US 3549271 A
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1970 HIDETSUGU KUBOTA 3,549,271
BACKFLOW RECOVERY PROPELLER DEVICE Filed 001;. 2, 1968 2 Sheets-Sheet l 2 I 30 k 3b4 IN VIL'N'I I IR Dec. 22, 1970 HIDETSUGU KUBOTA BACKFLOW RECOVERY PROPELLER DEVICE 2 Sheets-Sheet 2 Filed Odt. 2, 1968 Nh'Y IHDIS'ISUUU KUBO'IA A'ITOR United States Patent BACKFLOW RECOVERY PROPELLER DEVICE Hidetsugu Kubota, 122 Kaizuka, Kameda-rnachi, Naka-Kanbara-gun, Niigata-ken, Japan Filed Oct. 2, 1968, Ser. No. 764,575
Claims priority, application Japan, Oct. 12, 1967,
42/ 65,551 Int. Cl. B64c 11/48 US. Cl. 416124 1 Claim ABSTRACT OF THE DISCLOSURE A propeller device comprising a fixed main propeller and a freely rotatable backflow recovery propeller, both operated in the same direction on a common shaft. The recovery propeller has a collision surface for the backflow current of a high pitch and the opposite surface thereof is effectively of a low pitch. These two surfaces converge into a semicircular shaped leading edge whereby the blade thickness ratio of the backflow propeller progressively increases towards the end of the blade. Such a construction can substantially convert the backflow energy into a recovered propelling force.
The present invention relates to a backflow recovery propeller device.
An object of the present invention is to provide a propeller device in which the inertia of the twisted fluid flow being produced by the fixed main screw propeller is substantially utilized.
Another object is to provide a freely rotatable recovery screw propeller having a collision surface for the backflow current of a high pitch and the opposite surface thereof is thus effectively of a low pitch.
Other objects and advantages of the present invention Will be apparent from the following description taken in conjunction with the accompanying drawings in which:
FIG. 1 is a side view of an embodiment of the present invention,
FIG. 2 is a front view, and
FIG. 3 is a section of blade thickness ratio taken along line IIIIII of FIG. 1, showing a variation of blade thickness.
Referring to the drawings, 1 shows a propeller shaft, 2 a fixed main screw propeller, 3 a freely rotatable recovery screw propeller, 9 a cap, A is a direction of rotation and D a distance or gap between the main propeller 2 and the freely rotatable recovery propeller 3. 2a and 2b show leading and trailing edges of the main blade. 3a and 31) show also leading and trailing edges of the recovery blade. 3a and 3b show the smallest and the largest recovery blade thickness portion, the former being in a zone of stationary fluid and the latter in a zone of the rotating flow or twisted flow. Sal shows the end portion of the smallest thickness blade. 3171 and 3172 show the end portions of the inner blade. 3b3 shows a colliding surface. 3174 shows a semicircular shaped portion for the leading edge.
The recovery propeller device according to the present invention consists of the two screw propellers 2, 3 mounted on the shaft 1. The contour of the blade of the conventional main screw propeller 2 is made similar to the substantially straight line of the leading edge 3a of the adjacent recovery screw propeller 3. The trailing edge 2b of the main screw propeller 2 is made in a substantially straight line and slightly spaced from the leading edge 3a of the recovery screw propeller 3. The main screw propeller is fixed on the propeller shaft 1 and operates as a conventional type blade propeller. The freely rotatable recovery screw propeller 3 adjancent the main propeller 2 3,549,271 Patented Dec. 22, 1970 is movably mounted on bearings on the shaft 1. It is to be noted that a hub, in both sides of which sea water is prevented from flowing in by special oil seals. The lubrication thereof is eifected by a simple lubricating hydraulic system or by a sea water lubrication system having a special nonabsorbing synthetic resin.
The feature of the recovery blade includes making both sides of a helical configuration and thus forming a colliding surface 3113 for receiving the twisted backflow. Its opposite surface, i.e., a propulsion producing advance surface, or a backflow colliding surface is made in a substantially straight line. Thus the structural and functional combination of both sides renders blade thickness ratio that is small at the root, large at the blade end; that is, increasingly large inside the zone defined by the diameter of the main screw propeller 2 and suddenly decreases to an extreme at a zone extended from the boundary defined by the diameter of the main blade. The pitch of the advance surface of the recovery blade may preferably be about five times large as that of the main blade. This relatively high pitch ratio is theoretical but is reasonable.
The present invention comprises a backflow recovery screw propeller in which the opening ends of the helical surface of the advance surface and the helical surface or plain surface of the backflow colliding surface converged into a semicircular shaped leading edge. The helical surfaces of the left and right sides thus have elevation angles that are combined into one blade. A twisted backflow torque is absorbed by the backflow colliding surface to produce a rotating force. The driving surface renders a high pitch while the advance surface a low pitch so as to obtain an effective propulsion force. As described above the recovery screw propeller is arranged to form in a zone in the twisted rotating flow that is defined by the diameter of the main screw propeller and is arranged to have the smallest in blade thickness within the stationary fluid. Consequently the main blade produces an effective propulsion force.
