Boeing Y3 Composite 370-500 Seat Twin VLA Design "Ecoliner"

[keesje]

Last week I posted this topic on another forum, just thought Í should share.:) Henry Lam ( http://www.kaktusdigital.com) (http://www.kaktusdigital.com)/) found some time to create an exterior some artist impressions.

The 350-500 seat market segment
Looking at aircraft currently available there seems to be a market for larger aircraft. New VLA´s are launched by the bigger OEMS (747-8i and A380) and there is pressure to enlarge aircraft types seating over 300 passengers (A350XWB, Boeing 777 and Boeing 787. The 747-8i falls in the middle off this. Sales could indicate there might be room for a new passenger aircraft in say 10 years, the A380 seems too large for many airlines and markets.

Existing technology offers opportunities for very efficient design
New materials such as composites for fuselages and structures, large efficient turbofans such as Trent and GENX ovffer technology to make a significant step in efficiency in the 350-480 seat segment. Full length double deck offers gains in structural efficiently at limited fuselage lengths.
A solution could be a cross section offering 777 like maindeck flexibility: 9-10 abreast and a full length upperdeck significantly smaller then the A380, but far more practical then the limited 747 upperdeck.

http://www.kaktusdigital.com/images/y3_i01_small.jpg
Larger: http://www.kaktusdigital.com/images/large/y3_i01.jpg

Adding cabin length & width to rise capacity
Both sides of the Atlantic have been studying cabin configurations. Stretching length above 80m creates airport restrictions that are probably prohibitive for many airlines. Likely no passenger aircraft will longer then 777-300ER, A340-600 or A380-900 in foreseeable future. Adding width creates problems of it’s own in terms of evacuation, efficient use of space. It becomes very large and heavy.

http://i191.photobucket.com/albums/z160/keesje_pics/Ecoliner4crosssection15abreast.jpg?t=1192479291

Twin engine widebodies
Since Airbus introduced widebody twin in the seventies, scale of both turbofans and airframes have grown. There seems to be no real limit but Equipping 500 passengers with 2 engines above the Pacific, poles and Siberia might prove undesirable for many airlines, passengers and authorities.

A compromise could be to fit such an aircraft with 2 large engines and an APTU (Auxiliary Power and Thrust Unit) providing thrust during critical flight stages. Boeing studied it during the nineties. A twin + APTU seems to offer significant saving over a conventional four engined configuration.

A full composite twin VLA facilitating between 370 and 500 passengers (shorter + longer version) could have specification very competitive to current available aircraft types.

http://i191.photobucket.com/albums/z160/keesje_pics/Ecoliner3specifications-1.jpg?t=1192481730

I think in the next decade there will occur a gab in the VLA market under the A380. A big twin+ seems a feasible alternative / 747 replacement for many airlines. What do you think?

[chornedsnorkack]

Plenty of objections here.

A solution could be a cross section offering 777 like maindeck flexibility: 9-10 abreast and a full length upperdeck significantly smaller then the A380, but far more practical then the limited 747 upperdeck.

But this is problematic. If you look at the Ecoliner cross-section and compare it with 747 cross-section, it is glaringly inefficient, structurally, and would be extremely heavy!

You have very thin sidewalls, and absolutely no double-bubble discontinuity. This means that your thin sidewalls have to carry immense bending loads, and therefore be very heavy.

However, let´s imagine a full-length doubledecker with the exact cross-section of 747. You could shrink or stretch it, too. The 747 with short double deck was successfully stretched to 56,3 m of 747SP. Now imagine a 747SP with full length upper deck. What would the passenger capacity be?

And you can stretch it to 747-800 length, keeping the full length upper deck. This should cover a range of passenger capacities...

A compromise could be to fit such an aircraft with 2 large engines and an APTU (Auxiliary Power and Thrust Unit) providing thrust during critical flight stages. Boeing studied it during the nineties. A twin + APTU seems to offer significant saving over a conventional four engined configuration.

But what about a genuine three-holer?

Think of MD-XX. DC-10 cross-section is only slightly narrower than that of 777 - DC-10 is 602 cm wide, 777 is 620 cm wide. They have the same maindeck flexibility: you can seat 10 abreast on 777, though 9 abreast is more comfortable, and you can seat 10 abreast on DC-10 or MD-11 - Finnair does, although 9 abreast is more comfortable.

If you compare MD-11 with 777-200ER, they have pretty similar capacities: cross-section of 9...10 abreast as described, length 63,7 m for 777-200, 61,7 m for MD-11; maximum of IIRC 440 seats on 777-200, 410 seats on MD-11... MD actually fitted 421 seats for the evacuation test, but one passenger broke her neck, so only 410 seats are allowed.

Now, look at the MD-XX family, and compare it with B777-300ER/B777-200LR and A340-600/A340-500 families.

