Turbofan and turboprop/turboshaft engines for business aircraft of all sizes have made great strides over the last two decades in terms of improved efficiency and lower emissions in models including the GE Honda HF120, Pratt & Whitney PW800 and PW545D, Honeywell HTF7000 series, GE Passport, and Rolls-Royce Pearl. These new engines reduce fuel burn by up to 20% compared with legacy technology and feature innovative designs, materials, and production techniques. The efficiency gains come largely in the form of engines that deliver more thrust—and therefore faster times to climb and overall ranges—with nearly the same amount of fuel.

Unlike next-generation engines developed for airliners, which can gain efficiency by increasing fan size, new business jet engines rely on operating at higher temperatures and greater thermal efficiency with redesigned low-pressure turbines, exhaust nozzles, and shaped fan blades made together in a single forging called a blisk to save weight and reduce maintenance. Greater use of composites and additive manufacturing also saves weight and reduces parts counts, simplifying manufacturing and maintenance.

While long-established aircraft OEMs typically work closely with legacy engine manufacturers, a new crop of supersonic fixed-wing and at least one helicopter manufacturer have decided to develop their own engines, attempting to achieve new levels of performance and reduced costs.

Despite the daunting challenges associated with choosing this path, several of these companies are reporting significant progress, as is at least one company that is developing a novel-design diesel engine as a replacement option for a variety of legacy Part 23 and kit general aviation piston-powered aircraft as that sector of the aviation industry continues to confront the myriad of technical challenges accompanying the adoption of unleaded (UL) fuel as a substitute for 100LL.

AIN looked at the latest business and general aviation aircraft engine developments at the start of 2025 and their prospects for future applications.

Rolls-Royce Pearl 10X

Rolls-Royce spent the bulk of 2024 flight-testing its new Pearl 10X turbofan slated for installation on the new Dassault Falcon 10X ultra-long-range business jet. Those test flights, conducted on a Boeing 747-200 testbed aircraft, have now been completed after logging 36,000 nm and 2,300 hours at speeds up to 0.9 Mach at altitudes up to 45,000 feet. Initial deliveries to Dassault are expected next year, and the 10X is slated for customer deliveries in 2027.

Exact thrust rating for the 10X engine has yet to be determined. The Pearl 700, which will power the G800 and is currently flying on the recently certified Gulfstream G700, has a thrust rating of 18,250 pounds. A scaled version of the engine, the Pearl 15, also is used on the Bombardier Global 5500/6500 series. On the Gulfstreams, the Pearl delivers a 12% better thrust-to-weight ratio and a 5% better efficiency compared to Rolls-Royce’s previous BR700 series engines.

The Pearl is built around Rolls-Royce’s Advance2 engine core and low-emissions ALM combustor. The engine’s gearbox is designed for higher power extraction, and overall the engine is expected to yield lower noise and 5% better efficiency than on Rolls-Royce BR700 series business jet engines.

The design features a 24-blade titanium fan blisk, 10-stage HP compressor with six titanium blisks and 24:1 pressure ratio, shroudless two-stage high-pressure turbine with shroudless blade design with enhanced aerodynamics and blade cooling; and four-stage low-pressure turbine with higher fan power for more thrust with 3D airfoil geometry and 360-degree low eight cast stators. Composites are used extensively in a drive to reduce weight. The “slim-line” nacelle includes target door thrust reversers that are aerodynamically optimized. Other composite applications include bypass ducts, maintenance doors, fan track liners, spinners, and cable bushings. Enhanced acoustic treatment improves noise reduction.

Rolls-Royce also is proposing Pearl technology as the powerplant foundation for the uncrewed remote carrier system for the future combat air system being developed jointly by France, Germany, and Spain.

GE Passport & Catalyst

The GE Passport engine currently powers the Bombardier Global 7500 and will also be on the upcoming Global 8000. FAA-certified in 2016, the twin-spool design features a 52-inch, 18-blade titanium blisk fan, a 5.6:1 bypass ratio, and a 45:1 overall pressure ratio. It is GE’s first integrated powerplant design that builds the core and nacelle as an integrated unit.

