ADJUSTABLE FOLDING PROPELLER

Abstract: Folding propeller which consists of blades (1) hinged to a hub (7) in such a way that they can turn about 56 degrees from a position at rest, where they are pointing aft, to a working position towards a stop. The identical movements of the blades (1) are achieved by the use of two cog-wheel connections, where each cog-wheel consists of only one tooth. The two connections are arranged side by side but in opposite directions in order to ensure a fixed connection. The tooth faces (10) may be given the shape of an arc of a circle. The propeller blades (1) may be fixed to the hub mechanism by means of pins (2) arranged in the longitudinal axis of the blades (1). The pitch of the blades (1) may then be changed.

Description: Adjustable folding propeller. This invention relates to so-called folding" propellers whic " are screw prooellers with: foldable blades and are intended for use on sailing boats equipoed with an engine for auxiliary propulsion. Sailing boat prooellers where the blades are hinged at the hub and take uo a normal position pemendicular or nearly Deroendic lar to the driving shaft when the ship is oropelled by the engine but which are folded ut> by the water Dressure when the"-ship is using sails alone with the engine stooped, have been known for a long time under the name of folding Drooellers. The advantage of folding UP the propeller blades is that the relatively high resistance of a stopped τ>ropeller», or of a orooeller driven very slowly around by oassing water, is avoided. The hinged blades of nearly all tyoes of folding orooellers are in some way mechanically connected to each other in order to ensure that the oositions of the blades are identical as they move from the position at rest to the working oosition and vice versa. This ' is very imoortant, because different ositions of the blades will bring the orooeller out of balance and thus create dangerous vibrating forces. The most common way to ensure the identical movements of the blades is to arrange cog-wheel sectors at the hub end of the blades. The shafts, on which the blades are hinged to the hub, are then arranged in such a way that the cog-wheel sectors are in mesh with each other or with a common cog-rod. A movement of one blade will then cause a similar movement of the other blade or the other blades. There are however a number of disadvantages connected with this type of folding propeller. The centrifugal force will move the blades from the position at rest to a position Derpendicular to the. driving shaft when the engine is started and the hydro- dynamic force on the blades will try to pull them either forward or backward deoending on the direction of the rotation. A certain position of the blades in the working condition can easily be obtained when the prooeller is driving the boat forward, by arranging stoos which prevent the blades from moving further forward. A similar arrange- • ment is however not Dossible when the propeller has to drive the boat astern. The hydrodynamic force will then try to fold U the DroDeller and the blades will only remain in a position suitable for prooulsion if the centrifugal force on a blade is large compared to the hydrodynamic force. Unfortunately, it is not possible from practical reasons to make the blades so heavy that they will remain Deroendicular or nearly Deroendicular to the driving shaft under all backing conditions and the final position of the blades will therefore be one where the centrifugal forces and the hydrodynamical forces are counterbalancing each other. This position of equilibrium is not well determined because it is strongly affected by the propeller .blade geometry and the hydrodynamic working conditions. The virtual diameter of the propeller which is smaller than the maximum diameter because of the inclination of the blades may therefore be too small-resulting in a reduced perfor¬ mance of the proDeller. Further, it is not easy to manufacture the cog-wheel sectors at the end of the blades and there are difficulties in making them sufficiently strong. They are therefore exoosed to fractures and heavy wear and the blades will then have to be scrapϋed. The folding prooeller, according to the present invention, is characterised by the stops which only allow the blades to turn about 56 degrees from the position at rest to the working position and by the cog-wheel mechanism which consists of only two teeth- per blade placed side by side, one a little offset from the other. -Only one face of each tooth is used and for two teeth of one blade it will be the o p posite sides. The centrifugal force will pull the blades out to the working position when the driving shaft rotates. The turning moment of the centrifugal force around the hinge shaft of a blade is, according to simple and well-known Dhysical and geometrical laws, at a maximum when the blades are turned 45 degrees out from the Dosition at rest but is significantly reduced when the blades are turned to about 60 degrees. The hydrodynamic activity of the Drooeller is however " , at an ootimum, when the angle is 90 degrees and the virtual diameter of the propeller is as large as oossible, but is significantly reduced when the turning angle of the blades is less than 60 degrees. A good comoromise between an efficient hydrodynamic performance and the ability to stay in the working position against the stoϋ when going astern is therefore achieved when an angle of about 60 degrees is chosen for the working Dosition. The cog-wheel connection between the blades is, as mentioned before, made with only one tooth oer blade and this tooth is continuously meshed with the tooth of the opposite wheel. Cog-wheels with only one set of corresponding teeth will, however, only stay together if the torque, which has to be transferred from one shaft to the other, is Dressing the two teeth against each other. It is therefore necessary to arrange a similar oair of teeth besides the first pair, but directed in the oooosite way, if a fixed connection, independent of the direction of the torque and oower transfer, is required. A cog-wheel connection with only one oair of teeth in mesh will have a limited working angle. The abovementioned working angle of 60 degrees is therefore slightly reduced to about 56 degrees in order to ease the design of the mechanism. A pro p eller according to this invention has a number of advantages: - A minimum of material may be used for the blades, because they are fixed in a position, where the ability of the centrifugal force to keep the propeller folded out is at a maximum. - A p erformance like that of a fixed bladed propeller is achieved, because the blades remain in the same position going astern as when going forward. - The number of teeth in mesh is reduced to one per blade for each turning direction and only one face of a tooth is used. There is therefore no requirements for the thickness of the teeth so they may be given a simple and rugged shape which eases the manufacture and permits the use of materials with low strength. The folding propeller according to the present invention, in its most simple form, differs mainly from the well-known types in two ways. Firstly by the angular position in which the blades are fixed during propulsion ahead and astern and secondly by the connection of the blades using a .special cog-wheel mechanism, where only one face of the tooth is used. It may however, according to the invention, be advantageous to give the face of the teeth the shape of an arc of a circle. This is a reasonably good approximation to the normally used curve of evolution but,.-in the present case, where only one face of a tooth is used, it will further be possible to replace the teeth by circular cylinders which are fixed in such a way.that the working part of the cylinder surface is kept free. Moreover, it is, according to this invention, possible to manufacture the propeller blades seperately and to connect them to the hub mechanism by means of pins arranged in the longitudinal axis of the blades. The seperation of the different parts,, which is achieved in this way, will make the manufacture of the propeller easy and cheap and will make it possible to replace parts in case of extensive wear or damage, thus avoiding total scrapping of the r propeller. Finally, it will, according to this invention, be 5 advantageous to arrange the beforementioned pin for the connection of the blade to the hub mechanism in such a way that the blade may turn around it. Each pin must then be fixed to the hub mechanism by a bolt, which, when it is loosened, permits the blade to turn about 15 degrees. This 10 corresponds to a change of itch of the propeller blade between about 0.5 times the propeller diameter and about 1.2 times the propeller diameter. This is the pitch inter¬ val normally used for yacht propellers. In this way -it is possible to adjust the propeller, to suit the speed of the 15 boat and the power and number of revolutions of the engine. The drawings show an adjustable folding propeller according to the invention as follows: Fig.l shows the propeller during propulsion ahead and astern using the engine. 20 Fig.2 shows the propeller at rest, when the engine is stopped and the boat is propelled using sails. Fig.3 shows the principles of the special cog-wheel connection of the blades with one part of the double- connection fully drawn and the other part dotted and 25 with the positions of the four circular cylinders, which act as teeth, shown by a thin dot-and-dash line. Fig.4 shows the propeller hub. Fig.5 shows the part of the hub mechanism to which a blade 30 is connected. Fig.6 shows an assembly drawing of the propeller, from which a part of the hub is removed in order to expose the mechanism and for which hidden contours are shown dotted for the upper blade only. The propeller consists of two blades 1, each with a circular, cylindric pin 2 at the end, either directly manufactured with the blade or screwed into place. The pins are fastened in holes 3 by means of bolts 4 through holes 5 in the moving parts 6 of the hub mechanism. These moving parts are connected to the fixed part of the hub 7 by shafts 8, which are secured by screws 9. The moving parts of the hub mechanism are connected to each other by two cog-wheel connections Placed side by side. Each cog¬ wheel connection consists only of one tooth face 10 on each wheel. In the case shown, the teeth are formed by circular cylinders 11 of a length equal to half the thickness of the moving parts of the hub mechanism. The cylinders are Placed in holes 12 in the moving parts and may be fixed by brazing or in some other way. Stops for the movement corresponding to Positions at rest or at work are made UP by the surfaces 13 and 14.

