Patent Publication Number: US-2017355447-A1

Title: Thrust-Dependent Variable Blade Pitch Propeller

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims a benefit of U.S. Provisional Patent Application No. 62/348,693, filed Jun. 10, 2016, the content of which is incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to the design of a blade of a propeller, and more specifically, to a blade system that changes the blade pitch in different flight conditions. 
     BACKGROUND 
     Aerial vehicles such as quadcopters or airplanes may be reliant on the blade of a propeller to liftoff, hover, and directionally fly. Fixed pitch blades are only designed to be maximally efficient at one particular flight condition. Therefore, the efficiency of the fixed pitch propeller suffers during significant portions of flight. Blades that are able to vary the blade pitch are conventionally controlled through mechanical systems that require the input of a pilot. Instead of being efficient at only one flight condition, the propeller may be controlled to be increasingly efficient during many different conditions. However, these mechanical systems are prone to inaccuracies, mechanical failure, and/or human error. Additional mechanisms for auto-adjusting blade pitches focus on maintaining propeller blade speed as the aerial vehicle is in flight. However, these automated mechanisms are also expensive and lacking in reliability. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
       The disclosed embodiments have other advantages and features which will be more readily apparent from the following detailed description and the appended claims, when taken in conjunction with the accompanying drawings, in which: 
       Figure ( FIG. 1  illustrates a propeller with offset blades, in accordance with an example embodiment. 
         FIG. 2  illustrates an airfoil cross-section of the blade attached to a rotor hub, in accordance with an example embodiment. 
         FIG. 3  illustrates a top view of a blade with counterweights, in accordance with an example embodiment. 
         FIGS. 4A and 4B  illustrate a blade connector and an airfoil cross-section, respectively, at rest, in accordance with an example embodiment. 
         FIGS. 4C and 4D  illustrate a blade connector and an airfoil cross-section, respectively, while in-flight, in accordance with an example embodiment. 
         FIGS. 5A and 5B  illustrate cross-sectional views of a ball bearing blade connector, in accordance with an example embodiment. 
         FIG. 6A  illustrates a fluid filled connector, in accordance with an example embodiment. 
         FIG. 6B  illustrates a top view of a ball bearing blade-hub connector, in accordance with an example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The figures and the following description relate to preferred embodiments by way of illustration only. It should be noted that from the following discussion, alternative embodiments of the structures and methods disclosed herein will be readily recognized as viable alternatives that may be employed without departing from the principles of what is claimed. 
     Reference will now be made in detail to several embodiments, examples of which are illustrated in the accompanying figures. It is noted that wherever practicable similar or like reference numbers may be used in the figures and may indicate similar or like functionality. The figures depict embodiments of the disclosed system (or method) for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles described herein. 
     Overview Configuration 
     Disclosed by way of example embodiments is a propeller having a blade structured to alter the blade pitch depending on the amount of generated thrust that is exerted on the blade while in-flight. The propeller is for use with rotary winged aerial vehicles, e.g., quadcopters, airplanes. For ease of discussion, the embodiments herein will be described with respect to quadcopters. 
     The blade is designed to have an offset from its connection to a rotor hub. At rest, the blade of the propeller can be oriented with an initial blade pitch. In some embodiments, the initial blade pitch is the minimum blade pitch. Therefore, as the blade is put into rotational motion, the blade  130  with the initial blade pitch can generate thrust forces that cause the aerial vehicle to lift off of the ground. Additionally, the generated thrust forces imparted on the blade also generate a corresponding rotational torque on the blade. This torque causes the blade pitch to change towards a second blade pitch. In various embodiments, the second blade pitch is the maximum blade pitch of the blade  130 . In turn, this maximizes the efficiency of the blade. In addition to improving the efficiency of the blade, the variable blade pitch that depends on generated thrust may be achieved in-flight without the need for human input, thereby minimizing errors (e.g., human or mechanical) that often accompanies conventional mechanical control systems. 
