Patent Publication Number: US-8967526-B2

Title: Multi-role aircraft with interchangeable mission modules

Description:
This application claims priority to U.S. Provisional Application No. 61/372,941 filed Aug. 12, 2010, which is incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The field of the invention is aircraft. 
     BACKGROUND 
     Aircraft development is a capital-intensive and usually lengthy process. Further, because the viability of aircraft depend largely on their weight, conservatism in design can have powerful consequences on the viability of an aircraft. As a result of these two factors and other considerations, any given aircraft tends to be specialized for one role or mission during the design process. 
     At the same time, aircraft are used on and needed for a variety of missions and roles. Aircraft carry different payloads, including for example, passengers, cargo, sensors, and munitions. Beyond payload, other requirements can shape an aircraft design; for example, some missions require flight in a certain speed regime, while other missions require high fuel efficiency. 
     Prior art approaches to providing aircraft suitable for conducting specific missions tend to either (i) design a distinct aircraft for a specific mission, (ii) adapt an existing aircraft design for another mission through modifications (iii) attempt to bridge multiple missions in the design stage through an a priori requirement. 
     Each of these three prior art approaches has weaknesses. The first approach, to design a distinct aircraft for a specific mission, is extremely expensive and often impractical. In general, it has the least potential to meet multiple diverse requirements, therefore limiting its market. The second approach, post-hoc adaptation, is often used in adapting aircraft to new missions similar to the original design mission. Even this approach is expensive and time consuming, however. These difficulties arise in part because of formidable certification and qualification requirements. An example of aircraft post-hoc modification is the transformation of the Lockheed L-188 Electra civilian passenger transport into the Lockheed P-3 Orion naval maritime surveillance aircraft. The original mission (passenger transport) and the new mission (maritime surveillance) have similar flight envelope requirements, in terms of speed and altitude. 
     The third general approach, attempting bridge multiple missions in the design stage through an a priori requirement, often entails extraordinary costs and engineering effort. An example of this approach would be the Lockheed Martin F-35 family of supersonic fighter aircraft, attempting commonality between the F-35B short takeoff and vertical landing (STOVL) platform, the F-35C carrier based fighter platform, and the F-35A land-based conventional takeoff supersonic fighter platform. The F-35 program is renowned for being billions of dollars over budget and years behind schedule; this results at least in part from attempts to achieve high degrees of commonality among the aircraft in the family. The Boeing competitor to the F-35, as described in U.S. Pat. No. 5,897,078 struggled with similar issues in attempting to bridge diverse mission requirements, while still retaining some degree of parts-commonality among variants. 
     The &#39;078 patent and all other extrinsic materials discussed herein are incorporated by reference in their entirety. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply. 
     In summary, aircraft are sometimes designed to be flexible, yet this by-design flexibility can only go so far. Alternatively, different versions of aircraft are designed for specific needs, users, and missions. Only a few prior art aircraft and aircraft related developments known to the inventor have had elements of modularity, and no known prior art aircraft have achieved complete or even extensive modularity. 
     A few cargo aircraft have carried their cargo in removable cargo containers. Notably, the Fairchild XC-120 Packplane, Miles M.68 Boxcar, and Kamov KA-226 are the instances known to the inventor.  FIG. 1A  illustrates the Kamov KA-226 helicopter  110 , which features a main portion  112  of the aircraft and a removable cargo container  114 , which can be configured to carry passengers.  FIG. 1B  is a side view illustration of the Miles M.68 Boxcar  120 , which is a fixed-wing transport aircraft having a main portion  114  of the aircraft, and configured to carry cargo in a removable cargo container  124 . 
     While these prior art aircraft carry their cargo payload in removable containers, they cannot be said to be truly modular aircraft, because they do not change containers to change missions or roles. These prior art aircraft are really predominantly single-role transport aircraft that happen to carry their cargo in an external container that forms part of the aerodynamic fairing of the aircraft, rather than carrying their cargo in containers internal to the aerodynamic fairing of the aircraft like most air freighters. 
     In a similar vein, but for a different kind of aircraft, U.S. Pat. No. 4,736,910 to O&#39;Quinn is directed to a light fighter aircraft with interchangeable nose and tail sections. U.S. Pat. No. 3,640,492 is directed to aircraft having electronics or avionics equipment in removable portions of the aircraft structure or aerodynamic fairing. U.S. Pat. No. 7,234,667 to Talmage describes the division of an aircraft into sections, any of which could be recovered by parachute following an in-flight incident. U.S. Pat. No. 6,098,927 describes an aircraft with a removable fuselage section to increase or decrease the payload capacity of the aircraft. Related to this idea, the practice of extending or contracting fuselage sections by the addition or removal of fuselage plugs is known in the art, and is commonplace in stretched families of transports, including for example, the Airbus A318, A319, A320, and A321, which are substantially just stretched versions of the same aircraft accommodating 107-220 passengers. Unless the context dictates the contrary, all ranges set forth herein should be interpreted as being inclusive of their endpoints, and open-ended ranges should be interpreted to include only commercially practical values. Similarly, all lists of values should be considered as inclusive of intermediate values unless the context indicates the contrary. 
