The recent announcement by Rolls-Royce that their future engines will contain gearboxes has put GE and its CFM partner SAFRAN under considerable pressure.
GE/SAFRAN were together with Rolls-Royce proponents to go directly from Direct-Drive turbofans to Open Rotor designs for the next generation aircrafts. This left Pratt & Whitney as the only major engine manufacturer promoting high by-pass ratio geared turbofans as a better alternative for these aircrafts. With the Rolls-Royce announcement of Advance for 2020 (Carbon fanned tri-shaft) and Ultrafan (Geared big fan) for 2025, this has all changed. Suddenly Pratt & Whitney has strong support in their strategy and GE/SAFRAN stand out as loners.
By honing key technologies in their traditional two shaft turbofans GE, and GE/SAFRAN in CFM, have built a market leading position in all thrust classes, Regional (CF34), Single Aisle (CFM56) and Dual Aisle (CF6, GEnx, GE90). Their declared next step was Open Rotor for future Single Aisle while keeping Direct-Drive for larger engines.
Airbus and Snecma continue to research open rotor technology. Aviation Week has this story.
Now this solid position is threatened. The geared architecture has won the future regional market (CSeries, MRJ, E-Jet E2 goes PW GTF), market parity on the A320neo family and the 757 replacement studies by Boeing (dubbed NAS, New Airplane Study) will not go Open Rotor as Open Rotor only works up to M 0.75 and the 757 replacement will likely fly over 4,000nm, necessitating higher cruise speed. The NAS will thereby favor a geared turbofan instead of Open Rotor. Why not Direct-Drive? There are two major reasons:
GE/SAFRAN has shown with their CFM LEAP project that they can match the efficiency levels of a geared engine like Pratt & Whitney’s GTF, using its superior hot section technology to achieve the high efficiency. It cannot achieve the low noise levels of a geared fan however; engine noise stands in direct relation to fan rotational speed and pressure ratio.
It will thereby be the environmental factors that will put the most stress on GE/SAFRAN’s present strategy. Having lost the regionals to the geared camp, will it also lose the next generation short/medium haul? It will be interesting to watch the GE/SAFRAN over the next 18 months: does it change strategy or not? If one goes by the recent words of GE Aviation President David Joyce (who spoke at last week’s opening of their Indiana LEAP factory), he thinks his present line-up is fine for a 757 replacement, and he sees no urgent need for new developments.
By Leeham Co EU
SAFRAN is in the geared team with Clean Sky 2 I guess (WP1 and WP2)
Have a nice day
I suppose it is the SAGE part of CLean Sky you are referring to. As far as I know Snecma are in SAGE1 and SAGE2, both of which are open rotor demos, with SAGE2 being a geared open rotor.
Pushed “Post” to soon…
Geared TurboFan is in SAGE4. Do not remember off-hand if Snecma is a partner there or not.
What does Leeham Co EU mean? Are you based in Toulouse now? 🙂
It means we have someone in Europe and no, he’s not in TLS.
this Is the retrostyle fashion of an old design. The Turbo-prop
I wonder the penalty in speed and in single engine operations particularly in TO since you can’t (yet) feather the fan.
I think the RR engine/demo Ultrafan included pitch control of the fan…
Do you think that pitch control would be realistically applicable to a conventional turbofan? It’s already available for the LP compressor but I have never seen this on a fan. Is it because of the added complexity? Or maybe there is a reliability issue. Or maybe the potential efficiency gains do not justify this kind of advanced technology. Yet it is already on turboprop engines.
The day that we will read that the engine has not thrust reverser we will know the answer regarding the variable pitch fan blades.
In the LP compressors are the vane blades that are adjustable not the rotor blades!
You have a good point about the LP compressor, the mechanism is indeed in the stator, not in the rotor. It would be a lot harder to implement on a rotating disk! And the fan is no different in that respect.
You don’t retart by windmilling the Fan, do you?
You have to turn the gasgenerator i.e. HP( and IP?) spool.
The engine has to turn at a minimum speed in order to reignite. Normally this speed is achieved via the starter, which is its only job to do. But in the air the windmill will provide the necessary fan speed to permit ignition. Since the fan and the LP compressor are interconnected, compression will be achieved and the combustor will ignite when the ignition plugs are switched on, provided fuel is available.
Seems SAGE4 is an MTU led test on a PW GTF with component improvements, other members are the GTF team members Avio and GKN (aka Volvo Aero). Don’t think anyone in the GE camp is in SAGE4 (other then Avio of course now being owned by GE 🙂 ).
This editorial is music to my ears. It confirms what I always thought, that the future belongs to the GTF technology, not Open Rotor.
When Pratt & Whitney introduced the turbofan technology in the 1950s the other manufacturers had no choice but to follow suit. I think we can safely predict they will have to do the same with the GTF.
For CROR, beyond 2025 at least and constrainted by the noise limitation…however everything is possible in the future (๑•ᴗ•๑)
It is indeed possible that in 2025 CROR will no longer be on the drawing board. But that will only be because it will have been filed away as abandoned “Future Project”. And I am just half-joking. 🙁
I am not surprised to see Rool-Royce be the first to adopt the GTF technology. For when RR introduced the three-spool technology on the RB211 the idea behind it was similar to the the idea behind the GTF: to give more room to play with core speed in relation to fan speed. The three-spool was just one step away from the GTF. But it remains to be seen if RR will adapt the GTF to the three-spool or switch back to two-spool.
