Increasing The Tip Speed Ratio Of Windmill Blades Engineering Essay

Increasing The Tip Speed Ratio Of Windmill Blades Engineering Essay

For any energy bring forthing machine, efficiency is of extreme importance. For a windmill there are assorted facets that can be used to find its efficiency ; one of them is the tip velocity ratio. It is the comparing of the velocity at which the windmill blades rotate to the velocity of the air current. The velocity of the air current is a non an independent variable hence the lone portion that one can act upon is the velocity at which the windmill blades rotate in order to increase the tip velocity ratio. The velocity of rotary motion of the blades is determined by a battalion of variables. Hence my research inquiry is: “ How to increase the tip velocity ratio of windmill blades by altering the dimension of the blades? ”

In my experiment, to maintain the air current velocity changeless, a tabular array fan was used as the air current beginning. A non-contact type tachometer was step the RPMs. The constellation of the windmill was changed by changing the figure, length and thickness of the blades.

It was observed that as the form of the windmill blades became more aerodynamically efficient, the velocity of the rotary motion of the blades increased therefore increasing the tip velocity ratio. The most efficient constellation was found to be 3 blades, shorter length and a moderate thickness. However there is a demand for farther probe with more variables in order to exactly find how each facet influences the tip velocity ratio of the windmill blades and hence increases the efficiency.

Word Count: 246

Chapter 1: Introduction

1.1 What are windmills?

A windmill, by simple definition is a edifice with canvass or vanes that turn in the air current and generate power to crunch maize, generate electricity or draw H2O. They are constructions that use weave energy to bring forth energy.

However windmills do non bring forth energy, as energy can non be created or destroyed ; they merely convert the energy into more practical signifiers of energy. The beginning of energy for windmill is wind ; hence a windmill converts air current energy to mechanical or electrical energy. This transition is necessary as there is abundant energy in the air current but it can non be utilised in its native signifier, hence with the aid of a windmill it is converted to mechanical energy or electrical energy so that it can be used for power coevals. One can state that windmills follow work like transducers, electricalA devices that convert one signifier of energy into another ; except that they do non necessitate electricity to map.

In earlier yearss windmills were used to make domestic work such as crunching grain and cereal, doing pastes and pulverizations and pulling H2O. Windmills day of the month back to 1 CE in Greece ; nevertheless grounds of their being and use is merely found in the twelfth century in Europe. The use of windmills declined greatly due to a rise in the popularity of other beginnings of energy which were more efficient though polluting, yet many parts are significantly dependent on the energy yielded from windmills.

1.2 How do windmills map?

Windmills are simple mechanical machines that require wind as their beginning in order to map. In order to understand the operation of a windmill, we must understand the construct of air current and the function it plays in a windmill. Air traveling to an country of low force per unit area from an country of higher force per unit area is called air current ; fundamentally air in gesture is air current. Wind is produced due to the abnormalities in heating up of the Earth ‘s surface by the Sun. This creates the force per unit area and temperature differences and therefore air is put in gesture which is called air current. Wind is a free and unlimited signifier of energy, therefore the optimal pick as an input for windmills.

The basic construction and mechanism of a windmill is really simple. It consists of a strong heavy base upon which stands the tower of the windmill. In a basic windmill, a shaft is attached to a phonograph record which connects to the blades. The blades are the most of import constituent of the windmill, as it is the blades that respond to the air current which is the beginning of energy hence the input for the windmill and hence do the motion. When these blades are exposed to a air current beginning, the blades begin to travel which at the same clip moves the shaft. A generator is used when electricity is to be generated. The shaft has a magnet attached to one terminal of it, therefore when the blades which are connected on the other terminal rotate ; they cause the shaft to revolve excessively which rotates the magnet attached to it. This magnet is placed in a spiral of wire hence a traveling magnetic field is produced when the magnet in the spiral moves. Due to a alteration in the magnetic flux a traveling electric current is produced in the wires ; therefore electricity is generated. This electrical energy produced is transferred instantly through wires, as energy can non be stored in any signifier.

1.3 How can the efficiency of a windmill be modelled?

Windmills are non as efficient nor do they give as much output as other signifiers of energy production like atomic, thermic and hydraulic. But it is much easier, cheap and most significantly non-polluting.

