15th Aguest
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born in 15th aguest
Sunday, August 17, 2008
TECHNICAL SEMINAR ON PROPELLER BY PRASAD
Introduction
One of the final types of airplane propellers is the constant speed des
ign. Instead of changing the pitch manually, it is changed automatically by a governor. All you have to do is tell the system what your desired engine speed is. When the propeller speed starts to increase, the governor will detect it and increase the pitch to correct it. If the speed starts to decrease, the governor will decrease the pitch of the airplane propellers.
The characteristics of a composite propeller:
1) Easy to fabricate.
2) Mold can be made using an existing metal or wooden propeller as a plug.
3) By making the mold flexible and adjustable props with slightly different pitch values can be made
4) A fiberglass/epoxy propeller is about 50 to 70 percent heavier than a wooden prop but is lighter than a metal prop.
5) The weight difference results in different torsional vibration characteristics in power plants having a reduction drive.
6) A composite prop is much stronger than a wooden propeller.
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. 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.
Usually propellers have two, three, or four blades; for highspeed or high-powered airplanes, six or more blades are used. In some cases these propellers have an equal number of opposite rotating blades on the same shaft, and are known as dual-rotation propellers.
A propeller blade advances through the air along an approximate helical path which is the result of its forward and rotational velocity components. This action is similar to a screw being turned in a solid surface, except that in the case of the propeller a slippage occurs because air is a fluid. Because of the similarity to the action of a screw, a propeller is also known as an airscrew. To rotate the propeller blade, the engine exerts a torque force. This force is reacted on by the blade in terms of lift and drag force components produced by the blade sections in the opposite direction. As a result of the rational forces reacting on the air, a rotational velocity remains in the propeller wake with the same rotational direction as the propeller. This rotational velocity times the mass of the air is proportional to the power input. The sum of all the lift and drag components of the blade sections in the direction of flight are equal to the thrust produced. These forces react on the air, giving an axial velocity component opposite to the direction of flight. By the momentum theory, this velocity times the mass of the air going through the propeller is equal to the thrust.
A propeller blade must be designed to withstand very high centrifugal forces. The blade also must withstand the thrust force produced plus any vibratory forces generated, such as those due to uneven flow fields. To withstand the high stresses due to rotation, propeller blades have been made from a number of materials, including wood, aluminum, hollow steel, and plastic composites. The most common material used has been solid aluminum. However, the composite blade constructions are being used for new turboprop installations because of their very light weight and high strength characteristics.
For a small, low-power airplane, very simple, fixed-pitch, single-piece, two-blade propellers are used. The rotational speed of these propellers depends directly on the power input and forward speed of the airplane. Because of the fixed-blade angle of this type of propeller, it operates near peak efficiency only at one condition. To overcome the limitations of the simple fixed-pitch propeller, configurations that provide for variable blade angles are used. The blades of these propellers are retained in their hub so that they can be rotated about their centerline while the propeller rotates. For the normal range of operation, the blade angle varies from the low blade angle needed for takeoff to the high blade angle needed for the maximum speed of the airplane.
we specified hi grade aluminum alloy, type 6061, per Mil STD and ASM specifications.
