Developments in business aircraft engines
Makers strive to deliver cleaner, more efficient powerplants
By Owen Davies
Contributing Writer
When we last looked into aircraft powerplant developments (Pro Pilot, Oct 2022, p 24), nearly all engine makers were introducing new products, and most were working on development programs we had not considered before. This was also true when we examined electric powerplants (Pro Pilot, Jan 2024, p 30).
In contrast, this is largely a time of consolidation. Most jet engine makers are pursuing established programs or are beginning to enjoy their results. Yet there are still new engines to look at and research and development (R&D) programs worthy of attention. For dessert, we have the unexpected resurrection of an obsolete engine that could power future business aircraft.
Green power
This March, Rolls-Royce (R-R) began testing its 320-kW (429-hp) electric motor – a direct-drive unit for 9- to 19-pax electric and hybrid regional aircraft. But this could be the company’s last advance in electric aviation, as it announced plans to sell off its electrical division.
R-R will supply electric motors for Vertical Aerospace, but they were not expected to be ready in time for the second prototype – the VX4. The first was damaged in a crash last year, and was powered by UK-based Equipmake. Most likely the second will be powered by Equipmake, too.
For conventional aircraft, R-R has demonstrated that every engine in its lineup can run on 100% sustainable aviation fuel.
Safran has completed the first ground test series of its GENeUS 300 motor/generator. As a generator, it can deliver 300 kW (402 hp) with 96% efficiency and a power density of 10 kW/kg. It occupies 1/3 of the volume of a conventional generator.
The company applied for US type certification of its ENGINeUS 100 electric aircraft motor in November 2020. FAA has finally acted, although it has done so by proposing 33 special conditions to supplement Part 33 Airworthiness Standards: Aircraft Engines. Several of these conditions carry secondary requirements. In all, Safran must meet 51 new specifications before the motor is certified – in addition to those in Part 33 not specific to piston or turbine engines. This could take a while.
GE Aerospace
When last we looked at jet engines, GE and Pratt & Whitney Canada (P&WC) had just delivered their prototypes for the $4-billion US Air Force (USAF) Adaptive Engine Transition Program (AETP). GE’s XA100 and P&WC’s XA101 were intended for the upgraded Block 4 Lockheed Martin F-35 Lightning IIs. Both reportedly delivered the required 25% better fuel efficiency, 10% more thrust, and better thermal management. They could provide maximum thrust on demand and an economy mode for 30% more range or 40% more loiter time over target.
Which did the USAF pick? Neither. AETP engines won’t work for the F-35B variant, with vertical takeoff and landing (VTOL) capabilitiy, since carrier-based F-35s would require major re-engineering. This would leave the USAF paying for the refit on its own, and that could be a budget-buster. The service did not even request funding to continue the program in the 2024 fiscal year. The US Congress gave them $280 million anyway. However, the legislation forbids using the money to integrate a new engine into the F-35.
The competitors have shifted their attention to the new USAF priority – the $4.9-billion Next Generation Adaptive Propulsion (NGAP) program, which is intended to power the Next Generation Air Dominance (NGAD) fighter. NGAD is expected to start replacing the Lockheed Martin/Boeing F-22 Raptor before 2030. Unlike previous fighters, it will be a family of systems including the manned aircraft and Loyal Wingman drones, now renamed Collaborative Combat Aircraft.
Five companies – GE, P&WC, Boeing, Lockheed Martin, and Northrop Grumman – each received 10-year, $975-million contracts to develop their respective NGAP designs.
GE also faced P&WC in NASA’s Hybrid Thermally Efficient Core (HyTEC) program, which seeks to develop an engine with a small-diameter, high-pressure core. It is expected to reduce fuel burn and emissions by 5–10% with 4 times the power density of conventional engines. GE has received a $68-million cost-sharing contract to continue integrating core technologies over the next 5 years. P&WC has not.
Finally, last December, GE successfully tested a dual-mode ramjet that uses rotating detonation combustion in scramjet mode. Instead of a normal combustion chamber, the design sets detonations chasing each other around an annular ring. In theory, it will burn 25% less fuel than a turbofan of the same horsepower. GE believes it will allow transitioning from the turbofan to the scramjet well below the Mach 3.5 currently required. That would make manned hypersonic flight practical.
Pratt & Whitney Canada
P&WC has received Canadian type certification for the PW127XT-L, intended for regional airliners. The 2750-shp PW127XT series provides 3% better fuel efficiency than previous models and 20% lower maintenance costs. It requires only 2 scheduled maintenance events in 10 years and an overhaul every 20,000 hours.
Much of P&WC’s work now is going into the company’s F135 engine core upgrade. This more conventional engine for the F-35 is now favored by the US Department of Defense. Exceeding 40,000 ft-lb of thrust with improved fuel efficiency and a 50% increase in thermal management capacity, it can be fitted to all 3 F-35 variants. The first test is set for 2026, with aircraft in the field expected 3 years later.
For fiscal year 2024, the US Congress gave the NGAP program $497 million – more than double the Administration’s request. P&WC is on the job. The first design review of its XA103 NGAP prototype has been completed, and a detailed design review is under way. Ground testing is set for the late 2020s.