What about a a contra-rotating fan on a three spool engine providing a bypass ratio in excess of 20:1. First fan on the LP spool. 2nd fan and a reduction gear system on the IP spool and with the IP spool counter rotating to the HP and LP spool.
Those technologies look very promising on paper. But when confronted with the existing reality they don’t hold the road. The first reason is that they are inherently noisy. But there are other considerations as well that are related to practicality and complexity.
The beauty of the GTF is that it is ridiculously simple, immensely practical and intrinsically quiet. And it is already here, coming from the past and leading us into the future.
I’m talking about a ducted contra rotating fan, not an open rotor. 😉
The clue to a substantial reduction in noise for a ducted contra-rotating fan is, amon other Things, to try to make the fan blades as thin as possible. That’s exactly the course of action RR is pursuing with the new composite fan blades for the New Advance engine design and beyond. The current composite fan blades used on the GEnx, for example, are simply too thick for use on an engine using a ducted contra rotating fan.
Page 25: http://www.etc10.eu/mat/Mileshin.pdf
Another link: http://www.mtu.de/GB_2007_en/101.0.html
Is the geared turbo fan’s speed controlled manually by the pilot after take-off, or is it all automated? Signed, Learning
Please take a look at the picture of the reduction gear at the bootom of the linked article. The low pressure (LP) spool/shaft is attached to the ring in the centre, while the fan is attached to the outer ring. The 5 planetary gearboxes in between reduce the RPM of the LP spool from 10500 RPM to 3000 RPM for the fan. Hence, there’s only one gear setting and at engine start-up, the fan automatically rotates With a speed at a rate 3 times lower than that of the LP spool.
On modern engines the pilot has little control over engine parameters. Everything is decided by a computer that we sometime call FADEC. But GTF technology is a built-in technology. In other words it is fixed. Once the gear ratio is established it does not vary. The overall speed of the engine will change in response to pilot (or auto-pilot) input but the gear ratio remains constant throughout.
In case I have not understood your question properly I will now answer it differently. Normally the pilot would control the fan speed by selecting the proper throttle setting for take-off. After take-off the auto-pilot (or auto-throttle) will take over for cruise. It’s the same for all turbofan engines wether they have the GTF technology or not.
In order to prevent confusion in the minds of those not familiar with GTF technology it is important to mention that the overall fan speed will not change that much compared to a conventional turbofan. With a 3 to 1 gear ratio the fan will turn at about 80% of current speeds for conventional engines. This lowered speed is actually what makes the engine less noisy.
Many people don’t realize that on the GTF engine the core speed has been increased by 250%. That means the fan would normally have to turn at 250% the speed of a conventional engine. But because of the 3 to 1 reduction gearbox it will actually turn at only 80%.
The reason behind this is that there is a considerable gain in efficiency by having the core turn at a faster speed. Concomitantly there are equivalent gains to be made with a lower fan speed as it allows a larger fan to turn more slowly, which provides additional gains in terms of efficiency.
I am sure you know all this OV but I had to mention it because others don’t.
Now, please do note that the LP spools on the single aisle IAE-V2500 and CFM56-series engines already run much faster than the LP spool on the larger WB engines.
IAE V2527-A5: 5650 revolutions per minute (RPM) for the LP spool and 14950 RPM for the HP spool
CFM56-5B4: 5200 RPM for the LP spool and 15183 RPM for the HP spool
PW1127G for the A320neo:
RPM of 1800-20000 (estimated)* for the HP spool and 10500 for the LP spool.
Hence, the RPM on the LP spool for the PW1100G GTF engine has been increased by less than 200 percent over that of the LP spool on the IAE engine 😉
Now, on the GEnx-1B the RPM is only 2778. The larger the fan, the lower the fan tips go supersonic (i.e. a design constraint). That’s why a two spool GTF engine would need a gear reduction with a 4:1 ratio.
Actually my figure of 250% was benched against the CF34 I believe, which was used, if I recall correctly, as a reference for a so-called conventional engine for the Bombardier CSeries.
For the A320 the numbers are obviously different, but I cannot make a direct comparison because I don’t know the exact figures for the CF34. If we compare the GTF (A320neo) to the CFM-56 (A320ceo) the LP on the former turns exactly 200% faster than the LP on the latter. And indeed slightly less than 200% for the IAE V2500 (A320ceo).
Nice exchange OV! I always learn something when I read your posts.
Thanks Normand and OV. I never worked propulsion.
Just to nitpick a little: the core is usually (mostly) the HP spool. That is, the core (engine) is the HPC, combustor and HPT. The LP stuff is not considered part of the core.
You are absolutely right and I had noticed that after I read myself, but it was too late to change it. When I wrote that particular post it was specifically intended for the non specialist and I did not want to go into too much details, so I may have oversimplified it. Anyway, I stand corrected.
