Rotating the Hamilton Standard 54H60 propeller on a US Navy EP-3E Orion's number four engine as part of pre-flight checks. Hamilton Standard, a famous Aircraft Propeller parts supplier was formed in 1929 when United Aircraft & Transport Corporation consolidated Hamilton Aero Manufacturing WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout The Orion is an anti-submarine warfare aircraft

A propeller is essentially a type of fan which transmits power by converting rotational motion into thrust for propulsion of a vehicle such as an aircraft, ship, or submarine through a mass such as water or air, by rotating two or more twisted blades about a central shaft, in a manner analogous to rotating a screw through a solid. An anti-submarine weapon is any one of a range of devices that are intended to act against a submarine and its crew to destroy (sink the vessel or to destroy or reduce its capability A mechanical fan is an electrically powered device used to produce an airflow for the purpose of creature comfort (particularly in the heat ventilation, exhaust A rotation is a movement of an object in a circular motion A two- Dimensional object rotates around a center (or point) of rotation Thrust is a reaction force described quantitatively by Newton 's Second and Third Laws. Overview Fixed-wing aircraft range from small training and recreational aircraft to Wide-body aircraft and military cargo aircraft. A ship /ʃɪp/ is a large vessel that floats on water Ships are generally distinguished from Boats based on size A submarine is a Watercraft that can operate independently below water as distinct from a Submersible that has only limited underwater capability Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object Water is a common Chemical substance that is essential for the survival of all known forms of Life. Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five Look up SpecialSearch/{{lcscrew}}}}}|{{{2|{{{1|screw}}}}}} The blades of a propeller act as rotating wings (the blades of a propeller are in fact wings or airfoils), and produce force through application of both Bernoulli's principle and Newton's third law, generating a difference in pressure between the forward and rear surfaces of the airfoil-shaped blades and by accelerating a mass of air rearward. WING "ESPN 1410" is a commercial AM radio station in Dayton Ohio operating with 5000 watts at 1410 kHz with studios offices and transmitter located on David WING "ESPN 1410" is a commercial AM radio station in Dayton Ohio operating with 5000 watts at 1410 kHz with studios offices and transmitter located on David An airfoil (in American English) or aerofoil (in British English) is the shape of a Wing or blade (of a Propeller, rotor In Fluid dynamics, Bernoulli's principle states that for an Inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in Newton's laws of motion are three Physical laws which provide relationships between the Forces acting on a body and the motion of the An airfoil (in American English) or aerofoil (in British English) is the shape of a Wing or blade (of a Propeller, rotor

History

The principle employed in using a screw propeller is used in sculling. Scull redirects here The head bone is spelled " Skull " It is part of the skill of propelling a Venetian gondola but was used in a less refined way in other parts of Europe and probably elsewhere. A Gondola is a traditional Venetian rowing Boat. Gondolas were for centuries the chief means of transportation within Venice and still have For example, propelling a canoe with a single paddle using a "j-stroke" involves a related but not identical technique. A canoe is a small narrow Boat, typically human-powered though it may also be powered by sails or small electric or gas motors A canoe is a small narrow Boat, typically human-powered though it may also be powered by sails or small electric or gas motors In China, sculling, called "lu", was also used by the 3rd century AD .

In sculling, a single blade is moved through an arc, from side to side taking care to keep presenting the blade to the water at the effective angle. The innovation introduced with the screw propeller was the extension of that arc through more than 360° by attaching the blade to a rotating shaft. In practice, there has to be more than one blade so as to balance the forces involved. The exception is the Single-blade propeller system. A single-blade propeller is a notable configuration of a propulsion system used on Aerodynes to generate Thrust.

The origin of the actual screw propeller starts, in the West, with Archimedes, who used a screw to lift water for irrigation and bailing boats, so famously that it became known as the Archimedes screw. Archimedes of Syracuse ( Greek:) ( c. 287 BC – c 212 BC was a Greek mathematician, Physicist, Engineer The Archimedes' screw, Archimedean screw, or screwpump is a Machine historically used for transferring water from a low-lying body of water into Irrigation It was probably an application of spiral movement in space (spirals were a special study of Archimedes) to a hollow segmented water-wheel used for irrigation by Egyptians for centuries. Archimedes of Syracuse ( Greek:) ( c. 287 BC – c 212 BC was a Greek mathematician, Physicist, Engineer This article is about the contemporary North African ethnic group Leonardo da Vinci adopted the principle to drive his theoretical helicopter, sketches of which involved a large canvas screw overhead.

