Which Way The World's Next Generation Airliner?
A Look At The Past, The Present and The Possible!

By Joe Mizrahi

(Reprinted with the permission of Wings, April 1999, Vol. 29, No. 2, Sentry Magazines, Granada Hills, CA, pp. 8-19.  Thanks to Paul Spatrisano of Bend, Oregon for obtaining permission and providing the material to TWITT.)

Click here if you would like to go directly to the text material and scan the pictures as you go along.

Click on this link (http://www.up-ship.com/eAPR/ev1n3.htm) for more drawings and information on blended wing bodies.

ABOVE:  This is the  most promising future airliner both aesthetically and in terms of economical operation.  The BWB concept actually transforms John Northrop's historic flying wing proposition into tangible reality.  Cleaner, less expensive to build, stronger, quieter, easier to handle and still within the parameters of the 80 meter box.  Click here for more. ABOVE: The Boeing C-Wing also known as the "Klingon Battlecruiser" by its two creators J.H. McMasters and I.M. Kroo, departs from the standard tube with wings technology favored by Airbus.  Click here for more.
LEFT:  A more conventional shape for the 747 XL dropped the tube with wings layout and substituted a centerbody fuselage with a wing area of 9,000 sq. ft. and a span of 300 ft.  Its hybrid laminar flow control outer wing tips could be folded to reduce span to 170 ft., and the aircraft, utilizing the thick Griffith airfoil with slots on the trailing edge, plus Krueger bug shield leading edge high lift devices, would have been powered for four 95,000 lbs. thrust very high bypass turbo fans.  Accomodations for up to 800 passengers (50 abreast) would be provided, and airframe encompassing the 1,400,000 lb. (takeoff) weight would have been largely fashioned from composite materials.

ABOVE: C-Wing proposal compared to that of conventionally shaped transport of comparable 600 passenger capacity, shown in black.  This version has sharply reduced fuselage and wingspan, while absence of horizontal taile easily allows it to fall within the confines of the necessary 80 meter box, above which aircraft size leads to gate, runway and taxiway restrictions. 

The minimum wetted area for a given volume is a sphere.  The designers of the BWB airliner began with cylindrical pressure vessels in their initial layout (top drawing) and gradually pressed down until they had a flattened disk with wings (bottom sketch), its engines on the trailing edge, just outboard and to the rear of the centerbody.
ABOVE:  Comparison views of the conventional airfoil (dotten lines) with that of the advanced Griffith airfoil. 

BELOW:  Cross-section view of the C-Wing depicts passenger cabin profile of centerbody.


ABOVE:  One of the beauties inherent in a BWB airliner is it strength.  It readily absorbs both cabin pressure and wing bending loads, and in recent tests in the Stanford University wind tunnel, a 6% scale model easily passed all extreme flight envelope tests.

LEFT:  The BWB concept reduces the load on the outboard wing section airfoils, while the large centerbody chord provides enormous strength, requiring a much low sectional lift coefficient.  This reduced lift demand allows the large thick profile of the centerbody to hold passengers and cargo, without exacting a high compressibility drag penalty.  Due to its shape and structure, typical shocks evident on the thinner outboard wing panels become very weak on the centerbody.  Ahead of this shock, airflow is supersonic; behind it, the air slows and that sub-sonic area is highly suitable for engine installation.  The low effective wing loading of the BWB and its beneficial trim effect means that no exotic high lift system is necessary; only leading edge slats are necessary on the outboard wing, with all trailing edge devices made up of simple hinged flaps which double as elevons. 

