Propeller Hub Research Articles

HydrodynamicAnalysisofPropellersin Steady Flow Usinga Surface Panel Method

A surface panel method for the hydrodynamic analysis of a propeller operating in steady flow is described. The surface of propeller blade and hub is approximated by a number of small hyperboloidal quadrilateral panels with constant source and doublet distributions. The surface of trailing vortex sheet is also represented by hyperboloidal quadrilateral panels with a constant doublet distribution. The strength of source and doublet is determined by solving the boundary value problem at control point on each panel surface. Special emphasis was put on the Kutta condition of equal pressure on upper and lower surfaces at the trailing edge.Pressure distributions on the blade calculated by the present method are in good agreement with the experimental data. A better agreement of pressure distributions near the hub is observed when compared with those of a conventional lifting surface method. Open-water characteristics of propeller calculated by the present method are also in good agreement with experimental data.

A Research and Development of PBCF (Propeller Boss Cap Fins)

PBCF (Propeller Boss Cap Fins) was devised to enhance the efficiency of a ship's screw propeller by reducing the energy loss due to the propeller hub vortex and this was proposed in the paper presented to the Journal of the Society of Naval Architects of Japan, Vol. 163 (1988). The concept of PBCF is that the same number of small fins as that of the propeller blades are attached to the boss cap (hub cone) and that they rotate together with the propeller blades. The hub vortex is considerably weakened and the kinetic energy from the rotating flow around the boss cap is recovered by the fins and accordingly the propeller efficiency is significantly increased.Following the previous PBCF paper, research into the PBCF effect was carried out through the measurement of the flow behind the propeller by 3D-LDV, the force measurement of PBCF and the cavitation test in a propeller slipstream. The following points were clarified from the results of experiments : …Decrease of rotational flow velocities and acceleration of the flow of fore and aft direction behind the PBCF are confirmed quantitatively.…PBCF generates torque reduction and also makes a main propeller increase thrust.…The hub Vortex cavitation is eliminated by PBCF.As for the PBCF effect on actual ships, 4.3 % of the efficiency gains on average from the analysis of the data from eleven sea trials of various kinds of ships, and a significant efficiency gain from the analysis of actual voyage data were obtained. The certain scale effect between the model and the actual ship is considered to explain the difference in the efficiency gain.These results lead us to believe that PBCF is an excellent and practical energy-saving device because of its simple concept and the reliable efficiency gain of about 4 %.

Design and Testing of a Water Tip Jet Propeller

This work was directed at the problem of developing a lightweight, low cost means of propelling a short run underwater vehicle. The system described occupies a position midway between the straight rocket and the geared turbine/propeller drive fed by a gas generator. It expands the propellant gases through a turbine, uses the turbine to direct drive a centrifugal sea water pump, and ejects the pumped water through jets at the blade tips of a specially designed propeller. Exhaust gas from the turbine is released from the propeller hub at the blade trailing edges. The reduction in turbine back pressure produced by the suction effect on the exhaust gas significantly increases turbine efficiency and reduces the system's sensitivity to operating depth. This paper covers the analytical design and sea testing of the water tip jet propeller and summarizes the test results. The test data, consisting of measurements of propulsive power vs tip jet flow rate and pressure at various vehicle speeds, indicate that the proposed system can provide specific power levels superior to those obtainable from any other underwater propulsion system for vehicles requiring a run time of about 3 s to 2 min. It has additional advantages of, relative insensitivity to depth, low cost, low self-noise, and absence of reaction torque.

HUB SIZE SELECTION CRITERIA FOR CONTROLLABLE PITCH PROPELLERS AS A MEANS TO ENSURE SYSTEMS INTREGRITY

ABSTRACTIn a CP propeller the size of the hub largely influences the reliability of the system in operation. Accurate choice of the hub—size provides the best means to prevent the system from structural propeller failures and is therefore the best method to ensure reliability and optimized performance.Recent failures of high—power CP propellers, of which one Navy propeller had a serious mission failure, could have been avoided if a larger hub had been adopted.The paper contains two tools, available also to nonspecialists. One allows clear recognition of the technical degree of difficulty of all types of propellers and the other is a scale to determine the degree of load of each CP propeller hub. Information is given concerning the influence of the hub/diameter ratio on the hydrodynamic performance.

Session 3: Paper 21. Ball and Cylindrical Roller Bearings in Drivelines

This paper deals with ball and cylindrical roller bearings in drivelines where, year by year, requirements demand that smaller bearings meet conditions of steadily increasing severity. Clutch-operating bearings and those for manual gearboxes and overdrives are reviewed. The different requirements for bearings in front-wheel drives and automatic gearboxes are discussed, followed by a consideration of the requirements of propeller shafts, half-shafts and hubs.