Working
As Newton stated, "actio est reactio". For the propulsion problem, this means that a device accelerating air or water in one direction, feels a force in the opposite direction. A propeller accelerates incoming air particles, "throwing" them towards the rear of the airplane, and thus feels a force on itself - this force is called thrust. Looking more closely at propellers shows, that a propeller adds a velocity to then incoming velocity v. The first half of this acceleration takes place in front of the propeller, and the second half behind the propeller. Because the mass of air passing through the stream tube must be constant (conservation of mass), the increased velocity leads to a contraction of the stream tube passing through the propeller disk (neglecting compressibility)
Besides the contraction of the stream tube, a propeller also adds a swirl component to its outflow (wake). The amount of swirl depends on the rotational speed of the engine and eats up energy, which is not available for thrust anymore. Typical, well designed propellers loose about 1% to 5% of their power in the swirl of the propeller wake. The swirl angle (about 1°...10°) may cause non symmetrical flow conditions on parts behind the propeller, e.g. at the tail planes. The stream tube of a low bypass ratio turbo jet engine looks completely different, because the acceleration of the flow is mainly performed through the thermal expansion of the heated air. Here the incoming stream tube will usually have a smaller diameter than the exhaust stream, depending on operating conditions. The final extreme is the rocket engine, which has no incoming stream tube, but creates its exhaust jet only by expanding the gases created by a chemical reaction (e.g. by burning a fuel/oxygen mixture). The total mass contained in the exhaust flow is carried inside the rocket (fuel plus oxydator). Thrust, Power and Efficiency - Momentum Theory
The Thrust of a propeller depends on the volume of air (or water) accelerated per time unit, on the amount of the acceleration, and on the density of the medium. Based on momentum considerations, it can be expressed by the following formula:
Examining the quite simple formula reveals, that the thrust T increases when the diameter D increases (the first term is the area of the propeller "disk") or when the density of the medium increases. The acceleration of a propeller depends on the velocity v, thus it is generally not true that increasing the velocity v increases the thrust. But it can be said, that increasing the additional velocity , increases the thrust. For a propeller of a fixed diameter, working in a certain medium at a certain speed, thrust depends on the velocity increase only.
Power is defined as force times distance per time. Using the available thrust T to drive a vehicle at a certain speed v (which already is distance per time) we can calculate the propulsive power (sometimes also called available power) from:
Now, thrust is the one thing, the power to create this thrust the other. Of course we want to create as much thrust as possible from the smallest amount of power, which can be expressed by the term efficiency.
Efficiency of a propeller is defined as the ratio of available power to the engine power which is
Note, that this definition for efficiency contains the velocity v, which means, that the efficiency approaches zero as the flight speed goes to zero, because the thrust cannot become infinitely large. So this definition is not useful for the special case of static thrust.
Neglecting rota
tional losses, the power absorbed by the propeller can also be expressed by
which can be used to combine the equations above into a relation between the velocity and the efficiency for a given power and diameter:
Optimum efficiency according to momentum theory versus flight speed for different power loadings P/D² in [W/m²].
The density of the air is assumed to be 1.225 kg/m³. Curves have been calculated by
A propeller's efficiency is determined by
Dimension of Koolprop
Koolprop is designed and made for different airscrew driven vehicles, included airboats, hovercraft, Ultra light and Light Sport aircraft. There are a lot of different models for different applications, right and left hand rotation 63”-73” As a standard, they have 3 blades and intended for engines 40-120HP. You can use them with a lot of engines from Rotax 440 to powerful Rotax 914 and Subaru-Suzuki auto conversions. For example one model 67”-69” is especially recommended for G10-G13 Suzuki with 2.2-2.5 reduction ratio. I got 386lb static thrust with this prop (standard TBI G10) and excellent performances with my Eagle trike. Special reinforced blades up to 160HP.
Their design is similar (in some points) to Kievprop which is well known in North America. For example, Koolprop hub has exactly the same design, CNC machined with D16T aviation aluninum and anodised. You can use your old Kievprop hub and spinner with Kool blades. I have in stock and tested in flight both Kool and Kiev and can compare them. There are some points making Kool preferable for me. It is also hand-made but it is made with carbon-glass composite instead of fiberglass. Kool blade is rigid, it helps reducing idle wobbling and vibration. Its finish is epoxy gelcoat, more hard and smooth. As Kiev, Kool has integrated strong leading edge protection, but it is made with stainless steel (not copper). It looks more beautiful (always shiny) and stronger.