Windmill end product is normally measured utilizing multimeters, which are connected after the spiral that produced the electric current in the wires. But since in my experiment I have used rotary motions of the windmill blades alternatively of electromotive force and current as the dependant variables, the efficiency will be measured utilizing the values of Rotations per Minute ( RPM ) . The efficiency of the windmill will be modelled by change overing the RPMs of the windmill blades to speed, which will so be compared to the speed of the air current beginning. This ratio is called the tip velocity ratio.

The tip velocity ratio will be calculated for the optimal value of RPM for each variable. For illustration when measuring the variable length of blades, suppose at 0.20 m length the blades has the highest Revolutions per minute when compared to all other length tested ; the speed of the blades at this length will be calculated to compare to that of the air current beginning.

1.4 Why should windmills be investigated?

The sum of energy required these yearss is increasing quickly due to technological advancement and population growing. This has caused a displacement towards more efficient power beginnings, but these beginnings have negative impacts as in most instances they make usage of non renewable resources and besides their production causes environmental debasement. The energy ingestion and production has increased which has caused research workers to do more efficient equipments but in the procedure they have non been able to cut down the negative outwardnesss caused by them.

The addition of fouling energy beginnings has caused research and development for clean energy production. Windmills are one of these sorts of energy which is about harmless to the environment. They are one of the least expensive techniques to cut down emanations of gases and other harmful waste merchandises during the production of electricity.

Besides the lone input required by windmills is the air current, which is a free and unlimited beginning of energy. The construction of windmills is besides really simple and does non name for excessively much accomplishment or engineering as it makes usage of cardinal constructs of blade motion and a generator.

If the efficiency of windmills can be increased it will turn out to be really helpful to the environment as it will cut down the demand for expensive and fouling power generators. Therefore windmills assist the environment and besides the economic system excessively. Hence they have gained popularity late non merely in small towns and state sides but in towns and metropoliss excessively.

Chapter 2: The Experiment

2.1 Hypothesis

As the form of the blades becomes more aerodynamic, the efficiency of the windmills increases. The efficiency of the windmills could be in the signifier of greater speed of the traveling blades or the RPMs, as they are straight related to the speed and the power generated.

2.2 Experimental Set-Up

Windmill Tower

Apparatus:

1 square wood board with sides of 0.20m

1 square wood board with sides of 0.10m

4 trapezium shaped wood boards with parallel sides being 0.20m and 0.10m each and height 0.80m

1 Iron Rod of diameter 0.005m and length 0.2m

2 Rubber stoppers of diameter 0.005m

Superglue and Duct tape

Grease

Procedure:

Put the 0.20m square board on a level surface and paste its sides.

Place each of the trapezium shaped boards on the sides of square board and attach it on the glued sides of the board.

Glue the 0.10m square board on top of the square formed by the 4 boards.

Fasten the Fe rod on top of the tower with multiple tapes in a manner that merely 0.10m of the rod is in contact with the top surface of the tower.

The tower will look something like this:

Windmill Blades

Apparatus:

Balsa Wood sheets

Sand paper

Cutter and scissor

Scale

As the dimension of the blades is the independent variable in the experiment, ab initio basic blades are made which are subsequently modified as per demand.

Procedure:

The fixed form of the blade is a trapezium ; the two analogue sides are of 0.03m and 0.015m each and the tallness is 0.20m and one of the sides is consecutive.

Make markers on the wood harmonizing to the blade dimensions utilizing a graduated table and cut them out.

Make phonograph record with the wood with diameter 0.05m and pierce a hole in its Centre of diameter 0.005m

Apart from the setups mentioned above a tabular array fan, as the air current beginning for the experiment and a non-contact type tachometer, to enter the RPMs is required. A tachometer is an instrument that measures the rotary motion velocity of a shaft or a phonograph record, as in motor or other machine.

2.3 Method of Data Collection, Presentation and Processing

The independent variables tested in this experiment are:

Number of blades

Length of Blades

Thickness of blades

The dependant variable in every instance is the RPMs of the windmill blade measured by a non-contact type tachometer.

The tachometer used to mensurate the RPM is the most indispensable. It displays the reading for RPM on a digital screen to 1 denary topographic point. A non contact tachometer was to be used as there was no shaft involved in my experiment. Light beams are employed to mensurate the velocity. A piece of light reflecting tape is attached to one of the windmill blade ; the light beam is projected at the tape and held changeless at its topographic point. The tachometer receives the reflected visible radiation from the tape and it is from this interruption frequence that the RPM is calculated.