Beryllium Copper in the Aircraft Industry

AN alloy for which many uses are predicted in the aircraft industry is beryllium copper. The best known applications so far are found in instrument parts, beryllium copper being non‐magnetic, and in adjustable‐pitch propeller hub cones and retractable landing gear parts, where good wear resistance is required. The alloy also has possibilities in the working of magnesium. In magnesium working machines must be kept free from chips, tools must be kept sharp, and plenty of lubrication must be provided to avoid fire. Special tools have been designed to keep down friction heat, and they should be used in working with magnesium. These tools have wider clearance angles and their surfaces are smaller than tools used with other materials. The comparatively high hardness and shock resistance of beryllium copper permits it to be used for non‐sparking hand tools such as hammers, chisels, wrenches, wrecking bars, drift pins and scrapers.

Month in the Patent Office

In a variable‐pitch screw propeller each blade has a hollow root portion rotatably mounted over a spigot on the boss and a threaded sleeve member is located between them, one end of it terminating in a ram, the blades and spigots having relatively inclined threads co‐operating with threads on the sleeve member whereby, when pressure is applied to the ram, the parts are displaced so as to rotate the blades for pitch variation. The blade 4 has an inner bush 8, which is secured thereto by screws 10 and carries a bevel wheel 25. This sleeve is splined at 9 to engage splines on a ram sleeve 11, the upper part of which projects into a chamber 22 which is in communication by ducts 21 with passages in the propeller hub and shaft leading to a fixed pipe supply 13. The inner part of the ram member 11 has helical splines which engage corresponding helical keys on the boss spigot 9. With increase in revolutions, the sleeve block 4, under centrifugal force, tends to move outwardly and restraint thereto is applied by the fluid pressure in the space 22. A second set of supply ports 24 may be formed at a different position relative to the travel of the sleeve whereby the degree of movement of the sleeve can be controlled by using different pressures of oil supply. Where the weight of the ram members 11 is not sufficient, the gear‐wheels 25 may gear with others on axes at right‐angles which are secured to similar movable sleeves, but these do not directly operate other propeller blades. Alternatively, there may be fitted at the base of the sleeve a spring supplementing the centrifugal force and tending to cause it to move outwards, in which case the member 11 can be lighter in weight.

Simplification of Helmbold's Method on Marine Screw Propeller Design with a Few Suplementary Notes

The method of calculation regarding the elements of a screw propeller was published by Dr. Helmbold and simplified by Dr. Lerbs according to Betz-Prandtl's vortex theory, and Dr. Shigemitsu also gave descriptions on similer lines. These methods require complex calculations notwithstanding the insufficient accuracy of results, and are considered not to be fully adaptable to the phenomena on marine propellers. This paper deals with the method of the first named author modified to suit application to the marine propellers in a more simplified process, and suplemented with some studies made by the writer.In such cases as when the sizes of the propeller hub of the built-up type are considerably large as not to be neglected, the correction factors are shown in fig. 6 for the thrust coefficient and fig. 8 for the torque coefficient. Fig. 9 is drawn to determine easily λ and b0 when Csh and kdh are given, and Cag. t found by use of figs. 12 and 13 and an equation, Cag. t=K.r.M. With regard to the effect of the centrifugal force, figs. 10 and 11 and a simple equation, b''=b (1+AB) will be applicable.The wake variation within the region of the propeller disc can be reasonably treated with the centrifugal force by employing the equations, tan βr''=vr-v/γω+b'' and Ca·t=cosβr''/cosβ·Cag·t/Ka, where Ka is known by Numachi's curve. Finally, the pitch angle of each blade section is the algebraic sum of βr'' and incidence angle.The calculation curves and simple equations above-mentioned may be very convenient and useful for practical engineers to design marine propellers.

Month in the Patent Office

Hollow blades b for air‐screws are constructed from a metal block provided with a blind coaxial bore c first by forging, stamping or rolling to produce the requisite elongation of the block and to impart a cross‐section of desired shape. Secondly, by producing a deformation of the block wall by means of pressure exerted from the inside or from the outside, and finally to form the end a of the blade in a manner suitable for attachment to the propeller hub. When an external pressure is used the interior is filled with plastic material or fluid under pressure. Alternatively, a former or core is introduced having the desired inner shape of the blade. In another method the hollow block is placed in a mould having the required external form of the blade. Preferably the root a of the blade which is hollow is provided with a thread whereby it may be screwed on to radial pins on the hub block