     Example Blade 
     Referring now to Figure ( FIG. 1 , it illustrates an offset propeller  100  viewed from a top-down perspective, in accordance with an example embodiment. In one embodiment, the propeller  100  may comprise two opposing blades of the propeller (or blades)  130 , each blade  130  coupled via a connector  115  to an extension  160  of a rotor hub  150 . In some embodiments, the connector  115  is a part of the blade  130  such that the body of the blade  130  is connected to the rotor hub  150  through the connector  115 . Each blade  130  has a root  120  of the blade  130  nearest to the connector  115 , and a tip  125  of the blade  130  farthest from the connector  115 . The distance between the root  120  and the tip  125  may be referenced as the radius of the blade  130 . In various embodiments, the blade  130  is offset with an offset distance  140  relative to the rotor hub  150 . In various embodiments, the connector  115  of the blade  130  is aligned with the rotor hub  150  and the offset distance  140  represents the offset between the connector  115  of the blade  130  and the body of the propeller blade  130 . The offset distance  140  enables the generation of torque on the blade  130  when thrust forces are imparted on the blade  130 . 
     In various example embodiments, a portion of the extension  160  of the rotor hub  150  is surrounded by the connector  115 . Additionally, the extension  160  may have a channel path  110  that has a first end  112  and a second end  114 . For example, as depicted in  FIG. 1 , a portion of the extension  160  that includes the channel path  110  is encompassed by the connector  115 . 
     The channel path  110  may be located on the surface of the extension  160 . In one example embodiment, the cross-section of the extension  160  is circular and the channel path  110  travels along the circumference of the extension  160 . To enable the connector  115  to couple with the extension  160 , the connector  115  may have a reciprocal protrusion that, when coupled, substantially aligns with the channel path  110  of the extension  160 . In one embodiment, the channel path  110  and the reciprocal protrusion of the connector  115  are threaded, and therefore, can couple with one another. The connector  115  of the blade  130  may be rotated in a clockwise or counter-clockwise manner along the channel path  110  to achieve different blade pitches. 
     In one embodiment, the channel path  110  resides on a portion of the surface of the extension  160 . For example, if the extension  160  is circular, a first end  112  of the channel path  110  may be located at a first position on the surface of the extension  160  whereas the second end  114  of the channel path  110  may be located at a second position on the surface of the extension  160  such that the channel path  110  does not traverse the full 360 degrees (e.g., without traversing the perimeter) of the cylindrical extension  160 . In various embodiments, the channel path  110  traverses the perimeter of the cylindrical extension  160  multiple times (e.g., such as a threaded bolt and nut combination). 
     In various embodiments, the first end  112  and second end  114  of the channel path  110  may be located on the extension  160  to correspond to the maximum and minimum blade pitch of the propeller blade  130 , respectively, when the connector  115  is coupled to the first end  112  and second end  114 . Therefore, in some embodiments, the first end  112  and second end  114  of the channel path  110  on the extension  160  may differ by up to 40 degrees along the perimeter of the cylindrical extension  160 . In other embodiments, the first end  112  and second end  114  of the channel path  110  on the extension  160  may differ by up to 20 degrees along the perimeter of the cylindrical extension  160 . 
     Therefore, the connector  115  (and the blade  130 ) may be rotated along the channel path  110  and held at the first end  112  where the blade  130  achieves the maximum blade pitch. Alternatively, the connector  115  (and the blade  130 ) may be rotated in an opposite direction along the channel path  110  and held at the second end  114  where the blade  130  achieves a minimum blade pitch. In some embodiments, given that the channel path  110  terminates at the first end  112  and the second end  114 , the propeller blade  130  is unable to continue increasing or decreasing its blade pitch once the connector  115  is rotated to the first end  112  and second end  114 , respectively. Therefore, the blade  130  is held at the maximum and minimum blade pitch. In some embodiments, the first  112  and second end  114  along the channel path  110  are set by detents or structures located on the extension  160  of the rotor hub  150 . In other words, the detents or structures located on the extension  160  may define the maximum and minimum blade pitch. 
