Quiet propeller
Provided is a quiet propeller including a propeller blade having such a pitch angle not at its root portion but at its blade end edge portion with respect to a relative flow in the rotational direction, as to raise the internal pressure of a liquid thereby to eliminate a cavity, a water bubble or a cavitation at the blade root portion at the time of a high-speed rotation so that the propeller is rotated at a high speed by a small prime mover and by a prime mover capable of moving much fluid backward. In the quiet propeller, a propeller blade is curved backward at its leading end portion to form a slope portion, and a rotational front side end portion in the slope portion is formed into an arcuate shape in the side view whereas a rotational rear side end portion is so gradually extended backward from the rotational front side end portion as to become straight from the blade root to the blade end, thereby to form a deflecting slope face. At the rotating time, the fluid is pushed toward the back axis from the deflecting slope face in the slope portion.
1. A quiet propeller driven by a motor, comprising:
a boss at a center of the propeller; and
a plurality of blades extending from the boss, each of said plurality of blades having a leading edge with respect to a direction of rotation of said plurality of blades and a trailing edge with respect to said direction of rotation of said plurality of blades, a first portion of a back surface of the blade rising centrifugally toward a distal end of the blade from a bend line connecting a distal end of the leading edge to a distal end of the trailing edge, a diagonal line extending from an intersection of the leading edge with the bend line to a proximal end of the trailing edge, a first angle of the back surface of the blade close to the boss with respect to oncoming fluid flow being defined from 0 to four degrees, the leading edge being gradually thinner from the boss to a distal end of the blade, a second portion of the back surface of the blade rising toward the trailing edge between the diagonal line and the trailing edge, a front surface of the blade being planar between the leading edge and the trailing edge, a second angle of the back surface of the blade away from the boss with respect to the oncoming fluid flow ranging from 7 to 25 degrees, whereby fluid from the leading edge is gathered centripetally of the propeller by the tilted portion and the tilted back surface during rotation of the propeller.
2. The quiet propeller of claim 1 wherein the first angle of the back surface of the blade is 0 degrees.
3. A quiet propeller driven by a motor, comprising:
a boss at a center of the propeller; and
a plurality of blades extending from the boss, each of said plurality of blades having a leading edge with respect to a direction of rotation of said plurality of blades and a trailing edge with respect to said direction of rotation of said plurality of blades, a first portion of a back surface of the blade rising centrifugally toward a distal end of the blade from a bend line connecting a distal end of the leading edge to a distal end of the trailing edge, a diagonal line extending from an intersection of the leading edge with the bend line to a proximal end of the trailing edge, a first angle of the back surface of the blade close to the boss with respect to oncoming fluid flow being defined from 0 to four degrees, a second portion of the back surface of the blade rising from the diagonal line to the trailing edge, a front surface of the blade being planar between the leading edge and the trailing edge, a second angle of the back surface of the blade away from the boss with respect to the oncoming fluid flow ranging from 7 to 25 degrees, whereby fluid from the leading edge is gathered centripetally of the propeller by the tilted portion and the tilted back surface during rotation of the propeller.
4. The quiet propeller of claim 3 wherein the first angle of the back surface of the blade is 0 degrees.
5. A quiet propeller driven by a motor, comprising:
a boss at a center of the propeller; and
a plurality of blades extending from the boss, each of said plurality of blades having a leading edge with respect to a direction of rotation of said plurality of blades and a trailing edge with respect to said direction of rotation of said plurality of blades, a first portion of a back surface of the blade rising centrifugally toward a distal end of the blade from a bend line connecting a distal end of the leading edge to a distal end of the trailing edge, a diagonal line extending from an intersection of the trailing edge with the bend line to a proximal end of the leading edge, a first angle of the back surface of the blade close to the boss with respect to oncoming fluid flow being defined from 0 to four degrees, a second portion of the back surface of the blade rising from the diagonal line to the leading edge, a front surface of the blade being planar between the leading edge and the trailing edge, a second angle of the back surface of the blade away from the boss with respect to the oncoming fluid flow ranging from 7 to 25 degrees, whereby fluid from the leading edge is gathered centripetally of the propeller by the tilted portion and the tilted back surface during rotation of the propeller.
6. The quiet propeller of claim 5 wherein the first angle of the back surface of the blade is 0 degrees.