Abstract:
An unmanned rotorcraft has a lift module having a propulsion system and coaxial rotors driven in rotation by the propulsion system. The rotorcraft includes a payload support system adapted to couple an external payload directly to the lift module. The rotorcraft is devoid of provisions for human passengers.

Description:
BACKGROUND 
     1. Field of the Invention 
     The present application relates generally to rotorcraft, and more particularly to a remotely controlled co-axial rotorcraft for heavy-lift aerial crane operations and associated systems and methods. 
     2. Description of Related Art 
     Many industries use existing manned helicopter types, which are mostly based on 1960s technology. These aging, manned aircraft are generally ill-suited for crane operations, primarily due to inefficiencies inherent in the need to accommodate the human crew. A significant amount of lift capability is lost in order to provide for crew accommodations and safety, and helicopters designed initially as troop carriers are particularly inefficient in the heavy-lift crane role. In addition, carrying humans in the vehicle requires significant payroll, insurance, and training costs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features believed characteristic of the embodiments of the present application are set forth in the appended claims. However, the embodiments themselves, as well as a preferred mode of use, and further objectives and advantages thereof, will best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of a heavy lift rotorcraft according to the present application; 
         FIG. 2  is an exploded side view of the rotorcraft of  FIG. 1 ; 
         FIG. 3  is an exploded side view of a lift module of the rotorcraft of  FIG. 1 ; 
         FIG. 4  is a partial cutaway perspective view of a propulsion system of the rotorcraft of  FIG. 1 ; 
         FIG. 5  is a partial cutaway perspective view of the propulsion system of  FIG. 4 ; 
         FIG. 6  is a perspective view of a nacelle of the propulsion system of  FIG. 4 ; 
         FIG. 7  is an perspective view of an engine of the propulsion system of  FIG. 4 ; 
         FIG. 8  is an perspective view of a transmission of the propulsion system of  FIG. 4 ; 
         FIG. 9  is a lateral cross-section view of the transmission of  FIG. 8 ; 
         FIG. 10  is a 45-degree cross-section view of the transmission of  FIG. 8 ; 
         FIG. 11  is an exploded view of a gearset module of the transmission of  FIG. 8 ; 
         FIG. 12  is an exploded lateral cross-section view of gearset modules of the transmission of  FIG. 8 ; 
         FIGS. 13A and 13B  are plan and front, respectively, partial cutaway views of an intermediate gearbox of the rotorcraft of  FIG. 1 ; 
         FIG. 14  is a side view of a lift bar of the rotorcraft of  FIG. 1 ; 
         FIG. 15  is a perspective view of a co-axial rotor system of the rotorcraft of  FIG. 1 ; 
         FIGS. 16A and 16B  are plan and cross-section views, respectively, of a rotor blade of the rotor system of  FIG. 15 ; 
         FIG. 17  is a perspective view of rotor hubs of the rotor system of  FIG. 15 ; 
         FIG. 18  is a partial top view of rotors of the rotor system of  FIG. 15 ; 
         FIG. 19  is a perspective view a portion of the rotor system of  FIG. 15 ; 
         FIGS. 20A and 20B  are perspective views of portions of the rotor system of  FIG. 15 ; 
         FIGS. 21A and 21B  are perspective views of portions of the rotor system of  FIG. 15 ; 
         FIG. 22  is a 45-degree cross-section view of a yaw control system of the rotorcraft of  FIG. 1 ; 
         FIG. 23  is a perspective view of a portion of the rotorcraft of  FIG. 1 ; 
         FIG. 24  is a perspective view of a fuel tank of the rotorcraft of  FIG. 1 ; 
         FIG. 25  is an exploded view of the fuel tank of  FIG. 24 ; 
         FIG. 26  is an exploded perspective view a support module of the rotorcraft of  FIG. 1 ; 
         FIG. 27  is a partial cutaway perspective view of a portion of the support module of  FIG. 26 ; 
         FIG. 28  is a partial cutaway perspective view of a portion of the support module of  FIG. 26 ; 
         FIGS. 29A and 29B  are cross-section views of a leg of the support module of  FIG. 26 ; 
         FIG. 30  is a plan view of the legs of the support module of  FIG. 26 ; 
         FIG. 31  is a plan view of a transport configuration of the rotorcraft of  FIG. 1 ; and 
         FIG. 32  is a perspective view of a radio-controlled flying scale model according to the present application. 
