Abstract:
An aircraft and associated method of manufacture and operation. The aircraft can include a fuselage having a first portion and a second portion projecting upwardly from the first portion, with the first portion housing a passenger deck and the second portion being positioned above the passenger deck. A first wing can extend outwardly from the first portion of the fuselage and the second wing can extend outwardly from the second portion of the fuselage, with the second wing being positioned above and forward of the first wing. Accordingly, the fuselage can include a plurality of passenger doors simultaneously accessible to ground-based passenger load/unload equipment with at least one of the passenger doors positioned beneath the second wing.

Description:
TECHNICAL FIELD  
         [0001]    This present invention relates generally to tandem wing aircraft and methods for manufacturing and operating such aircraft.  
         BACKGROUND  
         [0002]    One goal of the commercial air transport industry is to convey passengers and cargo as quickly as possible from one point to another. Accordingly, many commercial transport aircraft operate at cruise Mach numbers of approximately 0.8-0.85. As the time constraints placed on air carriers and their customers increase, it would be advantageous to economically transport passengers and cargo at higher speeds. However, aircraft flying at transonic or supersonic speeds (greater than about Mach 0.85) have greater relative thrust requirements than comparably sized subsonic aircraft. To generate sufficient thrust at high altitudes and Mach numbers, while reducing the corresponding increase in drag, conventional transonic and supersonic aircraft include low bypass ratio turbofan engines or straight turbojet engines. Such configurations generally have a high specific fuel consumption at cruise conditions that generally outweighs any inherent advantage in aerodynamic efficiency, resulting in a net fuel efficiency significantly lower than that of lower speed aircraft. The low fuel efficiency can also result in increased atmospheric emissions.  
           [0003]    [0003]FIGS. 1A and 1B illustrate top isometric and bottom isometric views, respectively, of a supersonic cruise aircraft  10   a  in accordance with the prior art. The aircraft  10   a  can include a fuselage  13   a , a delta wing  12   a , a propulsion system  15   a  suspended from the wing  12   a , and an aft-tailed pitch control arrangement  17 . Alternatively, the aircraft  10   a  can include a tail-less or canard pitch arrangement. In either configuration, the longitudinal distribution of the exposed cross-sectional area of the aircraft, and the longitudinal distribution of the planform area tend to dominate the transonic and supersonic wave drag (i.e., the increase in drag experienced beyond about Mach 0.85 due to air compressibility effects). Accordingly, the fuselage  13   a  can be long, thin, and “area-ruled” to reduce the effects of wave drag at supersonic speeds.  
           [0004]    Area-ruling the fuselage  13   a  can result in a fuselage mid-region that is narrower than the forward and aft portions of the fuselage (i.e., a “waisted” configuration). Waisting the fuselage can compensate for the increased cross-sectional area resulting from the presence of the wing  12   a  and the propulsion system  15   a . The propulsion system  15   a  can include four engine nacelle pods  16   a  mounted beneath the wing  12   a  to minimize adverse aerodynamic interference drag and to separate the rotating machinery of the engines from the main wing spar and the fuel tanks located in the wing. Noise suppressor nozzles  18   a  are typically cantilevered well beyond a trailing edge of the wing  12   a , and can accordingly result in large cantilever loads on the wing  12   a.    
           [0005]    FIGS.  1 C-E illustrate a side view, plan view and fuselage cross-sectional view, respectively, of a configuration for a high-speed transonic cruise transport aircraft  10   b  having a fuselage  13   b , a swept wing  12   b , and engine nacelles  16   b  suspended from the wing  12   b  in accordance with the prior art. The fuselage  13   b  has a significantly narrowed or waisted portion proximate to a wing/body junction  19 . Accordingly, the fuselage  13   b  is configured to avoid or at least reduce increased drag in a manner generally similar to that described above with reference to FIGS. 1A and 1B. This configuration may suffer from several drawbacks, including increased structural weight, increased risk of flutter loads, and a reduced payload capacity. The configurations shown in FIGS.  1 A- 1 E can be structurally inefficient and can have reduced payload capacities as a result of the fuselage waisting required to reduce transonic and supersonic drag.  