     As depicted in  FIG. 1 , the channel path  110  may be oriented such that a first end  112  of the channel path  110  is distal to the rotor hub  150  in comparison to a second end  114  of the channel path  110  that is located proximal to the rotor hub  150 . In various embodiments, the first end  112  of the channel path  110  corresponds to the coupling point between the connector  115  and the channel path  110  such that the propeller blade  130  has a maximum blade pitch. Additionally, the second end  114  of the channel path  110  corresponds to the coupling point between the connector  115  and the channel path  110  such that the propeller blade  130  has a minimum blade pitch. 
     In various embodiments, the channel path  110  may have a particular geometry (e.g., linear) along the extension  160  of the rotor hub  150 . For example, the channel path  110  between the first end  112  and the second end  114  may follow one of a linear, polynomial, logarithmic, or exponential curve. The geometry of the channel path  110  may be designed such that a desired rate of change of the blade pitch can be achieved as the connector  115  rotates along the channel path  110  between the first end  112  and the second end  114 . 
     In some embodiments, the channel path  110  need not be a particular design located on a surface of the extension  160 . For example, the channel path  110  and connector  115  may be together embodied as one or more helicoidal wires. In other words, each helicoidal wire may be coupled to the extension  160  of the rotor hub  150  whereas a second end of the helicoidal wire may be coupled to the propeller blade  130 . The one or more helicoidal wires may be either left or right handed helices. In one embodiment, the helicoidal wire aids in maintaining the blade pitch of the propeller blade  130  at an initial blade pitch (e.g., minimum blade pitch). 
     In various embodiments, the extension  160  of the rotor hub  150  may be composed of stainless steel whereas the connector  115  of the blade  130  may be composed of nylon. Additionally, the surfaces of the channel path  110  of the extension  160  and the reciprocal protrusion of the connector  115  may be coated with a polymer or substance that may increase or decrease the coefficient of friction between the two surfaces. This may increase or decrease the overall torque required to rotate the connector  115  relative to the extension  160 . 
     Even though  FIG. 1  depicts two separate blades  130 , in some embodiments, the propeller may include three, four, or more blades  130  coupled to the rotor hub  150  via the connector  115 . It is noted that although the structural elements of the propeller  100  have been individually identified, the propeller  100  may be either comprised of one of more of the elements fit together, e.g., via adhesives and/or mechanical connectors, or may be a unibody construction. 
     The airfoil, which is a cross-section at a particular point along the blade  130 , may have significantly different designs depending on its location along the radius of the blade. For example, an airfoil at the root  120  of the blade  130  may have a significantly different composition than an airfoil at the tip  125  of the blade. In some embodiments, the blade  130  is designed with a particular twist along the length of the blade  130 . The blade twist is the change in blade pitch proceeding along the radius of the blade from the root  120  to the tip  125 . Given that lift increases quadratically with the rotational velocity of the blade  130 , the tip  125  of the blade  130  experiences significantly higher quantities of thrust as compared to the root  120  of the blade  130 , especially at higher rotational velocities. Therefore, the blade twist may be designed to provide proportionate amounts of lift across the radius of the blade. In some embodiments, the root  120  of the blade  130  may have the highest blade pitch whereas the tip  125  of the blade  130  possesses the lowest blade pitch. In other embodiments, other designs of the twist of a blade  130  can be implemented. 
     Forces Applied to a Blade 
     Turning now to  FIG. 2 , it illustrates an airfoil cross-section  260  of the blade  130  attached to a rotor hub  150 , in accordance with an example embodiment. This example embodiment may depict the airfoil cross-section  260  near the halfway point between the root  120  and tip  125  of the blade  130 . The connection between the blade  130  and the rotor hub  150  (e.g. where the connector  115  and the extension  160  are coupled) is depicted at location  270 . Further illustrated are the intrinsic characteristics of the airfoil cross-section including a chord line  240  of the blade  130  and a blade pitch ( 0 )  250 . Although  FIG. 2  depicts a particular example design of the airfoil cross-section  260 , one skilled in the art may envision a variety of different airfoil shapes. This may include varying intrinsic parameters of the airfoil including the camber, maximum camber length, thickness, maximum thickness, and chord length. 