In 1784, J. P. Paucton proposed a gyrocopter-like aircraft using similar screws for both lift and propulsion. At about the same time, James Watt proposed using screws to propel boats, although he did not use them for his steam engines. James Watt ( 19 January 1736 &ndash 25 August 1819 Boulton proved to be an excellent businessman and both men eventually made fortunes This was not his own invention, though; Toogood and Hays had patented it a century earlier, and it had become an uncommon use as a means of propelling boats since that time.

By 1827 Robert Welch had invented a screw propeller which had multiple blades fastened around a conical base; this new method of propulsion allowed steam ships to travel at much greater speeds without using sails thereby making ocean travel faster. Robert Welch may refer to Robert Stanley Welch (1928-2000 politician in Ontario Canada Robert W Propellers remained extremely inefficient and little-utilized until 1835, when Francis Pettit Smith discovered a new way of building propellers. Sir Francis Pettit Smith ( 1808 - 12 February 1874) was a British inventor and along with Frédéric Sauvage and John Ericsson Up to that time, propellers were literally screws, of considerable length. But during the testing of a boat propelled by one, the screw snapped off, leaving a fragment shaped much like a modern boat propeller. The boat moved faster with the broken propeller. ^[1]

At about the same time, Frédéric Sauvage and John Ericsson applied for patents on vaguely similar, although less efficient shortened screw propellers, leading to an apparently-permanent controversy as to who is the official inventor among those three men. Frédéric Sauvage (1786-1857 was a French boat builder who carried out early tests of screw-type marine Propellers In a public demonstration with a small boat on This article is about John Ericsson the Swedish-American inventor Ericsson became widely famous when he built the “Monitor” an armoured battleship that in 1862 triumphed over the Confederate States’ Merrimac in an American Civil War sea battle.

The first screw propeller to be powered by a gasoline engine, fitted to a small boat (now known as a powerboat) was installed by Frederick Lanchester, also from Birmingham. A Petrol engine or Gasoline engine is an Internal combustion engine with spark-ignition designed to run on petrol ( Gasoline) and similar volatile Frederick William Lanchester, Hon FRAeS ( October 23, 1868 - March 8, 1946) was an English Polymath and This was tested in Oxford. Oxford is currently bidding for the 2010 Wikimania Conference Oxford () is a city, and the County town of Oxfordshire, The first 'real-world' use of a propeller was by David Bushnell, who used hand-powered screw propellors to motivate his submarine "Turtle" in 1776.

A World War I wooden aircraft propeller on a workbench.

The twisted airfoil (aerofoil) shape of modern aircraft propellers was pioneered by the Wright brothers when they found that all existing knowledge on propellers (mostly naval) was determined by trial and error and that no one knew exactly how they worked. An airfoil (in American English) or aerofoil (in British English) is the shape of a Wing or blade (of a Propeller, rotor WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout They found that a propeller is essentially the same as a wing and so were able to use data collated from their earlier wind tunnel experiments on wings. WING "ESPN 1410" is a commercial AM radio station in Dayton Ohio operating with 5000 watts at 1410 kHz with studios offices and transmitter located on David They also found that the relative angle of attack from the forward movement of the aircraft was different for all points along the length of the blade, thus it was necessary to introduce a twist along its length. Angle of attack ( AOA, \alpha Greek letter alpha) is a term used in Aerodynamics to describe the Angle between the Their original propeller blades are only about 5% less efficient than the modern equivalent, some 100 years later. ^[2]

Alberto Santos Dumont was another early pioneer, having designed propellers before the Wright Brothers (albeit not as efficient) for his airships. He applied the knowledge he gained from experiences with airships to make a propeller with a steel shaft and aluminium blades for his 14 bis biplane. Some of his designs used a bent aluminium sheet for blades, thus creating an airfoil shape. These are heavily undercambered because of this and combined with the lack of a lengthwise twist made them less efficient than the Wright propellers. Even so, this was perhaps the first use of aluminium in the construction of an airscrew.

Aviation

Aircraft propellers (airscrews)

A propeller's efficiency is determined by

. In Physics, mechanical efficiency is the effectiveness of a machine and is defined as \text{Efficiency} = \frac{\text{Mechanical Advantage}}{\text{Velocity

A well-designed propeller typically has an efficiency of around 80% when operating in the best regime. [1] Changes to a propeller's efficiency are produced by a number of factors, notably adjustments to the helix angle(θ), the angle between the resultant relative velocity and the blade rotation direction, and to blade pitch (where θ = Φ + α) . A helix (pl helixes or helices) from the Greek word έλιξ, is a special kind of Space curve, i Blade pitch or simply pitch refers to turning the Angle of attack of the blades of a Propeller into or out of the wind to control the production or absorption Very small pitch and helix angles give a good performance against resistance but provide little thrust, while larger angles have the opposite effect. The best helix angle is when the blade is acting as a wing producing much more lift than drag.

