page_title: General Electric CJ805
section_title: CJ805-23
hierarchical_section_title: General Electric CJ805 / Design and development / CJ805-23
caption_attribution_description: English: General Electric CJ-805-23 mounted to Swissair Convair 990
context_page_description: The General Electric CJ805 is a jet engine which was developed by GE Aviation in the late 1950s. It was a civilian version of the J79 and differed only in detail. It was developed in two versions. The basic CJ805-3 was a turbojet and powered the Convair 880, while CJ805-23, a turbofan derivative, powered the Convair 990 airliners.
context_section_description: Several airlines asked Convair for a larger version of the 880 with potential transatlantic range. Such a design would be larger to hold more seating, as well as having to carry more fuel. To power it, a more powerful engine would be needed. By this time, the Rolls-Royce Conway was entering service, and the Pratt & Whitney JT3D was following close behind. These designs both had twin-spool compressors, as opposed to using variable stators, and the lower speed of the front, low-pressure, spool make it easy to power a fan.
  The problems RR and P&W had addressed with the two-spool system had been solved on the J79 with the variable stators, so in relative terms, the single compressor rotational speed was much faster than the low-pressure stage of these other engines. This meant it was not suitable for direct connection to a fan stage. Instead, GE solved this problem with the addition of a completely separate fan system at the rear of the engine, powered by a new turbine stage. The system was essentially a bolt-on extension to the existing design and had almost no effect on the operation of the original engine.
  Each turbine blade was an integral part of a "blucket", the outboard section of which was a fan rotor blade. Running freely on a stub shaft, a series of buckets, mounted on a disc, made up the aft rotor assembly. The efflux from the turbojet expanded through the (inner) turbine annulus, thus providing power directly to the fan blades located in the outer annulus. A full-length cowl, an annular exhaust system and a bucket thrust-reverser were fitted for the Convair 990.
  The unique feature of the -23 was the transonic single stage fan.  NACA had done a lot of research on multistage transonic compressors during the 50s.  Using this data, GE decided to design and test a high-pressure ratio single stage transonic fan.  Much to their amazement the unit more than met the design target, including that of high efficiency.  A modified version of this research unit was subsequently incorporated into the CJ805-23 aft fan.  With no experience of transonic fan design and little time available, Pratt & Whitney had to resort to using 2 fan stages to produce a similar pressure ratio for their JT-3D turbofan.  Although not an overhung design, the -23 transonic fan did not require any inlet guide vanes.  There was, however, a series of structural vanes to help support the fan casing.
caption: The turbofan CJ805-23 powered the Convair 990 airliners
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