         SUMMARY  
         [0006]    The present invention is directed toward tandem wing aircraft and methods for manufacturing and operating such aircraft. An aircraft in accordance with one aspect of the invention includes a fuselage having a first portion and a second portion projecting upwardly from the first portion. The first portion houses a passenger deck and the second portion is positioned above the passenger deck. A first wing extends outwardly from the first portion of the fuselage and a second wing extends outwardly from the second portion of the fuselage. The second wing is positioned above and forward of the first wing.  
           [0007]    In a further aspect of the invention, the fuselage can include a plurality of passenger doors simultaneously accessible to ground-based passenger load/unload equipment. At least one of the passenger doors is positioned beneath the second wing. In still further aspect of the invention, the aircraft can have a forward portion, an aft portion, and an intermediate portion between the forward and aft portions, with a cross-sectional area distribution of the aircraft increasing at least approximately monotonically from the forward portion to the intermediate portion, and decreasing at least approximately monotonically from the intermediate portion to the aft portion.  
           [0008]    The invention is also directed toward a method for loading and unloading an aircraft and includes positioning a first passenger load/unload device adjacent to a first passenger door of the aircraft, with the aircraft having a first wing and a second wing positioned forward of and above the first wing. The method can further include positioning a second passenger load/unload device adjacent to a second passenger door of the aircraft while the second passenger load/unload device is positioned beneath the second wing of the aircraft and while the first passenger load/unload device is positioned adjacent to the first passenger door. The method can still further include simultaneously moving passengers through both the first and second passenger doors.  
           [0009]    The invention is still further directed to a method for manufacturing an aircraft. The method can include providing a fuselage having a first portion and a second portion projecting upwardly from the first portion, with the first portion housing a passenger deck and the second portion being positioned above the passenger deck. The method can further include mounting a first wing to the first portion of the fuselage and mounting a second wing to the second portion of the fuselage with the second wing being positioned above and forward of the first wing. In a further aspect of the invention, the method can further include providing the fuselage with a plurality of passenger doors that are simultaneously accessible to ground-based passenger load/unload equipment, with at least one of the passenger doors being positioned beneath the second wing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIGS. 1A and 1B illustrate a supersonic transport aircraft configuration having a narrowed fuselage in accordance with the prior art.  
         [0011]    FIGS.  1 C- 1 E illustrate a subsonic/transonic transport aircraft having a narrowed fuselage in accordance with the prior art.  
         [0012]    FIGS.  2 A- 2 C illustrate an aircraft having a forward wing and an aft wing in accordance with an embodiment of the invention.  
         [0013]    [0013]FIGS. 3A and 3B illustrate cross-sectional views of an aircraft generally similar to that shown in FIGS.  2 A- 2 C in accordance with an embodiment of the invention.  
         [0014]    [0014]FIGS. 4A and 4B illustrate top plan views of aircraft having deck configurations in accordance with embodiments of the invention.  
         [0015]    [0015]FIG. 5 illustrates cross-sectional area distributions for aircraft in accordance with embodiments of the invention.  
         [0016]    [0016]FIG. 6 is a side elevation view of an aircraft having a forward wing, an aft wing, and nacelles mounted above the aft wing in accordance with an embodiment of the invention.  
         [0017]    FIGS.  7 A- 7 C illustrate an aircraft having an aft wing and an upwardly extending projection supporting a forward wing in accordance with another embodiment of the invention.  
     
    
     DETAILED DESCRIPTION  
       [0018]    The present disclosure describes high speed aircraft and methods for manufacturing and operating such aircraft. Many specific details of certain embodiments of the invention are set forth in the following description and in FIGS.  2 A- 7 C to provide a thorough understanding of these embodiments. One skilled in the art, however, will understand that the present invention may have additional embodiments, and that the invention may be practiced without several of the details described below.  