Total wingspans are pretty similar: 64,8 m for all three families, specifically to fit 65 m box.

The MTOW-s are 350 tons for B777-300ER/B777-200LR family, 380 tons for A340-600/A340-500 family, and 365 tons for MD-XX.

As for total length, it is 63,7 m for B777-200LR, 73,9 m for B777-300ER, and the MD-XX family has 61,7 m for MD-XX LR and 71,2 m for MD-XX Stretch.

One notable difference is wing area. A340-600/500 have somewhat more than 420 square m, B777-200LR/300ER something similar (how much exactly?), whereas MD-XX has 483 square metres.

How do you think would MD-XX Stretch handle?

And what about a three-holer from a generation after MD-XX?

Mind you, a humped partial doubledecker like 747 cannot be a trijet - Boeing tried to build one, but could not because the hump disturbed the airflow into the tail engine. But there is no reason why a full-length doubledecker cannot be a trijet, any more than there is a reason why a full-length widebody singledecker cannot. So, if a DC-10 stretched once more past the MD-XX Stretch does not give enough capacity, you could consider a doubledecker trijet.

[keesje]

chornedsnorkack, I think a trijet would be very heavy. The APTU envisioned would be a CFM class engine neadly fitting into the tail. It would provide the Ecoliner the required power at take-off with an engine failure while not requiring an engine to developped even larger then the GE90-115, while still providing twin cruise economics.

http://i191.photobucket.com/albums/z160/keesje_pics/ECOlLINErThrustatMTOWengineout.jpg

Henry (www.kaktusdigital.com (http://www.kaktusdigital.com)) made a very nice animation of the Ecoliner:

http://www.henrylam.net/ecoliner.html (http://www.henrylam.net/ecoliner.html)

rgds
keesje

[Groundloop]

You have very thin sidewalls, and absolutely no double-bubble discontinuity. This means that your thin sidewalls have to carry immense bending loads, and therefore be very heavy.

However even the 747 cross-section caused all sorts of structural problems its early years and provided oodles of work for MROs to carry our strengthening. Think it was described as "Section 41" work or something similar. Used to be a big advertising point for MROs in the 80s.

http://www.airliners.net/open.file?id=1281454

[chornedsnorkack]

chornedsnorkack, I think a trijet would be very heavy. The APTU envisioned would be a CFM class engine neadly fitting into the tail. It would provide the Ecoliner the required power at take-off with an engine failure while not requiring an engine to developped even larger then the GE90-115, while still providing twin cruise economics.

For some reason, it seems that airplanes want to keep the engines equal. The only exception is the fourth engine of Trident. From first principles, there would seem to be a good case for having a quad with a pair of large inboard engines and a pair of small outboard engines: this way, you do not have the critical case of an outboard engine out at the low airspeed of takeoff, and you can scale your fin and rudder to more modest asymmetric thrust torques. But for some reason, all quadjets other than Trident try to have all engines equal and scale their tail to outboard engine out - whether A380, A340, B747, B707, CV880, M119...

Do you know how exactly the weight and efficiency of engines scales with thrust? Would a MD-XX NG with, say, 3 GEnx engines be competitive with a 777-300ER with 2 Ge90-115 engines?

[keesje]

Chornedsnorkack, assuming all engines all equall tchnolgically advanced, a big engine (compressor / combuster / turbine) is more efficient then a equally advanced smaller engine. That why the A350 / 777 / 787 have two in stead of more engines.

Apart from that I think the aircraft types you mention developped during the last 50 yrs where not dealing with oil prices approaching $100 / barrel.
That makes it likely new developments next to the old ways of designing aircraft become more feasible.

I did a comparison of the same aircraft equipped with 4 new engines, it doesn't seem like a good idea :

http://i191.photobucket.com/albums/z160/keesje_pics/Ecoliner6APTU.jpg

Note that a tripple engined MD11 version would have 3 engine + 1 APTU = 4, while this aircraft has 3 powerplants with associated wiring, tubing, structure etc.

http://www.kaktusdigital.com/images/y3_aptu_small.jpg

About the thin side wall, lets remind ourselves these are only conceptual sketches, measuring the pictures and commenting is't usefull IMO.

http://www.kaktusdigital.com/images/y3_bank_small.jpg

[chornedsnorkack]

The way I see it, the alleged over 40 000 pound weight gain comes effectively from 40 000 pound difference from cruise fuel burn. Correct?

I looked for the tail engine air inlet on the video and could not see it. Would not a big APU with 16 t thrust require a substantial air inlet? It is over half the total thrust of MD-11 or Tristar tail engine, remember!

I accept that you plan to make the wall thicker in real life. But what precisely is the advantage of narrowing a 747 like double decker main deck? The fitting of double bubble is uncomfortable as it is, and narrowing the main deck will make matters worse.

