|The Williams FJ44-3 engine. The fan is 23 inches in diameter
The Williams FJ44 engine of the CitationJet family has a fascinating history as it's based on the F107 turbofan used on American cruise missiles like the ALCM and the Tomahawk. Williams International started out with marine turboshafts and APUs before getting into small turbofan engines. Sam Williams and his namesake company would rise to prominence in the aviation industry with miniature turbofans but his real dream was a civilian turbofan for general aviation. In the 1980s Williams envisioned a new class of turbofans based on the F107 design that would allow for a new class of general aviation aircraft that were jets half the cost and size of current bizjets with the field performance and economy of turboprop twins.
Sam Williams believed so much in his FJ44 engine design that development continued through the 1980s in the absence of any launch order or production application. Keep in mind that this class of engine had never been used in general aviation and Williams International had never made a civilian production jet engine. Through the 1980s, Williams lobbied numerous general aviation manufacturers about his concept for a light jet aircraft and how he had a superbly economical engine to make such an aircraft feasible. The first manufacturer to agree was Rutan's Scaled Composites who flew the Triumph in 1988. Rutan's design never entered production but it did mark the FJ44's first flight. The next manufacturer to agree to use twin FJ44s was Swearingen in its SJ30 design- even though the aircraft flew, Swearingen and the SJ30 have passed through many ownership changes serial production has yet to occur. Williams' big break came with the third manufacturer- Cessna was looking for an efficient and higher performing successor to its iconic Citation line and launched the Cessna 525 CitationJet family in 1992 with a very substantial order of Williams FJ44 engines, vindicating Sam Williams' dream.
The FJ44 is a joint venture between Williams International and Rolls-Royce and was the company's first civilian engine and first manned aircraft engine. Simplicity and reliability were key to this new class of aircraft and as such, the FJ44 engine has only 700 parts total, 1/4 that of many other bizjet powerplants. The Cessna CitationJet series was the first production application for the FJ44 engine. It wasn't enough to have a simple engine, it also had to have performance and basing the FJ44 on the F107 cruise missile engine gave the FJ44 that foundation. In fact, the F107 that the FJ44 is derived from was such an impressive accomplishment that it won the Collier Trophy- it has 1/10th the weight of the Pratt & Whitney JT8D engine but has the same specific fuel consumption and thrust-to-weight ratio. That performance pedigree translated over well into the FJ44 and it made the engine successful. On the Cessna CitationJet series, the economy and performance of the new engine made the new jet a leap in performance over the Citation 500 series it replaced. While aerodynamic improvements are part of the equation, the FJ44 engine's performance and economics are a large contributor. Compared to a Citation 500 at an identical mid-cruise weight, the CitationJet goes 13% farther with 17% less fuel and it does this 40% faster than the original Citation with the FJ44s having a lower thrust output than the JT15Ds used on the first Citations.
There are four engines in the FJ44 family. The lowest powered one was the first one, the FJ44-1 and it powers the Cessna CJ1 and CJ1+ of the CitationJet family and is also used on the Cessna Citation M2 as well as the Swedish jet trainer Saab Sk60. It has a thrust rating of 1900 to 2100 lbs. The FJ44-1 series first flew in 1988 and went into production in 1992.
The second engine in the family is the FJ44-2 and is based on the core and LP turbine of the FJ44 paired up with a larger fan and new compressor section for increased thrust. Its applications include the Cessna CJ2, the Beech/Raytheon Premier I, and the latest incarnation of the SJ30 design, Syberjet SJ30. Two of Rutan's designs fly with the FJ44, the Scaled Composites Proteus and the Virgin Atlantic Global Flyer that Steve Fossett flew around the world in solo nonstop in 2005. It's also used on two re-engining programs for the Citation 500 and the Learjet 25. The FJ44-2 has a thrust rating of 2300-2400 lbs thrust and went into production in 1997.
The next engine in the family is the FJ44-3 which has a new fan and compressor section for an increase in thrust rating to 3000 lbs. It powers the Cessna CJ2+ and CJ3+ and is used in Nextant's re-engining and remanufacture program of the Beech 400 as well as on a re-engining program for later Citation 500 variants. It went into production in 2004.
The top end member of the FJ44 family is the FJ44-4 with an increase in thrust to 3600 lbs with a larger fan and enlarged compressor. It also features a dual-channel FADEC for more efficiency. It powers the Cessna CJ4 along with the Beech 400XPR remanufacture/upgrade program for the Beech 400. The engine will also power the upcoming Pilatus PC-24 jet.
There is also a scale down of the FJ44 engine, the FJ33, which went into production in 2004 and has a thrust rating of 1000 to 1900 lbs. The fan is only 19 inches in diameter and it powers the Diamond D-Jet and the Cirrus Vision.
Unlike other manufacturers of small jet engines, the FJ44 has no turboprop derivative and there are no turboprops in the Williams portfolio. This is a reflection of Sam Williams' philosophy that given time and technological progress, light turbofans like the FJ44 will displace turboprop engines for most civilian aircraft applications. The FJ44 is one of the landmark engines of aviation history and Sam Williams has earned honors for creating an engine that gave rise to a whole new class of general aviation aircraft.
Source: The History of North American Small Gas Turbine Engines by Richard A. Leyes and William A. Fleming. American Institute of Aeronautics and Astronautics/Smithsonian Institution Press, 1999, pp383-429. Williams International http://www.williams-int.com/. Photos: Williams International