         [0019]    [0019]FIG. 2A is a side elevational view of an aircraft  100  having a fuselage  130 , a swept aft wing  120 , and a forward wing  110  that is swept and positioned above and forward of the aft wing  120 . The aft wing  120  and the forward wing  110  can be integrated with the fuselage  130  in a manner that results in a generally monotonically increasing and monotonically decreasing cross-sectional area distribution, as described in greater detail below. As is also described in greater detail below, the elevated forward wing  110  can have a reduced aerodynamic impact on the aft wing  120 , which can increase the stability and controllability of the aircraft  100 . The elevated forward wing  110  can also allow greater access to the aircraft  100  during loading and unloading than is available for existing aircraft having canards.  
         [0020]    In one embodiment, the fuselage  130  can have a lower portion  132  that extends aft for the entire length of the fuselage, and a projection  140  that extends upwardly from the lower portion  132  for at least a portion of the fuselage length. The aft wing  120  can extend outwardly from the lower portion  132 , and the forward wing  110  can extend outwardly from the projection  140 . Accordingly, the vertical separation between the forward wing  110  and the aft wing  120  can be increased compared to existing aircraft configurations that include a canard but lack the projection  140 . In one aspect of this embodiment, the forward wing  110  can have a surface area that is a substantial fraction of the surface area of the aft wing  120 . For example, the forward wing  110  can have a surface area that ranges from about 10% to about 50% of the surface area of the aft wing  120 . In one particular embodiment (shown in FIGS.  2 A- 2 C) the surface area of the forward wing  110  can be about 15% of the surface area of the aft wing  120 . In other embodiments, the forward wing  110  can be smaller, for example, in an embodiment described below with reference to FIGS.  7 A- 7 C.  
         [0021]    The lower portion  132  of the fuselage  130  can include a forward region  138  which generally increases in cross-sectional area, and an aft region  139  which generally decreases in cross-sectional area. The projection  140  can be blended with the lower portion  132  of the fuselage  130  and can accordingly include a forward region  148  that increases in cross-sectional area, and an aft region  149  that decreases in cross-sectional area. The axial locations of the foregoing regions of the fuselage  130  can be selected to coincide with the axial locations of other components of the aircraft  100  to produce a generally smooth cross-sectional area distribution, as described in greater detail below with reference to FIG. 5.  
         [0022]    In a further aspect of this embodiment, the lower portion  132  can house a first or lower passenger deck  133  and a cargo deck  134  positioned beneath the lower deck  133 . The cargo deck  134  can accommodate containers  165  and/or loose baggage. The projection  140  can house a second or upper passenger deck  143  and a flight deck  142  positioned forward of the upper deck  143 . The lower deck  133  and, optionally, the upper deck  143 , can include passenger doors  135  (including a forward passenger door  135   a  and an aft passenger door  135   b ) to allow passengers and crew to enter and exit the aircraft  100 .  
         [0023]    In yet a further aspect of this embodiment, the aircraft  100  can be supported on a main landing gear  104  and a nose gear  105 . The aircraft  100  can include a vertical stabilizer  102  with a rudder  103 . In one embodiment, the aircraft  100  can include a propulsion system  150  having one nacelle  152  extending through the vertical stabilizer  102 , and two nacelles  152  depending from the aft wing  120 . Each nacelle  152  can house a single engine  151 . In other embodiments, the propulsion system  150  can have other arrangements, such as those described in greater detail below with reference to FIGS.  6 - 7 B.  