For each of the variable, a specific figure of possible informations points are taken and at each information point, 10 readings of RPM are recorded. These values are recorded in a tabulated signifier and the average value of RPM for every information point is used for computation and analysis. The average values are presented in the essay and the 10 test values are included in the appendix at the terminal.

The informations point with the highest and the lowest Revolutions per minute will be taken and the speed of the windmill will be calculated for each of them. Last the tip velocity ratios will be compared.

2.4 Formulae

Conversion of RPM to Velocity ;

But this will give us the speed in whereas we need it in. Hence the equation is ;

2.5 Experiment

Control Variables:

The tabular array fan used ( wind beginning )

The velocity of air current from the tabular array fan

The room in which the experiment is performed

The tachometer used to mensurate RPM

The windmill tower

The stuff with which the blades are made

The surface intervention of the blades

The tallness at which the windmill tower is placed

The distance and angle at which the tabular array fan is placed

The other variables when one variable is being tested

The tabular array fan was kept at a distance of 0.15m from the windmill blades. The Centre of the fan is precisely in line with the Centre of the windmill blades. The windmill tower was placed on the floor and the tabular array fan was placed on a stool to make to the tallness of the tower.

All the blades used were made of the same type of balsa wood and it was maintained that the venas of the wood sheet were perpendicular to the consecutive side of the blade. The blades had the same surface intervention with a sand paper and their form and curve was unbroken indistinguishable. The mass of the blades was measured and kept changeless for blades of similar dimensions. This is to do certain that the mass does non falsify the RPMs as it is capable to gravitative force.

Common Procedure

Apparatus:

Blades

Phonograph record

Super Glue

Windmill tower

Tachometer

Table fan

Rubber Show-stoppers

Grease

Variables:

The independent variable alterations in every experiment but the dependent variable Idaho the same for all experiments: Revolutions per minute

Procedure:

Take a wooden phonograph record and grade points required on the perimeter of the phonograph record depending on the figure of blades attached and at these points make little cuts 0.005m deep for keeping the blades.

Carefully repair the blades at these points with superglue.

Slip the phonograph record with the blades attached on the Fe metal rod with the gum elastic stoppers on each side. Use some lubricating oil on the rod to assist in the free motion of the phonograph record.

Affix a 0.002m piece of reflecting tape on the top face of one of the blades.

Position the fan in forepart of the windmill with its Centre aligned to that of the windmill. Switch over on the tabular array fan and allow the windmill blades start rotating.

Position the optical maser visible radiation emitted from the tachometer in a manner that the tape on the blade passes through it. Keep the tachometer in one topographic point without traveling.

Note down 10 readings displayed on tachometer at regular intervals.

Repeat Steps 1 to 7 by altering the independent variable.

2.5.1 Fan Speed

The velocity of the air current beginning is required for comparing to the windmill blade velocity and ciphering the tip velocity ratio. Since the fan is the air current beginning in the experiment ; the velocity of the motion of the fan blades is the velocity of the air current beginning.

Using a tachometer, the RPMs of the fan blades is calculated and 10 tests are taken.

The velocity of the fan = 23.97ms-1

2.5.2 Number of Blades

2.5.2.1 Set-up, Procedure and Variables

Apparatus:

7 blades ; all of length 0.2m and thickness 0.005m

2 phonograph record with a hole at its Centre

Common setup

Variables:

Independent Variable – Number of blades

Dependent Variable – Revolutions per minute

Control Variables – Shape and dimension of blades are kept changeless.

Mass of all the blades is maintained.

Angle at which all the blades are attached is the same.

Procedure:

Follow the common process.

Repeat the stairss by attaching 3 and 4 blades.

2.5.2.2 Data Collection and Data Processing

3 different figure of blades were tested ; 2, 3 and 4.

10 tests of each figure of blades were taken.

The average values of the RPM obtained are:

Number of Blades

Average RPMs

2

76.83

3

90.69

4

79.64

These values of RPMs are converted to Rush with the expression ;

The diameter of the blades is ;

Number of Blades

Velocity ( ms-1 )

2

1.81

3

2.14

4

1.88

The value of speed is the highest with 3 blades and the lowest with 2 blades.

2.5.2.3 Outcome and Analysis

From the assorted blade Numberss tested, it is observed that the windmill with 3 blades produced the largest Revolutions per minute and speed which shows that the windmill with 3 blades is the most efficient.