     US Patent Application 2008/0017426 describes a somewhat modular ground vehicle, wherein a core vehicle can attach to a variety of interchangeable elements to serve different roles or missions. However, it should be noted that the field of ground vehicles is substantially different from the field of aircraft, and that aircraft are subject to stricter design constraints. For example, aircraft are highly weight sensitive and aerodynamic drag sensitive and poorly tolerate structural and powerplant inefficiencies, such as those built into the ground vehicle of 2008/0017426 for modularity. A person of ordinary skill in the art would not expect systems and methods that work on ground vehicles to also work on aircraft without significant additional inventive subject matter. 
     It should be noted that a key constraint for adapting aircraft to serve different roles and missions is the operator interface. As an example, consider the vastly different pilot interfaces found among helicopters, transport aircraft, fighter aircraft, and the ground stations of unmanned aircraft. If an aircraft is to serve multiple roles and missions, it must have a suitable and adaptable interface. This is a formidable challenge, and relatively little known prior art addresses this challenge. 
     U.S. Pat. No. 5,626,030 to Watson describes a ground-based flight simulator that uses parts of an actual aircraft. However, this reference does not provide a ground control station for an aircraft that is common to a cockpit of an aircraft. U.S. Pat. No. 5,880,669 to Romanoff, et al also describes an aircraft simulator system, but does not disclose a ground control station for an unmanned aircraft that is substantially identical to a cockpit for a manned aircraft. 
     Thus, there is still a need for aircraft that are quickly and economically adaptable to different roles and missions, not simply adaptable to different payloads—aircraft that are both modular and multirole. 
     SUMMARY OF THE INVENTION 
     The inventive subject matter provides apparatus, systems and methods of a flight-operable, truly modular aircraft. 
     In a first aspect, a modular aircraft combines an originally deployed wing member that provides at least 15% of the lift during at least some portion of cruise flight, a center section that provides at least 25% of the aircraft during such flight, and has one or both of (a) a forward coupling adapted to couple or decouple a fuselage to the center section during the operational life, and (b) a wing coupling adapted to couple or decouple the wing member during the operational life. Detachable leading and trailing edge couplings can be applied to the center section, and preferably assist in providing lift. 
     In this first aspect, the fuselage is optional, and where the fuselage is present, it may or may not include a cockpit. Although the aircraft may be shaped as a flying wing, having substantially no empennage, no horizontal tail, and no vertical tail, the optional fuselage may include an empennage, a horizontal tail, and/or a vertical tail. 
     Modularity can be achieved to a large extent by incorporating many components into the center section. For example, the center section can advantageously contain a propulsive engine, disposed so that it does not extend above or below the center section. In some contemplated embodiments, there are first and second engines disposed on opposite sides of the central cavity. The center section preferably houses at least 80% of all of the fuel, and the aircraft may have a fuel capacity greater than maximum takeoff weight. 
     The center section can also advantageously include avionics sufficient to operate the aircraft without receiving controls from outside the center section. In some embodiments, it is contemplated that the avionics can operate the aircraft through either or both of ground control and an on-board pilot control. Additionally or alternatively, the center section can include an on-board pilot interface. The center section can also advantageously receive one or more, and preferably all of the retracted landing gear for the aircraft. 
     In preferred embodiments, the center section is constructed in a manner that produces a centerline central cavity. This can advantageously be accomplished using forward and aft curved composite spars, and right and left inboard ribs. the central cavity can be quite large, for example having a width dimension at least 3% of the span of the aircraft, and a length dimension at least 20% of the length of the aircraft. Not only is the central cavity large horizontally, but it can be large vertically, preferably extending all vertically all the way to the upper skin and lower skins of the aircraft. The central cavity can also advantageously have a cargo dimensioned to interchangeably carry an ordnance launcher, a surveillance payload, and electronic countermeasures. 
     By placing so much of the flight-critical components in the center section, the wings (or outer wing sections) can be detachable. For example, a detachable wing member having a composite wing spar can couple to the forward and aft spars of the center section using a wing coupling with one or more hardpoints. The wing coupling can carry electrical connections between the center section and the wing member, and in some contemplated embodiments the wings can be hingedly coupled to the center section. Whether or not the wings are detachable, it is contemplated that they can be quite large. For example, aircraft contemplated herein can have a wing span of at least 80 ft, with left and right outer wing members having sufficient stiffness to produce a natural frequency of no less than 6 Hz when airborne. 
     Other hardpoints are contemplated that removably couple a cockpit module to the center section during an operational life of the aircraft, and that removably couple a tail section to the center section during an operational life of the aircraft. 
     Various kits are contemplated with one or more of the features discussed above. For example, kits are contemplated that comprise a fuselage, that include a replacement wing member that is not fungible with the originally deployed wing member, that include replacement leading and/or trailing edge portions, and that include center sections having horizontally curved forward and aft composite spars. 
