GE Aviation and Safran this week jointly launched a development program for what they call an “open fan” airliner engine design. Under the auspices of the two companies’ cooperative CFM International business unit, the RISE (Revolutionary Innovation for Sustainable Engines) initiative focuses on lowering fuel consumption and carbon emissions, and the team projects greater than 20 percent improvements over current high-bypass cowled turbofans. Harking back to the unducted-fan (UDF) engine concept that GE explored in the mid-1980s, the design leaves the fan blades exposed for maximum bypass, improving efficiency over ducted turbofan engines.
While CFM does not call the RISE program an engine launch, it does say the program “will demonstrate and mature a range of new, disruptive technologies for future engines that could enter service by the mid-2030s.” The RISE program also counts compatibility with sustainable aviation fuel (SAF), as well as hybrid-electric and hydrogen propulsion systems, as paramount to its goal of lowering carbon emissions.
The companies simultaneously announced an agreement extending the CFM International 50/50 partnership to the year 2050.
CFM views open fan architecture as “a key enabler to achieving significantly improved fuel efficiency while delivering the same speed and cabin experience as current single-aisle aircraft.” The GE/Safran lead engineering team is counting on modern technologies and materials, including composite fan blades, heat resistant metal alloys, ceramic matrix composites (CMCs) and hybrid electric capability. Additive manufacturing, also known as 3D printing, is fundamental to the success of the program, which is set to involve more than 300 separate component, module and full engine builds, according to CFM. A demonstrator engine is expected to enter testing sometime mid-decade, to be closely followed by flight testing.
Back in the 1980s, it was the Arab oil embargo that spiked oil prices and drove the move toward the inherent greater efficiency of using unducted fan blades. Research into lightweight blades that would not leave the engines as vulnerable to uncontained failure was apparently successful and the engine flew on a testbed aircraft. But a combination of economic factors, including substantially lower oil prices by the end of the decade, shelved the technology at the time.
Seems all the 70s and 80s failed fuel saving ideas are back, even converting fry grease for fuel.
Some of that ’80s tech didn’t fail, it simply became more desirable to stick with what was already known and available as fuel costs came back down. Now it is worth reconsidering more dramatic changes (ie open rotors) as fuel costs look to continue rising.
Most American airline customers (whether correct or not) do not like riding on anything that has a prop. Because of that the US airlines have had little success with prop airliners, the Q400 is a perfect example. The other issue that stopped work on unducted fans is noise. They are noisier than turbofans, unlikely they would ever pass stage 4 noise requirements. There were other technical issues that stopped research also. For example lack of available bleed air for deice.
Failed as in “too expensive” to use. Surprisingly if you believe in catastrophic man made global warming, the UDF makes it slightly easier to burn more fuel well into the future. Go figure.
Easily figured: there is NO replacement for burning fuel for commercial air travel for at least two decades, probably longer.
You get it. The delicious irony of making jets more efficient is that you will basically guarantee the feasibility of burning of fuel into the upper atmosphere for easily another generation or two.
I’m not sitting anywhere near one of them..
So does this eliminate the “uncontained fan disc” failure mode, or make it worse, since there is nothing around the fan to contain it should it fail? I should think the failure rate itself would be greatly reduced.
This is a great idea. But only drawback the UDF was extremely loud and one seems to asking what this engine be just as loud? If so then there no way it will get certified
About loud – what is out there that is a LOUD UDF? Puller, not pusher.
We know the Pisggio & Beech Starship planes are loud multi blade props because they are pushers.
Turbulent entry air to the prop causes noise.
Seems like all of the things that made the UDF unsuccessful 35 years ago, still exist today. Too noisy, the public doesn’t trust a turboprop, uncontained blade failure, ice exposure, ramp safety.
I’m all for fuel saving technology, but I don’t think this one has a customer, much less a market.
WOW! Props are coming back!
The interesting thing about this concept is the configuration: tractor/giant spinner vs. the UDF’s pusher/tailcone. It makes me wonder what “disruptive technology” they have for addressing the UDF’s famed noise. Like, total speculation here, does the small concentric inlet behind the main fan eat some of the fan’s noise? Furthermore, there does not seem to be a seam on the cowling for the 2nd row of blades. Does this suggest that the 2nd row are really variable pitch stator vanes rather than counter-rotating fan blades? If so, could these act to mitigate some of the decibels coming off the fan while not adding decibels of their own? If so, then this could be much quieter than the UDF, which as noted by others, would be a prerequisite for looking at unducted fan technology again.
I passengered in a Q400 in 2019. It was every bit as good as any small jet and in some ways better.
The photograph would seem to indicate that the second row of blades are actually stationary. Most likely variable guide vanes that would straighten the air stream around the engine. Since the bulk of the noise off of a propeller occurs near the tip of the blade, I assume that the use of the scimitar blades are intended to lower the noise output. If memory serves, McDonnell Douglas experimented with UDF designs on the MD-80 series aircraft back in the 1980’s. The main complaint was that while the engines produced less noise to the environment, they created an extremely irritating buzz or hum in the cabin. Perhaps the more rigid composite blades will not have that issue.
I do recall a test bed UDF on a DC9 way back & remember that there was not a solution for prop
de icing at the time.
In my previous career I worked at BFG deicing on that very item. Had a system that worked but could not find a material with the endurance to make the system last. When the UDF/MD95 project ended the company dropped the project and I was out of a job.