The propellers of an RAF Hercules C. 4 in feather position

Propellers are similar in aerofoil section to a low drag wing and as such are poor in operation when at other than their optimum angle of attack. In Fluid dynamics, drag (sometimes called fluid resistance) is the force that resists the movement of a Solid object through a Fluid (a Angle of attack ( AOA, \alpha Greek letter alpha) is a term used in Aerodynamics to describe the Angle between the Control systems are required to counter the need for accurate matching of pitch to flight speed and engine speed.

The purpose of varying pitch angle with a variable pitch propeller is to maintain an optimal angle of attack (maximum lift to drag ratio) on the propeller blades as aircraft speed varies. Early pitch control settings were pilot operated, either two-position or manually variable. Later, automatic propellers were developed to maintain an optimum angle of attack. They did this by balancing the centripetal twisting moment on the blades and a set of counterweights against a spring and the aerodynamic forces on the blade. Automatic props had the advantage of being simple and requiring no external control, but a particular propeller's performance was difficult to match with that of the aircraft's powerplant. An improvement on the automatic type was the constant-speed propeller. A Constant speed Propeller is a type of propeller that can change its blade pitch to take better advantage of the power supplied by an engine in much the same way that a transmission Constant speed propellers allow the pilot to select a rotational speed for maximum engine power or maximum efficiency, and a propeller governor acts as a closed-loop controller to vary propeller pitch angle as required to maintain the RPM commanded by the pilot. A governor is a device used to measure and regulate the Speed of a Machine, such as an Engine. In Control theory, a controller is a device which monitors and affects the operational conditions of a given Dynamical system. In most aircraft this system is hydraulic, with engine oil serving as the hydraulic fluid. However, electrically controlled propellers were developed during World War II and saw extensive use on military aircraft.

A propeller blade in feathered position

On some variable-pitch propellers, the blades can be rotated parallel to the airflow to reduce drag and increase gliding distance in case of an engine failure. This is called feathering. Feathering propellers were developed for military fighter aircraft prior to World War II, as a fighter is more likely to experience an engine failure due to the inherent danger of combat. A fighter aircraft is a Military aircraft designed primarily for air-to-air combat with other Aircraft, as opposed to a Bomber, which is designed Feathering propellers are used on multi-engine aircraft and are meant to reduce drag on a failed engine. When used on powered gliders and single-engine turbine powered aircraft they increase the gliding distance. Most feathering systems for reciprocating engines sense a drop in oil pressure and move the blades toward the feather position, and require the pilot to pull the prop control back to disengage the high-pitch stop pins before the engine reaches idle RPM. Turbopropeller control systems usually utilize a negative torque sensor in the reduction gearbox which moves the blades toward feather when the engine is no longer providing power to the propeller. A turboprop engine is a type of aircraft powerplant that uses a Gas turbine engine to drive a Propeller. Depending on design, the pilot may have to push a button to override the high-pitch stops and complete the feathering process, or the feathering process may be totally automatic.

In some aircraft (e. g. , the C-130 Hercules), the pilot can manually override the constant speed mechanism to reverse the blade pitch angle, and thus the thrust of the engine. WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout This is used to help slow the plane down after landing in order to save wear on the brakes and tires, but in some cases also allows the aircraft to back up on its own.

A further consideration is the number and the shape of the blades used. Increasing the aspect ratio of the blades reduces drag but the amount of thrust produced depends on blade area, so using high aspect blades can lead to the need for a propeller diameter which is unusable. In Aerodynamics, the aspect ratio of a wing is defined as the square of the wing span divided by the wing area A further balance is that using a smaller number of blades reduces interference effects between the blades, but to have sufficient blade area to transmit the available power within a set diameter means a compromise is needed. Increasing the number of blades also decreases the amount of work each blade is required to perform, limiting the local Mach number - a significant performance limit on propellers. Mach number (\mathrm{Ma} or M (generally ˈmɑːk sometimes /ˈmɑːx/ or /ˈmæk/ is the speed of an object moving through air or any Fluid

The three-bladed propeller of a light aircraft: the Vans RV-7A

Contra-rotating propellers use a second propeller rotating in the opposite direction immediately 'downstream' of the main propeller so as to recover energy lost in the swirling motion of the air in the propeller slipstream. The Van's RV-7 and RV-7A are two-seat single-engine low-wing homebuilt airplanes sold in kit form by Van's Aircraft Contra-rotating propellers, also referred to as coaxial contra-rotating propellers, apply the maximum power of a single piston or Turboprop engine Contra-rotation also increases power without increasing propeller diameter and provides a counter to the torque effect of high-power piston engine as well as the gyroscopic precession effects, and of the slipstream swirl. A gyroscope is a device for measuring or maintaining orientation, based on the principles of Angular momentum. However on small aircraft the added cost, complexity, weight and noise of the system rarely make it worthwhile.