     In a second aspect, a modular aircraft having originally deployed wing member that provides at least 20% of the lift of the aircraft during at least some portion of cruise flight has (a) center section that includes a centerline cavity, and avionics sufficient to operate the aircraft; (b) a forward coupling adapted to couple or decouple a forward component to the center section during the operational life; and (c) a wing coupling adapted to couple or decouple the wing member during the operational life. The aircraft can have any one or more of the features discussed above. 
     Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1A  is a side view drawing of a prior art rotorcraft with a removable cargo container, while  FIG. 1B  is a side view drawing of a prior art fixed-wing airplane with a removable cargo container. 
         FIG. 2  is a schematic perspective illustration of a preferred modular aircraft kit comprising a center section, various outer wing portions, and various mission modules. 
         FIG. 3  is a perspective exploded view illustration of an alternate preferred aircraft center section showing the supporting structure and key mechanical systems. 
         FIG. 4  is a schematic top-view illustration of a preferred modular aircraft. 
         FIG. 5  is a schematic top-view illustration of an alternate configuration of the preferred modular aircraft of  FIG. 4 . 
         FIG. 6  is plot of the lift distribution of the preferred modular aircraft of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     Along with the drawing, the following detailed description serves to elucidate various aspects of the present inventive subject matter. 
       FIG. 2  is a schematic perspective illustration of a preferred modular aircraft kit comprising a center section, various outer wing portions, and various mission modules. 
     The modular aircraft kit  200  comprises a center section  210 . The center section  210  advantageously features a left interface  215  for a left outer wing member and a right interface  216  for a right outer wing member. In especially preferred embodiments, the left and right interfaces  215 ,  216  are hardpoints configured to allow folding or removal of the outer wing members for compact stowage. The center section  210  is preferably equipped with provisions for propulsive means. A right engine housing  218  and a left engine housing  217  each fair over an inlet, turbofan engine, and exhaust. When coupled to electric power, a flight control system, and a fuel supply, the engine is capable of producing thrust for sustained flight of the modular aircraft. The center section  210  also has a substructure consisting of one or more spars and ribs (not shown). In preferred embodiments, removable aerodynamic or structural elements are attached to this substructure. Center section  210  is equipped with a right leading edge portion  211 , a left leading edge portion  212 , a right trailing edge portion  213 , a left trailing edge portion, and one or more center panels  207 . By removing or replacing the center panels  207  and other interchangeable elements, other mission modules or fuselages can be accommodated. The center section  210  also comprises a right wing member  209  and a left wing member  208  for generating lift. Internal to the center section  210  are a number of aircraft systems essential to flight. 
     A preferred manned aircraft  220  is advantageously composed of elements of the modular aircraft kit  200 . A center section  210  is configured to support a fuselage  227  featuring a cockpit  228 . The cockpit  228  advantageously includes provisions for a human pilot including an ejection seat, flight controls, an environmental control system, avionics, a clear windscreen or canopy, and instrumentation. The center section  210  supports a right outer wing member  222  comprising right control surfaces  223  attached at the right interface  216  for an outer wing in a manner that supports folding of the right outer wing member  222 . Similarly, the left outer wing portion  224  has left control surfaces  225  and is attached at the left interface  215  with the center section. The preferred manned aircraft  220  has no tail surfaces, empennage, horizontal tail, or vertical tail. All aircraft control is affected via control surfaces  223 ,  225  located on the right and left outer wing members  222 ,  224 . Also shown is landing gear  226  in an extended position, which advantageously retracts into the center section. To install the fuselage  227 , which can be viewed as a mission module, the center panel  207  and other parts of the center section are removed (or alternately, are never installed) from the center section  210 . The fuselage  227  is structurally attached at hardpoints (not shown) and electrical connections are made facilitate power and data signals between the fuselage  227  and center section  210 . Similarly, electrical connections are made between the outer wing members  222 ,  224  and the center section  210 . In preferred aircraft, control surfaces  223 ,  225  are electrically actuated, but other actuation means such as hydraulic, mechanical, and pneumatic are also contemplated. 
     A preferred unmanned aircraft  230  is also composed of elements of the modular aircraft kit  200 . In this case, the center section  210  is configured to support a mission module  237  advantageously containing payload and mission equipment, including, for example, elements selected from the list containing sensors, cameras, cargo, munitions, fire suppressant, datalinks, antennas, and radio communications equipment. The same outer wing portions  222 ,  224  are attached to the center section  210  as for the manned aircraft  220 . Indeed, the only difference between unmanned aircraft  230  and manned aircraft  220  is the selection and installation of mission module  237  and fuselage  227 , respectively. Unmanned aircraft  230  features the same landing gear  226 , engines, control surfaces, and systems as manned aircraft  220 . Unmanned aircraft  230  is advantageously equipped with a flight control computer containing flight control laws allow autonomous flight without human intervention. Unmanned aircraft  230  is also advantageously equipped with one or more datalinks (not shown) mounted in the mission module  237  or center section  210  allowing control via remote ground control station (not shown). Some preferred aircraft may comprise elements of U.S. application Ser. No. 11/506,571. 