     
    
    
     Where used in the various figures of the drawings, the same reference numerals designate the same or similar parts. Furthermore, when the terms “front,” “back,” “first,” “second,” “upper,” “lower,” “height,” “top,” “bottom,” “outer,” “inner,” “width,” “length,” “end,” “side,” “horizontal,” “vertical,” and similar terms are used herein, it should be understood that these terms have reference only to the structure shown in the drawing and are utilized only to facilitate describing embodiments of the present disclosure. 
     All figures are drawn for ease of explanation of the basic teachings of the present disclosure only; the extensions of the figures with respect to number, position, relationship, and dimensions of the parts will either be explained or will be within the skill of persons of ordinary skill in the art after the following teachings of the present disclosure have been read and understood. Further, the exact dimensions and dimensional proportions to conform to specific width, length, and similar requirements will likewise be within the skill of the art after the following teachings of the present disclosure have been read and understood. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Illustrative embodiments are provided below. It will of course be appreciated that in the development of any actual embodiment, numerous implementation-specific decisions will be made to achieve the developer&#39;s specific goals, such as compliance with assembly-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
     Logging, construction, wind generation, firefighting, and many other associated industries have a need for a modern, remotely controlled, co-axial rotorcraft designed specifically as a heavy-lift aerial crane, and an embodiment of such a rotorcraft is shown in  FIG. 1 . Users of such a vehicle would expect it to be convenient and highly efficient while being inexpensive to maintain and operate. 
     It is a purpose of this vehicle to capitalize on the lift efficiencies to be gained by removing humans, and the associated support and safety equipment, from the vehicle platform entirely. Removal of the traditional fuselage and required crashworthiness requirements allows the use of novel airframe configurations and construction techniques. Thus, a much higher portion of the total lift can be devoted to the crane function. The rotorcraft can now be much smaller for a given lift, resulting in further synergies. A co-axial design also eliminates the weight of a tail rotor drive components and supporting tail boom or other systems designed to counteract yaw induced by a single rotor. Another synergistic contribution to a low airframe weight is that the entire cargo weight is suspended from a cable attached directly to the transmission. Consequently, landing and ground handling loads on the airframe structure involve only the empty weight plus fuel, versus a fully loaded aircraft. 
     The novel features of this invention are based on three basic design philosophies. The first is to achieve a vehicle weight reduction to the point that the crane can lift items that weigh close to 72% of the total rotor lift capacity. Thus, in this embodiment the vehicle weight is reduced to 15,000 lb, resulting in a payload capability of 40,000 lb versus a loft capacity of 55,000 lb. The second is to pursue maximum use of identical modules and components in order to reduce production, acquisition and operating costs. It has been shown that the novel features and general architecture of this invention can be applied successfully over a wide range lift capabilities, thereby allowing a range of crane sizes to be offered to suit customer requirements. From this stems the third philosophy, which is to use low-cost flying scale models to pursue development and refinement of new remote control techniques. An additional advantage to the configuration is the ability of some embodiments to be disassembled for transport without the need to fly the rotorcraft to a location. This ability may include the disassembly or folding of the rotors, disassembly of a lift module from a support module, and/or disassembly or folding of the support module. 
     It is expected that during operation of this vehicle, people will be positioned well clear of the operating site so no loss of life would occur in the event of an accident. Additionally, in the rare occurrence of loss of control, the vehicle&#39;s small size and primarily composite airframe and rotor construction would also be an important factor in reducing any collateral damage. It is also anticipated that this vehicle will be operated at low altitudes in confined spaces, with only limited cross-country excursions. Operational hazard to other airborne vehicles is not expected to be a regulatory problem. 
     Referring to  FIGS. 1 and 2 , a heavy-lift rotorcraft  11  has a unique layout, comprising two distinct and separate modules: a lift module  13  and a support module  15 .  FIGS. 3 through 22  illustrate details of components of lift module  13 , and  FIGS. 23 through 31  illustrate details of components of support module  15 . 