Normand, suppose that a variable pitch fan will be associated with GTF how about the re-start in flight capabilities of a geared fan? the mechanic complexity associated worried me more than the fuel savings.
I must admit that I had never thought about this restart problem before. It’s a good point. The gearbox would obviously offer more resistance to windmill, and when associated with a variable pitch fan there could also be a windmill ineffectiveness if the fan blades are positioned at an inappropriate angle (feather being the worst).
Any ducted engine has a clear advantage over Open Rotor because blade containment is bug issue with the latter. And that is exactly what I had in mind when I mentioned practicality.
To answer your initial question properly, I would say yes Ducted Contra Rotating Fan definitely looks a lot better than Open Rotor and I should not have put the two in the same basket. DCRF is much more realistic than OR. Yet it might be more practical, but it remains very complex and noisy.
You principally can have the second counterrotating rotor/fan connected to the now freerunning gearbox to provide the counter moment to the first fan. You probably would not get an even power/rpm split. Not having to cope with the reactive gearbox forces would make the design significantly lighter though.
Your comment confirms what I say: it’s a complex technology.
Well, I was thinking about using only one gear reduction system and putting it on the IP spool.
For example, the TXWB RPM speed limits for take-off and maxium continuous speed limits are 2649 and 2614 for the low pressure spool (LP); 8298 and 8143 for the Intermediate pressure spool (IP): and 12361 and 12159 for the high pressure spool (HP). Hence, the RPM of the LP spool is seemingly low enough. On the two spool GEnX-1B and -2B series the maximum RPM is 2778 and 3026 for the LP spool and 13539 and 13424 for the HP spool.
On the two spool engines the single aisle aircraft the numbers are:
IAE V2527-A5: 5650 LP and 14950 HP
CFM56-5B4: 5200 LP and 15183 HP
PW1127G for the A320neo:
RPM of 1800-20000 (estimated)* for the HP spool and 10500 for the LP spool.
Thanks to the gear ratio of the gearbox of 3:1, the speed of the fan is reduced to only 3000 RPMs per minute.
Now, the second fan of a ducted contra rotating fan should rotate slightly faster than the first fan — let’s say by some 4-5 percent. Then a gear ratio of 3:1 is enough for the IP spool, and not the more demanding LP spool ratio of 4:1 which Pratt is aiming for in future product developments. Hence, thanks to the three spool architecture RR could conceivably make a relatively straight forward derivative engine using a ducted contra rotating fan. As I indicated, RR’s march to develop thin composite fan blades would account for most of the tricks required in order to make such an engine viable.
Well, I proposed a single gearbox in my post.
You’d need a gearbox with 1:6..8 reduction.
Input : the LP shaft
Fan1 : the output shaft that now drives the “One Fan”
Fan2 : sits on the gearbox itself driven ( counterrotational) by the reaction moment
( which in the current GTF setup has to be passed to the engine casing.)
Well, you seem too add complexity (i.e. moving parts) – and it’s a pretty huge reduction ratio (6:1 to 8:1?).
Made a wrong assumptiion.
I actually need a _lower_ gearbox reduction as the per fan rpms are only half the LP rpms divided by gearbox reduction. And it should not add complexity, just a second fan 😉 ( gearbox reduction defines the differential speed between the counter rotating fans.
Do you know which way RR leans for a GTF engine, two-spool or three-spool? If I recall correctly I believe you have said to me in a previous thread that RR was going two-spool for the GTF. Please correct me if I am wrong.
It’s a two spool architecture. It seems to be geared towards the single aisle market in its first iteration.
Click on the image gallery (i.e. image nr. 4).
Compressor: 1-stage geared fan, 3-stage LP, 9-stage HP
Turbine: 2-stage HP, 4-stage LP
In your discussion of the GTF technology, as applied to a ducted fan, you seem to imply that RR would use three-spool since you mention the IP and that can only be found on a three-spool.
And in your last post you specify that RR would develop a two-spool GTF for the narrowbody market. Should I read in this remark that RR would consider a three-spool GTF for the widebody market? I am talking about conventional design here, not ducted fan.
None of you guys work for P&W, GE or RR? They sure missed out
Ok, got it.
However, what happens if you want to run the fans at different speeds?
SNECMA, for example, has looked at a design for a ducted contra rotating fan where the first 10-bladed fan has a RPM of only 75 percent of that of the of 2nd 14-bladed fan.
The rpm _difference_ is hard linked to the LP spool ( via the gearbox ratio )
How that translates into Nf1 and Nf2 is dependent on moment uptake
on each fan.
Open rotor is no different to containment than a turboprop.
Except that OR has a few more blades and they don’t know where to put the engine on the aircraft. We are talking about two different animals here.
How is the increase in weight for the oil lubrication/cooling system for the gear?
I have no idea, what’s your point?
There is no doubt that the P&W GTF is a heavy engine, but most of this excess weight is due to the very large size of the fan. To put things in perspective for the uninitiated, the size of the fan on the CSeries is about the same size as the fan was on the early 747.