P&WC plans to begin flight testing its hybrid-electric demonstrator early next year. It will combine a 1-MW (1341-hp) electric motor with a 1-MW turbine. This powertrain is expected to cut fuel use by 30% from takeoff to landing. It is part of the Scalable Turboelectric Powertrain Technology (STEP-Tech) program – a platform for rapid prototyping of distributed propulsion concepts.
The Switch project, supported by the EU’s Clean Aviation program, is intended for future narrow-body aircraft. Two electric motors would provide only 5% of the thrust available from each engine. They would be used for taxiing or to provide surge power in high-demand moments.
In June, P&WC will deliver the design for ARPA-E’s Hydrogen Steam Injected Intercooled Turbine Engine (HySIITE.) It will burn liquid hydrogen and recycle water from the exhaust to improve power and cooling. This is expected to cut fuel consumption by about 35% and nitrogen oxides by about 80%. Of course, it will emit no CO2 at all.
Rolls-Royce
With a 140-in fan, the R-R Ultrafan is the largest jet engine in the world. A geared turbofan with a variable-pitch fan system built around the Advance3 3-shaft core, it produced 85,000 ft-lb of thrust in a full-power test in November 2023.
It is 10% more efficient than the 97,000-ft-lb Trent XWB, which itself was 10% more efficient than previous R-R engines. It can be scaled down to 25,000 ft-lb thrust or up to 110,000 ft-lb.
The Pearl 10X, built around the Advance2 core, delivers 18,250 ft-lb of thrust. An ultra-low-emission combustor and a new accessory gearbox with reduced power losses yield 5% more efficiency than previous engines in the line. R-R began flight testing the Pearl 10X on its Boeing 747 testbed in April. The engine will power the Falcon 10X, Dassault’s ultra-long-range flagship, scheduled to enter service in 2027.
The turbogenerator R-R began developing 2 years ago is already in testing. It can be scaled from 500 kW (670 hp) for long-distance air taxis to 1200 kw (1609 hp) for commuter planes up to 19 pax. The company expects to run it on anything from Avfuel to hydrogen.
R-R should be making a nice profit from its Pearl 700 engine soon. Based on the Advance2 core, the 18,250-ft-lb turbofan received US type certification in September 2023. The engine is set to power Gulfstream’s G700 and G800 business aircraft, which received type certification in March.
Safran
The EcoPulse hybrid-electric demonstrator entered flight testing at the end of November 2023. The aircraft is a Daher TBM 910 with its standard PT6A-66D turbine in the nose and 6 electric motors on the wings. Testing has been slow-going.
According to one report, by mid-March, the aircraft had accumulated only 1.5 hours under hybrid power. Nonetheless, Daher plans to add hybrid-electric TBMs to its lineup by 2027.
Safran Helicopter Engines plans to offer at least 3 distinct hybrid-electric power systems by the 2030s. Micro-hybridization would shut down one turbine in a twin-engined helicopter in cruise, letting the remaining engine run at optimal power.
Parallel hybridization would add an electric powertrain to a single-engine helicopter as a backup in case of engine failure, or to give a power boost during high-demand flight. Disruptive architectures would use hybrid powertrains for vertical/short takeoff and landing (V/STOL) applications.
Safran will supply a 600-kW (805 hp) turbogenerator for a 9-pax STOL aircraft from Electra Aero in the US. Electra’s high-wing design is expected to fly up to 500 miles at 200 mph. An 80%-scale demonstrator has already flown. Electra Aero should be a lucrative market for Safran. The company already has more than 1600 orders and options from 35 operators. The aircraft is expected to enter service in 2028.
Several aircraft developers have adopted Safran’s ENGINeUS 100 motor, which puts out 100 to 180 kW (134 to 240 hp). European type certification, anticipated last year, has yet to come through.
CFM International
At this 50/50 collaboration between GE Aerospace and Safran, R&D is all about Revolutionary Innovation for Sustainable Engines (RISE).
Unducted-fan turbines have been tried before, notably by GE in the 1980s. They were too noisy for use and not significantly more efficient than conventional engines. However, technology has come a long way since then. CFM expects the RISE prototype to deliver at least 20% better fuel efficiency than enclosed engines, and to cut CO2 emissions by 1/5. Company engineers believe open-fan architecture is the only way to achieve such reductions in a petro-fueled turbofan engine.
Testing of a RISE engine is expected around mid-decade.
Left field
The pulsejet that powered Germany’s V-1 “buzz bomb” during the London Blitz of WWII is making a comeback. The modern version has no moving parts, and it makes a lot less noise.
GE and P&WC both are both designing pulsejets, and Boeing has its own proprietary version. However, a Baltimore MD start-up called Wave Engine Corporation already has a pulsejet in the air on a drone testbed, and the engine has flown on a manned glider.
Unlike the pulsejets of old, the new design confines its detonations using pressure waves instead of metal valves. The basic parts count consists of 1 steel tube. It is a lot less complex and cheaper than turbofans, and it promises higher efficiency.
The company’s J-1 pulsejet is already on the market. It exceeds 50 ft-lb of thrust, and could propel a 100-lb drone. Another model will soon produce 250 ft-lb of thrust for aircraft up to 1000 lb. However, the company’s ultimate goal is to power an airliner. We would not put it
past them.