The propeller is usually attached to the crankshaft of the engine, either directly or through a gearbox. The crankshaft, sometimes casually abbreviated to crank, is the part of an Engine which translates reciprocating Linear Light aircraft sometimes forego the weight, complexity and cost of gearing but on some larger aircraft and some turboprop aircraft it is essential. A turboprop engine is a type of aircraft powerplant that uses a Gas turbine engine to drive a Propeller.

A propeller's performance suffers as the blade speed exceeds the speed of sound. As the relative air speed at the blade is rotation speed plus axial speed, a propeller blade tip will reach sonic speed sometime before the rest of the aircraft (with a theoretical blade the maximum aircraft speed is about 845 km/h (Mach 0. 7) at sea-level, in reality it is rather lower). When a blade tip becomes supersonic, drag and torque resistance increase suddenly and shock waves form creating a sharp increase in noise. For other uses see Supersonic. The term supersonic is used to define a speed that is over the Speed of sound ( Mach 1 For the music album by Converter see Shock Front For the 1977 horror film see Shock Waves A shock wave (also called Aircraft with conventional propellers, therefore, do not usually fly faster than Mach 0. 6. There are certain propeller-driven aircraft, usually military, which do operate at Mach 0. 8 or higher, although there is considerable fall off in efficiency.

There have been efforts to develop propellers for aircraft at high subsonic speeds. The 'fix' is similar to that of transonic wing design. Transonic is an Aeronautics term referring to a range of velocities just below and above the Speed of sound (about mach 0 The maximum relative velocity is kept as low as possible by careful control of pitch to allow the blades to have large helix angles; thin blade sections are used and the blades are swept back in a scimitar shape (Scimitar propeller); a large number of blades are used to reduce work per blade and so circulation strength; contra-rotation is used. A scimitar (ˈsɪmɪtə is a Sword with a curved blade design finding its origins in Southwest Asia A scimitar propeller is shaped like a scimitar sword, with increasing sweep along the leading edge The propellers designed are more efficient than turbo-fans and their cruising speed (Mach 0. 7–0. 85) is suitable for airliners, but the noise generated is tremendous (see the Antonov An-70 and Tupolev Tu-95 for examples of such a design). WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout

Aircraft fans

A fan is a propeller with a large number of blades. A fan therefore produces a lot of thrust for a given diameter but the closeness of the blades means that each strongly affects the flow around the others. If the flow is supersonic, this interference can be beneficial if the flow can be compressed through a series of shock waves rather than one. By placing the fan within a shaped duct – a ducted fan – specific flow patterns can be created depending on flight speed and engine performance. A ducted fan is a propulsion arrangement whereby a fan which is a type of Propeller, is mounted within a cylindrical shroud or duct As air enters the duct, its speed is reduced and pressure and temperature increase. If the aircraft is at a high subsonic speed this creates two advantages – the air enters the fan at a lower Mach speed and the higher temperature increases the local speed of sound. While there is a loss in efficiency as the fan is drawing on a smaller area of the free stream and so using less air, this is balanced by the ducted fan retaining efficiency at higher speeds where conventional propeller efficiency would be poor. A ducted fan or propeller also has certain benefits at lower speeds but the duct needs to be shaped in a different manner to one for higher speed flight. More air is taken in and the fan therefore operates at an efficiency equivalent to a larger un-ducted propeller. Noise is also reduced by the ducting and should a blade become detached the duct would contain the damage. However the duct adds weight, cost, complexity and (to a certain degree) drag.

See also Airscrew wind generator. A wind turbine is a rotating machine which converts the Kinetic energy in Wind into Mechanical energy.

Transverse axis propellers

Most propellers have their axis of rotation parallel to the fluid flow. There have however been some attempts to power vehicles with the same principles behind vertical axis wind turbines, where the rotation is perpendicular to fluid flow. A wind turbine is a rotating machine which converts the Kinetic energy in Wind into Mechanical energy. Most attempts have been unsuccessful. Blades that can vary their angle of attack during rotation have aerodynamics similar to flapping flight. Flapping flight is still poorly understood and almost never seriously used in engineering because of the strong coupling of lift, thrust and control forces.