In regards to the oil cooling/lubrication on the GTF it is my understanding that the reduction gearbox is part of the same circuit as the rest of the engine, like it would be for the accessory gearbox, if I am not mistaken. I also believe that the weight of the reduction gearbox itself is approximately 300 lbs, or less.
Actually, the GTF allows for fewer stages (disks). It’s all explained nicely here:
Yes I knew about the important blade count reduction. It’s almost in the thousands rather that in the hundreds. But I had not made the connection with weight, for I was concentrating on the lower maintenance.
It would be interesting to have a mapping of the GTF engine by weight gains and losses across the engine. This way we would know where they gained here and where they lost there.
Anyway, overall we have a relatively heavy engine, but a very simple one. This should have a beneficial impact on maintenance costs. Above all we have here an engine with an immense potential for performance improvements; the sky is the limit, literally.
One of the great advantages of an engine using a ducted contra rotating fan is that you can increase the bypass ratio without increasing the diameter of the fan. Hence, I’m primarily thinking about aircraft larger than the 777X. The 132 inch-diameter fan of the GE9X is about as large you can go on a conventional tube-and-wing aircraft. I believe that the technology required for a twin-engined A380 (i.e. A390X) will be available a decade hence. Such an aircraft could have an all new composite, very high aspect ratio wing, featuring a 90m wingspan (i.e. including 2 x 5m folding wingtips). Engine thrust required would be in the neighbourhood of 130,000 to 140,000 lbs. Therefore, an engine for an A390X, featuring a contra rotating fan and an overall pressure ratio of up to 70:1 wouldn’t necessarily have to have a much bigger fan diameter than that of the GE9X.
Interesting concept, OV-099. I’d like to see that.
I don’t work for RR so I don’t know which course of action they’ll eventually follow. However, when we start to talk about very large engines, then RR has IMJ a relatively straight forward option of using their three spool architecture as the foundation for a ducted counter rotating fan. It would allow for a high propulsive efficiency without having to significantly increase the size of the engine. Hence, a ducted counter rotating fan with a gear reduction assembly on the 2nd fan will be significantly more efficient than a conventionally geared single fan. If RR chooses not to go down this route, then I’m sure we’ll see larger RR geared two spool engines being developed for WBs.
According to Rolls Royce, three spool engines will still be a little bit too heavy for engines with thrust levels below 30,000 lbs. As RR seems to want to re-enter the single-aisle market, it seems to me that their UltrFan concept, at least initially, will be geared towards a possible A320neo re-engining undertaking post 2025. With an overall pressure ratio of 70:1 and a geared fan it should better the PW1100 GTF engine by some 10 percent in efficiency.
If we can get past the people designing aircraft engines here, I assume you can use the same high tech materials GE used in their engines and make the GTF more efficient on the hot end?
In a thread dedicated to engine technology you can expect the discussions to be a bit more technical than usual because it is almost impossible to discuss the relative merits of various engines without going into the engineering behind each one of them. After all the word engineering is derived from the word engine, is it not? 😉
Agreed, however, me thinks the people at said companies of GE, RR, PW, MTU know a wee bit more about it all than even the commentators here.
Commenting on what is being produced has merit and interest, wildly speculating on grand ideas that don’t see the light of day no so much in my view.
Is there an App for that? Call it Sim Engine instead of Sim City?
Of course we need one for Sim Airplane as well.
Just my take, it gets too unreal when there is enough real and interesting technology to sift through.
Agreed, however, me thinks the people at said companies of Airbus, Boeing, Bombardier and Embraer know a wee bit more about it all than even the commentators here.
I apologize for the plagiarism. 😉
You mean as opposed to the people designing aircraft on this and similar forums on a daily basis?
As Normand says, you need to dive in deeper (than on a/c’s) to understand the relative merits. Conceptually, engines are more complex than aircrafts. In an engine related post: deal with it.
And to answer your question: the short answer is yes. And this is what PW will do, they have some good stuff coming from their military side (I have been told). But currently, GE holds a lead in hot section tech, mainly through better materials.
So, if GE goes GTF, they can design a quite good engine. But they need to start on gearbox technology, it will take them some time to catch up, time which PW can/will use to improve their offering in the hot section. Is this why GE bought Avio, perhaps? PW’s chore is a little easier as you can add hot section tech bit by bit, ewither by retrofits or on new members in the same engine family.
When GE bought Avio I did not make the connection with the GTF, but now that you mention this as a possible motivation behind the deal I can see the logic behind it because Avio is indeed a gear specialist. If so it was a smart move, for GE will need all the expertise it can get if it decides to go the GTF way, which I think all the engine manufacturer will do, as they did in the 1950s for the turbofan.
GTF is no longer an option and is going to impose itself as a basic technological principal around which future jet engines will be designed. So like they had for the turbofan technology P&W has again a considerable head start. GE’s variable geometry inlet guide vane technology was also a major innovation but it did not make as big a difference as the turbofan did.
Today GE, Rolls-Royce and Snecma (Safran) find themselves in the catch-up mode. It remains a huge challenge for all of them to develop their own GTF. After all it took 20 years for Pratt & Whitney to come out with their first GTF engine, the PW1500G for the CSeries.
