Patent Abstract:
A retractable rotor system for an aircraft includes a rotor blade with a leading edge, a trailing edge, and an internal collapsible web. The leading edge includes a flexible portion whose lower edge contacts but is not structurally joined to the lower skin. When the leading edge is peeled forward from the lower skin, the blade elastically collapses to the thickness of its constituent layers. The rotor blade extends through a support frame connectable to the aircraft to secure the rotor blade to a spool. Rotating the spool retracts the rotor blade through the support frame while pulling the rotor blade over a fixed actuating member, placing the rotor blade in the collapsed condition and winding the rotor blade onto the spool. Rotating the spool in the opposite direction unwinds the rotor blade from the spool, through the frame, causing the rotor blade to relax into the expanded condition.

Full Description:
TECHNICAL FIELD 
     The present invention relates generally to rotors and, more specifically, to a collapsible rotor blade for an aircraft. 
     BACKGROUND 
     Rotors have been used in aircraft for some time and provide the aircraft with vertical take-off and landing (VTOL) capability, thereby increasing the terrain and environment in which the aircraft can be used. The greatest VTOL lift versus power is currently obtained by large diameter, open rotor aircraft, namely helicopters. However, the forward speed of helicopters is limited by the rotor due to the reduced relative airspeed of the retreating blades, which causes them to stall. Even at moderate forward speeds a great deal of power is required to overcome large drag forces due to pulling the large, spinning rotor and hub system through the air at speed, and the high Mach number of the forward traveling blades. It is therefore desirable to provide an aircraft rotor that provides for both VTOL lift capability as well as high aircraft speed. 
     SUMMARY OF THE INVENTION 
     A retractable rotor system for an aircraft includes a retractor connectable to the aircraft and having a spool rotatable in a first direction and a second direction opposite the first direction. A rotor blade extends along a radial axis and has a first end and a second end. The rotor blade is movable between a first condition having a first thickness to a second condition having a second thickness less than the first thickness. The rotor blade extends through a support frame connectable to the aircraft to secure the first end of the rotor blade to the spool. The spool is rotatable in the first direction to unwind the rotor blade from the spool and to extend the rotor blade away from the support frame and place the rotor blade in the first condition. The spool is rotatable in the second direction to wind the rotor blade on to the spool and to retract the rotor blade into the support frame and place the rotor blade in the second condition. 
     In another example, a retractable rotor system for an aircraft includes a retractor connectable to the aircraft and having a spool rotatable in a first direction and a second direction opposite the first direction. A rotor blade airfoil extends along a radial axis and has a first end secured to the spool and a second end extending away from the spool. The rotor blade airfoil includes a movable portion and a stationary portion each extending longitudinally along the rotor blade. The rotor blade is movable between a first condition having a first thickness that provides rigidity normal to the plane of the rotor blade, and a second condition having a second thickness less than the first thickness that provides flexibility normal to the plane of the rotor blade. A support frame connectable to the aircraft has a pair of passageways through which the rotor blade extends to secure the first end of the rotor blade to the spool. A fixed actuating member extends between the passageways and is positioned within the portion of the rotor blade that is in the first condition. The spool is rotatable in the first direction to unwind the rotor blade from the spool such that the actuating member causes the movable portion of the airfoil to move towards the stationary portion to place the rotor blade in the first condition. The spool is rotatable in the second direction to wind the rotor blade on to the spool such that the actuating member moves the movable portion of the airfoil away from the stationary portion to place the rotor blade in the second condition. 
     In another example, an aircraft includes a body and a pair of fixed wings and a rotor mast extending from the body. A gear positioned within the rotor mast is drivable by a motor or inner rotor shafts who&#39;s relative speed is controlled by a further system of gears and clutches. A plurality of retractable rotor systems each includes a retractor having a spool rotatable by the gear in a first direction and a second direction opposite the first direction. A rotor blade extends along an axis and has a first end secured to the spool and a second end extending away from the spool. The rotor blade airfoil includes a movable portion and a stationary portion each extending longitudinally along the rotor blade. The rotor blade is movable between a first condition having a first thickness that provides rigidity normal to the plane of the rotor blade and a second condition having a second thickness less than the first thickness that provides flexibility normal to the plane of the rotor blade. A support frame connected to the rotor mast has a pair of passageways through which the rotor blade extends to secure the first end of the rotor blade to the spool. A fixed actuating member extends between the passageways and is positioned within the portion of the rotor blade that is in the first condition. The spool is rotatable by the gear in the first direction to unwind the rotor blade from the spool such that the actuating member moves the movable portion towards the stationary portion to place the rotor blade in the first condition. The spool is rotatable by the gear in the second direction to wind the rotor blade on to the spool such that the actuating member moves the movable portion away from the stationary portion to place the rotor blade in the second condition. 
