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Radical Pratt and Whitney design

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posted on May, 2 2008 @ 10:43 PM
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I found this in a Flight blog. This is a VERY cool idea, that I doubt has a chance of ever flying. It makes a ton of sense though if they would just build it.

It's a new design for a short haul jet, that has one gas core mounted in the tail of the engine, driving two fans or turboprops mounted on the aft fuselage. It would use a gearbox to optimize the speed of the fans, be much quieter, and have a much higher bypass ratio.


Every once in a while, I like to go wading in the "Radical New Aircraft Design" bin that is the United States Patent and Trademark Office. Occasionally I come out with something written in patent speak that only a rocket scientist can decipher and I just stare blankly at, however, this time I came out with a real gem.

I give you Patent Number 20080099633, which was published yesterday, called Aircraft airframe architectures, a wholly innocuous title. An engineer at Pratt & Whitney came up with a radical new design to improve the fuel efficiency of a shorthaul aircraft. Rather than have two engines, the design calls for a "single gas generator core including a forward compressor driven by a rearward turbine about a core axis and configured to remotely drive multiple bladed propulsion elements."

Source




posted on May, 3 2008 @ 12:14 AM
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Ha! Almost twice the BPR! That is brilliant, though there are probably issues with the gear box to work out, the design is pretty elegant -- just crazy enough to work? You're using the entire rear fuselage, however, so there is a weight/space penalty over one large engine. Possibly even over two. It's almost a turboprop geared to two fans. Similar to the ducted fan idea used in the F-35B/C as well.
I'd like to hear more about it in the future.



posted on May, 3 2008 @ 09:14 AM
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they may well be using something like this sooner rather than later - the geared turbo fan engines are ready to be flight tested on the airbus a320



posted on May, 3 2008 @ 09:20 AM
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Thermodynamically it's no different from a high bypass turbofan. I guess you could have the fans going at different speeds, but I'm not sure what that gets you and it certainly doesn't seem to justify the extra mechanical complexity.

Maybe I'm missing something?



posted on May, 3 2008 @ 09:26 AM
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More power from the engine, because you're using two fans for one engine, so you get essentially twice the BPR. Less noise, since the engine is rear mounted, and it's going to be more efficient because of the BPR.

I know the geared turbofan is about to fly, they're doing a test on a 747SP too from what I remember hearing. But this particular design is a pretty radical change to normal, and I can't see them making such a huge change soon.



posted on May, 3 2008 @ 09:39 AM
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Originally posted by Zaphod58
More power from the engine, because you're using two fans for one engine, so you get essentially twice the BPR.


You don't need two fans to double the bypass ratio; you can use a single, larger fan and accomplish the same thing without a gear box and multiple drive shafts.



posted on May, 3 2008 @ 09:53 AM
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reply to post by mtmaraca
 


As size of the fan increases so does the stress on the fan. Adding a gearbox doesn't mean it won't work well. Turbo props and -shafts use gearboxes as well -- while I agree it does increase complexity, cost, and reliability, it also might offer design advantages over a single large fan. It's not as easy as it sounds to mount a huge turbofan high on the rear of the fuselage.

[edit on 3-5-2008 by _Del_]



posted on May, 3 2008 @ 09:55 AM
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Except that with this design you only need one engine, and two SMALLER fans to get the same result. You're saving a ton of weight and space, to get the exact same result that you would with two engines, with larger fans.



posted on May, 3 2008 @ 10:03 AM
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By definition, for a given core area, you need the same amount of fan area to get a given bypass ratio, whether that is one, two, or a hundred fans. So it's not more space efficient, and I can't imagine that it would be lighter with multiple fans, shafts, ducting, and gearbox either.



posted on May, 3 2008 @ 10:53 AM
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reply to post by Zaphod58
 


once they shown the engine concept and first design works as intended , then this sort of `twin intake 1 engine` would work well since most of the power comes from the fan anyway.

you can`t simply make the fan bigger without penalty , hence why P&W are going for a gearbox for a larger fan , using a smaller , leaner burning core



posted on May, 3 2008 @ 11:40 AM
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It's true that in a turbofan, most of the thrust comes from the fan; however, the energy comes from the same place as all jet engines: burning fuel. Power is extracted by the turbine to run the fan and compressor. The penalty associated with a large fan (in comparison to the part of the turbine that is powering it) is that more turbine stages are necessary to extract the power needed. This is especially true because as the fan gets larger, its optimum rotational speed decreases, so to run at optimum speed, the turbine must spin slower as well, which reduces its ability to extract power.