         [0024]    [0024]FIG. 2B is a top plan view of an embodiment of the aircraft  100  described above with reference to FIG. 2A. As shown in FIG. 2B, the aircraft  100  can include a strake  121  extending forward from the aft wing  120  toward the forward wing  110 . The strake  121  can provide additional lift and stability for the aircraft  100 , and can smooth the cross-sectional area distribution of the aircraft  100 . The forward wing  110  of the aircraft  100  can include a wing box  113  and trim surfaces  111  positioned aft of the wing box  113  and moveable relative to the wing box  113 . The aft wing  120  can include elevons  122  for pitch, trim, and roll control. The center of lift of the aft wing  120  can be positioned aft of the aircraft center of gravity  101 , and the center of lift of the forward wing  110  can be positioned forward of the center of gravity  101 . Accordingly, when the trim surfaces  111  are adjusted downwardly, they add to the lift generated by the aft wing  120  and the elevons  122  and increase the overall lift of the aircraft  100 . This is unlike existing commercial passenger aircraft having trim surfaces that are positioned aft of the aircraft center of gravity and which typically reduce the overall lift of the aircraft when actuated.  
         [0025]    The aircraft  100  is shown in FIG. 2B positioned near a terminal for loading and/or unloading in accordance with an embodiment of the invention. In one aspect of this embodiment, passengers can enter and/or exit the aircraft  100  through a first jetway  160   a  positioned next to the forward passenger door  135   a  and through a second jetway  160   b  positioned next to the aft passenger door  135   b . In a further aspect of this embodiment, the aft passenger door  135   b  (and the second jetway  160   b ) can be positioned beneath the forward wing  110 . In another embodiment, the passengers can embark and disembark via other load/unload equipment, such as stairways. In any of these embodiments, the forward wing  110  (by being mounted to the projection  140 ) can be located a sufficient distance above the aft passenger door  135   b  to allow the second jetway  160   b  (and/or other equipment) to be positioned next to the aft passenger door  135   b  without interfering with the forward wing  110 . Accordingly, passengers can enter and exit the aircraft  100  through multiple doors even though the wing/body junctions for the forward wing  110 , the aft wing  120  and the strake  121  occupy a substantial fraction of the overall aircraft length.  
         [0026]    The aircraft  100  can further include one or more galley doors  136  (shown in FIG. 2B as a forward galley door  136   a , an intermediate galley door  136   b , and an aft galley door  136   c ). Each of the galley doors  136  can be simultaneously serviced by corresponding galley service vehicles  161 . Because the forward wing  110  is mounted to the projection  140 , the galley service vehicles  161  can access the intermediate galley door  136   b  even though this galley door is positioned directly beneath the forward wing  110 .  
         [0027]    The aircraft  100  can be serviced by other ground support equipment simultaneously with loading and unloading passengers and servicing the aircraft galleys. For example, the cargo deck  134  of the aircraft  100  can be serviced by a container ramp  164  and/or a baggage ramp  162 , generally in accordance with existing operational procedures, and without interfering with the jetways  160  or the galley service vehicles  161 . In other embodiments, the cargo deck  134  can be serviced in accordance with other arrangements.  
         [0028]    [0028]FIG. 2C is a front elevational view of an embodiment of the aircraft  100  described above with reference to FIGS.  2 A- 2 B. In one aspect of this embodiment, the forward wing  110  can include upwardly canted forward wing tips  112  and the aft wing  120  can include upwardly canted aft wing tips  123 . Canting the forward wing tips  112  upwardly can further reduce the likelihood for interference between the forward wing  110  and ground-based equipment, such as the jetways  160  discussed above with reference to FIG. 2B. Canting the aft wing tips  123  upwardly can reduce the likelihood for interference between the aircraft  100  and neighboring aircraft parked adjacent to the aircraft  100 . For example, in one embodiment, the aircraft  100  can be positioned close enough to neighboring aircraft that the aft wing tips  123  extend over the wings of the neighboring aircraft in a “composite” parking arrangement.  