Like you have mentioned mneja, it will be easier for P&W to develop the GTF further and make improvements in particular to its hot section. All the other manufacturers will have to start from scratch and redesign their engines around that reduction gearbox.
This new reality will pave the way for P&W to reenter the widebody market where we are essentially in a duopoly right now, just like for the aircraft manufacturers.
RR is not a newcomer to the concept of geared fans. During the 1980s, GE and P&W/Allison developed the GE36 and PW579-D propfan demonstrator engines that dispensed with a gearbox, while RR looked at a geared open rotor engine although no full-scale demonstrator engine was produced. Also, using two fans and contra rotation for open rotor and ducted geared engines eliminates much of the eddies in the slipstream of the (first) fan, making the propulsive efficency about 7 percent higher compared to using only a single fan.***
The problem for GE/CFM is that they have now committed themselves to what essentially is a dead-end, technology-wise. CFM, for example, propably counts on selling more than 10,000 LEAP-X engines. However, the LEAP-X engines have little room for improvement — a serious design miscalculation on the part of GE/CFM.
RR, on the other hand, now seems to want to enter the single-aisle market a decade hence. RR can offer an UltraFan engine sized for the A32Xneo-series, and which IMJ could be at least 10 percent more efficient than the PW1100G and the LEAP-1A engines that are to be used on the neo. PW should be able to match the RR engine using a significantly upgraded PW1100G engine, but CFM will lose out if Airbus decides to bring RR on board post 2025 — and why shouldn’t Airbus do exactly that? You’d have a third engine option that would soon return to a duopoly on the A32Xneo-series, but now with CFM left out in the Cold and With far too few LEAP-X engines sold (i.e. MAX and neo).
So, in short; if Airbus allows RR to offer an all new UltraFan engine on the A32Xneo, Boeing will have to act and start to develop an all new single aisle aircraft ASAP. However, if Airbus launches an A360X supertwin programme by the end of the decade, Boeing would not only have to go for an all new single aisle project, but would have to do something to counter the A360X as well. Hence, the life-cycle for both the MAX and the 777X programmes would be severely curtailed.
***Why Does an Open Rotor Offer an Increase in Flight Mn Relative to Conventional Propeller?
There are three types of propeller performance loss
* Rotational – The torque input into the propeller has to be reacted by the air, resulting in rotational flow or swirl in the propeller wake, which is lost energy.
* Axial – Equivalent to propulsive (Froude) efficiency. To reduce axial losses – increase propeller diameter
* Profile – This is effectively the 2D drag on the aerofoil, including skin friction and compressibility losses. To reduce profile loss – maintain surface finish & aerofoil profile and Operate below drag rise Mach number (aerofoil design & sweep)
In order to keep the tips of the blades subsonic at cruise (reduced shock loss and cabin noise), the rotational speed of the rotor has to be reduced, which leads to rotational flow or swirl in the propeller wake.
The use of a second propeller to capture this swirl flow allows the overall efficiency to be significantly improved whilst maintaining a propeller diameter that can be integrated with the airframe.
OV, I am in complete agreement with you in regards to the GE/Snecma predicament. CFMI did not have much of a choice at the time because it takes a long time to develop a GTF from scratch.
As for Boeing they had the choice but I am not sure they made the right one. I always felt a little lonely into the camp of the very few who believed that waiting for revolutionary engine technology before launching the NSA was delusional.
Call me heretic if you want, but I believe there is no future in 2025. The future is already here: it’s called GTF.
Normand, the difference between GE/SNECMA and RR is that the former is already investing heavily in an engine that they hope will sell for another two to three decades. RR wisely chose to stay out of the single aisle fray for the time being and concentrate on WBs — that is, till they can develop something game-changing themselves. Hence, RR should easily have enough resources moving forward. A RR UltraFan GTF engine could be ready for the neo by 2025. Wouldn’t you agree that such an engine would change the game majorly in the sense that GE/SNECMA seemingly would have nowhere to go but down. A RR GTF UltraFan engine and an upgraded PW1100G could IMJ very well make the A32Xneo series viable until the mid 2030s — at least.
Mate, you are dreaming even if Rolls enters the competition for narrow body engine anytime in the future , it wouldn’t stand a chance to compete with existing strong playeres .. GFM has exclusivity for 737 and it competes with Pratt for the remaining market share in A320. .Rolls would lose….They are not that stupid to join the race in such a fiercely fought market..
In terms of OR. For an A320 sized plane, what will be the noise level difference between it and a normal engine?
Also, I remembered one of the issues of OR, being the very dangerous blade detachment scenario, has this been sorted yet?
The problem with OR is that at best it can eventually come close to the noise levels of the aircraft that are flying today under the current noise standards. But we are not there yet, far from it.
By the time they get there though, if they ever do get there, the noise standards will have changed and will then for forever be out of reach for OR technology. However, with the GTF engines the existing noise standards are already exceeded three times over.
The moral of the story is that OR will never be able to catchup. Notwithstanding the other problems OR has and which are as daunting.