P&W have already come up with an interesting solution to this problem, the geared turbofan. Obviously it is more complex than a traditional turbofan, but it is decidedly less complex than the two-fan design referenced in this thread. All I'm saying is the addition of an extra fan, shafts, ducting, gearbox, etc. doesn't seem to give any significant advantage over a geared turbofan with a single, large fan. Unless I'm missing something, were you to do the thermodynamic cycle analysis, the result would be the same in either case. I haven't done the analysis to compare the geared turbofan with a conventional one, however since P&W are producing them it seems like there must be some overall advantage at least for some applications. But this is one of those engineering trade-offs where there are pros and cons, and I don't see this outright replacing conventional turbofans in all applications either.



posted on May, 3 2008 @ 11:47 AM
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From the reading, this would be geared (pun sort of intended), towards the smaller short to medium haul aircraft. This isn't intended to be used in all applications, but it would be a good fit in the areas it IS intended to be used.



posted on May, 3 2008 @ 11:26 PM
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We also need to take into consideration the size of the aircraft.

It's designed for short-haul aircraft and short-haul aircraft tend to be relatively small (if they're regional) and smacking a relatively larger engine on a small airplane might not always be as efficient as simply having 2 smaller fans.

For larger aircraft like 777's and A340's, I see no real benefit to such a design.

Shattered OUT...



posted on May, 4 2008 @ 08:49 AM
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Originally posted by mtmaraca
All I'm saying is the addition of an extra fan, shafts, ducting, gearbox, etc. doesn't seem to give any significant advantage over a geared turbofan with a single, large fan.


It allows you to physically fit the thing on the aircraft


It also makes for a smaller nacelle area, with accompanying weight savings (although they will probably not compensate for the drivetrain), and accompanying drag savings.


Its hard to fit a 3m dia fan underneath an A320 wing, so Pratt aren't trying to - instead its two small ones off one core.



posted on May, 4 2008 @ 09:10 AM
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^^

the 737 has a serious problem - they had to customise the `standard` engine so it could be hung off the 737-NG`s wing - not only does it have a flat bottom to the nacelle but the fan is only 60" , not the 68" of the `normal` CFM56 , its also raised up and is inline with the wing and titlted upwards at 5 degrees as well - they are really at the limited for the engines for that aircraft


or , maybe 2 smaller nacelles driving 1 core.... would allow new engines and boeings best selling model ever to keep going



posted on May, 4 2008 @ 02:10 PM
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A quick question from someone who lacks knowledge on this subject.

Doesn't FAA regulations require two power plants for passenger transport aircraft, ultimately requiring 2 'core' engines to power the fans?

Go easy on me!



posted on May, 4 2008 @ 02:15 PM
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Yes and no. IIRC it depends on the number of passengers it can carry. If it's more than 30 (I THINK) then they have to have two engines. If it's LESS than 30, then they can have one engine. Not sure on the numbers there, but I believe that it's passenger count that decides how many engines.



posted on May, 4 2008 @ 02:20 PM
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Originally posted by kilcoo316

Its hard to fit a 3m dia fan underneath an A320 wing, so Pratt aren't trying to - instead its two small ones off one core.



Just pointing out that to get the cross-sectional area of one 3m diameter fan with two fans, they'd each need to be just over 2.1m in diameter. Maybe they should split it into three fans, then they could each be only 1.7m in diameter. I think there are better ways to deal with the space issue, like mounting the engine inside the fuselage and designing a conformal inlet to feed it. If I were designing the aircraft, I'd rather deal with that than the extra weight of the dual-fan system. You can disagree with me, that's fine, but don't give me the condescending little smiley as if you couldn't possibly fit a 3m fan, but you can fit 2 2.1m fans.



posted on May, 4 2008 @ 02:29 PM
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reply to post by mtmaraca
 


A conformal inlet generally provides inferior airflow. It's easier to provide that airflow with side mounted fuselage or under-wing fans than a central one mounted deep in the fuselage.

The .9 meters you mention are three feet of under-wing space in Kilcoo's example. You save alot of structure for undercarriage if you don't have to have that much extra clearance.



posted on May, 4 2008 @ 04:55 PM
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Yes clearly there are engineering trade-offs, I won't argue there. Without going through a rigorous analysis let me just state again that my feeling is that the weight penalty associated with adding an additional fan, shafts, gearbox, etc. won't be canceled out by other gains. Let me also point out that none of us knows for sure if this idea is good or worthless unless we did that rigorous analysis (this is a complex problem). In other words, I don't think it's obvious that this is a "brilliant," "very cool" idea that makes "a ton of sense" like the first couple of posts make it out to be. It's an idea, definitely "outside the box" and worthy of a patent, but not all ideas that are patented are worthy of production. The true value of this concept is unclear at best, given the information we have right now.



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