     In another example, a retractable rotor system for an aircraft includes a rotor blade with a rounded leading edge, a tapered trailing edge, and an internal collapsible web. The leading edge includes a flexible portion whose lower edge contacts but is not structurally joined to the lower skin. When the leading edge is peeled forward from the lower skin, the blade can be elastically collapsed to the thickness of its constituent layers. The rotor blade extends through a support frame connectable to the aircraft to secure the rotor blade to a spool. Rotating the spool retracts the rotor blade through the support frame while pulling the rotor blade over a fixed actuating member, placing the rotor blade in the collapsed condition and winding the rotor blade onto the spool. Rotating the spool in the opposite direction unwinds the rotor blade from the spool, through the frame, causing the rotor blade to relax into the expanded condition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an example aircraft including a retractable rotor system. 
         FIG. 2  is an enlarged view of a portion of the retractable rotor system of  FIG. 1 . 
         FIG. 3A  is a perspective view of a support frame and fixed actuating member of the retractable rotor system of  FIG. 1 . 
         FIG. 3B  is a sectional view of the support frame of  FIG. 3A  taken along line  3 B- 3 B. 
         FIG. 4A  is an isometric view of an actuating member of the retractable rotor system of  FIG. 1 . 
         FIG. 4B  is a side view of the actuating member of  FIG. 4A . 
         FIG. 4C  is a graph illustrating first and second ends of the actuating member of  FIG. 4A . 
         FIG. 5A  is a top view of a rotor blade of the aircraft of  FIG. 1 . 
         FIG. 5B  is a sectional view of the rotor blade of  FIG. 5A  taken along line  5 B- 5 B. 
         FIG. 5C  is an enlarged portion of  FIG. 5B . 
         FIG. 6  is a portion of an assembly view of the retractable rotor system of  FIG. 1 . 
         FIGS. 7A-7H  are schematic illustrations of the actuating member of  FIGS. 4A-4C  changing the condition of the rotor blade of the rotor system. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention relates generally to rotors and, more specifically, to a collapsible rotor blade for an aircraft.  FIGS. 1-6  illustrate an example retractable rotor system  60 . Referring to  FIGS. 1 and 2 , the rotor system  60  is provided on an aircraft  30 , such as a helicopter. The aircraft  30  includes a body  32  and a tail  38  and extends from a first or fore end  34  to a rear or aft end  36 . A rotor mast  62  extends vertically from the body  32  and operably connects the rotor system  60  to the aircraft  30 . The rotor system  60  acts as the main rotor for the aircraft  30  and selectively provides both lift and propulsion for the aircraft  30  in VTOL mode. A tail rotor  40  may be connected to the tail  38  for counterbalancing torque on the aircraft  30  applied by the rotor system  60  in VTOL mode. A pair of fixed wings  50  extends outwardly from the body  32  for high speed flight mode. Each wing  50  may include a means of propulsion, e.g., propeller or jet engine (not shown), for providing propulsion to the aircraft  30  in high speed flight mode. 
     The rotor system  60  includes at least two articulating base assemblies  90 , a rotor blade  200  extending through each articulating base assembly  90 , and a retractor  300  associated with each rotor blade  200  for selectively winding and unwinding the rotor blade  200  to retract (in the direction A in  FIG. 1 ) and extend (in the direction B in  FIG. 1 ) the rotor blade  200  relative to the base assembly  90 . As shown, the rotor system  60  includes a pair of rotor blades  200  extending in opposite directions from the rotor mast  62 , each with a corresponding base assembly  90  and retractor  300 . It will be understood that the rotor system  60  may include more rotor blades  200  symmetrically arranged about the rotor mast  62 , each with a corresponding articulating base assembly  90  and retractor  300 . In any case, the blades  200  are rotatable about an axis  64  of the rotor mast  62  in the direction indicated generally by R 1  in  FIGS. 1 and 2 . 