Kool blade is straight, classical-style. It makes its blade a little more efficient than the same diameter scimitar-style one. It could be important, especially if you are restricted in diameter. Most Kool models have antivortex blade tips like wings of modern airplanes. Koolprop set included 3 blades, hub, all hardware, pitch protractor and soft blade covers. Finish is excellent black gelcoat with white tips. It can be ordered with Carbon-fiberglass 8”diam 9” length spinner and 60mm (2.25") hub spacer.Koolprop specifications.- Diameter 63"-73"- Maximum blade width 5.8"- Maximum speed of rotation 3000 rpm- Power of engine 40-120HP- Range of operation temperatures +55 -20C*- Stainless steel integrated LE protection.- Available in left and right hand rotation, for pusher and tractor plane.
Propeller engine: engine of propulsion or traction equipped with blades.
Carburetor: apparatus where fuel is mixed with to feed an internal combustion engine.
Crank: arm perpendicular to an axle used to create circular motion.
Piston: cylindrical part that moves up and down in a tube and transmits power produced by the fuel.
Cylinder: type of roller that applies uniform pressure.
Valve: regulation device.
Exhaust: device composed of parts that allow the expulsion of spent gases.
Propeller blade: blade, arm of the propeller.
Spark plug: ignition device of an internal combustion engine.
Propeller Angle of Attack
The diagram to the right shows the two blades on a typi
cal propeller. Some propellers have more than two blades but all the concepts developed here will still apply.
Each blade cross-section is moving along an arc around the crankshaft as well as traveling forward. As a result its motion is a helix.
The drawbacks of a composite propeller:
1) It may be too strong! In an aircraft with retractable gear a belly landing may result in a damaged crankshaft.
2) However, the leading edge of the prop is not as hard as metal. Therefore, grit and gravel will damage the leading edge of the prop. A pusher prop in particular needs continuous maintenance on dirt air strips.
3) The hub of a composite propeller may shrink if made of poor plastics and if the prop flange gets too hot (eg pusher propellers).
CONCLUSION:
Using the quite simple momentum theory, we can already deduct important information about the performance of propellers. We can study the influence of the propeller diameter on efficiency as well as how it depends on flight speeder the density of the air (corresponding to a certain altitude). We learn that an efficient propeller should have a small power loading per disk area, i.e. a large diameter is required.
The momentum theory does neither take the platform of the blade into account nor the characteristics of the airfoil sections. For the design or the analysis of a propeller more sophisticated models are necessary, but the momentum theory always gives a good estimate for the maximum efficiency which we can expect.
It is possible to extend the momentum theory to include rotational losses, which results in an additional efficiency loss of 2 to 5 percent for typical propellers. These losses depend on the velocity of rotation and favor low torque, high rpm conditions.
Prasad.SS
AERO-DEPT
PMRIT.
------------------------------------------------------------------------------------------
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. 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.
Propeller
A propeller is like a spinning wing. Instead of pushing air behind a plane, the airfoil shaped blades pull an airplane forward just as an airplane’s wings lift it upward. The amount of thrust created by a propeller depends on how fast and at what angle its blades cut through the air. Probably the most important parts of an airplane, after the wing, are the propeller and engine. The propeller (or, on jet aircraft, the jets) provides the thrust that moves the plane forward A propeller is really just a special, spinning wing. If you looked at the cross section of a propeller, you'd find that a propeller has an airfoil shape and an angle of attack. Just by looking at the propeller pictured above, you can see that the angle of attack changes along the length of the propeller -- the angle is greater toward the center because the speed of the propeller through the air is slower close to the hub. Many larger propeller aircraft have more elaborate three-blade or four-blade props with adjustable pitch mechanisms. These mechanisms let the pilot adjust the propeller's angle of attack depending on air speed and altitude.
