If a non-ducted fan (open fan), as a solid future for commercial aircraft engines, CFM International wants to dispel all doubts. And for good reason, the Franco-American engine manufacturer, a joint venture between Safran Aircraft Engines and GE Aerospace, continues to lay the groundwork for its Rise Demonstration Program, the successor to the concept. Open rotor remains at the ground testing stage (in 2017), and will preview the next-generation engine for medium-range aircraft entering service by 2035.
On the French side, Safran Aircraft Engines has just unveiled a high-speed test campaign in the giant S1MA wind tunnel at Onera in Modane. Launched last year, it should run until next spring.
The campaign is based on a 1/5 scale demonstration called ECOENGINE. With 200 hours of testing planned, it will enable Safran aircraft engines to continue to mature the concept of unducted fan architecture. Current tests should allow the engine manufacturer to verify the aerodynamic performance of this configuration with the support of the Onera teams. According to Eric Dalbis, Strategy Director of R&T and Innovation at Safran Group, and Pierre Cotensau, Technical and R&T Director of Safran Aircraft Engines, the future engine that will be derived from the Rise will have to use 20% less fuel than the current Leap engine. Acoustic performance is also studied. This will be crucial, as it is a question of leaps and bounds at least in terms of noise footprint and to expect more restrictive regulations in the future. All without the attenuation previously offered by the fan shroud.
Impressive propeller
Unlike a classic turbojet, where the fan blades (the large propeller at the front of the engine) are integrated into the casing, the open fan concept relies on the blades in the open air, so without a fairing. . This makes it possible to have a larger fan diameter while reducing the engine’s aerodynamic drag and thus optimizing its performance. The future Rise demonstrator, which should conduct ground and then flight tests between 2025 and 2027, will thus have a diameter of about 4 meters, twice as large as Leap. It will also run three to four times slower than this. “The most efficient is a large propeller that turns slowly”
, explains Pierre Cotenseau. This fan is completed by a flow straightener, i.e. a stationary vane placed behind to redirect the air flow. These two rows of blades will be equipped with a step, which will give them the possibility of pivoting on themselves depending on the phases of flight. By reversing the pitch, and therefore pushing the air forward, they will also act as a thrust reverser for braking after landing.Conversely, the rear of the engine with the compressor and gas turbine is reduced in contrast, with less significant air flow. This will allow you to go from 1:10 to about 1:50 in the dilution ratio (the difference between the airflow produced by the fan, which produces 90% of the thrust, and the flow through the combustion chamber). . This will help improve propulsion efficiency.
According to the engine manufacturer, this innovative architecture can generate significant savings in fuel consumption. That could represent about two-thirds of the roughly 20% drop in consumption expected between the current generation of Leap and a future open fan. The rest of the benefits will come from the rest of the engine, which will allow for lighter materials and higher temperatures and therefore better combustion, as well as the introduction of innovations such as electric hybridization that will allow power to be controlled at certain specific flight phases. With engines fully compatible with Sustainable Aviation Fuels (SAF), Pierre Cotensue has announced a potential reduction in CO2 emissions of around 80%, but also in non-CO2 emissions such as NOx, particulates and unburnt. It also suggests that this type of open fan architecture could also, in the long run, be adapted to integrate hydrogen.
Future middle distance
All these researches should make it possible to best prepare for the start of a future industrial program following the decision of an aircraft manufacturer – mainly Airbus or Boeing – to launch a new medium-haul aircraft with open fan technology. For the moment, it is the European aircraft manufacturer that is most interested. Airbus is preparing a flight test campaign with the engine mounted under the wing of an Airbus A380, in parallel with tests conducted by Safran Aircraft Engines and GE Aerospace independently and under the CFM International banner. This should be done by the end of the decade. Its aim will be to study the integration of engines on aircraft and to ensure that the benefits offered by an open fan are not canceled out by poor compatibility between the two. For the moment, the option of under-wing integration with a low wing (i.e. the conventional configuration of current airliners) seems favorable. This can facilitate future device integration into the operational world. Boeing has not closed the door for the moment, but prefers to focus on other projects for the time being.
Aircraft manufacturers will make their final choice before the end of the decade. The goal for Safran and GE is to be ready to come on board at that point. To achieve this, Safran Aircraft Engines and other organizations of the Safran group are mobilizing around 1,000 employees on the RISE programme. The investment amounts to one billion euros, of which several hundred million euros are provided by the state, by the Council for Civil Aeronautical Research (CORAC) and by Europe through the Clean Aviation Research Programme. And GE Aerospace is leading a similar effort on its side. However, Safran continues to shy away from other technologies, Eric Dalbis assures, not wanting to close the door permanently because there’s no indication that aircraft manufacturers will be willing to adopt a disruptive architecture instead of a more traditional configuration.
Industrial distribution
This R&T (Research and Technology) phase of Udaya will also enable better definition of industrial sharing between Safran Aircraft Engines and GE Aerospace. Their joint venture is based on an equal distribution of income, without prorating based on each partner’s development or production costs. The two engine manufacturers therefore each have an interest in achieving equal sharing of the technical and industrial burden upstream of the program, as was the case on the CFM56 and Leap.
But if the work on these two engines was simple – the cold parts of the engine (upstream of the combustion chamber) for the Safran aircraft engine and the hot parts (downstream) for GE Aerospace – it turned out to be more complicated for the open fan of the future. Key developments from blower and cooler segments, industrial sharing will be reviewed. If most of the zones have already been allocated according to the historical division, there are few remaining “Gray Areas”
will be shared between the two partners. In the meantime, they are moving in parallel in these areas with the aim of retaining the best options based on their technical but also financial dimension.