     Referring to  FIGS. 3A and 3B , the articulating base assembly  90  is made of typical aircraft material and includes a support frame  94  having a generally rectangular shape defining an interior space  140 . The support frame  94  extends along a centerline or axis  96  from an outboard first end  98  to an inboard second end  100 . The support frame  94  is connected to the rotor mast  62  on the aircraft  30  by one or more hinges  92  that allow the support frame  94  to articulate in multiple directions relative to the centerline  96 . For example, the support frame  94  may rotate about the centerline  96  in the direction generally indicated by R 2  in  FIG. 3A . Alternatively or additionally, the support frame  94  may tilt relative to the centerline  96  in the direction generally indicated by T, e.g., the second end  100  may pivot about the hinge  92  relative to the first or outboard end  98 . 
     The support frame  94  includes an outer wall  110  at the outboard end  98  and an outer wall  120  at the inboard end  100 . An inner surface  112  of the outer wall  110  defines a passageway  114  through the outer wall  110 . The passageway  114  has a generally airfoil shape and is sized to slidably receive one of the rotor blades  200 . The passageway  114  therefore includes a rounded leading edge  116  and a more tapered trailing edge  118 . 
     An inner wall  130  is located axially along the centerline  96  between the outer walls  110 ,  120  and within the interior space  140 . The inner wall  130  divides the interior space  140  into a portion  142  between the inner wall  130  and the outboard wall  110  and a portion  144  between the inner wall  130  and the inboard wall  120 . An inner surface  132  of the inner wall  130  defines a passageway  134  through the inner wall  130 . The passageway  134  has a generally rectangular shape. A curved guide member  148  may extend from the inner wall  130 , into the second portion  144  of the interior  140 , and downward towards the retractor  300  (see  FIG. 3B ). The guide member  148  is secured to or integrally formed with the inner wall  130  at a position above the second passageway  134 . 
     A pair of rollers  160  (shown in phantom) is provided within cavities (not shown) of the inner wall  130  and extends along the length of the inner wall  130 . The rollers  160  are supported for rotation relative to the inner wall  130  along axes (not shown) perpendicular to the centerline  96  of the support frame  90 . The rollers  160  partially extend into the passageway  134  and are vertically spaced apart a predetermined distance from one another. 
     A fixed actuating member  150  is secured to the support frame  94  and extends between the inner wall  130  and the outer wall  110 . More specifically, the actuating member  150  extends from a first or outboard end  152  positioned within the passageway  114  of the outer wall  110  to a second or inboard end  154  secured to the inner wall  130  at a position below the passageway  134  in the inner wall  130 . The outboard end  152  of the actuating member  150  extends into the outboard end  116  of the passageway  114  and is spaced from the inner surface  112 . The actuating member  150  has a generally shoehorned shape configured to unzip or peel open the movable portion  209  of the rotor blade  200  as the rotor blade  200  is retracted in the direction A to be wound on the retractor  300 . Although one example construction of the actuating member  150  is described, it will be appreciated that the actuating member  150  may exhibit any shape and/or contour capable of performing the aforementioned unzipping or peeling action on the retracting rotor blade  200 . 
     Referring to  FIGS. 4A-4B , the actuating member  150  has a generally curved, frustoconical shape. The outboard end  152  of the actuating member  150  terminates at an end surface  156 . The inboard end  154  of the actuating member  150  terminates at an end surface  158 . As shown, the end surfaces  156 ,  158  each has a round or elliptical shape and the actuating member  150  has a round or elliptical cross-section along its entire length between the end surfaces  156 ,  158 . It will be appreciated, however, that the end surfaces  156 ,  158  and/or portions of the lengthwise cross-section of the actuating member  150  may have one or more additional or alternative shapes, e.g., circular or polygonal. A longitudinal centerline  159  of the actuating member  150  may extend along a curved or arcuate path. 
       FIG. 4C  illustrates the end surfaces  156 ,  158  of the actuating member  150  superimposed on an x-y Cartesian coordinate system. The lengthwise cross-section of the actuating member  150  undergoes several spatial changes between the end surface  156  and the end surface  158  relative to the x-y coordinate system shown. In particular, the elliptical cross-section of the actuating member  150  rotates counterclockwise, moves generally rightward in the x-y plane, and increases in size as the lengthwise cross-section moves from the outboard end surface  156  to the inboard end surface  158 . 
