page_title: Power-egg
section_title: United Kingdom
hierarchical_section_title: Power-egg / Applications / United Kingdom
caption_attribution_description: English: Title: THE FIRST OPERATION OF NO 1 SQUADRON, ROYAL AUSTRALIAN AIR FORCE FROM TENGAH, SINGAPORE, AUGUST 1950. One of the first Avro Lincoln aircraft to set off from Tengah on a bombing operation to inaugurate No 1 Squadron's anti-bandit activities in Malaya, revving up its engines before taxying out to the runway.
context_page_description: 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.
context_section_description: A scheme for unitised engine installations was initiated by the Air Ministry in 1937 and after consultation with the Society 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. 
  The Bristol Aeroplane Company devised an installation known as a "power egg" for the Hercules engine in 1938, an example of which was exhibited at the 1938 Paris Aeronautical Salon. The Hercules installation was used on the Bristol Beaufighter, Armstrong Whitworth Albemarle, Vickers Wellington, Short Stirling, and Handley Page Halifax.
  After an early "Power Unit" installation was devised by Rolls-Royce (RR) for the  Merlin X and used in the Armstrong Whitworth Whitley and Vickers Wellington, a more advanced "Power Plant" design was devised for the Merlin XX,, a unitized Merlin XX-series engine installation and nacelle being designed and first used on the Beaufighter Mark II which was later also used on the Miles M.20, Avro Lancaster and Avro York, and the post-war CASA 2.111. Merlin Power Plant production rose from just over 100 in 1939 to nearly 14,000 by 1944, mostly destined for the Lancaster.
  A new installation was subsequently designed as the "Universal Power Plant" (UPP) radiator and cowling installation developed for the Avro Lincoln (Merlin 65, 68, and 85) and also used on the Vickers Windsor (Merlin 85), and subsequently used on the Avro Tudor (Merlin 100-series), Canadair North Star/Argonaut (Merlin 600-series), and Avro Shackleton (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 56 in (1.4 m) circular bulkhead. In the North Star (A Canadian-built variant of the Douglas 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. 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 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 and Tyne turboprops, and later with podded jet engines such as the Conway and RB211 being supplied as complete RR-designed units with all cowling panels and nacelle fittings, including thrust reverser, ready for attachment to the engine pylon.
caption: Universal Power Plant (UPP) Merlin 85 installations on an Avro Lincoln
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