[keesje]

Limiting frontal area=drag is a design goal. Wide fuselages create a lot of unused frontal area on the cargo deck as well as above the ceiling, like on the 777. Boeing tried to turn it into a added value, but the market told Boeing they don't like the sky loft ideas.

The ecoliner concept uses the lower part of the 777 standarizing cargo hold, wing torsion box etc

http://i191.photobucket.com/albums/z160/keesje_pics/Ecoliner1concept.jpg

As you can see the upperdeck of the ecoliner has a diffrent shape then the 747 upperdeck, making room for serious luggage stowage and use as 6 abreast economy a serious alternative, unlike the 747.

A ten abreast maindeck is not required for the envisaged market segment, below the A380, 370-500 seats. It can be done like on the 777, but is not standard for mainline long haul services.

On the APTU air inlets : those are retractable and melt into the fusealge during cruise. Dependent on size I can see about 4 of them. I think that is also what Boeing considered for the 777 hgw in the nineties.

[chornedsnorkack]

Limiting frontal area=drag is a design goal. Wide fuselages create a lot of unused frontal area on the cargo deck as well as above the ceiling, like on the 777.

Indeed. Which is why you should either a) shrink the width till you have a rather limited attic, as on A300/A330 family, or b) expand the fuselage until you have sufficient headroom on upper deck. 777 is too wide for a single-decker and too narrow for double-decker.

uses the lower part of the 777 standarizing cargo hold, wing torsion box etc

But you are violating the circular shape of the upper fuselage and losing all the advantages of a pure tension bubble structure. This costs immensely in pressure vessel weight and therefore induced drag.

As you can see the upperdeck of the ecoliner has a diffrent shape then the 747 upperdeck, making room for serious luggage stowage and use as 6 abreast economy a serious alternative, unlike the 747.

Ah. So 6 abreast economy on B747 is not serious, for some reason?

If you want a plane with upper deck slightly wider than 747, but not as wide as that of A380, then you should make the main deck wider, not narrower, than that of B747. So, what I suggest is a slightly expanded 747.

A ten abreast maindeck is not required for the envisaged market segment, below the A380, 370-500 seats. It can be done like on the 777, but is not standard for mainline long haul services.

If you stick to 9 abreast main deck then you cannot make your plane bigger than 777-300, basically. There is a big gap between 10 seats in the whole cross-section, as on 777, and 16 seats, as in 10 on main deck and 6 on upper deck for 747. But 15 abreast, 9 abreast main deck and 6 abreast upper deck, is IMO so bad for the pressure vessel efficiency that you are better off accepting 16 abreast and shrinking the fuselage to 747SP length.

[keesje]

"Ah. So 6 abreast economy on B747 is not serious, for some reason?"

I tried to specify economy class once on 744 upperdeck yrs ago with a big airline, limiting factor became the luggage stowage. Seatwise you can accomodate about 60-64 passengers. Logistical (galley, crew (de-)boarding but speciallly luggage wise) you create an operational drama.

"If you stick to 9 abreast main deck then you cannot make your plane
bigger than 777-300, basically."

Praticle lenght is limitted to about 80m. As you noted a very wide cabin doesn't seem like a good idea. To go beyond 400 seats with real product specifications an extra deck becomes the next best option IMO.
Boeing looked at it in the nineties.. http://s191.photobucket.com/albums/z160/keesje_pics/?action=view&current=Boeing763_246Ctotal.jpg

I think the A350XWB / 787 and A380 also do not have circular pressure vessels which are threoretically ideal. However this is not the only factor determining weight & operating costs. If you make the nearly circular damage can be limited.

http://www.flightglobal.com/assets/getAsset.aspx?ItemID=13916

Like groundloop mentioned MRO companies made good money with Section 41 modification lines. http://www.pprune.org/forums/images/infopop/icons/icon14.gif

P.S how do you do Quotes on this forum?

[chornedsnorkack]

"Ah. So 6 abreast economy on B747 is not serious, for some reason?"
I tried to specify economy class once on 744 upperdeck yrs ago with a big airline, limiting factor became the luggage stowage. Seatwise you can accomodate about 60-64 passengers. Logistical (galley, crew (de-)boarding but speciallly luggage wise) you create an operational drama.

