This application is a non-provisional patent application claiming the benefit of the filing data of U.S. patent application Ser.  No.  62/172,965 filed on Jun. 9, 2015, and titled “Multicopter Propeller Guard System” which is hereby incorporated by reference. 
The embodiments described herein relate to a propeller guard system for an aerial vehicle.  More specifically, the embodiments relate to dynamically changing the angular position of the propeller guards. 
An unmanned aerial vehicle (UAV), sometimes called an unmanned air-reconnaissance vehicle or a drone, is a non-piloted aircraft.  UAVs are known in the art and can be operated via remote control or can be flown autonomously based on pre-programmed flight plans or more complex dynamic automation systems.  UAVs have built-in electronics or devices, including but not limited to an accelerometer, gyroscope, GPS antennae, collision detection system, etc.  in order to be flown autonomously and to gather real-time orientation and position information.  This information is used to control the flight of the UAV.  Besides being flown by hobbyists, UAVs are currently used in a number of military roles, including reconnaissance and attack.  They are also in a small but growing number of civil roles, such as firefighting where a human observer would be at risk, police observation of civil disturbances, reconnaissance support in natural disasters, or any scenario in which direct human observation may be hazardous.  Accordingly, UAVs are often used in dangerous missions to mitigate risk to human life. 
One example of a UAV is a multicopter.  A multicopter is an aerial vehicle that has two or more rotors, also known as propellers.  Examples of multicopters include, but are not limited to, bicopters (i.e., two propellers), tricopters (i.e., three propellers), quadcopters (i.e., four propellers), hexacopters (i.e., six propellers), and octocopters (i.e., eight propellers).  The motion of the multicopter is controlled by changing the relative speed of each propeller.  Specifically, motion about the three symmetry axes of the multicopter, known as roll (i.e., rotation about the front-back axis), pitch (i.e., rotation about the side-side axis), and yaw (i.e., rotation about the vertical axis), can each be controlled by changing the relative speed of each propeller.  For example, roll and pitch can be achieved by speeding up propellers on one side and slowing down the propellers on the other side, while yaw can be achieved speeding up propellers that are diagonally across from each other.  Horizontal motion is achieved by causing the multicopter to lean towards the intended direction of travel, and vertical motion is achieved by simultaneously speeding up each propeller (i.e., ascent), or by simultaneously slowing down each propeller (i.e., descent).