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Apower-egg is a complete "unitized"modular 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 beforemean time to failure 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 orKraftei 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 initialMotoranlage format which used some specialized added components depending on what airframe it was meant for use on, and theTriebwerksanlage format, a more complete unitization format usually including exhaust and oil cooling systems.
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Inline and radial engines were both incorporated into theKraftei concept: theJunkers Jumo 211 was a pioneering example of engine unitization, as used on both theJunkers Ju 88 using a novel annular radiator for both main engine coolant and engine oil cooling needs (viewable on theNational Museum of the U.S. Air Force's restoredJu 88D-1 reconnaissance aircraft[1]), with exactly the same nacelle packaging used to power theMesserschmitt Me 264 V1's first flights. Both the examples of theDornier Do 217 medium bomber powered by inline engines, and the Axis Powers' largest-flown powered aircraft of any type, theBlohm & Voss BV 238 flying boat used essentially the same unitizedDaimler-Benz DB 603 powerplants, complete with "chin" radiators under the nacelles as integral components. A differingKraftei physical packaging is also believed to have been crafted by theHeinkel firm for the DB 603 engines used on itsHeinkel He 219A 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'sHe 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.[citation needed]
The air-cooledBMW 801 fourteen-cylinder, twin-rowradial engine 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 aMotoranlage (the original format of theKraftei concept) or the more comprehensively consolidatedTriebwerksanlage format unitized powerplant – the BMW-designed forward cowling ring always used with the 801incorporated the engine's oil cooler, making it an easy task for aviation engineers to use for such a "unitized" mounting concept.[citation needed]
One known survivingMotoranlage-packagedBMW 801 radial still exists and is on restored display at theNew England Air Museum,Bradley International Airport, Windsor Locks, CT,[2] with preserved examples of aJu 88R-1 night fighter andJu 388L-1 reconnaissance aircraft, one each in the United Kingdom and the United States respectively, also having unitizedKraftei-installation BMW 801 radials on them.[citation needed]
Project 651E, originally envisaged as a modification of theJuliett-class submarine, consisted of a small mostly self-contained additional 600 kW nuclear reactor, model VAU-6, the so-calledDollezhal 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.[3]
A scheme for unitised engine installations was initiated by theAir Ministry in 1937 and after consultation with theSociety of British Aircraft Constructors (SBAC) a system was devised allowing standardised dimensions and bulkhead fittings for both inline and radial engine installations of similar power.[4]
TheBristol Aeroplane Company devised an installation known as a "power egg" for theHercules engine in 1938,[5] an example of which was exhibited at the 1938 Paris Aeronautical Salon.[6] The Hercules installation was used on theBristol Beaufighter,Armstrong Whitworth Albemarle,Vickers Wellington,Short Stirling, andHandley Page Halifax.[7]
After an early "Power Unit" installation was devised byRolls-Royce (RR) for theMerlin X and used in theArmstrong Whitworth Whitley andVickers Wellington, a more advanced "Power Plant" design was devised for the Merlin XX,[8] a unitized Merlin XX-series engine installation andnacelle being designed and first used on the Beaufighter Mark II which was later also used on theMiles M.20,Avro Lancaster andAvro York, and the post-warCASA 2.111. Merlin Power Plant production rose from just over 100 in 1939 to nearly 14,000 by 1944, mostly destined for the Lancaster.[9]
A new installation was subsequently designed as the "Universal Power Plant" (UPP) radiator and cowling installation developed for theAvro Lincoln (Merlin 65, 68, and 85) and also used on theVickers Windsor (Merlin 85), and subsequently used on theAvro Tudor (Merlin 100-series),Canadair North Star/Argonaut (Merlin 600-series), andAvro Shackleton (Griffon 61 and 62).[citation needed]
Capable of mounting either the 27 litre Merlin or the larger 37 litreGriffon, the UPP attached to the nacelle firewall via the SBAC standard 56 in (1.4 m) circular bulkhead. In the North Star (A Canadian-built variant of theDouglas DC-4) the UPP design had to be changed slightly due to having to use the non-standard Douglas 60 in (1.5 m) DC-4 bulkhead attachment, resulting in the North Star's cowling panels being tapered slightly rather than parallel-sided.[10] 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, aHucknall 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.[11]
Rolls-Royce continued the practice of unitised engine packages post-war with theDart andTyne turboprops, and later withpodded jet engines such as theConway andRB211 being supplied as complete RR-designed units with all cowling panels and nacelle fittings, includingthrust reverser, ready for attachment to the engine pylon.[12]
In the United StatesPratt & Whitney produced aR-2180-E Twin Wasp E "power egg" installation certificated in 1945 for use as an engine upgrade for theDouglas DC-4, however finding few buyers, it was eventually only used on theSaab 90 Scandia.[13]