Abstract:
The invention is a propeller support system for damping vibrations of a propeller shaft and propeller on an aircraft. In detail, the support system includes a bearing support for the propeller and a drive system to move the bearing support along the propeller shaft as a function of propeller RPM.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to the field of propeller driven aircraft and, in particular, to a propeller mounted on an extended driveshaft and having adjustable damping.  
         [0003]     2. Description of Related Art  
         [0004]     Typical propeller driven aircraft have fully supported propellers, even when the engine is separated there from. For example, U.S. Pat. No. 2,153,603 Aircraft Power Plant Installation by R. C. Wells discloses an engine mounted within the wing of an aircraft near its center and a shaft driving a propeller extending out from the leading edge of the wing. As many as three separate propeller shaft supports are provided to achieve a desired weight distribution U.S. Pat. No. 4,546,939 Power Unit For Hang-Gliders by J. W. Kolecki discloses a propeller drive shaft supported almost the entire length of the glider. A damping device is employed for the purpose of preventing vibrations caused by the power plant from being transmitted to the airframe.  
         [0005]     U.S. Pat. No. 3,286,681 Propeller Shaft Support by J. Plum discloses a flexible drive shaft for use on a boat. Here the drive shaft rotates while bowed so that the propeller is normal to the water flow where it is attached to the propeller. The bow is maintained by a front bearing mounted on a strut extending out of the bottom of the boat and an aft support that is part of the rudder, which is downstream from the propeller. U.S. Pat. No. 1,953,599 Boat Propulsion Device by G. P. Grimes discloses the typical outboard motor for a boat. Here a long drive shaft is supported by a rigid shaft which extends parallel to the drive shaft and provides a support bracket near the propeller. None of the prior art discloses the use of a propeller shaft with a flexible damper.  
         [0006]     Thus, it is a primary object of the invention to provide flexible propeller shaft and support therefore wherein the lightness of a cantilevered shaft allows the propeller disk to be placed farther from the wing making it quieter and allowing the vertical component of the blades to aid directional stability.  
         [0007]     It is another primary object of the invention to provide a flexible propeller shaft and support therefore that will find its own center to revolve around allowing the large rotating mass of the propeller to be entirely isolated from the rest of the vehicle.  
       SUMMARY OF THE INVENTION  
       [0008]     The invention is a propeller support system for damping vibrations of a propeller shaft having first and second ends with a propulsion system coupled to the first end and a propeller mounted on the second end. In detail, the support system includes a bearing support for the propeller shaft and an actuation system to move the bearing support along the propeller shaft as a function of propeller RPM. Preferably a flexible coupling is incorporated for connecting the first end of the propeller shaft to the propulsion system.  
         [0009]     In one embodiment the bearing support includes an elastic damping strut having first and second ends; with the first end terminating in a bearing in slidable engagement with the propeller shaft and a second end slidably mounted to the aircraft. The actuation system is adapted to move the damping strut in a direction along the axis of the propeller shaft. Preferably the actuation system includes a hydraulic actuator coupled to the second end of the damping strut. The actuation system can be used during normal operation, or if conditions allow it, the actuation can be disabled after flight testing has found the safest fixed location.  
         [0010]     In a second embodiment, the bearing assembly includes an inner race in slidable contact with the propeller shaft, an outer support member and a visco-elastic damping member sandwiched between the inner race and the outer support member and joined to both. The actuation system in this case includes the outer support member having a rack gear and a motor assembly with an output shaft having a pinion gear in engagement with the rack gear. Thus rotation of the pinion gear cause the outer support member to translate.  
         [0011]     Thus the bearing assembly can be moved along the propeller shaft as a function of RPM to damp out vibrations caused by the rotation of the propeller shaft that is unsupported at the distal end.  
         [0012]     The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description in connection with the accompanying drawings in which the presently preferred embodiments of the invention are illustrated by way of examples. It is to be expressly understood, however, that the drawings are for purposes of illustration and description only and are not intended as a definition of the limits of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a top view of an aircraft having a pusher type propeller propulsion system.  
         [0014]      FIG. 2  is a partial cross-sectional view of the aircraft shown in  FIG. 1  taken along the line  2 - 2  illustrating the damping system.  
