Hey guys,

As the title suggests, what are the big advances in propulsion heading into the 20s and into the 30s?

At the moment we have GE/Safran in a strong position with leap, especially given its popularity on the neo. But, what’s next for cfm and leap? My understanding is that cfm have focused on mainly engine core tech and materials, rather than the p&w approach of fan and gearbox tech. Cfm seem to be pushing the boundaries of temps and pressures with leap. What’s the next step? Gearbox?

GE. What happens after nx and 9x? I know they’re in very different size categories but which engine is more advanced. The nx came first but are there still technologies in this engine that haven’t yet transferred to the 9x?
Is an updated genx in the works for a 787 re-engine? What tech will it have? Where do the efficiency advances come from?

P&W. Is there any sign on Pratt on a wide body anytime soon? Apart from 767. What are they doing in house to prepare for the next advance in engine tech? Or are they relying on simply scaling up their gtf for a bigger aircraft? How advanced is the gtf core in comparison to leap or even 9x?

RR. Not sure where to start. Big issues on the T1000. How is the -10 variant going? How is the T7000 engine performing? And the xwb? From a tech standpoint, where do RR sit co pared the ge and Pratt?
I know they have ultrafan in the works. Apart from a gear box, will this be a fairly limited tech rise engine? Ie. xwb with a gb?

Sorry for all the questions. Just wanted to start a topic dedicated to the engines of the next 10-15 years.

We’re already in the 20s, so what you see is what you’re getting. We must be nearing the limits of chemistry and engine thermo- and aero-dynamics unless there’s a huge metallurgical advance.

Open Rotor. Ever higher turbofan BPR's are going to come with ever diminishing returns until they hit the point where the cowl drag (and weight) is so massive that further gains of any significance in subsonic engine efficiency can only come from open rotor.

744SPX wrote:

Open Rotor. Ever higher turbofan BPR's are going to come with ever diminishing returns until they hit the point where the cowl drag (and weight) is so massive that further gains of any significance in subsonic engine efficiency can only come from open rotor.

Noise, safety, and speed. I don't see how these get resolved with an open rotor.

Speed can get resolved, if the NASA ATP program is any indicator, (double digit efficiency advantage over equivalent tech turbofan engines up to .9 mach) but noise and safety will require some creativity and may never be satisfactory for everyone. None of the current open rotor designs/proposals use the ultra-high sweep blade design of the ATP which was optimized for mach .82-.84.

DocLightning wrote:

744SPX wrote:

Open Rotor. Ever higher turbofan BPR's are going to come with ever diminishing returns until they hit the point where the cowl drag (and weight) is so massive that further gains of any significance in subsonic engine efficiency can only come from open rotor.

Noise, safety, and speed. I don't see how these get resolved with an open rotor.

I wouldn't be worried about any of those. Safran's open rotor testing showed that its demonstrator wasn't any louder than its LEAP turbofan. In the late 1980s, GE proposed to MBB (West German contributor to Airbus) an open rotor version of the GE38 that cruised at Mach 0.8 with an SFC of 0.519 lb/lbf/hr -- about what today's narrowbody turbofans can do. The fuselage would just need a little extra armor in a couple of places.

I think customer acceptance is the bigger obstacle. Plus I'm not sure that the big 3 engine OEMs would be the most inclined to do open rotor. GE and Rolls Royce might feel burned from their previous propfan sales efforts. And Pratt & Whitney has bashed open rotor in recent times. In 2015 PW said it wanted to add PIP improvements so that by 2025, it would be within 10% of open-rotor performance -- enough to prevent other OEMs from doing open rotor engines, it thinks. For the other OEMs, it makes more sense to make an unducted propfan to catch up, since you get an easier double-digit efficiency improvement, versus having to grid out numerous out low-single-digit percentage gains (or fractions of a percent) in the engine core.

CowAnon wrote:

DocLightning wrote:

744SPX wrote:

Open Rotor. Ever higher turbofan BPR's are going to come with ever diminishing returns until they hit the point where the cowl drag (and weight) is so massive that further gains of any significance in subsonic engine efficiency can only come from open rotor.

Noise, safety, and speed. I don't see how these get resolved with an open rotor.

I wouldn't be worried about any of those. Safran's open rotor testing showed that its demonstrator wasn't any louder than its LEAP turbofan. In the late 1980s, GE proposed to MBB (West German contributor to Airbus) an open rotor version of the GE38 that cruised at Mach 0.8 with an SFC of 0.519 lb/lbf/hr -- about what today's narrowbody turbofans can do. The fuselage would just need a little extra armor in a couple of places.

What kind of "a little extra armor" is going to contain a blade-off event like that?

DocLightning wrote:

What kind of "a little extra armor" is going to contain a blade-off event like that?