     In preferred modular aircraft kits, other (not originally deployed) mission modules would also be installable in the center section  210 . For example, a cargo module  240  would interface with center section  210  via structural hardpoints  243  and an electrical interface  245 . The cargo module  240  could comprise a hatch portion  244  for loading or unloading cargo, and an empennage comprising a vertical tail  241  and a horizontal tail  242 . Other cargo modules are also contemplated with no empennage wherein all flight control and stability assurance are obtained via control surfaces located on outboard wing portions. 
     An alternate unmanned aircraft  250  is also composed of elements of the modular aircraft kit  200 . In this case, the center section  210  has no fuselage or mission module attached or mounted to it. Instead, all mission equipment is stowed internal to the center section  210 , accessible via removable panels or hatches. In this manner, the drag of the central portion of the aircraft is reduced because there is no fuselage or mission module creating additional frontal area. Alternate unmanned aircraft  250  comprises a different right outboard wing portion  252  and a different left outboard wing portion  254  from corresponding components of aircraft  220  and  230 . These wing portions  252 ,  254  can be seen to be substantially entirely flat, not having dihedral or curvature out of plane. Right control surfaces  253  are mounted on the right outboard wing portion  252 , while left control surfaces  255  are mounted on the left outboard wing portion. Additionally, a right boom  257  is also attached at the right interface  216  with the center section. The right boom  257  cooperates with a left boom  258  to support an optional empennage  259  for providing pitch and directional stability and control to the aircraft  250 . The outboard wing portions  252 ,  254  are attached to center section  210  by means of folding mechanisms. 
     The folded alternate unmanned aircraft  260  allows for compact stowage. Here, the right wing portion  252  and left wing portion  254  are rotated up over the center section  210  such that the wing tips approach the aircraft centerline  261 . 
     Thus, it is seen that any manner of workable variations can be achieved by substituting various elements of the modular aircraft kit  200 . Outer wing portions of different spans, taper ratios, sweeps, airfoils, and planforms can be substituted to tailor aircraft performance to intended missions. It is contemplated that some outer wing portions can have different control surface configurations, with any suitable number of slats, plain flaps, slotted flaps, or split flaps. Some outer wing portions could advantageously be equipped with large embedded antennas as needed for certain missions. Similarly, any number of various fuselages or mission modules could be coupled to the center section  210 . Such fuselages or mission modules could accommodate varied payloads with different sizes and packing requirements, including, for example, passengers, pallets, munitions, radars, and RF jamming equipment. In especially preferred modular aircraft kits, the essential systems for aircraft functioning are contained in the center section  210  to allow for rapid reconfiguration. In this manner, the flight control computer, standard communications equipment, navigation sensors, fuel tanks, fuel pumps, generators, electric power system, and engines are located within the center section  210 . With contemplated mode of modular operation, an aircraft could begin its operational life with one set of originally deployed outer wing members, and then exchange them for another, non-fungible set of outer wing members selected from an aircraft kit  200 . 
     One list of contemplated missions for a single aircraft with interchangeable mission modules includes: aerial mapping, maritime patrol, police surveillance, aerial spraying, air ambulance, air interdiction, close air support, ground strike, light water bomber for firefighting, refrigerated cargo, cargo accommodations with a roller floor and tie downs, combination cargo and passenger transport, air drop cargo, standard passenger transport, luxury passenger transport, communications relay, radio frequency signal jamming or interception, missile launch, and small vehicle launch. 
       FIG. 3  is a perspective exploded view illustration of an alternate preferred aircraft center section  310  showing the supporting structure and key mechanical systems. The alternate preferred aircraft center section  310  comprises a supporting substructure, including a forward spar  340 , an aft spar  342 , a right center spar  344 , a left center spar  346 , right and left inboard ribs  350 ,  351 , right and left second ribs  352 ,  353 , right and left third ribs  354 ,  355 , and right and left outboard ribs  356 ,  357 . In this preferred embodiment, both the forward spar  340  and aft spar  342  are curved and run between a left interface  315  of the center section  310  and a right interface  316 . These spars serve as the primary structural members to react forces generated by lifting surfaces on the center section  310  and from outboard wing members (not shown). 
     The forward spar  340 , aft spar  342 , right inboard rib  350 , and left inboard rib  351  define a central cavity  380  that can accommodate payloads or cargo, and has unobstructed access both upward and downward in a conventional flight orientation (when no skin panels, mission modules, or fuselage modules block this access). This upward and downward access is useful for sensor range of sight, launching munitions, maintenance access, air drop of cargo, and installation of fuselage modules or payloads that require a depth dimension greater than the maximum depth of forward and aft spars  340 ,  342 . The central cavity  380  has a centerline cavity length  398  and a maximum cavity width  396 . Notably, to achieve the open central cavity  380 , the right center spar  344  must terminate at the right inboard rib  350  while the left center spar  346  terminates at the left inboard rib  351 . One of ordinary skill in the art would not contemplate a discontinuous center spar, because the highest bending moments and stresses occur near the center of a wing structure. Normally, structural members have the greatest dimensions (height, depth, and thickness) where bending moments and stresses are highest because this yields a more efficient and lower weight structure. Termination of major structural member (such as the left and right center spars  344 ,  346 ) at the point of greatest bending moment does not follow from best engineering practices. At its outer extent, near the right interface  316  of the center section  310 , the right center spar  344  splits into a y-shape to better support a right outer wing portion. 