         [0015]      FIG. 3  is a partial cross-sectional view of  FIG. 1  taken along the line  3 - 3  shown in  FIG. 2  further illustrating the damping system.  
         [0016]      FIG. 4 a  views similar to  FIG. 2  illustrating a second embodiment of the invention.  
         [0017]      FIG. 5  is a flowchart of the operation of the damping system.  
         [0018]      FIG. 6  illustrates a damping system similar to  FIG. 2  wherein the damping system is not adjustable.  
         [0019]      FIG. 7  illustrates a damping system similar to  FIG. 4  wherein the damping system is not adjustable 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]     Referring to  FIG. 1 , the aircraft, generally designate by numeral  10 , includes a fuselage  12  having a longitudinal axis  14  and a, wings  16 A and  16 B. Tail booms  18 A and  18 B extend from the wings  16 A and  16 B respectively and mount ruddervators  20 A and  20 B, respectively. A motor  22  is mounted in the fuselage  12 . A propeller shaft  24  extending outward from rear of the fuselage  12  along the longitudinal axis  14  having a first end  26 A coupled to the motor  22  by a coupling  27  and by its second  26 B to a propeller  28 .  
         [0021]     In a first version the system illustrated in  FIGS. 2 and 3 , a damper assembly  30  includes a bearing assembly  36  is mounted in fuselage structure that includes a bearing  38  in slidable engagement with the propeller shaft  24  some distance away from the propeller  28 . A visco-lastic bushing  40  is bonded to bearing  38  and to an outer sleeve  42  movably mounted in the fuselage structure. The sleeve  42  includes a rack gear  48  that protrudes into a slot  50 . A motor  52  includes an output shaft  54  terminating in a pinion gear in engagement with the rack gear  48 .  
         [0022]     In a second version of the invention as illustrated in  FIG. 4  and  5  and identified by numeral  59 , a semi-flexible damping strut  60  is used. The damping strut  60  includes a first end  62 A terminating in an outer bearing assembly having a bearing  64  in slidable engagement with the propeller shaft  24 , which acts as an inner race. The second end  62 B acts as an inner race and is slidably engagable with an outer race  66  mounted in the fuselage structure. A hydraulic cylinder  68  includes an output strut  70  in engagement with the second end  62 B of the strut  60 . Thus actuation of the hydraulic cylinder  68  will cause the first end  62 A of the strut  60  to move fore or aft as a function of propeller shaft rotational speed to provide damping therefore.  
         [0023]     Because the weight and balance of each propeller and shaft therefore will have some differences, it is most likely that they will have to tested upon installation on each particular aircraft. Thus each aircraft will most likely have a custom program wherein the position of the damping system on the propeller shaft will be determined as a function of propeller rotational speed. Thus referring to  FIG. 5 , the operation of the system will use a controller  80  that will automatically adjust the position of the damper system as a function of propeller RPM.  
         [0024]     Referring to  FIGS. 6 and 7 , it is possible to use an unsupported driveshaft  24  and propeller  28  with a fixed position propeller shaft damping system if the unsupported length (length between the bearing and propeller) is sufficient to allow the propeller to seek its own center of rotation bearing mounting system. The damping system is still required in order to absorb vibration loads as the propeller accelerates to its operational rotational speed. Thus in  FIG. 6 , a non adjustable version of the damping system, now indicated by numeral  30 A The aircraft structure  36 A is now adapted to restrain the damping system  30 A. What is critical is the length  82  of the unsupported shaft  24 , which must be sufficient to allow the propeller  28  to seek its own center of rotation. Illustrated and  FIG. 7 , is a non adjustable version of the damping system originally shown in  FIG. 4 , now indicated by numeral  59 A. In this case the shaft, now indicated by numeral  62 A, has end  84  rigidly attached to the aircraft. However, it is desirable to have an adjustable shaft damping system to determine the optimum location of contact therewith.  
         [0025]     While the invention has been described with reference to particular embodiments, it should be understood that the embodiments are merely illustrative as there are numerous variations and modifications, which may be made by those skilled in the art. Thus, the invention is to be construed as being limited only by the spirit and scope of the appended claims.  
       INDUSTRIAL APPLICABILITY  
       [0026]     The invention has applicability to aircraft industry.