     As currently illustrated in  FIG. 2 , the airfoil may have a blade pitch of θ  250 . In some embodiments, the blade  130  has a blade pitch of θ  250  at rest. As the blade  130  begins to increase in rotational velocity, the blade pitch increases. In various embodiments, the blade pitch of the blade  130  may be between a maximum blade pitch of 20 degrees and a minimum blade pitch of 1-2 degrees. The blade root  120 , blade tip  125  (and other portions of the blade  130 ) may have different blade pitch ranges. 
     Also depicted in  FIG. 2  is the centrifugal force  230  applied on the blade  130  in a direction away from the rotor hub  150  (i.e. out of the page as illustrated in  FIG. 2 ). The centrifugal force  230  causes the connector  115  of the blade  130  to move laterally away from the rotor hub  150  relative to the extension  160  of the rotor hub  150 . The lateral centrifugal force  230  may cause a torque on the blade  130  that acts in the counter-clockwise direction, the torque stemming from the channel path  110  of the extension  160  as it guides the connector  115 . Specifically, as discussed above in regards to  FIG. 1 , given that the first end  112  of the channel path  110  is located distal to the rotor hub  150  in comparison to the second end  114  of the channel path  110 , the lateral centrifugal force  230  causes the connector  115  to rotate towards the first end  112  of the channel path  110 . In other words, the torque from the centrifugal force  230  causes the propeller blade  130  to rotate in a counter-clockwise manner and to increase blade pitch  250  of the blade  130 . Altogether, increasing centrifugal force  230  results in a counter-clockwise torque on the blade that increases the blade pitch  250 . 
     Additionally, the generated thrust  210  is applied at the center of thrust  205  of the airfoil cross-section  260 . The generated thrust  210  forces are depicted as acting in a vertical direction. However, it may be appreciated that the generated thrust  210  force may also include a horizontal force component. Given that the blade  130  is rotatably coupled to the rotor hub  150  and offset by an offset distance  140 , the generated thrust  210  provides a torque on the blade  130  around the connection  270 .  FIG. 2  further depicts the lever arm of the generated thrust  210 , hereafter referred to as R 1    280 . The distance of the lever arm R 1    280  can be tailored by the offset distance  140  between the connector  115  and the body of the propeller blade  130 . In various embodiments, the distance R 1  may be around 20 millimeters. One skilled in the art can appreciate that the blade  130  may be designed so the location of the center of thrust  210  may be different by varying the characteristics of the blade such as the blade camber. 
     The torque, τ, generated on each airfoil cross-section  260  by the thrust force  210  may be calculated as 
       τ= T*R   1  
 
     where T is the generated thrust  210  on each airfoil cross-section  260 . This equation assumes that positive torque occurs in the clockwise direction. The overall torque on the blade  130  may be calculated by summating the individual torque on each airfoil cross-section  260  across all airfoil cross-sections. At rest (e.g. before takeoff), the blade pitch may be held at an initial position by components in the connector  115  which will be discussed in  FIGS. 4 and 5 . As the generated thrust  210  increases, the corresponding torque is positive (e.g. clockwise). Therefore, the generated thrust  210  on the offset blade  130  causes a clockwise rotation of the blade  130 . 
     The torque deriving from the centrifugal force  230  (causing a counter-clockwise blade rotation) and the torque due to the generated thrust  210  (causing a clockwise blade rotation) oppose each other and determine the overall blade pitch  250  of the blade  130  while in flight. The magnitude of the generated thrust  210  is proportional to an incidence angle (i) and the square of the rotational velocity of the blade  130 . The magnitude of the centrifugal force  230  is also proportional to the square of the rotational velocity of the blade  130 . Therefore, as both forces scale as the square of the velocity, the ratio between the two forces remain independent of the rotational velocity of the blade  130 . The coupled connector  115  of the blade  130  and extension  160  of the rotor hub  150  may be designed so that the torque balance between the centrifugal force  230  and the generated thrust  210  remains a constant ratio. In other words, the torque balance remains independent of the rotational speed of a propeller blade  130 . 