Well, I’m not sure I necessarily agree. One problem with open rotors is the lower operational speeds rerquired. Mach 0.76 seems to be as high as you can get. However, that seems to be OK for single aisle aircraft flying trunk routes. Hence, an all new family of aircraft (i.e. 100-150 seats), having a design range of , say, 2000nm would be IMO be a perfect match for open rotors. Also, the noise issue is solvable if you put the engines on the top aft of the aircraft and use a noise-shielding tail design. The clue, of course, is to also use geared fans that reduce the rotor speeds significantly.
The noise is a problem for passengers obviously, but also for residents on the ground. What might be acceptable for passengers might not even be legal in the future for the airport environment.
Besides, OR could only expect to be a niche market, like the turboprop. It will never replace the jet engine because of its limitations. But we are not there yet. And we might never be either. There are too many constraints and they won’t go away just by doing more research and development.
When we look at airplanes today they are exactly the same as they were fifty years ago. There is little difference between a 707 and a 777. It’s going to be the same for engines. Both airframes and engines are mature. The rest is optimization.
We have been talking of an SST for fifty years. Where is it? Open this, ducted that, it’s all fantasy to me. I must be getting old 🙂
You can noise isolate the fuselage.
You can not do the same for housing on the ground with a comparable investment.
Interesting configuration. It looks like tail-chasing could be an issue, but the weight penalty might not bite hard enough to notice much since the design range is relatively short. Rear mounted engine configurations have obviously had a lot of success in smaller sizes and short to mid ranges.
Regarding the Mach 0.76 speed limit, inlets are the often overlooked and less sexy component of the subsonic propulsion package. In my opinion, they almost always are worth every pound they add.
“Rear mounted engine configurations have obviously had a lot of success in smaller sizes and short to mid ranges.”
Exactly, and with rear mounted engines the wings can be made very light as well.
“Exactly, and with rear mounted engines the wings can be made very light as well.”
Not to mention aerodynamically clean, with the added benefit of no breaks in the HL devices, excepting the yahudi for the gear.
But then you have to route the engine weight over the fuselage into the wing via stronger structure while wing mounted engines reduce forces on wingbox and fuselage.
This is aggravated by heavier and larger modern engines.
Due to CG restraints the tail needs to be short having impact on tail surface sizes.
Very good points.
Yes, I’m aware of that, but we’re talking about a relatively small aircraft. For example, the old, but quite light DC-9-30 has a significantly lower OEW than the C-series CS-100.
Well both have a similar MTOW/OEW fraction ( 0.55) and carry ~10t max fuel while the CS-100 has nearly twice the range _and_ carries 8% more pax.
The DC-9-30 has 15% higher wingloading. it is a plane designed for cheap fuel on short ranges while the CS-100 is for expensive fuel and longer range.
“Due to CG restraints the tail needs to be short having impact on tail surface sizes.”
This, coupled with the increased positive pitching moment due to a long fuselage forebody, is the tail-chasing issue I mentioned. This issue has been properly managed on many successful aircraft.
Managing the external noise issue using the tail surfaces, in my opinion, is much more difficult. While there will be some reduction, I’m not sure it will be anywhere near sufficient to meet the most stringent airport standards.
What I could imagine is a dual (core) geared engine working on a single fan in a shrouded tail arrangement. This is aerodynamically advantageous.
( Took the double engine single prop propulsion units as a reference )
“Well both have a similar MTOW/OEW fraction ( 0.55)”
Which is a bit high for a 3000nm ranged Aircraft (CS-100). The CS-300 has, of course, a more favourable OEW/MTOW fraction.
” ~10t max fuel while the CS-100 has nearly twice the range _and_ carries 8% more pax.”
Well, put the same kind of engines on a slightly larger, “unmodified” DC-9-40 and it would increase range by about 50 percent to around 2300nm instead of 1500nm (i.e heavier engines accounted for).
“The DC-9-30 has 15% higher wingloading. it is a plane designed for cheap fuel on short ranges while the CS-100 is for expensive fuel and longer range.”
Sure, but add modern materials, construction techniques and an optimised, supercritical airfoil as well (i.e. adding at least 15 percent in efficiency), and the maximum range of a “new” DC-9-40 should be about the same as the CS-100.
Except that the kind of engines your are talking about would not fit at the back of a DC-9!
Well, the engines on the DC-9-40 only needed JT8D engines with a maximum of 16,000 lbs of thrust each. The LEAP-X and PW1000G-series have much greater thrust cababilty (x2 for the A321neo). Also, the IAEV2500 engine on the MD-90 has a fan diameter of 63″. That’s only 5.4″ less than the LEAP-1B on the MAX. Hence, a DC-9-40 could use a LEAP-1B, or preferably a LEAP-X with a smaller core and fan if 68,4″ would be too big. Of course, none of this will come to fruition. 😉
Normand, SST is a whole different ballgame. It’s the economy -stupid! 🙂
The fact of the matter is that the current crop of single aisle aircraft are really too range capable. Hence, they are too much aircraft for many trunk routes. Even the C-series has a range of upwards of 3000nm. Hence, you don’t have to stop at 150 seats. In fact, I could foresee a demand for two types of single aisle aircraft (i.e. 100-250 seats). One short range type (i.e. 1500-2000nm range) flying around with open rotors and the the second one being similar to todays 737s and A320s. The short range type of single aisle aircaft would be significantly lighter and would require significantly less powerful engines. Again, that seems to me, at lest, to be a perfect match for an open rotor application — and IMJ, the open rotor “noise issue” for those kind of applications should be relatively easy to get around.