     The rotor blade  200  is illustrated in more detail in  FIGS. 5A-5C . The blade  200  has an elongated shape and extends radially along a centerline  202  from an inboard first end  204  to an outboard second end  206 . The apparent taper of the rotor blade  200  is due only to the perspective of the drawing. The blade  200  extends perpendicularly relative to the centerline  202  between a fore or leading edge  201  and an aft or trailing edge  203 . The blade  200  includes a first portion  208  defining the majority of the blade  200  that is largely stationary, and in concert with the collapsible web members  230  constitutes a closed aft section. The blade  200  includes a second portion  209  extending from the first portion  208  that is largely movable, and closes the forward axial cross-section of the blade  200  only when in the first greater thickness condition. The first and second portions  208 ,  209  collectively define an inner surface  214  that defines an interior  216  of the blade  200 . 
     The first portion  208  may constitute one or more layers of a material with a high yield strain such that the first portion  208  can sustain a relatively large bending deformations without yielding. In one example, the first portion  208  constitutes a single sheet or layer of Titanium 6-6-2-sta. Alternatively, the first portion  208  may constitute nylon. In any case, the first portion  208  is formed into a high performance airfoil shape by existing means, such as cold rolling for Titanium or extrusion for nylon. The distribution of material thickness along the blade  200 , i.e., number of layers in the portions  208 ,  209 , and their respective thickness(es), of the blade  200  may be configured to ensure the center of gravity of the blade  200  axial cross-section is not positioned aft of the quarter chord to help maintain blade aerodynamic pitch stability. 
     The second portion  209  extends forward from the first portion  208  and helps form the leading edge  201  of the blade  200 . The second portion  209  includes a movable portion or edge  210  that cooperates with a stationary portion  212  on the first portion  208  to substantially close the leading edge  201 . As shown, the movable and stationary edges  210 ,  212  are configured to abut or overlap one another at a position below the chord  220 , although the edges  210 ,  212  may alternatively abut or overlap one another along or above the chord  220 , and either or both may be movable (not shown). The movable and stationary edges  210 ,  212  are configured to move relative to one another while extending or retracting the rotor blades  200  during operation of the aircraft  30 . 
     The second portion  209  may be formed by one or more layers of material that are thinner or more elastic than the layer of the first portion  208  (see  FIG. 5C ). In one example, the second portion  209  constitutes a series of stacked layers which are bonded together only where they attach to the first portion  208 . In other words, a first end of each layer in the second portion  209  is directly secured to the first portion  208  and to one another, and the remainder of each layer in the second portion  209  is free from connection to the other layers in the second portion. Due to this construction, the minimum elastic radius of the second portion  209  is dictated largely by the individual layer thicknesses rather than the total thickness of the layer group. In another example (not shown), the second portion  209  constitutes a layer of material thicker than the layer of the first portion  208  with a much higher yield strain than the material of the first portion  208 , e.g., an elastomer. In any case, the bottom of the movable portion  210  is configured to overlap and be biased into firm engagement with the foremost portion of the stationary portion  212 . In this condition, the axial cross-section of the blade  200  ( FIG. 5B ) has comparable shape, tension, bending, and torsion strength as a conventional helicopter blade. It will be understood that the axial cross-section in  FIG. 5B  is exaggerated in the direction of the chord  220  for clarity. 
     One or more collapsible web members  230  are positioned within the interior  216  of the blade  200  and extend along the length of the blade  200 . Each collapsible web member  230  may constitute a conventional compression spring or the like that helps maintain the airfoil shape of the blade  200  when the blade  200  is fully retracted from the support frame  90 . Each collapsible web member  230  is secured to the inner surface  214  of the blade  200  via bonding or the like. Securing the collapsible web members  230  to the inner surface  214  of the blade  200  in this manner closes the shear path through the blade  200  so that it can support bending and torsion. Each collapsible web member  230  may be positioned closer to the leading edge  201 . When the collapsible web member  230  is uncompressed and the blade  200  unconfined, the blade  200  has a thickness t 1  measured in a direction through and substantially perpendicular to the centerline  202  of the blade  200 . 