     Overall, the center section has a center span  392  between the left interface  315  and right interface  316 . Depending on the nature of the outer wing portions (not shown) selected for attachment to the center section  310 , the assembled aircraft can have a total span that is substantially greater than the center span  392  of the center section  310 , including, in preferred embodiments, an overall span that is 2×, 2.5×, 3×, 3.5×, or even 4× the span  392  of the center section  310 . The substructure of the center section  310  also has a substructure length  394  between the aftmost portion of the aft spar  342  and the foremost portion of the forward spar  340 . In preferred embodiments, the substructure length  394  is greater than the cavity length  398  and between 1.25×, 1.5×, 1.75×, 2×, 2.5×, and 3× the cavity width  396 . In this instance, and where other upper limits are not expressly stated, the reader should infer a reasonable upper limit. In this instance, for example, a commercially reasonable upper limit is about 5× the cavity width. 
     The substructure of the center section  310  advantageously supports aerodynamic fairing elements including a right leading edge portion  311 , a right trailing edge portion  313 , and upper surface skin panels  308 ,  309 . These fairing elements cooperate to serve as a portion of the center section  310  for generating lift, having a total area (left and right sides) at least equal to the product of the cavity length  398  and cavity width  396 . 
     The center section  310  and its substructure also carry a variety of systems essential to the functioning of an aircraft. In preferred embodiments, the center section  310  supports at least one engine inlet  322 , a left side engine  324 , a generator  328 , and an exhaust duct  326 . For clarity, in  FIG. 3 , only the left side engine  324  is shown. Cooperatively, the left side engine  324  and right side engine (not shown) provide adequate thrust to sustain level flight of an assembled aircraft. In some preferred embodiments, the left and right engines cooperate to provide a maximum thrust that is not greater than 20%, 30%, 40% or 50% of the maximum takeoff weight of the aircraft. In some preferred embodiments, the engine  324  is installed in such a manner that it does not extend above or below the center section  310 , even if portions of an inlet or exhaust might extend above the center section. Additionally, a set of left fuel tanks  360  and right fuel tanks (not shown) provide fuel supply to the aircraft engines. An exemplary fuel tank  362  is supported by a combination of spars, ribs, and skin panels when installed in the center section  310 . In some preferred embodiments, the total fuel capacity of the aircraft in pounds is greater than the maximum takeoff weight of the aircraft in pounds. Preferred aircraft are also equipped with a four leg landing gear system entirely housed in the center section  310  when retracted, and comprising a right main leg  370 , a left main leg  371 , a right nose leg  372 , and a left nose leg  373 . The left and right nose legs  372 ,  373  provide a steering capability. 
     For modularity, the center section  310  is advantageously constructed to support interchangeable mission modules, fuselages, and outer wing portions. In preferred embodiments, a left outer wing portion (not shown) is supported by a folding system including a set of right forward folding attachments  336  and right aft folding attachments  338  that rotatably support an outer wing portion, and react the considerable flight bending moments generated by an outer wing portion into the forward spar  340 , aft spar  342 , and left center spar  346 . The center section  310  also supports a variety of mission modules or fuselages by means of hardpoints  332 ,  334  that allow mission modules to be mechanically fastened in a manner that facilitates quick disconnection and reconnection while still reacting loads. 
     In especially preferred embodiments, the aft spar  342 , forward spar  340 , and center spars  344 ,  346  are of carbon-epoxy composite construction. The caps of the forward spar  340  and aft spar may comprise high modulus carbon fibers in pultruded form. Hardpoints  332 ,  334  and folding attachments  336 ,  338  are preferably constructed of high strength metal including for example titanium or steel. 
       FIG. 4  is a schematic top-view illustration of a flight-operable, modular aircraft  400  having an operational life. Some contemplated operational lives include 2000 hours 3000 hours, 5000 hours, 10000 hours 20000 hours, 30000 hours, 50000 hours, of flight time. An aircraft center section  410  couples to a right outer wing member  402  and a left outer wing member  404 . The outer wing members installed at the start of the aircraft&#39;s operational life are said to be originally deployed. The left and right outer wing members are advantageously each sized and configured to provide at least 12, 15, 20, 25, 30, or 35% of the total lift of the aircraft during at least some portion of substantially straight and level cruise flight. In preferred embodiments, the center section  410  is shaped and configured to produce at least 20, 25, 30, 35, 40, and 50% of the total lift of the aircraft during the same portion of the cruise flight. An aircraft flight will typically comprise takeoff, climb, cruise, an optional loiter, cruise, descent, and landing in sequence. A cruise flight condition means sustained self-powered flight at a given cruise altitude and cruise speed. Contemplated cruise altitudes include 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, and 65 thousand feet above sea level. Contemplated cruise speeds correspond to Mach numbers of 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, and 0.9. 