OV, I would like to hear what you have to say about the eventual return of Pratt & Whitney in the widebody market. There are very few discussions here about this important topic, yet we all know that they are hard at work on such a project.
In the near term, at least, it depends on what Airbus decides to do with the A330 and A380. If they determine that the technology readiness is mature enough (i.e. TRL 5) for a 4:1 reduction gear, then I wouln’t be surprised to see a PW GTF engine on at least an A380neo. I tend to believe that RR will be on board for both an A330neo and an A380neo. As for GE, they seem to have jumped into bed with Boeing by all accounts. Futhermore, in order to avoid a permanent trans-Atlantic split on WB engines and airframes (i.e. Boeing/GE and Airbus/RR), I sincerely hope that Pratt will be providing an engine for a WB Airbus in due course.
If you were CEO of Pratt & Whitney, in which power segment would you start developing in anticipation of future market shifts (30-50K, 50-70K, 70-80K, 80-90K or 90-100K+)?
70-80,000 lbs of thrust — that is if Airbus came calling sometime in the near future . That thrust class would suit an A330neo, A380neo and the A350-800 (i.e frame shrunken by 7-8 fuselage frames instead of the original 10 frames originally planned for; and keeping the original MTOW at 248 metric tonnes and having a required thrust level of 75,000 lbs). For the longer term. I’m not so sure. With the apparent, imminent launch of an A330neo, we’ll probably not see the launch of an all new 200-300 seat, intermediate ranged aircraft family any time soon — from neither A or B. Perhaps if Airbus were to go ahead with an all new A360X super twin family, an all new thrust class of 100-120,000 lbs engines would be required a decade hence. Depending on what Boeing decides vis-à-vis a 757/739-MAX replacement, PW could, of course, choose to further grow the PW1000G-family.
“The open rotor “noise issue” for those kind of applications should be relatively easy to get around.”
I will not reveal to you, at least publicly, what crossed my mind when I read that! 🙂
Well, you shouldn’t read anything sinister into it. 🙂
Normand, if you research The Q-FAN study by Hamilton standard and NASA 30 years ago(!!) you will discover amazingly that the variable pitch fan GTF technology was already tested then. The goal was not fuel reduction (like today) but noise reduction. I wrote an article about for my Group if y wish a copy I can email to you let me know .
Yes I would be interested to read your article. Please email it to Scott so that he can forward it to me after.
Thoughts please on the following:
Eliminate the gear box – drive a high speed variable freq alternator off the LP turbine running at very high speed – then make the fan and nacelle into an electric drive with the tips of the fan containing the rotor magnetic fields.
Technology Submission – State of the Art – Novel InFlow Tech – Featured Project Development; 1-Gearturbine, 2-Imploturbocompressor:
Atypical InFlow Thermodynamic
Technology Proposal Submission
Novel Fueled Motor Engine Type
*State of the art Innovative concept Top system Higher efficient percent.*Power by bar, for Air-Planes, Sea-Boats, Land-Transport & Dynamic Power-Plant Generation.
-Have similar system of the Aeolipile Heron Steam device from Alexandria 10-70 AD. -New Form-Function Motor-Engine Device. Next Step, Epic Design Change, Broken-Seal Revelation. -Desirable Power-Plant Innovation.
YouTube; * Atypical New • GEARTURBINE / Retrodynamic = DextroRPM VS LevoInFlow + Ying Yang Thrust Way Type – Non Waste Looses
-This innovative concept consists of hull and core where are held all 8 Steps of the work-flow which make the concept functional. The core has several gears and turbines which are responsible for these 8 steps (5 of them are dedicated to the turbo stages). The first step is fuel compression, followed by 2 cold turbo levels. The fourth step is where the fuel starts burning – combustion stage, which creates thrust for the next, 5th step – thrust step, which provides power to the planetary gears and turbines and moves the system. This step is followed by two hot turbo steps and the circle is enclosed by the final 8th step – bigger turbine. All this motion in a retrodynamic circumstance effect, wich is plus higher RPM speed by self motion. The Reaction at front of the action.
*8-X/Y Thermodynamic CYCLE – Way Steps:
1)1-Compression / bigger
2)2-Turbo 1 cold
3)2-Turbo 2 cold
4)2-Combustion – circular motion flames / opposites
5)2-Thrust – single turbo & planetary gears / ying yang
6)2-Turbo 2 hot
7)2-Turbo 1 hot
8)1-Turbine / bigger
-With Retrodynamic Dextrogiro vs Levogiro Phenomenon Effect. / Rotor-RPM VS InFlow / front to front; “Collision-Interaction Type” – inflow vs blades-gear-move. Technical unique dynamic innovative motion mode. [Retrodynamic Reaction = When the inflow have more velocity the rotor have more RPM Acceleration, with high (XY Position) Momentum] Which the internal flow (and rotor) duplicate its speed, when activated being in a rotor (and inflow) with [inverse] opposite Turns. The Reaction at front of the action. A very strong Novel torque power concept.-Non waste parasitic looses for; friction, cooling, lubrication & combustion.
