering example of engine unitization, as used on both the

Junkers Ju 88 The Junkers Ju 88 is a German World War II ''Luftwaffe'' twin-engined multirole combat aircraft. Junkers Aircraft and Motor Works (JFM) designed the plane in the mid-1930s as a so-called ''Schnellbomber'' ("fast bomber") that would be too fast ...

using a novel annular radiator for both main engine coolant and engine oil cooling needs (viewable on the

National Museum of the U.S. Air Force The National Museum of the United States Air Force (formerly the United States Air Force Museum) is the official museum of the United States Air Force located at Wright-Patterson Air Force Base, northeast of Dayton, Ohio. The NMUSAF is the ...

's restored Ju 88D-1 reconnaissance aircraft ), with exactly the same nacelle packaging used to power the

Messerschmitt Me 264 The Messerschmitt Me 264 was a long-range strategic bomber developed during World War II for the German ''Luftwaffe'' as its main strategic bomber. The design was later selected as Messerschmitt's competitor in the ''Reichsluftfahrtministerium' ...

V1's first flights. Both the examples of the

Dornier Do 217 The Dornier Do 217 was a bomber used by the German ''Luftwaffe'' during World War II as a more powerful development of the Dornier Do 17, known as the ''Fliegender Bleistift'' (German: "flying pencil"). Designed in 1937 and 1938 as a heavy bomber ...

medium bomber powered by inline engines, and the Axis Powers' largest-flown powered aircraft of any type, the

Blohm & Voss BV 238 The Blohm & Voss BV 238 was a German flying boat, built during World War II. It was the heaviest aircraft ever built when it first flew in 1944, and was the largest aircraft produced by any of the Axis powers during World War II. History Develop ...

flying boat used essentially the same unitized

Daimler-Benz DB 603 The Daimler-Benz DB 603 was a German aircraft engine used during World War II. It was a liquid-cooled 12-cylinder inverted V12 enlargement of the DB 601, which was in itself a development of the DB 600. Production of the DB 603 commenced in ...

powerplants, complete with "chin" radiators under the nacelles as integral components. A differing ''Kraftei'' physical packaging is also believed to have been crafted by the

Heinkel Heinkel Flugzeugwerke () was a German aircraft manufacturing company founded by and named after Ernst Heinkel. It is noted for producing bomber aircraft for the Luftwaffe in World War II and for important contributions to high-speed flight, with ...

firm for the DB 603 engines used on its

Heinkel He 219 The Heinkel He 219 ''Uhu'' (" Eagle-Owl") is a night fighter that served with the German Luftwaffe in the later stages of World War II. A relatively sophisticated design, the He 219 possessed a variety of innovations, including Lichtenstein S ...

A night fighter, as what appears to be the same exact engine installation design used for the He 219A was also used for the quartet of ordered airframes for the same firm's He 177B four-DB 603-engined heavy bomber design's prototype series, as both airframe types' engine "units" used annular radiators and cylindrical cowls of identical appearance to enclose them. The air-cooled

BMW 801 The BMW 801 was a powerful German air-cooled 14-cylinder-radial aircraft engine built by BMW and used in a number of German Luftwaffe aircraft of World War II. Production versions of the twin-row engine generated between 1,560 and 2,000 PS ( ...

fourteen-cylinder, twin-row

radial engine The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders "radiate" outward from a central crankcase like the spokes of a wheel. It resembles a stylized star when viewed from the front, and is ca ...

was also provided in both formats for a number of German designs, especially for twin and multi-engined airframes, with the "M" or "T" first suffix letter designating whether it was a ''Motoranlage'' (the original format of the ''Kraftei'' concept) or the more comprehensively consolidated ''Triebwerksanlage'' format unitized powerplant – the BMW-designed forward cowling ring always used with the 801 incorporated the engine's oil cooler, making it an easy task for aviation engineers to use for such a "unitized" mounting concept. One known surviving ''Motoranlage''-packaged

radial still exists and is on restored display at the

New England Air Museum The New England Air Museum (NEAM) is an American aerospace museum located adjacent to Bradley International Airport in Windsor Locks, Connecticut. The museum consists of three display hangars with additional storage and restoration hangars. Its co ...

Bradley International Airport Bradley International Airport is a public international airport in Windsor Locks, Connecticut, United States. Owned and operated by the Connecticut Airport Authority, it is the second-largest airport in New England. The airport is about halfw ...

, Windsor Locks, CT, with preserved examples of a Ju 88R-1 night fighter and Ju 388L-1 reconnaissance aircraft, one each in the United Kingdom and the United States respectively, also having unitized ''Kraftei''-installation BMW 801 radials on them.

Soviet Union

Project 651E, originally envisaged as a modification of the

Juliett-class submarine The Project 651, known in the West by its NATO reporting name Juliett class, was a class of Soviet diesel-electric submarines armed with cruise missiles. They were designed in the late 1950s to provide the Soviet Navy with a nuclear strike capab ...