     Lift module  13  is dedicated primarily to the payload lift function and combines the propulsion, transmission, rotors, and energy source into a single, self-contained unit. In the preferred embodiment, rotorcraft  11  has a rotor system  17  comprising upper and lower counter-rotating rotors  19 ,  21 , each rotor  19 ,  21  having a plurality of blades  23 . Rotors  19 ,  21  are driven in rotation about a mast axis  25  by a propulsion system  27 . In the embodiment shown, propulsion system  27  comprises a pair of turbine engines  29  and a transmission  31 , though system  27  may alternatively comprise electric motors or other types of engines. A plurality of yaw actuators  33  are located on lift module  13  for rotating rotorcraft  11  in yaw about mast axis  25 , thereby eliminating complex differential-collective yaw mechanisms. 
     Lift module  13  is preferably mounted above the center of support module  15 , which provides inertial stabilization in flight plus a platform for supporting lift module  13  during landings and takeoffs. Support module  15  comprises a centerbody  35  and a plurality of legs  37  extending from centerbody  35  in a radial array. 
     To reduce the need for heavy structural components in support module  15 , a payload support system suspends an external payload directly from lift module  13 . In the embodiment shows, a payload lift bar  39  is connected directly to transmission  31 , and a payload ring  41  allows an external payload (not shown) to be suspended by a cable  43  attached to ring  41 . 
     Rotorcraft  11  has an onboard flight-control systems (not shown) that may operate in an autonomous mode, or rotorcraft  11  may be operated by one or more external control devices. For example,  FIG. 1  shows operators  45 ,  47  located on a nearby structure using external flight-control devices  49 ,  51  to emit wireless control signals  53 ,  55  for operating rotorcraft  11 . Signals  53 ,  55  are received by the onboard flight-control system for controlling both the flight and payload of rotorcraft  11 . In the embodiment shown, for example, an operator  45  has primary control of rotorcraft  11  to provide situational awareness, and a second operator  47  has vernier control to make fine adjustments needed to position a payload. 
     Referring now to  FIG. 3 , lift module  13  is shown in an exploded view. In addition to the components described above, lift module  13  comprises a blade actuation system  57 , a rigid support platform  59 , and an energy storage device  61 . Energy storage device  61  may be a fuel tank or other component, such as a battery or capacitor, for storing energy used to operate propulsion system  27 . Transmission  31 , yaw actuators  33 , and energy storage device  61  are all assembled onto platform  59 , which is preferably formed from a composite material, such as a graphite/epoxy composite. The figure also shows the lug  63  on a lower portion of transmission  31  for mounting payload lift bar  39 . 
     Propulsion system  27  is shown in detail in  FIGS. 4 through 22 . Referring to  FIGS. 4 through 8 , the illustrated embodiment of system  27  comprises a pair of turbojet engines  29 , each enclosed in a nacelle  65 . Engines  29  are preferably mounted onto transmission  31  and are also connected to platform  59 . Engines  29  are oriented to be generally perpendicular to mast axis  25  and are located on opposite sides of transmission  31 . Engines  29  may be, for example, General Electric T64-GE 416 turboshaft engines, each engine  29  rated at 4380 shp at 14300 rpm and having specific fuel consumption of 0.48 lb/hp per hour. While shown with two turbine engines  29 , rotorcraft  11  may comprise one or more turbine engines  29 , or rotorcraft may be powered by other types of combustion engines, such as reciprocating or rotary. Alternatively, rotorcraft  11  may be powered by electric motors or other types of propulsion devices that produce rotary motion. 
     Engines  29  are supported at the front by right and left intermediate gearboxes  67 ,  68  and at various locations by engine mounts  69 , which connect engines  29  to support platform  59  and maintain the position of engines  29  relative to each other. Engine mounts  69  may be, for example, metal tubes or may be other appropriate structures, such as composite plates or a combination of types of mounts. 
       FIG. 6  shows the preferred construction of engine nacelle  65 . Nacelle  65  comprises a rigid substructure  71 , comprising three ring frames  73 , a longeron member  75 , and a composite back-plate  77 , substructure  71  configured for surrounding and being supported by an engine  29 . At the front end of substructure  71 , a forward ring frame  73  supports an inlet cowl  79 . An upper access door  81 , shown in an open position, is hinged along one longitudinal edge to an upper edge of back-plate  77  and configured so that the other longitudinal edge is generally adjacent to longeron  75  when door  81  is moved to a closed position. Similarly, a lower access door  83  is hinged to a lower edge of back-plate  77  so that an opposite edge is adjacent to longeron  75  when door  83  is moved to a closed position. To provide for minimized weight, substructure  71 , cowl  79 , and doors  81 ,  83  are preferably formed from lightweight composite materials, such as graphite/epoxy sheets and/or honeycomb. The contours of nacelles  65  may be designed specifically to allow access doors  81 ,  83  for both nacelles  65  to be manufactured using the same mold, thereby saving manufacturing costs. 