The drawback of a prop plane is that it can't be very fast--if you need a plane that flies faster than 400 knots, you need a jet. Prop planes don't fly as high as jets do; a King Air will fly up to 31,000 feet above sea level, while business jets routinely ply the skies above 41,000 feet
Contra-rotating propellers, also referred to as coaxial contra-rotating
propellers, apply the maximum power of a single piston or turboprop engine to drive two propellers in opposite rotation. Contra-rotating propellers are common in some marine transmission systems, in particular for medium to large size planing leisure crafts. Two propellers are arranged one behind the other, and power is transferred from the engine via a planetary gear transmission. Contra-rotating propellers should not be confused with counter-rotating propellers, a term which describes twin-engined aircraft with the airscrew on one engine turning clockwise and the other counter-clockwise.
Four Types of Airplane Propellers
Fixed Pitch
One of the first types of airplane propellers is the fixed pitch design. The pitch of these propellers is determined by the manufacturer. Therefore, the performance of your airplane will be limited by the propeller. You will often be given a choice of pitches best suited for climbing or cruising. Airplane propellers that are designed for climbing will have a relatively fine pitch. Those that are made for cruising will have a relatively coarse pitch.
In-flight Adjustable
One of the next types of airplane propellers is the in-flight adjustable design. The
se propellers allow you to adjust the pitch of the propeller during flight. This allows you to achieve many different power settings when combined with the throttle control. You will be able to stay within the constraints of the engine speeds while attaining a range of airspeeds.
Ground Adjustable
Another type of propeller is the ground adjustable variety. Instead of bei
ng able to adjust the pitch during flight, you will have to adjust these airplane propellers before takeoff. You will be able to adjust the pitch based on the type of flying you will be doing. These airplane propellers are a great way to test out different pitches. You can easily find the pitch that is best to use with your plane and your flying style.
One of the final types of airplane propellers is the constant speed des
ign. Instead of changing the pitch manually, it is changed automatically by a governor. All you have to do is tell the system what your desired engine speed is. When the propeller speed starts to increase, the governor will detect it and increase the pitch to correct it. If the speed starts to decrease, the governor will decrease the pitch of the airplane propellers.The characteristics of a composite propeller:
1) Easy to fabricate.
2) Mold can be made using an existing metal or wooden propeller as a plug.
3) By making the mold flexible and adjustable props with slightly different pitch values can be made
4) A fiberglass/epoxy propeller is about 50 to 70 percent heavier than a wooden prop but is lighter than a metal prop.
5) The weight difference results in different torsional vibration characteristics in power plants having a reduction drive.
6) A composite prop is much stronger than a wooden propeller.
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. 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.Usually propellers have two, three, or four blades; for highspeed or high-powered airplanes, six or more blades are used. In some cases these propellers have an equal number of opposite rotating blades on the same shaft, and are known as dual-rotation propellers.
A propeller blade advances through the air along an approximate helical path which is the result of its forward and rotational velocity components. This action is similar to a screw being turned in a solid surface, except that in the case of the propeller a slippage occurs because air is a fluid. Because of the similarity to the action of a screw, a propeller is also known as an airscrew. To rotate the propeller blade, the engine exerts a torque force. This force is reacted on by the blade in terms of lift and drag force components produced by the blade sections in the opposite direction. As a result of the rational forces reacting on the air, a rotational velocity remains in the propeller wake with the same rotational direction as the propeller. This rotational velocity times the mass of the air is proportional to the power input. The sum of all the lift and drag components of the blade sections in the direction of flight are equal to the thrust produced. These forces react on the air, giving an axial velocity component opposite to the direction of flight. By the momentum theory, this velocity times the mass of the air going through the propeller is equal to the thrust.
A propeller blade must be designed to withstand very high centrifugal forces. The blade also must withstand the thrust force produced plus any vibratory forces generated, such as those due to uneven flow fields. To withstand the high stresses due to rotation, propeller blades have been made from a number of materials, including wood, aluminum, hollow steel, and plastic composites. The most common material used has been solid aluminum. However, the composite blade constructions are being used for new turboprop installations because of their very light weight and high strength characteristics.