An of import construct needed to be considered when proving a windmill for the figure of blades to be used is the creative activity of Eddy currents which works against the motion of the windmill itself. Windmills with 3 blades had sufficient spread between them to forestall the formation of Eddy currents.

The map for speed includes the diameter of the windmill which is non affected by the figure of blades hence the entire dependance of speed is on the RPMs.

The windmill with 2 blades wobbled somewhat which caused non unvarying readings for RPMs. Besides 2 blades caused the cover country to look like a watercourse line though the rotor swept country remains the same. Though the 2 blades are balanced in footings of their weight but there are immense empty infinites in the rotor swept country that are exposed to the air current beginning but can non use it in any manner which causes a decrease in RPMs.

The windmill with 4 blades was balanced but due to the weight produced lower RPMs than a 3 blade windmill. Besides a greater retarding force is caused with an addition in the figure of blades as the air displaced signifier one blade is reflected on to the other doing retarding force on that blade. However the difference in the speed between 3 and 4 blades is little.

2.5.3 Length of Blades

2.5.3.1 Set-up, Procedure and Variables

Apparatus:

18 blades, 3 blades of each length and all of thickness 0.005m

6 phonograph record with a hole at its Centre

Common setup

Variables:

Independent Variable – Length of blades

Dependent Variable – Revolutions per minute

Control Variables – Number and thickness of blades are kept changeless.

Mass of all the blades of equal length is maintained.

Angle at which all the blades are attached is the same.

Procedure:

Follow the common process.

Repeat the stairss by attaching the 3 blades of other lengths.

2.5.3.2 Data Collection and Data Processing

6 different blade lengths were tested ; 0.20m, 0.18m, 0.16m, 0.14m, 0.12m and 0.10m

10 tests of each blade length were taken.

The average values of the RPM obtained are:

Length of Blades ( m )

Mean RPMs

0.20

70.05

0.18

78.51

0.16

95.64

0.14

111.26

0.12

132.56

0.10

160.90

These values of RPMs are converted to Rush with the expression ;

The diameter of the blades is altering in each reading as the length of blades is the independent variable ;

Length of Blades ( m )

Diameter ( m )

Velocity ( ms-1 )

0.20

0.45

1.65

0.18

0.41

1.69

0.16

0.37

1.85

0.14

0.33

1.92

0.12

0.29

2.01

0.10

0.25

2.11

The value of speed is the highest for 0.10m blade length and the lowest for 0.20m blade length.

2.5.3.3 Outcome and Analysis

From the assorted lengths tested, it is observed that the windmill with blade length 0.10m produced the largest Revolutions per minute and speed.

The construct of blade length and its speed is the production of clash and air retarding force. The more the rotor swept country, the more is the air retarding force as there is a greater surface country which is exposed to the air current beginning therefore more opponent force. It is a common misconception that more swept country will increase the efficiency as more energy will be captured by the blades but the negative consequence of longer blades is the opposition they cause.

The speed map has ‘Diameter of the blades ‘ as one of the variables. When the length of the blades is shortened, the diameter of the windmill becomes lesser ; therefore ideally it should diminish the speed excessively as the diameter is multiplied. However the shortening of the blades has a greater consequence on the RPMs which causes the speed to increase with a lessening in the length of the blades.

Hence when the shortest length of the blade was used, the greatest Revolutions per minute and speed is produced. The difference between the speed of the shortest blade and the longest blade length is more than double.

2.5.3 Thickness of Blades

2.5.4.1 Set-up, Procedure and Variables

Apparatus:

12 blades, 3 blades of each thickness and all of length 0.02m

4 phonograph record with a hole at its Centre

Common setup

Variables:

Independent Variable – Thickness of blades

Dependent Variable – Revolutions per minute

Control Variables – Number and length of blades are kept changeless.

Mass of all the blades of equal length is maintained.

Angle at which all the blades are attached is the same.

Procedure:

Follow the common process.

Repeat the stairss by attaching the 3 blades of other thicknesses.

2.5.4.2 Data Collection and Data Processing

4 different blade thicknesses were tested ; 0.003m, 0.005m, 0.007mand 0.01m

10 tests of each blade length were taken.