     Operation of each engine  29  provides for rotary power about each engine axis  85 , and the direction of rotation is shown as arrows  87 . Each engine  29  is fitted with an accessory gearbox  89  to provide electrical power and hydraulic pressure for use in operation of flight control and auxiliary systems of rotorcraft  11 . Power for rotating rotors  19 ,  21  is taken off the front of each engine  29  by the associated intermediate gearbox  67 ,  68 . Gearboxes  67 ,  68  preferably comprise as many identical components as is practicable, and each gearbox comprises a gear reduction system, which steps down the engine rpm delivered to transmission  31 . For example, gearboxes  67 ,  68  may reduce the rpm from 14300 rpm to 2868 rpm at an input to transmission  31 . 
     Referring still to  FIG. 8  and also to  FIGS. 9 through 13 , transmission  31  comprises a gear system for redirecting torque supplied by engines  29  from intermediate gearboxes  67 ,  68  to coaxial mast assembly  91 . Mast assembly  91  comprises upper rotor mast  93  and lower rotor mast  95 , masts  93 ,  95  being rotated in opposite directions about mast axis  25  by transmission  31 , as shown by arrows  97 ,  99 . Transmission  31  has a gear case  101  that encloses the gear system, which amplifies engine torque introduced via gearboxes  67 ,  68 . Gear case  101  is preferably formed from aluminum castings and mounted with integral buttress plates  103  onto platform  59 , which is used to attach lift module  13  to support module  15 . 
       FIGS. 9 and 10  are lateral and 45-degree, respectively, cross-section views of transmission  31 , and  FIG. 11  is an isolated view of a gear module  105 . Transmission  31  capitalizes on convenient features of the co-axial contra-rotating mast design by maximizing the use of identical gear modules  105 , and identical modules  105  can be utilized to save design, manufacturing, inspection, and development test costs.  FIG. 12  illustrates how the upper gear module is assembled into the upper portion of case  101  facing upward for driving lower rotor mast  95  in the counter-clockwise direction (as seen from above transmission  31 ). An identical gear module  105  is assembled facing downward in the lower portion of case  101  for driving upper rotor mast  93  in the clockwise direction (as seen from above transmission  31 ). 
     Each gear module  105  is a planetary gearset, comprising a crown gear  107 , planetary gears  109  carried in a cage  111 , and a ring gear  113 . Crown gear  107  comprises an outer bevel gear  115  having gear teeth  116  configured to engage and be driven by a pinion gear  117  having gear teeth  118 . Each pinion gear  117  rotates on an axis generally perpendicular to mast axis  25  and is driven by an output shaft  120  of an intermediate gearbox  67 ,  68 . Crown gear also has a central, integral sun gear  119  with teeth  121  for engaging teeth  123  on planetary gears  109 , each of which can rotate relative to cage  111  about an associated shaft  125 . Central splines  127  of cage  111  engage corresponding splines  129  on mast  95  or splines  131  on mast  93 . Ring gear  113  is a circular ring having gear teeth  133  on an inner surface for engaging teeth  123  on planetary gears  109 , and ring gear  113  has teeth  135  on an outer surface for use with a yaw control system (described below). Crown gears  107 , cages  111 , and ring gears  113  are able to rotate about mast axis  25  relative to case  101  of transmission  31 . 
     To rotate rotor masts  93 ,  95 , torque is transferred from gearboxes  67 ,  68  to each pinion  117  via output shafts  120 , pinions  117  rotating in opposite directions. Teeth  118  of each pinion  117  engage with teeth  116  of both crown gears  107 , each pinion  117  thereby driving crown gears  107  in opposite directions. Teeth  121  of each sun gear  119  engage teeth  123  of associated planetary gears  109 , and teeth  123  also engage teeth  133  of ring gear  113  to cause differential rotation of cages  111  relative to ring gears  113 . An additional yaw rotation can be superimposed equally on both cages  111  by a pair of vertical balance shafts  137  which are rotatably carried in case  101  and have upper and lower pinions  139  that engage outer teeth  135  of upper and lower ring gears  113 . Vertical balance shafts  137  and pinions  139  balance out differential torque between upper and lower ring gears  113  so that yaw motion can be applied equally to each ring gear with no motion of the ring gears relative to each other. Though shown in the figures with four shafts  137 , transmission  31  may have more or fewer shafts  137  to accommodate the expected loads during operation. Assembled modules  105  act as a differential gear set which converts engine torque at input pinions  117  into output torque at co-axial rotor masts  93 ,  95 . In addition to the torque balancing function, shafts  137  provide for yaw control of rotorcraft  11 , and a rotary actuator  141  is connected to each balance shaft  137  for rotating the shaft  137  along its longitudinal axis relative to case  101 . The yaw control is described below in relation to  FIG. 22 . 