     In various embodiments, an additional force on the propeller blade  130  that derives from a front wind may affect the blade pitch of a propeller blade  130 . For example, while in flight, the aerial vehicle (and the propeller blades  130 ) may experience the front wind, which refers to incoming wind that opposes the direction in which the aerial vehicle is flying. In various embodiments, the front wind may affect the generated thrust force  210  on a propeller blade  130 ; however, the front wind may not affect the centrifugal force  230  on a propeller blade  130 . Therefore, the front wind may alter the balance of torques that derive from the thrust force and the centrifugal force and thereby cause the propeller blade  130  to change its blade pitch. As a note, when an aerial vehicle is taking off, landing, or hovering, the front wind may be minimal because forward movement of the aerial vehicle may be minimal. Therefore, the force imparted on the propeller blade  130  due to the front wind may be minimal when taking off, landing, or hovering. 
     When the aerial vehicle is traveling at a forward velocity, the body of the aerial vehicle may be oriented forward (e.g., downward relative to the horizon). Therefore, a front wind on the propeller blade  130  may be in an opposite direction of a component of the thrust force  210 . In some scenarios, the front wind directly opposes the thrust force  210  itself. In other words, the front wind reduces the thrust force  210  relative to the centrifugal force  230 , thereby enabling the propeller blade  130  to rotate counter-clockwise (e.g., due to larger torque from centrifugal force  230 ) and increase the blade pitch. 
     As the aerial vehicle increases in forward velocity, the front wind experienced by the aerial vehicle (and the propeller blades  130 ) may increase. In various embodiments, the angle of incidence for a propeller blade  130  changes as the forward velocity changes. For example, the angle of incidence may be the angle between the chord line  240  (see  FIG. 2 ) of the propeller blade  130  and the relative direction of a combined flow of air (e.g., due to both the front wind and rotational wind experienced by the propeller blade  130  as it rotates). In various embodiments, an increase in the forward velocity would cause a corresponding decrease in the angle of incidence. Therefore, as the forward velocity increases, the blade pitch of the propeller blade  130  is increased in order to maintain the angle of incidence. In other words, the decrease in the angle of incidence due to the increase in forward velocity is counteracted by the increase in the angle of incidence due to an increase in the blade pitch of the propeller blade  130 . 
     In various embodiments, the magnitude in the change in blade pitch to counteract the effects of an increase in front wind may be dependent on the blade geometry. As one specific example, a smaller propeller blade  130  may increase the blade pitch from 20 degrees at rest up to 35 degrees in flight in order to counteract the effects of the increased front wind. Alternatively, a larger propeller blade  130  may increase the blade pitch from 12 degrees at rest up to 40 degrees in flight in order to counteract the effects of the increased front wind. 
     As another example, as an aerial vehicle is decreasing in forward velocity (e.g., braking), the body of the aerial vehicle may be oriented backward (e.g., upward relative to the horizon). In this scenario, the front wind on the propeller blade  130  may be acting in the same direction of a component of the thrust force  210  or opposite of the thrust force  210  itself. Therefore, the front wind increases the thrust force  210  relative to the centrifugal force  230 , thereby enabling the propeller blade  130  to rotate clockwise (e.g., due to a larger thrust force  210 ) and decrease the blade pitch. 
     In various embodiments, as the aerial vehicle decreases forward velocity, the front wind experienced by the aerial vehicle (and propeller blades  130 ) decreases. The propeller blades  130  may operate in an opposite fashion relative to the description above when the aerial vehicle was increasing in forward velocity. Specifically, as the front wind decreases, this may cause a corresponding increase in the angle of incidence. Therefore, the blade pitch of the propeller blade  130  is decreased to counteract the effects on the angle of incidence caused by the decreasing front wind. 