The fanwing is one of the few types that has actually flown. FanWing or fan wing is a concept for a type of Aircraft. It is distinct from existing types of aircraft such as airplanes and helicopters in that it uses a Fixed It takes advantage of the trailing edge of an airfoil to help encourage the circulation necessary for lift. In the context of a Fluid flow relative to a body the lift force is the component of the Aerodynamic force that is Perpendicular to the flow

The Voith-Schneider propeller pictured below is another successful example, operating in water. The Voith Schneider Propeller (VSP also known as a cycloidal drive is a specialized marine propulsion system

Marine

A propeller is the most common propulsor on ships, imparting momentum to a fluid which causes a force to act on the ship .

The ideal efficiency of any size propeller is that of an actuator disc in an ideal fluid. An actual marine propeller is made up of sections of helicoidal surfaces which act together 'screwing' through the water (hence the common reference to marine propellers as "screws"). Three, four, or five blades are most common in marine propellers, although designs which are intended to operate at reduced noise will have more blades. The blades are attached to a boss, which should be as small as the needs of strength allow - with fixed pitch propellers the blades and boss are usually a single casting.

There are also controllable pitch propellers (CPPs), where the blades can be rotated normal to the drive shaft by additional machinery at the hub and control linkages running down the shaft. A controllable pitch propeller (CPP or variable pitch propeller is a special type of Propeller with blades that can be rotated around their long axis to change their This allows the drive machinery to operate at a constant speed while the propeller loading is changed to match operating conditions. It also eliminates the need for a reversing gear and allows for more rapid change to thrust, as the revolutions are constant. This type of propeller is most common on ships such as tugs where there can be enormous differences in propeller loading when towing compared to running free, a change which could cause conventional propellers to lock up as insufficient torque is generated. The downside of a CPP is the large hub which increases the chance of cavitation and the mechanical complexity which limits transmission power.

For the smaller motors there are self-pitching propellers. The blades freely move through an entire circle on an axis at right angles to the shaft. This allows hydrodynamic and centrifugal forces to 'set' the angle the blades reach and so the pitch of the propeller.

A propeller that turns clockwise to produce forward thrust, when viewed from aft, is called right-handed. One that turns anticlockwise is said to be left-handed. Larger vessels often have twin screws to reduce heeling torque, counter-rotating propellers, the starboard screw is usually right-handed and the port left-handed, this is called outward turning. Counter-rotating propellers, are found on twin- and multi- Engine, propeller-driven Aircraft and have propellers that spin in opposite directions The opposite case is called inward turning. Another possibility is contra-rotating propellers, where two propellers rotate in opposing directions on a single shaft. Contra-rotating propellers, also referred to as coaxial contra-rotating propellers, apply the maximum power of a single piston or Turboprop engine

Azimuthing propeller. An Azimuth thruster is a configuration of Ship propellers placed in pods that can be rotated in any horizontal direction making a Rudder unnecessary Vertical axis propeller.

The blade outline is defined either by a projection on a plane normal to the propeller shaft (projected outline) or by setting the circumferential chord across the blade at a given radius against radius (developed outline). The outline is usually symmetrical about a given radial line termed the median. If the median is curved back relative to the direction of rotation the propeller is said to have skew back. The skew is expressed in terms of circumferential displacement at the blade tips. If the blade face in profile is not normal to the axis it is termed raked, expressed as a percentage of total diameter.

Each blade's pitch and thickness varies with radius, early blades had a flat face and an arced back (sometimes called a circular back as the arc was part of a circle), modern propeller blades have aerofoil sections. The camber line is the line through the mid-thickness of a single blade. The camber is the maximum difference between the camber line and the chord joining the trailing and leading edges. The camber is expressed as a percentage of the chord.

The radius of maximum thickness is usually forward of the mid-chord point with the blades thinning to a minimum at the tips. The thickness is set by the demands of strength and the ratio of thickness to total diameter is called blade thickness fraction.

The ratio of pitch to diameter is called pitch ratio. Due to the complexities of modern propellers a nominal pitch is given, usually a radius of 70% of the total is used.

Blade area is given as a ratio of the total area of the propeller disc, either as developed blade area ratio or projected blade area ratio.

