Pratt & Whitney is celebrating 100 years of aircraft engine innovations while marching full-speed ahead to the next generation of more efficient and sustainable propulsion technologies.
According to Michael Winter, the chief scientist at Pratt & Whitney parent company RTX, changes in engine architecture over the past 100 years have led to several step-changes in capabilities. For example, the invention of the air-cooled radial engine in the 1920s improved the thrust-to-weight ratio by a factor of 2.5 compared with earlier piston engines.
Founded in 1925 by Frederick B. Rentschler, pioneer of the air-cooled radial engine design, Pratt & Whitney’s first engine was the R-1340 Wasp, which led to the popular Wasp series of engines that are still in service today. At the time, the Wasp engine family delivered unprecedented performance and reliability improvements that transformed military and commercial aviation. During World War II, the Ohio-based manufacturer produced more than half a million of those engines, mostly for use by U.S. defense forces.
Pioneering Early Jet Engine Architectures
When gas turbine technology began to take off in the 1940s, the U.S. government wouldn’t allow Pratt & Whitney to pursue the technology because it needed a steady supply of Wasp engines, Winter explained. “After the war ended, the order book just literally hit a cliff, and the company needed to decide: how do we get into gas turbine engines?” The answer was the axial-flow, twin-spool turbine engine—the J57.
“We needed to have a different architecture to get back into the game,” Winter said, “and so what they invented with the J57 in 1958 was a twin-spool gas turbine.” This engine architecture uses two concentric shafts, or spools, to drive two sets of compressors and turbines.
“Instead of really just relying on hot gas spewing out the back to make it go faster and forward, what we came up with was to put a fan in the front like a propeller, and to have that be on a separate shaft,” Winter explained. “You have the same basic machine on the inside—the compressor, a combustor, and a turbine that spins really fast—but now there's a big, long shaft that turns a fan in the front, and then there's a turbine in the very back that basically makes that fan go. So now it's a combination of push and pull. That led to about a 15% efficiency change.”
The J57 became the world’s first 10,000-pound-thrust aircraft engine and remained the most powerful jet engine on the market for years. “It was originally done for a military engine, but it enabled the economics that let commercial aviation in the 1960s really take off,” Winter said. Originally built for the Boeing B-52 bomber, the J57 evolved into what would become the company’s first commercial turbojet engine, the JT3C, which powered Boeing’s 707 and the Douglas DC-8. It was subsequently developed into the J52, a scaled-down version that powered the U.S. Navy’s A-6 Intruder attack aircraft and Hound Dog cruise missile.
In 1958, the company introduced the JT3D, a turbofan version of the JT3C turbojet, on Boeing’s 747. The JT3D added an up-front fan to the existing architecture that increased thrust by 35% and reduced fuel burn by 15% to 22%, according to Pratt & Whitney.
Geared Turbofans Enter the Scene
Over the course of the next few decades, engine technology didn’t change much. Fans were getting bigger, and the amount of bypass—air that bypasses the engine core and gets accelerated by the fan to produce more thrust—increased as well, leading to modest efficiency gains. The next big step change in engine efficiency didn’t arrive until 2015, when Pratt & Whitney introduced an ultra-high-bypass engine known as the Geared Turbofan (GTF), which entered service with the Airbus A320neo series.
With the introduction of the GTF engine, Pratt & Whitney delivered a solution to a paradoxical problem that had plagued engine makers since the 1950s. “The challenge was that with the turbine in the back, the faster it spins, the more efficient it is, but with the fan in the front, the slower it spins, the more efficient it is. So it's always been a paradox,” Winter explained. “Pratt & Whitney broke that paradox by putting a gearbox into the part right where the fan is, so the fan could slow down.” This enabled a 16% efficiency gain and 75% less noise than previous generation engines.
In 2021, Pratt & Whitney announced an updated version called the GTF Advantage. The 34,000-pound-thrust turbofan cut fuel burn for the A320neo by just 1% while delivering 4% to 8% more takeoff thrust. More durable materials and increased airflow in the engine’s hot section reduce operating temperatures and increase time-on-wing by easing maintenance requirements. Both EASA and the FAA certified the GTF Advantage earlier this year.
Beating the Heat
Inside the GTF engine, as the air travels through stages of a compressor, air pressure and temperature rise. Along with higher temperatures and pressures comes greater thermal efficiency, but that efficiency gain is limited by the maximum temperature that the metals inside the engine can withstand. “The one thing that kept us from going to higher thermal efficiency was that the temperatures were too hot,” Winter said. “We’re above the melting point of the metals.”
Pratt & Whitney’s solution to this durability problem was to turn the turbine blades into what Winter called the “world’s most sophisticated heat exchangers” through a combination of special coatings and thousands of tiny laser-drilled holes. The holes allow cooling air on the inside of the turbine blades to ooze out, much like in an air-hockey table, he explained.
Because that “cooling” air coming from the compressor is still hot enough to melt rock, Pratt & Whitney added special coatings to make the metals inside the engine more heat-resistant. According to Winter, these coatings include nickel-based superalloy crystals and ceramic matrix composites.
At Pratt & Whitney’s turbine airfoil production facility in Asheville, North Carolina, engineers use highly automated machinery to drill and coat the turbine blades with superalloys. The company built the 1.2 million-sq-ft facility, which became operational in 2023, to support high-volume production in response to growing demand for the GTF and F135 engines.
Pratt & Whitney has invested about $1 billion into the Asheville blade-and-vane plant, including a recent $285 million project to build an advanced casting foundry to produce the airfoil structures to be drilled and coated.
In 2023, the Asheville facility produced approximately 200,000 high-pressure turbine airfoils. Following the facility’s expansion, the company aims to produce 300,000 parts per year. The facility currently employs around 900 people, and by 2028 Pratt & Whitney aims to increase that number to more than 1,200 employees.
Electrification Is the Future
Winter predicts that, in the future, all commercial jet engines produced by RTX and even its competitors will use some form of the geared-turbofan architecture. And while that basic architecture may not change much, he believes there’s still plenty of room for improvement.
“The airframe companies have said that, until they see double-digit improvements, they won't make a new airplane. And we do see a path forward to do that,” he said, noting that a key enabling technology will be hybrid-electric powertrains.
“If you look at thermal efficiency relative to what theoretically is possible, we've come about halfway. And so there is one way ahead of us, but the temperatures and pressures are higher, which is why we're building these new factories here in the United States—to be able to take advantage of those and reach for those greater efficiencies.”
At the same time, Pratt & Whitney and Collins Aerospace, its sister company under RTX, are actively engaged in several hybrid-electric aircraft programs. These include the RTX hybrid-electric flight demonstrator, which aims to start flight-testing a hybridized Dash 8 turboprop next year.