The design borrows extensively from the CFM LEAP engines developed to power Airbus’ narrow-bodied “neo” (new engine option) variants and includes a 10-stage HP compressor with both titanium blisks and nickel alloy blades.

The cowling, exhaust cone, and mixer make extensive use of advanced composites and ceramics, and the nacelle, developed with Safran, reduces weight and drag. GE claims the engine has an 8% lower specific fuel consumption compared to the Rolls-Royce BR725 on the Gulfstream G650.

An upgrade to the engine on the Global 8000, also available via STC on the Global 7500, will enable those aircraft to achieve an industry-leading top speed of Mach 0.94. Jennifer Ratica, president of Passport and CFE for GE Aerospace, told AIN that the update does not involve “turbo-machinery” changes but rather software alterations. However, she said those changes, which require FAA approval, “are going to unlock some potential that we had already designed into our engine.”

Melvyn Heard, GE’s general manager for business aviation, told AIN that as of October, the Passport was powering a Global 7500 fleet approaching 200 aircraft that had amassed 400,000 flight hours and 140,000 cycles. “Overall, the operators are very happy,” he said. Heard said the health usage and monitoring system (HUMS) on the engine is streaming “terabytes” of data “that allows us to get a lot smarter on how we understand aircraft operations,” identify trends across the fleet, and quickly take any required actions.

GE is using the Passport as the demonstration platform, in collaboration with NASA, on the agency’s Hybrid Thermally Efficient Core (HyTEC) program aimed at driving further fuel efficiencies in the next generation of commercial jet engines for 2030 and beyond. Part of that strategy involves using the engine core to drive substantially more electric systems on aircraft via electric motors embedded with the main engines. (Pratt & Whitney also is working with NASA on the program.)

HyTEC also will focus on the development of advanced high-pressure compressors and turbine aerodynamics and enhanced combustor materials including ceramic matrix composites.

Participation in HyTEC is a component of CFM International’s Revolutionary Innovation for Sustainable Engines (RISE). CFM is a long-running engine joint venture between GE and Safran that has been responsible for the production of more than 37,000 commercial jet engines over the last 50 years.

Meanwhile, GE’s 1,300 shp Catalyst turboprop engine for the Beechcraft Denali is nearing the completion of certification as of press time. The engine features single-lever power control with Fadec, a three-stage power turbine, a reverse-flow combustor with advanced fuel nozzles, and a four-stage axial single centrifugal compressor that yields a 16:1 pressure ratio.

Advanced technology incorporated into the design includes a variable-geometry turbine with stator vanes that turn in flight, enabling increased pressure and temperature inside the engine. The package produces 20% fewer CO2 emissions, 18% better specific fuel consumption, and 10% more thrust compared to comparable engines, according to GE. An international team of 400 engineers and technicians worked on the program from GE facilities in the Czech Republic, Italy, Germany, and Poland.

Honeywell HTF7000 series

The Honeywell HTF7000 series currently powers the Bombardier Challenger 300, 350, and 3500 series; Gulfstream G280; Embraer Legacy 450/500 and Praetors; and Cessna Citation Longitude, providing takeoff thrust between 6,944 and 7,665 pounds. Approximately 3,000 engines are currently in service, and the list of aircraft it flies on could be growing. In early December, Honeywell signed a $17 billion agreement with Bombardier for avionics and other upgrades to the installed fleet as well as “focus on evolutions of power, reliability, and maintainability, led by the next-generation model of Honeywell's HTF7000 engine,” according to the company, fueling rumors that Bombardier is looking at a new entry in the super-midsize business jet category.

Compared with the company’s ubiquitous 3,000- to 5,000-pound-of-thrust TFE731 geared engine series that began powering business jets in the 1970s, the HTF7000 series is a direct drive model that offers substantially more thrust with a new core capable of variants that can generate up to 12,000 pounds of thrust and incorporates advanced materials and designs including a high-efficiency, low-emission combustor.