Forces acting on an aerofoil

The force (F) experienced by an aerofoil blade is determined by its area (A), chord (c), velocity (V) and the angle of the aerofoil to the flow, called either angle of incidence or angle of attack (α), where:

The force has two parts - that normal to the direction of flow is lift (L) and that in the direction of flow is drag (D). Both are expressed non-dimensionally as:

and

Each coefficient is a function of the angle of attack and Reynolds' number. In Fluid mechanics and Heat transfer, the Reynolds number \mathrm{Re} is a Dimensionless number that gives a measure of the Ratio As the angle of attack increases lift rises rapidly from the no lift angle before slowing its increase and then decreasing, with a sharp drop as the stall angle is reached and flow is disrupted. Drag rises slowly at first and as the rate of increase in lift falls and the angle of attack increases drag increases more sharply.

For a given strength of circulation (τ), Lift = L = ρVτ. The effect of the flow over and the circulation around the aerofoil is to reduce the velocity over the face and increase it over the back of the blade. If the reduction in pressure is too much in relation to the ambient pressure of the fluid, cavitation occurs, bubbles form in the low pressure area and are moved towards the blade's trailing edge where they collapse as the pressure increases, this reduces propeller efficiency and increases noise. The forces generated by the bubble collapse can cause permanent damage to the surfaces of the blade.

Propeller thrust

Single blade

Taking an arbitrary radial section of a blade at r, if revolutions are N then the rotational velocity is 2πNr. If the blade was a complete screw it would advance through a solid at the rate of NP, where P is the pitch of the blade. In water the advance speed is rather lower, V_a, the difference, or slip ratio, is:

Slip = (NP − V_a) / NP = 1 − J / p

where J is the advance coefficient (V_a / ND) and p is the pitch ratio (P/D).

The forces of lift and drag on the blade, dA, where force normal to the surface is dL:

where:

These forces contribute to thrust, T, on the blade:

where tanβ = dD / dL = C_D / C_L

As ,

From this total thrust can be obtained by integrating this expression along the blade. The transverse force is found in a similar manner:

Substituting for V₁ and multiplying by r, gives torque as:

which can be integrated as before.

The total thrust power of the propeller is proportional to TV_a and the shaft power to 2πNQ. So efficiency is TV_a / 2πNQ. The blade efficiency is in the ratio between thrust and torque:

showing that the blade efficiency is determined by its momentum and its qualities in the form of angles , where β is the ratio of the drag and lift coefficients.

This analysis is simplified and ignores a number of significant factors including interference between the blades and the influence of tip vortices.

Thrust and torque

The thrust, T, and torque, Q, depend on the propeller's diameter, D, revolutions, N, and rate of advance, V_a, together with the character of the fluid in which the propeller is operating and gravity. These factors create the following non-dimensional relationship:

where f₁ is a function of the advance coefficient, f₂ is a function of the Reynolds' number, and f₃ is a function of the Froude number. The Froude number is a Dimensionless number comparing inertial and gravitational forces Both f₂ and f₃ are likely to be small in comparison to f₁ under normal operating conditions, so the expression can be reduced to:

For two identical propellers the expression for both will be the same. So with the propellers T₁,T₂, and using the same subscripts to indicate each propeller:

For both Froude number and advance coefficient:

where λ is the ratio of the linear dimensions.

Thrust and velocity, at the same Froude number, give thrust power:

For torque:

. . .

Actual performance

When a propeller is added to a ship its performance is altered; there is the mechanical losses in the transmission of power; a general increase in total resistance; and the hull also impedes and renders non-uniform the flow through the propeller. The ratio between a propeller's efficiency attached to a ship (P_D) and in open water (P'_D) is termed relative rotative efficiency.

The overall propulsive efficiency (an extension of effective power (P_E)) is developed from the propulsive coefficient (PC), which is derived from the installed shaft power (P_S) modified by the effective power for the hull with appendages (P'_E), the propeller's thrust power (P_T), and the relative rotative efficiency.

P'_E/P_T = hull efficiency = η_H

P_T/P'_D = propeller efficiency = η_O

P'_D/P_D = relative rotative efficiency = η_R

P_D/P_S = shaft transmission efficiency

Producing the following:

The terms contained within the brackets are commonly grouped as the quasi-propulsive coefficient (QPC, η_D). The QPC is produced from small-scale experiments and is modified with a load factor for full size ships.

Wake is the interaction between the ship and the water with its own velocity relative to the ship. The wake has three parts - the velocity of the water around the hull; the boundary layer between the water dragged by the hull and the surrounding flow; and the waves created by the movement of the ship. the first two parts will reduce the velocity of water into the propeller, the third will either increase or decrease the velocity depending on whether the waves create a creast or trough at the propeller.