If a conventional main screw propeller having blades of a thin thickness is used as the secondary freely rotating screw propeller, the propulsive force is substantially cancelled by the thrust produced opposite to the propelling direction which is produced on the backflow colliding surface. The secondary propeller will be thus moved in the opposite direction, even if the pitch ratio thereof is about two times that of the main propeller. In this case, efficiency will increase somewhat at about the slip ratio, but since the efficiency will be down, the use of said secondary propeller is virtually impossible at the normal slip ratio. The secondary propeller with thin blades is obviously small in blade thickness ratio and carries away backward. There is produced an opposite thrust substantially cancelling the propulsive thrust on the rotating advance surface and definitely does not increase the efliciency.
-In the propeller device according to the present invention, the effective resistance is produced by mutual collision of the fluid between both propellers and the energy which would be lost in the backflow is substantially recovered. With decreasing energy transmitting in the fluid, total propulsion efliciency is raised. The rotating direction of the main screw propeller and of the recovery screw propeller are the same. In order to absorb the maximum momentum of the twisted flow produced by the main screw propeller the driving of the screw propeller is obtained entirely by the very high pitch. The advance surface of the screw propeller blade producing the more effective thrust is given the necessary rotating power factor to absorb entirely the backflow torque. This is suitable in the /8%() rotating rate of the main screw propeller. In order to determine the blade area and the pitch, both sides converge, as described above, on the opening in the backflow colliding surface and the leading edge constitutes a semicircular shaped portion. The blade thickness ratio is made small atthe root and large at the blade end.
As the both propellers rotate in same direction, the effects of the mutual relationships of the blades affect the lattice effect occur. Then asthe efliciency rises, the pitch factor in hydrodynamics become high. Thus propelling efliciency is raised in a zone of low factor in hydrodynamics. There is no effect of the twisted rotating flow in the zone outside the diameter of the main propeller. It is not necessary to cope with the eifect of the complicated fluid flow produced by the propeller, only the advance surface by virtue of its very thin blade thickness. While the twisted backflow produced by the main propeller is pushed at a right angle to the working surface of the main blade,
,such flow collides with thebackflow colliding surface of the same but at a higher pitch. The freely rotating recovery blade is thus rotated by collision of the fluid, and
then some slip does occur. Fluid collision with a rebound of slip fluid is continuously produced between the both propellers. Such state is the effective resistance that occurs atthe back of the propeller and produces a state of high pitch. That is, the quantity of kinetic energy. transmitting fluid through the main blade decreases and the low pitch propelling efficiency increases in the main blade. Total efiiciency of the main blade efiiciency and blackflow. recovery amounts to about 20-30% in propelling efliciency compared with the conventional main propeller.
In order to obtain the highest eificiency for the pitch for the recovery propeller, a pitch. of about five times larger than as that of the main propeller in a slip ratio situation of about.20% for the propeller device, a pitch is selected of about four times larger than of the main propeller; In a slip ratio of about a pitch is selected of about"3.5 times larger than that of the main propeller. In slip ratio about Of course blade area ratio and the like must be considered.
According to a feature of the present invention, the change of bladethickness ratio shownin FIG. 1 makes a colliding surface of .the backflow a surface coincided with the advance surface, plain surface in axial direction or the helical surfaces of both left and right sides. The
blade thickness ratio is made the smallest, considering that in a zone outside the diameter of the main blade there in no substantial effect on the backflow. The advance propelling surface can determine a pitch by the backflow recovery and thus a slip ratio of the highest eificiency of the propeller is achieved. The reason why the leading edge of the recover blade propeller has a semicircular configuration and' not a tapered aerofoil is that if an aerofoil is used, the backflow colliding surface becomes increasingly large and flows in the opposite direction to produce a harmful resistance.
1. A propeller device comprising a power operated shaft having a hub portion, a main screw propeller axially and rigidly mounted on said shaft, a backflow recovery screw propeller axially positioned adjacent said main propeller and mounted to rotate relatively free on said shaft, a cap member axially positioned adjacent said recovery propeller and mounted on one end of said shaft, said main and recovery propellers operatively rotated in the same direction, said recovery propeller having helical shaped surfaces on both sides thereof, said sides converging to form a leading edge having a semicircular configuration, said recovery propeller having a thickness in the longitudinal direction that progressively increases more than one half of the longitudinal distance from the hub portion to the propeller end, the longitudinal distance nearest the end of the propeller having a constant uniform thickness of substantially less than any of the progressively increasing portion whereby the structure of the recovery propeller will substantially convert the backflow force produced thereby into a forward recovered propelling force.
References Cited UNITED STATES PATENTS 2,126,221 8/ 1938 Sessums -13525 FOREIGN PATENTS 332,124 7/1930 Great Britain 170-13525 91,268 10/1921 Switzerland 170-135.25
EVERETTE A. POWELL, 111., Primary Examiner