The Boeing 777 is an enormous aircraft, and nearly all of its variants have a higher maximum takeoff weight (545,000 lbs – 766,000 lbs) than an Airbus A340-200 or A340-300 (606,000 lbs – 610,000 lbs). However, the 777 has just two engines, while the A340 is powered by four. To get this behemoth off the ground with just two engines, these turbofans have to be enormous.
Many first-generation 777 variants and all second-generation variants (777-300 ER, 777-200LR, and 777F) are powered by the General Electric GE90. This family of high-bypass turbofans comprises the largest and most powerful engines in commercial aviation, outsizing other large engines used on the 777, and these engines produce the same power as 1,500 SUVs. This article details why enormous engines like the GE90 had to be developed to power the 777.
A Two-Turbofan Configuration Means More Power Per Engine
Boeing’s insistence on the jet having just two engines meant that each engine had to produce a colossal amount of power to make a similar output to a four-engined aircraft. Boeing chose not to build a jet with four engines because the 757 and 767 models demonstrated that twin-engine jets could have lower program costs with much higher efficiency. The Boeing 777-200 burns 6,080 kg of fuel per hour, while the largest variant, the 777-300ER, burns 7,500 kg of fuel per hour.
On the other hand, the A340-300 burns 6,500 kg of fuel per hour despite seating fewer passengers, according to All I Know About Aviation. Furthermore, after 1985, twin-engine aircraft were given the required Extended-range Twin-engine Operational Performance Standards (ETOPS) needed for long-range flying, meaning four engines were no longer a necessity for long-haul flying.
Boeing’s commitment to a two-engine aircraft undoubtedly paid off, and the 777 offered 10% more efficiency per seat-mile than the Airbus A330, despite it being a newer and smaller jet. Seven out of the eight airlines that worked directly with Boeing during the 777 development later placed substantial orders for the aircraft, and they also returned for newer variants. The only outlier was Qantas.
Developing The GE90
The GE90 emerged in 1990 from competition to build an enormous turbofan engine for the 777, facing up against Pratt & Whitney and Rolls-Royce. The three manufacturers proposed huge jet engines with fan diameters ranging from 2.8 to 3.1 meters to produce the required power. The GE90 was developed in collaboration with Snecma (France), IHI (Japan), and Avio (Italy). The major innovation used in the GE90 was that its 22 fan blades were made from carbon fiber composites
This represented a substantial upgrade from the titanium fan blades that were traditional at the time. The carbon fiber blades had double the strength but a third of the weight of titanium blades. This technology had been used previously in the experimental GE36, which was a hybrid turbofan-turboprop engine that McDonnell Douglas considered using to power the MD-90. However, this engine was substantially smaller, producing just 25,000 lbf (110 kN).
The GE90 had substantially fewer fan blades than General Electric’s previous large turbofan, which had a much greater diameter. The CF6 had 38 blades, producing a heavier and less aerodynamic engine. Despite its advancements, the GE90 remained in competition with the two other engines powering the first-generation 777s. The then-CEO, Brian H. Rowe, lobbied hard to develop a GE90 variant for the Airbus A330, but Airbus declined and focused on the A340 as its main long-haul product.
The GE90 Engine Performance
The table below breaks down the GE90’s key performance specifications. This data applies to the first wave of GE90 engines (variants -76B/-77B/-85B/-90B/-94B) and was used by the first generation of 777s. Meanwhile, the second wave, variants -110B1/-113B/-115B, are heavier and produce higher thrust. These engines have curved fan blades, compared to the first generation’s straight fan blades.
|
Length |
286.9 in (7.29 m) |
|---|---|
|
Fan diameter |
123 in (3.1 m) |
|
Weight |
17,400 lb (7,893 kg) |
|
Takeoff thrust |
81,070–97,300 lbf (360.6–432.8 kN) |
|
Bypass ratio |
8.4 – 9 |
|
Thrust-to-weight ratio |
5.59 |
The GE90 also came with a host of adaptations to reduce the environmental impact of aviation. For instance, the engine reduced fuel burn by 5-6% compared with its contemporaries, which came with a reduction in emissions. NOx emissions were also reduced to as low as 10 parts per million, a 33% reduction compared to similar engines. Air pollution wasn’t the only type of environmental damage mitigated by the GE90, as the engine also produced a lower amount of noise.
