Abstract:
A cooling air bypass is disclosed which prevents premature failure of an engine in the event the cooling air from an external blower is somehow obstructed or shut off.

Description:
OVERVIEW OF INVENTION 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates generally to engine cooling. In particular, the present disclosure relates to apparatus, systems and methods for cooling a rotary engine of an unmanned aerial vehicle in the event of a failure of the primary cooling blower. 
         [0003]    2. Background 
         [0004]    Many wankel or rotary engines used for propulsion of unmanned air vehicles (UAV) require airflow through the engine core for rotor cooling as well as distribution of lubricant. Without this airflow the engine quickly overheats which could lead to catastrophic engine failure. Airflow is caused by a pressure delta: air flows from high pressure regions to low pressure regions. In some small wankel engines, the pressure delta is small; the high pressure is provided by the ram air of forward motion of the UAV and the low pressure is provided by suction on the back side of the propeller as shown in  FIG. 1 . In this figure, a rotary engine  10  is driving a propeller  12  in the rotary direction of arrow  14 . The propeller  12  provides the thrust necessary to move the UAV forward, which causes a cooling airflow over the engine. 
         [0005]    In larger or more advanced wankel engines, rotor air cooling is provided by a belt driven fan. This allows for much higher pressure delta across the engine which provides higher airflow and thus better cooling and dispersion of lubricant. The schematic for belt driven fan cooling is shown below in  FIG. 2 . As shown in this figure, a rotary engine  10  is driving a propeller  12  in the direction of arrow  14 . An air blower  16  is powered by the rotary engine  10  by a drive belt  20  which is connected between a pulley  22  on the rotary engine and a pulley  24  on the air blower  16 . Cooling air is provided to the rotary engine through the blower outlet  18 . Many larger UAVs currently employ this system. A major weakness of this set up however is that the drive belt  20  is prone to failure. In the event that drive belt  20  breaks or the blower otherwise fails, cooling air is unable to pass through the blower  16  and the engine  10  will overheat and fail, which may cause the UAV to crash. 
         [0006]    Therefore, the forced cooling systems as shown in  FIG. 2  require an improvement that will prevent the engine from overheating in the event the drive belt fails or the blower is otherwise not working properly 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is an isometric view of the prior art, 
           [0008]      FIG. 2  is a simplified front plan view of the prior art, 
           [0009]      FIG. 3  is a simplified front plan view of an embodiment of the invention, 
           [0010]      FIG. 4  is a partial cutaway view of the blower outlet in accordance with an embodiment of the invention, 
           [0011]      FIG. 5  is an isometric view of the blower outlet in accordance with an embodiment of the invention, and 
           [0012]      FIG. 6  is a partial cutaway view of the blower outlet in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0013]    Embodiments in accordance with the present disclosure are set forth in the following text to provide a thorough understanding and enabling description of a number of particular embodiments. In some instances, well-known structures or operations are not shown, or are not described in detail to avoid obscuring aspects of the inventive subject matter associated with the accompanying disclosure. For example, rotary engine use on UAVs is well known. They are also used on various ground and water vehicles. A person skilled in the art will understand, however, that the invention may have additional embodiments, or that the invention may be practiced without one or more of the specific details of the embodiments as shown and described. 
         [0014]    Referring to  FIG. 3  where a rotary engine  10  with an air blower  16  is shown. Attached to the rotary engine  10  is a propeller  12  which is rotated in the direction of arrow  14  in order to provide aerodynamic thrust to move a vehicle like a UAV or the like. The air blower  16  is in fluid communication with the engine  10  through a blower outlet/conduit  18 . The air blower  16  is configured to supply cooling air to the engine  10  to prevent the engine from overheating and pre-mature failure. The air blower  16  is driven by a drive belt  20  which is connected between a pulley  22  on the engine  10  and a pulley  24  located on the air blower  16 . An air bypass  26  is disposed on the blower outlet  18 . 
         [0015]    Referring now to  FIGS. 4 and 5 , which shows a close up view of the blower outlet  18 . The air bypass  26  is comprised of a bypass housing  30  which is affixed to a wall of the outlet  18  and a sealing member  28  which is disposed inside of the housing  30 . The sealing member  28  is configured to allow cooling air to enter the blower outlet  18  as shown by arrow  34  when the air blower  16  fails and cooling air as shown by arrow  32  is otherwise blocked. As shown in  FIG. 4 , the sealing member  28  is a reed type valve that will swing to an open position when the pressure on the outside of the blower outlet  18  is higher than the pressure internal to the blower outlet  18 . While a reed valve is shown, many other types of check valves exist that can perform essentially the same function. These types of valves may include a ball check valve, a diaphragm check valve, a swing check valve and a lift-check valve. Using this arrangement, when cooling air is flowing in the path as shown by arrow  32 , the sealing member  28  will remain sealed and not allow cooling air to flow in the path as shown by arrow  34 . However, this arrangement will allow the sealing member  28  to open if the cooling air provided by the blower  18  is not occurring. 
         [0016]    In the event of a belt or blower failure, airflow from the blower  16  will stop. However, the low pressure caused by propeller  12  will cause a pressure differential across the engine  10  and air bypass  26 , which will open the sealing member  28  and allow air to flow through the engine  10  to provide cooling and distribute lubricant. Although operation in this mode will reduce the performance of the engine, it will maintain similar performance as the configuration shown in  FIG. 1  and this may prevent catastrophic failure of the engine and loss of the vehicle. 
         [0017]    Referring to  FIG. 6  (where like numerals show like features), an alternative embodiment of the air bypass  26  is shown, which is comprised of a first sealing member  28   a  and a second sealing member  28   b.  This arrangement of two redundant sealing members may provide a more reliable air bypass feature.