       FIGS. 13A and 13B  are plan and front, respectively, partial cutaway views, showing details of left intermediate gearbox  68 . In another effort to reduce cost, intermediate gearboxes  67 ,  68  are mostly identical, though gear sets within gearboxes  67 ,  68  may have different parts to achieve the correct direction of rotation of the associated pinion  117 . As shown, an output shaft  143  of engine  29  turns an input gear  145 , which turns one side of intermediate gear  147 . The other, smaller side of intermediate gear  147  turns another intermediate gear  149 , further reducing the engine rpm and increasing torque, and a shaft  151  connects gear  149  and bevel gear  153 . Bevel gear  153  turns a larger, perpendicular bevel gear  155  for further reducing engine rpm, increasing torque, and redirecting the torque to output shaft  120 . As described above, output shaft  120  is connected to pinion  117  for rotating crown gears  107 . As an example of the change in engine rpm and torques achieved by gearboxes  67 ,  68  and gear modules  105 , depending on the selected gear ratios, an input torque of 8000 ft-lb at 3000 rpm may be magnified to a rotor torque of 80,000 ft-lb at 300 rpm. 
       FIG. 14  illustrates lift bar  39 , which is preferably formed from a composite material, such as a graphite/epoxy composite. Depending on the size of rotorcraft  11 , lift bar may be of substantial length, and the embodiment shown, for example, has a length of approximately 80 inches. As described above, lift bar  39  is attached at the upper end to lug  63  on the lower portion of case  101  of transmission  31 . Lift bar  39  extends through the center of support module  15  and has a payload ring  41  on the lower end of bar  39 . The advantage of this configuration is that the forces of an external payload suspended from lift bar  39  are passed directly to case  101 , and support module  15  can be constructed without the need to support the external payload. 
       FIGS. 15 through 21B  illustrate the overall configuration of co-axial rotor system  17 . Rotors  19 ,  21  preferably have five blades each, though more or fewer blades may be used in appropriate applications. As viewed from above rotors  19 ,  21 , upper rotor  19  rotates in the clockwise direction, indicated by arrow  157 , and lower rotor  21  rotates in the counter-clockwise direction, indicated by arrow  159 . 
       FIGS. 16A and 16B  show plan and cross-section views of an example blade  23 , which, in the embodiment shown, has a length L of 27.5 ft and a chord C of 20 in. Blade  23  preferably comprises a graphite/epoxy composite skin  161  covering an aft blade section machined from graphite honeycomb  163 , and blade  23  has a hollow graphite/epoxy composite spar section  165 . Blades are connected to a mast  93 ,  95  by a hub  167 , which comprises five arms  169 . Each blade is rotatably connected to an arm  169  so that blade is rotatable about a pitch axis  171 . 
       FIG. 17  shows upper and lower rotor hubs  167 . Upper hub  167  rotates in the clockwise direction and is splined to the smaller, upper mast  93 . Lower hub  167  is splined to the larger, lower mast  95  and rotates in the counter-clockwise direction. Both hubs  167  are preferably machined from identical titanium billets in order to reduce material and machining costs. Three holes  173  are provided each hub  167 , and they are used in lower hub  167  to allow three actuation rods to pass through lower hub  167 . 
     Pitch angle, or angle of attack, about pitch axis of each blade  23  is controlled with a blade control arm cuffs  175 , a cuff  175  being rotatably connected to an outer end of each arm  169  of hubs  167  and able to be rotated about pitch axis  171 . Each cuff  175  has a control arm  177  extending from the central portion of cuff  175  and offset from pitch axis  171 .  FIG. 18  shows a plan view of rotors  19 ,  21 , and the view shows the azimuth positions of control arms  177  relative to blades  23  of each rotor  19 ,  21 . 