-Shape-Mass + Rotary-Motion = Inertia-Dynamic / Form-Function Wide [Flat] Cylindrical shape + positive dynamic rotary mass = continue Inertia positive tendency motion. Kinetic Rotating Mass. Tendency of matter to continue to move. Like a Free-Wheel.
-Combustion 2Two continue circular [Rockets] flames. [ying yang] opposite one to the other. – With 2TWO very long distance INFLOW [inside propulsion] CONDUITS. -4 TURBOS Rotary Total Thrust-Power Regeneration Power System. -Mechanical direct 2two [Small] Planetary Gears at polar position. -Like the Ying Yang Symbol/Concept.
-The Mechanical Gear Power Thrust Point Wide out the Rotor circumference were have much more lever [HIGH Torque] POWER THRUST. -No blade erosion by sand & very low heat target signature profile. -3 points of power thrust; 1-flow way, 2-gear, 3-turbine. *Patent; Dic. 1991 IMPI Mexico #197187 All Rights Reserved. Carlos Barrera.
·2-IMPLOTURBOCOMPRESSOR; One Moving Part System Excellence Design – The InFlow Interaction comes from Macro-Flow and goes to Micro-Flow by Implossion – Only One Compression Step; Inflow, Compression and outflow at one simple circular dynamic motion Concept.
*·“Excellence in Design” because is only one moving part. Only one unique compression step. Inflow and out flow at the same one system, This invention by its nature a logic and simple conception in the dynamics flow mechanics area. The invention is a wing made of one piece in a rotating motion, contained in a pair cavity system connected by implocavity, and interacting dynamically with a flow, that passes internally “Imploded” through its simple mechanism. This flow can be gas (air) or liquid (water). And have two different applications, in two different form-function; this one can be received (using the dynamic flow passage, as a receiver). Or it can be generated (with a power plant, generating a propulsion).
An example cut be, as a Bike needs a chain to work from motor to wheel. And for the Imploturbocompressor application, cut be as; in a circumstance at the engine, as an A-activate flow, and with a a tube flow conduit going to the wheel as a B-receiving-flow the work use.
To see a Imploturbocompressor animation, is posible on a simple way, just to check the Hurricane Satellite view, and is the same implo inflow way nature.
And when the flow that is received and that is intended to be used at best, must no necessarily by a exhausting or rejection gas, but must be a dynamic passing gas or liquid flow with the only intention to count it or to measure it. This could be possible at the passing and interacting period when it passes inside its simple mechanism. This can be in any point of the work flow trajectory.
In case the flow that is received is a water falling by gravity, and a dynamo is placed on the rotary bar, the Imploturbocompressor can profit an be obtained by generating? electricity such as obtained by the pelton well, like I say before. The “Imploturbocompressor”, is a good option to pump water, or a gas flow, and all kinds of pipes lines dynamic moves.
Or only receive the air-liquid flow, in order to measure its passage with a counter placed on the bar, because when this flow passes through the simple mechanism of a rotating wing made of only one piece it interacts within the implocavities system. And this flow can be air wind, with the difference of can have an horizontal work position, and that particle technical circumstances make an easy way for urban building work new use application, and have wind flow from all the sides 180 grades view. The aforementioned information about this invention refers to technical applications, such as a dynamic flow receiver. (whether being gas or liquid).
With the appropriate power plant and the appropriate dimensioning and number of RPM this invention is also feasible to generate an atmospheric air propulsion and the auto-propulsion of an aircraft. Being an effective and very simple system that implodes and compresses the atmospheric air permits the creation of a new concept of propulsion for aircrafts, due to its simple mechanism and innovative nature. At the place of the aircraft were the system appears and the manner how the propulsion direction can be oriented with a vectorial flow (no lobster tail) with I call “yo-yo system” (middle cut (at the shell) to move, one side loose), guided and balanced is feasible to create a new concept of TOVL-vertical take-off landing, Because the exhaust propulsion can going out radial in all the 360 vectorial positions, going out direct all the time in all the vectors direction. With his rotor cover for an better furtive fly, like going down of a bridge for example.
Likewise, with the due form and dimensioning, and considering the liquid density and the due revolutions for this element there could be generated a propulsion (water) in order to move an aquatic ship, whether on surface or under water. Also can be a good option to pump liquid combustion for a rocket propulsion.
Making a metaphoric comparison with the intention to expose it more clearly for a better comprehension of this innovative technical detail, it would be similar to the trajectory and motion of a dynamic flow compared with a rope (extended) that passes through the system would have now a knot (without obstructing the flow), so the complete way of the flow at the imploturbocompresor system have three direct ways and between make two different turns; direct way (entrance) – turn – direct way (implocavity) – turn – direct way (exit), all this in a 1 simple circular move system concept.
Its prudent to mention that the curves and the inclinations of the blades of a rotating wing made of this invention, is conferred by its shape and function a structural rigidity allowing it to conduct and alter appropriately the dynamic flow passing through its system.