     Adjusting the Torque Balance Due to Changes in Environmental Conditions 
       FIG. 3  illustrates a top-down view of a blade  130  with counterweights, in accordance with an example embodiment. The counterweights  320 ,  325 , and  330  alter the moment of inertia of the blade  130 . As previously described, the centrifugal force  230  is directed away from the rotor hub  150  which translates to a counter-clockwise rotation of the blade  130  (e.g., increasing blade pitch) relative to the rotor hub  150 . However, the counter-clockwise rotation of the blade  130  is dependent on the moment of inertia of the blade  130 . Therefore, the torque deriving from the centrifugal force  230  may be increased through the addition of the counterweights  320 ,  325 , and  330 . The location of each counterweight  320 ,  325 , and  330  may affect the overall moment of inertia of the blade  130 . For example, the farther a counterweight is located from the rotor hub  150  (assuming equally sized counterweights), the larger the increase in the moment of inertia of the blade  130 . Referring to  FIG. 3 , counterweight  330  may increase the moment of inertia of the blade  130  more in comparison to the effects of counterweight  320 . 
     Having control over the counter-clockwise rotation of the blade  130  due to the centrifugal force  230  is important in different environmental conditions. For example, in hot, humid, or high elevation environments, the generated thrust  210  on a blade  130  is lower because of a lower density of air molecules in the environment. Given that the centrifugal force  230  does not depend on density of air molecules, the torque balance on the blade  130  from the generated thrust  210  and centrifugal force  230  may be unbalanced. Therefore, to compensate for the change in torque from changes in the generated thrust  210  due to varying environmental conditions, counterweights  320 ,  325 , and/or  330  may be added or removed to adjust the moment of inertia of the propeller blade  130 . As shown in  FIG. 3 , these counterweights  320 ,  325 , and  330  can be added along the length of the blade  130 . 
     In various embodiments, the counterweights  320 ,  325 , and  330  may be placed at any location on the blade. These locations may be predetermined. For example, the circular counterweights  320  depicted in  FIG. 3  may reside in a reciprocal cavity on the blade  130  that have been preset. In other embodiments, the counterweight  320  may be affixed or attached to the blade  130  on either the top or bottom surface of the blade  130  at any location. 
     Altering the Blade Pitch 
       FIG. 4A  illustrates the blade connector  115  coupled with the extension  160  of the rotor hub  150  at rest, in accordance with an example embodiment. The extension  160  of the rotor hub  150  may include a channel path  110  and one or more detents  410 . Optionally, a spring  420  may be coupled between the extension  160  of the rotor hub  420  and an optional block  430  of the connector  115 . In various example embodiments, the connector  115  may be coupled to the extension  160  of the rotor hub  150  through only the channel path  110  (e.g., no detent  410  or spring  420 ). In other example embodiments, the channel path  110  is included along with one of the detent  410  or the spring  420 . 
     The extension  160  may have a single channel path  110  that the connector  115  is coupled to. The ends of the channel path  110  define the maximum and minimum rotation of the connector  115 . Additionally, the extension  160  may have one or more detents  410  that prevent the connector  115  from laterally decoupling with the extension  160 . The connector  115  is at a second end  114  of the channel path  110  that positions the blade at its minimum blade pitch. To better illustrate this,  FIG. 4B  depicts the corresponding airfoil cross-section  260  at rest, in accordance with an example embodiment. The blade pitch φ  470  is minimized in this scenario as the connector  115  is located at the second end  114  of the channel path  110 . In various embodiments, this second end  114  of the channel path  110  is the most proximal location of the channel path  110  to the rotor hub  150  in comparison to any other portion of the channel path  110 . In various embodiments, such as the embodiment shown in  FIG. 4A , the channel path  110  may be located on a portion of the surface of the extension  160 . For example,  FIG. 4A  may depict a side view of the extension  160  and the connector  115 . Therefore, the channel path  110  may be located on a side surface (e.g., left side surface) of the extension  160  as opposed to a top or bottom surface of the extension  160 . 
       FIG. 4C  illustrates the blade connector  115  coupled with the extension  160  of the rotor hub  150  while in-flight, in accordance with an example embodiment. In this embodiment, the clockwise torque applied by the generated thrust  210  (due to the reducing effects of a front wind) is smaller than the opposite torque derived from the centrifugal force  230 . Therefore, the connector  115  rotates counter-clockwise along the channel path  110  to a first end  112 . In various embodiments, this first end  112  is where the channel path  110  terminates and therefore, represents the farthest rotation that the connector  115  may rotate to. Here, the first end  112  represents the most distal location of the channel path  110  to the rotor hub  150  in comparison to other portions of the channel path  110 .  FIG. 4D  depicts the corresponding airfoil cross-section  260  in this scenario, in accordance with an example embodiment. Here, the blade pitch is significantly increased to φ′  475 . 