Considering the nacelle of a GE9X can handle one of those massive blades coming off, I would think something similar would be sufficient to protect the aft fuselage. Especially if they are mounted like Boeing's "Fozzie" narrowbody concept from 2006 or the easyJet "ecoJet" from 2007 where they are in the absolute back of the plane and mounted high. The fuselage back there is likely not even part of the pressure vessel.

DocLightning wrote:

CowAnon wrote:

DocLightning wrote:

Noise, safety, and speed. I don't see how these get resolved with an open rotor.

I wouldn't be worried about any of those. Safran's open rotor testing showed that its demonstrator wasn't any louder than its LEAP turbofan. In the late 1980s, GE proposed to MBB (West German contributor to Airbus) an open rotor version of the GE38 that cruised at Mach 0.8 with an SFC of 0.519 lb/lbf/hr -- about what today's narrowbody turbofans can do. The fuselage would just need a little extra armor in a couple of places.

What kind of "a little extra armor" is going to contain a blade-off event like that?

There have been studies about this. One concluded that the fuselage would need 0.35 or 0.5 inches of CFRP thickness for a couple of 24-inch fuselage-length sections, with a total weight penalty of a few hundred pounds. From Weight Assessment for Fuselage Shielding on Aircraft With Open-Rotor Engines and Composite Blade Loss, a NASA/FAA study in 2013:

The circumferential length of the region requiring 0.50 in. of shielding was ~100 in. per side. With the required shielding width of 24 in., the total shielded surface area for either the forward or the aft rotor is 4,800 in.2. Using a density of 0.0645 lb/in.3 for the T700S/PR520 composite, the required shielding weight is ~155 lb for each rotor. The circumferential length of the region requiring a thickness of 0.35 in. was ~54 in. per side. With the required width of 24 in., the area for either the forward or aft rotor is 2,592 in.2. The resulting shielding weight is ~59 lb for each rotor. Adding the weights of 0.5 in. and 0.35 in. thick shielded regions gives a total shielding weight of ~214 lb for each rotor. Adding the forward and aft counter-rotating rotor shielding weights together yields a total weight of ~428 lb. As mentioned previously, because no specific distance between the forward and aft rotors was assumed, there was no assumed overlap between shielded areas.

If a portion of the composite shielding can serve both shielding and fuselage structural functions, then the weight specifically attributed to shielding may be reduced. Using a part of the composite structure for a dual purpose is a reasonable assumption considering the structural properties of the T700S/PR520 composite material. Assuming a fuselage thickness required to meet structural requirements of 0.2 in. (as was done in the FAA Open-rotor Analysis (Ref. 11)) over the total shielded area of 7,392 in.2, leads to an estimated fuselage weight of ~95 lb for each rotor. Subtracting the 95 lb weight from the total shielding weight reduces the additional weight required for shielding each rotor to ~118 lb, or ~236 lb for the complete counter-rotating configuration. The fixtures that would be required to attach the shielding to the fuselage would be airframe specific. As a result, the potential additional weight required for these attachments has not been estimated. These attachment fixtures, and the shielding, would not need to be in the primary load path of the fuselage. Therefore, they should only be required to support the shielding, and should not add significant weight.

Why does an open rotor need extra shielding? No one can or does armor a plane for a propeller-off event. Isn't an open rotor just a many-bladed prop in certification terms?

kitplane01 wrote:

Why does an open rotor need extra shielding? No one can or does armor a plane for a propeller-off event. Isn't an open rotor just a many-bladed prop in certification terms?

Open rotors rotate much faster than propellers. The blades probably have more energy if they should come off.

Starlionblue wrote:

kitplane01 wrote:

Why does an open rotor need extra shielding? No one can or does armor a plane for a propeller-off event. Isn't an open rotor just a many-bladed prop in certification terms?

Open rotors rotate much faster than propellers. The blades probably have more energy if they should come off.

I understand they are different. But in terms of certification ... I thought there was things-contained-in-a-cowling (i.e. turbines) and things-in-the-open-air (i.e. propellers) and only the first had to be contained after failure.

kitplane01 wrote:

Starlionblue wrote:

kitplane01 wrote:

Why does an open rotor need extra shielding? No one can or does armor a plane for a propeller-off event. Isn't an open rotor just a many-bladed prop in certification terms?

Open rotors rotate much faster than propellers. The blades probably have more energy if they should come off.

I understand they are different. But in terms of certification ... I thought there was things-contained-in-a-cowling (i.e. turbines) and things-in-the-open-air (i.e. propellers) and only the first had to be contained after failure.

The rule isn't really about contained-in-a-cowling as opposed things-in-the-open-air. You have to go back to why some things need to be contained, in this case the risk of something critical being damaged, or a passenger being injuried/killed. Given the energy level differences between a fan blade and a propeller blade, the risk levels are different, so one needs to be contained and the other does not.

If a propeller blade had the potential to do as much damage as a fan blade if it detaches, you'd have to rethink how that is dealt with, cowling or no cowling.