     Referring to  FIG. 6 , the retractor  300  is coupled to the rotor mast  62  and is configured to selectively retract and extend each blade  200  relative to the corresponding support frame  90  and relative to the axis  64  of the rotor mast  62 . The retractor  300  includes a spool  302  supported for rotation about an axis  304  in the directions indicated generally by R 3  and R 4 . In particular, the spool  302  may be operably connected to a worm gear  66  within the rotor mast  62  such that rotation of the worm gear  66  by a motor or planetary gear &amp; clutch system (not shown) of the aircraft  30  results in rotation of the spool  302 . The spool  302  is secured to a sprocket  310  that rotates with the spool  302 . A shaft  322  adjacent the rotor mast  62  is secured to a spur gear  320  and a sprocket  314  that rotate with the shaft  322 . The gear  320  on the shaft  322  is in meshed engagement with the worm gear  66  within the rotor mast  62 . The sprocket  314  on the shaft  322  transmits torque to the sprocket  310  on the spool via a chain  312 . Consequently, rotation of the worm gear  66  in either direction is transmitted to the gear  320 , which causes the shaft  322  to rotate and transmit the torque to sprocket  314 , through the sprocket  314  to the chain  312 , through the chain  312  to the sprocket  310 , and ultimately to the spool  302 , thereby causing rotation of the spool  302  about the axis  304  in one of the directions R 3  or R 4 . Although only a single retractor  300  is described it will be appreciated that, in the illustrated example, the worm gear  66  within the rotor mast  62  is in meshed engagement with a pair of gears  320  on opposing sides of the rotor mast  62 —each gear  320  being associated with a different retractor  300  and causing rotation of a corresponding spool  302 . In other words, rotation of the worm gear  66  results in simultaneous rotation of all spur gears  320  in meshed engagement therewith and, thus, rotation of all spools  302  operably coupled to the worm gear  66  in the same direction R 3  or R 4 . 
     When the rotor system  60  is assembled (see  FIG. 2 ), the retractor  300  is operably connected to the rotor mast  62  and the hinge  92  secures the support frame  90  to the rotor mast  62  above the retractor  300 . In this configuration, the guide member  148  extends partially around, and is spaced from, the spool  302  while following the general circumferential contour of the spool  302 . The rotor blade  200  is slidably received in the corresponding support frame  90 . In particular, the first end  204  of the blade  200  is oriented such that the leading edge  201  is aligned with the leading edge  116  of the passageway  114  in the outer wall  110 . The first end  204  of the blade  200  is then passed through the airfoil-shaped passageway  114  such that the actuating member  150  is positioned within the interior  216  of the blade  200  adjacent the leading edge  201 . The first end  204  of the blade  200  subsequently extends through the first portion  142  of the interior space  140 , between the rollers  160  extending into the second passageway  134 , and into the second portion  144  of the interior space  140 . The first end  204  of the blade  200  then extends beneath the curved contour of the guide member  148  downward towards the retractor  300 , and is ultimately secured to the spool  302  in a manner that allows the blade  200  to be wound on and unwound from the spool  302  upon rotation thereof. The configuration for each support frame  90 , corresponding blade  200 , and retractor  300  is identical to that described. 
     As noted, actuation of the rotor system  60  causes the worm gear  66  within the rotor mast  62  to rotate about the axis  64 . Torque from the worm gear  66  is transferred through each gear  320  and shaft  322  to each sprocket  314 , which transfers the torque to the corresponding sprocket  302  through the chain  312 . Since the first end  204  of each blade  200  is secured to the corresponding spool  302 , rotation of the spools  302  in the direction R 3  winds the blades  200  on to the spools  302 , thereby retracting the blades  200  into the corresponding support frames  90 , as indicted by the arrows A. Conversely, rotation of the spools  302  in the direction R 4  unwinds the blades  200  from the spools  302 , thereby extending the blades  202  away from the corresponding support frames  90 , as indicted by the arrows B. 
     Due to the hollow interior  216  of the blade  200  and thin construction of both the first and second portions  208 ,  209 , when the movable portion  209  is peeled forward and approximately co-planar with 208, the blade  200  can be readily vertically compressed, i.e., in the direction of the thickness t 1 , to allow for passage of the blade  200  between the rollers  160 , downward bending towards the retractor  300 , and winding about the retractor  300 . To this end, a low density, non-structural material may be bonded to the first portion  208  at the trailing edge  203  to maintain roughly constant chordwise thickness when the blade  200  is flat so that the blade  200  wraps straight on the spool  302 . 
     Referring to  FIGS. 7A-7H , when the spools  302  rotate in the direction R 3 , the actuating members  150  act on the retracting blades  200  to facilitate collapsing of the blades  200  sufficient to allow the collapsed blades to pass between the rollers  160  and be wound onto the spools  302 . Although retraction of only a single blade  200  is discussed, it will be appreciated that any and all blades  200  in the rotor system  60  are simultaneously retracted with the help of the corresponding actuating members  150  and rollers  160  for each additional blade  200 . 