     Optionally, the spring  420  is configured to return the blade  130  to its original blade pitch. For example, at resting position, the resting spring  420  is neither compressed nor stretched (as depicted in  FIG. 4A ). When in-flight, as shown in  FIG. 4C , the spring  420  is in tension, held between the extension  160  of the rotor hub  150  and the block  430  of connector  115 . As the propeller blade  130  decreases its rotational velocity, the spring  420  may revert back to its resting state as illustrated in  FIG. 4A , thereby causing the connector  115  to rotate back along the channel path  110  to an initial resting position at the second end  114 . Thus, the blade pitch will be restored to the initial blade pitch value φ  470 . 
     In various embodiments, characteristics of the spring  420 , such as the spring constant of the spring  420 , can be chosen to enable the balance in torques between the torque derived from the generated thrust  210  on the blade  130  and the torque derived from the centrifugal force  230  on the blade  210 . For example, the spring  420  may be at rest in the initial position shown in  FIG. 4A  (e.g., the connector  115  is coupled with the first end  112  of the channel path  110 . In other words, the spring  420  may oppose any displacement that forces the spring  420  away from the initial position. For example, during flight, the spring  420  may be in tension (e.g., see  FIG. 4C ) and therefore, the spring  420  may oppose any further counter-clockwise torque on the blade  130  derived from the centrifugal force  230 . Additionally, while in flight, the spring  420  may aid the clockwise torque on the blade  130  derived from the thrust force  210 . Therefore, in various embodiments, the spring constant of the spring  420  can be selected such that the torque balance between the centrifugal force  230  and the generated thrust  210  remains a constant ratio as the propeller blade  130  increases and/or decreases in rotational velocity. 
       FIGS. 5A and 5B  illustrate a cross-sectional view of a ball bearing connector  115  and the extension  160 , in accordance with an example embodiment. This example embodiment shows one or more ball bearings  550  that may fix the maximum and minimum limits of angular rotation of the connector  115  relative to the extension  160 . In various embodiments, this ball bearing connector  115  is implemented along the channel path  110  on the extension  160 . In other words, the ball bearing  550  can be guided by the channel path  110  on the extension  160  to roll along a surface  560  of the extension  160 . 
     The extension  160  may be designed such that a protrusion  570  of the extension  160  prevents the ball bearing  550  from rolling any further in a particular direction. On the other hand, the ball bearing  550  is free to roll along a surface  560  of the extension  160 . The ball bearing  550  may be coupled to a reciprocal cavity  580  of the connector  115 . Therefore, a clockwise rotation of the connector  115  will cause a corresponding clockwise movement of the ball bearing  550  along the surface  560  of the extension  160 . For example,  FIG. 5A  illustrates the cross-section view of the connector  115  and extension  160  at a resting state. As the connector  115  rotates, the connector  115  may cause the ball bearings  550  to roll along the surface  560  of the extension  160 .  FIG. 5B  illustrates the same cross-sectional view of the connector  115  and extension  160  when high quantities of generated thrust  210  is applied to the blade  130 . Here, the ball bearings  550  have rolled to a second protrusion  575  of the extension  160 . Accordingly, the reciprocal cavity  580  of the connector  115  (and the blade  130 ) is rotated to achieve a minimal blade pitch. 
     Reducing Blade Pitch Oscillation 
     The blade pitch of a blade  130  often oscillates during in-flight conditions. For example, assuming that an aerial vehicle, is flying with a horizontal velocity, the blade pitch of a blade  130  may vary depending on whether the rotating blade is traveling forward in the same direction as the aerial vehicle or in the opposite direction of the aerial vehicle. For example, the blade  130  may oscillate due to external forces such as forces from the incoming front-wind. Therefore, those oscillations may be transferred to the connector  115  and cause lateral or vertical movement of the connector  115  relative to the extension  160 . Overall, the blade pitch may be altered. Therefore, current embodiments disclosed herein reduce the oscillation of the blade pitch through a dampening mechanism, e.g., a mechanical dampener, in the connector  115 . 