         [0029]    [0029]FIG. 3A is a cross-sectional view of an aircraft  100  in accordance with an embodiment of the invention, taken substantially along line  3 A- 3 A of FIG. 2A. In one aspect of this embodiment, the lower portion  132  of fuselage  130  can have an at least slightly elliptical shape with a transverse major axis. Further details of fuselages having such shapes are included in pending U.S. patent application Ser. No. 09/969,801, filed Oct. 2, 2001 and incorporated herein in its entirety by reference. The lower portion  132  can include a floor  129  that separates the lower deck  133  from the cargo deck  134 . In one embodiment, seats  131  positioned in the lower deck  133  can define a lower seat plane  137  that is positioned generally above the aft wing  120 . In another embodiment, the lower seat plane  137  can be positioned at or below the aft wing  120 . In any of these embodiments, the lower seat plane  137  is positioned below the forward wing  110  (FIG. 2C), as described in greater detail below with reference to FIG. 3B.  
         [0030]    [0030]FIG. 3B is a cross-sectional view of an aircraft  100  in accordance with an embodiment of the invention, taken substantially along line  3 B- 3 B of FIG. 2A. In one aspect of this embodiment, the fuselage projection  140  can extend above the lower portion  132  and can have a generally elliptical shape with a transverse minor axis and a vertical major axis. The seats  131  in the upper deck  143  can be arranged to define an upper seat plane  147  that is positioned above the aft wing  120  and below the forward wing  110 . The lower seat plane  137  is accordingly positioned beneath the upper seat plane  147  and beneath the forward wing  110 .  
         [0031]    [0031]FIG. 4A is a partially exploded, cross-sectional plan view of the lower portion  132  of the fuselage  130 , and the fuselage projection  140  superimposed on an outline of the lower portion  132 . As shown in FIG. 4A, the fuselage projection  140  can include seats  131  arranged for first class passengers, and the lower deck  133  can include seats  131  arranged for business class and economy class passengers. In one aspect of this embodiment, the fuselage  130  can have a length of about 80 meters and can be configured to carry about 300 passengers. In another embodiment (shown in FIG. 4B), the lower portion  132  of the fuselage  130  can include a lower deck  133   a  having a cargo area  128  configured to carry cargo containers  165 , and can further include a passenger area  129  having seats  131  for business class and economy class passengers. In one aspect of this embodiment, the lower deck  133   a  can include a cargo door  427  positioned just aft of the aft wing  120  (FIG. 2B) and just forward of the aft galley door  136   c . In another embodiment, the aft galley door  136   c  can be supplemented or replaced by an aft galley door  436   d  positioned on the opposite side of the aircraft  100 . In yet another aspect of this embodiment, the lower deck  133   a  can have a “combi” configuration in which seats can be removably placed in the cargo area  128  for selected flights. Accordingly, a single aircraft  100  can be easily reconfigured depending on whether a particular flight benefits more from additional passenger seats or additional cargo space. In other embodiments, the aircraft  100  can have other lengths and/or other seating and/or cargo carrying arrangements.  
         [0032]    [0032]FIG. 5 is a graph of the cross-sectional area as a function of body station for aircraft  100  in accordance with embodiments of the invention. The total cross-sectional area of the aircraft  100  (line  406 ) includes contributions from the fuselage (line  406   a ), the aft wing (line  406   b ), the forward wing (line  406   c ), the propulsion system (line  406   d ), and the vertical tail (line  406   e ). The total area cross-sectional area (line  406 ) can be generally monotonically increasing from the forward tip of the aircraft  100  to a maximum cross-sectional area (located in an intermediate portion of the aircraft  100 , and at about station  1875  in one embodiment) and then generally monotonically decreasing to the aft tip of the aircraft  100 . In one aspect of this embodiment, the cross-sectional area distribution can include a dip aligned with the trailing edge of the forward wing (located at about station  1175  in one embodiment) and a dip aligned with the trailing edge of the wing-mounted engines (located at about station  2150  in one embodiment). In another embodiment, these dips can be reduced or eliminated (as indicated by line  406   f ) by altering the integration of these components. For example, the area of the strake  121  (FIG. 2B) can increase more rapidly to account for the reduction in cross-sectional area at the trailing edge of the forward wing  110 . In another embodiment, the nacelles  152  (FIG. 2B) can be integrated with the aft wing  120 , for example, in a manner described in greater detail below with reference to FIGS.  7 A-C. In still further embodiments, the aircraft  100  can have other component arrangements for achieving these and other area distributions.  
