Power-egg
The power-egg, a literal translation into English of the German term Kraftei, was a design feature in German Second World War era aircraft. The power-egg was a completely "unitized" modular engine installation, consisting of engine and all ancillary equipment, which could be swapped between suitably designed aircraft, with standardised quick-changing attachment points and connectors. In aircraft so designed the power-egg was removed before mean time to failure was reached and a fresh one installed, the removed engine would then be sent for maintenance. In ideal conditions spare engines were placed in sealed containers protected from damage and the elements, to be opened when needed. These 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 Triebswerksanlage format, a more complete unitization format usually including exhaust and oil cooling systems.
Inline and radial engines were both incorporated into Kraftei units : the Junkers Jumo 211 was a pioneering example of engine unitization, as used on both the Junkers Ju 88, with the exact same nacelle packaging used to power the Messerschmitt Me 264 V1's first flights. Both the examples of the Dornier Do 217 medium bomber powered by inline engines, and the Axis Powers' largest-flown powered aircraft of any type, the Blohm & Voss BV 238 flying boat used essentially the same unitized Daimler-Benz DB 603 powerplants. The BMW 801 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 a Motoranlage or Triebswerksanlage format unitized powerplant.
One known surviving Motoranlage-packaged BMW 801 radial still exists and is on restored display at the New England Air Museum, Bradley International Airport, Windsor Locks, CT. [1]