ABOVE: Double-decked BWB interior is configured for ten 150" wide passenger cabin bays, at least 74" high on the upper deck and 84" on the lower deck.  Layout is shown from top in in the upper drawing and from the side and front in the lower.  Windows are located along the leading edge of each cabin bay, with a promenade aisle curving around and back from the forward flight deck.  Galleys and lavatories are located aft.  Entrance and exit to the interior is via main cabin doors forward and through doors aft of the rear spar.  Cargo bays are located outboard of the passenger cabin, with pressurized fuel tanks outboard of them.  Location of the 3 engines to the rear radically minimizes cabin noise. ABOVE:  Interior of the C-Wing design demonstrates that most passengers in coach class are carried within the wing centerbody, leaving the tube portion of the fuselage for business and first class.  This forward tube portion, with its canards, has a much smaller diameter than the fuselage of the conventional large body airliner.
A New Shape For A New Century

    With the advent of the rectangle, and then the tube with wings, twin characteristics of airliners and commercial flight since the early Twenties, airline manufacture has adhered to a well-established pattern.  Whether a Ford Trimotor, Douglas DC-3 or -4, the long line of Boeings up through the 777, and the entire Airbus family, passengers have entered a more or less long cylindrical tube, which given enough push (jet engines) or pull (propellers) has then sped them away to their various destinations. 
    In 1966, when Boeing's 747 was launched, it was believed that the tube with wings configuration had reached the apogee of the form's usefulness.  That very large aircraft was powered by four engines, yet in 1990 Boeing offered still another tube with wings airliner, almost as large, but with only two engines, the 777.  In its latest -300 models, already in production, that design will have a fuselage length which exceeds the 747's by more than ten feet.  Boeing has also been contemplating an even larger four-engined 747, the 747 XL (Xtra Large), a sort of scaled up flying watermelon that could seat up to 650 passengers.  But that what many engineers consider to be a foreshortened freak will not be translated to metal, at least not by Boeing. 
     Boeing's 777 variant and those spun off from it will not greatly alter current airport facilities or operations, but a new giant from Airbus will.  Known as the A3XX, and currently under final design, this behemoth, which may debut as early as 2005, will have a wingspan of 253 feet and a length of 250 feet.  The fin will tower 75 feet above the tarmac, but no ordinary tarmac will be able to support its massive one million, eighty four thousand pound takeoff weight.  Such a huge shape will also cause problems with wake vortex, passenger circulation and comfort, plus the daunting attendant psychology in flying in something that big.  At a greatly higher price than the newest 747, it will only hold 75 more passengers without any significant increase in speed or range. 
   The reason these super jumbos are going to become reality has already been discussed.  In the future, the world's airlines will have to move many more people than they do now, and each international takeoff will have to be maximized in terms of passengers transported.  This prediction brings us to the subject of this article.  Long before Airbus decided to go ahead with their super-jumbo Boeing evaluated a potential successor for its own 747, since the extended range 777 was only an intermediate solution to moving more people. 
    At a symposium held in January 1998 at Reno, Nevada, Boeing came up with two ambitious, but practical alternatives to answer the real need for a very large transport airplane of the future.  They are presented here.  Each one would cost at least seven billion dollars to bring to fruition, but in the following discussion, the reader will see that either design is far superior to the standard tube with wings already chosen by Airbus, and one is a truly breathtaking solution. 