         [0033]    One feature of embodiments of the aircraft  100  described above with reference to FIGS.  2 A- 5  is that the fuselage  130  can have a lower portion  132  from which the aft wing  120  extends, and a fuselage projection  140  from which the forward wing  110  extends. Accordingly, the forward wing  110  can be positioned above and forward of the aft wing  120 .  
         [0034]    Another advantage of this feature is that the access to the aircraft  100  can be increased. For example, at least one of the passenger doors  135  can be positioned beneath the forward wing  110 , which can allow passengers to enter and exit the aircraft through more than one jetway. At least one of the galley doors  136  can also be positioned beneath the forward wing  110 , which can increase the access to the aircraft  100  by service crew. As a result of both features, the amount of time required to turn the aircraft  100  around between flights can be reduced. One advantage of this feature is that the aerodynamic impact of the forward wing  110  on the aft wing  120  can be reduced when compared to existing canard/wing arrangements. For example, the increased vertical separation between the forward wing  110  and the aft wing  120  can reduce or eliminate the likelihood for trailing edge wakes and/or tip vortices generated by the forward wing  110  from impinging on or significantly impacting the performance of the aft wing  120 . Accordingly, the stability, controllability and overall performance of the aft wing  120  can be improved.  
         [0035]    Another feature of embodiments of the aircraft  100  is that components (such as the fuselage lower portion  132 , the fuselage projection  140 , the forward wing  110 , the aft wing  120 , and the nacelles  152 ) can be integrated in a manner that produces a generally monotonically increasing and monotonically decreasing cross-sectional area distribution. For example, in one embodiment, the wing-mounted nacelles  152  can be axially aligned with the aft region  149  of the fuselage projection  140 , which has a decreasing cross-sectional area. The strake  121  can be aligned with the aft region  149  and/or with the trailing edge of the forward wing  110 . An advantage of this feature is that the aircraft  100  will be less likely to generate shock waves as the speed of the aircraft approaches the speed of sound. Accordingly, in one embodiment, the aircraft  100  can fly at subsonic cruise speeds in excess of Mach 0.90. For example, in one particular embodiment, the aircraft  100  can fly at a subsonic cruise speed of from about Mach 0.95 to about Mach 0.98. In other embodiments, the aircraft  100  can have other subsonic cruise Mach numbers, and in still further embodiments, the aircraft  100  can be configured for supersonic cruise Mach numbers. For example, an aircraft  100  having an overall layout generally similar to any of those described above with reference to FIGS.  2 A- 5  can cruise at supersonic Mach numbers of from about 1.2 to about 1.6.  
         [0036]    Still another feature of embodiments of the aircraft  100  described above with reference to FIGS.  2 A- 5  is that the fuselage projection  140  can house an upper passenger deck  143  and/or a flight deck  142 . The upper passenger deck  143  can increase the payload of the aircraft  100  without increasing its length, and can accordingly allow airlines to carry more passengers and/or cargo without significantly restricting the number of gates available to the aircraft  100 . By positioning the flight deck  142  in the fuselage projection  140 , the pilots&#39; forward visibility can be improved. This may be particularly beneficial for aircraft having supersonic or high subsonic cruise speeds because such aircraft may have longer and sharper nose sections than existing subsonic transport aircraft.  