For a small, low-power airplane, very simple, fixed-pitch, single-piece, two-blade propellers are used. The rotational speed of these propellers depends directly on the power input and forward speed of the airplane. Because of the fixed-blade angle of this type of propeller, it operates near peak efficiency only at one condition. To overcome the limitations of the simple fixed-pitch propeller, configurations that provide for variable blade angles are used. The blades of these propellers are retained in their hub so that they can be rotated about their centerline while the propeller rotates. For the normal range of operation, the blade angle varies from the low blade angle needed for takeoff to the high blade angle needed for the maximum speed of the airplane.
we specified hi grade aluminum alloy, type 6061, per Mil STD and ASM specifications.
Working
As Newton stated, "actio est reactio". For the propulsion problem, this means that a device accelerating air or water in one direction, feels a force in the opposite direction. A propeller accelerates incoming air particles, "throwing" them towards the rear of the airplane, and thus feels a force on itself - this force is called thrust. Looking more closely at propellers shows, that a propeller adds a velocity to then incoming velocity v. The first half of this acceleration takes place in front of the propeller, and the second half behind the propeller. Because the mass of air passing through the stream tube must be constant (conservation of mass), the increased velocity leads to a contraction of the stream tube passing through the propeller disk (neglecting compressibility)
Besides the contraction of the stream tube, a propeller also adds a swirl component to its outflow (wake). The amount of swirl depends on the rotational speed of the engine and eats up energy, which is not available for thrust anymore. Typical, well designed propellers loose about 1% to 5% of their power in the swirl of the propeller wake. The swirl angle (about 1°...10°) may cause non symmetrical flow conditions on parts behind the propeller, e.g. at the tail planes. The stream tube of a low bypass ratio turbo jet engine looks completely different, because the acceleration of the flow is mainly performed through the thermal expansion of the heated air. Here the incoming stream tube will usually have a smaller diameter than the exhaust stream, depending on operating conditions. The final extreme is the rocket engine, which has no incoming stream tube, but creates its exhaust jet only by expanding the gases created by a chemical reaction (e.g. by burning a fuel/oxygen mixture). The total mass contained in the exhaust flow is carried inside the rocket (fuel plus oxydator). Thrust, Power and Efficiency - Momentum Theory
The Thrust of a propeller depends on the volume of air (or water) accelerated per time unit, on the amount of the acceleration, and on the density of the medium. Based on momentum considerations, it can be expressed by the following formula:
Examining the quite simple formula reveals, that the thrust T increases when the diameter D increases (the first term is the area of the propeller "disk") or when the density of the medium increases. The acceleration of a propeller depends on the velocity v, thus it is generally not true that increasing the velocity v increases the thrust. But it can be said, that increasing the additional velocity , increases the thrust. For a propeller of a fixed diameter, working in a certain medium at a certain speed, thrust depends on the velocity increase only.Power is defined as force times distance per time. Using the available thrust T to drive a vehicle at a certain speed v (which already is distance per time) we can calculate the propulsive power (sometimes also called available power) from:
Now, thrust is the one thing, the power to create this thrust the other. Of course we want to create as much thrust as possible from the smallest amount of power, which can be expressed by the term efficiency.
Efficiency of a propeller is defined as the ratio of available power to the engine power which is
Note, that this definition for efficiency contains the velocity v, which means, that the efficiency approaches zero as the flight speed goes to zero, because the thrust cannot become infinitely large. So this definition is not useful for the special case of static thrust.
Neglecting rota
tional losses, the power absorbed by the propeller can also be expressed bywhich can be used to combine the equations above into a relation between the velocity and the efficiency for a given power and diameter:
Optimum efficiency according to momentum theory versus flight speed for different power loadings P/D² in [W/m²].
