The Williams FJ44 is a family of small, two-spool, turbofan engines produced by Williams International/Rolls-Royce for the light business jet market. Until the recent boom in the Very Light Jet market, the FJ44 was one of the smallest turbofans available for civilian applications. Although basically a Williams design, Rolls-Royce was brought into the project, at an early stage, to design, develop and manufacture an air-cooled HP turbine for the engine. The FJ44 first flew on July 12, 1988 on the Scaled Composites/Beechcraft Triumph aircraft.
Production started in 1992 with the 1900 lbf (2.58 kN) thrust FJ44-1A, which comprises a 20.9 in (531 mm) diameter single stage fan plus a single intermediate pressure (IP) booster stage, driven by a 2 stage low pressure (LP) turbine, supercharging a centrifugal high pressure (HP) compressor, driven by a single stage high pressure (HP) turbine. The combustor is an annular design and the bypass duct full length. Specific fuel consumption at 1900 lbf (2.58 kN) thrust at SLS, ISA is understood to be 0.456lb/hr/lbf. A derated version, the 1500 lbf (2.03 kN) thrust FJ44-1C has an SFC of 0.460lb/hr/lbf.
An uprated version, the 2,300 lbf (10,000 N) thrust FJ44-2A, was introduced in 1997. It has a 21.7 in (551 mm) diameter fan, with two additional booster stages to increase core flow. Owing to stressing considerations, the centrifugal compressor is throttled-back aerodynamically to a lower HPC pressure ratio than the -1. Other features include an exhaust mixer and an electronic fuel control unit.
The 2400 lbf (3.25 kN) thrust FJ44-2C is similar to the -2A, but incorporates an integrated hydro mechanical fuel control unit. Further uprates include the 2004 introduction of the 2820 lbf (3.82 kN) thrust FJ44-3A, which is similar to the -2A, but features an increased diameter fan and dual channel FADEC (Full Authority Digital Engine Control) unit. The 2490 lbf (3.38 kN) thrust FJ44-3A-24 is a derated version of the -3A.
In development (as of early 2006) is the 3500 lbf (4.75 kN) thrust FJ44-4, which has a hi-tech fan of larger diameter than the -3 unit.
In 2005, a new low end version, the FJ44-1AP, was introduced, with a 1965 lbf (2.66 kN) takeoff thrust, 5% better specific fuel consumption, and lower internal temperatures. The -1AP is similar to the -1A, except for a higher pressure ratio fan, a new combustor and LP turbine, a new full length bypass duct/exhaust mixer and a dual channel FADEC.