The successor to the GE90 will be the GE9X, set to power the 777X, which is expected to yield even higher performance. It is the most powerful commercial aircraft engine ever built, maxing out at a world-record 134,000 lbs (597.4 kN) of thrust. The manufacturer invested $2 billion in this engine program, which uses multiple next-generation technologies, such as 3D printing, which were not available when the GE90 was developed. This engine has six fewer fan blades than the GE90.
The Second Generation Of The GE90
The GE90 is a family of engines rather than a monolith, known for its iconic roar that has become a fan favorite. A second generation of GE90s emerged with Boeing’s development of a second generation of 777s in the late 1990s (777-200LR, 777-300ER, and 777F). These were to have a longer range, requiring more powerful engines. Boeing asked its partners to develop an engine that could provide 100,000 lbf (440 kN) of thrust, an enormous amount of power requiring an engine heavier than that used by previous 777 generations.
GE set about developing the GE90-115B engine, while Rolls-Royce proposed developing the Trent 8104 engine. General Electric defeated the rival proposals, signing an agreement to develop the GE90-115B in 1999. This deal stipulated that Boeing would only offer GE890 engines on second-generation 777s. This engine had its first run in November 2001. The table below details the critical performance specifications for the second-generation GE90 engines (-110B1, -113B, and -115B).
|
Length |
286.67 in (7.281 m) |
|---|---|
|
Fan diameter |
128 in (3.3 m) |
|
Weight |
19,316 lb (8,762 kg) |
|
Takeoff thrust |
110,760–115,540 lbf (492.7–513.9 kN)[c] |
|
Bypass ratio |
9 |
|
Thrust-to-weight ratio |
5.98 |
General Electric far exceeded Boeing’s demands for the 777 second-generation engines, producing a powerplant yielding over 110,000 lbf. One key innovation was the curvature of the fan blades, which allows for a more efficient engine as they help accelerate airflow through the engine and reduce vibration at high speed. Curved fan blades also allow for more thrust to be achieved at smaller fan diameters. This is one of the reasons the second-generation GE90 produces substantially more thrust.
The second GE90 generation remains in production, and the engine had a bumper year in 2011, accumulating 400 airline and freight operator commitments with a list price of $11 billion. This improved on the previous record of 250 in 2007. A key reason was Emirates’ order of 50 GE90-115B-powered Boeing 777s. Bill Millhaem, the General Manager of the GE90 Program at GE Aviation, said that:
“The Boeing 777 and GE90 engine combination is growing in popularity with customers worldwide and is the best-selling aircraft-engine combination in its class. Total orders for the GE90 engine family now exceed 2,000 engines with a backlog of 800 engines that will be delivered in the next four years.”
Examining The Other Engines That Power The Boeing 777
The 777-300ER, 777-200LR, and 777F are all powered by the GE90, and the 777-200 and -200ER also use the GE90. However, the 777-200, -200ER, and -300 variants also have the option to be powered by the Pratt & Whitney PW4000 or the Rolls-Royce Trent 800. As a result, all three of the aviation industry’s most iconic aero engine manufacturers are involved in the 777. These are still enormous engines producing 77,200 lbf – 98,000 lbf, but are a touch smaller. The PW4000 is also different because it is used in other aircraft beyond the 777. The table below breaks down the key specifications for both of these engines, which serve as rivals to the GE90 on the Boeing 777.
|
Characteristics |
PW4000-112 |
Trent 800 |
|---|---|---|
|
Maximum thrust |
77,440 lbf – 99,040 lbf |
76,580-92,940 lbf |
|
Length |
190.4 in (4.84 m) |
179.8 in (4.57 m) |
|
Diameter |
112 in (2.84 m) |
110 in (2.8 m) |
|
Weight |
15,095-16,260 lbs (6,847 kg -7,375 kg) |
13,400 lbs (6,080 kg) (Dry) |
|
Overall pressure ratio |
34.2-42.8:1 |
33.9-40.7:1 |
Indeed, although the PW4000-112 is exclusive to the 777, the -94 variant is also known for powering the Boeing 747-400, the Boeing 767, the McDonnell Douglas MD-11, the Airbus A300-600, and the Airbus A310, while the PW4000-100 also powers the Airbus A330. Meanwhile, the Rolls-Royce Trent 800 engine also only powers aircraft from the 777 family.