History of ship and submarine screw propellers

Propeller on a modern mid-sized merchant vessel

James Watt of Scotland is generally credited with applying the first screw propeller to an engine, an early steam engine, beginning the use of an hydrodynamic screw for propulsion. James Watt ( 19 January 1736 &ndash 25 August 1819 Boulton proved to be an excellent businessman and both men eventually made fortunes A steam engine is a Heat engine that performs Mechanical work using Steam as its Working fluid. Fluid dynamics is the sub-discipline of Fluid mechanics dealing with fluid flow: Fluids ( Liquids and Gases in motion

Mechanical ship propulsion began with the steam ship. A steam engine is a Heat engine that performs Mechanical work using Steam as its Working fluid. The first successful ship of this type is a matter of debate; candidate inventors of the 18th century include William Symington, the Marquis de Jouffroy, John Fitch and Robert Fulton, however William Symington's ship the Charlotte Dundas is regarded as the world's "first practical steamboat". William Symington (1764–1831 was a Scottish Engineer and Inventor, and the builder of the first practical Steamboat. John Fitch ( January 21, 1743 &ndash July 2, 1798) was an American Inventor, Clockmaker, and Bronzesmith Robert Fulton ( November 14, 1765 &ndash February 24, 1815) was a U William Symington (1764–1831 was a Scottish Engineer and Inventor, and the builder of the first practical Steamboat. The Charlotte Dundas is regarded as the world's "first practical Steamboat " the first towing steamboat and the boat that demonstrated the practicality of steam power Paddlewheels as the main motive source became standard on these early vessels (see Paddle steamer). A paddle is a tool used for pushing against Liquids either as a form of propulsion in a Boat or as an implement for mixing A paddle steamer is a ship or boat driven by a Steam engine that uses one or more Paddle wheels to develop thrust for propulsion. Robert Fulton had tested, and rejected, the screw propeller.

Sketch of hand-cranked vertical and horizontal screws used in Bushnell's Turtle, 1775

The screw (as opposed to paddlewheels) was introduced in the latter half of the 18th century. Turtle was the world's first Submarine used in battle It was invented in Connecticut in 1775 by American Patriot David David Bushnell's invention of the submarine (Turtle) in 1775 used hand-powered screws for vertical and horizontal propulsion. David Bushnell (1742 - 1824 of Saybrook Connecticut, was an American Inventor during the Revolutionary War. Turtle was the world's first Submarine used in battle It was invented in Connecticut in 1775 by American Patriot David The Bohemian engineer Josef Ressel designed and patented the first practicable screw propeller in 1827. Josef Ludvík František Ressel (in Czech or Joseph Ludwig Franz Ressel (in German or Josip Ressel (in Slovenian and Croatian ( June 29, 1793 Francis Pettit Smith tested a similar one in 1836. Sir Francis Pettit Smith ( 1808 - 12 February 1874) was a British inventor and along with Frédéric Sauvage and John Ericsson In 1839, John Ericsson introduced the screw propeller design onto a ship which then sailed over the Atlantic Ocean in 40 days. This article is about John Ericsson the Swedish-American inventor Mixed paddle and propeller designs were still being used at this time (vide the 1858 SS Great Eastern). History Concept After the Great Exhibition of 1851 which had publicized Australia's wealth and natural resources waves of people were eager to emigrate from

In 1848 the British Admiralty held a tug of war contest between a propeller driven ship, Rattler, and a paddle wheel ship, Alecto. The Admiralty was formerly the authority in the United Kingdom responsible for the command of the Royal Navy. A paddle is a tool used for pushing against Liquids either as a form of propulsion in a Boat or as an implement for mixing Rattler won, towing Alecto astern at 2. 8 knots (5 km/h), but it was not until the early 20th century paddle propelled vessels were entirely superseded. The screw propeller replaced the paddles owing to its greater efficiency, compactness, less complex power transmission system, and reduced susceptibility to damage (especially in battle)

Voith-Schneider propeller

Initial designs owed much to the ordinary screw from which their name derived - early propellers consisted of only two blades and matched in profile the length of a single screw rotation. Power transmission is the movement of Energy from its place of generation to a location where it is applied to performing useful work. System (from Latin systēma, in turn from Greek systēma is a set of interacting or interdependent Entities, real or abstract The Voith Schneider Propeller (VSP also known as a cycloidal drive is a specialized marine propulsion system A screw is a shaft with a helical groove or thread formed on its surface and provision at one end to turn the screw This design was common, but inventors endlessly experimented with different profiles and greater numbers of blades. The propeller screw design stabilized by the 1880s.