     As the spool  302  rotates in the direction R 3 , the axial cross-section of the blade  200  passes through the airfoil-shaped passageway  114  in the outer wall  110  and subsequently over the outboard end  152  of the actuating member  150 . The actuating member  150  acts on the retracting blade  200  to facilitate collapsing of the blade  200  from the expanded thickness t 1  (see  FIG. 7A ) to a collapsed thickness t 2  (see  FIG. 7H ) less than the expanded thickness t 1 . Referring to  FIGS. 7A-7H , the configuration of the actuating member  150  (see  FIGS. 4A-4C ) causes the movable portion  210  of the blade  200  to move upward and away from the stationary portion  212  as the blade  200  retracts across the actuating member  150  towards the rotating spool  302  until the blade  200  transitions from the fully expanded condition ( FIG. 7A ) to the fully collapsed condition ( FIG. 7H ). In particular, the actuating member  150  moves the movable portion  210  from a position extending below the chord  220  to a position co-planar with or above the chord  220  as the blade  200  moves from the end surface  156  (see  FIG. 7A ) of the actuating member  150  to the end surface  158  (see  FIG. 7H ). By moving the movable portion  210  in this manner, the actuating member  150  elongates the airfoil shape of the blade  200 , which facilitates vertical compression of the blade  200  by the rollers  160  to the collapsed thickness t 2 . 
     Due to the length and configuration of the actuating member  150 , adjacent axial cross-sections of the blade  200  exhibit different stages of transition between the expanded condition and collapsed condition. More specifically, the closer the axial cross-section of the blade  200  is to the inboard end  154  of the actuating member  150  adjacent the rollers  160 , the closer that axial cross-section is to reaching the collapsed condition. Once the particular axial-cross section of the blade  200  passes over the entire length of the actuating member  150  the peeled section of the blade  200  is vertically compressed between the rollers  160  to a thickness t 2  that is less than the thickness t 1  and approaches the collective thickness of the layers forming the blade  200 , i.e., the blade  200  is compressed flat such that the interior  216  is substantially or wholly eliminated. The rollers  160  overcome the bias of the collapsible web  230  in order to vertically compress the blade  200  and place the blade  200  in the fully collapsed, substantially flat condition in which it can be wound on the spool  302 . Vertical compression of the blade  200  is facilitated by the first end  204  of the blade  200  being bent along the guide member  148  and downward towards the spool  302  to be wound thereon. 
     Due to the material selection and material thickness of the blade  200 , vertical compression of the blade  200  occurs without plastic deformation thereof. Furthermore, the combined material thickness(es) of the blade  200  when collapsed is such that the minimum elastic bend radius of the blade  200  is smaller than the radius of the spool  302 . Consequently, the collapsed blade  200  is readily wound upon the rotating spool  302  during retraction of the blade  200 . The flat blade  200  provides little resistance to flapping or torsion since it has minimal vertical section modulus and effectively an open shear flow. This allows the portions of the blade  200  outboard of the support frame  90  to behave like a standard helicopter blade. 
     Referring to  FIG. 2 , the collapsed portions of the blade  200  exit the rollers  160  and pass into the second portion  144  of the interior  140 . It will be appreciated that the rollers  160 , in combination with the tension applied to the blade  200  by the rotating spool  302 , may cause the portion of the blade  200  adjacent the inboard end  154  of the actuating member  150  to reach the collapsed condition prior to entering the rollers  160 . 
     In any case, the collapsing process—peeling of the movable portion  210  by the actuating member  150  and compression by the rollers  160 —is repeated for each successive axial cross-section of the blade  200  along the length of the blade  200 . Consequently, each successive, collapsed axial cross-section of the blade  200  passes downward through the second portion  144  of the interior  140  and along the curved guide member  148  to be wound on to the rotating spool  302 . This occurs until the second end  206  of the blade  200  is positioned within the passageway  114  in the outer wall  110  of the support frame  90 , i.e., the blade  200  does not extend radially outward of the support frame  90  relative to the axis  64  of the rotor mast  62 . The retraction, winding, and placement of the second end  206  of the blade  200  occurs simultaneously for all blades  200  in the rotor system  60  due to the meshed engagement of the worm gear  66  with the gear  320  of each retractor  300  present. Once all the blades  200  are fully retracted, the aircraft  30  may commence with fixed wing  50  flight. Further drag reductions may be achieved by closing a streamlined fairing (not shown) over the retracted rotor/hub system for high speed flight. 