     The right outer wing member  402  comprises a spar  426  for structural support, a control surface  403  to assist in trim and control of the modular aircraft  400 , an actuator  470  to drive the control surface  403 , and wiring  472  to carry power and command signals from a flight control computer  462  located in the aircraft center section  410 . In some preferred embodiments, the originally deployed left outer wing member  404  is substantially a mirror image of the originally deployed right outer wing member  402 , and also comprises a left control surface  405  and left spar  427 . It is contemplated that preferred modular aircraft  400  could exchange an originally deployed right outer wing member  402  a replacement right outer wing member  406  that is not fungible with the originally deployed right outer wing member  402 . At the same time, flight control laws, as codified and executed in the flight control computer  462 , would adapt to this change of wing members as necessary. 
     The center section  410  is built around an aircraft core  490 , an element advantageously configured to enable aircraft system modularity. The aircraft core  490  comprises a forward curved spar member  422 , an aft curved spar member  424 , and left and right hardpoints  432 ,  430  that accommodate attachment of outer wing members, folding of outer wing members, and are located in the immediate vicinity of connections for electrical power or signals for powering the outer wing members. The hardpoints  430 ,  432  serve as wing couplings adapted to couple or decouple outer wing members  402 ,  404  during the operational life of the aircraft. The right wing hardpoint  430  can be viewed as a coupling that carries load between a composite spar  426  of the detachable right outer wing member  402 , and the fore and aft curved spars  422 ,  424 , resepectively. The hardpoints  430 ,  432  can also be advantageously configured as hinges to allow folding of the outer wing members  402 ,  404  for compact stowage. The aircraft core  490  is also advantageously equipped with forward hardpoints  491  that serve a forward coupling adapted to couple or decouple a fuselage or mission module to the center section  410  during the operational life. In preferred embodiments, the forward hardpoints  491  are attached to the curved forward spar  422 . Aft hardpoints  492  may cooperate with forward hardpoints  491  in supporting or coupling a fuselage  480 , mission module, or payload to the aircraft core  490  and center section  410 . 
     The preferred modular aircraft  400  is optionally equipped with a fuselage  480 . Preferred fuselages  480  are optional and can be coupled or decoupled from the aircraft during the operational life. Fuselage  480  is equipped with a cockpit  482  comprising an on-board pilot interface and means for on-board pilot control, including instrumentation and display screens  482 , inceptors  486 , and an ejection seat  487 . Fuselage  480  is equipped with forward mounts  488  and aft mounts  489  which couple to aircraft forward hardpoints  491  and aft hardpoints  492  to support the optional/removable fuselage  480 , and allow the installation or removal of the fuselage in less than two hours. Other fuselages or mission modules are contemplated, including those without cockpits or means for on-board pilot control, which can couple to the aircraft  400  using the same forward and aft hardpoints  491 ,  492  such that fuselages can be changed out during the operational life of the aircraft  400 . In preferred embodiments, the fuselage coupling or the wing coupling that attaches the right outer wing member  402  to the center section  410  also carries electrical connections. In especially preferred embodiments, a quick disconnect connector is located within two feet of a structural hard point. Some preferred fuselages  480  or mission modules are equipped with a targeting system  441  such as a radar that is operable by each of a pilot in the cockpit and also by a ground controller. 
     It is further contemplated that in some especially preferred embodiments, mission modules need not be a single-piece fuselage. The modular nature of the aircraft core  490  having a series of couplings and hardpoints allows it to be viewed as a multi-way receptacle for accessories, including a nose portion of a mission module that could attach to forward hardpoints  491  or other couplings, a tail portion of a mission module that could attach to aft hardpoints  492  or other couplings, optionally a central portion of a mission module, skin panels, a first outer wing portion, a second outer wing portion, and various leading edge and trailing edge pieces. In this manner, mission equipment and mission modules can be rapidly tailored to meet emerging needs, without the requirement of having to change an entire fuselage. In some instances, only the nose portion of a fuselage or mission module might be interchanged, for example to accommodate an alternate targeting system  441 . 
     The aircraft core  490  also has a leading edge coupling  496  to support attachment of a removable leading edge  522 , and a trailing edge coupling  497  to support attachment of a removable trailing edge  524 . This enables coupling or decoupling right and left leading edge portions during the operational life of the aircraft, where the leading edge portions are configured to assist in providing lift to the aircraft during the at least some portion of cruise flight. The center section  410  of the aircraft  400  comprises an aircraft core  490  as well as a leading edge fairing  522  and trailing edge fairing  524 . The aircraft core  490  comprises a right engine  436  and a left engine  438  which cooperate to provide a propulsive force for the aircraft. In preferred embodiments, the engines  436 ,  438  are installed such that they do not extend above or below the center section  410  skin surfaces. A preferred installation of the right engine  436  involves support from a right inboard rib  494  or from an upper surface extension of a right center spar that does not extend across the central cavity  499  such that the engine that is not structurally supported from directly below the engine. 