The average values of the RPM obtained are:

Thickness of Blades ( m )

Revolutions per minute

0.003

63.94

0.005

122.78

0.007

108.65

0.010

89.54

These values of RPMs are converted to Rush with the expression ;

The diameter of the blades is changeless in each reading as the length of blades is fixed at 0.1m ;

Thickness of Blades ( m )

Velocity ( ms-1 )

0.003

1.00

0.005

2.10

0.007

1.81

0.010

1.28

The value of speed is the highest for 0.005m blade thickness and the lowest for 0.003m blade thickness.

2.5.4.3 Outcome and Analysis

From the assorted blade thicknesses tested, it is observed that the windmill with 0.005m thickness produced the largest of RPMs and speed.

The construct of blade thickness and its speed is the weight and clash. The more the blade thickness, the more is the weight of the windmill which reduces the capacity of the windmill blades to revolve faster. Besides the increased thickness of the blade will do more clash which excessively hinders fast rotary motions.

The map for speed includes the diameter of the windmill which is non affected by the thickness of blades hence the entire dependance of speed is on the RPMs which reduces with an addition in thickness.

The blades of 0.003m thickness wobbled a batch and about broke. Evidently blades of more thickness would be used but in existent state of affairss the air current velocity will be higher and therefore there excessively is a hazard of breakage of the blades if the blades are excessively thin and therefore excessively weak.

The blades of 0.007m and 0.010m thickness were excessively heavy and resulted in inconsistent motion. They besides kept halting in the in-between and required a little initial force that was applied by manus to get down off. The force of the mass playing downwards was call offing out to the force provided by the air current beginning therefore impeding the free fast motion of the blades.

Hence when the blades of 0.050m were used, the greatest Revolutions per minute and speed is produced. The difference between the speed of this blade and the thickest blade is about dual.

2.6 Tip Speed Ratio

To detect how the tip velocity of the windmill has been increased, the lowest value of speed obtained when the most unsuitable conditions were used will be compared to with the highest value of speed obtained when the most optimal conditions were used.

Optimum Valuess

Worst Valuess

Number of blades= 3

RPMs= 90.69

Velocity= 2.14ms-1

Number of blades= 2

RPMs= 76.83

Velocity= 1.81ms-1

Length of blades= 0.10m

RPMs= 160.90

Velocity= 2.11ms-1

Length of blades= 0.20m

RPMs= 70.05

Velocity= 1.65ms-1

Thickness of blades= 0.005m

RPMs= 160.14

Velocity= 2.10ms-1

Thickness of blades= 0.003m

RPMs= 76.63

Velocity= 1.00ms-1

Mean RPMs= 137.24

Average Velocity= 2.12ms-1

Mean RPMs= 74.50

Average Velocity= 1.49ms-1

From these values it is noticed that the tip velocity ratio has been increased by experimenting and measuring the best dimension for the blade.

It might look like the difference between the tip-speed ratios in both the state of affairss is non much but these values are in footings of ratios. Besides the experiment was carried out at a really little graduated table as the theoretical account of a windmill was made ; in existent windmills, the construction is much larger and so is the air current velocity.

Chapter 3: Mistakes

3.1 Beginnings of Mistakes

The figure of informations points was less -3 information points for figure and 4 for thickness of blades. More informations points increase the preciseness of the result.

The surface and the corners of the blades were sanded with emery paper. There is no step of this hence it would hold caused little deformations in the information.

The room in which the experiment was performed was non ever to the full closed, the windmill blades could hold been in the influence of air current force and alteration in temperatures

3.2 Methods of Improvement

More informations points should be used for the independent variables as it provides a wider scope to detect and analyze doing the informations more dependable.

All the values measured and calculated should incorporate their uncertainnesss as it gives a better thought of the result.

In the experiment, the brooding tape through which the tachometer records the RPMs was pasted on one of the blades of the windmill. The tape can besides be stuck on all the blades and the RPMs can be measured and so be divided by the figure of blades for greater truth.

Orthogonality of the Fe rod and besides the tabular array fan to the floor. Though it was made certain that the Centre of the tabular array fan was aligned precisely with the Centre of the windmill but the angle formed between the Fe rod and the perpendicular vector of the fan was non taken into consideration.

Use of an alternate method of cut downing clash between the phonograph record and the Fe rod alternatively of lubricating oil.

Performing the experiment under normal outside atmosphere conditions without the use of an unreal air current beginning but natural air current.

Chapter 4: Decision

The most favorable constellation for the windmill was found to be –

3 Blades

0.10m Blade length hence shorter length

0.005 Blade thickness hence moderate thickness

These dimensions gave the highest values for RPMs and hence velocity.