     Referring now specifically to  FIGS. 19 through 21B , cyclic and collective inputs to the co-axial rotor are controlled by a multi-level blade-actuation system, which translates motions from three electro-hydraulic linear actuators  179  mounted on case  101  of transmission  31  into discrete pitch changes of each blade  23  on rotors  19 ,  21 . The pitch changes may be in the form of cyclic pitch changes, which tilts a swashplate to variably change the pitch of each blade  23  as rotor  19 ,  21  rotates, or collective pitch changes, which vertically translates a swashplate to change the pitch of each blade  23  by a set amount throughout the rotation of rotor  19 ,  21 . 
     Actuators  179  impart cyclic and collective motions onto the actuator swashplate  181 , comprising non-rotating section  183  and rotating section  185 . Actuators  179  are pivotally connected to non-rotating section  183  at mounts  187 , allowing for relative motion between swashplate assembly  181  and actuators  179  as shaft  189  of each actuator extends or retracts from actuator body  191 . Rotating section  185  is able to rotate relative to non-rotating section  183  and is constrained to this one degree of freedom relative to non-rotating section  183 , causing input from actuators  179  to non-rotating section  183  are transferred to rotating section  185 . Cyclic and collective inputs from actuators  179  cause swashplate  181  to tilt about spherical bearing  193  (shown in  FIG. 20B ) that is located in the center of swashplate  181 . Bearing  193  is connected via splines  195  to the upper portion of case  101  of transmission  31  in order to constrain motion in the azimuth, but splines  195  accommodate vertical collective motion of swashplate  181  via vertical translation along splines  195 . Non-rotating section  183  is constrained in azimuth relative to case  101  by a scissors link  196 , which allows freedom of motion about spherical bearing  193  in axes perpendicular to mast axis  25 . Likewise, rotating section  185  is constrained to rotate together with lower rotor  21  by a similar scissors link  197  connected to mast  95 . 
     Three actuator rods  198  are pivotally connected at a lower end to mounts  199  on rotating section  185  and extend upward through holes  173  in lower hub  167 . Actuator rods  198  are pivotally connected at an upper end to a central portion of blade-control swashplate  201  located between rotors  19 ,  21 , and rods  198  transfer the cyclic and collective motions of swashplate  181  to swashplate  201 . Swashplate  201  comprises a lower rotating section  203  and an upper rotating section  205 , and sections  203 ,  205  are able to rotate relative to each other. Sections  203 ,  205  and constrained to this one degree of freedom relative to each other, causing cyclic and collective input from actuator rods  198  to section  203  to be transferred to section  205 . Because rotors  19 ,  21  rotate in opposite directions, sections  203 ,  205  also rotate in opposite directions, as shown by arrows  207 ,  209 . Cyclic and collective inputs from actuator rods  198  cause swashplate  201  to tilt about spherical bearing  211  (shown in  FIG. 21B ) that is located in the center of swashplate  201 . Bearing  211  is connected via splines  213  to the upper portion of mast  95  in order to rotate bearing  211  with lower section  203 , and splines  213  accommodate vertical collective motion of swashplate  201  via vertical translation along splines  213 . Lower section  203  rotates together with mast  95  and is connected to mast  95  by a scissors link  215 , which allows freedom of motion about spherical bearing  211  on axes perpendicular to mast axis  25 . Likewise, upper section  205  is constrained to rotate together with lower rotor  21  with a similar scissors link  217  connected to mast  93 . 
     Referring specifically to  FIGS. 19 and 21A , cyclic and collective motions of blade-control swashplate  201  are transferred to control arms  177  of blade cuffs  175  on upper rotor  19  by five control rods  219  and to control arms  177  of blade cuffs  175  on lower rotor  21  by five control rods  221 , one control rod  219  or  221  for each blade  23 . Each control rod  219  is pivotally connected at a lower end to a mount  223  on upper section  205  and at an upper end  225  to an associated control arm  177  on upper rotor  19 . Likewise, each control rod  221  is pivotally connected at an upper end to a mount  227  on lower section  203  and at a lower end  229  to an associated control arm  177  on lower rotor  21 . Blades  23  on upper rotor  19  are controlled by upper section  205  acting on control arms  219 , which extend upward, and blades  23  on lower rotor  21  are controlled by lower section  203  acting on control arms  221 , which extend downward. This configuration allows for cyclic (tilting) and collective (vertical translation) inputs to be transferred from actuators  179  to actuator swashplate  181 , then through actuator rods  198  to swashplate  201 , then through control rods  219  from upper section  205  to blade cuffs  175  on upper rotor  19  and through control rods  221  from lower section  203  to blade cuffs  175  on lower rotor  21 . 