Dave Marinick, president of engines and power systems for Honeywell Aerospace Technologies, told AIN that the company is continuing to pursue HTF7000 engine upgrades, in part, to stay “well ahead of emissions standards” including noise. Marinick also said the company is “very interested in hybrid” engine technologies and that the HTF7000 “has an opportunity to be configured for hybrid.” Overall, he said the company is preparing for an era of “more electric aircraft” with technologies that include hydrogen fuel cells, noting that the company “first burned hydrogen in our APUs (auxiliary power units) more than 20 years ago” and that Honeywell is currently working on a “1-megawatt class proton exchange membrane fuel cell that we believe can also find a subscription in a future aircraft architecture.”

However, of more immediate customer interest, Honeywell unveiled its Ensemble health usage and monitoring system in October that monitors more than 50,000 engine parameters and automatically collects, downloads, and transmits the information after each flight.

Ensemble allows customers and Honeywell to approach maintenance more proactively and reduce administrative burdens, particularly for customers already enrolled in a Honeywell maintenance program because it eliminates the need to access a portal and log data as the system runs continuously in the background.

Pratt & Whitney Canada PW545D & PW800

The PW545D is the latest variant in the engine maker’s series of PW500 turbofans and will power the new Cessna Citation Ascend midsize business jet that is expected to enter service in 2025. The PW545D received Transport Canada certification in May 2024, quickly followed by FAA validation. Features include Fadec with integrated autothrottle, an advanced mixer, and compressor efficiencies that will reduce fuel burn and noise.

More than 4,600 PW500 series engines are in service powering a range of Cessna Citation and Embraer jets. The PW545D supports the company’s flight, acquisition, storage, and transmission (FAST) health usage and monitoring system, and customers with FAST enrolled in the OEM’s Eagle Service Plan (ESP) can take advantage of a 6,000-hour TBO option.

The larger PW800 series turbofans currently provide power in the 10,000- to 20,000-pounds-of-thrust class and are flying aboard Gulfstream’s G500 and G600 and the recently certified Dassault Falcon 6X. Compared with legacy engines in the class, the PW800 is more fuel efficient and requires 40% less maintenance and 20% fewer scheduled inspections, according to the company. The engine shares a common core with the PW1000G developed for airline applications.

Williams FJ44-4C

Engine maker Williams has been selected to power Honda’s new light jet entry, the Echelon. Williams already powers most of the light jet market with its FJ44 and FJ33 series engines on aircraft including Cessna Citation CJs, Cirrus Vision Jet, Premier, and Pilatus PC-24. Overall, more than 8,000 light jet engines are enrolled in the company’s TAP Blue product support program. Williams’ engines feature innovations including blisk fans and rotating fuel nozzles.

Build Your Own

For some aircraft OEMs, either technical or price point barriers—and sometimes both—force them to chart a new path, either building onto an existing engine or designing anew from scratch. The path to do so is often lengthy and complex.

Hill Helicopters’ GT50

CEO and founder Jason Hill said the price point of off-the-shelf OEM engines made developing its 500 shp single-stage gas turbine in-house an imperative. “Producing a next-generation turbine engine is a very big deal, not because it’s difficult, but because it is absolutely crucial to being able to deliver next-generation light aircraft at commercially viable prices,” he said in December.

Hill maintains that he can get unit costs under $100,000, based on an annual run rate of 500. And that’s important when you are marketing a new-design, five-seat kit helicopter, the HX50, for under $1 million.

Hill is attacking the problem with a design with a heavy dose of 3D printing (aka additive manufacturing) and a modular design that is “simpler, more efficient, lighter, and easier to manufacture” with “an extremely low parts count” and that is “easy to maintain.”

“Our fuel nozzles are actually removable from the outside of the engine, so they can be changed and checked and modified,” Hill said. “The fuel manifolds can be accessed from the outside as well.”