The C-Wing Klingon Battlecruiser

    To paraphrase John McMasters of the Boeing Company, "innovation for it own sake can be a great waste of time, but individuals with a sufficient depth of knowledge in more than one technical discipline can, working in teams, exploit the unorthodox to create a very workable design.
    The ideal cruising aircraft is a simple, elegant flying wing, and everything that does not contribute directly to generating lift should be integrated in or on that wing, if it is to retain an aerodynamic purity.  In every large aircraft of this type, one that might accommodate up to 800 passengers, the possible laminarization of the wing could not be taken advantage of until it was think enough and large enough to carry that many people.  So, if your goal is 600 passengers or more, you might want to choose the very thick subsonic Griffith airfoil, invented over a half century ago in England.  With slots top and bottom and a number of additions, this basic football-shaped section, when viewed in profile, would provide the necessary lift, but its span would be on the order or 300 feet and passengers in the center section of this flying wing would sit 50 abreast. 
   A more promising alternative would be to take the basic wing structure, as described, graft a central tubular fuselage extending ahead and behind its center section on it, remove the hybrid laminar flow control outer wing panels and replace them with inward and rear-facing smaller horizontal winglets located at the tips of standard vertical winglets.  In addition to reducing the span and eliminating the horizontal tail of a conventional alternative, sweeping the wing and the horizontal winglets by 35 degrees, allows the latter act as a horizontal stabilizer relative to the rest of the wing. 
    This configuration, which was patented by Boeing in 1995, not only lessens induced drag, keeping it within acceptable limits, but also down sizes the airplane all around, resulting in a fin and rudder 20 feet lower than what would be necessary on a scaled up conventional shape. 
   As conceived by John McMasters, I.M. Kroo and Richard J. Pavek, the C-Wing shape would be thick enough for spanwise distribution of payload, thus reducing high lift requirements, and would be commodious enough to seat 36 abreast.  A canard, or foreplane, would act as a control surface during cruise, becoming part of the necessary high lift system when flaps were extended, as would the stabilizing surfaces of the aft swept horizontal winglets.  Two engines forward and two aft would supply adequate power and also reduce noise.  In effect, the C-Wing maximizes the positives found in the basic Griffith Wing layout. 
   An alternative layout with only three engines showed even more promise, with approach speeds of 135 mph, compared to 155 mph for a conventional shaped aircraft accommodating the same 126,00 pound payload.  Range would be identical, 7,400 miles, although the C-Wing design in all its variants would be heavier by some 125,000 pounds and would  require an additional 700 feet of runway to get off, but it could land within 5,400 feet, nearly 1,000 feet shorter than its large conventional rivals.  It would also require and burn more fuel per passenger mile. ( http://www.lmasc.com/ama/gallery.htm