, consisted of a small mostly self-contained additional 600 kW nuclear reactor, model VAU-6, the so-called Dollezhal egg. This nuclear powerpack aimed to greatly prolong submerged capabilities of what was otherwise a normal diesel-electric submarine with long duration idling and underwater recharging of batteries. The system was developed but did not see unclassified service through 1985.

United Kingdom

255 Squadron RAF Beaufighter MK II at RAF Hibaldstow Sept 1941

A scheme for unitised engine installations was initiated by the

Air Ministry The Air Ministry was a department of the Government of the United Kingdom with the responsibility of managing the affairs of the Royal Air Force, that existed from 1918 to 1964. It was under the political authority of the Secretary of State ...

in 1937 and after consultation with the

Society of British Aircraft Constructors A society is a group of individuals involved in persistent social interaction, or a large social group sharing the same spatial or social territory, typically subject to the same political authority and dominant cultural expectations. Socie ...

(SBAC) a system was devised allowing standardised dimensions and bulkhead fittings for both inline and radial engine installations of similar power. CASA C-2

The

Bristol Aeroplane Company The Bristol Aeroplane Company, originally the British and Colonial Aeroplane Company, was both one of the first and one of the most important British aviation companies, designing and manufacturing both airframes and aircraft engines. Notable a ...

devised an installation known as a "power egg" for the

Hercules Hercules (, ) is the Roman equivalent of the Greek divine hero Heracles, son of Jupiter and the mortal Alcmena. In classical mythology, Hercules is famous for his strength and for his numerous far-ranging adventures. The Romans adapted the Gr ...

engine in 1938, an example of which was exhibited at the 1938 Paris Aeronautical Salon. The Hercules installation was used on the

Bristol Beaufighter The Bristol Type 156 Beaufighter (often called the Beau) is a British multi-role aircraft developed during the Second World War by the Bristol Aeroplane Company. It was originally conceived as a heavy fighter variant of the Bristol Beaufort ...

, Armstrong Whitworth Albemarle,

Vickers Wellington The Vickers Wellington was a British twin-engined, long-range medium bomber. It was designed during the mid-1930s at Brooklands in Weybridge, Surrey. Led by Vickers-Armstrongs' chief designer Rex Pierson; a key feature of the aircraft is its g ...

Short Stirling The Short Stirling was a British four-engined heavy bomber of the Second World War. It has the distinction of being the first four-engined bomber to be introduced into service with the Royal Air Force (RAF). The Stirling was designed during t ...

, and

Handley Page Halifax The Handley Page Halifax is a British Royal Air Force (RAF) four-engined heavy bomber of the Second World War. It was developed by Handley Page to the same specification as the contemporary twin-engine Avro Manchester. The Halifax has its or ...

Avro Lincoln of 1 SQN RAAF at RAF Tengah in 1950

After an early "Power Unit" installation was devised by

Rolls-Royce Rolls-Royce (always hyphenated) may refer to: * Rolls-Royce Limited, a British manufacturer of cars and later aero engines, founded in 1906, now defunct Automobiles * Rolls-Royce Motor Cars, the current car manufacturing company incorporated in ...

(RR) for the Merlin X and used in the

Armstrong Whitworth Whitley The Armstrong Whitworth A.W.38 Whitley was a British medium bomber aircraft of the 1930s. It was one of three twin-engined, front line medium bomber types that were in service with the Royal Air Force (RAF) at the outbreak of the Second World ...

and

, a more advanced "Power Plant" design was devised for the Merlin XX, a unitized Merlin XX-series engine installation and

nacelle A nacelle ( ) is a "streamlined body, sized according to what it contains", such as an engine, fuel, or equipment on an aircraft. When attached by a pylon entirely outside the airframe, it is sometimes called a pod, in which case it is attached ...

being designed and first used on the Beaufighter Mark II which was later also used on the

Miles M.20 The Miles M.20 was a Second World War British fighter developed by Miles Aircraft in 1940. It was designed as a simple and quick-to-build "emergency fighter" alternative to the Royal Air Force's Spitfires and Hurricanes should their production ...

Avro Lancaster The Avro Lancaster is a British Second World War heavy bomber. It was designed and manufactured by Avro as a contemporary of the Handley Page Halifax, both bombers having been developed to the same specification, as well as the Short Stirlin ...

and Avro York, and the post-war

CASA 2.111 The CASA 2.111 was a medium bomber derived from the Heinkel He 111 and produced in Spain under licence by Construcciones Aeronáuticas SA (CASA). The 2.111 models differed significantly in details from Heinkel's wartime He 111H design while using ...