     In operation, the aircraft  30  rotates the blades  200  in the direction R 1 , takes off vertically, and transitions to a moderate forward flight speed in standard helicopter mode. When the aircraft  30  is in the air and fixed wing  50  flight is desirable, the tail rotor  40  may be rotated aft and power is redirected from the rotor system  60  to the tail rotor  40 , which now acts as a pushing propeller for the aircraft  30 . Alternatively, power may be directed to forward or aft facing propellers (not shown) elsewhere on the aircraft  30  for fixed wing propulsion. The rotor system  60  can then transition to unpowered autorotation. The aircraft  30  speed is increased further using its fixed wing propeller(s) until the fixed wings  50  can support the aircraft&#39;s weight. The rotor system  60  collective is then reduced to a zero-lift state. At this time, the rotor system  60  is actuated to rotate the spools  302  in the first direction R 3  to retract all blades  200  inward toward the respective support frame  90  in the direction A, and allow for high speed fixed wing  50  flight. 
     When it is desirable to perform vertical takeoff and landing or return to helicopter flying mode, the rotor system  60  is actuated to rotate the spools  302  in the direction R 4  to extend all blades  200  outward away the respective support frame  90  in the direction B. With each blade  200 , as the spool  302  rotates in the direction R 4 , the actuating member  150  acts on the extending blade  200  to facilitate expansion of the blade  200  back to the thickness t 1 . The process for placing the blade  200  in the expanded condition is identical to the process described above with regards to  FIGS. 7A-7H , but in reverse order. Consequently, as the collapsed axial cross-sections of the blade  200  are unwound from the rotating spool  302 , each passes upward along the guide member  148 , through the second portion  144  of the interior space  140 , and between the rollers  160 . The collapsed axial cross-sections of the blade  200  then move on to the inboard end  154  of the actuating member  150  and pass along the length of the actuating member  150  towards the outboard end  152 . 
     Moving the blade  200  across the actuating member  150  in this direction causes the movable portion  210  to move downwards and towards the stationary portion  212 , allowing the blade  200  to transition from the collapsed condition to the expanded condition. The axial-cross sections of the blade  200  move off the actuating member  150  and pass through the passageway  114  in the outer wall  110  in the fully expanded condition of  FIG. 7A . Once the axial cross-sections of the blade  200  move away from the rollers  160  and support frame  90 , the collapsible web member  230  is allowed to fully expand and bias the blade  200  towards the expanded condition. The collapsible web member  230 , in cooperation with the airfoil-shaped passageway  114  in the support frame  90 , helps maintain the blade  200  in a substantially rigid, airfoil shape once the blade  200  is fully extended from the support frame  90 . 
     The rotor system  60  is advantageous in that the blades maintain a high quality airfoil shape while exhibiting high strength and stiffness in the expanded condition, all while providing the degrees of freedom expected of a helicopter rotor blade and having the capability of being compactly stored in the collapsed condition. Furthermore, the extended blades maintain a smooth, carefully controlled airfoil profile to provide the high lift and low drag needed for current helicopter applications. The extended blades also exhibit sufficient bending stiffness to support the non-uniform radial lift distributions seen in forward flight without excessive bending. Moreover, the root or first ends of the extended blades are capable of accepting collective and cyclic pitch inputs and provides flapping freedom comparable to current helicopter rotors. High hover efficiency can be maintained due to low rotor disk loading and minimal forward flight drag penalty exists during operation, especially if a fairing is closed over the retraced rotor/hub system. In summation, the rotor system achieves in flight rotor retraction and high speed VTOL in a compact package that is not much larger than current rotor mechanics. 
     Additionally, the extended blades&#39; torsion stiffness is sufficient to efficiently transmit rapid cyclic pitches from the root to the entire radius, comparable to current helicopter blades. The partially retracted blades&#39; bending stiffness is sufficient to prevent the forward facing blades from buckling in forward flight with the lower centripetal forces seen during extension and retraction. All of the above advantages are achieved with minimal changes to the familiar control or dynamics of helicopter flight. In fact, the rotor system described herein may be configured for retrofitting on existing helicopter rotor masts with reduced cost and complexity in installation. 
     What have been described above are examples of the present invention. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the present invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the present invention are possible. Accordingly, the present invention is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims.

Technology Classification (CPC): 1