         [0037]    In other embodiments, the aircraft can have other arrangements that include some or all of the foregoing features. For example, as shown in FIG. 6, an aircraft  600  can include a fuselage  630  having a lower portion  632  that supports an aft wing  620 , and a fuselage projection  640  that supports a forward wing  610 . The aircraft  600  can further include a propulsion system  650  having a tail-mounted nacelle  652  and two wing-mounted nacelles  652  that project above the upper surface of the aft wing  620 . With this arrangement, the aft wing  620  can mitigate at least some of the noise generated by the exhaust plume emanating from the wing-mounted nacelles  652 , which can allow for the installation of lower bypass ratio engines. The aft wing  620  can also shield the wing-mounted nacelles  652  from damage caused by foreign objects, such as debris kicked up from the runway by the main landing gear  604 .  
         [0038]    FIGS.  7 A- 7 C illustrate an aircraft  700  in accordance with another embodiment of the invention. In one aspect of this embodiment, the aircraft  700  can include a fuselage  730  having a lower portion  732  and a fuselage projection  740  positioned above the lower portion  732 . The lower portion  732  can support an aft wing  720 , and the fuselage projection  740  can support a forward wing  710 . The forward wing  710  can have a size relative to the aft wing  720  that is smaller than, larger than, or about the same as the relative size of the forward wing  110  described above with reference to FIG. 2A. The fuselage  730  can have a narrowed, vertically elongated, elliptical shape proximate to the forward wing  710 , resulting in a generally smooth, monotonically increasing area distribution despite the presence of the fuselage projection  740  and the forward wing  710 . The fuselage  730  can have a rounder, wider shape aft of the forward wing  710 .  
         [0039]    In a further aspect of this embodiment, the fuselage projection  740  can house a flight deck  742 , but does not include additional passenger seating beyond that provided by the lower portion  732 . By mounting the forward wing  710  to the fuselage projection  740  and above the aft wing  720 , the aerodynamic impact of the forward wing  710  on the aft wing  720  can be reduced and/or eliminated, and access to the aircraft  700  during loading/unloading can be improved, in a manner generally similar to that described above.  
         [0040]    The aircraft  700  can include an aft body  707  having elevons  722  for pitch control and trim, canted tails  702  provide for directional stability and control. The aircraft  700  can further include a propulsion system  750  having two engine nacelles  752  mounted to and integrated with the aft wing  720  and the aft body  707 . In one aspect of this embodiment, the nacelles  752  can be longitudinally aligned with a tapering aft region  739  of the fuselage  730  to provide a generally monotonically increasing and decreasing cross-sectional area distribution for the aircraft overall. Further details of integrated nacelles are included in pending U.S. patent application Ser. No. 09/815,390 filed Mar. 22, 2001 and incorporated herein in its entirety by reference. In other embodiments, the components of the aircraft  700  can have other arrangements that support the forward wing  710  in a position substantially above the aft wing  720 .  
         [0041]    One feature of an embodiment of the aircraft  700  shown in FIGS.  7 A-C is that the forward wing  710  can be positioned above the aft wing  720  without extending the fuselage projection  740  over a substantial length of the aircraft  700 . Accordingly, this configuration can be suitable for aircraft having capacities that do not require the additional length of the fuselage projection shown in FIGS.  2 A- 2 C. Another feature of an embodiment of the aircraft  700  described above with reference to FIGS.  7 A- 7 C is that the propulsion system  750  can include two nacelles  752  integrated with the aft wing  720  and/or the aft body  707 . An advantage of this feature is that the integrated nacelles  752  can produce a smooth overall cross-sectional area distribution, and the twin engine configuration can reduce initial engine cost when compared to configurations that include more than two engines. Conversely, an advantage of the three-engine, podded arrangement described above with reference to FIGS.  2 A-C is that the overall thrust of the aircraft can be reduced because two-thirds of the overall thrust remain available in an engine out condition. The podded arrangement can also allow easy access to the engines.  
         [0042]    From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. For example, aspects of the invention described separately in the context of different embodiments of the invention can be combined in other embodiments. Accordingly, the invention is not limited except as by the appended claims.