Since open rotors are missing the cowling but still carry as much energy as turbofan blades, the risk assessment becomes different from both turbofans and turboprops.

Starlionblue wrote:

kitplane01 wrote:

Starlionblue wrote:

Open rotors rotate much faster than propellers. The blades probably have more energy if they should come off.

I understand they are different. But in terms of certification ... I thought there was things-contained-in-a-cowling (i.e. turbines) and things-in-the-open-air (i.e. propellers) and only the first had to be contained after failure.

The rule isn't really about contained-in-a-cowling as opposed things-in-the-open-air. You have to go back to why some things need to be contained, in this case the risk of something critical being damaged, or a passenger being injuried/killed. Given the energy level differences between a fan blade and a propeller blade, the risk levels are different, so one needs to be contained and the other does not.

If a propeller blade had the potential to do as much damage as a fan blade if it detaches, you'd have to rethink how that is dealt with, cowling or no cowling.

Since open rotors are missing the cowling but still carry as much energy as turbofan blades, the risk assessment becomes different from both turbofans and turboprops.

I rather think you have to go to what the rules say. I believe (without being certain) that the written rules distinguish between a propeller and a jet turbine blade. Maybe the rules would change if someone tries to certify an open rotor, or maybe they would be certified under current rules which I think (without being certain) would mean that they would be certified as propeller blades, with no requirement for containment.

ClarkeKent wrote:

P&W. Is there any sign on Pratt on a wide body anytime soon? Apart from 767. What are they doing in house to prepare for the next advance in engine tech? Or are they relying on simply scaling up their gtf for a bigger aircraft? How advanced is the gtf core in comparison to leap or even 9x?

Someone posted a link on a recent CivAv thread mentioning how Pratt & Whitney are trying to catch up on ceramic matrix composites.

Pratt & Whitney to produce advanced metal and CMC turbine airfoils in North Carolina (Composites World, 12/17/2020)

Also, the GTF is supposedly the first turbofan to have fan blades primarily of aluminum. With GE and RR both incorporating lighter carbon composites on their blades, I wonder if PW will have to reconsider its choice.

Pratt, Alcoa Pioneer Use of Aluminum Fan Blades] (AIN, 7/28/2014)

PW might test a GTF engine that increased the bypass ratio from 12 to 18 (FlightGlobal, 6/16/2021). That's more than the RR Ultrafan's BPR of 15.

GE/Safran will begin ground and flight testing of an open single rotor/variable-pitch stator combo (CFM RISE) starting in the mid-2020s, but that wouldn't enter service until 2035 (Dominic Gates, Seattle Times, 6/15/2021). If Boeing needed a new powerplant this decade, it would have to be a more conventional type.

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What are the prospects for centrifugal compressors? I had read that mass flow or thrust issues limited their application to regional jets. However, the Ivchenko-Progress/Motor Sich D-27 propfan actually puts out nearly 27,000 pounds of thrust and has a centrifugal compression stage -- enough to power 150-180 seat narrowbody planes. Would/should centrifugal compressors be seriously considered in future designs?

CowAnon wrote:

PW might test a GTF engine that increased the bypass ratio from 12 to 18 (FlightGlobal, 6/16/2021). That's more than the RR Ultrafan's BPR of 15.

GE/Safran will begin ground and flight testing of an open single rotor/variable-pitch stator combo (CFM RISE) starting in the mid-2020s, but that wouldn't enter service until 2035 (Dominic Gates, Seattle Times, 6/15/2021). If Boeing needed a new powerplant this decade, it would have to be a more conventional type.

===
What are the prospects for centrifugal compressors? I had read that mass flow or thrust issues limited their application to regional jets. However, the Ivchenko-Progress/Motor Sich D-27 propfan actually puts out nearly 27,000 pounds of thrust and has a centrifugal compression stage -- enough to power 150-180 seat narrowbody planes. Would/should centrifugal compressors be seriously considered in future designs?

Are we thinking the 737 replacement is waiting for RISE?
Are there any developments in the 787 space regarding a possible re-engine in the future?

The second article opined that Boeing would need to launch a single-aisle clean-sheet replacement later this decade, but that would be too early for the RISE, and only a more conventional engine with smaller efficiency improvement would be available.

For me this means Boeing better hurry up with its Truss-Braced Wing. TBW or the blended-wing body will be the only way to leapfrog Airbus if Boeing launches this decade. The TBW has the advantage of being more similar/familiar to the current tube-and-wing planes and being Boeing's own intellectual property. If Boeing launches with either of those concepts, clearance no longer becomes an issue, and it can use an older-style open rotor concept with larger diameters. Pratt & Whitney would seem to be the most able to produce something like that quickly (since it already has gearboxes in the right thrust range), but they seem to be the most opposed to open rotor out of the big 3 engine makers.

What all of this means for the 787 I don't know. Besides the 737 replacement, there's still the MOM, so a 787 re-engine might be lower on Boeing's list of priorities.