http://www.boeing.com/commercial/airports/acaps/7474sec2.pdf
Boeing shows the ways to get 72 seats (page 25) and even 85 seats (page 28) on upper deck. I cannot see where the supposedly allowed 110 seats could go.
But as for luggage, the upper deck width between the outsides of armrests is shown as 346 cm (page 29), and 345 cm (page 31). Comparable with 707/727/737/757 single deck. The height of main deck is given (241 cm), but the height of upper deck is not.. Generally, the overhead space on 747 upper deck is less than on Boeing narrowbodies - but 747 has the floorlevel bins lacking on narrowbodies. How does the total available luggage space compare?
Do you happen to know the actual height of 747 upper deck - floor to top of ceiling vault?
I think the A350XWB / 787 and A380 also do not have circular pressure vessels which are threoretically ideal. However this is not the only factor determining weight & operating costs. If you make the nearly circular damage can be limited.
767 is not a circular pressure vessel, either
But if you cannot have circle, your next best choice is double bubble. Still a pure tension structure, though now the floor carries pressurization loads, holding the walls together.
P.S how do you do Quotes on this forum?
Looks difficult, yes, because there is no Reply with Quote option. I use Quote icon above the reply box (the last to the right) and then have to copy and paste from the thread presented beneath.

[Nichibei Aviation]

Dear Keesje, I have been following your developments on Airliners and find your idea's very interesting.
I congratulate you for the time and passion you spend on this project.

I agree with you that the twin double-decker is the solution for economical travel and I 've been thinking about it some times already.

The only problem I see in your project is the single engine take-off performance and the APTU. There are 3 problems:

-Considering that the APTU is a CFM-56 class system, and using it only at critical moments such as tkof would make it a waste of weight as these engines usually weigh around 6000lbs.
-Considering your design of the air intake through a pipe placed at 90 degree angle to the airflow, the engine air intake will not be sufficient to provide the full-rated thrust. Also, the 90 degree angle air intake angle will create extensive drag. Even if the angle is decreased, these problems will not be entirely eliminated.
-Placing an engine device in the aft section is troublesome due to the different control surfaces present in that area: elevators, rudders. Several uncontained engine failures have resulted in crashes...

The engine failure at take-off is a difficult argument.
This is my solution:
If an engine that has failed could be used as a ram/rocket jet engine, the argument would be no more. These sort of engines burn alot more fuel in shorter periods, which means that you can get rid of all that fuel you'd like to get rid of, and at the same time generate enormous thrust that will enable the aircraft to climb. If engines could be designed in this way, the one engine inoperative problem would be no more.
I'm putting a copyright on this idea :)

Procedure will be easy: engine failure/X-feed selection/full-fuel injection/continuous ignition/establish climb speed,...

The B757 at manchester that suffered a contained EF is a good example showing that this could work.

[chornedsnorkack]

If an engine that has failed could be used as a ram/rocket jet engine, the argument would be no more. These sort of engines burn alot more fuel in shorter periods, which means that you can get rid of all that fuel you'd like to get rid of, and at the same time generate enormous thrust that will enable the aircraft to climb. If engines could be designed in this way, the one engine inoperative problem would be no more.
I'm putting a copyright on this idea

Ram engines do not and cannot work on low airspeeds/takeoff.

Rockets do, but they require oxidizer tanks and systems.

My suggestion is use the good engine. Reheat/afterburner on a bypass engine is a known procedure. It is extremely inefficient at low speeds (at high speeds reheat is actually better than turbine!), but it has the advantage of being inherently simple, lightweight and reliable - you could have an engine which is lightweight and efficient in cruise but has immense thrust/weight with reheats on!

[Nichibei Aviation]

You are right about the RAM slow speed properties.

I also found this solution: emergency oxygen supply tanks linked to the engines that can be used as rocket engines. The only problem will be the combustion capability of Jet A1.

[ETOPS773]

Keesje,

First of all, congratulations on the very well thought out and informative concept. I must say the renderings & especially the video look absolutely fantastic and you've created a magnificent looking aircraft.

Just a little comment or two...

I would drop the thrusting APU concept. It's a good, and logical idea, but 30,000lbs+ of thrust would be a very tall order.

A simplified afterburner / reheat system on an existing turbofan such as a GE90 would be an easier option because by it's very nature it would be mechanically simpler, and a nice little bonus would be that during it's operation, it would burn great amount of fuel, which in turn would help get the aircraft down to landing weight much quicker.

I think the ingredients should be 2 x Genx'd GE90-115 with reheat. The APU could be a fuel cell.

[keesje]

For your entertainment Henry Lam made a Youtube on this Ecoliner:
http://youtube.com/watch?v=CVWQ5h5UOfk&feature=related

and soon there will even be a MS Flight Simulator version :8

Unfortunately I don't have FS since I replaced my first Pentium, 5 yrs ago..

[keesje]

2 new visual were made by Henry Lam. he sels these customized artist impression quick & affordable on existing and non existing aircraft but also like to play around :):

One in flight :

http://www.kaktusdigital.com/images/Y3_cruise.jpg

and during take-off :

http://www.kaktusdigital.com/images/Y3_takeoff.jpg


Since starting the post, prospects for the 747-8i haven't improved. Lufthansa remains the only customer for the 747-8i.

I really wonder if Boeing and Lufthansa will push it through..