Power-egg

A BMW 801 Kraftei (power egg), being unloaded from a Gotha Go 242 transport glider. Russia, March 1943. Note the engine is already fitted with its cowling and cooling fan

A power-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 before mean 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 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.