       FIG. 22  illustrates a novel yaw trim and control system for a co-axial rotorcraft. In the prior art, many aircraft having co-axial, contra-rotating rotor systems are controlled in yaw by additional complex swashplate assemblies, which apply collective pitch differentially to the two rotors or utilize braking systems on either rotor. These systems are usually heavy, complicated, and expensive. 
     The present system utilizes relatively small and lightweight rotary actuators  141  to rotate rotorcraft  11  with respect to both differential ring gears  113  housed within transmission  31 . Actuators  141  may be of any appropriate type, such as electric, pneumatic, or hydraulic and preferably feature reversible drive with a clutch to disengage a non-functioning actuator  141 . Actuators  141  rotate balance shafts  137  in transmission  31 , causing pinions  139  to rotate transmission case  101  around upper and lower ring gears  113 . High opposing torques from ring gears  113 , which are normally reacted within housing  101 , are instead reacted by pinions  139 . The opposing torque in pinions  139  is balanced within each shaft  137 , so that only relatively low torques are required to turn the housing  101  relative to ring gears  113 . Because transmission  31  is mounted with buttress plates  103  to platform  59 , as is support module  15 , rotation of shafts  137  cause rotorcraft  11  to yaw about mast axis  25 . 
       FIG. 23  illustrates components of an onboard flight-control system. Cyclic, collective, and yaw control actuators are all controlled remotely via radio-control links with the rotorcraft  11 , as shown in  FIG. 1  and described above. In the preferred embodiment, receivers, transmitters and electronic control functions will be housed in three electronic control modules  231 , each module  231  being mounted in one of the airframe legs  37 . Convenient doors  233  are provided in the legs to gain ready access to these modules  231 . Control modules  231  provide triplex redundancy with advanced loss-of-signal or signal-dropout logic circuits. In addition, numerous remote video cameras  235  are positioned on support module  15  to provide real-time positional information to the operators. 
       FIGS. 24 and 25  illustrate fuel tank system  237 , which is supported from rigid composite platform  59  so that it is positioned within centerbody  35  (see  FIGS. 1 and 2 ) of support module  15 . System  237  comprises multiple crashworthy tanks  239  in a circular array and carried by a Kevlar basket  241 , which extends downward from, and is suspended from, platform  59  and transfers loads from tanks  239  to platform  59 . Tanks  239  are shaped to form an aperture  243  in the center of the assembly, allowing lift bar  39  to pass through the center of the array of fuel tank  239 . Tanks  239  are preferably molded from graphite/epoxy composite, and may have a thickness varying from 0.12 in at the top to 0.28 in at the bottom. Each tank preferably has a 300 gal (US) capacity. Tanks  239  are preferably retained within basket  241  by thin Kevlar bands  245 , which encircle tanks  239  and are designed to react bursting loads from the hydrostatic pressure of fuel within tanks  239 . In addition, tanks  239  are also supported by lightweight foam blocks  247  to keep the tanks tightly fitted within centerbody  35 . 
     Referring specifically to  FIG. 25 , two filler hoses  249  at the top of tanks  239  facilitate rapid refueling, and tanks  239  may be configured as a single fuel system, a group of separate tanks  239 , or as main and auxiliary tanks  239 . A sump pump  251  at the base of each tank  239  is mounted in a lower tray  253  of support basket  241 , and tray  253  also supports dividers  255  between tanks  239 . Vent lines  257  can be conveniently nested within fuel tank system  237 . 
       FIGS. 26 through 31  illustrate components, overall configuration, and construction of support module  15 , with transmission  31  and platform  59  of lift module  13  also shown in  FIGS. 26 and 27 . In the preferred embodiment, each leg  37  comprises a central flange  259  and a support structure, such as beam  261 , which extends generally horizontally from flange  259 . Legs  37  are preferably constructed as a single piece formed entirely from graphite/epoxy composite layers bonded to a honeycomb core. Ideally, thick outer face sheets provide for damage protection and are stabilized by a thinner inner face sheet. 