     It is thus seen that, in some preferred embodiments, the central cavity  499  of the aircraft core  490  can be viewed as an open bay entirely inside the aircraft, and supported on only four sides by a fore and aft spar and left and right inboard ribs. In such instances, the central cavity  499  is free from supporting structural members such as spars running laterally across, through, above, or below the central cavity  499 . While many such aircraft could benefit from such structural supporting members to provide strength and stiffness near the centerline of the aircraft where bending moments are high, the present inventive subject matter contemplates eliminating all such supporting members in order to create a flexible and modular central cavity  499  which can accommodate any manner of payloads. In preferred embodiments, even skin or door surfaces which may be installed above or below the central cavity  499  to provide an aerodynamic fairing for reduced drag, are non-structural, and carry no more than 2% or 5% of the total bending moment across the centerline of the aircraft. 
     The aircraft core  490  also contains one or more flight control computers  462 , and one or more sensors  466 , and communications that cooperate to serve as avionics sufficient to operate the aircraft without receiving controls from outside the center section  410 . Preferred aircraft  400  have center sections  410  that contain substantially all of the avionics functionality and are advantageously equipped with fault-tolerant flight control computers and redundant sensors that communicate via an aircraft network bus. Preferred aircraft are also advantageously equipped with one or more communications devices  464 , including for example, line-of-sight datalinks, voice radios, beyond-line-of-sight datalanks, transponders, satellite communications radios, and other data radios. In preferred embodiments, the communications devices  464  allows for receiving communications and commands from off-board persons or devices as well as the transmission of flight data and sensor data to off-board persons or devices. In some contemplated aircraft, the flight control computers  462  are capable of receiving inputs or commands from either or both on-board pilot control and ground control such as a ground station. In instances where the flight control computers  462  receive input from both off-board and on-board pilots, the flight control computers  462  advantageously act as an arbiter to determine which set of inputs drive the vehicle core flight control. In especially preferred embodiments, the aircraft core  490  is equipped with substantially all of the systems content required to fly the aircraft  400  except for flight control surfaces and their actuation. This segregation of systems content helps enable overall aircraft modularity. 
     The aircraft core  490  is further advantageously equipped with left and right forward landing gear  451 ,  450  and left and right aft landing gear  453 ,  452  that attach to ribs or spars  422 ,  424  via hardpoints. These four landing gear members are preferably retractable and are advantageously configured to retract into the center section  410  such that they do not extend further forward of the forward curved spar  422  or further aft of the aft spar  424 , and are entirely bounded by the structural elements and skins of the center section  410  when in the fully retracted position. Some preferred aircraft cores  490  resemble a trapezoid, resulting from the cooperation of the forward curved spar  422 , aft curved spar  424 , right hardpoint  430 , left hardpoint  432 , and left and right inboard ribs  493 ,  494  in providing structural support for the aircraft&#39;s operations. 
     The aircraft core  490  is advantageously equipped with a fuel supply  437  such as one or more fuel tanks operationally coupled to the propulsive engines  436 ,  438 . The total fuel supply is preferably distributed both to the right and the left of the central cavity  499 , and the engines  436 ,  438  are preferably disposed on either side of the central cavity  499 . It is contemplated that the fuel supply  437  can be sized and configured to house at least 80% or at least 90% of the aircraft total fuel and be housed entirely within the bounds of the aircraft center section. 
     In preferred embodiments, the horizontally curved forward spar  422  and horizontally curved aft spar  424  are major structural elements bridging the loads generated by left and right outboard wing members  404 ,  402 . Each of the two carries at least 30% and at most 70% of the bending load during at least some portion of substantially straight and level cruise flight. In especially preferred embodiments, the spars  422 ,  424  are made of carbon-epoxy composite and are constructed in pre-curved molds and run continuously and laterally between a right wing coupling  430  and a left wing coupling  432 . A right inboard rib  494  and left inboard rib  493  run longitudinally between the forward spar  422  and the aft spar  424 . The aircraft core  490  thus comprises forward and aft curved composite spars  422 ,  424 , and right and left inboard ribs  493 ,  494 , the spars and ribs operatively coupled to provide the centerline central cavity  499 . 
     With reference to both  FIG. 4  and  FIG. 5 , which depict different configurations of the same flight-operable modular aircraft  400 , the central cavity  499  has a width dimension  514  and a length dimension  512  as well as a depth and an internal volume. In preferred embodiments, the width dimension  514  is at least 3%, 4%, 5%, 7%, or 9% of the total span  502  of the flight-operable modular aircraft  400 , and at most 10%, 15%, or 20% of the span  502 . The length dimension  512  is at least 15%, 20%, 25%, 30%, 40%, 50% or 60% of the total length  510  of the aircraft  400  and at least 70% of the length of the aircraft core  490 . In preferred embodiments, the central cavity has a cargo coupling  495  that is configured and dimensioned to carry an interchangeable payload  440 . Contemplated interchangeable payloads include an ordnance launcher, a surveillance payload, electronic countermeasures, and other sensors, RF equipment, and munitions. 