Chapter 5: Appendix

Table 1- Fan RPM

Revolutions per minute

2289.4

2284.8

2290.1

2283.0

2287.7

2289.3

2288.5

2291.1

2292.8

2290.9

Mean RPM of fan blades = 2288.8 Velocity = 23.97 ms-1

Table 2- Windmill RPM -Number of Blades

RPMs ( 2 Blades )

RPMs ( 3 Blades )

RPMs ( 4 Blades )

75.5

89.7

82.0

76.9

88.1

83.0

75.9

94.0

75.9

77.6

93.2

79.6

78.2

90.3

78.7

76.4

90.1

78.2

74.7

92.9

81.2

76.8

88.7

81.9

77.4

93.4

72.9

78.9

86.5

83.0

2 Blades

3 Blades

4 Blades

2 Blades ; Mean RPM = 76.83 Velocity = 1.81 ms-1

3 Blades ; Mean RPM = 90.69 Velocity = 2.14 ms-1

4 Blades ; Mean RPM = 79.64 Velocity = 1.88 ms-1

Table 3- Windmill RPM- Length of Blades

RPMs ( 0.20m )

RPMs ( 0.18m )

RPMs ( 0.16m )

67.6

77.0

91.8

68.1

72.1

96.5

71.7

78.0

98.0

71.6

80.6

99.6

67.3

79.3

93.8

69.0

81.3

98.8

71.8

82.8

96.2

70.6

80.2

92.9

68.3

76.6

93.2

74.5

77.2

95.6

RPMs ( 0.14m )

RPMs ( 0.12m )

RPMs ( 0.10m )

111.5

129.5

159.7

106.7

133.8

160.5

108.2

132.0

157.1

108.9

134.3

161.0

110.2

132.4

166.6

111.1

132.0

165.5

111.8

131.0

158.9

114.3

136.9

161.3

114.4

132.8

158.1

115.5

130.8

160.4

0.20m

0.18m

0.16m

0.14m

0.12m

0.10m

Blade length 0.20m ; Mean RPM = 70.05 Diameter = 0.45m Velocity = 1.65 ms-1

Blade length 0.18m ; Mean RPM = 78.51Diameter = 0.41m Velocity = 1.69 ms-1

Blade length 0.16m ; Mean RPM = 95.64 Diameter = 0.37m Velocity = 1.85 ms-1

Blade length 0.14m ; Mean RPM = 111.26 Diameter = 0.33m Velocity = 1.92 ms-1

Blade length 0.12m ; Mean RPM = 132.56 Diameter = 0.29m Velocity = 2.01 ms-1

Blade length 0.10m ; Mean RPM = 160.90 Diameter = 0.25m Velocity = 2.11 ms-1

Table 4- Windmill RPM- Thickness of Blades

RPMs ( 0.003m )

RPMs ( 0.005m )

RPMs ( 0.007m )

RPMs ( 0.010m )

75.4

156.6

136.6

96.1

76.9

165.0

139.1

97.9

75.9

156.4

137.3

96.6

76.6

162.1

138.5

97.5

78.1

159.8

141.4

99.5

76.4

164.0

138.2

97.2

74.4

163.0

135.0

95.2

77.1

156.0

138.8

97.7

77.6

162.8

139.6

98.5

79.0

155.6

142.6

100.4

0.003m

0.005m

0.007m

0.010m

Blade thickness 0.003m ; Mean RPM = 76.73 Velocity = 1.00 ms-1

Blade thickness 0.005m ; Mean RPM = 160.14 Velocity = 2.10 ms-1

Blade thickness 0.007m ; Mean RPM = 138.70 Velocity = 1.81 ms-1

Blade thickness 0.010m ; Mean RPM = 97.68 Velocity = 1.28 ms-1

Chapter 6: Extension

The mechanism of windmills might look really simple ; nevertheless it is non merely the figure, length and thickness of the blades that affect the RPMs in a windmill. Other of import factors include: the angle at which the blades are attached, the axis on which the blades are attached, the angle which the axis of the windmill makes with the land, the angle at which the air current force acts upon the face of the windmill blades, the stuff with which the blades are made, the tallness of the windmill tower. Some of these factors non all can be tested with a research lab theoretical account hence a existent life windmill would be required.

The values obtained are through experimentation under closed criterion conditions which is non the status under which existent windmills perform. For this ground more variables originate for experimentation and rating.