In the early days of steam power for ships, when both paddle wheels and screws were in use, ships were often characterized by their type of propellers, leading to terms like screw steamer or screw sloop. A steam engine is a Heat engine that performs Mechanical work using Steam as its Working fluid. A paddle wheel (also called side wheel or stern wheel) is a large wheel fitted with Paddles which is used to propel a Boat. A screw sloop is a Propeller -driven Sloop-of-war. In the 19th century during the introduction of the Steam engine, Ships driven by propellers

Propellers are referred to as "lift" devices, while paddles are "drag" devices.

Cavitation damage evident on the propeller of a personal watercraft. Cavitation is defined as the phenomenon of formation of vapour bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapour pressure

Cavitation can occur if an attempt is made to transmit too much power through the screw. Cavitation is defined as the phenomenon of formation of vapour bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapour pressure At high rotating speeds or under heavy load (high blade lift coefficient), the pressure on the inlet side of the blade can drop below the vapour pressure of the water, resulting in the formation of a pocket of vapour, which can no longer effectively transfer force to the water (stretching the analogy to a screw, you might say the water thread 'strips'). The lift coefficient ( CL or CZ) is a non-dimensional coefficient that relates the lift generated by an Airfoil, the Vapor pressure (also known as equilibrium vapor pressure or saturation vapor pressure) is the Pressure of a Vapor in equilibrium This effect wastes energy, makes the propeller "noisy" as the vapour bubbles collapse, and most seriously, erodes the screw's surface due to localized shock waves against the blade surface. Cavitation can, however, be used as an advantage in design of very high performance propellers, in form of the supercavitating propeller. The supercavitation propeller is a variant of a Propeller for propulsion in water where Cavitation (formation of water vapour is actively employed to gain increased (See also fluid dynamics). Fluid dynamics is the sub-discipline of Fluid mechanics dealing with fluid flow: Fluids ( Liquids and Gases in motion A similar, but quite separate issue, is ventilation, which occurs when a propeller operating near the surface draws air into the blades, causing a similar loss of power and shaft vibration, but without the related potential blade surface damage caused by cavitation. Both effects can be mitigated by increasing the submerged depth of the propeller: cavitation is reduced because the hydrostatic pressure increases the margin to the vapor pressure, and ventilation because it is further from surface waves and other air pockets that might be drawn into the slipstream. Fluid statics (also called hydrostatics) is the Science of Fluids at rest and is a sub-field within Fluid mechanics.

14-ton propeller from Voroshilov a Kirov class cruiser on display in Sevastopol

Skewback propeller

An advanced type of propeller used on German Type 212 submarines is called a skewback propeller. Ships of the class; Kirov: Named after Sergei Kirov. Built at the Ordzhonikidze Yard, Leningrad. Sevastopol ( see pronunciation below) is a port city in Ukraine, located on the Black Sea coast of the Crimea Peninsula Development At the beginning of the 1990s the German Navy was seeking a replacement for the Type 206 submarines Initial study started on a Type 209 As in the scimitar blades used on some aircraft, the blade tips of a skewback propeller are swept back against the direction of rotation. In addition, the blades are tilted rearward along the longitudinal axis, giving the propeller an overall cup-shaped appearance. This design preserves thrust efficiency while reducing cavitation, and thus makes for a quiet, stealthy design. Stealth technology also known as LOT (Low Observability Technology is a sub-discipline of military Electronic countermeasures which covers a range of techniques used with ^[3]

See Also: Astern propulsion. Astern propulsion (as applied to a ship is a maneuver in which a ship's propelling mechanism is used to develop Thrust in a retrograde direction

See also

Propeller phenomena

• propeller walk

Propeller variations

• Azipod
• Azimuth thruster
• Helix
• Impeller
• Jet engine
• Kitchen rudder
• Kort nozzle
• Paddle steamer
• Pleuger rudder
• Propulsor
• Pump-jet
• Screw propulsion
• Voith-Schneider
• Cleaver
• Bow/Stern thruster

Materials

• Composite materials

Notes

External links

• Aircraft-Info.net - Propeller Aircraft
• Build your own balsa propeller for modeling
• Prop Scan Marine Propeller Technology
• Pleuger Propeller
• Titanic's Propellers
• Propeller Carving Step-by-step
• Propeller Duplicator
• A thesis containing information on a marine circulation control propeller
• Boat Props Information
• IACS Unified Requirement K: Propellers