     Each flange  259  comprises an integral upper ring section  263  and an integral lower ring section  265 , each being arcuate. Upper ring sections  263  and lower ring sections  265  cooperate to form a central frame, with upper ring sections  263  of adjacent legs  37  attached to each other to form a circular central ring, and lower ring sections  265  attached in the same manner to form a lower central ring. In this way, flanges of legs  37  are attached together to form central body  37 . To provide for attachment, each ring section  263 ,  265  has an attachment face  267  on each end of each ring section  263 ,  265 . In the embodiment shown, each face  267  has a part  269  of a “bathtub”-type alignment fitting, in which a hole on one face  267  receives a lug protruding from the adjacent face  267 . Bolts or other fasteners are used to retain adjacent faces  267  together to form upper and lower circular structural frames. 
     Centerbody  35  has a removable upper fairing  271  that covers transmission  31  and has provisions for gaining access to transmission  31  and blade actuation system  57 . Centerbody  35  is capped on its underside by a rigid structural lower fairing  273 , which is removable for access to the lower interior of centerbody  35 . Fairings  271 ,  273  are preferably formed of lightweight, composite material and construction. Lower fairing  273  supports a lightweight, composite payload ring  275 , which is designed as a guide for payload cable  43 . At the outer end of each leg  37  is a landing gear assembly  277  for supporting support module  15  above a support surface. It should be noted that legs  37  may optionally include compartments for additional internal components, which may include, for example, auxiliary energy storage devices. Another expected use of storage in legs  37  may be for water tanks for firefighting applications. 
       FIGS. 28 through 29B  illustrate the minimal plan view shape of leg beam  261 , which are contoured stream-wise to minimize drag interference on the vertically downward airflow from rotors  19 ,  21 . An aerodynamic wing section  279  is formed as a hollow cross section which tapers down outboard toward pedestal  281  for landing gear  277 . Wing section  279  has its chord axis  283  in the vertical plane, providing for a low-drag profile when exposed to the rotor down airflow, as shown as flow lines  285  in  FIG. 28 . At centerbody  35 , wing section  279  flares out into flange  259 , including integral upper ring section  263  and lower ring section  265 . 
       FIG. 30  shows the preferred embodiment of support module  15 , which is a composite structure comprising three identical legs  37 , each presenting a slender, low-drag profile in the plan view with an ample ground turnover width W of 14 feet. Configurations of support module  15  having more legs can be used, but these have significant weight disadvantages, present problems with maintaining wheel contact on uneven terrain, and require longer field assembly times. 
       FIG. 31  shows a possible configuration for transport of a disassembled rotorcraft  11 . One Leg  37  has been disassembled from the other legs  37 , and blades  23  have been removed from rotor hubs  167 . As shown, legs  37  and blades  23  are loaded together with the remainder of lift module  13  onto a transporter  291 , which may be, for example, a typical flat bed of a semi-trailer, and transporter  291  may be equipped with devices to assist assembly and dis-assembly. In this manner, rotorcraft  11  may be moved to a location without the need to fly rotorcraft to the location or without the need for a specialized transport method. 
       FIG. 32  shows a radio-controlled flying scale model  293  of a heavy-lift rotorcraft, and an operator  295  operates model  293  with controller  297 . This is an ideal means of pursuing development of a full-size vehicle, such as rotorcraft  11 , and a handful of these inexpensive models would suffice in minimizing initial development costs and investment risks. Development may include a model  293 , for example, of approximately ⅙ th  scale. Model  293  could be powered by four small 35 hp engines  299  horizontally disposed about 301 centerbody in a radial manner, and driving directly into the transmission. As far as is possible, model  293  would incorporate most of the engineering aspects of the full-sized rotorcraft  11  and would be a valuable tool for developing the operational and remote control techniques that will be required and as trainers for operating personnel. 
     It is apparent that an assembly with significant advantages has been described and illustrated. The particular embodiments disclosed above are illustrative only, as the embodiments may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. It is therefore evident that the particular embodiments disclosed above may be altered or modified, and all such variations are considered within the scope and spirit of the application. Accordingly, the protection sought herein is as set forth in the description. Although the present embodiments are shown above, they are not limited to just these embodiments, but are amenable to various changes and modifications without departing from the spirit thereof.