       FIG. 6A  illustrate a fluid filled connector  115 , in accordance with an example embodiment. In various embodiments, the connector  115  contains a fluid  635  within a self-contained chamber. The self-contained chamber of the connector  115  is sealed off from the surrounding environment. For example, an O-ring seal  630  may seal the surface between the connector  115  and the extension  160  to prevent any fluid  635  from leaking to the exterior. In various embodiments, the fluid  635  may be a brake fluid, thereby providing a dampening mechanism to reduce the oscillations that the connector  115  may experience relative to the extension  160 . In various other embodiments, the fluid  635  may be a hydraulic fluid or high viscosity fluid. Additionally, within the self-contained chamber, the connector  115  is coupled to the extension  160  of the rotor hub  150  through the channel path  110  located on the extension  160 . 
     In various embodiments, the connector  115  may have further designs within the self-contained chamber to increase the dampening effect of the fluid  635 . For example, there may be protrusions  645  along the sides of the self-contained chamber that increases the surface area in which the fluid  635  is in contact with. 
       FIG. 6B  illustrates a top view of a ball bearing connector, in accordance with an example embodiment. In various embodiments, the connector  115  may remain coupled to the extension  160  through the channel path  110  on the extension  160 . The connector  115  may contain a cavity  660  for receiving a ball bearing  650 . Similarly, the extension  160  of the rotor hub  150  possesses a reciprocal cavity  665  to receive the same ball bearing  650 . The ball bearings  650  may serve to limit the lateral movement of the connector  115  to prevent the connector from decoupling with the extension  160 . Additionally, the ball bearings  650  may dampen oscillatory movements. For example, the ball bearings may be designed to receive and absorb the oscillatory movement of the connector  115 . 
     ADDITIONAL EMBODIMENT CONSIDERATIONS 
     The disclosed embodiments of the variable pitch propeller provide advantages over conventional propellers. For example, the pitch of the blade may be optimized for all in-flight conditions. In doing so, the efficiency of the blade, and in turn the overall propeller, is improved and overall power consumption may be reduced. Moreover, these benefits are further enhanced on quadcopters where four propellers are engaged. Reducing power consumption may provide benefits such as extending battery life in the quadcopter, thereby increasing flight time, and/or requiring smaller battery sizes, thereby reducing overall weight of the quadcopter. 
     Additionally, conventional blades are typically controlled through human intervention by means of a mechanical swashplate. To optimize the blade pitch during in-flight conditions, the individual must have training in aerodynamics to understand how to adjust the mechanical swashplate to achieve a particular blade pitch. Even so, human intervention often results in human and/or mechanical error. The current embodiment may optimize the blade pitch for in-flight conditions without the need for human intervention by relying on the torque balance generated by the generated thrust and centrifugal force on the blade. 
     Finally, the disclosed embodiments of the variable pitch blade may be employed for larger blade sizes. Larger blades are significantly more efficient as they can generate higher levels of thrust at a particular rotational speed as compared to smaller blades. However, larger blades are significantly more sensitive to wind forces and thus, cannot be implemented as a fixed pitch blade. This variable pitch blade, as disclosed herein, enables the use of larger, more efficiently designed propeller blades for aerial vehicles. 
     Throughout this specification, as used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. 
     In addition, use of the “a” or “an” are employed to describe elements and components of the embodiments herein. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise. 
     Finally, as used herein any reference to “one embodiment” or “an embodiment” means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment. 
     Upon reading this disclosure, those of skilled in the art will appreciate still additional alternative structural and functional designs for variable pitch blades as disclosed from the principles herein. Thus, while particular embodiments and applications have been illustrated and described, it is to be understood that the disclosed embodiments are not limited to the precise construction and components disclosed herein. Various modifications, changes and variations, which will be apparent to those skilled in the art, may be made in the arrangement and details of the apparatus disclosed herein without departing from the spirit and scope defined in the appended claims.