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April 20, 2024
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The engines that power the widebody planes had a difficult start.  PW’s JT9D had some teething troubles as did Rolls-Royce’s RB211.  General Electric developed its CF6 based on an earlier design, the TF39, and the CF6 also had some teething troubles.   (An interesting tidbit –  the TF39 was developed for the C-5 Galaxy, which recently has been re-engined with the CF6)  These engines and their subsequent generations and derivatives went on to serve with distinction – and still do to this day.

The JT9D went to be replaced by the PW4000, while Rolls-Royce kept its RB211 name and GE kept the CF6 name.  What started out as a  ~50,000 lb engine thrust class is what we are discussing here.

These engines are  important from the perspective that they power airline icons in terms of large aircraft.  If you have been flying for years and on a long haul flight, one of these three engines got you from point A to point b, likely without any mishap at all.  These engines set the standard for all future engines as being among the most reliable ever made.  The lessons learned from the early versions were relentlessly refined into what we see on aircraft today.

The category is a three horse race.  It was this class of engine that powered the 747, 767, A300/310/330, DC10/MD11 and TriStar.  So as you can imagine, this was, and still is, a big market for the three engine OEMs. The chart illustrates how the original engine designs were refined and grew in power over the time period.

The purpose of the chart is to show readers how the power evolved for each firm. Note how each firm saw thrust development over time – the thrust choices are particularly varied for Pratt & Whitney.

Rolls-Royce offered its first RB211 in 1972 on the Lockheed TriStar (L1011-1)  and this engine offered 41,030 lb of thrust. This engine went on to power a fair number of Boeing 747-400s as well as a much smaller selection of Boeing 767s (Basically those at British Airways). Of course, the engine saw a number of improvements with later generations. The final version offered in 1991 (RB211-524H-T) came with 60,600 lb thrust.  The chart shows Rolls-Royce had a stable program with power rising by 47.7% over 19 years on nine versions of the original engine.

General Electric first offered its CF6 in 1978 with 45,600 lb thrust on the 747-100B.  This engine also saw numerous tweaks and by 2004 was offering 72,000 lb thrust for the A330.  This is a power growth of 57.9% over 26 year period.  There are 33 versions of this engine, which shows GE’s relentless tweaking to extract improvements from the original design.

Pratt & Whitney offered its first PW4000 in 1987 with 50,000 lbs thrust.  Previously PW offered the JT9D in 1972 at 46,300 lbs thrust on the DC-10-40, and the final JT9D was offered in 1983. Like GE, it tweaked the design relentlessly, seeking higher power as the chart illustrates.  The engine has gone through 23 versions and by 2009 was offering 70,000 lb thrust on the A330.  Over 22 years the engine saw thrust rise by 40%. But note that there is a version of the engine (PW4098) that was offered for the 777-300ER that came with 99,040 lb thrust.  (The 777-300ER is offered with the GE90 exclusively)

Interestingly the original Rolls-Royce RB211 had a thrust to weight ratio of 4.5 and ended up at 6.4.  GE’s CF6 started off with a thrust to weight ratio of 5.1 and is now at 6.4.  The PW4000 started off with a thrust to weight ratio of 5.4 and is now at 5.7.

Finally, a key number for any engine is weight – lighter is always better.  The Rolls-Royce engine weighs 9,470 lbs, the GE weighs 11,225 lbs and the PW weighs 9,332 lbs.

These “big fans” were the forerunners of what we see coming out today on the latest airplanes.  These were the first of the high power high bypass engines.  Their influence will be felt for a long time yet.

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