The Blended Wing Body

   Additional weight and more fuel necessary to transport the same payload just as far will probably doom the C-Wing alternative, but when Boeing absorbed McDonnell Douglas, they also acquired the thinking of three more innovative design engineers, R.H. Liebeck, M.A. Page and B.K. Rawdon, who were working on the Blended Wing Body (BWB) transport of the future.
   If ever a design represented innovation matched with utility, this one is the embodiment of that concept.  According to  intensive, well-reasoned calculations, the aircraft they propose would carry 800 passengers over a 7,100 nautical mile range and be ready to enter service in the year 2010.  Quite an accomplishment considering that its fuel burn will be 27% lower than its conventional Airbus A3XX rival, with a take off weight 15% lower.  Empty weight will be 12% less.  It will only require three instead of four engines, and will match or exceed  conventional performance, despite having 27% less thrust.  Those factors combined with 20% better lift/drag capability translates to the phenomenal savings in fuel already mentioned. 
   With a double-decked interior cabin located in the central portion of the blended wing, the extension serves to stiffen, buttress and extend structural integrity and aerodynamic overlap to the entire wing structure.  The blended wing layout also serves as a very resilient bending structure, dramatically reducing the cantilever span of the thin wing section, distributing weight along the span more efficiently. This reduces the peak bending moment and shear to half that of a conventional configuration.  Its shape also reduces total wetted area, or those portions of the aircraft which come in contact with the air.  In this imaginative layout there is no need for a conventional tail.  Unlike standard configurations, the blended wing's outboard leading edge slats are the only high lift devices required and, because the three buried engines aft of the central wing structure ingest the wing's boundary layer airflow, effective ram drag is also reduced. 
   A cylindrical pressure vessel was the starting point for what became the BWB fuselage.  In order to seat passengers in reasonable comfort, it originally had a volume of 55,000 sq. ft.  The minimum wetted area for this given volume, enclosing a passenger cabin for 800, plus galleys, lavatories and baggage, is best realized as a sphere, but a sphere is not conducive to streamlining, unless it can be flattened into a disk.  In the case of the BWB, a streamlined disk integrated with the wing initially resulted in reducing total wetted area by 7,000 feet.  Further revisions and modifications dealing with engine and control surface integration led to a total surface area of 29,700 feet, a reduction of an additional 33%.
( http://oea.larc.nasa.gov/PAIS/BWB.html
   In this deign the fuselage is not only a wing, but a mounting for the engines that power it, along with their inlets, as well as a pitch control surface. By continuing to blend and smooth the streamlined disk, with a bullet nose added for enhanced visibility from the flight deck, the designers have come up with an aircraft that will fly at Mach .85, with an optimized wing loading fully 33% lower than that of conventional large size, long-range aircraft with less passenger carrying capacity.  Since the wing blending hides most of the trapezoidal wing within the centerbody of the aircraft, the cost of wing area on drag is greatly lessened.  In short, because the BWB planform has such a large chord, it requires a much lower sectional lift coefficient to preserve an elliptic span load, thus allowing the centerbody's thickness to maximize payload volume without a high compressibility drag penalty. 
   In layman's terms, the low effective wing loading of the BWB meant that exotic high lift systems are not needed.  A leading edge slat is necessary on the outboard wing, but all trailing edge devices are simple hinged flaps, which also serve as elevons.  Low wing loading reduces control power demands.  The small winglets provide primary directional stability and control, and split drag rudders, similar to those found on the B-2 bomber, are used for low-speed, engine-out conditions. 
    On a 5% scale model tested in Langley's wind tunnel (http://lisar.larc.nasa.gov/ABSTRACTS/EL-1998-00245.html), the BWB showed relatively small center of gravity variations, good stall characteristics and excellent control power through the stall, the BWB handling extremely well in the normal flight envelope.  Further tests at Stanford University explored extreme flight envelope characteristics and revealed so significant problems that could not be readily addressed and solved.  ( http://aero.stanford.edu/BWBProject.html
   Like all next generation aircraft, the BWB will be constructed with composites.  Bending and pressure loads on the structure can be carried by a 5-inch thick sandwich and deep hat stringer shell, or a deep skin/stringer alternate, both of which are already in wide application.  Passengers will be accommodated in five longitudinal bays, each the width of a DC-8 cabin.  Coach class will have six seats with an aisle between.  Business class will have two/two seating with an aisle.  Each separated section will be the length of a DC-9 fuselage. 
   Galleries and lavatories will be located aft.  In addition to a forward view through windows mounted along the curve of the wing, flanking the flight deck's bullet nose, an additional promenade aisle will allow passengers to walk along the curve of the leading edge.  On the ground, entrance and exit will be accomplished by means of main cabin doors in the wing's leading edge and through doors aft of the rear spar.  Cargo will be carried outboard of the passenger bays, with fuel in cells further out on the wing, thus allowing a great deal of space between the tanks and the passenger compartment. 
   In addition to performance, comfort and capacity, the BWB concept has an inherently low acoustic signature.  Exhaust noise will not be reflected off the wing's undersurface.  There is little additional airframe noise caused by complex mechanism, such as slotted flaps.  The aft location and staggered positions of the engines lessens the possibility of shards and debris from a failed powerplant penetrating the pressurized cabin or fuel tanks, destroying flight controls or causing the remaining engines to fail.  Compared to conventional cylindrical tube fuselages, the center body pressure vessel of the BWB is much stronger, thus improving chances of survival in a crash. 
      Will such an aircraft ever be built?  That's the decision the manufacturer will have to make.  But if a large subsonic aircraft to take the place of the 747 is really needed, it appears that the BWB concept offers the most for the necessary investment.  It's lighter, more commodious, more fuel efficient, requires far less power, and is certainly more aesthetic in appearance.  True, looks aren't everything, but that old aviation adage still holds true, "If it looks good, it will fly good," and the BWB aircraft, in addition to much improved economy, simplicity and handling, certainly has any potential flying watermelon beaten hands down. 
   Eigthy-five years ago, when Boeing first began making a name for itself, in addition to farseeing design and exceptional engineering excellence, a willingness to invest in the cutting edge of future flight inevitably characterized it planes.  Innovation has always been a prominent feature of Boeing's corporate initials.  Taking a page out of it enviable history, it should, one again, invest in that future.  The BWB airliner is the right plane at the right time and will, once again, keep Boeing in the forefront of economically viable aerospace technology. (Click here to read an article from the Seattle Times on the blended wing.)

(The remainder of the article covered the history of commercial airliners from other countries, and it included a large number of very good pictures of these aircraft.)

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