. Merlin Power Plant production rose from just over 100 in 1939 to nearly 14,000 by 1944, mostly destined for the Lancaster. Avro 696 Shackleton AEW2, UK - Air Force AN1667777

Avro 696 Shackleton AEW2, UK - Air Force AN1667777

A new installation was subsequently designed as the "Universal Power Plant" (UPP) radiator and cowling installation developed for the

Avro Lincoln The Avro Type 694 Lincoln is a British four-engined heavy bomber, which first flew on 9 June 1944. Developed from the Avro Lancaster, the first Lincoln variants were initially known as the Lancaster IV and V; these were renamed Lincoln I and ...

(Merlin 65, 68, and 85) and also used on the

Vickers Windsor The Vickers Windsor was a Second World War British four-engine heavy bomber, designed by Barnes Wallis and Rex Pierson at the Vickers-Armstrongs factory at Brooklands. Design and development As a possible replacement for the pre-war Vickers ...

(Merlin 85), and subsequently used on the

Avro Tudor The Avro Type 688 Tudor was a British piston-engined airliner based on Avro's four-engine Lincoln bomber, itself a descendant of the famous Lancaster heavy bomber, and was Britain's first pressurised airliner. Customers saw the aircraft as ...

(Merlin 100-series), Canadair North Star/Argonaut (Merlin 600-series), and

Avro Shackleton The Avro Shackleton is a British long-range maritime patrol aircraft (MPA) which was used by the Royal Air Force (RAF) and the South African Air Force (SAAF). It was developed by Avro from the Avro Lincoln bomber, which itself had been a devel ...

(Griffon 61 and 62). Capable of mounting either the 27 litre Merlin or the larger 37 litre Griffon, the UPP attached to the nacelle firewall via the SBAC standard circular bulkhead. In the North Star (A Canadian-built variant of the

Douglas DC-4 The Douglas DC-4 is an American four-engined (piston), propeller-driven airliner developed by the Douglas Aircraft Company. Military versions of the plane, the C-54 and R5D, served during World War II, in the Berlin Airlift and into the 1960s ...

) the UPP design had to be changed slightly due to having to use the non-standard Douglas DC-4 bulkhead attachment, resulting in the North Star's cowling panels being tapered slightly rather than parallel-sided. The UPP installation had the advantage that all engines were interchangeable between nacelle positions, i.e., an inboard engine could be exchanged with an outboard engine, and engine types (Merlin or Griffon) and Mark No.s could be mixed and flown on the same aircraft, a

Hucknall Hucknall, formerly Hucknall Torkard, is a market town in the Ashfield district of Nottinghamshire, England. It lies 7 miles north of Nottingham, 7 miles south-east of Kirkby-in-Ashfield, 9 miles from Mansfield and 10 miles south of Sutton-in ...

Lancaster test bed being flown with two Merlins for the North Star in one position, and with two Merlins for the Tudor in the others. Rolls-Royce continued the practice of unitised engine packages post-war with the

Dart Dart or DART may refer to: * Dart, the equipment in the game of darts Arts, entertainment and media * Dart (comics), an Image Comics superhero * Dart, a character from ''G.I. Joe'' * Dart, a ''Thomas & Friends'' railway engine character * Dar ...

and Tyne turboprops, and later with podded jet engines such as the Conway and

RB211 The Rolls-Royce RB211 is a British family of high-bypass turbofan engines made by Rolls-Royce. The engines are capable of generating of thrust. The RB211 engine was the first production three-spool engine, and turned Rolls-Royce from a signif ...

being supplied as complete RR-designed units with all cowling panels and nacelle fittings, including

thrust reverser Thrust reversal, also called reverse thrust, is the temporary diversion of an aircraft engine's thrust for it to act against the forward travel of the aircraft, providing deceleration. Thrust reverser systems are featured on many jet aircraft ...

, ready for attachment to the engine pylon.

United States

In the United States

Pratt & Whitney Pratt & Whitney is an American aerospace manufacturer with global service operations. It is a subsidiary of Raytheon Technologies. Pratt & Whitney's aircraft engines are widely used in both civil aviation (especially airlines) and military aviat ...

produced a R-2180-E Twin Wasp E "power egg" installation certificated in 1945 for use as an engine upgrade for the

, however finding few buyers, it was eventually only used on the

Saab 90 Scandia The Saab 90 Scandia was a civil passenger aeroplane, manufactured by the Svenska Aeroplan Aktiebolaget (SAAB), in Linköping, Sweden. In 1944, as it was becoming clear that hostilities in Europe (the Second World War) would soon be at an end, SA ...

."World Encyclopedia of Aero Engines - 5th edition" by

Bill Gunston Bill Gunston (1 March 1927 – 1 June 2013) was a British aviation and military author. He flew with Britain's Royal Air Force from 1945 to 1948, and after pilot training became a flying instructor. He spent most of his adult life doing research ...

, Sutton Publishing, 2006, P.164

References

{{Reflist

External links

"Interchangeability"
a 1939 ''Flight'' article

a 1944 ''Flight'' article

a 1942 ''Flight'' article

a 1942 advertisement in ''Flight'' Aircraft engines