The density of the air is assumed to be 1.225 kg/m³. Curves have been calculated by
A propeller's efficiency is determined by
Dimension of Koolprop
Koolprop is designed and made for different airscrew driven vehicles, included airboats, hovercraft, Ultra light and Light Sport aircraft. There are a lot of different models for different applications, right and left hand rotation 63”-73” As a standard, they have 3 blades and intended for engines 40-120HP. You can use them with a lot of engines from Rotax 440 to powerful Rotax 914 and Subaru-Suzuki auto conversions. For example one model 67”-69” is especially recommended for G10-G13 Suzuki with 2.2-2.5 reduction ratio. I got 386lb static thrust with this prop (standard TBI G10) and excellent performances with my Eagle trike. Special reinforced blades up to 160HP.
Their design is similar (in some points) to Kievprop which is well known in North America. For example, Koolprop hub has exactly the same design, CNC machined with D16T aviation aluninum and anodised. You can use your old Kievprop hub and spinner with Kool blades. I have in stock and tested in flight both Kool and Kiev and can compare them. There are some points making Kool preferable for me. It is also hand-made but it is made with carbon-glass composite instead of fiberglass. Kool blade is rigid, it helps reducing idle wobbling and vibration. Its finish is epoxy gelcoat, more hard and smooth. As Kiev, Kool has integrated strong leading edge protection, but it is made with stainless steel (not copper). It looks more beautiful (always shiny) and stronger.
Kool blade is straight, classical-style. It makes its blade a little more efficient than the same diameter scimitar-style one. It could be important, especially if you are restricted in diameter. Most Kool models have antivortex blade tips like wings of modern airplanes. Koolprop set included 3 blades, hub, all hardware, pitch protractor and soft blade covers. Finish is excellent black gelcoat with white tips. It can be ordered with Carbon-fiberglass 8”diam 9” length spinner and 60mm (2.25") hub spacer.Koolprop specifications.- Diameter 63"-73"- Maximum blade width 5.8"- Maximum speed of rotation 3000 rpm- Power of engine 40-120HP- Range of operation temperatures +55 -20C*- Stainless steel integrated LE protection.- Available in left and right hand rotation, for pusher and tractor plane.
Propeller engine: engine of propulsion or traction equipped with blades.
Carburetor: apparatus where fuel is mixed with to feed an internal combustion engine.
Crank: arm perpendicular to an axle used to create circular motion.
Piston: cylindrical part that moves up and down in a tube and transmits power produced by the fuel.
Cylinder: type of roller that applies uniform pressure.
Valve: regulation device.
Exhaust: device composed of parts that allow the expulsion of spent gases.
Propeller blade: blade, arm of the propeller.
Spark plug: ignition device of an internal combustion engine.
Propeller Angle of Attack
The diagram to the right shows the two blades on a typi
cal propeller. Some propellers have more than two blades but all the concepts developed here will still apply.Each blade cross-section is moving along an arc around the crankshaft as well as traveling forward. As a result its motion is a helix.
The drawbacks of a composite propeller:
1) It may be too strong! In an aircraft with retractable gear a belly landing may result in a damaged crankshaft.
2) However, the leading edge of the prop is not as hard as metal. Therefore, grit and gravel will damage the leading edge of the prop. A pusher prop in particular needs continuous maintenance on dirt air strips.
3) The hub of a composite propeller may shrink if made of poor plastics and if the prop flange gets too hot (eg pusher propellers).
CONCLUSION:
Using the quite simple momentum theory, we can already deduct important information about the performance of propellers. We can study the influence of the propeller diameter on efficiency as well as how it depends on flight speeder the density of the air (corresponding to a certain altitude). We learn that an efficient propeller should have a small power loading per disk area, i.e. a large diameter is required.
The momentum theory does neither take the platform of the blade into account nor the characteristics of the airfoil sections. For the design or the analysis of a propeller more sophisticated models are necessary, but the momentum theory always gives a good estimate for the maximum efficiency which we can expect.
It is possible to extend the momentum theory to include rotational losses, which results in an additional efficiency loss of 2 to 5 percent for typical propellers. These losses depend on the velocity of rotation and favor low torque, high rpm conditions.
Prasad.SS
AERO-DEPT
PMRIT.
------------------------------------------------------------------------------------------
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