The engine also uses air-blast atomized fuel injectors for better efficiency and fewer emissions. Hill has refined a new annular combustor that will run on both conventional and synthetic biofuels. The company has reached the final stages of completing the aerodynamic optimization and is developing bearings, turbine blisks, gears, transmissions, and fabricated metal components. It plans to have a completed engine running by the end of June 2025.

DeltaHawk: Confronting the Challenges of UL

The FAA-industry collaboration to eliminate the use of leaded avgas in general aviation aircraft by 2030 with UL (unleaded) fuels continues to face technical and supply challenges. Meanwhile, piston engines capable of running on jet-A are seen as one possible solution to the problem posed by the continued use of leaded avgas.

DeltaHawk is developing a family of fuel-efficient general aviation diesel engines as a replacement and original power for piston-engine general aviation aircraft. The company’s jet-A-fueled 180-hp DHK180 engine received FAA certification in 2023. This year, the company announced agreements with OEMs Piper Aircraft and Vulcanair Aircraft to power models of those companies’ aircraft, including Piper’s PA-44 Seminole twin. Piper and DeltaHawk are jointly developing a related STC for the Seminole. DeltaHawk also is collaborating with kit plane manufacturers including Bearhawk Aircraft.

DeltaHawk is working on variants up to 235 hp. The clean-sheet design features an inverted-V engine block, turbocharging and supercharging, mechanical fuel injection, liquid cooling, direct drive, and 40% fewer moving parts than other engines in its category, according to the company.  The engine is controlled via mechanical linkages, has a limited number of sensors, and is designed for most components to be externally accessed including the fuel pump.

Super & Hypersonics

Boom Symphony

Working with key suppliers including StandardAero and ATI, Boom Supersonic is developing its own 35,000-pound-thrust, twin-spool, medium-bypass turbofan Symphony engine for its Overture supersonic passenger aircraft (55 seats in airline configuration). The engine is designed to power the Overture to supersonic speeds without employing afterburners.

It incorporates a traditional turbofan design with an axisymmetric supersonic intake, variable geometry exhaust nozzle, and a cooled high-pressure turbine. The hollow-core blades are mated to a 72-inch main fan. The engine is designed to run on 100% sustainable aviation fuel and meet ICAO Chapter 14 noise restrictions.

The first 3D-printed parts have been produced for Symphony, including fuel nozzles and turbine center frames. The purpose-built engine already has run 30 engine hardware rig tests for key engine components including fans, nozzles, and combustors.

Fully operational engine core tests that will analyze the performance of the compressor, combustor, and turbine section are slated for late 2025. Forging of the engine’s superalloys for the compressor and turbine began in November.

ATI is providing the high-temperature materials and components for Symphony’s high-pressure compressor integrated blade and disk stages and for its turbine assembly including nickel-based superalloys. StandardAero will assemble, test, and support the engine from its San Antonio, Texas facility where it will have the capacity to assemble up to 330 engines annually.

Boom is aiming to have the aircraft certified and into production by 2030 from its factory in Greensboro, North Carolina.

Hermeus

Hermeus is developing the Chimera II, a turbine-based combined cycle engine capable of transitioning from turbojet to ramjet modes and powering aircraft to Mach 5 hypersonic speeds. For Chimera II, the company will modify a commercially available, off-the-shelf Pratt & Whitney F100 engine (29,160 pounds of thrust) with its proprietary inlet, precooler, ram burner, and bypass system derived, in part, from 3D printing.

The F100 propels the aircraft to Mach 2.8 and then the ramjet system kicks in to do the rest. The F100 originally was developed for military aircraft including F-16 and F-15 fighters. The Chimera II is slated to fly on the Hermeus Darkhorse uncrewed aircraft and build on the work of the company’s Chimera engine program, which uses GE’s smaller 5,000-pound-of-thrust J85 engine as its core. Darkhorse is expected to provide the technological foundation for Hermeus’s Halcyon Mach 5 passenger aircraft.