       FIG. 5  is a schematic top-view illustration of an alternate configuration of the preferred modular aircraft of  FIG. 4 , without the optional fuselage  480  installed and without showing many of the internal systems contained in the aircraft core  490 . In this view, the aircraft  400  is equipped with no fuselage, a right outer wing member  402 , a left outer wing member  404  removable leading edges  522 ,  523  and removable trailing edges  524 ,  525 . A payload is carried in the internal central cavity  499 . The internal central cavity  499  is preferably covered by one or more non-structural skin panels  580  such that the central cavity  499  has no overhead structural support. In preferred embodiments, there is no structural support above or below the central cavity  499 . In some embodiments, the bottom of the internal cavity may be covered by moving payload doors. Preferred central cavities  499  extend vertically to an upper skin and a lower skin or non-structural payload doors. Other portions of the aircraft core  490  may be covered by one or more skin panels  581 . The skin panels  581  may have provisions for engine inlets  571 ,  572  and engine exhausts  573 ,  574  that cooperate to allow air to flow through engines  436 ,  438  even if the engines  436 ,  438  have a buried installation and are housed between the upper and lower skins of the center section  410 . 
     The aircraft  400  has a total span  502  that is the sum of a center span  506  associated with the center section  410 , a right span  504  associated with the right outer wing member  402  and a left span  508  associated with the left outer wing member  404 . The center section extends laterally between the left and right attachments for the outer wing members  402 ,  404 . Left and right are defined relative to a centerline  590  of the aircraft  400 . Preferred total spans of the aircraft are between 30 and 180 feet, between 50 and 160 feet, between 70 and 140 feet, and between 90 and 130 feet, or least 80 feet, or at least 100 feet. Due to the modular nature of the aircraft  400 , the total span  502  of the aircraft  400  can change during its operational life. 
     It is contemplated that, despite the considerable total span as described above, some preferred aircraft  400  can be constructed in such a way that the overall vehicle, comprising forward and aft curved composite spars  422 ,  424  and right and left outboard wing members  402 ,  404  has sufficient stiffness to produce a natural frequency of no less than 5 Hz or no less than 6 Hz when airborne. This high structural stiffness can advantageously delay or prevent aeroelastic flutter from occurring. 
     As shown, the aircraft  400  of  FIG. 5  is shaped as a flying wing, having substantially no empennage, no horizontal tail, and no vertical tail. Some preferred aircraft are substantially flat, having a dihedral or anhedral of no more than ten degrees, and a maximum thickness-to-chord ratio of no more than thirty percent. Elements of  FIG. 4  and  FIG. 5  could be combined to form a kit. One exemplary kit could comprise a flight-operable modular aircraft  400  without an originally deployed fuselage, as well as an optional/removable fuselage  480 , a right outer wing member  406  that is non-fungible with an originally deployed right outer wing member  404 , and a leading edge portion  522 . 
     In preferred embodiments, the wing coupling that attaches the right outer wing member  402  to the center section  410  also carries electrical connections. In especially preferred embodiments, a quick disconnect connector is located within two feet of a structural hardpoint. 
       FIG. 6  is plot of the lift distribution of the preferred modular aircraft of  FIG. 5  at a cruise flight condition. The horizontal axis  602  extends from the left semi-span of the aircraft  400  to the right semi-span of the aircraft  400 . The vertical axis  604  is non-dimensional and represents the local lift coefficient for curve  610  and the product of local chord and local lift coefficient divided by the chord at the right extent of the center section (c×c 1 /c ref ) for curve  620 . Curve  620  is proportional to dimensional local lift at a wing section. Thus, shaded area  622  represents the total lift generated by the left outer wing member  404 , shaded area  626  represents the total lift generated by the right outer wing member  402 , and shaded area  624  represents the total lift generated by the center section  410 . In preferred embodiments where the aircraft  400  is a flying wing, substantially all of the lift is generated by these three sections together. In especially preferred embodiments, the center section generates between 30% and 70% or between 40% and 60% of the total lift of the aircraft during sustained flight at a substantially straight and level cruise condition. 
     At a nominal, non-accelerating cruise flight condition, the aircraft lift is approximately equal to its weight. If the aircraft is not refueled or resupplied in flight, the weight in cruise is less than the weight at takeoff. Aircraft conventionally have a maximum takeoff weight, which is the greatest weight at which the aircraft can safely takeoff. Under normal operation, without refueling or resupply, the aircraft weight will continuously decrease until landing as fuel is burned. Powered aircraft are conventionally equipped with a fuel supply capable of holding a maximum quantity of fuel. It is contemplated that some preferred aircraft  400  without provisions for aerial refueling could be equipped with a fuel supply  437  sized and dimensioned with fuel capacity greater than maximum takeoff weight. In this manner, the aircraft would be not be able to takeoff with its fuel supply  437  filled to capacity. One of ordinary skill in the art simply would not think of over-sizing the fuel supply to such a degree, because there is no perceptible benefit. The present inventive subject matter, however, contemplates that an aircraft core  490  could accommodate future growth of an aircraft  400  in this manner. 
     It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refers to at least one of something selected from the group consisting of A, B, C . . . and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.