Claims: C L A I M S 1. A folding propeller with blades (1) hinged to a hub (7) in such a Way that they will be unfolded - against af stop, during propulsion ahead and astern using an engine, to a position where they are turned about 40° - 70° forward from the folded up position. This folded up position corresponds to forward propul¬ sion using sails where the blades (1) point aft in the direction of the propeller shaft. 2. A folding propeller according to claim 1 / where the uniform movement of the different blades (1) is controlled by a cog-wheel mechanism consisting of two pairs of cog-wheels placed side by side. Each cog-wheel uses the face (10) of one tooth only and this is in constant mesh with the tooth on the corre¬ sponding cog-wheel. The faces (10) of the two teeth, which are placed side by side, point in opposite directions. 3. A folding propeller according to claim 2,• where the faces (10) of the teeth are given the shape of circular arcs. 4. A folding propeller according to claim 3, where the teeth are made from circular cylinders (11) fixed to the hub (7) mechanism by brazing or in some other way. 5. A folding propeller according to claims 1, 2, 3 or 4 With seperately manufactured blades (1) connec¬ ted to the hub (7) mechanism by means of pins (2) placed at the hub (7) end in the longitudinal axis SUBSTITUTESHEET of the blades (1) in such a way that the pitch of the propeller may be adjusted Within certain limits appropriate for a yacht propeller, by turning the blades (1) around the pin axis. SUBSTITUTESHEET ISA/SE

Inventors: MUNK TORBEN, MUNK, TORBEN
Applicants: CON FOL APS, CON-FOL APS.
Application year: 1986
Main classification: B63H1
IPC codes: B63H1